Groundwater : drought, pollution & management : proceedings of the International Conference on Groundwater-Drought, Pollution & Management, Brighton, UK, 1-3 February 1994 9789054103516, 9054103515

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GROUNDWATER DROUGHT, POLLUTION & MANAGEMENT

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PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON GROUNDWATER — DROUGHT, POLLUTION & MANAGEMENT BRIGHTON / UK / 1-3 FEBRUARY 1994

Groundwater Drought, Pollution & Management Edited by

CHARLES REEVE & JACQUELINE WATTS HR Wallingford Ltd, UK

A.A.BALKEMA / ROTTERDAM / BROOKFIELD / 1994

Papers presented at the International Conference on Groundwater: drought, pollution & management held at Brighton, England: 1-3 February 1994. Organised and sponsored by HR Wallingford Ltd and co-sponsored by the UK Overseas Development Administration, UK National Rivers Authority, International Association for Hydraulic Research, International Association of Hydrogeologists, European Institute for Water and International Groundwater Modelling Centre, Europe.

The texts of the various papers in this volume were set individually by typists under the supervision of each of the authors concerned. Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by A.A. Balkema, Rotterdam, provided that the base fee of US$1.00 per copy, plus US$0.10 per page is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, USA. For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged. The fee code for users of the Transactional Reporting Service is: 90 5410 351 5/94 US$1.00 + US$0.10.

Published by A.A. Balkema, P.O. Box 1675, 3000 BR Rotterdam, Netherlands A.A. Balkema Publishers, Old Post Road, Brookfield, VT 05036, USA

ISBN 90 5410 3515 © 1994 A.A. Balkema, Rotterdam Printed in the Netherlands

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Groundwater—Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

04 Table of contents

54

aot

Preface

Ix

Organisation

XI

1 Dry climate problems The National Well Inventory, Sultanate of Oman J.C. Barnett & GV.Smith

3

Agricultural production or conservation of groundwater? A case study of the Wajid aquifer, Saudi Arabia M. Eid Al;Ahamadi, G.Jones & J.Dottridge

13

Groundwater utilisation and management in the state of Karnataka in India R. Prasad

23

2 Salinity management and re-use Linked enhanced discharge — Evaporative disposal systems C.Otto & R.Salama

35

Exploitation of freshwater lenses — Implementation of scavenger wells in Pakistan

45

C.R.C.Jones & J.J. Van Wonderen

Experimental citrus irrigation with reclaimed wastewater on a Spanish coastal aquifer

55

M.V.Esteller, A.Durdn, I.Morell, P.Garcia-Agustin & L.Lapena

3 Pollution Atrazine concentrations in chalk aquifers and the implications for future water treatment PJ.Aldous & J.-Turrell

= 67

Removal of organic compounds from a groundwater in an urban area near London F Bourgine, J.L.Chapman & H. Kerai Groundwater as the source of the pollution of the coastal waters of the Black Sea in Georgia

15 / 83

/

B. Kalandadze, G.Samarguliani & I. Khomeriki

Groundwater quality monitoring with special reference to aquifer protection L.Clark, K.Lewin, C.P.-Young, N.C. Blakey, D.Chadha & M.Eggboro

87/

4 Nitrate

A preventive action against nitrate water pollution into drainage basin M.-C. Huau Analysis of groundwater pollution by nitrates in a Spanish coastal aquifer under intensive horticultural land-use J.Guimera & L.Candela

Evaluation of DRASTIC — A regional aquifer vulnerability assessment procedure C. Barber, L.E. Bates & H.Allison

5 Surface/Groundwater interaction Possible effects of climatic changes on low flows of Estonian rivers M.M.Timofeyeva

131 Vv

Conjunctive use of surface and groundwater for small-scale irrigation in Zimbabwe 1. Moyo

145 ¥

Representation of river-aquifer interactions in regional groundwater models

155 %

M.Nawalany, A.Recking & C. Reeve

6 UK drought management Anglian Water’s groundwater drought strategy E.J.Smith

Drought in the south — Implications for the management of groundwater resources

167 is

179 A

G.D.Warren

Application of an integrated model to chalk catchments A.J.Wyness, P.W.Rippon & R.B.Wardlaw

Vi

197 /

7 Artificial recharge Artificial recharge developments in the United States R.D.G.Pyne

Disaen

Drought management using artificial aquifer recharge in north London M.J.O’ Shea

223

Experience with artificial groundwater recharge in Karany M. Knézek & P.Kubala

j35

8 Management ' An expert system for water resources management D.Chaffey, K.Ahmad, S.Griffin & P.Shaw

Dg

The optimal economic exploitation of groundwater: An alternative to the capacity expansion of existing multipurpose water resources systems M.R.Mazzola

Za) A

Author index

264

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Groundwater— Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Preface

The old Chinese saying ‘a city can be moved but not a well’ exemplifies the importance of groundwater. An aquifer is a receptacle, a fixed resource, and unlike air or flowing surface water, one that is virtually nonrenewable. If it becomes too badly depleted or polluted it must be abandoned. Groundwater provides about three-quarters of Europe’s population with their water supplies. Industrial, agricultural and domestic consumers depend heavily on water drawn from convenient aquifers which are replenished by regular and consistent rainfall. Over abstraction and pollution are presently depleting and degrading aquifers at rates which are simply not sustainable. The nitrate ‘time bomb’ of agricultural chemicals leaching inexorably down through the soils now affects nearly 25% of Europe’s farmland at levels above the EC’s drinking water standard. Industrial and municipal waste disposal practices add more damaging threats from organic and toxic chemicals. Groundwater withdrawals exceeding natural replenishment are lowering water tables and causing contamination of the resource through the intrusion of seawater and upconing of mineral-rich fossil water. Without urgent remedial action, between 20,000 and 60,000 km’ of Europe’s groundwater systems will be rendered unusable over the next 50 years, with a dramatic effect on the sustainability and costs of future water supplies. There is increasing concern internationally about the long term sustainability of groundwater resources. The sustainable use of groundwater is complicated by reductions in groundwater recharge which result from drought. This has been a serious problem in many European countries in recent years and has led to a significant reduction in the quantity of water stored in underground reservoirs. Drought in the African continent could result in the greatest environmental and human disaster ever to occur. Sustainable use can only be achieved through proper groundwater management as part of an integral approach to resources (surface water, environment, physical planning). Groundwater should be managed in such a way that no loss of potential function occurs and the diversity of the ecosystems is maintained. Within England groundwater forms approximately 35% of the water supply. This average value masks significant regional variation. The greatest contribution to the IX

water supply is in the Southem region of the National Rivers Authority where groundwater is 74% of the water supply. Brighton is in this region and is thus an appropriate venue for the conference. The main topics covered by the conference are: — dry climate problems — salinity management and re-use — pollution — nitrates — surface/groundwater interaction — UK drought management — artificial recharge — management I should like to acknowledge the contribution made by members of the National and International Organising Committees. In particular I should like to thank the National Organising Committee who have been extraordinarily committed and instrumental in their assistance. Finally, I should like to thank Jacqueline Watts, our Conference Organiser for the efficient and enthusiastic way in which she has carried out her many duties. Charles Reeve

HR Wallingford Ltd

Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Organisation

UK ORGANISING COMMITTEE Dr Charles Reeve (Chairman), HR Wallingford Ltd Dr Lewis Clark, WRc Medmenham

Mr Brian Connorton, Thames Water Utilities Dr Stephen Foster, British Geological Survey

Prof. John Lloyd, University of Birmingham Prof. John Mather, Royal Holloway and Bedford New College, University of London Mr Bruce Misstear, Mott MacDonald Mr Howard Robinson, Aspinwall & Company Dr Andrew Skinner, National Rivers Authority

CONFERENCE ORGANISER Jacqueline Watts, HR Wallingford Ltd INTERNATIONAL ORGANISING COMMITTEE Dr Chris Barber, Commonwealth

Scientific and Industrial Research Organisation,

Australia Prof. Jean Fried, European Institute for Water, Belgium

Prof. Peter Kjeldsen, Technical University of Denmark Dr J.W. Lyklema, International Groundwater Modelling Centre, Europe Miss Kym Morton, Geological Society of South Africa Prof. Marek Nawalany, Warsaw University of Technology, Poland

ACKNOWLEDGEMENTS The valuable assistance of the UK and International Organising Committees and Panel of Referees is gratefully acknowledged.

XI

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Groundwater — Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

The National Well Inventory, Sultanate of Oman J.C. Barnett & G.V.Smith Ministry of Water Resources, Sultanate of Oman

ABSTRACT: The Sultanate of Oman, one of the driest countries in the world, relies mainly on groundwater for agricultural, industrial and rural domestic water supplies. Recent overabstraction has led to the decline of a number of traditional water sources, threatening the livelihood of rural communities which have endured for thousands of years. Saline intrusion has penetrated many areas of the Batinah Plain, where most of the nation’s agricultural produce is grown. The Ministry of Water Resources has commissioned a national well inventory, with the task of surveying an estimated 170,000 wells throughout the country, and of assessing present patterns of water use. With integrated assessment of groundwater reserves, this is intended to provide the information necessary to manage the nation’s groundwater resources, so that national development priorities can be sustained.

1 INTRODUCTION The Sultanate

of Oman,

on the southeast

corner

of the Arabian

Peninsula,

is one

of the driest regions in the world. The people of Oman rely almost entirely on groundwater for agricultural, industrial and rural water supplies. As boreholes and dug wells with motorised pumps have progressively replaced more traditional types of abstraction, mining of groundwater has intensified. Overabstraction is leading to declining groundwater levels in most agricultural areas, and is inducing seawater intrusion beneath the Batinah Plain, which provides most of the Sultanate’s agricultural produce. There is now an urgent need to determine the distribution of groundwater resources and their pattern of use, in order to produce a plan for sustainable management of these resources, and to arrest and reverse the consequences of

present overabstraction. Accordingly the Ministry of Water Resources (MWR) has implemented the National Well Inventory Project, with the task of surveying an estimated 170,000 wells throughout the country, and of collecting information on water use and areas of different crops. With the active interest and support of His Majesty Sultan Qaboos bin Said, the Ministry is committing all necessary manpower, equipment

and materials to enable the inventory to be completed within three years. Since the problem of overabstraction is so widespread, it is necessary to carry out the inventory on a national scale, to allow comprehensive management plans to be drawn up. inventory

The

started

1“ December

on

1992, with

eighteen

field

teams

in

1993,

operation. An expansion to thirty - four teams will be effected by October with a further expansion to sixty - four teams planned for early 1994. The information being collected is used to produce comprehensive reports on hydrogeology and water use, catchment by catchment, for the entire country. These reports

will form

the essential

The

northern

AND

of water

resources,

at the

scales.

local, regional and national

2 TOPOGRAPHY

basis for management

RAINFALL

part of Oman

consists

of a rugged

mountain

elevation of over 3000 m, and a coastal plain (the Batinah

range

rising to an

Plain), some 250 km long

and 20-30 km wide, where most of the country’s agriculture is concentrated (Figure 1). There are also localised areas of agriculture on piedmont and intermontane alluvium on both sides of the watershed formed by the mountain range. In the south a smaller coastal plain (the Salalah Plain), about 75 km long and 5-10 km wide, is backed by an escarpment rising to over 1000 m in elevation. The central part of the plain supports irrigated agriculture. The rest of the country, including all of the interior, consists mainly of desert plains of gravel and sand, with the sand sea of the Empty Quarter along the border with Saudi Arabia. The average annual rainfall over most of Oman, including the Batinah Plain, is less than 100 mm, so that the climate may be described as one of almost continuous drought, with occasional slightly wetter years. Recharge to groundwater occurs mainly where runoff from the mountains infiltrates into piedmont and intermontane alluvium, and into alluvial sediments on the coastal plains.

3 HISTORICAL

WATER

- USE

Most water supplies in the past were obtained by means of underground canals conveying groundwater for many kilometres from the water - table to the surface, or by surface canals tapping shallow underflow in wadi gravels. In areas of shallow water - table, hand - dug wells were also used for water supply, but abstraction was limited by the necessity of drawing water by hand, or by means of draught animals. The canals, whether underground or surface, are termed aflaj (singular: falaj) in Oman. Many of them were originally constructed 1500 - 2000 years ago and have been in use ever since. Aflaj are self - regulating, since periodic fluctuations in recharge from rainfall lead to variations in yield, necessitating adjustment of cropped areas from year to year. They have thus proved an effective method for long-term use of scarce water resources. Aflaj are communally owned and managed, with water being distributed in rotation to each landholding, in cycles ranging from 4 - 16 days, although in most

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1 LOCATION MAP - OMAN

SAND MOUNTAIN

cases the cycle is of 8 days. These cycles are well suited to the water needs of the traditional crops of date palms, alfalfa and wheat, but they do not facilitate the growing of vegetables and fruit, which generally need more frequent watering. The recent advent and increasing use of motorised pumps has seen a growing reliance on bores and dug wells, with consequent overabstraction in many areas.

4 THE

PRESENT

SITUATION

The availability of pumped supplies from individually-owned dug wells and boreholes has enabled cultivation of fruit and vegetables, providing a much higher economic return than from more traditional crops. It has also allowed the expansion of agriculture into areas which were previously unexploited because of deeper water - tables. As a result the area under agriculture has increased markedly since the early 1970’s, the increase being as much as fourfold in some regions. Overabstraction, with consequent mining of groundwater storage, is now occurring in almost all agricultural areas of the Sultanate. In inland areas the amount of groundwater storage is quite limited, so that water levels are declining rapidly. Many aflaj are drying up because of abstraction from wells upstream from their source, thus threatening the economic and communal life of communities which have endured for as long as two thousand years. Many aflaj now have to be supplemented from pumping wells. Even

on

the

Batinah

Plain,

where

the

alluvial

sediments

form

an

extensive

unconfined aquifer several tens of metres thick, water - tables are dropping in some areas by up to 0.5 m/year. The water - table in some of the more intensely farmed districts is now 5 - 10 m below sea level. As a result seawater intrusion has penetrated 2 - 3 km inland along some parts of the coastline, turning previously fertile farmland into a wasteland of dead and dying date palms. The affected areas are mainly on the best soils near the coast, where the smaller traditional

farms are

located. The much larger new farms, further inland, are as yet largely unaffected. The problem of overabstraction has already been recognised for some time, and some remedial measures have already begun, for example: a) Treated waste water is used for irrigation of parks and gardens in the capital area. b) Public awareness campaigns, urging water conservation, are conducted by radio, newspapers and television and by way of lectures in schools and civic centres. c) Better use of existing resources, by installing more efficient irrigation systems, is being encouraged. d) A number of recharge dams have been constructed, and others are planned, to intercept and regulate the infrequent surface water flows which would otherwise bypass farming areas. These

various

actions,

although

worthwhile

in themselves,

have

yet to show

significant effect on the general pattern of overabstraction. MWR commitment has also led to the development of appropriate water management policies and significant progress has been made. Major activities include review of current legislation on water and water use, preliminary studies on metering and establishment of protection (exclusion) zones around existing 6

municipal wellfields. The National Well Inventory Project is a key element in the MWR’s programme to manage the water resources of the Sultanate, and follows a registration programme for all existing wells and bores, which was completed in July 1990, with 167,000 wells having been registered. Any well constructed since then, or any material modification to an existing well, requires a permit.

5 PROJECT

START-UP

Three pilot projects were set up in October 1991, in which field procedures and organisation were tested and improved in preparation for the national project. The pilot projects were located in areas representing different geographical and agricultural situations, and of known water stress, namely Barka, Al Buraymi and Salalah. On completion of the 12-month pilot-project period, staff were recruited in preparation for the start of Phase 1 of the national project on 1“ December 1992. Training programmes were established to provide a general background in water resources and basic mathematics and a thorough understanding of inventory procedures. These programmes ranged from 1-3 months duration according to individual staff requirements. The start of the national project was preceded by a public awareness campaign in newspapers, and on radio and television, to inform the public about the inventory and to invite their cooperation. Pamphlets and posters were also distributed, and lectures given to schools and other community organisations.

6 ORGANISATION AND STAFFING INVENTORY PROJECT Eighteen

field teams are now operating

are mainly concentrated

on the Batinah

OF THE

NATIONAL

WELL

from four regional project offices.

Efforts

Plain, with eight teams based in Barka, and

six in Sohar. Two teams are operating from each of the other two regional offices, at Al Buraymi and Salalah. Support staff are located at each regional project office. A headquarters office in Muscat manages and coordinates all technical, operational and quality control aspects for the entire project, and provides administrative and support services, including procurement of equipment and materials. The project now employs 137 people, of which 84 are technical staff, and 53 administrative and support staff. All field teams and most support staff are Omani nationals. Recruitment of additional staff for Phase 2 of the project is underway, with the aim of having 34 inventory teams in the field by October 1993, with 15 teams each in Barka and Sohar, and. two each in Al Buraymi and Salalah, as at present. A total of 81 additional staff will be employed, of which 66 will be technical and 15 administrative. Phase 3 of the project, planned for early 1994, will see 64 field teams in operation, and the opening

of three

new regional offices, each with ten field teams, at Ibri,

it

REFERENCE

Ae Fe

fea

NO. a

9.

AGRICULTURAL

9.1

PROPERTY

(A pad G gSysSI! pladiols GasWy slid! obly JAS!) |

(m2)

TOTAL CROPPED AREA (INCLUDING TREES)

(m?)

TOTAL DEVELOPED BUT

(m2)

TOTAL UNDEVELOPED

(m2)

UNCROPPED AREA

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(NOTE: COMPLETE PROPERTY & LAND USE SKETCH IN SECTION 8)

TOTAL PROPERTY AREA

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2.2 Climate

The climate is arid with average annual rainfall of between 30 and 40 mm, increasing towards the mountains. The inter-annual variation in rainfall is high. There are marked seasonal changes in weather, with mean daily maximum temperatures ranging from 16°C in January to 36°C in July. Winter and spring are mild, with rainfall between December and May, peaking in March and April. In contrast, the summers are extremely hot and dry, with relative humidities below 16%.

Evaporation rates are very high, with monthly values at least 10 times the rainfall, even in the spring. Measured pan evaporation ranges from 3300 to 3900 mm/year. Estimates of potential evapotranspiration vary more widely, depending on the assumptions involved in the method of computation (Al-Ahamadi, 1991). Average annual rates for the climate station at As Sulayyil ranged from 1755 mm from the Jensen Haise method and 2155 mm from the Blaney-Criddle method to 2376 mm from Thornthwaite’s method. The latter is considered to be the most representative for the arid conditions. As the rainfall occurs in occasional, intense storms, there is potential for rapid run-

off, associated with the steep unvegetated slopes of the western mountains, isolated hills and the main scarp of Jebel Tuwayq. The pattern and morphology of numerous channels confirms this possibility, but unfortunately no measurements of surface flows have been attempted.

2.3 Geology The study area is located near the western margin of the Arabian platform, close to the outcrop of the Arabian Shield. The Wajid Formation is the oldest member of the sedimentary sequence in southern Saudi Arabia and rests unconformably on Precambrian crystalline rocks. It dips eastwards and is unconformably overlain by the cherty limestones of the Khuff Formation. Although originally dated as Lower Permian, trace fossils in the Wajid outcrop have indicated a Cambrian to Ordovician age (Dabbagh and Rogers, 1983). The outcrop of the Wajid Formation runs approximately north-south for over 300 km, up to 100 km wide, as shown in Figure 2. Step faults, trending NW-SE, divide the formation into blocks and the outcrop is limited by the faults bounding the Kumdah graben (Italconsult, 1969). The maximum thickness of the formation is 550 m, but rarely exceeds 300 m in the outcrop area. The sandstones are of continental origin in the south, grading to marine sandstones in the north (Garfield, 1985). The lower part of the formation comprises mostly fine-grained micaceous sandstones, overlain by thick, massive or cross-bedded, medium to coarse-grained sandstone, with thin conglomeratic layers (Kellogg et al, 1986). Parts of the study area are covered by superficial deposits; aeolian sand, fan gravels at the base of the Tuwayq escarpment and extensive alluvial gravels in the channels of Wadi Ad Dawasir.

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45°

Figure 2. Simplified Geological Map, showing Distribution of Aquifers

2.4 Hydrogeology There are two aquifers in the study area; the Wajid sandstones and the Quaternary alluvium. The resources of the shallow, alluvial aquifer are very limited, because the alluvium is normally thin, although it reaches a maximum of 90 m in the main wadi, of restricted extent and largely unsaturated. The eastern part of the alluvium close to the boundary with the thick dune sands is dry. Test pumping of five wells in the thicker part of the alluvium gave an average transmissivity of 600 m’/d. Historically, wells dug into the shallow aquifer were the main water supply for the small local population, but now many of the wells are dry and there is very little abstraction. Consequently there are few recent measurements of water levels in the Quaternary aquifer, although past observations showed that the groundwater flow followed the directions of surface drainage. Some recharge from rainfall occurs, with a sharp rise in groundwater levels observed after major floods, eg those in November 1967 (Al-Ahamadi, 1991). The Wajid Formation is the main regional aquifer and has supported the successful implementation of irrigated agriculture in Wadi Ad Dawasir. The aquifer is unconfined in its extensive outcrop area and, dipping eastwards, becomes confined by younger sediments. In the area of detailed study, the aquifer top is between 300 and 500 m below ground level. Analysis of pumping tests from eight boreholes in the confined aquifer showed a range of transmissivity values from 460 to 2200 m7/d, typically 1600

m’/d with an average value of 4x10* for the confined storage coefficient.

In 1965, when the earliest wells were drilled in the Wajid aquifer, most confined boreholes overflowed at the surface. Water levels ranged from 90 m above ground level in the confined zone to 40 m below ground level in the outcrop area (Italconsult, 16

1969). By 1987, the piezometric levels in the confined aquifer had fallen to between 43 and 150 m below surface. The pre-development flow pattern was predominantly from south to north, with the flow converging towards Wadi Ad Dawasir, which formed a natural discharge area for the Wajid aquifer through leakage into the alluvium. This pattern has now been modified by pumping. The flow directions suggest that recharge, probably through infiltration of surface runoff, occurs in the southern part of the Wajid outcrop. Previous estimates of recharge vary from 0 to 90 MCM/year (Italconsult, 1969), but values between 20 and 40 MCM/year are more likely.

2.5 Water Quality The chemical trends in the Wajid groundwaters support the interpretation of the flow converging towards a discharge zone in Wadi Ad Dawasir. The water in the Wajid aquifer is dominantly of Ca-Cl type. Normally a trend of deteriorating water quality from outcrop to the confined aquifer would be expected, but the measurements of EC and TDS reveal a different pattern. In the unconfined aquifer, the total dissolved solids increase gradually towards central part of the wadi, from 650 mg/l in the southwest to 900 mg/l in the northeast. The lowest measured TDS values, 400 mg/l occur in the confined aquifer near As Sulayyil in the eastern part of the study area. The TDS of the confined groundwater also increases towards Wadi Ad Dawasir, indicating flow in a westerly direction, opposite to the geological dip. Na-Cl waters, with higher salinities between 1200 and 8000 mg/l, are found in the shallow alluvial aquifer and from some Wajid boreholes in the main wadi, where there is hydraulic continuity between the two aquifers. Although not ideal for drinking, most of the groundwater is suitable for livestock and irrigation. With the exception of the few saline wells, the water has a low sodium hazard and medium to high salinity hazard and thus, with care, it can be used for

irrigation on all types of soil in the project area.

2.6 Groundwater

Use

Abstraction from the Wajid aquifer increased rapidly between 1984 and 1988, as illustrated by the growing numbers of boreholes shown in Figure 3. As the study area is large and isolated, remote sensing was used to define the growth of irrigated agriculture.

Six Landsat

images

of the area, taken

between

1972

and

1988, were

processed to show distinctly the contrast between the crop circles and surrounding desert. Comparison of successive images allowed accurate definition of the amount and location of irrigation, and hence the rate of groundwater abstraction. The irrigated areas are shown on Figure 4. Much of the agricultural development in the Wadi Ad Dawasir area has taken place in large farms, where huge areas are irrigated by centre pivots, usually spaced 1 km apart. Each well supplies two centre pivot systems, 500 m long, which are used to irrigate a circular field 1000 m in diameter with crops such as alfalfa,wheat and other grains. In the confined area, the boreholes are typically between 400 and 650 m deep, pumped at rates between 6500 and 10000 m°/d, for an irrigation season of 180 days per

Wee

cee

we

oy

boreholes irrigation of Number

0 1972

1974

1976

1978

1980

1982

1984

1986

1988

Year

Figure 3 Growth of Irrigated Agriculture, indicated by Numbers of Boreholes

Figure 4 Irrigated Areas in 1988, derived from Interpretation of Landsat Image 18

(m) level Depth water to

Year 1985

Figure

1986

1987

5 Hydrographs of Observation Wells in the Confined Wajid Aquifer

year. The total abstraction from the aquifer was calculated by combining these values with the number of boreholes, giving estimates of 400 MCM in 1984, rising to 4000 MCM in 1988. As shown by Figures 3 and 4, the development of groundwater exploitation and irrigated agriculture in the study area is intensive, on a very large scale and has been extremely fast. There appear to have been no controls imposed on the number, location or density of the boreholes and little monitoring of the effects on piezometric levels. However, from the available data, the trend is clear. Figure 5 shows the hydrographs of three observation wells, which illustrate both the long term trend, a decline of 10

m/year, and the superimposed seasonal fluctuations of 50 to 60 m. As these fluctuations are due to seasonal pumping and not the result of intermittent recharge, the amplitude is expected to increase as abstraction is intensified. Circumstantial evidence of falling water levels due to local and regional drawdown and interference effects is provided by the lowering of pumps and deepening of boreholes after only a few years’ operation (Al-Ahamadi, 1991).

2.7 Prediction of future trends

To forecast the effects of the high abstraction rates on the future piezometric levels in the Wajid aquifer, a groundwater model of the study area was set up, using the widely accepted MODFLOW package (McDonald and Harbaugh, 1988). The model was calibrated in two stages; a steady state calibration for 1974 with little pumping, followed by transient conditions from 1974 to 1989 with increasing abstraction. Although there are some uncertainties in the data base, the model produced a good 19

simulation of observed flow patterns and changes in piezometry with time. Subsequently, the model was run predictively to assess the effects of continuing the present high abstraction for a further 20 to 40 years. The results showed that the rapid drawdown in the wellfield areas will continue, reaching 500 m after 20 years, with an accompanying increase in pumping lift and energy costs. This demand is met partly from storage as a large portion of the confined Wajid becomes unconfined and partly by regional throughflow, which is diverted towards the wellfields.

3 CONCLUSIONS The case study of the Wajid aquifer provides a striking example of rapidly growing, large scale groundwater exploitation. The development of irrigated agriculture in Wadi Ad Dawasir is very successful, with the production of large quantities of fodder and wheat, which required a storage capacity of 500 000 tonnes by 1987. Despite the large numbers of boreholes, there has been little systematic evaluation of the resources and

recharge to the Wajid aquifer, and there is evidence of large drawdowns, declining regional water levels and some decrease in borehole yields. The modelling study produced gloomy forecasts of extensive dewatering of the aquifer, although based on the conservative assumption that abstraction would continue at 1987 rates. The information from the detailed study of Wadi Ad Dawasir highlights three important aspects that are missing from the groundwater development; monitoring, management and control. It must be emphasised that these features are not unique to the study area, nor to Saudi Arabia, but illustrate the key issues to be addressed in the exploitation of groundwater for irrigated agriculture. In all groundwater development schemes, a continuous programme of monitoring abstraction rates, piezometric levels and water quality provides essential data for comparison of past and present conditions and assessment of the effects of changes in abstraction. Planned development also requires a resource assessment at an early stage, to be revised as necessary when additional data are collected from new drilling. From these basic data, a management plan for the aquifer should be formulated to balance the benefits of short term, high rates of exploitation against those of prolonged abstraction at a lower rate. Implementation of a plan would inevitably require controls on drilling and pumping, through licensing or a similar system, to prevent ad-hoc development. To balance the long term objectives of enhanced agricultural production and future availability of water, a determined approach to aquifer management is essential.

REFERENCES Al-Ahamadi, M.E. 1991. Hydrogeology of the Wadi Ad Dawasir basin, Southern Saudi Arabia. Unpublished PhD thesis, University of London. Dabbagh, MLE. and J.J.W.Rogers. 1983. Depositional environments and tectonic significance of the Wajid sandstone of south Saudi Arabia. J. African Earth Sci., 1:47-57. El Khatib, A.B. 1980. Seven green spikes. Kingdom of Saudi Arabia: Ministry of Agriculture and Water.

20

Garfield, L. 1985. Evolution of the sedimentary environments of the cover rocks of the Arabian Peninsula. Kingdom of Saudi Arabia: Ministry of Petroleum and Mineral Resources. Italconsult. 1969. Water and Agricultural Development Surveys for Area II and III, Final report: Wadi Dawasir selected area, Geohydrological Investigation. Kingdom of Saudi Arabia: Ministry of Agriculture and Water. Kellogg, K.S., D.Janjou, L.Minoux & J.Fourniguet. 1986. Geological map of the Wadi Tathlith quadrangle, Sheet 20G. Kingdom of Saudi Arabia: Ministry of Petroleum and Mineral Resources. McDonald,

M.G. and A.W. Harbaugh.

1988. A modular three-dimensional finite

difference groundwater flow model, Techniques of Water Resources Investigations, Book 6. Washington: US Geological Survey. Parker, M. 1989. With huge exports of wheat, agriculture in Saudi Arabia: A spectacular success. The Muslim World League J., 17:57-58.

21

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Linked enhanced discharge — Evaporative disposal systems Claus Otto & Ramsis Salama CSIRO Division of Water Resources, Perth, W.A., Australia

ABSTRACT: Land and stream salinization in the Western Australian wheatbelt has developed as a result of clearing of native vegetation which caused a change in the hydrological balance. This includes a 10 to 30 fold in crease in recharge and discharge. Enhanced discharge by windmill pumping is a viable method to reduce excess pressure heads of deep semi-confined aquifers in discharge areas and consequently lower the water table at shallower depth. It is a low cost, interim solution to halt and prevent salinization in the wheatbelt of Western Australia. Long-term field experiments in three catchments and

modelling have shown that pumping (15-30 m3d-!) can reduce water levels by 1 to 2 mata radial distance of more than 2 km after several years of pumping. In some areas the pumped groundwater can be reused for irrigation or livestock. For highly saline water, disposal requires on-farm evaporation ponds or sacrificial basins which are hydraulically linked to the pumping scheme. The enhanced discharge method should be part of an integrated catchment management program (eg crop rotation, revegetation) for the restoration of saline land and streams. The technology is transferable and applicable to other irrigated and non-irrigated salt-contaminated regions.

INTRODUCTION One of Australia's largest and most environmental problems is land and stream degradation. Dryland salinity is one of the major contributors to this problern and affects the productivity of large areas of agricultural lands, decreases the water resources available for consumption, and degrades the ecological values of wetlands, lakes, rivers and their associated habitat. In South Western Australia progressive clearing of over 16x10® ha of native vegetation

since the turn of the century (George, 1990a) and their replacement with dryland farming systems dominated by annual shallow-rooted pastures and cereal cropping are the cause for secondary (man-induced) soil salinity (Peck et al., 1983; Peck et al., 1987; Schofield et al., 1988). Clearing has also seriously affected the quality of surface waters. About 3% of arable agricultural land (about 4500 km2) is adversely affected (A.B.S, 1990). It is estimated

to increase at an annual rate of about 6%, unless successful

groundwater management systems are adopted. Clearing caused a shift in the hydrological balance and lead to an 10 - 30 fold increase in recharge in the intake areas of the catchment (George, 1990b; Johnston, 1987; Peck et al., 1983; Salama et al., 1992). This induced an increase in saline groundwater discharge due to elevated hydraulic heads

in the aquifers. The salt-bearing groundwaters rise to the surface and the water evaporates

35

leaving behind the salt. The extent of salinization increases from catchment divide to valley floor (Salama et al., 1993) and upstream of geological structures (Engel et al., 1987). The

rise in water levels rejuvenated groundwater flow through paleao channels and increased baseflow to drainage lines (Salama et al., 1992).

The management of excess groundwater can be achieved by either reducing the groundwater recharge and/or enhancing groundwater discharge. Revegetation strategies (tree

planting) can be effective in reducing recharge in upgradient regions (Schofield, 1992).

However, even if rates of recharge are reduced to preclearing levels, piezometric levels in discharge areas may continue to rise at the present rate for long periods due to lateral spreading of groundwater mounds in recharge areas since clearing. It is therefore inevitable that salt areas will continue to increase for some considerable time despite implementation of revegetation strategies, unless ways of controlling groundwater levels in the short term can be found. Hydrogeological techniques can be applied to target salinized regions directly and to reduce water levels in salt-affected and water-logged areas immediately. Preliminary modelling of first order catchments (Salama et al., 1992), indicate that pumping can reduce groundwater pressures for distances up to 2 km away from a pumping borehole. Based on these findings a project was carried out in 3 catchments in Western Australia as part of CSIRO Land and Water Care program. The main objectives of the project were to evaluate techniques for enhancing rates of saline groundwater discharge by pumping at a minimum effective rate necessary to reduce pressures and water levels from local and regional aquifers and to experiment with methods of disposal of saline groundwater into terminal lakes, saline streams and evaporation ponds. This paper will summarized the results from a 2 year enhanced discharge trial in a catchment area in the northern wheatbelt of Western Australia (East Perenjori, Figure 1); and will discuss disposal options for the saline effluent, specifically the feasibility of on-farm linked pumping - evaporative disposal systems (Quairading, Figure 1).

BACKGROUND The East Perenjori catchment is located in the northern part of the wheatbelt of Western Australia (Figure 1). The climate is Mediterranean with hot dry summers and mild wet winter. The first-order catchment is located 30 km east of Perenjori and has an area of 139 km2 (Figure 2). It is an elongated basin (23 km long, 5-8 km wide). Elevations range from 270 to 366 m above m.s.1., annual rainfall is about 310 mm.

The experimetal evaporative disposal system near Quairading

is located in the eastern flank

of the rejuventated Salt River paleaochannel system (Figure 1) which drains a total catchment area of about 8.8x104 km2. The channel is filled with alluvium of coarse sands within a sequence of clays and sands clays. Elevation is about 214 m above m.s.1., annual

rainfall is about 330 mm. General Geology

The catchment lies within the Western Gneiss Terrain (deformed and banded gneiss, metasediments, iron formation) and the Southern Cross Province of the Yilgarn Craton (greenstones, gneisses and granitoids). The occurrence of a network of dykes, faults and basement highs create conditions for a complex array of hydraulic barriers to groundwater flow. The Yilgarn Craton is dissected by two major groups of subvertical basic dykes: one group (dolerite or gabbro) is east-west trending, widely spaced and distributed throughout the Yilgarn Craton. The other group is north-west trending and comprised of dense swarms

36

Geraldton fe 50)

Locality Kalgoortie@

7 \

e002) Esperance 0)

2000

4000

metres

QS 1400

1200

800 Albany

KEY

@

Location of catchments Sa

oe

1. Cuballing catchment 2. East Perenjori catchment 3. Wallatin Creek catchment

4. Linked v=)

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Approximate

“Jot

the Wheat

pee

Abe

—:—- Catchment boundary

kiometres —600—

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fsohyel of average annual rainfall (mm)

s

--f=

system

QA Relict

EGEG

drainage

Lineaments Duricrust Rock outcrop

[___] Basement high

boundary

Belt.

Figure 1 Location map of the enhanced discharge and the linked pumping-disposal system sites and the boundary of the

Figure 2 Geomorphological! features and windmill site at East Perenjori catchment

wheatbelt

of relatively thin dykes (theoleiitic dolerite) that are concentrated around the craton margins (Myers, 1990).

The craton is covered by transported or residual, unconsolidated to indurated regolith. It includes alluvial, aeolian and colluvial sediments, with remnants of siliceous, ferruginous and calcerous duricrusts. Unconsolidated to semiconsolidated, dominantly sandy alluvium occurs along most major drainages. Alluvial deposits grade laterally into colluvial, diluvial and residual deposits, and all have undergone varying amounts of aeolian reworking in most areas (Hocking et al., 1990).

Hydrogeology The sedimentary sequence which covers most of the alluvial channels and extends towards the flanks and the weathered and fractured bedrock in the cleared catchments are now in most cases saturated with groundwater. The aquifer types range from unconfined in the sandplains and alluvial sediments to semiconfined-confined in the underlying weathered bedrock. The degree of confinement depends on the thickness and the degree of weathering of the aquitard. Long term pumping in similar catchments in the wheatbelt showed that transmissivities range from 2 to 50 m2d-1 (George, 1990b; Otto, 1993; Salama et al., 1992:

Salama et al., 1993). The East Perenjori catchment (Figure 2) is 90 % covered by superficial sediment and weathered material, which included lateritic duricrust, alluvium and colluvium. Basement rock crop out along the sides of the catchment. Surface water drains to the northeast into

37

Mongers Lake through a main channel which originates in the upper part of the catchment. The channel follows along a northeast lineament which passes through a zone constricted by basement rock. The central part of the catchment is constricted by NE-SW trending basement highs which cut across the relict channel which has been reactivated as a drainage

system by increased surface runoff and groundwater discharge after clearing (Salama et al. 1992). A perched aquifer can be found on top of a hardpan in the valley floor areas. In absence of a hardpan a shallow unconfined aquifer developed. A second unconfined aquifer extends below the sandplains and over most of the alluvial channels and becomes semiconfined below clayey layers. A semiconfined to confined aquifer extends over most of the catchment and is formed of weathered material at the divide and fluvial sediments in the valleys. Groundwater from deep aquifers upstream of the basement high have highest

salinity levels (40 000 mL-}). ENHANCED DISCHARGE Site installations and methods

Free-energy pumps (windmills: post tower 6 m, wheel 3.7 m, 100 mm pump) were installed in the semi-confined aquifers of the catchments. The discharge rates varied between 15 to 30 m3d-!, depending on the wind velocities. A piezometer network monitored the changes in water levels at different depths since June 1990 (Figures 3 and 4). Water levels were measured using Wesdata® loggers and probes. Automatic climate stations recorded daily atmospheric pressures, relative humidities, solar radiation, wind speed and rainfall. Daily water samples were collected using automatic water samplers. The samples were analyzed for electrical conductivity (EC) and chloride (Cl). Transmissivity and storativity values were obtained by pumping test analyses using Theis's method for unsteady flow (Table 1).

Table 1 Hydrogeological parameters of the East Perenjori catchment

area (m2

East Perenjori 3.2x107

pre-clearing recharge post-clearing recharge

88 m3d-1 41-82 m3d-!

discharge

total 184 m3d-!, to drain

; transmissvity

122 m3d-1 2.3 m2d-1

storativity

15-3

drawdown rate at 100 m

1.5- 3 mmd-!

’

Recharge and discharge

Uniform recharge rates of 1 and 5-10 mmy”! for pre and post clearing periods, respective ly, have been assumed in this study to calculate the volume of recharge (Johnston, 1987; Peck

et al., 1983; Salama et al., 1992; Salama et al., 1993b); Table 1).

The hydrogeologic system compensated for the increase in recharge by increasin g the

38

lateral hydraulic gradient towards the area of groundwater discharge, increasing the transmissivity of the unconfined aquifers and expanding the area of groundwater discharge. The vertical hydraulic gradients in discharge areas increased with depth causing groundwater to flow upward. Consequently, the seepage velocities and discharge rates also increased. The discharge volume for the part of the catchment which contributes to the investigated discharge area was estimated by flow net analysis (Table 1). This was further validated by estimates of recharge over the area which contribute to the discharge.

Results

Pumping started at East Perenjori in August 1990. Waterlevel drawdown in the well closest to the pump (PO1), was nearly 5 m for the period from August 1990 to April 1991 (Figure 3). The water level recovered to its initial level in September 1991, but from mid September the water level continued to decline again. For well PO2 the maximum drawdown of about 3.5 meters was reached by the end of February 1991. Since then the water level has rose by about 1 m in the middle of February and at the end of October 1991. This was caused by reduced pumping rates and rainfall during the winter. The drawdown in well PO3 was

295

Figure 3 Water level drawdown for wells PO1-3 at East Perenjori due to windmill pumping; see Figures 4 for well locations and depths

294

293

292

OD.) A.H Water (metres Level

291

Soria

a

ier

tet

tote

ttl

ie

JEMAMJIJAS ON DIJFMAMJIJSJAS OND 1990 1991

Eest

scolo

1:

502

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no

pumping

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(m,

East

AHD)

ecole

1:

Perenjorl

S00

one

year

hydreul

tc

pumping

heeds

(m,

AHD)

Figure 4 Composite water level maps (heads, m AHD) before and after one year pumping at East Perenjori

39

subdued but steady since pumping commenced. Drawdown was about 1.4 m between August 1990 and March 1991. In the winter months the water level rose by 0.5 m. In East Perenjori the pre-pumping water level map (Figure 4) shows that the groundwater flow is channelled by the surface drain in a northern direction. After pumping a cone of depression has developed and the contours reveal a steeper hydraulic gradient towards the windmill. The area of drawdown extends beyond well PO2 (Figure 4).

Discussion

The results for East Perenjori and other investigated catchments (Salama et al., 1993b) show that in a discharge area with a high piezometric head, pumping reduces the pressure heads in the unconfined and confined aquifers. When the deeper aquifer is pumped at an optimal rate, the upward vertical gradient is reversed, and diffuse discharge ceases. In all catchments, it has been shown that pumping will reduce water levels by 2-5 m in the vicinity of the pumping well and by about 0.2 m in an area of one hectare around the pumping well. This will immediately focus the area of discharge to a single point in the landscape. It will halt the trend of the expanding saline area through diffuse discharge within the area influenced by pumping and will give land managers the opportunity to apply well planned long term vegetation options. At the same time the creation of a cone of depression around the pumping well will improve the surface infiltration and will enhance the leaching of salts from the salt affected areas. From modelling it was concluded that the enhanced discharge will be effective beyond a radial distance of 3 km after 5-10 years of pumping. Management scenarios In a first order catchment, the management strategies most likely to halt and eventually reverse land and stream salinization are reforestation and pumping. Complete reforestation would reduce groundwater discharge and restore saline land, but this option would obviously not allow any agriculture. Tree replanting of 25% of agricultural area between areas of recharge and discharge is considered to be sufficient to control salinity (Salama et al., 1992). Reforestation, however, will affect the deeper confined aquifers, only if the trees are planted in the recharge area. The engineering option by pumping should be contemplated as a short term solution to the problem of rising water levels. This method can be applied at the beginning of a catchment rehabilitation strategy. Enhanced discharge by windmill pumping has been shown to reduce excess pressure heads in semi-confined and confined layers, provided the discharging wells are placed in areas of high water tables, in highly transmissive areas with adequate aquifer thicknesses and upstream of geological structures. In East Perenjori groundwater of good quality for stock and other farm uses occurs in the midslope sandplains and in the weathered bedrock in the upper areas of the catchment. Presently, the entire catchment water requirements are supplied by 5 windmills producing water at the rate of 5 - 10 m3d-! per pump. The excess water from the upper catchment discharges to the valley and upstream of the basement high A (Figure 2). Here, the installed windmill pump lowered the water level by 5 m in the proximity of the well after one year of pumping. Currently, the effluent is pumped into the main drainage line which drains into the saline Mongers Lake.

LINKED PUMPING - DISPOSAL SYSTEMS

The problem of all salinity control strategies which produce saline water, is how to dispose

40

of the saline water. The operation and subsequent disposal of saline effluent into the environment is regulated by State agencies and permission to apply these methods is required.

Modes of disposal Reuse is considered the major disposal option in irrigation regions when the salinity of the water is less then 3000 mgl-!. Maintaining the appropriate salt balance in the root zone is essential for long term viability which depends on plant salt tolerance, soil properties and other factors. It is believed, however, that total reuse is not a sustainable option because

non-exported salt can cause eventual soil degradation and groundwater salinization. Reuse must be accompanied by another method of disposal to avoid salt buildup. Higher saline water (TDS < 6 000 mgl-!) can be reused for feed stock. It is estimated that at a pumping rate of 30 kLd:!, the resource could supply about 6000 sheep per day (Laing, 1977). This would be in conjunction with other management options a valuable asset to land manager in the wheatbelt . Discharge of saline effluent to a river system or lake depends largely on the extent of the downstream water use, the river regime and on the environmental susceptibility of the river course, flood plains and lakes. River disposal is generally suitable in downstream reaches if water salinity is less then river salinity. Experiences with evaporation basins in a number of countries and Australia (eg Murray Basin) indicate that long term problems may exists (Murray Darling Basin Ministerial Council, 1986). This disposal options should be seen-only as a temporary and partial solution.

Basins

have been

natural depressions,

saline lake, salinas and billabongs.

Recently, constructed basins have become more common. They vary in size serving farms to large regions and land management schemes. Evaporation basins leak. Leakage can cause adverse salinity, water logging effects and further down gradient groundwater salinization. Other costly disposal options are deep aquifer injection, desalinization plants and pipeline outlets to the sea (Evans, 1989).

Of all the options, the concept of on-farm evaporative holding basins or sacrificial evaporation areas is considered the most feasible and practical solution to dispose of saline effluent in the wheatbelt of Western Australia. The basins are unlined. Leakage from evaporation basins and the build-up of water mounds beneath the basins has to be controlled. The adverse effects by saline seepage on surrounding farm land and downstream properties have to be kept to a minimum. This can be achieved by choosing the hydrogeologically most suitable site for an evaporation basin in a catchment and by linking the evaporative disposal system to the operating enhanced discharge pumping scheme. This linkage necessitates that the basin is in hydraulic communication with the pumped aquifer system and that leakage is contained by the pumping.

Field study

In 1991-1992 the feasibility of an on-farm linked pumping - evaporation disposal system was studied south of Quairading in the Salt River palaeochannel system.(Otto, 1993; Figure ). The uncompacted shallow evaporation basin with a nominal surface of 3080 m2 is located on severely salinized farmland which was identified as an area of saline groundwater discharge. A pumping well producing saline groundwater (TDS 42 000 mel!) at a rate of 115 m3d-! is positioned 30 m SW of the basin. Groundwater is pumped from the overpressured deep semi-confined basement aquifer. Observation wells monitor water level

changes at different depths in and in the near vicinity of the basin. A climate station and Class A evaporation pans in and outside of the basin measured meteorological parameters. 41

Results and discussion

From hydrographs of the monitoring system it was concluded that the evaporation basin is hydraulically linked to the unconfined and pumped semiconfined aquifer system. Initial drawdown in the first week of pumping was reduce by recharge from the basin. Leakage from the evaporation basin is approximately half the evaporation in the summer months, and about three times as high in the winter months. The leakage rate is increased by operating the basin at high stage levels and reduced groundwater pressures in the aquifer system due to pumping. From water level measurements and modelling it was concluded that the radius of pumping drawdown exceeds 1 km, and that the leakage recharge boundary did not extent beyond 100 m from the basin. The salinity in the basin gradually increased during the summer months. Groundwater salinity increased in the shallow wells (1 m) around the basin, but remained nearly the same in the deeper wells (5 - 18 m) and the pumping well. Traditionally, sites are selected where there is substantial thickness of low-permeable clay. In a linked system the presence of clay layers in the subsurface are not vital. The selection of a site should be based on a hydrogeological investigation. Hydraulic factors which are considered favorable for selecting a site: increasing hydraulic heads with depths which characterize areas of groundwater discharge and counteract vertical downward leakage; a shallow water table; hydraulic continuity between aquifer systems; a shallow lateral hydraulic gradient to reduce spreading of lateral leakage and a leaking basin base to warrant hydraulic linkage with the aquifer system. The site should be positioned within the cone of depression. Other factors which need to be considered in the site selectiva are: size of the basin; land

use (eg salinized land can be sacrificed as a site); topography; distance to pumping well; soil type; slope; flooding in winter; vegetation and social and environmental effects. Factors which must be considered in the design of an on-farm evaporation basin are: pumping rate (recharge into the basin); evaporation rate of the area; rainfall in the winter months and possible leakage rate. The larger the area of the basin the larger will be the evaporation loss from the water. The surface area should be kept as large and the slopes of the basin as shallow as possible. The amount of water pumped in enhanced discharge schemes is relatively small, thus the basins will only be several decameters wide and long. The basins are excavated and the moved soil build up the retaining walls of the basin. Compaction might reduce seepage. Some basins might seal themselves after a couple of years by clogging. The life time of an evaporation basin is primarily a function of the ability to dispose of salt. If no salt export occurs, gradually the salt crust will build up and the capacity of the basin will be reduced. This might occur in several decades (Evans, 1989). Leakage represents a minor export mechanism in a linked pumping -disposal system. Saline leachate is recycled into the basin. With time the salt concentration of the basin's water will become saturated and salt will crystallize. The life time of a basin in a linked system is shorter then for evaporation basins when uncontrolled leakage is allowed to occur into the regional aquifer system. The practice of using multiple basins in sequence, so that the final basin contains the most highly saline water often extends the life of the primary basin. The salt could be harvested if there is a market demand.

CONCLUSIONS Enhanced discharge by windmill pumping is a viable heads of deep semi-confined aquifers in discharge areas at shallower depths. The method should be part of an program for the restoration of saline land and streams.

42

method to reduce excess pressure and consequently lower water levels integrated catchment management The technology is transferable and

applicable to other irrigated and non-irrigated salt-effected regions in Australia and the world. Long-term field experiments and modelling have shown that windmill pumping (1530 m3d-!) in the wheatbelt can reduce water levels by 1 to 2 m at a radial distance of more than 2 km after several years of pumping. Some pumped groundwater can be reused for irrigation or feed stock . Disposing the saline groundwater in leaking evaporation basins which are hydraulically linked to the enhanced discharge scheme enables farmers to minimize adverse effects by leakage.

REFERENCES A.B.S, 1990. Australian Bureau of Statistics, Year Book: Australia. Engel, R., D.J. MacFarlane and G. Street, 1987. The influence of dolerite dykes on saline

seeps in South-Western Australia: Australian Journal of Soil Research 25: 125-136. Evans, R.S., 1989. Saline water disposal options in the Murray Basin: BMR Journal of Australian Geology & Geophysics 11: 167-185. George, R.J., 1990a, The 1989 Saltland Survey: Journal of Agriculture Western Australia 31: 159-166.

George, R.J., 1990b. The nature and management of saprolite aquifers in the wheatbelt of Western Australia: Land Degradation & Rehabilitation 2: 261-275. Hocking, R.M. and A.E. Cockbain, 1990. Regolith: Geology and Mineral Resources of Western Australia: Geological Survey of Western Australia Mem. 3: 591-601. Johnston, C.D., 1987. Water and solute movement in deeply weathered lateritic soil, profiles near collie, Western Australia: M.Sc.: University of Western Australia.

Liang, I.A., 1977. Water supplies om wheatbelt farms: Jounral of Agriculture Western Australia 18: 66-67. Murray Darling Basin Ministerial Council, 1986. Report of working group of options for salinity reduction: Murray Darling Basin Ministerial Council: May 1986. Myers, J.S., 1990. Western Gneiss Terrane: Geology and Mineral Resources of Western Australia: Geological Survey of Western Australia Mem. 3: 13-31.

Otto, C.J., 1993. Performance of an Evaporation Basin in a Linked Pumping - Disposal System near Quairading, Western Australia: CSIRO Division of Water Resources: (in prep.) Peck, A.J., J.F. Thomas and D.R. Williamson, 1983.

Salinity issues: effects of man on

salinity in Australia: Australian Goverment Publishing Service: Water 2000 Consultants

Report No. 8.

Peck, A.J. and D.R. Williamson, 1987. Hydrology and salinity in the Collie River Basin: Journal of Hydrology 94: 1-198.

43

Salama, R.B., G.B. Davis and D.R. Williamson, 1989. A feasibilty study for salt extraction

from groundwater brines in the salt river system, near Quairading, WA, including water and salt balances and environmental aspects: CSIRO Division of Water Resources: To Salt Industries PRY Ltd. Salama, R.B., P. Farrington, G.A. Bartle and G.D. Watson, 1991. The use of water level

patterns in the wheatbelt of Western Australia to indicate recharge and discharge areas.: International Hydrology and Water Research Symposium : Perth, Western Australia: 841-846. Salama, R.B., P. Farrington, G.A. Bartle, G.D. Watson and D. Laslett, 1992.

Quantitative

prediction of effects of land use management to reduce salinisation: CS/RO Division of Water Resource: Report No. 92/9.

Salama, R.B., P. Farrington, G.A. Bartle and G.D. Watson, 1993. The role of geologcal structures and relict channels in the development of dryland salinity in the Wheatbelt of Western Australia: Australian Journal Earth Sciences 40:, 45-56. Salama, R.B., C.J. Otto, G. Bartle and G. Watson, 1993.

Management of saline

groundwater discharge by long-term windmill pumping in the wheatbelt of Western Australia: Journal of Applied Hydrogeology : (submitted).

Schofield, N.J., 1992. Tree planting for dryland salinity control in Australia: Agroforestry Systems: 20:, 1-23.

Schofield, N.J., J.K. Ruprecht and I.C. Loh, 1988. The impact of agricultural development on the salinity of surface water resources of South-West Western Australia: Water Authority of Western Australia: Report No. WS 27.

44

Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Exploitation of freshwater lenses — Implementation of scavenger wells in Pakistan C.R.C.Jones & J.J. Van Wonderen Mott MacDonald, Cambridge, UK

ABSTRACT: Traditionally, freshwater lenses which are underlain by bodies of saline groundwater have been exploited using skimming wells fitted with a single pump. The success of these wells cannot always be guaranteed, particularly at high discharges, since upconing of saline water may eventually cause pollution of the abstracted groundwater. An alternative approach now being implemented through the LBOD project in Sindh, Pakistan is to construct scavenger wells. These are similar to standard irrigation or drainage

tubewells but are fitted with two pumps: one (fresh) in the upper section of the well and the Other (saline) at the bottom. This arrangement permits the freshwater to be kept separate from the saline water. Following detailed studies in 1988 to 1989 and construction and testing of 4 pilot wells, up to 380 scavenger wells will be built from an ODA grant for an estimated £9.9 million. These wells are expected to recover over 10.0 m*/s of freshwater as well as provide drainage along 105 km of canal bank. The design ANE ye and construction practices are presented. ——2283 MGP

INTRODUCTION

a ~ JRS re

The Left Bank Outfall Drain Stage 1 Project (LBOD) in Sindh Province, Pakistan will provide improved irrigation facilities and drainage to around 0.5 M ha at an estimated cost of £5 000 million. The LBOD project is being executed by the Water and Power Development Authority (WAPDA) of the Government of Pakistan with financial support from a consortium of international donor agencies. The area is mostly underlain by a permeable aquifer containing thick beds of well sorted fine and medium sands. The aquifer is predominantly saline and over 2 000 tubewells of up to 56 l/s capacity are being installed to combat waterlogging and salinisation (Hasnain et al 1992). Water shortage is a constraint on increased agricultural production and recovery of any freshwater from irrigation return flows and leaking canals has high benefits. The boundaries of the project area have been selected to avoid areas where sufficient fresh groundwater exists to permit skimming wells to succeed. Instead, scavenger wells are planned along those major canals shown on Figure 1 where seepage is only sufficient to have formed thin lenses of freshwater overlying the regional saline water body. Scavenger wells can provide a means of recovery of fresh groundwater occurring in lenses too thin for conventional skimming wells to be economic. As shown in Figure 2, scavenger wells pump both the fresh and the saline groundwater but through separate

45

Area

Amurji Branch

SANGHAR DISTRICT PSWI1A

NAWABSHAH _—_—

Le

Ali Bahar Branch

Legend

{

[ /Ha/year every 20 days between March and October; the rest of the year depending on the rainfall distribution. No other suplemental nutrients were applied throughout experiments. Treated wastewater is used in A and B plots and groundwater in C plot. The lythology of the unsaturated zone in the surrounding area is quite homogeneous, with predominance of clays in the first 120 cm., sands between 120 and 235 cm., clays between 235-295 cm and gravel in the deepest level. The watertable is found about 2.85 meters depth. Parameters analized in the soil-solution samples collected in the cups, and also in treated wastewater and groundwater samples were pH, conductivity, chloride, bicarbonate, sulphate, calcium, magnesium, potassium, sodium, nitrite, nitrate, ammonium, phosphate, boron, chemical oxygen demand (COD) and biological oxygen demand (BOD). In this work, only nitrate, nitrite, ammonium, chloride, boron, sodium, phosphate and

COD are considered because of their importance in the vegetative development of citrics or their harmful for the growing, as well as the potential contaminant load for groundwater. Cations were analyzed by atomic absorption spectophotometry. Boron, phosphate and nitrogen compounds using UV-visible spectrophotometry and chloride by with the titrimetic method with silver nitrate.

56

72)= --\_--’

SPAIN

;

mrt

-

c/

Benicasim

seen, ee

a

&

Aad

N

Pe) \Vall d‘Uixo

Figure 1. Plan showing the location of the experimental site.

1098765432

Depth

(m)

Figure 2. Schematic layout of site instrumentation ( ™ cups,

57

@ tensiometers).

In order to stablish the possibility of groundwater pollution due to infiltration of wastewater, the evolution of chemical parameters characterizing the pollution (nitrate, nitrite, ammonium, phosphate, boron and potassium) were studied along the unsaturated zone during a year. Along this period, twelve samplings were performed five days after of each wetering, by both irrigation and rain episodes. Also, two samplings (September 1992 and January 1993) were carried out to determine the influence of citrics on the different behaviour of several parameters. In first-November 1992, fourth and fifth leaves were collected from each tree. The

samples were oven dried at 68°C. Atomic absortion spectrophotometry (Chapman and Pratt, 1961) was used to mesaure sodium, calcium, magnesium and potassium. Phosphorus and boron were analyzed by UV-vis. spectrophotometry. Total nitrogen was determined by microkjeldalh] method (Bremner, 1965). Chloride was analyzed by silver ion tritation with a Corning-926 chlorimeter (Gillian, 1971).

3 RESULTS AND DISCUSSION In table 1, the differences between reclaimed wastewater and intersticial water of soil

solution

samples

ammomium

at 2,40 meters

of plot A are shown.

Phosphate,

nitrite and

are present of inestimable values at 2,40 meters, but potassium reached

values of 2 mg/l, COD about 34 mg/l O, and DBO 15 mg/l O,.

Table 1: Average values of the controlled parameters (units mg/l, conductivity s/cm). Parameter

Reclaimed

Interticial

water

water

pH

Cond

Ton

7.76

1638

2725

HCO; ~ Elis SO, 2Mg 2+ Na t+

434 206 226 33 169

Ca 2+

126

Kt

15

Parameter

NO,”

Reclaimed

Intersticial

water

water

10

139

NH, +

4.34

0.13

190 204 190 56 t12

NO, O.M. B PO, 3D.B.O.5

0.19 38 1.09 19 48

0.13 28 0.73 0.17 15

341

D.Q.O.

90

34

2

In figure 3, the nitrate content in soil-solution samples at 2.40 meters in A plot is shown. A decrease of the nitrate mass entering into the aquifer can be observed, and the last measures (February and March) can be interpreted as the outlet of the nitrate mass existing in the unsaturated zone before starting the experience. : ItIsinteresting to consider the boron behaviour because higher contents than 2 mg/l in Irrigation water this can be an important risk to the vegetative development of the orange trees (Pomares, 1986). Boron is partially involved in ionic exchange processes but its undisociated

character, as boric acid, in treated wastewater

minimizes

this

influence (Page and Chang, 1990). The boron content in wastewater was about 1.1 mg/l but only 0,7 mg/l can be averaged as reaching the aquifer (Figure 3). Other parameters which are in relative high contents in treated wastewater, did not reach the aquifer, at least in appreciable amount, due to several processes such as adsortion, oxidation and precipitation. Therefore can be considered that the wastewater leaching throuhg the unsaturated zone suffers an important self-purification. The data above mentioned could be influenced by the biological activity of the trees, which can modify several parameters, specially the nitrogen species and others because of the high evapotranspiration rates. In order to estimate these influences, a comparative study between parcels A and B (with citrics) for differents months, was carried out (Figure 4 and 5). When we compare the figures 4 and 5, we observed that a notable washing process cause a decrease in the solute content due not only to the wet period without also to the intensive irrigation, thus the concentration of ions in the upper unsaturated zone decreased during the experience. Other procces was studied the effect of nutrients uptake by roots of orange trees that could modify the concentration of dissolved salts in the intersticial solution. This effect was not appreciable in this experience, which could be due to the short length of the roots. In table 2 the parameters determined in leaves trees of B plot ( crop irrigated with reclaimed wastewater), C plot (crop irrigated with groundwater) and the limit values that could restric the performance of trees (control plant) (Embleton et al, 1973) are shown. Nitrogen concentrations found in leaves were lower in trees irrigated with groundwater than with treated wastewater, showing that irrigation with wastewater could be a source of nitrogen. However, these plants have higher nitrogen requeriments, which could be supplied as an additional single fertilizer application or dissolved in the irrigation water. We deduced that the use of treated wastewater for itrigation could reduce the amount of fertilizers helping in this way to minimize groundwater pollution by nitrates, which is one of the main problems in the studied area.

Table 2:

Distribution of mineral elements in leaves of plants irrigated with reclaimed wastewater and ground water.

Elements

Units

Plot B

Plot C

N ClNat Ga 7* Mg 2+ Kt P B

% % % % % % % mg/l

2.05 0.08 0.06 4.96 0.18 1S 0.17 178.6

1.65 0.07 0.10 4.10 0.18 2.06 0.21 152.4

59

Control plant

2.40-2.60 < 0.30 < 0.16 3.00-5.50 0.26-0.60 0.70-1.09 0.12-0.16 101.0-260.0

-Jun

29-Jul

17-Sep

6-Nov

26-Dec

14-Feb

$-Apr

Date

B mg/l oc oo ecoeoooo COKRFNWRUAXIBMLO -Jun 29-Jul 17-Sep

6-Nov

26-Dec

14-Feb

S-Apr

Date Figure 3 Evolution of the concentration ions nitrate and boron at 240 cm depth

mg/l Cl

0

0

mg/I Cl

200 400 600

0

20

wilt50-.300

20

40

Se

O.

40

S

3|—3

60

7.060 a4

BS

80

e 2

80

100

100

120

120

Figure 4. Evolution of chloride in plot A (- - - -) and B ( September 1992 (a) and January 1993 (b)

60

) for

mg/l NO3

0

200

400

ypdaq (wd)

yydaq (wd)

100

0

(wa) yydoq

150

300

yydag (wd)

20 40 cS fe = 60 ey =

80

cS

8= 2

=

100 120 Figure 5. Ions evolution in plot A (- - - - - ) and B( ____ ) for September 1992 (a) and January 1993 (b).

61

When we studied the effect of the chloride and sodium concentrations, toxic ions to

the plant, they showed low levels in leaves. If compared the plants irrigated with both types of water, a higher sodium concentration were found in the groundwater than reclaimed wastewater. These results seem to indicate that the use of treated wastewater to irrigate citric crops is not harmful for growing. The presence of boron in plants irrigated with reclaimed wastewater was higher than when irrigated with groundwater, but the levels found in leaves are not toxics to the plant when compared with the control plant. Others mineral elements studied in the leaves showed an effective concentration for the nutrition of the plants (Table 2).

CONCLUSIONS No limitations to the use of treated wastewater to irrigate citric crops were observed over 1-yr period. Emphasis in this report should be done in the future Results shown that toxic ions levels in plants were not elevated and the source of N could be effective. This could reduce the amount of fertilizers, helping in this way to mininize groundwater pollution by nitrates. On the other hand, self-purification of traited wastewater in the unsaturated zone could be enough in order to preserve the groundwater quality.

ACKNOWLEDGEMENTS

This work is included in a more complete study about agricultural pollution in the Castellon Plain aquifer, funded by the National Plan of Agriculture (AGR91-1165 Project.CICYT). Also, this work has been supported by the Generalitat Valenciana throungh the financing of the doctoral scholarship for M.V. Esteller. We would like to thanks Mr. Juan Marcos Alberto and Mr Miguel Cerezo for theirs help in the experimental work and the personal of Sewage Treatment Plant of Castell6n.

REFERENCES

Arar, A. 1991. Wastewater reuse for irrigation in the near east region. Wat. Sci. Tech.

23: 2127-2134. Asano, T. 1990. Irrigazione con acque urbane recuperate: L’experienza della California Ingegneria Ambientale XIX. 3/4: 159-169. Gilliam, J.W. 1971. Rapid measurement of chloride im plants materials. Soil Sci Soc. Am. Proc. 35: 512-513. de Bustamante, I. 1990 Land application: its affectiviness in purification of urban and industrial wastewaters in La Mancha, Sapin. Environ. Geo. Water Sci. 16, (3): 179185. Basiouny, F. M. 1982. Wastewater irrigation of fruit trees. Biocycle 23 (2): 51-53. Bremner, J.M.1965. Total nitrogen. In C.A: Black (Editor). Methods of soil analysis Part 2. Academic Press. N.Y. Agronomy, 9: 1149-1178.

62

Chapman, H.D. and Pratt, P.R. (1961). Methods of analysisi for solis. Plants and waters. University of California. Elliot, L.F. & F.J. Stevenson 1977. Soils for management of organic wastes and wastewater. Published by SSSA, ASA ana CSSA. Madison Wis. Emblenton T.W., W.W. Jones, K. Labanauskas & W. Reuther 1973. Chapter 6 Leaf analysis as a diagnostic tool and guide to fertilization. In W. Reuther (Editor) The Citrus Industry University of California. Press Berckley. Vol 3: 183-212 Kirkham, M.B. 1986. Problems of using waste water on vegetable crops. Hortscience. 21: 24-27. Martinez, S. & A. Sastre 1992 Evolucién de las caracteristicas quimicas del agua recogida en la zona no saturada en una finca experimetal regada con vinanzas. Hidrogeologia y Recursos Hidraulicos Tomo XVI: 273-284. Monserrat, X. 1991. Aplicacién de aguas residuales en Sant Jordi (Mallorca). La zona no Saturada y la contaminacidn de las aguas subterraneas C.LE.H.A.M. Barcelona Mujeriego, R. & L. Sala 1991. Golf course irrigation with reclaimed wastewater Water Sci. & Tech. 24: 161-172. Neilsen G.M., D.S. Stevenson & J.J. Fitzpatrick 1989. The effect of municipal wastewater irrigation and rate of N fertilization on petiole camposition, yield and quality of Okanagan Riesling Grapes. Can J. Plant Sci. 69: 1285-1294 Pomares, F. 1986. La salinidad del suelo en los citricos. Report of I. V.I.A. Conselleria de agricultura y pesca, Generalitat Valenciana, Page, ALL. & AC. Chang 1990. Destino de los componentes del agua residual en el suelo y en los acuiferos. Los microelementos In R. Mujeriego (Editor) Manual practico de riego con agua residual municipal regenerada: Univ. Politécnica de Catalufia, Barcelona: 347-358. Ramos, C., D. Gomez de Barreda, J. Oliver, E. Lorenzo & J.R. Castel 1989. Aguas

residuales para riego: Un ejemplo de aplicacién en uva de mesa. In E. Cabrera & A. Sahuquillo (Eds) El agua en la Comunidad Valenciana. Generalitat Velenciana.: 167184 Sopper, W.E. and Kardos, L.T. 1973. Vegetation responses to irrigation with treated municipal wastewater. In W.E. Sooper and L.T. Kardos (Eds), Recycling treated municipal wastewater and sludge through forest and cropland. Pennsylvania State University Park, Pa.: 271-294 Virgos, L.I. & M. Varela 1992. Eliminaci6n de vinazas por aplicaciOn al terreno en Daimiel (Ciudad Real). Evolucién hidroquimica. Hidrogeologia y Recursos Hidraulicos Tomo XVI: 245-260

63

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3 Pollution

Groundwater— Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Atrazine concentrations in chalk aquifers and the implications for future water treatment P.J.Aldous Thames Water Utilities Ltd, Reading, Berkshire, UK

J.Turrell WRc Plc, Marlow, Buckinghamshire, UK

ABSTRACT: The results of a research programme funded by Thames Water Utilities Ltd to determine the presence, concentration and likely persistence of atrazine in Chalk groundwaters is presented. Atrazine concentrations were determined for Chalk matrix porewaters from both unsaturated and saturated zones using a new and novel application of an immunoassay analytical technique. These results are compared with those obtained from the more conventional GC-MS analysis. The immunoassay technique provides a level of detail previously unobtainable. The results indicate that the use of atrazine in the non-agricultural environment has caused contamination of Chalk porewaters. These results are discussed and tentative predictions of long term atrazine concentrations in Chalk groundwaters are made. Suggestions for further quantitative predictive work are discussed, together with the implications of the use of alternative herbicides, environmental protection measures and the future management of advanced water treatment (AWT). 1 INTRODUCTION The quality of drinking water has become a major issue for public and political debate and in particular the standards for pesticides have been a focus for such attention. The UK standard (HMSO 1989) for individual pesticides in drinking water of 0.1 pgl"', is derived from the 1980 EC Drinking Water Directive (EEC 1980). It is not the intention of this paper to discuss the origins and validity of the pesticide standard; however it is worthy to note that the European (and hence UK) standard applies to all pesticides irrespective of their toxicity, and is therefore not a health based standard. This

puts the

standard at variance with all other limits throughout the world for pesticides in drinkin water, and effectively sets the UK water supply limit as a surrogate zero (POST 1993). The presence of pesticides above the standard in drinking water means that such water fails regulatory standards. As a result, water utility companies have had to agree to Gace with the Secretary of State to take actions to ensure compliance within an agreed timescale. This has involved water companies in major research_ and investment programmes on treatment methods to remove pesticides and significant increases in bills to customers. Thames Water Utilities Ltd is contributing to research in this area investing over £5 million in pilot and large scale trials prior to_a £200-300m capital investment programme in advanced water treatment (AWT) (Foster et al 1991a). _ : Atrazine and simazine, are the two most commonly reported pesticides found in groundwaters (Clark et al 1991a, Foster et al 1991b, Croll 1991 and Gomme et al

1992). However, these particular pesticides have limited uses in agriculture but are mre used to control weeds on roads, railways and footpaths. The presence of atrazine and simazine in groundwaters can be explained by a combination of both the very high application rates (FWR 1991a) and the rapid drainage routes to surface and Wee ie groundwaters, e.g. via soakaways, in this environment. | The announcement of a ban on the sale and use of atrazine and simazine in the non67

agricultural environment (MAFF/HSE 1992) has been welcomed by the water industry. The effect of this environmental protection measure, partly brought about by the and transport and local pressure applied to regulatory bodies (NRA and MAFF), authorities, iy water industry Posen campaigns (ENDS 1991 and 1992) is expected

to show benefits rapidly, with the improvement of surface water quality within 12 months. However, it is much more difficult to predict when an improvement in groundwater quality will occur, given the much longer transport times for water movement through both the unsaturated and saturated zones of the ground. The major aquifer used in England for water supply is the Cretaceous Chalk. This aquifer provides good quality groundwater requiring minimum treatment and is therefore the most cost efficient resource for water supply. However, at 15 Chalk groundwater sources either AWT has been installed or is being planned for the removal of future pesticide concentrations at these sites is of atrazine. An understanding required to be able to plan and efficiently manage this major capital investment. To be able to predict with confidence future atrazine trends in the Chalk aquifer it is necessary to understand the contaminant transport properties of the pesticide. A wide ranging research programme has been funded to investigate and solve this problem. This paper presents the results of part of the research programme, which was to determine the presence and concentration of atrazine which may be held within porewaters located in the chalk matrix.

2 CHALK

GROUNDWATER

FLOW AND CONTAMINANT

TRANSPORT

The hydrogeological behaviour of the Chalk aquifer has been extensively reported (e.g. Price 1987). In resume the Chalk consists of two main flow mechanisms defined by distinct hydraulic characteristics. The first and dominant mechanism is that controlled by the many fractures and the joints. The second zone is that of the matrix. These two

mechanisms represent fast (2000 - 50 md") and slow (0.5 - 2 myr') groundwater flow

respectively. The primary flow mechanism, defined by the presence of numerous joints, fractures and fissures provides the main permeability of the Chalk. The interconnection and solutional development of these features leads to the extremely high transmissivities which are observed in some areas of the Chalk aquifer. The fracture flow mechanism of the Chalk aquifer has a high permeability (depending on the spacing and frequency of the fractures and dont) but low porosity. The matrix consists of particles of coccolith and formanifera fragments, which are between 0.5 to 3 um in diameter. These provide a high intergranular porosity of between 25-45%. However, the small grain size and tight packing of the particles results in a very low intergranular permeability.

The importance of pesticide contamination and understanding the processes and controls on pesticide movement and behaviour in the groundwater environment has only recently received attention. The majority of published work and data relates to concentrations of pesticides detected at groundwater sources used for potable supply or from observation boreholes (Gomme et al 1992 and Lees and McVeigh 1988). These results reflect typical concentrations of pesticides to found in the fracture water from the saturated zone. More recent work (Clark et al 1991b) has started to assess pesticide fluxes in groundwater recharge. However, little knowledge exists on the likely pesticide concentrations to be found in porewaters from the chalk matrix in either the saturated or unsaturated zones. The important role of porewaters in influencing nitrate concentrations has previously been reported (Foster 1975). This is based upon a general hydraulic principle that free diffusion occurs between the mobile groundwater in the macropores/microfissures of the fracture zone and the micropores of the chalk matrix. It is not unreasonable to assume the same principle applies to pesticide movement, although the molecular structure of atrazine is significantly different to that of nitrate. Therefore, to be able to formulate the simplest *black box’ pesticide budgeting models for predictive work,

reasonably accurate estimates of the concentrations of pesticides in both the fracture and matrix zones of the Chalk aquifer are necessary. The aim of this work was to determine both the presence and concentrations of atrazine in matrix waters for the unsaturated and saturated zones of the Chalk aquifer.

68

3 CHALK

AQUIFER POREWATER

PROFILES

FOR ATRAZINE

The general monitoring and analysis of the presence of pesticide residues in free fracture zone groundwaters is complex. This has been acknowledged by many workers. The monitoring and analysis of pesticide residues in porewaters involves a further level of complexity. Porewater analysis techniques have been developed (Connor 1978 and Edmunds and Bath 1976) for specific research studies and are now becoming more widely used as the importance and role of the matrix zone is appreciated. These techniques however are not sensitive or precise enough to measure the concentrations of pesticides in porewaters. This warranted development of a new analytical approach for the determination of pesticides in porewaters from the chalk matrix. 3.1 Porewater analytical techniques The fundamental problem of determining pesticide concentrations in matrix porewaters is that of obtaining and extracting an adequate volume of clean sample to enable the analytical analysis to be either performed or to reach acceptable analytical detection levels and precision. The conventional analysis of Chalk matrix or porewaters for pesticides has followed solvent extraction and analysis by GC-MS (Gas Chromatography Mass Spectrometry). However, the main drawbacks of this method are that it involves large quantities of Chalk (250 g per sample) and lengthy sample extraction procedures which makes each individual analysis very costly. A limit of detection of about 0.1 ugkg™' can be achieved which is equivalent to about 0.5 pgl'in the porewater, if all the pesticide is in the orewater. In practice the 0.1 ugkg" detection fienit is likely to be equivalent to a much ee detection limit in the porewater because of adsorption and matrix effects. Therefore, the fairly high limit of detection, but particularly the high cost of analysis limits its applicability and in almost all cases limits the number of analyses that may be performed. Due to these limitations of the conventional’ GC-MS method an alternative method was developed based upon an immunoassay technique specifically for the detection of atrazine. The new technique used in this work involves the extraction of small volumes ( 1 pl is sufficient for 5 replicate analyses) of porewaters by centrifugation (Edmunds and Bath 1976) followed by immunoassay analysis. The immunoassay technique relies on the use of polyclonal antibodies which bind to both triazine and an atrazine-enzyme conjugate for a limited number of antibody binding sites and produces a blue colour in an analysis plate. The blue colour developed is inversely proportional to the amount of atrazine in solution. The plate kit used in this study was manufactured by Guildhay, and developed hee to manufacture by WRc on behalf of the Foundation for Water Research (FWR 1991b). Although initial validation of this technique was for the routine analysis of atrazine in otable waters, other potential uses of the technique such as the analysis of porewaters ad previously been considered by WRc prior to its use in this work, although not roven. The advantages of using the immunoassay technique are that it is a specific, reliable, cheap, screening method of atrazine analysis for groundwaters with an acceptable detection limit below? 0.1 pgl'. In the work reported, a reliable limit of detection of 0.06 pgl' was achieved using less than 1 ml of water per sample. Thus this method

offers distinct advantages over the conventional solvent extraction and GC-MS analysis method particularly for aquifer profiling. 3.2 Porewater profiles from the Chalk aquifer

Three sites were chosen for the recovery of Chalk samples for analysis for atrazine in the porewaters present. These sites were : 1. The base of a soakaway trench adjacent to a major ’A’ class road (Site A). 2. Adjacent to the track ballast of a major railway line (Site B and C). 3. On a field under typical arable cultivation (Site D). _

At the major ’A’ class road site, the reliable data set indicated that atrazine had been

used every year for the last ten years prior to the commencement

69

of drilling.

At the major railway site, atrazine had been applied annually since the early 1960's up until 1991 when applications changed to diuron (an alternative herbicide to atrazine). Therefore at this site no application of atrazine had occurred in the preceding year to the commencement of drilling activities. At the ’field’ site no recorded applications of atrazine were found. _ At these four sites chalk cores were recovered during borehole drilling by percussive methods under controlled conditions. The drilling equipment was steamed cleaned offsite, prior to commencing drilling, and in addition all equipment was washed between boreholes using a high pressure water jet. After clearance of surface vegetation a 1.2m trial pit was dug at each location and a representative soil sit was bagged every 30 cms. A light percussion drilling rig was used to collect "U-100’ samples through the unsaturated zone and upto 10 m below the water table. Contact of ’U-100’ core recovery liners with the ground was carefully avoided at all times. The recovered cores were immediately extruded and wrapped in a double layer of polythene tubing. Prior to sealing, each core was divided in two and an on-site geological profile completed, : the bags were then sealed and frozen on-site. The immunoassay technique was successfully employed to obtain atrazine profiles for all sites. The porewater profiles are shown in Figure 1. The detected atrazine

concentrations range from

0.06 ygl', the limit of detection, to nearly 7 gl’.

In profile A from the road site, atrazine was clearly detected, with a peak concentration of 0.4 ugl' at the water table. The presence of the peak at the water table is possibly an effect associated with the increased volumes of recharge entering the soakaway at this location and the reduced unsaturated zone depth between the base of the soakaway and the water table of only 1.90 m. The peak concentration in this instance will be affected by the higher hydraulic flux in the winter months acting as dilutant, while the intensity of rainfall after application will determine the peak loading on the soakaway and hence the groundwater. Pumped groundwater samples collected trom the completed boreholes on site indicated higher than expected concentrations of atrazine of 1.97 and 4.62 gl”. Profiles B and C were obtained adjacent to the track ballast of the major railway line. The results show that atrazine has penetrated through the unsaturated zone into the saturated zone of the aquifer as well defined peaks. The absence of a peak within the unsaturated zone may be due to no atrazine application occurring during the year prior to the drilling. The profile at site C has a major peak at a depth of Sm, which corresponds with that at 6 m in borehole B, the peak concentrations are 2.8 ugl' and 6.7 pgl' respectively. In general results from the two boreholes correlate well. These minor differences may be due to changes in the structure of the Chalk at these two locations, although the drilling sites were only 15 m apart, the width of the railway track. It is evident that the reliance on diffusion processes to disperse the atrazine following applications, to background concentrations is an unreliable protection measure. The results support the case that atrazine applied to the railway track is draining from the ballast relatively quickly thborigl the unsaturated zone and penetrating the groundwater as a recognisable pulse of pesticide. Given the high oa ugl') concentration of atrazine detected at site C, groundwater samples collected rom sites B and C and three other observation boreholes all within 100m of the each other only gave results of between 0.11 and 2.17 ygl'. The profile obtained from the field site (Site D), shows the difficulty in evaluating the impact of the use atrazine in agriculture on groundwater quality. This profile represents a perfect background borehole, with virtually no atrazine detected. The limit of detection was 0.06 pgl' with the maximum detected concentration 0.07 ugl!. A pumped water sample was also collected from this borehole, and on analysis by Gas Chromatography (GC) this indicated an atrazine concentration of Ni (2.0) > Ti (1.3) and the summary index is 8.6 indicating a low contamination level. The subsoil is more contaminated but the pollution is still only moderate. The concentration coefficients are: Co (10.0) V (6.0) >C (3.0)) > Ni

(2.3) > Ti (2.2) > Mn (1.3), and the summary index is 19.6. This indicates that there is somé movement of metals from the shallow to the deeper soil horizons.

85

In zone C (Fluviosol) the concentration coefficients are: Co (10.0) > V (6.0) > Ni (2.3) > Ti (2.2) > Cu (1.5) > Mn (1.3) and the summary index is 18.3. This indicates that the surface soils are most contaminated in this zone. In the deeper soils (40-80cm) the summary index is very high, 30.8. This shows significant transfer of pollutants from the surface soil and points to a transfer of mobile elements (Co, Cu, Ni) deep into the subsurface waters.

4.

CONCLUSIONS

The soils of the Poti catena, when compared with the soils of the coastal sediments near Poti port, show very little evidence of contamination derived from industrial activities. In the catena soils, highly toxic heavy metals (Se, As, Pb, Cd, Cr) never occur. Of the metals measured in the catena soils, V, Ni, and

Cu are considered slightly biotoxical. This lack of intense pollution in the catena, particularly with reference to highly toxic elements, should not be treated with complacency. There is clear evidence of mobilisation of metals in the catena and evidence of pollution and mobilisation in the coastal sediments. It is suggested that if this pollution is not remedied then the mobilised elements will inevitably affect groundwater, surface waters and, ultimately the coastal and marine waters. If this is allowed to occur then it will produce a more serious environmental problem for the region.

5:

REFERENCES

Perelman, A. 1986. Particularites de la migration hypergene des elements chimiques dans contaxts geologigues et la paysage different, Moscow: semin. des meth de prosp. geochimic.

86

Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 54103515

Groundwater quality monitoring with special reference to aquifer protection L.Clark, K. Lewin, C.P-Young & N.C. Blakey WRc Environmental Management, Medmenham, Bucks., UK

D.Chadha NRA Northumbria-Yorkshire Region, York, UK

M.Eggboro NRA North West Region, Warrington, UK

ABSTRACT: The National Rivers Authority (NRA) has a duty under the Water Resources Act 1991 to monitor for pollution in groundwater and to maintain or improve its quality. Waste Regulation Authorities (WRAs) have a duty under the Control of Pollution Act 1974 to ensure that landfill sites do not cause pollution - yet there are no clear UK guidelines on the monitoring of groundwater around and beneath landfill sites. WERc has been contracted to prepare guidelines and protocols under two contracts: one for sampling and monitoring groundwater (by the NRA) and the other for landfill sites (by the DoE, Waste Technical Division). Great care has been taken to ensure the compatibility of the guidelines and protocols from the two contracts. Sampling methods and protocols for groundwater that are employed by the various NRA Regions, EC Countries and in North America have been examined and evaluated to identify the best practices. Recommendations for designs of sampling sites and a series of protocols to cover different sampling situations have been produced. These protocols will be incorporated into a practical manual for field use by samplers. Similar *best practice’ recommendations and protocols will be employed in DoE guidelines applied to landfill monitoring. Monitoring groundwater quality is the only way to check whether aquifer protection is being achieved. The implementation of these guidelines and protocols will be fundamental in this evaluation. 1 INTRODUCTION The National Rivers Authority (NRA) has a duty under the Water Resources Act 1991 to monitor the extent of pollution in ’controlled waters’ which include groundwaters, for the purpose of maintaining and improving the quality of controlled waters (Sections 84/85). They also have a duty under Section 19 of the Act to take action for the purpose of conserving, redistributing or otherwise augmenting water resources. These duties are spelled out by the NRA in their publication,"Policy and practice for the protection of groundwater" (1992). The monitoring of landfills similarly has been recognised increasingly in recent years to be of importance. Recent UK legislation, for instance the Town and Country Planning (Environmental Impact Assessment) Regulations (1988) and the proposed Directive on waste in landfill (CEC 1991), require the surveillance in and around landfills should include the determination of ‘background’ conditions and the monitoring should be done in such a way that changes are detected and corrective action taken well before the

87

impact has reached the point where environmental damage or breach of regulatory standards is inevitable. In addition the operation of quality assured monitoring schemes at landfills will become essential requirements in the process of obtaining Certificates of Completion under the UK Environmental Protection Act (1990). The requirements for monitoring at a landfill and in the surrounding aquifers clearly are coincident. There are no harmonised national guidelines or protocols in UK for the sampling or monitoring of either landfills or groundwater. WRc have been employed to prepare such guidelines and protocols under two contracts; one for groundwater (by the NRA) and the other for landfills (by the DoE, Waste Technical Division).

A survey of methods used for sampling groundwater in the various NRA Regions, EC Countries and in North America have been used to produce recommendations for the design of sampling sites and a series of protocols to cover different sampling situations. Similar recommendations and protocols have been produced for the DoE to apply to landfill monitoring. Great care has been taken by WRc to ensure the documents produced for the NRA and the DoE are compatible. The Guidelines for landfill monitoring have been presented at an International Symposium in Sardinia (Blakey et al 1993) and are expected to be published by the DoE through HMSO shortly. This paper, therefore, will concentrate on the guidelines and protocols for the sampling and monitoring of groundwater. The paper will discuss in particular those aspects of sampling and monitoring that we consider most important in fulfilling the statutory duties mentioned.

2 OBJECTIVES OF GROUNDWATER

MONITORING

The design of a groundwater quality monitoring network will depend on the objectives of the monitoring. It is therefore essential early in the formulation of the network design to agree on the objectives of groundwater monitoring as a whole, and the objective of each monitoring point in particular. The following definitions of the objectives of sampling and monitoring used in this paper are based on those from Foster and Gomes (1989). 1. Potable Water Supply Surveillance. To obtain the background groundwater quality in pumped boreholes in an aquifer and to use this to show regional variations in groundwater quality to assist with catchment management or resource management. 2. Evaluation Monitoring. To determine the baseline groundwater quality at points __, Inan aquifer in order to show whether or not the quality is deteriorating. ; _ ==» 3. Defensive Detection Monitoring. To show whether polluted water (for example, saline intrusion) is approaching a potable source. ena

Offensive

Detection

Monitoring.

To

show

whether

or

not

the

quality

of

per, ,|,t groundwater is deteriorating due to specific sources of point or diffuse pollution. 3 MONITORING NETWORK DESIGN The main objectives of monitoring can be related to the design for a National groundwater monitoring network. The network that could be installed most cost effectively would comprise a core of the existing potable water supply boreholes. Additional evaluation monitoring would utilise existing observation boreholes infilling between the water supply boreholes. Any gaps then would be filled by using other continuous supply sources or by drilling new purpose-built boreholes. There is no statutory requirement for Water Utilities, other borehole owners or

88

regulatory authorities to monitor the raw water of their sources. The Private Water Supplies Regulations 1991 under the Water Industry Act 1991, stipulate only the monitoring requirements for the discharge to supply, not the raw water. These boreholes owned by the Utilities do represent an enormous investment and an existing network of potential sampling points. It is suggested that, as far as possible, these public supply boreholes should be used and advantage taken of this National asset. This network then would act as the core of a National monitoring network to protect resources from pollution. The NRA has inherited from the previous Regional Water Authorities a network of observation boreholes. These should be used to infill the areas between the potable supply boreholes. The majority are used only for water level measurements in UK at present. We suggest that the existing network of observation boreholes could be evaluated and restored to make them suitable for the National monitoring network. Defensive and offensive monitoring schemes are set up in response to definite threats, landfill (offensive) or saline intrusion (defensive). The design of such schemes may not be the responsibility of the regulatory authority although the structures and the sampling methods used should follow Nationally-agreed protocols (Blakey et al 1993). It should be stated that in setting up an offensive or defensive monitoring scheme early co-operation with the regulatory authorities is always very helpful. Offensive detection monitoring is principally aimed at point source pollution but is used also in the investigation of diffuse agricultural pollution in the Nitrate Sensitive Areas in the UK. Defensive detection monitoring is generally put in to warn against a specific threat so may be regarded as most relevant to the monitoring of point source pollution. The potable water supply surveillance and evaluation monitoring, which will make up by far the largest part of the groundwater monitoring network under NRA responsibility, are meant to detect long-term and regional changes in groundwater quality. Their main purpose therefore is to monitor the effects of diffuse sources of pollution though each monitoring point also may monitor the superimposed effects of point sources of pollution in its vicinity. The main recommendation for network design would be that the function of each sampling point in the network should be clearly defined and _ potential monitoring points which cannot be shown to contribute positively to the objectives of the monitoring should be excluded. The network should be based as far as possible on existing boreholes to minimise costs but each structure must be shown to be suitable for its purpose. Those deemed unsuitable should be modified or abandoned.

4 MONITORING SITE DESIGN The basic axiom in site design is that the monitoring structure must be able to fulfil its defined role. Potable water supply surveillance is taking advantage of existing operational structures so there is little opportunity for modifying the structures. However, the structure of the borehole and its relationship to the hydrogeology must be established so that the origin of the groundwater monitored, the catchment area of the source and the significance of any quality variations can be understood. The headworks of the borehole may need altering so that the raw water can be sampled directly from the rising main before any chlorination. The design of observation boreholes is more controversial. The design of the

traditional UK observation boreholes is to penetrate a considerable thickness of an aquifer at diameters ranging from 50 to 200 mm. In competent rocks it will be uncased

89

; or in incompetent strata screened, through much of its depth. We suggest that data obtained from boreholes with this design must be treated with utmost caution. Such boreholes may (and in many cases do) connect different aquifers with differing hydraulic heads so that water of different qualities move up or down the borehole which then acts as a conduit for pollution to enter the aquifer. The samples obtained from such a hole will not be representative of the aquifer adjacent to the sampling point. Any conclusions drawn from the analysis of such samples must be carefully qualified. Two designs considered acceptable for monitoring purposes are the multiple completion and nested completion. The multiple completion is of separate narrow (50 mm ID) boreholes drilled to different depths at the same point in an aquifer. The boreholes are each completed with a short screen or open section set at different depths. A nested design is similar in concept but several narrow casing/screen strings are installed in the same borehole with short screens set at different depths and separated by impermeable seals. The modification of existing boreholes can be undertaken relatively cheaply. Possible modifications of unsuitable designs are shown in Figure 1. WRc have undertaken several such modifications with demonstrable success. In one borehole in the Chalk, head differences of several metres are shown in what was considered a fissured but relatively uniform aquifer. The acceptable designs described are necessary to avoid cross contamination between aquifers but also to ensure that monitoring and sampling are restricted to points in an aquifer. The idea that the groundwater flow and the movement of solutes are uniform through an aquifer’s thickness is demonstrably untrue. To understand movement through an aquifer one must study it in three dimensions (3D) and the nested or multiple completions allow this to be done. Without this 3D approach the movement and impact of pollutants cannot be predicted so the aquifer cannot be effectively protected. In

the

case

of offensive

monitoring

around

landfills

and

contaminated

sites,

monitoring is much more intensive than is general in groundwater monitoring. Under the impetus of the Superfund budgets available in the USA sophisticated monitoring facilities and sampling equipment have been designed. These are discussed in Blakey et al (1993) and related publications; suffice it to say that in most cases they elaborate the 3D approach to monitoring. The modification of sampling points that have yielded long historical records of water quality or levels should be considered carefully. The point may be retained to continue to produce a record of uncertain validity but of historical value, but in most cases it is recommended that such sites are replaced by a new installation of approved design but with overlap of a year or more between starting the new record and closing the old site. This will ensure continuity of the record trends. 5 GROUNDWATER

SAMPLING

A great variety of sampling equipment has been designed over recent years and is discussed

in numerous

publications

(Stuart,

1984,

Clark,

1992). The

purpose

of a

monitoring structure is to make available samples of groundwater representative of the water from a specific sector of an aquifer or point in the aquifer. The purpose of sampling equipment and sampling techniques is to obtain that water for analysis in the state in which it occurs in the aquifer, ie., it is unchanged physically or chemically. Groundwater sampling is a complex subject but we believe that four aspects need particular stress if a sound monitoring programme is to be established:

90

e

On-site measurements Sampling frequency and analytical suites Sampling protocols

e

Sampling QA/QC

oO

5.1 On-site measurements

Several quality determinands change rapidly after the sample has been taken and so need to be measured

immediately

on

sit* The

most

important

are temperature,

pH, Eh,

Dissolved Oxygen and alkalinity. The latter is commonly ignored but is necessary to understand the carbonate equilibrium in the sample. Dissolved gases have to be measured on site or preserved in a pressure vessel for laboratory analysis. The equipment necessary for on-site analyses is described in Hitchman (1983) and has not changed significantly since. 5.2 Sampling frequency and analytical suites

The frequency of sampling and the suites of analyses to be undertaken will vary from Situation to situation but, because they have severe budgetary implications, should be decided when setting up a monitoring programme but with sufficient flexibility to be changed as the programme matures. The analyses of the numerous determinands listed in the CEC Drinking Water Directive would make monitoring prohibitively expensive if undertaken on every sample. This comprehensive suite can be divided into other suits to cover specific situations (Table 1). In general groundwater monitoring the most important of these suites would be suite 2, the Inorganic Analysis. Broad guidelines on a suggested frequency of sampling tied to the maturity of the programme are given in Table 2.

Table 1 Groundwater analytical suites PARAMETER

Organoleptic

SUITES

7

fs

Physico-chemical

2

Major ions Bacteria Metals and List II

Organic

1

Aromatic Hydrocarbons Halogenated Aliphatic Hydrocarbons

Oo DH ON

+ 10

Phenols and alky! phenols Chlorophenols Pesticides

11

91

Table 2 Recommended analytical suites for groundwater Potable Water Supply Surveillance

Defensive Monitoring

Evaluation Monitoring

Offensive Monitoring

Suite 1

Suite 1

Suite 1

Suite 2

Start of

plus 7

Monitoring Programme

Suite 1 to be repeated at 5 year intervals During Monitoring Programme

Site specific

Suite 2 to be on an annual basis as minimum

Other suites dictated by local conditions

REVISED ORIGINAL DESIGN

REVISED

NESTED DESIGN

hh iy

4

ORIGINAL DESIGN

NESTED DESIGN

—

isl

Surface

Ss

Ss

Water level ERA

Cement

YF]

Sodium bentonite grout

inet oA

Water level YA

ia@e imme

H

Cement’

FH / Sodium bentonite grout

NSH Sige alee ey

is

HY

NI INNR EL

:

Pw ;

a

aes

Surface

i]

Casing

‘ Casing

Z L

Screen Z Z

cama

FH/

+ “

a /E

=i

Screen

|

ies

sesa HAM

OS eee

H

aes oe tN:

gig

“1

aoe

Annular sealant

oa re Sage

Casi asing

e H

rT

Screen Ry

Inflow

(Sodium bentonite pellets)

Coarse sand filter

f

=a8

HH

afer Ht+-H

t]

fe

Casing

a

ay

-—

me

-

We,

ame

pig i

a

Screen

:

Z|'7 sae

S54

Bloe

Casing

Outflow

:

RN

MULTIPLE AQUIFER SYSTEM

Y Screen Y

FISSURED AQUIFER

Figure 1. Observation borehole design modifications

5.3 Sampling protocols

The most common method of taking groundwater samples in UK is probably still some form of bailer or depth sampler. The use of bailers should be discouraged absolutely as they rarely take representative samples and depth samplers should only be used if it can be shown that the samples are taken from adjacent to an active part of the aquifer and are representative of water in that aquifer. The method of groundwater sampling to be encouraged is by pumping. It is recommended that three times the volume of water in the borehole water column should

92

TOC (mg/l c)

50 000 fate sas a cell2

40 000

First use of inertial pump for sampling -.-..;

io :

{62} 6

;

I

Start of regular

van

30 000

i

monitoring by depth sampler

20 000

10 000

Figure 2 Landfill leachate monitoring by depth sampler and inertial pump

Function

Purpose Structure

Potable Water Evaluation Supply Surveillance | Monitoring

Defensive Monitoring

To give background | To monitor

To monitor pollution |To monitor pollution

groundwater quality |baseline quality

approaching source | from pollution sources

Fumped Non-pump ed sources | springs

ioe Stele

tise

Observation boreholes

Offensive Monitoring

Observation boreholes, some of specialised designs

eth

Figure 3 Protocol matrix be purged before a sample of the water is taken. This ensures that most, if not all, the

stale water in the borehole is removed and that the sample taken is representative of the aquifer conditions. In large boreholes a special purge pump may be used to remove the necessary volumes but in the approved designs the purging can be done by the sampling pump. Figure 2 shows the importance of taking pumped samples. The example is from a borehole sampling landfill leachate over one year. The samples were taken using a depth sampler when monitoring began but, when the data were questioned, the sampling method changed to using an inertial pump and following the recommended protocol. The depth samples suggested little contamination was present but the pumped samples show the true leachate composition. Those depth samples were a waste of time and a lot of money. No sampling method/equipment will fulfil absolutely the criterion of providing

93

unaltered samples. It is, therefore, essential that a fixed programme or protocol should be followed whenever groundwater is sampled so that sampling errors are at least constant and samples can be compared on a nationwide basis. A sampling protocol matrix (Figure 3) has been produced in which a series of protocols to cover different

situations have been related to the groundwater system and the objective of the monitoring. These protocols are now under consideration by the regulatory authorities.

5.4 Sampling QA/QC

The water industry employs QA/QC procedures routinely for their laboratory analytical procedures but does not use them in field sampling and monitoring. We consider this omission a serious lapse and suggest that a QA/QC plan is a prerequisite for an adequate monitoring programme. An integrated QA/QC system would cover both lab and field procedures. The sources of variability and uncertainty in groundwater quality data arise from the natural variation in groundwater itself, variations due to sample collection and handling and variations due to analytical methods. Different QA/QC samples are used to distinguish these three main sources of variability/uncertainty. The QA/QC sample types are: e e

e

e e

Spiked sample: Sample to which a known amount of determinand has been added. Used as a estimate of accuracy and to assess matrix interference. Trip blank: Sample of deionised water taken on sampling trip. Poured into another bottled in the field then returned for analysis. To assess sample handling. Field blank: Sample of deionised water taken on sampling trip. Passed through the sampling equipment into sample bottle for analysis. Used to assess the effect of the sampling equipment. Replicate sample: Samples taken from the same borehole in quick succession. To assess the natural variability of the groundwater. Split sample: A subdivided single sample. The subsamples are analysed to estimate analytical precision.

The sample organisation distinguishing these QA/QC The QA/QC effort in a programme but may reach programme.

6

must have an archive samples from the actual monitoring programme 20% of total effort in

system capable of recording and groundwater samples. will vary with the maturity of the a complex situation or early in a

CONCLUDING REMARKS

The setting up of a National groundwater monitoring network is considered essential for the effective protection of our groundwater resources. The basis of monitoring and sampling methodologies have been discussed with recommendations made when changes in practice are considered essential. This applies particularly to the design of observation boreholes and the adoption of QA/QC in sampling. The core of the monitoring strategy however, will be the adoption of a matrix of sampling protocols that will be applied Nationwide to ensure comparability of monitoring data across the UK.

94

ACKNOWLEDGEMENTS The authors would like to thank the NRA, DoE and WRc for permission to publish this paper. The opinions expressed in the paper are those of the authors and do not necessarily reflect the opinions or policies of those organisations.

REFERENCES Blakey, N.C., Young, C.P., Clark, L. and K. Lewin

1993. A UK

strategy for landfill

monitoring. Sardinia ’93. International Symposium, S. Margherita di Pula, Italy. Clark, L. 1992. Methodology for monitoring and sampling groundwater. NRA R&D Note 126. WRc plc. Medmenham. Council of the European Communities. 1980. Council Directive relating to the quality of water intended for human consumption (80/778/EEC). CEC Brussels.

Council of the European Communities. 1991. Proposal for a Council Directive on the landfill of wastes. Official Journal of the European Communities. C190/1. Foster, S.S.D. & D. Gomes 1989. Groundwater quality monitoring: An appraisal of practices and costs. Pan American Center for Sanitary Engineering and Environmental Sciences (CEPIS), Lima Peru.

Hitchman, S.P. 1983. A guide to the field analysis of groundwater. Fluid Processes Research Unit. Report FLPU 83-12. British Geological Survey. National Rivers Authority 1992. Policy and practice for the protection of groundwater. NRA. Bristol, UK. Stuart, A. 1984. Borehole sampling techniques in groundwater pollution studies. Fluid Processes Research Group. Report FLPU 84-15. British Geological Survey. United Kingdom Government 1974. Control of Pollution Act, Part 1. HMSO. UK.

United Kingdom Government 1988. Town and Country Environmental Impact) Regulations (1988). HMSO. UK.

Planning

(Assessment

United Kingdom Government 1990. Environmental Protection Act. HMSO. UK. United Kingdom Government 1991. Water Resources Act. HMSO. UK. United Kingdom Government 1991. Water Industry Act. HMSO. UK.

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4 Nitrate

Groundwater— Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

A preventive action against nitrate water pollution into drainage basin M.-C. Huau SAUR, St. Quentin Yvelines, France

ABSTRACT: Nitrate water pollution from farming sources (cattle breeding and soil fertilization) is well-known. Resolution of the problem is likely to be achieved by changes in land use and husbandry systems. That includes restrictions in the use of nitrogen fertilizers and modifications in farming practices such as cattle breeding. SAUR, one of the three most important group in the world specialized in drinking water supply and sanitation, has initiated with Sanitary departmental administration a preventive action in Vendee department. Launched in january 1992 with the support of agricultural departmental administration, the "ferti-mieux" scheme is composed with three steps choice of pilot area, farm technical program, communication action. Apremont drainage basin located in Vendee has been chosen due to high nitrate concentration into surface waters, farmers dynamism and financial support of departmental administration.

INTRODUCTION In a large part of the northern EEC countries, nitrate-N concentration in soil water samples at 1 m depth exceeds 50mg/I (standard level). This concentration concerns about 25% of European Community farm surfaces and more than 50% of remaining surfaces could reach this level in the future. This is due to agricultural intensive farming. In France, Vendee department shows high risk of nitrate water pollution caused by intensive farming and nature of water resource. In Vendee, drinking water production comes mainly from natural surface waters. Nine large dams provide drinking water to 95% of inhabitants.

Apremont dam is the second most important dam in Vendee and water quality often exceeds 50mg/l. Nitrate content evolution from 1989 to 1992 in Apremont drainage basin is described in diagram n°1.

1 THE "FERTI-MIEUX"

SCHEME:

DEFINITION

The scheme is an advisory scheme for farmers which are involved into the chosen pilot area. Two objectives : to modify husbandry systems and fertilization practices to reduce nitrate contamination into water In the long term, the main goal is the surface water protection. 4S)

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RAINFA LL AND

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ae

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N NITRATE 'S CON CENTRA TION (mg/l)

NITRATE NITRATE CONTENT TE

FROM FROM

1989T O 1992

TREATMENT (4,5%) WASTEWATER TREATMENT

PLANTS (4,0%)

2 CHOSEN

PILOT AREA IN THE SCHEME:

"LA VIE" RIVER

Apremont drainage basin presents the following characteristics : -

The river : La Vie "La Vie" drainage underbasin superficy : 170ha Capacity : 3 800 000 m3 height of water : 8 meters Total drainage basin superficy : 276 km2

Apremont dam provides water to the drinking water treatment plant managed by SAUR (the third water supplier company in the world). Production capacity : 36 000 m3/j Annual production : 6 250 000 m3 in 1989. Palluau and Le Poire sur Vie constitute the two administrative districts of Apremont drainage basin. They fit with two rivers respectively, “La Petite Boulogne" and "La Vie". Administrative map is shown in figure n°l. Dynamism and active mobilization of farmers which are located into "Le Poire sur Vie" allowed the choice of the pilot area squaring with "La Vie" drainage underbasin. So high nitrate concentration in soil is due to farming intensive use and husbandry systems. 91,5% of N-inputs come from agricultural activity. An estimation of N-input sources into Apremont drainage basin shows (in diagram 2): -

3 AGRONOMIC

point sources pollution from cattle breeding (38,2%) diffuse sources pollution from land utilization (53,3%) point sources pollution from discharge of urban wastewater (8,5%)

DIAGNOSIS

FARM CHARACTERISTICS INTO APREMONT DRAINAGE BASIN (1988 and 1992 RGA data) Farm holdings structure

Canton of POIRE

size of holdings (ha) % less than 5 ha % over 50 ha full active farmers

% farmers /active pop.

S.A.U. Repartition Agricultural surface (SAU) (ha) Fodder crops surface (% SAU) with maize with permanent grass (STH)

101

Canton of PALLUAU

About livestock, it can be observed increasing sows and yet populations (+100% from 1979 to 1989) and foster cows instead of milch cows. It can be noticed an average of : - 1,8 cattle / ha SAU (UGB/ha) - 0,2 pig / ha SAU - 20 fowls / ha SAU.

Concerning the "Poire sur Vie" following characteristics :

canton,

milch cows

farm holdings have these

breeding +

out of soil

Potassium

4 NITRATE LEACHING RISKS ANALYSIS Nitrogen flux of Apremont drainage basin CANTONS waterplants

POIRE

T/an

N-output (T/an) from population breeding

324

%

45,6

PALLUAU

140 48

TOTAL BASIN’

T/an

464

%

46,4

land

320 45,3

139 47,9 459

45,9

_Natural factors contribute to increase nitrate risk of pollution : leaching, soil erosion and drainwater which facilitate nitrate losses into surface waters. According to Loire Water Agency, the quantity of farm nitrogen found back into waters squares with about 20% of farm N-output.

102

TOTAL DRAINAGE BASIN LIMIT

i

ss

LOCAL COMMUNITIES LIMITS

i

——

SELECTED PILOT AREA LIMIT

aes

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APREMONT DRAINAGE BASIN

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FIGURE

5 THE PROGRAM

2

APREMONT

DRAINAGE

\suR vie

BASIN

IN THE SCHEME FOR THE PILOT AREA

According to farmers’ wishes, technical actions include : -

fertilization and husbandry optimization with :

- soil. analyses

~ CORPEN balances

ae Yrot

103

- parcels trials with N zero point - manuring of fields and spreading plans - spreadings and husbandry advices -

pollution reduction from point sources of breeding with : - animal manures analyses - cattle breeding buildings repairing consistent with the legal standards

-

battle with the natural erosion using : - a hedge mapping -a pH mapping

Finally, It contains : -

communication action is an important part of the program. informative bulletins spreadings notice boards close to fields practical shows

Three kinds of Public :

.

the farm writting

public

which

participates

-

the large agricultural profession such surgeons, inseminators, the milk control

-

the general public informed bulletins spreading

to

the

as,

bulletin

veterinary

with the local municipal

6 CONTROL AND MONITORING OF WATER QUALITY The drainage basin is monitored at the same time. This is coordonated by SAUR with the permanent collaboration of the "DDASS" public drinking water and sanitation watchdog and the SATESE wastewater assistance advisory board. Monitoring is conducted according to a precise monthly schedule or, during wet spells when rainfall exceeds 30mm, on a weekly basis. Special

attention

is paid to the exact

area

of the "Ferti-mieux"

scheme, i.e. the "La Vie" river, from its source at Belleville to its arrival in

La Chapelle Palluau.

In order to establish a comparison,

samples were

taken from the

main tributary, the "Petite Boulogne". The chosen number of samples from "La Vie" river was 8, and 4 from the "Petite Boulogne”. The location of the control points is presented on the enclosed map n°2.

Two types of analysis were performed : -

conventional analyses, with physico-chemical measurements of pH, temperature, suspended solids, dissolved oxygen, organic matter, conductivity and measurements of the nitrogenous substances NH4,NO2,NO03,TKN

104

-

plus bacteriological and pesticide measurements, in addition to the conventional analysis carried out at two points on the "La Vie" and at two points on the "Petite Boulogne" once every three months.

Finally, for each water quality measurement the flow-rate is recorded. The planned gauging station should be equipped with a continuous sampling system.

7 THE PARTNERS IN THE SCHEME A ccordination committee has been set up to decide upon a programme, a budget and the objectives to be chosen over the course of the scheme, which was launched in october 1992 and is set to last for at least three years. The committee has two distinct groups of members working continuously together : water specialists and agronomy specialists. The partners are : -

the the the the the the the the the

Chamber of Agriculture of the Vendée department departmental water authorities DDAF departmental forestry commission DDASS drinking water and sanitation watchdog SAUR water supply company SATESE wastewater assistance and advisory board Vendée Conseil Général farmers’ unions farmers’ cooperatives

CONCLUSION The extensive involvement of both the agricultural sector and the authorities in this project has given rise to a constructive and comprehensive programme.

water

The department of Vendée, whose drinking water principally derives from surface water sources, is thus taking part in the protection of the quality of its water supplies. The "ferti-mieux" field project was successfully launched thanks to a number of favourable political and finiancial decisions. This advisory scheme, undertaken jointly by leaders of the agricultural and water sectors, is a sure means of taking preventive action against agriculture-related nitrate pollution in water.

REFERENCES D., MUNTZER R., LAIGLE P., CARBIENER ACKERER Contamination L., ZILLIOX M., TREMOLIERE C., SCHENCK eaux souterraines par les nitrates dans la plaine d’Alsace. Incidences ; pas. ar Vagriculture. CARLOTTI B., 1992. Bases de préconisation de la fertilisation azotée cultures, CORPEN. 105

C., des de des

COMIFER, 1981. Dosage de l’azote minéral du sol en vue de la prévision future azotée. Note. MACHET JM, MARY B., 1990. Impact of agricultural pratices on the residual nitrogen in soil and nitrate losses. In "management systems to reduce impact ofnitrates". Ed JC GERMON, 126-146. ONNIS C., 1990. Etude du fractionnement des apports d’azote sur la culture du mais. Rapport de BTS. Productions végétales 19pp. SEBILLOTTE M., MEYNARD JM., 1990. Systemes de culture, systéme d’élevage et pollutions azotées. In "Nitrates, Agriculture, Eau" CALVET

Ed. INRA, Paris 289-312. SETP, Cabinet PRAUD, 1989. Qualité des eaux de la retenue d’Apremont. SIAEP Haute Vallée de la Vie, Vendée. Rapport final. TARDIEU F., 1989. Comment juger l’efficacité du systéme racinaire comme capteur d’eau. Perspectives agricoles "Les racines". Tiré des n° 1:1.9.91:22.9128: TAUREAU JC., 1985. La fertilisation azotée du mais. Perspectives agricoles (91). Encart ITCF conseils. TAUREAU JC., ALLIOT B., 191. Opération Nitrates moins en Eure et Loire. Perspectives agricoles (154), 75-86. ZIEGLER D., 1987. Principes du raisonnement de l’apport d’azote sur prairies a base de graminées. Persp. Agric. (115) 148-154.

106

Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Analysis of groundwater pollution by nitrates in a Spanish coastal aquifer under intensive horticultural land-use J.Guimera & L.Candela Geotechnical Engineering Department, International Center for Groundwater Hydrology, Technical University of Catalonia, Barcelona, Spain

ABSTRACT: The Maresme coastal aquifer is heavily polluted by nitrates. A nitrogen balance has been performed taking into account natural contributions and artificial, and its evolution through the upper 3 metres of the vadose zone in experimental plots. Fertilization timing is the main cause of the pollution, since the fertilizer application before crops is rapidly leachate during the first days after plantation, due to irrigation or rain, depending on the crops and season. Plants do not take profit of it, and more nitrogen has to be applied during the crop. Nitrate leaching in the unsatured zone is reduced with experimental crops. We demonstrate that accurate agricultural practices reduce pollution processes in groundwater.

1 INTRODUCTION Groundwater pollution by agricultural practices has been widely reported during the last two decades in many aquifer all over the world (Vrba and Romijn, eds. 1986; Follet, ed.

1989). This kind of pollution is usually exposed by high nitrate contents in groundwater. They are related to overfertilization of crop lands which form the recharge area of the polluted aquifer. Other nutrients applied to crop lands, such as phosphate or potassium, and organic compounds like pesticides, can be dissolved and mobilized from surface downwards

to the water table through the vadose zone. However, nitrate molecule is

highly mobile and plays a major role in the pollution process from agricultural activities. Whereas nitrate pollution usually is a nutrient and water balance issue efforts are concentrated in: — Understanding the natural terms of nitrogen cycle — Improving fertilization efficiency and nitrogen uptaking by plants — Ammeliorating water use in irrigation areas Because of the magnitude of the problem, specific studies on the relationship between groundwater quality and agricultural activities developed on surface have been carried out. Many case studies showing the effect of nitrogen leaching on groundwater quality are reported by Parker (1990), Foster (1986), Pekny et al. (1989), Benes et al. (1989), Follet (ed. 1989), Adriano et al. (1989), Vrba and Svoma (eds. 1982), Vrba (ed. 1986), Steenvoorden (1986), Vetter and Steffens (1981), Custodio et al. (eds. 1981) among others. Varela (ed. 1991) and Candela and Ramos (1992) report an updated state of the art of the Spanish problem. Although is out of the scope of this paper to report a detailed state of the art of nitrate pollution in Spain, some specific features are outlined below. According to the abovementioned authors Varela (ed, 1991) and Candela and Ramos

107

(1992), groundwater pollution by nitrates, along with seawater intrusion in coastal aquifers causes the most severe damage to groundwater quality in Spain. Agricultural production has observed a high development in Spain during the last decades, as well as the EEC countries. Such a development has been based on intensive irrigated crops and vegetable species of rapid growth wich, at the same time, are based on an extensive use of inorganic fertilizers. During the last 25 years irrigated crop lands have

increased from 10° ha up to 3x10® ha in the country. These crops usually take place on top of highly vulnerable aquifers (detritical, coarse grained, vadose zone thinner than 30 m and of scarce resources renovation) frequently located on high pressure demand areas (coastal zones)

The most severe pollution occurs in coastal aquifers, specially in the mediterranean coast. In coastal areas, high valuable horticulture crops, citrus orchards, flower and tropical crops are grown being many of them developed in greenhouses. The aquifers use to be narrow strips of detrictical unconsolidated materials with a natural recharge sparse in time and space. Many cases of nitrate content above 100 mg/l are present (Figure 1).

4

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Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Possible effects of climatic changes on low flows of Estonian rivers Marina M.Timofeyeva Estonian Meteorological and Hydrological Institute, Tallinn, Estonia

ABSTRACT: The possible consequences of climatic changes on low river flow and groundwater systems are considered. Relationships were developed and evaluated between each of four typical low flow characteristics and two meteorological parameters (air temperature and precipitation) for seven major Estonian rivers. Time series analysis of the current conditions has shown an increase in the values of both the four selected low flow characteristics and the two meteorological parameters for the period 1980-1990. Subsequently, a multiple regression model was applied to simulate the possible future changes in the low river flow. As input parameter for the multiple regression model, future changes in the air temperature and precipitation were used. The latter two input parameters were defined by using the resulls of an existing general atmosphere circulation model and paleoclimatic scenarios.

1

INTRODUCTION

Nowadays there seems to be a strong evidence of climate changes occuring as a result of anthropogenic influences. AS a consequence of changes in the thermal balance of the atmosphere, the groundwater system also is changing. Due to a strong interaction between groundwater and low river flow (low river flow is supplemented by groundwater flow only), the low river flow can be considered to be an indicator of the groundwater system behaviour.

Many studies of the influence of global climate changes on water resources, hydrological regime of rivers, and water supply indicate the following (Shiklomanov 1989, Budyko 1974, Vinnikov 1981, Russak 1992):

(a) the positive anomaly of air temperature, especially in the cold period of the year, was found in the last 10-15 years for Northern hemisphere basins; (b) the observed air temperature increase was most in occurs The increase 100 years. for the last significant western and central Finland, including Canada, many regions Russia; 131

increase (c) the air temperature year has caused winter river flow phenomenon was not observed for the for the last 10-15 years; (ad) the most significant changes the Earth have occured in the last

in the cold period of This to increase. but 100 year, enture

in

hydrological

8-10

the only

regimes

of

years.

One of the most important directions for study of the hydrological consequences of global warming is the evaluation in extreme parameters characterizing of possible changes river flow, such as maximum discharges and low flow discharges. Scientists from Scandinavian countries, Australia and Japan among others have defined that, as a result of global warming, flow variability increases, droughts and floods are longer and extremer. The temporal variability of low river flow in Estonia was studied to provide insight about the hydrological system behaviour as a consequence of possible climate changes, especially with regard to drought periods.

2 OBJECTIVE

AND

METHODS

The main objective of the work is to study the influence of changes of climatic parameters on river flow in Estonia.

possible future low

The value and variability of low flow are very important characteristics due to their frequent usage in different hydrological, water management and environment-related problems. Low flow problems have become more pronounced in the recent years, partly as a result of increasing load of polutants on waterbodies. Evidently, the pollutant concentration in river water reathes-its maximum values during low water period. Because the Estonian river network consists mainly of small basins (average size 500-1000 km2) mostly only low discharges of water can occur. In principle, the following methods quantitative estimation of the effect the hydrological system:

could be applied for of global changes on

(a) statistical relationships between flow and meteorological parameters (used in this study); (b) water balance methods for long-term records over a long period of time; (c) application of results of existing models for general atmosphere circulation; as (d) development of deterministic hydrologic models of river asins.

This study was carried out by using various statistical methods for analysis of (1) variability of river flow and (2) climate parameters. Long-term observation series on hydrology and meteorology were used. Time series analysis was applied for definition of representative periods. The results of a

132

model of general atmosphere circulation and of scenarios of the climatic parameters were used future changes in low river flow.

paleoclimatic to determine

Based on the aforementioned objective following specific actions were carried

study,

of the out:

the

1. Definition of study area and parameters (Section 3); 2. Elaboration of the regression model using meteorological parameters as predictors (Section 4); 3. Time serie analysis of hydrological and meteorological parameters, its time variability (Section 5); 4. Forecast of regional changes of low flow on Estonian rivers (Section 6).

3 STUDY

AREA

AND

PARAMETERS

The study area contains seven watersheds located in Estonia (Figure 1). The gauging stations selected for the study were chosen such that the long-term data were not affected by anthropogenic effects (water reservoirs, effect of sluices, amelioration, etc.). Especially the effects of recent anthropogenic activities were avoided. It is expected that the current conditions on the rivers will be maintained in the future. Otherwise, the civil engineering river constructions, as well as drainage of groundwater due to mining, and drainage due to land-reclamation would change the hydrological regime in the basins. The locations of gauging stations used in this study is shown in Figure 1.

Bay oF Finuanp

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coefficient expressing the quotient of time in t-th year to average value for the whole time

parameter,

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curve

minimum

discharge

average

discharge

minimum

discharge

(*for rivers was used) -~ December

Purtse

in

time

year.

was performed for the following meteorological parameters: :

precipitation

in August; air temperature in July; - July : precipitation in June; air temperature in June; - winter : precipitation in January; air temperature in February;* in March air temperature and Kasari

in November; discharge:precipitation air temperature in December. in mm, and air precipitation in m3/s, were River discharges the year As a time index, in degrees Celsius. temperature number was used.

Joint plots differential-

to

average

of the time-series integration curves

2d. 135

analysis based on in Figures are presented

2a

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Groundwater —Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Conjunctive use of surface and groundwater for small-scale irrigation in Zimbabwe I.Moyo Loughborough University of Technology, Leicestershire, UK

ABSTRACT Surface water in Zimbabwe is unreliable and poorly distributed. More than half of the country is occupied by intrusive granites which furnish low yields enough only to supply villages for drinking and stock. Collector wells can be used to enhance the yields of the boreholes in the crystalline basement. Alluvial aquifers occur in dry parts of the country and they give considerably higher yields enough for irrigation of large areas. Dependence on either surface or ground water alone is risky. Conjunctive use is considered as a solution to the inadequacies of both water sources for irrigation.

1. INTRODUCTION The basic resources of land and water for irrigation development in Zimbabwe are reasonably well defined. There are some 14 million mega litres (Ml) of surface water

run-off, an estimated 1 million Ml of potentially arable land. There figures between the suitable land and readily cost effectiveness in developing these

groundwater and at least 700 000 ha of actual or however, bypass the problem of the relationships available water. They also take no account of resources.

Zimbabwe's mean annual rainfall exhibits considerable variations and each year's rainfall is concentrated over a very few months. The amount of water that can be assured from flow is generally low. Moreover, loss due to evaporation is high, the mean annual evaporation being approximately double the mean annual rainfall. More than half of Zimbabwe is occupied by intrusive granites which are not a very favourable type of rock for an aquifer. The aquifers of the crystalline basement scattered across the central and southern part of the country, furnish low yields.

The inadequacies of both surface and ground water when used independently for irrigation are enormous. Dependence on surface water alone has proved to be very risky in most parts of the country where rainfall is low and poorly distributed. The

sum total of the evidence available is that there is an urgent need for simple and inventive ways of exploiting groundwater for extensive use by farmers. Conjunctive

145

Figure 1 Zimbabwe location map (source: Department of Meteorological

Services

(1981)

)

use of surface and ground water is considered an effective solution to the scarcity of water resources for irrigation. 2. HYDROGEOLOGY 2.1 Geology

About 60% of Zimbabwe consists mainly of Precambrian granites and gneiss with a few inclusions of schists and greenstone belts. This is in the Eastern zone which is

separated from the Western zone by a line running north-east to south-west, see figure 3. The Western zone accounts for the remaining 40% and includes some intrusive granitic formations but consists mainly of less ancient rocks. About 4.6% of Zimbabwe's national land consists of Dambos (Dambo Research Unit 1987). Dambos are defined by the Dambo Research Unit (1987) as "low lying, gently

sloping treeless tract of country which is seasonally waterlogged by seepage from the surrounding high ground assisted by rainfall and frequently contains the natural drainage channel for the removal of excess run off from this surrounding high ground." Parent material in these wet land depressions is rarely undisturbed usually consisting of 146

fos Mofu

Piateau “|

BORDER

EASTERN

Figure 2 Names of places and main geographic features (source: Department of Meteorological Services (1981) )

colluvium and sheetwash deposition from upslope or alluvium from flooding. Dambos play a very significant role in the rural areas through garden irrigation which enables vegetables to be grown in the dry times of the year and in the drought years. 2.2 Groundwater Resources

Two categories are identified. The crystalline rocks and the non-crystalline rocks. In the crystalline rocks one of the areas near Mvurwi to the central-eastern part of the country contains rocks in a thick sedimentary series which forms a clearly defined slope with a lower group consisting mainly of sands with dolomites, quartzites and slate and an argillaceous upper group of quartzites and slates. Boreholes drilled 45 to 60 m into the fractured slates yield up to one litre per second (United Nations, 1989). Another crystalline area of significance is the Intrusive Granites. This occupies more than half of the country. The granites found in this area are the least favourable type of rock for the constitution of groundwater aquifers as the porosity is confined to the fractured and altered parts of the contact zone of the gold beds.

In the non-crystalline rocks Kalahari Alluvium is significant. The largest beds are found in three river valleys in the south-east, south-west and to the north. Most of the boreholes in these river valleys supply water in sufficient quantities for irrigation.

147

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Figure 1 River-aquifer system.

The river bed is assumed to have a rectangular cross-section. It is located in the middle of the rectangular, homogeneous and confined aquifer and it only partially penetrates the aquifer. A constant water level in the river is assumed. At both ends of the aquifer constant piezometric heads o’, and ", - are specified. They are assumed to be equal to each other and less than the piezometric head in the river, i.e. 0’, = 0", = 6, < o,. This implies that the interaction between the river and the aquifer is symmetric in space. Physically the interaction is a seepage through the sediments which have accumulated at the river bed and banks. The seepage is proportional to the difference between the piezometric heads in the river and the aquifer and reciprocal to the flow resistivity through the sediments - c. The resistivity c is also assumed to be homogeneous. Because of the geometric symmetry of the case, only one half of the river-aquifer system needs to be considered.

2.2 Two-dimensional model of the river-aquifer interaction

The steady state flow equation for the system illustrated in Figure 2 is,

a, O70ao |

Te

0

(1)

where T, = (D,-D,),.

(2) 156

d

—*

Q

Figure 2 River-aquifer interaction (2-D)

The boundary conditions for the region are as follows:

Sae||

ox

=O

) Letty ™

(3)

o°.

The analytical solution of these equations in described by Nawalany, 1993.

2.3 Three-dimensional model of the river-aquifer interaction In order to solve the groundwater flow problem in three dimensions we subdivide a flow domain Q into two parts - I and I] - see Figure 3 and solve two separate flow problems for the two parts of Q. After that we match the solutions along the common boundary I ,, in terms of piezometric heads and normal fluxes, i.e.:

(4)

6'(x,z) = 9"(x,z) and

0o'(x,z) _ do'(x,z) ox

Ox

for x=H, and for all ze[O,D,-D,].

Solution for region I Piezometric head in region I o'(x,z) must satisfy the flow equation:

Fo2 29 Oxaoze

tor

xe[0,H]

(5)

ze(0,D,-D]

and the following boundary conditions:

157

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a

cee ae

for xe[0,H]

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Solution for region I

The piezometric head 6" = 9'-o, (abbreviated hereafter as 6) must satisfy the flow equation:

xe[H,,.L,] m2 + &> =a()

One

Gre

a

ze[0,D,]

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161

The total resistance, R,, which ensures that the flow from a 2-D horizontal model is the same as that from a fully 3D model, may thus be represented as,

R, = R, (1 + H, / 2D,

(11)

4 IMPLICATIONS Two dimensional The implications of the findings described in this paper are wide ranging. condition, boundary Cauchy a as interaction river-aquifer represent which models flow horizontal equation 7, will overestimate the total flow from a river into an adjacent aquifer. This means that these models would exaggerate the impact interaction with the aquifer has on rivers flows. If two dimensional models are used to investigate river low flow problems they are likely to overestimate the impact that changes in the groundwater abstractions, and thus changes in the groundwater flow regime, will have on river flows. These models are likely to underestimate the changes required in the groundwater regime to achieve a certain augmentation of river flow since they overestimate the interaction between the river and the aquifer.

The problem of 2-D horizontal flow models overestimating river-aquifer interaction could be alleviated by the introduction of an apparent resistance, but, an exhaustive investigation of the factors which affect this parameter has yet to be carried out so it should be used with caution in practical problems. If the correct simulation of river-aquifer interaction is a critical component of an investigation, as would be the case for low river-flow studies, a fully 3-D groundwater model must be used. Such a model is unlikely to be required to simulate groundwater flow in the area far from the river. The coupling of the 3-D model close to the river with a 2-D horizontal model of the groundwater system away from the river may be the best solution for the correct addressing of river-aquifer interaction problems.

5 CONCLUSIONS

AND RECOMMENDATIONS

Regional (2D-horizontal) models of groundwater flow always overestimate the total flow into the aquifer in the presence of the river-aquifer interaction.

By making certain assumptions it is possible to introduce a correction term, the apparent resistance, so that the flow calculated from influence on the of the river bed to be calculated

calculated from a 2D-horizontal flow model would be equal to the (exact) flow a fully 3D representation of the system. The factors which have the greatest apparent resistance are the penetration, the resistance coefficient due to the clogging and banks and the river width. A formulation which allows the apparent resistance for large values of the river bed and bank clogging coefficient is proposed.

Since in general there is no clear (easy) relationship between the ratio Q/Q, and parameters of the river-aquifer system it is more proper to use the full three-dimensional model for calculating total flow in the aquifer if the river-aquifer interaction needs to be taken into account

Two extensions of the work described in this paper are proposed. interactions to be investigated for the following conditions : -

unconfined groundwater flow

-

more elaborate geometries of the river bed cross-section.

162

These would allow river-aquifer

6 ACKNOWLEDGEMENTS This work was a part of research on the river-groundwater interaction carried out by the groundwater modelling group within the Operations Department at HR Wallingford. The authors would like to acknowledge the substantial help of the two young colleagues Mr Jakub Loch and Grzegorz Sinicyn (from IEE) who contributed to the computational aspects of the project.

The authors would like to express their thanks for the financial support from HR Wallingford and the British Council.

7 REFERENCES Ineson, J. and R.A.Downing 1964. The groundwater component of river discharge and its relationship to hydrogeology. Journal of the Institute of Water Engineers, 18, pp 519-541.

Nawalany, N 1993.

Mathematical Modelling of River-Aquifer Interactions.

HR Report SR 349.

Recking, A 1992. A study of the representation of River-Aquifer Interactions in Regional Groundwater Models. Unpublished Training Course Dissertation

163

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6 UK drought management

jnenegsnsiniiguah AU & “~

Groundwater— Drought, Pollution & Management, Reeve & Watts (eds)

© 1994 Balkema, Rotterdam, ISBN 90 5410 3515

Anglian Water’s groundwater drought Strategy Edward J.Smith Anglian Water Services Limited, Cambridge, UK

ABSTRACT : Despite the worst drought this century over the Anglian Region of England, with unprecedented low groundwater levels, abstractions were maintained to satisfy essential public water supplies. Abstraction regimes were modified and river support schemes activated to maintain a balance between the need for public water supplies and the need to safeguard the long term integrity of the groundwater system and its environments. 1 INTRODUCTION Anglian Water Services is the largest, in respect to geographical area, of the recently privatised water companies of the United Kingdom (Figure 1). The Company provides water supplies of the order of 1100 MI/d to around four million people in what is one of the driest parts of the country (Anglian Water Plc 1992). The annual replenishment of water resources is on average 150 mm being derived from an average annual rainfall over the Company’s area of some 610 mm and an annual average evapotranspiration rate of 460 mm. This can reduce to 40 mm in a 1 in 100 year drought. Approximately half the water supplied is derived from underground sources in the Cretaceous

Sandstones.

Chalk, Jurassic Limestones and Sandstones and Permo-Triassic

The remaining surface water derived sources are primarily pumped

storage reservoirs,

in particular Grafham

and Rutland Water, and to a lesser

degree direct river intakes. This mix of water resources offers the ideal opportunity for conjunctive use to improve security of water supplies particularly during drought sequences. The period August 1988 to August 1992 represented one of the driest sequences of weather in the Anglian Region this century with a return period in excess of 1 in 200 years. This presented a challenge to the Company in maintaining essential public water supplies during a period of unprecedented low groundwater storage and heightened environmental awareness and concern.

167

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AGvas

Raw Water Transfer

Triassic

Sandstone Surface Water Jurassic

Works

Sands

Cretaceous Chalk

Figure 1

Reservoirs

rh.

isc

Rivers

Anglian Region’s major water resources

168

Okm

a]

:Long Term Average 610

RAINFALL (

a = & = fe) > & Wi 7) Ww iv ~

(GWL)

4

=

ic 2 GROUNDWATER LEVEL (m) 1977-87

Figure 2

2

Rainfall and groundwater levels 1977 to 1992

BACKGROUND

TO THE DROUGHT

The decade following the 1976 drought was one of the wettest periods on record

this century and was characterised by high water tables and abundant base flow to rivers (Figure 2).

On analysis it is evident that the drought commenced during the summer of 1988 and was perpetuated by a sequence of dry, mild winters interspersed with warm, dry summers through to the spring of 1992. Rainfall over the period August 1988 to August 1992 had a return period in excess of 1 in 200 years (Institute of Hydrology and British Geological Survey 1992) and recharge to the aquifers over

this period was less than 50% and in some localities less than 25% (Jones 1992). Figures provided by the British Geological Survey’s National Groundwater Archive indicate that the depletion of resources over the Chalk aquifer in the Anglian region was without parallel this century. As a consequence groundwater dependent surface rivers recorded unprecedented periods of below average flows extending over 40 months. However despite low rainfall overall there were interspersed periods of intense rain which gave rise to runoff from clay catchments particularly in the west of the region allowing adequate winter refill of the Company’s major pumped storage reservoirs.

The drought effectively ended during the summer of 1992 when above average rainfall over a consecutive period of 5 months reduced the soil moisture deficit to

zero by November 1992 and groundwater level recovery commenced in earnest. 169

Humber Estuary

“ GRIMSBY

Ancholme

Great Eau

Fossdyke

Transfer

Canal River Great Eau

Potential : ¥ Saline

Ingression

4M |»

Treated Water

Raw Water

Transfer

Transfers

e

estaction

Boreholes

Figure 3. Humber Bank water resources

depending on hydrological activity. During the period 1988-1992 annual average abstraction was reduced progressively from 135 MI/d to 111 M1I/d, the latter value confirming the drought yield previously predicted. The shortfall was made up from supplies from Covenham Reservoir and a surface water intake at Cadney on the River Ancholme. This in turn was supported by the River Trent through operation of the TrentWitham-Ancholme transfer scheme (Figure 3).

The conjunctive use of resources successfully over-came a period of excessively low levels in the Northern Chalk aquifer.

However to accommodate this the

Company had to invest in considerable extra infrastructure, in particular major irunk mains, and had to incur additional operational costs.

170

3.

ABSTRACTION

STRATEGY

The policy adopted by the Company during the drought (1988-1992) was to maintain essential public supplies having due regard to the status of the groundwater resources and the water dependent environments they support. The exercise was not just one of securing water supplies but also one of influencing demand by encouraging the public to "use water wisely". This was carried out primarily through publicity campaigns but also with selective hosepipe bans. Within the Anglian Region periods of low effective precipitation are not

uncommon and as a result there is a history of water resource management involving engineering works such as interbasin transfers to support river flows and the development of mathematical models to manage systems (National Rivers Authority 1993). The philosophy adopted has been to see the groundwater resource as an asset both for public water supply and for the environment. In doing so it has been necessary during periods of drought to operate river support schemes, modify abstraction regimes and extend the concept of conjunctive use of surface and groundwaters. During the period 1988 to 1992 the Company invested some £25 million in drought related schemes in pursuing this policy. Early on during the drought a policy decision was made to keep the Company’s large surface water reservoirs of Rutland and Grafham as full as possible to enable additional transfers to be secured

to the groundwater prone drought areas. of the schemes involved.

4

NORTHERN

The text which follows highlights some

LINCOLNSHIRE CHALK AQUIFER

It has been recognised for some time that the aquifer has been over licensed and that abstraction during periods of low recharge could lead to saline intrusion from the Humber Bank (Figure 3). To address this and the overall management of the aquifer, a mathematical model was developed to help produce abstraction rules (University of Birmingham 1978). A maximum abstraction of 140 Ml/d was imposed to reflect the sustained yield of the aquifer with lower limits introduced during periods of below average recharge. The Company needs to respond to any shortfall in abstraction during periods of drought at relatively short notice. To facilitate this the groundwater model was used to determine the abstraction regime which could be sustained through the worst recorded drought without causing saline ingression. The outcome was an

average abstraction of some 110 MI/d, a figure subsequently used for planning purposes. During periods of below average water table the groundwater model is run by the National Rivers Authority, in conjunction with information supplied by the

Company on projected demands, to determine the abstraction regime that could be supported under the most likely recharge scenario. The optimum abstraction regime selected is that which ensures a positive seaward hydraulic gradient is 171

maintained.

This exercise is usually undertaken at the beginning of the annual

groundwater level recession and the model is updated every three to six months. 5

SOUTHERN

LINCOLNSHIRE LIMESTONE AQUIFER

The Southern Lincolnshire Limestone aquifer has been extensively mathematically modelled (Rushton 1982) although it is only recently that a reasonable representation of the mechanics of flow in the aquifer and the relationship with the Rivers West and East Glen has been well represented. Historically there has been evidence of an impact of groundwater abstractions on river flows particularly towards the confluence of the West and East Glens where traditionally artesian overflowing conditions prevailed (Figure 4). In recognition of this abstraction licensed quantities were reduced from over 90 MI1/d to 64 MI/d

during the 1980’s.

|

River East Glen

; Limestone

Area of Potential Artesian Overflow

Outcrop

Conditions and Confined Limestone

Me

River West

pohly

iy

OURNE

Kate's Bridge Gauging Station

Transfer

River Gwash Rutland Water

Public Water Supply

Dip of Strata

Abstraction Boreholes

>

Figure 4. Southern Lincolnshire Limestone hydrology 172

However it was recognised that this constrained the development of an aquifer which historically was used extensively for public water supplies. The resource historically was reliable, characterised by prolific borehole yields often in excess of 15 MI/d, and low operating costs due to artesian conditions and inherent good water quality characteristically low in agro-chemical and industrial contaminants. To reflect the need to satisfy both in-river needs and public water supply a river augmentation scheme was devised utilising Rutland Water. Compensation water

from the reservoir to the River Gwash is enhanced during periods of low river flow and transferred to the River West Glen to maintain, when possible, a target flow of 250 I/sec at Kate’s Bridge gauging station. These arrangements are formalised in abstraction licences and operating agreements between the Company and the National Rivers Authority. The scheme was operated in earnest during the recent drought and although target flows were not always achieved environmentally acceptable flows were maintained.

6

CAMBRIDGESHIRE

CHALK AQUIFER

The Cambridgeshire Chalk between Thetford and Newmarket is uscu extensively for public water supply. The licensing policy of the National Rivers Authority and its predecessors was to set aside a percentage of the available resource for in-river needs and the environment (National Rivers Authority 1993). The actual quantities required remain uncertain but such a policy reduces the possibility of ’overlicensing’. The reliability of abstraction from boreholes used for public water supply under low, ’drought’, groundwater levels has also been uncertain. As the drought progressed concern was expressed by the National Rivers Authority on the impact of the dry weather and abstraction on river flows and environmentally sensitive wetlands. Similarly the decline in groundwater levels over the outcrop chalk was leading to unprecedented low groundwater levels and

a subsequent decline in borehole yields. Evidence from the Company’s Source Reliable Output Investigations, which involved step testing and geophysical logging, suggested the decline would be nonlinear, accelerating as the upper fissures became dewatered (Sir M MacDonald & Partners 1991). Detailed source monitoring of groundwater levels and abstractions confirmed this at some sources. To counter this two measures were taken. Firstly, a transfer of treated water into the affected area was commissioned,

backed up primarily from Rutland Water. Secondly, a strategy of satellite boreholes was implemented in the vicinity of affected sources which in effect spread the load on the aquifer and reduced the impact of fissure dewatering on borehole yields. Apart from securing an adequately designed and constructed borehole the location of the borehole itself was of critical importance. Sites had to be selected which were not too distant from the sourceworks, thus minimising high pipeline and

operational costs, but of sufficient distance to ensure benefit from reduced drawdowns. In addition there were also constraints on the purchase of land and the willingness of landowners to sell. In some circumstances the landowners 173

themselves were farmers who were suffering from the drought, either directly or

indirectly, as a consequence of spray irrigation bans.

There were also environmental and regulatory matters to consider. Hydrogeologically the selection of satellite boreholes would point towards devel-

opment closer to river valleys where invariably yields are higher and the reduction

in the water table less severe. However, the likelihood that this would not be sanctioned by the licensing authority due to its likely impact on the river and associated wetlands, lead to less than ideal sites being selected. However,

irrespective of these constraints this policy in combination with imported water was successful in maintaining water supplies.

7

RIVER WENSUM

SUPPORT

Many rivers which flow across the Chalk in the Anglian Region have a high baseflow component. As such they have reliable ’drought’ flows sustained almost exclusively by the Chalk and to a lesser degree by overlying superficial deposits.

Historically such rivers were used extensively for direct river abstraction and apart from bankside storage where appropriate for water quality protection, raw water storage is minimal. The majority of such abstractions are located on the edge of the Chalk, such as at the Marham and Stoke Ferry intakes (Figure 1). As a result maximum advantage is taken of the base flow available with minimal impact on the upper reaches which are often environmentally sensitive, supporting Sites of Special Scientific Interest and salmonid fish. However the location of intakes at the bottom end of reaches can have its disadvantages. In the case of the River Wensum the original intake at Heigham has been surrounded by urbanisation and industrialisation thus rendering the intake susceptible to both groundwater and surface water pollution incidents. To accommodate this a new intake was commissioned further upstream at Costessey prior to the drought in 1987 which has now become the major intake maintaining supplies to Heigham Water Treatment Works with a capacity of 60 Ml/d. However the abstraction licence contains a cessation clause associated with a minimum required river flow condition which limits the reliability of abstraction during periods of low flow. This is compounded by the fact that the river is subject to artificial level and flow control associated with riparian owners who have historical mill rights. These rights are exercised to maintain river levels for environmental enhancement such as riverside meadows and fisheries. It is evident that during periods of low river flow and summer drought conditions there are sudden declines in river flow (Figure 5). It is believed that this is brought about by a combination of artificially high river levels, which encourage high evapotranspiration losses from the flood plain, and the diversion of river flows to maintain and fill adjacent water storage as mill gates are raised. This combination leads to periods of low flow in the river such that there is insufficient flow above the cessation flow to maintain the required works output. To address this the Company has designed a wellfield to support the river 174

12

;

:

:

AVLQ - AVERAGE LICENCE QUANTITY MRF - MINIMUM RESIDUAL FLOW

1992

——

—1991

11

DISCHARGE CUMMECS Oo, Oe One So sa SS _

0

CRESS

Qn JAN

FEB

i Map" Sy dint he bh | hoLemmeOn AD Mi wma ypIoo Nah wissenio) Sent | he MAR

APR

a

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

Figure 5. River Wensum flows

Wensum.

The wellfield consists of three sites with a combined yield of some 25

Ml/d. The wellfield was commissioned during the drought and will be subject to long term testing and environmental assessment over the next several years when conditions are suitable. Initial indications suggest that the net river gain is high, possibly of the order of 90%, and due to the need to operate the scheme for only

short periods when there is a sudden decrease in flows, it is likely that this gain will be sustained for the duration of the supported period.

8

GROUNDWATER

NITRATE BLENDING

The occurrence of high nitrates in the Chalk groundwater in Norfolk has been well documented and attempts have been made to engineer low nitrate solutions (Hiscock, Lloyd, Lerner, Carey 1989). The Company is in the process of

securing compliant water quality through a combination

of nitrate removal,

primarily by ion-exchange, and through blending with low nitrate water. The majority of the Chalk groundwater at outcrop and the baseflow which

supports rivers is subject to nitrate concentration in excess of 50 mg/I particularly during the early winter following the first flush groundwater recharge. Following the 1976 drought there was a rapid rise in nitrates as a consequence of the build

up of solutes in the soil over the previous 18 months. Nitrate concentrations have not been so marked following the 1988-1992 drought despite a theoretically longer period for solute build up. This has been attributable to the dilution effect of the heavy rains which terminated the drought during the summer of 1992 and the change in agricultural practice towards autumn sown crops and more selective 175

This has to some degree given some encouraging signs nitrate applications. regarding future nitrate concentrations. However irrespective of this the Company, like several others in the UK, has been given undertakings to meet minimum acceptable water quality concentrations by specific dates, the latest being December 1994. To achieve this with the least environmental impact the opportunity to develop low nitrate groundwater was explored. This involved development of deep groundwater underlying the Chalk which had been unexplored previously. The Sandringham Sands aquifer which forms part of the Lower Greensand of the Jurassic/Cretaceous boundary of North West Norfolk is relatively under-developed. The primary aquifer is the Chalk which has been developed in pretcrence due to its higher permeability, higher borehole yields and the need for less complex borehole design. Following a feasibility and pilot study in 1988 a wellfield was designed and constructed consisting of five production sites (British Geological Survey 1989). A wellfield output of 9 MI/d has been secured and is utilised to assist nitrate reduction.

As a consequence

of this, abstraction from the Chalk

aquifer has declined in sympathy thus assisting the aquifer and its environments particularly during periods of drought.

9

SUMMARY

AND CONCLUSIONS

Despite unprecedented low groundwater levels during the 1988-1992 drought over the Anglian Region of England groundwater abstractions to satisfy essential public

water supplies were maintained.

This was achieved by spreading the abstraction

load on aquifers, particularly where high level fissure flow was predominant, and by developing deeper aquifers underlying the Chalk. However in some circumstances it was recognised well in advance that depressed

groundwater

levels and current abstraction

rates could lead to unacceptable

environmental effects including saline ingression and accommodate this a drought action plan was instigated supplies primarily from large surface water reservoirs by enhanced river transfers. The impact of the drought on the water dependent

depletion of wetlands. To by the Company to augment in the west of the region and

environments has yet to be

quantified. The impact of abstractions similarly has to be ascertained. It is the Company's view that an acceptable balance between satisfying public water supplies and protecting the environment was achieved. Action taken to reduce abstractions in aquifers predicted to be under potential Stress proved to be the correct strategy as indeed did the maximisation of surface water storage. Overall however the groundwater resource proved to be more robust than was thought initially and by judicious management abstraction rates were generally maintained. On reflection, post drought, it is considered that a sound drought strategy was pursued which reflected the needs of the Company’s customers and of the environment. Certainly the Company has emerged from the recent drought in a 176

more secure water supply position, having brought forward capital expenditure to meet the water resource requirements of its customers.

ACKNOWLEDGEMENTS The author is grateful to John Simpson, Managing Director of Anglian Water Services Limited for permission to present this paper and to colleagues for their achievements during the drought and for their comments on the paper. The views expressed in this paper are those of the author and not necessarily those of Anglian Water Services Limited.

REFERENCES

Anglian Water Plc. 1992 Annual Review.

British Geological Survey 1989. Sandringham Sands and Chalk groundwater mixing - the Hillington project. Technical Report WD/89/17C. Hiscock,

KM.,

J.W.

Lloyd,

D.N.

Lerner

& M.A.

Carey

1989.

An

engineering solution to the nitrate problem of a borehole at Swaffham, Norfolk, U.K. J. Hydrol. 107. p267-281.

Institute of Hydrology and British Geological Survey. summary for Great Britain. Jones, H. 1992. The English

drought:

Irrigation News No 21.p.34-36. National Rivers Authority 1993. draft. NRA, Anglian Region.

Impact on

Water

resources

Rushton, K.R., E.J. Smith & L.M. Tomlinson.

1982.

1992.

Hydrological

groundwater resources.

strategy

consultation

An improved under-

standing of flow in a limestone aquifer using field evidence and mathematical models. J. Inst. Wat. Eng. and Sci. 42 p.369-387. Sir M. MacDonald & Partners 1991. Source reliable output study. 1 to 4. University of Birmingham 1978. South Humberside salinity research project, final report.

acs

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Groundwater — Drought, Pollution & Management, Reeve & Watts (eds) © 1994 Balkema, Rotterdam, ISBN 90 54103515

Application of an integrated model to chalk catchments A.J.Wyness & PW. Rippon Mott MacDonald, Cambridge, UK

R.B.Wardlaw University of Edinburgh, UK

ABSTRACT: The recent drought in the UK has focused attention on the requirement for effective groundwater management practices in order to reduce the impacts of groundwater abstractions on river flows to acceptable levels. Quantification of the impacts and the assessment of alternative management strategies requires the use of mathematical models. The Integrated Catchment Management Model (ICMM) is described, which incorporates a modified version of the Stanford Watershed Model for groundwater recharge estimation and an integrated finite difference catchment model to simulate groundwater and river flows. The feature which distinguishes ICMM is the effective representation of the interface between the aquifer and surface water systems. The calculation of flow between river and aquifer and the routing of river flows forms an integral part of the iterative solution technique employed in the model. The model has been applied to a number of Chalk catchments in southern England, and a number of features of ICMM are highlighted from these studies. The integrated modelling approach maximises the use of readily available hydrological and hydrogeological data, and gives the water resource planner a sound framework and support for decision making.

1 INTRODUCTION The recent drought in the south and south east of England has focused attention on the need to be able to assess water resources management strategies for a number of Chalk

catchments where groundwater is an important source of public water supply. In many instances, groundwater abstractions coupled with the reduction in recharge to the Chalk aquifer system between 1989 and 1991 caused river flows to reduce to unacceptable levels, detrimental to river ecology, landscape and amenity. Press attention to a number of these rivers such as the River Darent in Kent and the publication, by the NRA, of a list of the 40 most affected rivers in England and Wales, has resulted in a new public awareness of the effect of groundwater abstractions on river flows. Consequently, evaluation of the impacts,

or perceived impacts of groundwater abstractions on river flows during the recent drought has become an important aspect of water resources management. Many questions have arisen as rivers have dried up; what influence did historical groundwater abstraction have on recorded river flows, and

what would have been the flow response during the recent drought if groundwater abstractions had not taken place?

197

could the resource system be managed in a way that reduces the interterence ot groundwater abstractions on river flows? would channel lining or river augmentation from river support boreholes improve river flows during extreme droughts? how will future land use patterns change river flows?

what impact on river flows would potential climatic changes have?

In many instances, river support boreholes have been constructed in an attempt to improve river flows during drought conditions (such as the Rivers Nar and Wensum in Norfolk, the River Slea in Lincolnshire). These facilities have, generally, been short term, immediate solutions to the problem and have had only limited value in terms of improving the understanding of the interaction between the river and aquifer system. The above questions can best be answered if one considers the resource system as a whole with simulation of both the groundwater and surface water components. Evaluation and quantification of the impacts of groundwater abstractions on surface water systems have been topics of research for over 20 years. Freeze and Harlan (1969) first outlined a modelling approach to spatially represent the surface and subsurface hydrological processes. This work provided some of the inspiration for the development of the Systeme Hydrologique Europeen (SHE) (Abbot et al, 1986). This model simulates surface processes (interception, evapotranspiration and overland flow), vertical flow in the unsaturated zone, and two dimensional flow in the aquifer systems using a discretised representation of groundwater systems. The distributed nature of this type of model makes it demanding in terms of hydrological and hydrogeological data. For example, 2400 parameters were defined in a SHE model of the Wye catchment (Bathurst, 1986). The most difficult area in a distributed model is the definition of soil properties, which exhibit significant spatial variability. Wardlaw (1978) recognised this problem commenting that distributed models of the unsaturated zone were not practical, particularly when one considers the hysteresis that exists between hydraulic conductivity and moisture content.

The approach developed by Mott MacDonald, which follows from the work of Wardlaw, is to simulate the surface and unsaturated zone processes using a lumped parameter model: a modified version of the Stanford Watershed Model (Crawford and Linsley, 1966). This is coupled to an integrated finite difference model where the interaction between the river and aquifer systems is fully integrated in the model. The Integrated Catchment Management Model (ICMM) has been used successfully in a number of catchments in the south and south-east of England, including the Rivers Darent and Cray in Kent, the Rivers Meon and Hamble, the Wallop Brook and Bourne Rivulet in Hampshire, the River Allen in Dorset and the River Little Ouse in East Anglia. This paper discusses the different components of ICMM and highlights the features of particular interest relating to the different catchments studied. An overview of the system is presented in Figure 1.

2 OVERVIEW

OF THE MODELLING

SYSTEM

The catchment model incorporates a multi-layer aquifer system integrated fully with the surface water system. The mathematical solution to the model takes into account the interrelationship of water levels and flows in both the aquifer and surface water systems.

198

E

GSM GEOLOGICAL STRUCTURE MODEL Parametercue Defining Natiars

SWM

E

STANFORD WATERSHED MODEL

. GEOM

Groundwater f}Surface Run off

Aquifer

Recharge

Geometr y :

solereysien Geometry

& Interflow

Parameters

Defining

oa Characteristics Parameters

Defining

Characteristics o Internal Rivers

INTEGRATED SURFACE/ GROUNDWATER MODEL

Data/

Prograny Subroutine

i

;

Results

L

M

s

-PLOT

Graphical

Presentation

3

to Computer Screen#

H

:

Figure 1 : Structure of Integrated Catchment Management Modei

2.1

Stanford

Watershed

Model

A modified version of the Stanford Watershed Model, known as the River Basin Model (Fleming and McKenzie, 1982), has been further adapted to produce groundwater recharge estimates for input into the catchment model and to separate the components of overland flow and interflow from total runoff. The Stanford model can be segmented and subdivided to give a less lumpy representation of the prototype, although this can only be justified if there is data on which to calibrate the individual sub-units of the model, or if there are sufficient rain gauges to define sub-unit rainfall inputs. The model has a total of 32 parameters (excluding those relating to snow), of which four

require calibraiion. These reiate to infiltration and soil moisture storages. The model is calibrated against scriptions of the processes of infiltration through the soil profile to the water table and surface interception, retention and overland flow have been given by Crawford and Linsley (1966) and by Fleming (1975). The data requirements to run the model are as follows:

precipitation potential evapotranspiration groundwater and surface water abstractions river support discharges surface water catchment topographical characteristics land use historical river flows for calibration of the model.

199

OO

LEGEND Tee ai) Seca sete

Observed Daily Simulated Daily (Stanford model) Simulated Monthly (Catchment model)

(Catchment Area 93 km4

(cumecs) Station Gauging Mill Loverley Flow at

Aug-84

Nov-84

Feb-85

Jun-85

Sep-85

Dec-85

Mar-86

Jul-86

Figure 2 Stanford and Catchment Model Simulated Flows (River Allen at Loverley Mill)

The Stanford model has many advantages over simple, soil moisture balance techniques. In soil water budgeting techniques, such as the Penman-Grindley Method (Penman 1950, Grindley 1967,1969), the model is not generally calibrated. It is possible to test such recharge estimates against a lysimeter or by testing soil moisture estimates against neutron probe measurements, although such field data are generally not available. Long term annual recharge estimates from water balance techniques can also be compared with observed mean annual river flows to estimate the adequacy of the method employed. Since the Stanford model is calibrated against observed river flows, much of the uncertainty associated with water balance methods is removed. The Stanford model has been used to define the recharge for a number of integrated models. However, in a number of catchments difficulties arise with the simulation of the early winter flow response, particularly following a long, dry summer. Figure 2 shows the simulated and observed flows for the River Allen catchment at Loverley Mill (a catchment of 93 km’). In November and December 1984, there is a significant oversimulation of streamflow. This is caused by a number of inter-related factors: -

the Chalk aquifer exhibits variable transmissivity with depth throughout the catchment, which is not simulated by Stanford;

-

annual groundwater fluctuations are of the order of 30 m and therefore travel times through the unsaturated zone should vary significantly; land preparation for winter crops may change the soil infiltration and storage characteristics.

-

In the catchment model of the River Allen, the simulation of the early winter river flows were improved by adopting a non-linear transmissivity distribution in the Chalk, with low permeability defined for the bottom 90% of the Chalk aquifer and high permeability at the

200

top, covering the average range of annual groundwater fluctuations. At the end of summer, the transmissivity is very low. The early winter recharge does not result in immediate baseflow, as simulated by Stanford, until storage in the aquifer has been replenished and the transmissivity has increased substantially. Tests are presently being undertaken at Edinburgh University to incorporate a delayed recharge function to improve the simulation of early winter baseflow in the Stanford model. Two methods are being tested: either through the variation in unsaturated zone storage properties to simulate the different travel times between winter and summer or by including temporary stcrage to delay recharge.

The problem of widely varying surface geologies can also pose a problem in applying the Stanford model. In a sub-catchment of the Little Ouse in East Anglia, drift deposits (mainly Boulder Clay) overlie Chalk. The Chalk outcrops in the lower part of the sub-catchment. Chalk and Drift exhibit very different recession characteristics: Chalk baseflow recedes very quickly following winter rain, while discharges from drift deposits recede at a much slower rate. The Stanford model uses a Horton type recession, derived from observed river flow hydrographs. Using a single set of recession, storage and infiltration characteristics for the catchment results in either a poor simulation of winter flows if the characteristics of the drift deposits are adopted, or an undersimulation of summer flows if Chalk parameters are adopted as shown in Figure 3. By subdividing the model into two segments each with different recession characteristics, the river flows in both summer and winter are improved. In effect, infiltration through the unsaturated zone is controlled by two separate mechanisms with baseflow controlled by the different recession characteristics of the segments.

2.2

Catchment

Model

The catchment model is the main simulation module of ICMM. The model is based on the Multi-Layer Aquifer Model described by Van Wonderen (1987) which has been adapted to include the simulation of the interaction between aquifer and surface water systems. The model adopts the integrated finite difference method (IFDM), the theoretical basis of which has been described by Narasimhan and Witherspoon (1976). The model uses an iterative scheme to solve the system of simultaneous equations which describes the mass balance for cach model polygon and river clement. The finite difference todet yiid can be subdivided in areas of particular interest giving a grid of irregular polygons. The flexibility in subdivision is a major advantage of the model: abstraction sites, model boundaries and river courses can be modelled with greater accuracy; other areas for which less detail is required are simulated with a courser mesh of polygons thus reducing computation time. Rivers are

defined in the model by "internal boundary elements" between adjacent model polygons. An example of a catchment model grid is shown in Figure 4, as used for the Rivers Darent and Cray catchments. In the model, groundwater flow is based on Darcy’s law. The components of the mass balance include the following:

-

-

lateral flow in aquifer layers, including flow across active external boundaries; baseflow and leakage between the rivers and the aquifer system; vertical leakage between aquifer layers; storage changes in aquifer layers; recharge;

201

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Ly WY UY yy

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Model Polygon

roe Model River Elements

River Lake or Gravel Pit

Scale 4

Catchment Boundary

°

Figure 4 ICMM Network (for Rivers Darent and Cray, Kent)

202

-

groundwater abstractions; rejected recharge (spring flows) resulting from water table levels rising to ground surface.

The mechanism of movement of water between aquifers and the river system is dependent on the geometry and hydraulic properties of the river/aquifer system in the immediate vicinity of the river element. Two types of mechanisms are normally used in Chalk catchments as shown in Figure 5:

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