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DECEMBER 1992

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6


EISSN 0310-0367 Volume 19, No. 6, December 1992

Australian Water & Wastewater Association Incorporated ARBN 054 253066 FEDERAL SECRETARIAT Executive Director - Chris Davis Business Manager - Margaret Bates PO Box 388, Artarmon 2064 Telephone (02) 413 1288 Facsimile (02) 413 1047

FEDERAL PRESIDENT Barry Sanders, Phone (09) 420 2453

FEDERAL SECRETARY Greg Cawston , Phone (042) 29 0236

FEDERAL TREASURER John Molloy, Phone (03) 615 5991

BRANCH SECRETARIES Canberra, ACT Alan Wade, D.E.L.P. PO Box 1119, Tuggeranong 2901 Phone (06) 207 2350 New South Wales Nick Apostolidls, GCEC, 39 Regent Street Railway Square 2000 Phone (02) 699 9922 Victoria John Park, Cl- Water Training Centre, PO Box 409, Werribee 3030 Phone (03) 741 5411 Queensland Don Mackay, PO Box 412, West End 4101 Phone (07) 840 4844 South Australia Nei l Palmer, Cl- State Water Laboratories, E&WS Private Mai l Bag, Salisbury 5108 Phone (08) 381 0268 Western Australia Bill Chapman,

WAWA PO Box 100, Leederville 6007 Phone (09) 420 2462

Tasmania Annette Ferguson, GPO Box 503E, Hobart 7001 Phone (002) 28 2757 Northern Territory Lindsay Monteith, PO Box 351, Darwin 0801 Phone (089) 81 5922

EDITORIAL CORRESPONDENCE E.A. (Bob) Swinton, 4 Pleasant View Crescent, Glen Waverley 3150 Office Phone-Fax (03) 560 4752 Home (03) 560 9306

ADVERTISING Ann Sykes-Smith, Appita, 191 Royal Parade, Parkvi lle 3052 (03) 34 7 2377 Fax (03) 348 1206

PRODUCTION EDITOR John Grainger, Appita, 191 Royal Parade, Parkville 3052 (03) 347 2377 Fax (03) 348 1206

CONTENTS 3 My Point of View Association News 4 News from the Executive 5 It Seems To Me 6 Association News 9 IAWQ 10 IAH 12 Industry News 16 National Water Quality Management Strategy 17 Fresh & Marine Water Quality Guidelines 19 Murray-Darling Basin Strategy Features: Hydrogeology 20 The Murray Basin Hydrogeological Map Series W.R. Evans 24 River Murray Salinity Mitigation Schemes in South Australia R.J. Newman 28 Salinity and Groundwater Control - Shepparton Region W. Trewhella 32 Groundwater Pumping - An Effective means of Salinity Control J. Nolan 34 A Groundwater Blue-Green Algae Relationship? T.J. Verhoeven 37 Perth Coastal Groundwater Schemes D. Hopkins 40 Groundwater Flow near Shallow Lakes L.R. Townley and J.V. Turner 42 The Great Artesian Basin ... A Need to Conserve Water J.R. Hillier Of Interest 44 The Industry Commission Report, July 1992 Water Resources and Wastewater Joanne Henshall 45 Book Review 46 Community Consultation ... the Queensland Regional Conference 47 Product Information 48 Conference Calendar

OUR COVER Our cover is a montage over a corner of the Ouyen map, one of the new Murray Basin Hydrogeological Map Series. The series has made use of all the expertise in the Basin by a co-operative effort from all the relevant agencies, irrespective of State boundaries. Existing and developing data-bases have been collated into a common format, as described in the paper by W R Evans in this issue, and embodied into a CAD system which can be used as well as the hard-copy sheets to help understanding of the groundwater processes. The sheets are available from the principal agency in each State and from the Australian Geological Survey Office in Canberra. They have already been applied in practice on both regional and local scale.

PUBLICATION Water Is bi¡monthly. Nominal distribution times are the third weeks of February, April , June, August , October, December.

IMPORTANT NOTICE The Australian Water and Wastewater Assoc iation assumes no responsibility for opinions or statements of facts expressed by contributors or adve rtisers, and edi torials do not necessarily represent the official policy of the organisation. Display and classified advertisements are included as an Informational service to reade rs, and are reviewed by the editor before publication to ensure th eir relevance to the wate r envi ronment and to the objectives of !he Association . All mate rial in Wa ter Is copyright and should not be reproduced wholly or in part wi thout the written permission of the editor.

WATER December 1992

1


TECHNOLOGY

THE MURRAY BASIN HYDROGEOWGICAL MAP SERIES by WR EVANS BACKGROUND The Murray-Darling Basin covers about 1 000 000 square kilometres or one-seventh of Australia. It hosts a range of significant natural resources, the economic value of which accounts for about one-third of the national output from rural industries. It is vital to Australia's balance of trade and to the existence of almost 3 million people who depend on its natural resources. The Basin supports onequarter of the nation's cattle and dairy farms, about one-half of its sheep, lambs and cropland, and almost three-quarters of its irrigated land. The production derived is valued at some $10 000 million annually. There is widespread concern at the extent of land degradation, deteriorating water quality, rising groundwater levels and loss of native flora and fauna throughout the Basin. In 1987 estimates placed the losses due to land degradation in cropping and irrigation areas in excess of $220 million annually. In addition, there are losses due to poor water quality of about $35 million annually and unquantifiable losses due to further degradation of the environment. Most of this degradation can be attributed to groundwater processes. Added to this concern is the knowledge that much of this degradation is irreversible or, at best, expensive to rehabilitate. The degradation problems are continuing. By the year 2040 about 1 300 00 ha of irrigated land is expected to be salinised or waterlogged due to high water-tables (MDBC, 1990). It is also estimated that about 1 000 00 ha is at risk of significant dryland salinisation by rising groundwater levels (MDBC, 1992). In both cases Basin managers emphasise that the worst case scenario for the future is the 'do-nothing' scenario. The Murray-Darling Basin Ministerial Council has embarked on a major initiative to increase the effort directed at redressing the degradation. The Natural Resources Management Strategy has been developed with the objective of promoting and coordinating effective planning and management for equitable, efficient and sustainable use of the land, water and other environmental resources of the Basin. The Strategy identifies Groundwater as one of eleven Resource Management Elements. In addition natural resource management issues, which are invariably dominated by groundwater processes, have been identified for the eight broad geographic regions comprising the Basin. One of the major areas of coordinated Government action, defined in the strategy, is the management of groundwater to combat degradation through salinisation and enable sustainable land and water use. This action, amongst others, takes the form of the Murray Basin Hydrogeological Map Series.

THE DEGRADATION PROCESS In order to develop strategies to combat the problems, an understanding of the controlling processes is essential. The key to an understanding of the causal mechanism of much of the degradation lies in the relationship between the groundwater and surface water systems. The agricultural practices over the last 80-100 years have brought about a fundamental change in the hydrologic cycle. The removal of a large proportion of the existing native vegetation and replacement by shallower rooted plant species, has resulted in increased aquifer recharge (from lower areal evapotranspiration). In addition, irrigation development has locally increased recharge to groundwater. This increased recharge is now working its way through the groundwater system. Regional groundwater levels are rising, and in places have reached, or are in capillary reach of, the ground surface. As has been pointed out before, salinity is a groundwater problem. A better understanding of the groundwater system will provide managers with a data-base against which 'better' management

20

WATER December 1992

Ray Evans has over 17 years experience involved with ground water research and investigations at the national level. He is currently a Principal Research Scientist with the Environmental Geoscience and Groundwater Program, Australian Geological Survey. He is the Project Leader of the AGS'.S' Murray-Darling Basin Hydrogeology Project. As well, he is Chairman of the Murray-Darling Basin Commission's Groundwater Working Group, and a member of its Salt Interception Working Group.

decisions can be tested . Further, the data-base must have the ability to be turned into information that can be subsequently assimilated by a wide variety of consumer groups.

NORTHERN

iI

TERRITORY

I

I

II I

QUEENSLAND

I

·-----~-....l--,

I1 I

SOUTH AUST RALIA

'

I

1

/------....--',.,I

I

MURRAY BASIN

0

~ \JSMANIA

130° 00 · 3 1°00 ' PARACHILNA SH 54-ll ORROROO

INDEX

TO 1: 250 000

CURNAMONA

BROKEN Hill

MAPS BARNA TO

147°00 ' 31°00 '

COBAR

SH 54-14

SH 55-14

OL ARY

NYMAGEE

5154-1 ANA BRANCII SI 54-7 ILOURA SI 54-11

OUYEN

SJ 55-1

3 e • oo · 13 e • oo ·

SJ 548

MELBOIJlHE

WARBLIHON

SJ 55-5

SJ 55-6

3 e • oo · 147 °00 '

Fig. 1 - Index map of the 1:250 000 map sheets that constitute the Murray Basin Hydrogeological Map Series


TECHNOLOGY THE HYDROGEOWGICAL MAP SERIES Against this background the State geological and water agencies, in co-operation with the Australian Geological Survey Organisation (AGSO - formerly the Bureau of Mineral Resources), initiated a groundwater project in 1979 to examine the Murray Basin unencumbered by State boundaries. The project's aims have been to establish a basin-wide geological and hydrogeological framework, and to provide basin-wide perspective on the groundwater systems and processes which result in surface salinisation. In 1987 the Murray-Darling Basin Ministerial Council agreed to a program of hydrogeological mapping and data-base development for the Murray-Darling Basin, to be completed by June 1994. The program was to be split into two components. The first, complete coverage of the Murray Basin at a scale of 1:250 000. The location of map sheets within the series is shown in Figure 1. The second component consisted of hydro geological mapping at a reconnaissance scale of 1:1 000 000 in the Darling River Basin. This second component is not considered further in this paper. The mapping will ultimately provide an integrated high quality groundwater data-base, making use of all available groundwater expertise in the Basin by involving all relevant agencies in a cooperative program to collate and enhance existing computerised databases.

SAL INITY / YIELD MATR IX BORE YIELD Lis

Legend

The concept of what was needed on the face of the maps was given careful consideration. The AWRC 'Guidelines for the preparation of Australian Hydrogeological Maps' (AWRC, 1988) was adopted. These guidelines recommend that for mapping at scales of 1:250 000, a salinity/yield matrix should be used as the full-colour feature (Figure 2). This salinity/yield approach meets the objectives of the mapping exercise which explicitly includes reference to both useable groundwater resource - a combination of good quality water and high-yield aquifers - and groundwater salinity hazard. It was recognised that the project may require flexibility with the legend at a later date and appropriate changes may be necessary. The maps are full-colour and consist of a standard 1:250 000 scale map sheet area, surrounded by other information thought necessary to meet the proj ect objectives. HYDROGEOLOGICAL Salinity

Area

Aquifer

Yield

¾

Oe~th to Standing Water Laval

1ml

Aquifer Thickness 1ml

Estimaled

Hydrauli c Storativity/ Conductivity Specific yie ld

100-130

3.0-3.5

2.5.10- 3

Waikerie-0v11l1nd Corner

Tml

40

80

1.5-2.5

0.02-0.06

/4iJ'..

Noora - Yamba

Tps

1-5

35-40

7,2

Be, ri-Barmera

Tp s

5-20

20-30

8,2

l ox1on

Tps

5-20

20-3 0

Ranmark

o,

1-2

15- 20

2-S luttH 1ndl

~

iX Ix 3

X. 2

%'

22

2-30

10-20

12-30

80

1,3

Al l purpose, domestic and irr ig ation

500- 1000

2,1

2,2

2,3

Most purpo ses

1000- 1500

3,1

3,2

3,3

1500-3000

4,1

4,2

4,3

4,4

3000-7000

5, 1

5,2

5,3

5,4

7000- 14000

6,1

6,2

14000-35000

7,1

7,2

35000- 100000

8,1

B,2

9, 1

9,2

§

....>z :a

~

> 100000

Some livestock (beet catt le, sheep)

limit ed indusuial use, ore proce ss ing

limited industrial us e, ore proce ssing

9,3

9,4

Brine production, 01e proce ss ing

Comments lrr ig11ion supplies of up to 60 l ine avail1bl1 from full y penur11 ing bore Arn of hiah groundwater discharge to rive, (200 tonnes/day of ult) Upward l11hg1 fl am confined h r I aquife r hes caused mounding in water labla

Water tibia mound b1n11th iuigat ion aru con1ributu about 13 tonnu/day of ult to 1ivern11r81r1i

2-S !cutn sud ) !lint 0.5-2.5 n nd)

0.1-0.2

Wau, table mound beneath i11 ig11ion 1111 1i sing at 0.1 lo 0.3m/yur. D11inage collec11d in tile dr1ins and pumped to l(au rapko Island 0ispoulBuin on 1iver flats. The combined effect contr ibu tes 85 tonnes/day ol ult to rinr

0.01-0.1

lirigation 1111 on floodplain tile drained with dr1inag1 wat11 pumped to Naora Evaporartion Basin. Underl ying Tml a11uian beneath fl oodplain

(cnrn

1ml 0.002-0.04

Drainage of p11ch1d irr ig1 tion w1t1r in10 weter !1bl1 1quifar causes saline discharge to the 1iv11 of ipprox. 105 tonnu/day ol ult Cur,ently a multi-1quihr system. Tpn pe1ched wltei table, Tml w1111 tabl e and conl ined

M01gan-Pu1nong lust of River Mur,ay )

Tml

30-60

50

1-3

0. 1- 0.2

81n111h uus of Qca, tnchanced u charge through sinkholes can ruult in a ihin laye1 ol frnhtr (som1 1imu < \000mg/ll wau, onrl ying ulin1 groundwater

BlanchelownPurnong (wes t ol River Mu11 ay )

Tml

40-50

10-50

1-2

0.1-0.2

Uplift associued with M01gan F1ult has caused 1quile1 thinning with a 11s11lt1n1 p81mubilit y birder 101 groundwau1 /low toward the river

Whole sh111

re,,

flowing - 80

30-350

1-5 Olne y Fm. 5-10 W11ina Stnd

2x 10 -" 1

WATER December 1992

Mo st livestock (no\ pigs, horse s)

The following information is 'ncluded on the face of the map: • The shallow aquifer system as main map at 1:250,000 scale, including; salinity/yield categories watertable contours (constructed using point source heads, ie no density corrections) basic geology man-made water features, irrigation areas, channels, dams, locks, etc. • salinity/yield matrix • two cross-sections

0.1-0.2

sud!

limited irrigation , all livestock

Fig. 2 - The Salinity Yield Matrix used for the Map Series (which is colourcoded, as shown on the Cover picture of the Journal). The nine-fold salinity distribution is contrasted against the four-fold aquifer yield distribution to give an aquifer characterisation at a regional scale.

2-6 1CU1St 11nd l 0.5-2.5 Uine stnd l

0.05- 0.1

Most purpose s, upp er

limit for drinking

~

Groundwate r disch11 g1 aru, uud u disposal basin. Unde,lying Tml confin ed aquifer also ver y saline in this aru , due lo downward l11k1g1 from Tps

SHd l

(cltys ,sU11)

Waikerie

7,3

1,2

0.1-0.2

0.5 ltint

10-20

2

1,1

lm/dnl

40- 60

··'

<500

>50

CHARACTER ISTICS

Tml

7,3

5-50

Estimattd

Wanbi- Peebinga

3

0.5-5

....~

Objectives

The objectives of hydrogeologically mapping the Murray basin at 1:250 000 scale are to generate a set of maps which will • show the influence of groundwater on land salinisation and surface water salinity, • delineate useable groundwater resources, • highlight present and potential salinity hazard, and • enhance community awareness and understanding of groundwater systems and processes. and provide a groundwater data-base for the Murray Basin in order to facilitate land and water resource management decisions.

<0.5

0ischargu by upw ard lukag, into Tml. Artesian benulh rivtr ltoodpltin and Noora - Yamba 1111. Complllely undeveloped ov11 map ar u

Table I - The hydrogeological characteristics table from the Renmark sheet. This table shows representative hydraulic parameters for local areas within the map sheet area. This table provides information that will allow first order hydrogeological analysis for the resolution of the more simple groundwater-related problems.


TECHNOLOGY • inset maps for each significant deeper aquifer at 1:1 000 000 scale consisting of; potentiometric contours salinity/yield structure contours including bedrock surface and optional structural features (faults, blocks, etc) contour maps showing difference in 'fresh water head' between each aquifer (Figure 3) • inset maps at 1:1 000 000 scale showing depth to watertable zones, < 2m, 2-5m, > 5m in 10m contours (Figure 4) • a hydrogeological characteristics table detailing information on aquifer hydraulic parameters on a regional basis (Table 1) • aquifer and rock relationship diagrams • hydrographs, including rainfall • small isohyet and reliability maps There has been much debate as to which aquifer, in a multi-layered aquifer system, should be represented as the main feature on hydrogeological maps. In the Murray Basin, there may be up to 3 main aquifers at any one location, and at least 2 in all cases. For this mapping exercise, the shallowest aquifer (the unconfined aquifer) was chosen. This was done in light of the project objective to show the influence of groundwater on land salinisation and surface water salinity. After all, it is groundwater from the shallowest aquifer that eventually interacts with the land surface, irrespective of which aquifer may be providing the driving pressure regime for the water movement.

APPLICATIONS The maps produced so far have been used for both broad scale water planning issues and for specific local issues, as follows: On the broad scale, they have been used; • to provide a hydrogeological framework for the Wimmera and Mallee Dryland Salinity Management Plans • to provide a regional hydrogeological framework for Land and Water Management Planning in some New South Wales irrigation areas • to assist Landcare groups make decisions about the importance of groundwater resources in their particular areas • as a major input to Community Education, thereby assisting farmers and others to understand salinity processes • to assess the groundwater resource potential for farmers looking for new water supplies • to identify to irrigators and other community members the key recharge areas and consequently the potential for altering recharge due to land management • to identify the regional watertable depth for a range of government departments, community groups and individuals • as a major assistance in the development of a hydrogeological understanding as input to the management of the South Australian/Victorian Border Groundwater Agreement • to show the extent of irrigation induced watertable mounds to irrigators in the Riverland • to assist in the prediction of watertable levels over the next 20 years in both the Renmark irrigation area and the South Australian Mallee Dryland On the local scale the maps have been used; • to assist in the planning for the disposal of urban runoff by the Mildura Shire • to assess the potential effects of groundwaters, which may be polluted by pesticides, on workers, by the Australian Workers Union • to understand groundwater effects beneath intensive rural industries (principally feedlots) in the Narrandera area • to assess town water supply availability in the Narrandera area · • to assist in siting a new landfill by the Shire of Kerang • to assess the possible effects of groundwater inflows to wetlands • to assist in the siting of a new woodlot for the disposal of sewerage effluent by the Sunraysia Water Board in the Mildura area • to assist in the review of applications for Transferable Water Entitlements adjacent to the Murray River.

PROGRESS REPORT In total, there are 26 maps to be produced in this series, as shown in Figure 1. As at November 1992, 8 maps have been printed and another 8 maps are being produced. Completion of the entire series will take another 18 months.

Fig. 3 - Head difference map for the Renmark sheet. The map portrays contours of equal head difference between water levels in the deepest aquifer and those of the unconfined aquifer. These differences are corrected for salinity (density) and are expressed as equivalent fresh water head values. Positive values show upward potential for flow, negative values show downward potential.

Fig. 4 - Contours of equal depth to the watertable. By combining this information with the hydrographic information and the head difference map, a first order salinity risk map may be constructec,t.

The strong co-ordination effort between various agencies responsible for map production has resulted in a substantial increase in co-operation and the elimination of the traditional geological 'faults' at the State or map boundaries. The maps, and the underlying data-bases, are already providing a fundamental underpinning for tackling the massive land, surface water and groundwater salinisation issue of the Murray Basin.

ACKNOWLEDGMENTS The Hydrogeological Map Series is a collaborative effort between the various water authorities of South Australia, Victoria and New South Wales. As such, I acknowledge the various inputs of all the people working on this Series. The author publishes with the permission of the Executive Director, Australian Geological Survey Organisation.

REFERENCES Australian Water Resources Council, 1988 - Guidelines for the preparation of Australian Hydrogeological Maps. Water Management Series No. 13, AGPS, Canberra. Murray-Darling Basin Commission, 1990 - Report on a Drainage Program for the Murray-Darling Basin. Murray-Darling Basin Ministerial Council Technical Report, August 1990. Murray-Darling Basin Commission, 1992 - Dry/and Salinity Management in the Murray-Darling Basin, Stage 1. Report on the Dimensions of the Problem. MurrayDarling Basin Ministerial Council Technical Report, March 1992.

WATER December 1992

23


TECHNOLOGY

RIVER MURRAY SALINITY MITIGATION SCHEMES IN SOUTH AUSTRALIA by R. J. NEWMAN THE SCHEMES Two salinity mitigation schemes are being constructed next to the River Murray between Lock 3 near Overland Corner, Woolpunda and Lock 2 at Waikerie. (Fig. 1) The $25 million Woolpunda Scheme involves 49 bores, on either side of the Murray. Each bore is 100m deep. Sixteen ML/ d of groundwater at about 25 000 mg / L is pumped through 85 km of · pipelines. The $12 million Waikerie scheme involves 18 bores on the south side only, pumping 20 ML/ d through 35 km of pipelines. Both schemes dispose the saline water to the Stockyard Plain Basin in the Mallee 15 km from the river. The Engineering and Water Supply Department of South Australia has been responsible for the investigation and construction of the works which are funded through the Murray Darling Basin Commission under the Salinity and Drainage Strategy. Construction work began in 1989 and was completed in 1991 for Woolpunda and will be complete in early 1993 for Waikerie. Both projects have been completed ahead of schedule and within budget. The two scheme will interrupt some 250 tonnes of salt per day after several years when they become fully effective, giving a reduction in the average salinity at Morgan of better than 50 EC. At low entitlement flows a saving of 150 EC is predicted. The economic benefit to downstream users will be more than $4 million per year. This will be partly offset by increased salinity contributions from the upstream states, as they take up their rights

to salinity credits under the MDBC Salinity and Drainage Strategy. Since the drought of 1967, South Australia has taken a great interest in the salinity of the Murray. Intensive data collection has enabled the identification of the important sources of salinity increases within SA. During the periods of low flow, salinity levels can rise to more than 1000 EC or 700 mg / L at Morgan. This causes reduced yield from irrigated crops and impacts on urban users by increasing corrosion and causing excessive use of soaps, detergents and industrial water treatment. More importantly the underlying trend in rising salinity levels causes concern about the long term viability of the Murray as a water resource for South Australia. Salinity mitigation projects have previously been constructed at Renmark, Rufus River and Noora. Further investigations are being undertaken at Loxton, Chowilla, Bookpurnong and Pike River. The river system is operated to manage salinity.

THE SETTING The River Murray, downstream of Overland Corner, has cut down through the uplifted Murray Group Limestones forming a spectacular steep sided gorge about one kilometre wide and 40 m deep. The river is now 200 m wide and meanders through the gorge. Irrigation areas are generally on the higher land near Waikerie (30 to 40 m above the river). The crops are principally citrus, vines and stonefruit. The water is supplied by community pumps through pipes. Improved irrigation methods have been widely adopted including water on order

Bob Newman is Senior Engineer, Water Resources Investigation, forthe E. W.S. He graduated, Civil Engineering, in the , I U.K. in 1967 and has specialised in • geotechnical engineering. He has been involved in the management of salinity investigations for the River Murray since the mid 1980s.

!;.,', f

' '

irrigation scheduling. Perched water tables, which caused waterlogging of the rootzones, quickly developed above the shallow Blanchetown Clays. Some 300 bores drain leachate water into the highly saline native groundwater and into the river. These drainage bores have avoided the large cost of comprehensive drainage schemes used elsewhere in SA. High water tables and salt have degraded the floodplain next to the irrigated lands.

SALT WADS TO THE RIVER The reaclfof the Murray between Lock 3 and Lock 2 has been identified as a major contributor of salt. Salt load accessions are about 300 tonnes/ day during prolonged low river flows. The salt load per kilometre ranges from two to eight tonnes/day, which is about three times the average for SA. Between 1982 and 1988 detailed instream measurements (run of river salinity surveys) enabled the pattern of salt load increase to be determined.

LEGEND •

Bore Pipeline

~

Extent of Alluvium Valley

~

Area o f Irrigation

WOOLPUNDA SCHEME 10 kilometre s

Fig. 1 - The River Murray from Overland Corner to Morgan; the Woolpunda Scheme involves 49 bores on either side of the river, the Waikerie Scheme

involves 18 bores on the South side only. Both schemes dispose saline groundwater to the Stockyard Plain Disposal Basin.

24

WATER December 1992


TECHNOLOGY Salinity differentials are now continuously recorded by five toroidal coil salinity instruments anchored in the river. An ultrasonic flow station measures the river flow. This is the only accurate method of stream measurement for the low velocities generally prevailing in the river in SA. Figure 2 illustrates the flow, salinity differentials, and salt loads for the Woolpunda reach during 1990/ 91. This year involved a major flood event peaking at 10 500 ML/ din November. Features which are noteworthy include: • the base salt load 200 - 300 t/ d, • the suppression of salt inflow on the rising limb of the flood hydrograph , • the massive salt load accession following the flood recession.

EVAPOTRANSPIRATION FROM RIVER FLATS

I'

/

:·. ::: ·.- :·:.: : -.:_:-.-·~~-LE ·-::·: . -~~~ J;? _.--:-:-. -. -. . •', ,• ;,...-., .... ~ .·-.· ~ ·. . ·. ·, \: MURRAY GROUP: ·-_-_-._ . · .::; AQUIFER .·:_.' ·: ::_

.. ..

RENMARK GROUP AQUIFER

Fig. 2 - 1990/ 91 Flow and salinity measuresment through the Woolpunda reach.

GROUNDWATER FWWS It has been shown that the saline groundwater inflow in both the Woolpunda and Waikerie reaches are each about 10 ML/ d. However, whereas the Woolpunda reach receives only native groundwater, the Waikerie reach receives a blend of native groundwater and direct irrigation leachate which has a lower salinity. In the Woolpunda reach, between Overland Corner, and Holder (Renmark Beds) groundwater flows by upward leakage from the underlying confined aquifer through the Etterick aquitard (Fig. 3). The pressure in the Renmark Beds is some 15 metres higher than river level and is caused by the recharge areas at the margins of the Murray Basin in Victoria and NSW. This flow contributes about 200 tonnes per day to the river. The groundwater inflows in the Waikerie reach (85 tonnes/day) are principally induced by irrigation groundwater mound. Figure 4 shows the regional gradients and the mounds. The salinity of the groundwater is generally about 20 000 mg/ L.

10 km

SCALE

N

1 BERRI

Ground water

mound

14

14

Fig. 3 - Natural groundwater flow towards the river in the Woolpunda reach, showing the interception bores on either side (600m away) of the river.

The Murray Group Limestone aquifer has a permeability of around 2 m/ d, and extends some 60 metres below river level. This depth

WOOLPUNDA SIS - RIVER MURRAY SALT LOADS July 1910 to June 1991 2 5 0 0 , - - - - - - - - - - - - - - - - - - - -- ---~120

allows the opportunity to develop a groundwater interception scheme. If the aquifer were much shallower the number of bores required would be excessive.

INVESTIGATION AND DESIGN

Hydrologic investigations since 1980 have identified the extent and distribution of salt loads to the river. Between 1984 and 1990, c ::) intensive hydrogeologic investigations (.) determined the source and nature of the 100 w groundwater accessions. 2000 Confidence in the concept design for ....>z::::; these two schemes came as these two 80 independent approaches of investigation ~ 1500 began to generate a similar understanding of the salt loads. Figure 5 illustrates this .,> 60 aspect of the investigation and design for ....0 Woolpunda. The zone hatched 'hydrology' IC: 1000 is an envelope of the results of eight runC: 40 {:. of-ri ver surveys. The zone hatched 'hydrogeology' shows the computed results 500 from the groundwater studies with a 20 confidence Jim.it of 20 per cent. The 'design' line represents the target groundwater flux 200 used in the design of the system. The bores o~-------------- - - -- ----------_J_ o for the Woolpunda scheme are about one km apart and about 600 m from the river. The pumping system requires a capacity of Fig. 4 - Water Table Contours in the Murray Group aquifer; showing the igroundwater mounds beneath about 150 per cent of the design flux in order ultimately to achieve effective interception. the irrigation areas.

-

WATER December 1992

25


TECHNOLOGY 15 14 13 12 11 10

E

"'>,

"'

"O

0 <(

0

9 8 7

...J

6

<(

5

.......J

(J)

4 3 Adopted Interc eption capaci ty Sall lo ad in groundwa ter

2

20 % err or bo un ds Salt lo ad ran ge In r iver ~

;;;

0 39 2

396

400

i

404

4 08

412

4 16

420

424

RIVER DISTAN C E (k m)

Fig. 5 - Distribution of salt loads through the Woolpunda reach: (i) as measured by instream salinity measurements; and (ii) as computed by groundwater analyses. The scheme is designed to intercept the upper bound + 10%.

The installed capacity allows a further 10 per cent yield to allow for maintenance and breakdowns. In the Woolpunda reach the design attempts ultimately to intercept the majority of the steady state flux. In the Waikerie reach the design targets the high salinity deeper flows carrying about 85 per cent of the salt. At Waikerie the production bores are located close to the south side of the river and are completed in the lower Murray Group Limestones (generally below the Monoman alluvium. The hydraulic design of the scheme involved a delicate manipulation of the capacity of each element of the scheme. There are no booster pumps, relift pumping stations, or flow control valves. The borehole pumps provide the entire driving force for both schemes. The system is designed to optimise between capital cost and long term power requirements whilst maintaining some flexibility for future tuning. The actual output from each pump is determined by its local pumping head which is in turn the result of the behaviour of the whole system. Each pump must be precisely configured to match its performance with the hydrogeologic yield requirement. The pipeline system design involved different constraints to conventional water supply systems together with careful consideration of corrosion resistance of materials.

having no impact on neighbouring land outside of the site. The site comprises degraded, cleared, agricultural land which had a very low productivity. Locally it is the lowest land and is about 20 m above the regional limestone saline aquifer. It is a stranded groundwater discharge zone following the draining of the ancestral Lake Bungunnia in the last half million years. The surface soils are substantially gypsum deposits combined with clay sediments. A pond will develop with an area of 7 km 2 • This will allow about two thirds of the water to evaporate leaving 15 ML/ d to infiltrate (carrying all the salt!). The salinity will peak at about 80 000 mg/ L.

ENVIRONMENTAL ASSESSMENT A public environmental impact assessment was undertaken for each project. The issues raised included:

• vegetation clearance and disturbance; • pipeline route selection; • alternative drainage option s for irrigation; • dealing with the symptoms of salinity rather than the cause. In general the projects were well supported because they address the important issue of water quality and have some opportunity to alleviate the decline in floodplain vegetation . The issue of dealing with the symptom of salinity rather than the cause is worthy of some thought. It is recognised that agricultural practice has intensified our sensitivity to river salinity and has also aggravated salt accessions. These engineering schemes deal economically with the salinity problem, addressing in part the natural salt loads and in part the irrigation-induced salt loads. Together with order projects under the Salinity and Drainage Strategy, they will effectively reduce salinity in the river; however they will not address the underlying trend of increasing salinity caused by past actions of agriculture. These schemes give us a breathing space of perhaps 40 years before salinity levels start to rise again above present levels. Agricultural practices have begun changing, particularly at the instigation of the MurrayDarling Basin initative, but it will take a concerted effort and some hard decisions if the salinity trend is to be controlled over the next 40 years. In• the meantime further salinity mitigation schemes will no doubt be required. Obviously we have started with the easier schemes; although the author woould argue these have not been easy!

CONSTRUCTION The schemes have been constructed under the project management direction of the Engineering & Water Supply Department. Construction has been principally by contract, the major site activity being pipelaying. The construction of the submerged steel pipeline crossing the river is shown in Figure 6. The production bores are generally about

DISPOSAL OF SALINE GROUNDWATER The combined schemes will pump about 40 ML/ d of groundwater containing about 700 t/ d of salt, or about 250 000 tonnes per year. The water will be pumped to a disposal site at Stockyard Plain some 15 km from the river. The site was selected after exhaustive investigations because it allows safe disposal of the salt to the saline regional aquifer with a tolerable future impact on the river, whilst

26

WATER December 1992

Fig. 6 - Construction of the submerged river crossing; A 550 mm dia MSCL pipeline is floated across the river and buried in a two metre dredged trench.


TECHNOLOGY

SALINITY AND GROUNDWATER CONTROL SHEPPARTON REGION by W. TREWHELLA ABSTRACT The Shepparton Region is a major irrigated area with a gross annual value of regional output of more than $2.5 billion. Some 200 000 ha already have high watertables, and soil salinity is increasing. By year 2020 it is estimated that the direct annual loss to salinity will be $40 million, unless watertables are controlled. The Shepparton Salinity Plan has been developed for this purpose, and is now being implemented. Vertical drainage by groundwater pumping from the shallow Shepparton Formation aquifers is a major ¡ component of the Plan. Pumping will be carried out using both private pumps (which reuse pumped groundwater for supplementary irrigation) and public pumps installed for salinity control. The development of the groundwater pumping program is described, including the constraints imposed by the variability of the aquifers and the limited opportunities for discharge of salt from the Region.

INTRODUCTION The Shepparton Irrigation Region is an intensively irrigated area centred on Shepparton in the Goulburn Valley. It has a total area of about 500 000 ha, of which about 280 000 ha is irrigated with water diverted from the Goulburn, Campaspe and Murray Rivers. The climate is warm temperate, with average annual rainfalls ranging from 380 to 500 mm / yr. The best soils are intensively irrigated for dairying and horticulture, but large areas are irrigated less intensively for mixed farming enterprises. Removal of the native vegetation and the introduction of irrigation have increased accessions to groundwater to levels well above the carrying capacity of the underlying aquifers. This has resulted in high watertable levels regionally, with groundwater discharge and soil salinisation in some areas. Areas where the watertables are consistently within 2 m of surface are at risk to salinity, but severe problems generally only occur if the watertable is less than Im below surface. The Shepparton Salinity Management Plan has been developed to combat the problem. It combines improved irrigation management and regional drainage to reduce surface waterlogging and minimise accessions to groundwater. However, it recognises that accessions will always exceed the capacity of the aquifer systems and therefore gives high priority to subsurface drainage, particularly vertical drainage by groundwater pumping. This introduces the need for appropriate disposal of the subsurface drainage effluent, which ranges from brackish to highly saline. The Plan is designed to ensure that irrigation within the Region is sustainable, and that the irrigation and drainage works are managed in an environmentally responsible manner.

HYDROGEOLOGY The Region is located on the extensive alluvial plains deposited by the prior Murray, Goulburn and Campaspe river systems. The main geological units are the Renmark Group and the Calivil and Shepparton Formations. The Renmark Group and the Calivil Formation are the major regional aquifers, and are generally 80 to 100 m below the present land surface. They generally consist of coarse alluvial sands, gravels and pebbles which are commonly referred to as the 'deep leads'. The aquifers are effectively confined or semi-confined. Prior to development, pressure levels were believed to be some 30 m below surface, and the aquifers carried recharge from the upland areas to the south and east under the plains to discharge in the Mallee areas to the north and west. Pressures have risen in the last 50 years at a rate of 10 to 20 cm/ yr and are now generally about 10 m below surface. However, they are within 2 to 4 m below surface at several localities in the Goulburn and Campaspe valleys. In some places groundwater pumping for irrigation has stabilised the pressure levels,

28

WATER December 1992

Bill Trewhella graduated B.E. (Civil) from Melbourne in 1959 and has worked in the Rural Water Corporation, (under its various names) ever since, in the field of Land anti Water Management. He is currently Regional Investigations Engineer in the Tatura office.

but the levels are still rising elsewhere. The rises are due to increased recharge in the areas upstream and downstream, as well as local recharge. Recent modelling work (RWC, 1991) suggests that recharge rates to the 'deep lead' within the Region are generally very low (less than 5 mm/ yr), but can be up to 30 mm / yr near the southern and eastern margins. The Shepparton Formation is a complex mixture of clays and sands, with aquifers scattered irregularly at all depths. The aquifers are up to 3 km wide and 5 m thick, and highly variable in texture. Transmissivities range up to 1000 m 2/ day, but are commonly 200 to 500 m 2/ day. The upper aquifers are unconfined or semiunconfined, and are recharged from local irrigation and rainfall . The deeper aquifers tend to be semi-confined, and may be recharged by leakage from both the upper and lower strata. Recharge rates to the upper aquifers can be up to"300 mm/ yr under irrigation on the very sandy soil types. However, clay-loam soils predominate and recharge rates regionally are believed to average 50 to 60 mm/ yr or less. Except for the most sandy soil types when under intensive irrigation, most recharge occurs under conditions of prolonged winter or spring rainfall when evaporation is low. As a result of irrigation the soils and subsoils are now commonly near saturation when rainfall occurs, so that conditions are ideal for recharge to occur. The watertable levels in the Shepparton Formation predevelopment probably were similar to the pressures in the underlying aquifers. Some of the earliest irrigation areas had high watertables and salinity in the 1930s, but systematic recording of watertable levels commenced in a few areas only in the 1960s. With intensification of irrigation since the 1960s the area with high watertables has spread steadily. In August 1991 220 000 ha had watertables within 2 m of surface, and 78 000 ha had watertables within 1 m (Fig.I) . It has been predicted that 274 000 ha will have watertables within 2 m of surface by 2020 (Draft Shepparton Land and Water Salinity Management Plan, 1989). The Shepparton Formation aquifers are filling up from the top, i.e. the uppermost aquifers are filled rapidly by local recharge and a small part of the recharge leaks to the lower aquifers (Fig.2). Because of the low to moderate transrnissivities and the low hydraulic gradients (generally about 1:2000) lateral dissipation is slow, and watertables rise quickly. The watertable response to development may be slow initially because the overburden soils are dry and have storage capacity. Once 'wetting up' has occurred, however, watertables can rise rapidly, and rates of up to 1 m/ yr have been recorded. Without subsurface drainage the watertable levels generally approach a quasi-equilibrium at depths of 1 to 2 m below surface (Fig.3). Capillary return from the watertable to the plant rootzone or soil surface between irrigations and rainfall events balances accessions. At the sub-regional scale the nett recharge approaches zero, and the groundwater flow system is dominated by local (vertical) inputs and outputs. Groundwater outcrops have formed


Fig. 1 -

consistent with the leakage of a small part of the surface recharge through these formations to the 'deep leads'. tfpward gradients have been record ed in some low -lying or undeveloped areas . Unfortunately, the aquitards between the aquifers have not been studied or monitored, and it is not known whether the leakages occur generally or only where aquifers at different levels interconnect. Groundwater salinities are also variable, particularly within the shallow aquifers. The 'deep lead' salinities mostly range from 500 to 6000 mg/ L (TDS), although salinities up to 20 000 mg/ L have been recorded in poorly developed aquifers in the Corop area. They generally follow a consistent trend of increasing salinity moving downstream, as expected for aquifers in transit from defined recharge areas to discharge areas. Salinities in the shallow aquifers range from 200 to 15 000 mg/ L, but are most commonly 500 to 3000 mg/ L. The aquifers associated with the Murray system generally have lower salinities than those elsewhere. Local variability overrides any trends, and very sharp contrasts can occur. This is due to both the complex deposition processes (as the landscape was subjected to successive phases of stream activity) and the flushing action of recent irrigation accessions, particularly on the lighter soil types.

High water table areas, August 1991

PREVIOUS WORKS Salinity problems have been increasing since the 1930s. The initial response was to improve surface drainage, although limited areas of horticulture were tile drained. In the late 1960s trials commenced with groundwater pumping from the shallow aquifers to lower the underlying pressures and restore the natural drainage capacity of the soils. At about the same time landholders began to realise that the shallow groundwater is a useful supplementary irrigation supply, particularly for drought years. In 1973 and 1974 extreme rainfalls caused very rapid watertable rises, with widespread waterlogging and salinity problems occurring in the orchards. As it was clear that groundwater pumping from the shallow aquifers would provide effective salinity control for most areas where it was feasible, the State and Federal Governments funded an emergency program of groundwater pumping for the orchards. Under this program the then State Rivers and Water Supply Commission installed 70 public pumps, and hired nine existing private pumps for use as needed . This program provides salinity control for an estimated 3500 ha of orchards and a further 14 500 ha of pasture areas which are interspersed amongst the orchards. The pumped groundwater is discharged to the regional supply channels and drains, and most groundwater pumped in summer is reused within the Region. However, all groundwater pumped outside the irrigation season reaches the Murray River. It was recognised that a much larger area would ultimately require protection. However, additional disposal of saline groundwater to the Murray was unacceptable without offsetting works to protect water quality for downstream users. The need for an overall control strategy for both land and water salinity was acknowledged, ano in 1987 the Murray Darling Basin Commission proposed its Salinity Control and Drainage Strategy. This included works to protect and improve downstream water quality in the Murray, while still allowing limited disposal of salt from drainage works in the upstream areas. At about the same time the Victorian Government appointed a community group, the Salinity Pilot Program Advisory Council (SPPAC), to work with the relevant government agencies and a Consultant (Dwyer Leslie Pty. Ltd .) to produce a comprehensive salinity management plan for the Region. The Draft Shepparton Land and Water Salinity Management Plan was presented to Government in 1989, and was endorsed with some modifications.

WATER TAIL£

• ]

t.

i [

r

""DEEi'·I..EA0S CAlM. -·

.. ···.... . DISTRIBUTION OF MAIN AQUIFERS & PIEZOMETRIC LEVELS IN SHEPPARTON REGION

Fig. 2 -

Typical cross-section

MURRAY VALLEY BORE 44 387 N.S. = 111.87 m AHO

112

[j G'.j

110 108

~

106

~ 104 ~ 102 o 100 ~

6 ~

98 96

94 92 1964

1980

1970

1990

TIME Fig. 3 -

Typical bore hydrograph

permanent lakes in some local low spots. Areas with inadequate leaching of salt applied with irrigation water or subject to long-term nett discharge of groundwater become saline. Pressure levels in the deeper Shepparton Formation aquifers generally lag behind those in the upper aquifers and commonly equilibrate at lower levels. The downward hydraulic gradient is

THE SHEPPARTON SALINITY MANAGEMENT PLAN The Plan aims to protect as much of the Region as possible from salinity, and to provide the basis for sustainable and environmentally responsible irrigation development . It has four programs - Farm Program, Surface Drainage Program, Subsurface Drainage Program, and Environmental Program. It attacks the problem from two directions, by reducing accessions and by providing subsurface drainage. A strong emphasis is placed on reducing accessions because the scope for subsurface drainage is limited by the restrictions on discharge of salt from the Region. However, it recognises that intensive irrigation is not practicable without some accessions to

WATER December 1992

29


groundwater. The accessions are always likely to be greater than the safe carrying capacity of the underlying aquifers, and high watertables and local groundwater- discharge will occur unless subsurface drainage is provided. The total capital cost of the Draft Plan as presented to Government was estimated to be $646 million, and the Nett Present Value (if implemented over 30 years) was estimated to be $265 million. Without the Plan the Regional annual salinity loss was estimated to increase from $27 million to $40 million by the year 2020. The cost of the Plan was to be shared amongst the major beneficiaries, who were considered to be the landholders, Local Government (representing the regional community), and the State and Federal Governments. Based on the total capitalised cost of the Plan, it was agreed that the regional community would pay half the cost and the State and Federal Governments would pay the other half. The regional community's share includes some capital contributions and all ongoing operation, maintenance and replacement costs. In a unique (at that time) arrangement, Local Government agreed to pay 17 per cent of the annual costs for all publicly operated surface and subsurface drainage works. This contribution recognises the damage caused to council infrastructure (in particular roads), as well as flowon economic and social effects of lost agricultural production on ¡ urban interests. The Plan is currently being revised in the light of the Government response, including limits placed on salt disposal to the Murray. However, the main thrust of the Plan is being implemented and subsurface drainage is being given a high priority. Given the limited salt disposal available, a major effort is being made to increase the safe reuse of pumped groundwater within the Region.

Subsurface Drainage Options Where soil and aquifer conditions are suitable vertical drainage can be provided by groundwater pumping. Pumping from the underlying aquifers lowers the groundwater levels and restores the internal drainage capacity of the soils. If the aquifer is unconfined this may control the watertable and prevent both waterlogging and salinity. If, however, the watertable is perched above an aq uitard pumping may have little effect on the watertable. For much of the Region the situation lies between the two extremes, and pumping from the shallower aquifers of the Shepparton Formation provides some drainage relief. Provided that the drainage rate is greater than the 'leaching rate' required to safely transport salts applied with irrigation water below the plant root-zo ne, the plants will be protected against salinity even though occasional waterlogging may occur. Horizontal or tile drainage (using perforated pipes laid at appropriate depths and spacings) is a feasible alternative in most situations, but close drain spacings are required for heavy soil types. The high capital cost generally limits its use to high-value crops (such as horticulture) in situations where groundwater pumping is ineffective. The cost of tile drainage can be reduced by increasing the drain spacing and accepting a lower standard of drainage. One of the limitations of pumping compared to tile drainage is its inability to target precisely the areas to be protected. However, where it is feasible and particularly if there is scope for reuse of the pumped groundwater, it is more cost-effective than tile drainage. The Plan currently supports tile drainage only for protection of horticulture, and then only if pumping is impracticable. A pilot tile drainage system is being installed in pastures in one area where there is clearly no possibility of groundwater pumping, and this will be used to assess its applicability on a larger scale.

Level of Service The initial groundwater pumping program in the orchard areas aimed to maintain shallow aquifer piezometric levels (and watertables where possible) more than 2 m below surface. Initial planning for the Salinity Management Plan had the same target. However, it quickly became apparent that the salt loads mobilised in areas of moderate to high groundwater salinity were much greater than could be safely managed regionally, and well above what could be discharged to the Murray under the Salinity and Drainage Strategy. The proposed level of service was therefore reviewed . The predominant land use within the region is irrigated pastures, which are very shallow-ro oted and much less sensiti ve to water logging than fruit trees. In fact, the pastures prefer a watertable

30

WATER Dece mber 1992

at about I m below surface during the g1,owing season, provided that it has low salinity. This provides a continuous water supply and reduces the need for irrigation. The shallow groundwater can be used as a storage for excess water applied at each irrigation, with little or no nett recharge to the gro undwater system. However, long periods of gro undwater discharge must be avoided and there must be nett leaching of salts applied with irrigation water. Otherwise there will be a long-term build up of salt in the shallow groundwater or the plant root zone. Some nett vertical drainage must be provided so that excess salt can be carried below the root zone into the underlying groundwater. In turn there must be equivalent removal of salt from the groundwater system to maintain the existing groundwater salinity. The Plan therefore tries to optimise the amount of groundwater pumped with the level of drainage service provided.

Private Pumps The Plan gives priority to private gro undwater pumps in areas of low salinity groundwater, where the water pumped can be safely reused on the farm after dilution with channel water. In practice the volume of additional water gained is somewhat less than the volume pumped, because some of the water could have been used by the plants as a result of capillary return from the shallow watertable. Given the shape of the drawdown curve associated with groundwater pumping, the area near a pump will tend to be overdrained when the minimum drainage rate is provided for the more distant areas. This effect is likely to be increased as a result of the intermittent pumping required for most irrigation schedules . However, it is impossible to optimise the system design with any precision because of the variability of both the aq uifers and the overburden soils. The Plan therefore provides a package of incentives to encourage landholders to reuse gro undwater where they have the ability to use significant volumes. In general this is where the groundwater salinity is less than about 2000 mg/ L, but considerable effort is being devoted to developing more salt tolerant commercial ¡ crops to raise this limit. Some salt must be removed from the system to protect the quality of the groundwater. Again, it is impossible to optimise precisely the amount of salt which must be removed, and Salt Disposal Allocations are based on a simple 'rule of thumb'. This is the estimated salt load introduced each year with irrigation water within the nominal area of influence of tJ:ie pump. This will be effective only if sufficient pumps are installed to ensure that no pump is acting as a sink for groundwater from surro unding areas. Salt disposal offfarm could be minimised by installing a pump on every property so that safe reuse of the pumped groundwater could be maximised. However, this would require excessive capital costs and the Plan tries to balance the costs with the optimum groundwater reuse and salt disposal. Salt disposal from the private pumps is allowed only under strictly controlled conditions and when there are high winter flows in the Murray, so that downstream effects are minimised. At these times the pumps are allowed to discharge to the regional drainage system, or to irrigation channels which have outfalls to the drainage system. The Plan has set a target to protect 85 000 ha by installing some 365 additional private pumps and encouraging more consistent use of some 395 existing pumps. The average capital cost is about $25 000, and the average volume reused is about 100 ML/yr. Public Pumps The scope for onfarm reuse is limited where groundwater salinities are higher, and it becomes more attractive to install strategically placed public (Salinity Control) pumps which can protect relatively large areas. Because of the constraints on salt disposal these pumps canno t be operated to provide continuous control of groundwater levels. The Salinity Control pumps are operated for about four months each year. Half of this pumping is scheduled for the irrigation season, when almost all will be reused regionally from the irrigation channels and drains. The other half will occur in the winter at times of high flow in the Murray to minimise effects on downstream users. Again, this policy is a compromise between capital cost and salt disposal. More continuous operation of the pumps would provide a better level of service for areas close to the pumps, and would also extend the area receiving limited protection at the margins. However, the additional area protected wo uld not increase in direct proportion to the increased salt load discharged.


Public pumps generally cost about $70 000 and serve 200 ha. However, this cost includes significant costs for investigation and optimisation of each site, and also for. consultation with the local landholders. Under the Plan guidelines landholders identified as receiving direct benefit will be rated to recover 41.5 per cent of the operation, monitoring and replacement costs. The remainder of the annual costs will be shared by irrigators generally and Local Government. Where the groundwater salinity is very high (more than 7000 mg/L), it becomes impossible to manage discharges to the regional channels and drains and the cost penalties for discharge to the Murray become very high. Evaporation basins can be used, provided that suitable sites are available. However, the capital costs are higher, and each site requires economic justification. The Draft Plan proposed the installation of 426 public pumps (including 50 disposing to evaporation basins) to protect about 85 000 ha, but the limited salt disposal now allowed to the Murray makes it unlikely that this will be achieved. However, options to increase the Region's Salt Disposal Entitlement are being actively pursued, and it can be expected that some increase will occur over the life of the Plan.

SITE DEVEWPMENT Investigation Methods Location of pumping sites is based on a combination of geomorphic interpretation, evaluation of available drilling information, geophysical survey and exploratory drilling. The Geonics EM34 electromagnetic survey equipment is used primarily to identify anomalies for exploratory drilling. The EM equipment helps to target the most prospective parts of the highly variable Shepparton Formation at minimal cost. More sophisticated analyses cannot be justified given the low cost of exploratory drilling (with flight augers) to shallow target depths. Slotted PVC casing pipe is installed through hollow augers at most sites, and this allows reliable sampling for groundwater quality and monitoring of water table levels. It also facilitates gamma-logging, which provides a reliable indication of the locations of sand lenses within the predominant clay strata and ensures that bore screens are accurately located. Promising sites are usually pump tested for several weeks at better than 50 per cent of design capacity to get reliable estimates of longterm capacity and groundwater salinity. Rigorous analysis is difficult because of the high variability of the formations and the effects of local recharge. The aquifers are subject to both local inhomogeneity and irregular distribution of sharp boundaries. Recharge cannot be estimated with any confidence, and is likely to vary considerably during the period of a test. Tests are analysed using standard Theis methods to derive 'apparent' aquifer characteristic values which may be applied for the pumping period which is of interest. Tests are also monitored for a lengthy recovery period in order to validate, so far as possible, the estimates made. The scope of the investigations for public pumps is much greater than for private pumps. Each site must be optimised in relation to the areas most at risk, as well as to other existing sites in the vicinity. Careful evaluation is required of the likely impact on water quality in the receiving channel or drain. Economic location of the site is also constrained by the need to consider costs of providing power, access for maintenance, and delivery pipeline.

Pumping Systems Well-point systems are commonly used for both private and public pumps tapping the shallow aquifers. This is because the available drawdown is limited by the shallow depth of the aquifer, and wellpoints allow higher pumping capacity than conventional tubewells. Each well-point can operate at or about the limiting drawdown set by either the top of the aquifer (or bore screen) or the suction limit of the pump. As either the available drawdown or the depth to the water table increases beyond the suction capability of a centrifugal pump, the capacity advantage shifts across to the single bore with a submersible pump located at the appropriate depth to achieve the required drawdown. Most well-point systems consist of six to 20 well-points spaced from five to 20 m apart. The well-points usually consist of 50 to 100 mm PVC bore casing with slotted PVC pipe as a screen across the main sand or aquifer interval. The well-points are washed or

GAS TAN<

-

DISCHARGE

LNe-WELU'OltlTS Uoually 6 to a AT e to 10ffl cantrH.

: ~

Fig. 4 -

-

-

Typical well point system

jetted into position, and the annulus around the screens may be gravel packed. Use of a fine gravel pack is essential in fine sands to provide an efficient and effective screen. It also provides useful insurance against sand variability and possible poor locations of screens in better quality aquifers. The key components of a well-point system are shown in Fig. 4. The need for a gas tank depends on the amount of gas naturally occurring in the groundwater and the standard of construction of the subsurface works. Poorly constructed works can result in leakage of gas or slugs of gas from poorly laid headerlines. Although inefficient, a gas tank with air automatic exhaust system may be the cheapest means of dealing with these faults. A good quality centrifugal pump with high suction capacity is the most efficient pump, but is generally only capable of handling small gas loads. For small installations where operational efficiency is not critical, a self priming pump may provide adequate gas handling capacity without a gas tank. However, a separate priming pump would still be recommended unless the headerline is expected to be close to or below the water-tabre when starting the system.

CONCLUSION Implementation of the Plan has so far been slow because of the need to develop detailed guidelines for both the private and public pump programs. However, there is now a strong demand for assistance for pump installation. In the last half of 91/92 grants totalling $180 000 were given for 13 private pumps, and the 92/ 93 budget of $400 000 is already over- committed. Cost sharing (rating) guidelines for public pumps have also been completed recently, and demand is strong. It is expected that four sites will be confirmed this year and detailed designs completed ready for construction in 93 / 94. The subsurface drainage program has developed real momentum, but will unfortunately be constrained by the limited government funding available. Nevertheless, there is a comprehensive strategy in place which has both government and community support, and the next 10 years will see considerable progress towards the protection of one of Australia's most valuable agricultural regions.

REFERENCE Rural Water Commission (1991), 'Riverine Plain Groundwater Model Stage 1 Report; RWC Investigations Branch, Unpublished Report No.1990/ 42.

WHY LOOK ELSEWHERE? If it's to do with our industry LOOK ... AND ADVERTISE IN OUR MAGAZINE WATER December 1992

31


TECHNOLOGY

GROUNDWATER PUMPING - AN EFFECTIVE MEANS OF SALINITY CONTROL by J. NOLAN SUMMARY Land salinisation occurs in areas where groundwater is close to the surface. Effective management of salinisation, particularly within irrigation areas with good quality groundwater, is best achieved by groundwater pumping for both reuse and disposal combined with surface drainage and on-farm works to minimise recharge. Unfortunately the community perceives the benefits of surface drainage and on-farm works to be superior to groundwater pumping for salinity control. Sub-surface drainage implementation rates can . be accelerated by promoting groundwater pumping benefits through existing salinity education programs, the linked development of surface and sub-surface drainage implementation programs, the continuation of existing groundwater pumping incentives scheme and further research into saline groundwater disposal.

INTRODUCTION Rising groundwater levels within the Murray Basin are rapidly reducing the agricultural productivity of Australia's premier agricultural region for both the domestic and export markets. The causes are well known; land clearing, irrigation and the use of pastures and crops with low water demand. Over the past decade there has been a growing awareness of the problem both within the community and government. During this time we have witnessed the formation of the Murray Darling Basin Commission, the implementation of the Salt Action: Joint Action program in Victoria and the Salt Action program in New South Wales. Significant human and financial resources have been allocated to investigation and research culminating in the formation of a number of salinity management plans. These plans are now being implemented by regionally based management committees funded by both the community and government. The focus of this paper is directed primarily towards salinity management strategies in irrigation areas where good quality groundwater is present. Salinity management plans in these areas generally include on-farm, surface drainage, and sub-surface drainage components.

SALINITY MANAGEMENT STRATEGIES On-Farm

On-farm activities which can reduce recharge to the watertable and hence rate of watertable rise, include landforming, improved on-farm drainage, and drainage water reuse. Recharge reduction is achieved by reducing the frequency, duration and area of surface ponding. Where the groundwater salinity is low, on-farm groundwater pumping and reuse with, in some cases, dilution with channel water can provide salinity protection provided that the groundwater salt balance is maintained by off-site disposal. The planting of trees along shelterbelts can also reduce groundwater recharge, however the reduction is unlikely to be significant as trees dewater only the soil profile in close vicinity to the rootzone (Department of Agriculture and Rural Affairs; 1988). Surface Drainage

Surface drainage has several benefits. The most significant of these are the substantial reduction in road construction and maintenance costs, (based upon a survey conducted by two Shepparton Irrigation Region Shires), increased agricultural productivity due to the decrease in the frequency and duration of waterlogging, and a reduction in recharge of up to 19 per cent (SPPAC, 1989). Surface drains include public and community based drainage schemes. Public drains, operated and maintained by water authorities, are generally located in areas of intense irrigation or

32

WATER December 1992

John Nolan is Senior Hydro geologist in the Melbourne office of Gutteridge, Haskins & Davey. He holds the degree of MEng.Scf. Prior to Joining GHD in 1990 he worked for the Rural Water Corporation of Victoria, and has been involved in a wide variety of groundwater and environmental assessment projects in Australia and overseas.

high value crops, or where outfalls from community drains are necessary. Community drains are generally situated in small catchments, and outfall to public drains. They are managed and maintained by the community and have a lower standard of service relative to public drains. Although drainage waters can be reused during the irrigation season, winter disposal to streams is inevitable. Sub-Surface Drains

Sub-surface drainage is the only management strategy which is totally effective in controlling high water.tables within irrigation areas. It can be achieved by groundwater pumping in areas with permeable aquifers, or by tile drainage where aquifers are absent. Where aquifers are permeable with good quality groundwater, the most economical method of sub-imrface drainage is considered to be private pumping for local reuse and during winter off-site disposal into drains or channels to maintain a salt balance. Other good quality groundwater reuse options include public schemes whereby groundwater is pumped into the channel distribution system for conjunctive use. Reuse with poor quality groundwater increases rootzone salinities thereby restricting agricultural productivity. In these areas, public pumping schemes with off-site disposal or discharge to evaporation basins are necessary. In areas with low permeability sediments dewatering can only be achieved by tile drainage. Where the water quality is moderate some local reuse is possible on salt tolerant species, however, as the majority of the low permeability areas have poor quality groundwater, disposal to evaporation basins is generally necessary. Other on-farm methods of saline groundwater disposal are currently under investigation. Disposal of saline groundwater to rivers is controlled by the Murray Darling Basin Commission. In Victoria and New South Wales disposal to the River Murray is restricted to discharges which are equivalent to a salinity increase of 15 Electrical Conductivity units (¾Si em at 25 ° C) at Morgan, South Australia.

COMPARATIVE ASSESSMENT OF STRATEGY BENEFITS The effective management of land and stream salinity is best achieved by adopting a combination of strategies that are sustainable and maximise the economic benefits through reduced salinisation. Thus when limited public and private funding is available, expenditure should be directed towards remediation strategies which provide the greatest economic returns. Some of the irrigation areas in which groundwater pumping for reuse and disposal is feasible are the Shepparton Region (Victoria), the Berrigan Irrigation District (NSW), and the Murrumbidgee Irrigation Districts (NSW). Of these the Draft Shepparton Land and Water Salinity Management Plan (SLWSMP), prepared by the Salinity Pilot Program Advisory Committee (SPPAC; 1989), is


currently being implemented. The indicative capital costs in addition to benefit/ cost ratios of various components of the SPACC's preferred plan, based upon the Draft SLWSMP, are shown in Table 1. Table I -

Economics of Preferred SIRLWSMP Components

Capilal CoSI (SM)

Component

Capital ised Value Benefits Benefit/ (Sa linily) Cos! Ralio• (SM)

On-Farm La ndform s and Farm Drainage Drainage Reuse Tree Planting

194 49 46 289

250

1.03

145 47 19 II 222

177

0. 7

Surface Drainst ' Public (Rural Water Corpora1ion) Community Wa ter Authority Drainage Course Decla ration

Sub-Surface Drainage+' 45 35 80

On-Farm Publi c Works

514

2.6

• Ca pi tal a nd recurrent costs a re includ ed in this ra ti o. t The sur face des ign benefit s are sa linit y a nd waterlogging redu ct ion (280Jo ), wate r reuse {1 8%}, a nd road constructi o n a nd maint ena nce (5 6%). :I: T he sub-sur fa ce drain age strategy is aimed at providing sa lini ty protection to 213 000 ha o f the 279 000 ha o f irr igated a rea. I Th e req uired sa lt di sposal qu ota fo r surface and sub-s ur face drain age is 2.7 a nd 16.7 EC un it s respective ly.

Since the preparation of the draft plan the surface drainage strategy has been revised to exclude schemes with benefit/cost ratios of less than 1.0, and the sub-surface drainage benefit/cost ratio has been reassessed to be slightly below 2.0. Despite these revisions the • sub-surface drainage strategy still provides the greatest economic return. Implementation funding is obtained through the Murray Darling Basin Commission (MDBC) Drainage Program, the Federal Water Resources Advisory Committee and the Victorian Salinity Program, Salt Action: Joint Action. Capital expenditure on surface and subsurface drainage through the MDBC Drainage Program over the past two financial years and the State Salinity Program for the Shepparton Region in 1990/ 91, SPAC (1991), is shown as follows:

Surface Drainage Sub-Surface Drainage

MDBC (SM) 1991 / 92

1992/ 93

Salinily Program (SM) * 1990/ 91

1.58

1.59

2.42

0. 53

0. 74

0. 50

• Combined Co mmuni ty an d Sta te Expenditure

During 1990/ 91 the capital expenditure for on-farm works was $22.5 million, or 40 times the expenditure for groundwater pumping . This table indicates that expenditure for surface drainage in comparison to sub-surface drainage has reduced from a factor of about five to two in this three year period. The implementation rates for both drainage strategies is restricted by the need for expenditure on strategy development, feasibility design and further investigations. For example, in 1992/ 93, 22 per cent of the MDBC sub-surface drainage funding was allocated to the farm exploratory drilling scheme (FEDS) program. The FEDS program involves the investigation of sub-surface conditions on private land to determine the suitability of individual sites for private and public scale pumping schemes . Whilst the SL WSMP recognises groundwater pumping offers greater benefits than surface drainage, the proposed expenditure does not equate with its estimated benefits.

CAUSES OF SLOW SUB-SURFACE DRAINAGE IMPLEMENTATION Since the commencement of irrigation within the Murray Basin landowners have lobbied government to construct surface drainage schemes as part of the irrigation supply infrastructure with the expectation that the schemes will be funded by government. Today the community still views surface drainage as desirable as the benefits are visible and obvious. Unfortunately the benefits of groundwater pumping are not so visible, are sometimes slower to take affect, and groundwater/ salinity processes are often difficult to ~omprehend .

Other reasons for the slow rate of implementation are : • Groundwater supply costs in most areas are greater than that of channel water. • The beneficiaries who will ultimately contribute to the cost through service rating levies are difficult to identify . • Off-site discharge options are limited to areas with outfalls to surface drains. • Groundwater pumping with disposal to the River Murray is restricted by limited availability of salt disposal entitlements, which within the Shepparton Region are currently established at 10 EC units at Morgan, South Australia. (The draft SL WSMP relies on 16.7 EC units). • The benefit/ cost ratios of saline groundwater disposal to evaporation basins is low .

CONCLUSIONS Salinity within the Murray Basin is causing substantial economic loss and environmental degradation. To halt the expansion subsurface drainage with access to disposal, for salt balance maintenance, needs to be implemented without delay. Various strategies are available to augment the existing subsurface drainage programs. Refocussing existing community-based salinity education programs to emphasise the benefits of groundwater pumping to landowners is the primary requirement. In developing these programs hydrogeologists must take active roles in advising the community and in developing equitable approaches to the funding and implementation of salinity management plans. Other strategies include the reappraisal of surface drainage priorities to ensure that they are compatible with sub-surface drainage outfall requirements, the continuation of existing private groundwater pumping incentives schemes, and further research into saline groundwater disposal options.

REFERENCES Depa rtment of Agriculture and Rural Affairs (1988) 'The quantification of On-farm Options for Salinity Control', A Working Paper prepared by DARA for the Project Ma nagement Ad visory Committee of the Shepparton Irrigation Region Land a nd Sa linity Ma nagement Plan. Go ulburn Broken Salinity Program Council (1991) 'A nnual Report 1990-1991 '. Shepparton Pilot Program Advisory Council (I 989}1'Draft Shepparton Land and Water

Salinity Management Plan'.

EDITORIAL MATTERS: The Journal Committee welcome the submission of papers relating to water resources, hydrology, treatment, supply, wastewater treatment and disposal, and related scientific and management matters. A length of 3000-5000 words is preferred. Material should be submitted to the Editor as hardcopy, typed or printed double space, with wide margins (for the convenience of the referees and the editor). Two copies are preferred. Once a paper has been accepted, perhaps after some amendments required by the referees, authors should, if possible, also submit a copy of the amended material on a disk (IBM or Macintosh, preferably in ASCII 'text only', or in a standard word-processing format). Alternatively, pages from electric typewriters or laser printers (not dot matrix printers) can be computer-scanned by the typesetter. Diagrams must be suitable for photo-reduction to a width of 57mm or 90mm without loss of clarity. (This can be checked by using a photo-copier with a reduction facility) . Photographs can be either B & W or colour prints, provided that the contrast is adequate. Each author is required to supply brief biodata relevant to the particular paper, and a personal photograph (B & W or colour). The Committee also welcomes brief progress reports or papers of about 1000-1500 words which can be published less formally as Technical Notes, rather than as full papers. Letters to the Editor, Industry News items and Personalia can also be submitted.

WATER December 1992

33


TECHNOLOGY

A GROUNDWATER-BLUE-GREEN ALGAE RELATIONSHIP? by T. J. VERHOEVEN INTRODUCTION While public attention on the blue-green aglae problem during the 1991/92 summer focussed on Australia's waterways (particularly the Darling-Barwon River System in western NSW), water resource managers were a lso le arning of a groundwater relationship. From an examination of the factors that affect algal - bloom development and of the impacts of blooms, the possible role of groundwater is described.

BLUE-GREEN ALGAE Blue-green a lgae are primitive photosynthetic organisms found in many environments including inland waterways, estuaries and the sea. When in low numbers they are important in the aquatic biology of our waterways. However, their numbers can often rise to a level where their noxious properties can become disastrous to water reso urce users. The characteristics of blue-green algae and influencing factors include: • possession of gas vacuoles providing buoyancy regulation, which allows them to overcome the spatial separation betwen light and nutrients in the water column; • nitrogen fixing capability enabling them to dominate in low nitrogen waters; • production of spore or 'akinetes' providing a means of seed ing water bodies; • production of toxins which kill or inhibit predators and which may inhibi t competitors.

FACTORS AFFECTING BLUEGREEN ALGAL BWOMS The multiple causes and effects of these blooms form a complex interactive system summarised in Figure 1 which is drawn from the final report of NSW Blue-Green Algae Task Force (1992). An understanding of the relationship is necessary if the role of groundwater is to be understood, and if s u ccessful management is to b e implemented. In resource management, decisions will need to be made on the best target area, be it at the causes, the algae itself or at the effects of their growth . Algal growth is determined by many environmental factors (physical, chemical and biological). The conditions which favour the development of blue-green algal blooms are: • high nutrient levels, particularly phosphorus; • low nitrogen:phosphorus (N:P) ratios (less than 29:1); • high water temperature (above 20°); • high pH (pH 8-10) and low carbon dioxide concentration;

34

WATER December 1992

• ab undant zooplankton (blue-greens are relatively inedible); • low flows, leading to long retention times and calm water conditions; and • reduction in turbidity to moderate levels leading to increased light intensity. As show in Figure 1, blue-green algal blooms have a wide range of socia l, economic and environmental impacts. There are impacts on water supplies, human health, livestock, fish, wildlife, recreation and tourism; the costs run into millions of dollars annually. There are also major cost implications for water treatment works if upgrading is required to handle increasing taste and odour problems, toxins and organic loads arising from algal blooms.

GROUNDWATER FACTORS AFFECTING ALGAL BWOMS Conditions mostly favour the development of blue-green algal blooms during summer, particularly along the shallow margins of water storages and lakes or when the rivers are at low flow, approximating a chain of connecting pools. Groundwater inflow to these waterways can then comprise a large proportion of the net flow, and can influence the factors which enhance or inhibit bloom development.

Physical factors Groundwater inflows can help maintain more constant water temperatures in small s urface water bodies, aiding bloom development. Simi larl y, groundwater inflows of high pH help enhance conditions. For example, high flows in the Darling River have a pH of 7-8 which favour the less problematic greens over blue-greens; whereas the pH of low flows during the 1991 blue-green algal bloom measured 8.6-9.7 and the corresponding gro undwater inflows had a pH of up to 8.9 (Williams, 1991).

John Verhoeven gained his MEng.Sc. from the Universi y of New South Wales and has worked throughout the Northern Territory and New South Wales. He is Manager Environment Branch of the NSW Department of Water Resources and also Chairman of the NSW Blue-Green A lgae Task Force.

In periods of drought, large groundwater inflows in small streams can reduce retention time and inhibit bloom development, whereas inflows in large weir pools could help increase retention time and serve to prolong the impact of an algal bloom.

Chemical factors Nutrients in groundwater may h elp enhance bloom development. Although phosphorus is derived from a range of point and diffuse sources, it is usually not encounter~d in high concentrations in groundwater (for example fertiliser-derived phosphorus is often quite immobile in soils since it is bound to clay minerals and other soil components). However, in sandy soils overlying a shallow gro undwater table (eg Perth, or the Botany Basin) or where land disposal of phosphorus-rich wastewaters exceeds a soi l's assimilative capacity, phosphorus can reach the groundwater table. Movement of these groundwaters into a waterway will add avai lable phosphorus to the water column and enhance algal bloom development (the recommended limit for phosphorus in our waterways in 50 µg / L).

POINT SOURCES -----++ Nutrients (P & N:P)

- - - - + Humans Stock

DIFFUSE SOURCES / '---..+ Light(+ Low Turbidity) -+

Domestic Animals Wildlife (not to fi sh)

+Deoxygenatlon -(lnstream Effects DROUGHT "'... / , , + Temperature----->< Including Fish) FLOW AND / - + Lack of Turbulence ALGAE RELEASE ~ ------ Aesthetic - s c u m s "Odour MANAGEMENT + Long R e t e ~ / OFF RIVER SOURCES

+ Seeding

\

~ Water Supplies

+ Biological (eg Predation) + Chemical (eg high pH)

-Taste and Odour Organic Load Affect Treatment

+ Environmental ~water Chemistry Biological FEEDBACK INFLUENCE

eg NUTRIENT RELEASE COMPETITION

Fi~. 1 -

Blue-Green Algal Blooms -

Major Causes and Effects


On the other hand , groundwater may be high in nitrate concentration; the movement of such groundwater into a waterway may help increase the N:P ratio and help favour the growth of green algae over blue-greens. G ro und water inflows high in sul fa te concentration added to the algal orga nic matter (in the bottom sediments) suitable for the metabolism of sulfate-reducing bacteria can activate the bacteria in the sediments. T he bottom water waterway can become anoxic, with resolubilisation of some of the phosphorus bound in the sediments. T he resulting feedback can release a pulse of soluble reactable phosphorus into the water column , causing an algal bloom (Donnelly et al, 1992). Such conditions exist along the Darling River, fo r example. Although sulfate concentrations in the river are generally not high (10-3 0 mg/ L), in early 1991 sulfate concentrations of 70 mg/ L were measured in sections of the ri ver, fo r example near . Louth , indicating possible inflow sul fa terich saline groundwater. Also, at times of low ri ver flow, saline gro und water infl ows into ri ve r bed depressions may occur (examples are known fo r the Darling Ri ver). T he cha nge in the ionic balance of the ri ver caused by these inflows could cause sediment flo cculation , res ulting in mu ch lower t ur bidi ties co in cid in g wit h low fl ow a nd war m condi tions. If the ri ver water has high concentrations of phosphorus (such as in t he D ar lin g Rive r) , a lga l growth can commence. T he need to fur ther understand the relationship between groundwater and bluegreen algae has been recognised by the NSW

RJ NEWMAN continued f rom page 26 about 100 m deep. Fibreglass slotted casing has been used at Woolpunda, however, open hole completions, with surface casing, have been used at Waikerie. Pipelines greater than 300 mm diameter h ave been laid in HOBAS glass reinforced plastic and smaller pipes are uPYC. Pumps are Grundfos stainless steel grade 316 o r better a nd a re suspe nd ed on Wellmaster flexible risers for easy withdraw! fo r maintenance. A crane truck is used to withdraw a pump in 20 minutes . The schemes have involved a major upgrade of the local electricity distrubiton system . Land acquisition has involved close to 100 property owners and has requi red continuous consultation with the local community.

IMPLEMENTATION A ND MONITORING Th e Woolpund a sch em e has been implemented in fou r phases. Initially the first 24 bores were pumped at twice the longterm design rate as the first half of the pipeline became available. This accelerates

36

WATER Dece mber 1992

Blue-Green Algae Task Force. In its Fina l Repo rt (1 992) t h e Task Froce h as recommended research into an assessment of nu trients iri the sedi ments of water bodies, and an assessment of the ro le of gro undwater in triggering algal blooms in rivers such as the Darling.

ALGAL BW OM IMPACTS AND GROUNDWATER A lgae contingency plans A lgae co ntingency pl a ns have been developed in many states, to varying degrees, to plan for the effecti ve management and co ntro l of a lga l bl oo ms, in o rd er to minimise their occurrence and impact. T he plans including mo nitorin g, communi cations and response components. For states such as News South Wales, Victoria and South Australia where most communities re ly o n s urface wa ter suppli es, th e contingency plans are costly and need to be comprehensive (including the identification of alternative water sources) to safeguard public health . However, the algae conti ngency plans fo r many regions in Q ueensland and Nort hern Territory are simpler and far less costly. Becau se d o mes ti c water suppli es a re ground water sourced, public health issues in these regions relate onl y to recreational use of surface waters. Water suppl y From the experience of the 1991/ 92 summer, many communities currently on surface water supply will be considering the use of groundwater as an alternative (du ring algal blooms) or as a replacement source.

t he a bilit y o f t he sc hem e to remove groundwater fro m 'storage'. The Waikerie Scheme will be built in two phases. the details of Phase Two will be verified after operation of Phase One fo r at least one year. The schemes will progressively become fully effecti ve over about fi ve years. An intensive monitoring system has been developed including a detailed assessment o f the operationa l performance of the bore pumps, salinity and flow measurements in th e ri ve r toget he r with t he reg ul ar monitoring of about 150 observation wells. It is imperati ve that the scheme continues to operate at peak effi ciency because of the high power requi rements. Pumping water of this salinity is not stra ightfo rward. Corrosion is a lways a concer. Another problem which has had to be overcome is the effect of chemical and biological deposition in the pumps and pipelines. Chlorination of the pumps and ri sers has b ee n impl eme n ted u sin g electrolysis of the saline water. At the time of writing the Woolpunda scheme has been progressively implemented over the last year or two. It is still too early to see convincing evidence of interceptio n in . t he ri ve r, bu t th e des ig ne rs take

Pas to ralists, fa rmers and irrigators will also be considering the greater security of water quality provided by a ground water source. For irrigators in particular, the advantage of using groundwater include security of qua lity, greater securi ty of quantity, and lower maintenance costs of irrigati o n equipm ent (n o clogging of pumps, pipelines and sprinklers with algal biomass). These advantages need to be weighed against the generally higher cost of extracting gro undwater.

CONCLUSIONS While public attention on the blue-green algae problem has foc used on our sur face water reso urces, there is also an important relatio n shi p with gro undwa ter. A n understanding of the re lationship of the complexity of causes and effects is vital if the ro le of groundwater is to be understood, a nd if sucess ful ma nage ment is to be im p le m ente d. T he ava il a bili ty of ground water influences the structure and cost of algal contingency plans, and the provision of water supplies fo r a ra nge of uses.

REFERENCES Donnell y, T H ., O lley, J .M. , M u rray, A.S. a nd Wasson R.J. (1992) A lgal Blooms in the Darling River: 'Run

of River' St udy Wentworth to Collarenabri December 1991; CS I RO D ivision o f Water Resources C o nsul tantcy Report No. 92/ 13 J uly 1992 . New South Wa les Blue-Green A lga e Tas k Force (1 992);

Blue- Green A lgae: Final Rep ort of the Task Force; pub lis hed by the NSW Depa rtm en t of Wate r Resources; Augu st I 992. W illi ams R.M . (199 1); Groundwater inflow lo the

Darling River Mungindi to Wentworth: Run of River Study (1990/ 91); NSW D epart m e nt of Wat er Resources, Technica l Services Di visio n Re port TS9 1.04 1; A ugusl 199 1.

co n f id ence fr o m th e res ul ts of th e production drilling program which bear out the interpretations of the investigations. T he drawdown cones aro und the production bores are continuing to expand and are now approaching the ri ver. Some 180 000 tonnes of salt has been di verted fro m the aquifers near the ri ver.

ACKNOWLEDGEMENTS T hese proj ect have involved a team of inves tigators, designers and constructors and consultants over many years. the author expresses particular recogni tion of the efforts o f Ken Smi th a nd Peter Stace (hydro logy), Andrew Telfer, Nick Wat kins, Steve Barnett, Zac Sibernaler and Dave Clar ke (hyd rogeo logy), Ed Collingham (geotechnical) , Grant Lewis and Lance Gladigau (planning), Ken Ridley a nd Tom Wos ni ak (h ydra uli cs ) , Dave Kerry (pipelines), Jim Giffo rd and Ro d Wood (estimating), Greg Moore (materials), Rob Burnell and Biran Little (construction) and Peter Forward (operations), together with numerous patient d raughtsmen . Members of the Salt Interception Wo rking Grou p of the Murray Darling Basin Commissio n prov id ed o ngo ing peer rev iew of t he investigation and design process.


TECHNOLOGY

PERTH COASTAL GROUNDWATER SCHEMES by D. HOPKINS ABSTRACT The Water Authority of WA is proposing to develop the groundwater resources along a coastal strip north of Perth. The area is known as the North West Corridor and has been earmarked for urban development (Figure 1). The aquifer in the area is highly transmissive and wellfield drawdown in the area will be low. Groundwater schemes in the area will be used primarily to satisfy local demand. Urban development in the area has potential to pollute the groundwater system and appropriate water resource protection strategies have been incorporated into land use planning for the area. The Coastal Groundwater Schemes have a low environmental impact and present a low cost opportunity to harness a resource which would otherwise be under-utilised .

HYDROGEOWGICAL SETTING The area is immediately adjacent to the coast and is characterised by sand dunes overlying limestone. The soils of the area are thin and dominated by highly permeable calcareous sands. Solution channels are widely developed in the limestone resulting in a highly transmissive aquifer. This has the advantage of reducing the influence on drawdown cones from groundwater wells. The sand and limestone formation is of quaternary age and is underlain by shales and sands of the older Leederville Formation. The base of the quaternary formations is typically at about minus 30 m AHD (Australia Height Datum).

GROUNDWATER Groundwater in the area is unconfined and forms a water table 5 to 20 m from the surface, depending on the topography. Recharge

Derek Hopkins is the Supervising Engineer, Groundwater North Section in the Groundwater and Environment Branch of the Water Authority of WA. Derek is a Civil Engineer who graduated from the University of Central Queensland in 1977. He has worked in the water resources and groundwater area for over 11 years throughout Western Australia. He is responsible for the investigation, development and management of groundwater resources in the northern part of the State. to the aquifer is from two main sources: • direct recharge from rainfall; and • throughflow from the Gnangara Mound in the east. Water table contours run approximately parallel to the coast (Figure 1). The average hydraulic gradient for the area is about 0.4 m per km. This is indicative of an aquifer with high hydraulic transmissivity. Pump testing indicated that transmissivity values were as high as 12 000 m 3 / m / day (corresponding to hydraulic conductivity of 450 m/ day).

WATER QUALITY The groundwater in the area is typical of water from limestone aquifers, with elevated levels of calcium carbonate. The hardness is in the range 150-200 mg/L calcium carbonate but is still acceptable for drinking purposes. The NH & MRC guideline for hardness is 500 mg/ L. Salinity of the water is in the range 350-800 mg/ L TDS with large areas of the aquifer below 500 mg/ L TDS. · Iron levels are generally low but in some areas can exceed the NH & MRC guideline value of 0.3 mg/1.~ Test pumping from investigation bores has confirmed that iron levels toward the base of the aquifer are higher than iron levels near the water table. Production bores will be designed to blank out the aquifer near the base in order to reduce iron levels.

SALTWATER INTERFACE Investigation drilling has identified a saltwater interface penetrating up to 300 m inland from the coast. Tidal influence has' been measured up to 200 m inland, again confirming that the aquifer was highly permeable. The interface is sharp, with a thin mixing zone due to the small fluctuation in the water table (0.2-0.3 m). Flow through the aquifer restricts the inland extent of the saltwater interface. The saltwater interface has been modelled and observation bores have been constructed near the coast to measure and monitor changes in the position of the interface. Figure 2 shows a cross section through the coast and the aquifer. In the Quinns area, the depth/height ratio of the saltwater interface appears to be greater than the Ghyben/ Hirschberg approximation of 40, and may be as high as 60. This could be explained by anisotropy in the aquifer. This aspect is poorly understood and difficult to investigate. In view of the uncertainty regarding the movement of the saltwater interface, monitoring bores have been strategically located to provide early warning against further inland movement of the interface.

PROPOSED DEVEWPMENT The Water Authority believes that the unconfined groundwater in the coastal strip of the north-west urban corridor can be successfully developed for public water supply. The development of this resource will be in the form of four separate groundwater schemes: Whitfords, Quinns, Eglington and Yanchep-1\vo Rocks. At full development the schemes will supply approximately 40 million kL from the unconfined aquifer. This is about 20 per cent of the present demand for the Perth metropolitan area.

WATER December 1992

37


TECHNOLOGY

~o 35 30

--

ZS

------- ------

--- -- -- --

------

------

20 15 10

,/ /

t----lll_OUN>_W_A_TE_R_L£VE __ L_ _ 1.0 41

. SJ

.,o •IZJ ~14J

-15 1350

·ZS

-30

\

470

\

-20

SALT WATER

"

-20.1 -22.1

",

FRESH WATER

'

0

l--,.---,----,~~....;....'•.:.:".,...°'--,•""--.:.,',-..._~~"""T"""~~---,-..-...,...--r°'-'',-..,....--,---,......,~~-,--.---,-~ 0

LEGEND:

0

N

..,

0

0

SLOTTED INTERVAL

.

0

., 0

.

.,

0

0

KM

- - APPRO XIMATE GROUND LEVEL

518 Sail-lty mg/I

Fig. 2 -

Section through aquifer

PRODUCTION BORES AND CLUSTERING Test production bores constructed into the coastal limestone have been pump tested at high rates (up to 5000 kL per day) with minimal drawdown. Production bores have been designed (Figure 3) to take full advantage of the available saturated aquifer. The saturated aquifer is generally less than 30 m and screens and pump settings must be carefully designed to maximise bore yield. With long term drawdown of about 5 m, peak pump output has been restricted to 5000 kL/ day or 58 L /s . In order to optimise infrastructure costs a system of bore clustering has been investigated. Based on pump test results a group of three bores can be clustered at 50 m spacings to maximise the use of control equipment, treatment and dosing facilities and land purchase. Mutual interference between the three bores will only add about a further 0.8 m drawdown.

--ro.3.,.

rd

O m . - ~ ~......

2·5m.----

:

444 mm

~

HOLE.

254 m.m 1.D, F.R.P. CR5\~G fllTH 'LINE

GRIIVEL.

LOC.K' J"OINi.!> ,

PACK

SCHEME DESIGN Groundwater Schemes have been designed to include a single collector main running parallel to the coastline about 1.5 km inland. Each scheme will consist of 10-13 shallow wells constructed to a depth of up to 60 m. Some wells will be clustered and initially operated by direct injection into the water mains. Collector mains will only be constructed at a later date when a central collection and treatment system becomes viable. Each production bore will comprise a variable speed submersible pumping unit with associated drive gear to produce constant flows up to 5000 kL/day at variable head.

38·9 m.- - - -

F.R .P. TO 5.5, 254mm I .D . .5 ,5, PIPE

t--+i-- J "OIN -

42·Zm.----

2B~ mm 0.D."' 250 "'"' l.D. S. S. .:ICRE.EN - l·Om"' IIPERTURE. 4B•2B

m.----

254 mm l.D . 5.5 . PIPE.

~O·Z& M - - - -

288mm O.D.x 250mn, I .D. 5.S. SCREEN- 1·0 mm APERTU~E.

.5G<¼m.----

254 rnm I.D.

58·.3!o""-----

S.S. PIPE.

28!: "'m O.D. x 2S0m"' l .D. .:,,5 ,

WATER TREATMENT AND COST The ground water does not need treatment to meet NH & MRC guidelines, however, it is proposed to partially sequester the water to mask the relatively high hardness. This process will involve the dosing of a sequestering agent (Calgon) to inhibit the scaling of calcium carbonate in hot water systems. This action has the effect of lowering the Langelier index. Chlorine gas for disinfection and fluosilicic acid for fluoridation will also be added to the water.

38

WATER December 1992

5C~Ef:N - l · OmM I\PERTURE.

',&,44,...__ _ __

C~ME: NT

I".

ALL

2, ,

CENTRP,L l:,ER ~

Fig. 3 -

.!>TAll'iL.E.~~

STEE.L. U:'>E.D

AT

1::,

Gf:nt:>E.

~"'

PLUG - 0·3-m LONG

~•.

Cf:NTR E6

(.qppfl.QX . )

Production bore

Continued on page 43


TECHNOLOGY

GROUNDWATER FWW NEAR SHALWW LAKES: NEW INSIGHTS AND IMPLICATIONS FOR MANAGEMENT by L. R. TOWNLEY and J. V. TURNER SUMMARY This report presents the findings of a three-year study funded by the Water Authority of WA, the Environmenta l Protection Authority of WA and LWRRDC. Although the study focussed on lakes and wetlands of the Swan Coastal Plain near Perth, the results can be applied to a wide range of types of surface water bodies, including rivers, streams, channels, canals and drains. The results of our research demonstrate the importance of controlling land use activities in areas both upgradient and downgradient of lakes and wetlands. It is well-known that the boundaries of surface water basins and groundwater systems do not coincide. We have shown that most of the larger lakes on the Swan Coastal Plain near Perth receive gro undwater which has entered the unconfined aquifer as recharge up to 15 km away, at the top of the regional groundwater mound. When recharge is high, reverse flow regions can form on the downgradient sides of wet lands, thus supplying water in a direction opposite to the average regional flow. The aquifer volume from which groundwater eventually discharges into a water body is known as its capture zone. Conversely, the aquifer volume which contains recharge from a water body is known as its release zone.

OBJECTIVES •

• •

The objectives of the study were: to develop hydrological modelling tools which would allow us to predict the size and shape of the groundwater capture and release zones of any surface water body of interest. to understand fully the two- and threedimensional groundwater flow patterns which occur near surface water bodies. to verify model predictions using a variety of physical, hydrogeological, chemical and stable isotopic measurements in the field, to develop methods of including threedimensional effects in the twodimensional plan models normally used for simulating regional groundwater flow, and to investigate management issues, such as rates of subsurface contaminant and nutrient migration towards wetlands.

GROUNDWATER FWW PATTERNS A major goal in our research was to define capture and release zones. We have confirmed the fact that wetlands on the Swan Coastal Plain generall y act as f!owt h rough lakes. That is, they receive groundwater through bottom sediments on

40

WATER December 1992

their upgradient sides and discharge lake water to the unconfined aquifer on their downgradient sides. We have systematica ll y simulated groundwater flow two-dimensionally in

Fig. l lake.

Sc hematic diagram of a flow-through

vertical section, two-dimensionally in plan, and in three dimensions. By computer modelling, we have obtained a number of key results: Flow patterns in vertical section: effects of lake geometry The groundwater flow pattern near a surface water body depends largely on the geometry of the water body in relation to the aquifer. We describe the geometry by simple ratios such as the length of the water body in the direction of average regional gro undwater flow, divided by the thickness of the aquifer. A second important ratio involves the width of a water body, in the direction perpendicular to the direction of average gro und water flow. Water bodies which are short re lative to the aquifer thickness receive water from a layer of the aquifer close to the water table. In an isotropic aquifer, a water body with length equal to the aquifer thickness draws water from the top half of the aquifer. A water body five or ten times longer than the aquifer thickness draws water from virtually the whole thickness of the aqu ifer, and discharges water to the same depth. The simplest way to understand these results is to think of each droplet of water following "short " lake

[I

~ +

I[ "long'' lake

EI

_,, __/"-.____-

IE

Fig. 2 - Effect of lake length on the depth of capture and release zones.

Both authors are with the CSIRO Division of Water Resources in Perth. Dr Lloyd Townley is a Senior Research Scientist. He graduated BE (Civil) from The University of Sydney in 1976. MS (Environmental Engineering Science) ,a from Caltech in 1978, and PhD (Hydrology and Hydrodynamics)from MIT in 1983. Dr Jeffrey Turner is a Principal Research Scientist. He graduated BSc (Chemistry)from The University of WA in 1975 and PhD from Flinders Univers ity (Isotope Hydrology), in 1980.

. the path of least resistance from its source (in a recharge area) towards its discharge point (a distant river or the sea). It is easier for water at the base of an aq uifer to rise 50 m into a wetland, to travel hundreds of metres horizontally in the water body and then to flow 50 m downwards again, than to travel hundreds of metres along the bottom of the aquifer, where there is negligible driving force becase the water surface above is flat. The depth of water in a surface water body has little effect on the amount of water which flows through it. Similarly, for a lake of constant area, the dynamics of water level fluctuations are not influenced by actual depths. Lakes and wetlands on the Swan Coastal Plain are so shallow that their depth is negligible with respect to aquifer thickness. It is the latter, in relation to lake length and width, which controls groundwater flow. For seasonal wetlands, changes in water surface elevation are intimately tied to changes in surface area. From a physical point of view, the effect of fluctuating area is to cause fluctuations in geometry (as defined above) and therefore to modify the depth and width of capture and release zones. Effects of aquifer resistance The effect of a resistive lining, such as silt or peat, is to make a water body behave as if it is shorter in the direction of average


ground water flow. The net effect is equivalent to a shortening of the effective water body length by a factor unlikely to exceed two. Similarly, the effect of aquifer anisotrophy is to make a surface water body appear shorter by the square root of the anisotropy ratio, i.e., the ratio of horizon ta l to vertical hydra ulic conductivities. Effect of recharge The effect of regional recharge is sign ificant, as we have discovered literally dozens of possible flow regimes which can occur under different circumstances. One configuration, which we expect to occur in winter months when recharge occurs, is that groundwater on the downgradient side of wetlands can flow in a direction opposite to the regional flow. This reverse f low zane is driven by a local water table mound which forms downgradient of the lake. This has important impbcations for the definition of buffer zones, because it indicates that both gro undwater and surface water can flow back into a wetland from its downgradient side. Flow patterns in plan An isolated lake intercepts a width of the regional flow roughly twice as wide as the lake itself. The tendency for a lake to attract groundwater can again be explained in terms of the path of least resistance for a droplet of water. Several lakes clustered a long a line perpendicular to the direction of regional gro undwater flow will intercept much of the approaching groundwater at shallow depths. If lakes are separated by less than twice their widths, effectively all of the sha llow groundwater will be captured . The depth of captured groundwater will still depend on the lengths of the lakes in the direction of regional flow, relative to aquifer thickness. Modelling tools We have developed numerous tools for identifying groundwater flow patterns near surface water bodies. An interactive program called FlowThru [Townley et al., 1992] for 386 PC's and Macintosh computers has been developed as a tool to assist in visualisation of groundwater flow patterns in a vertical section. Particle tracking software has been developed for use in plan and in three dimensions. By systematically comparing results in plan and in three dimensions, we have developed two methods for representing lakes in regional plan models. The first is based on enhanced transmissivities within the boundary of a lake. The second uses a two-layered modelling approach with Jakes represented as a highly conducting layer with effective porosity set to unity.

FIELD VALIDATION Deuterium and oxygen-18 concentrations in an open water body are enhanced by the process of evaporation. Thus deuterium and oxygen-18 levels in gro undwater on the downgradient side of a lake allow us to determine the geometry of its release zone [Furner et al., 1984). Comparing the depth of the release zone with model results allows

~owergup Lake - Deuterium - o2H( 0 t 00 ) Generalised Cross Section Vertical Exaggeration: 10 Screen Position: •

40

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-9.3

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-6.6

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7.5

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380000 0.5 km

Fig. 3 - Distribution of deuterium in a vertical section through Nowergup Lake, showing its release zone.

us to determine the effective aquifer anisotropy and then to predict the depth and width of the capture zone. Similar results can be achieved using concentrations of conservative dissolved ions such as chloride. A series of lakes in the direction of regional flow will resu lt in the outflow from one becoming inflow to the next. Natural chemical tracers have allowed us to observe such behaviour on the Swan Coastal Plain.

NUTRIENT TRANSPORT AND BUFFER ZONES The health of surface water bodies is adversely affected by inflows of nutrients (nitrate and phosphate) from the unconfined aquifer. This was a primary motivation for our study, but we now believe that the dominant source of nutrients for wetlands on the Swan Coastal Plain comes from surface drainage rather than groundwater inflow. Our abi lity to identify capt ure zo ne s is app li cable to other pollutants such as hydrocarbons which may be transported over significant distances in the subsurface. There is no clear definition of a buffer zane from a hydrological point of view. The only way to isolate a water body from waterborne contaminants, to keep it in absolutely pristine condition, would be to ensure that no development takes place with in the surface water catchment of the water body, and also within its groundwater capture zone. The likely reality is that absolute protection will never be possible. But for the first time, our results allow predictions of the size of gro undwater capture zones.

FURTHER READING Early modelling results are described by Nield and Townley (in press). The final report for our study is nearing completion, and numerous manuscripts are being prepared.

ACKNOWLEDGEMENT Significant contributions to this work have been made by Simon Nield (now with Mackie Martin & Associates) and by Anthony Barr, Michael Trefry, Ken Wright,

Vit Gailitis, C hri s Harris and Co lin Johnston (all of CSIRO). Field data for Nowergup Lake are from bores constructed by the Geological Survey of W.A.

REFERENCES eild, S.P., a nd Townley, L. R. (in press). A fram ework for qu a ntita ti ve anal ys i of surface wa ter -;-- a groundwater interaction , I: Flow geom etry 111 a vertica l section , accepted for Water Resources Research. Townley, L.R. , Ba rr, A.O., and Nie ld , S.P. (1992) . FlowThru : An internactive program for calcu lat111 g groundwater now regimes near sha llow surface water bo di es, CS I RO Division of Water Resources, Technica l M emorandum 92/1, Version I. I. Turner, JV., A llison. G.B. , a nd Holmes, J.W. (1984). The wa ter ba la nce of a sma ll ,la ke using stable isoto pes a nd tri tium. JHy dro l., 70, 199-220.

Letter to the Editor From Peter Wotton, 3 M Energy Control Products

Dear Sir, In the October edition of 'Water Journal' in the account of the presentation given by David Magill of Avanti on 'inline sewer grouting', comment is made that this system may offer some health & environment concerns. Readers should be advised that these relate solely to acrylimide and acrylate grout systems and not to water curing urethane grouts. Unlike the acrylic based grouts which are large ly monomers (i .e. sing le sma ll molecules) and so are liable to physical and chemical erosion, the urethane grouts form stab le long chain polymers which cannot . easily be eroded. Indeed the Scotchseal urethane grouts have been approved by the EPA in the USA for use in potable water supplies for some years and have recently been approved by the Water By-laws Advisory Service in UK and also by the Hong Kong authorities for a similar function. Urethane grouts are simply not under threat in America or other parts of the world. 'All grouts ain't grouts!' Your faithfully P. Wotton

WATER December 1992

41


TECHNOLOGY

THE GREAT ARTESIAN BASIN A NEED TO CONSERVE WATER by J. R. HILLIER INTRODUCTION The Great Artesian Basin occupies about 20 per cent of the Australian Continent (Figure 1). It is a sedimentary sequence reaching a thickness of over 2000 metres, with several distinctly different aquifers occurring in the sequence. Water from the basin is directly responsible for the agricultural development of the area. It is the main supply for stock and domestic supplies on properties, and is used by many towns. Water flows naturally to the surface throughout much of the basin, with the pressure which causes this flow one of the basin's greatest assets in the remote grazing lands. However, this great natural feature is also the basin's greatest threat, as free flowing bores give the impression of a limitless resource. Many bores, because of a combination of poor bore construction, poor maintenance, corrosive water and indifference by owners waste huge quantities of water. Distribution systems often consist of poorly maintained drains and sometimes natural drainage lines, with the result that 85 per cent of the water which currently flows from the basin is wasted. Obviously, this wastage of such a valuable resource is unacceptable.

EARLY DEVEWPMENT The first recorded bore to obtain water from the Great Artesian Basin was drilled near Bourke in New South Wales in 1878. Within a few years, early geologists had formed first impressions of the enormity of this resource and bores were being drilled throughout the basin. By 1900, in Queensland alone some 670 bores had been drilled with total flow estimated at 365 000 megalitres/year. No bores were controlled - all flowed at their full capacity, some up to 10 megalitres/ day. Although creeks were widely used for distribution of the water from the first drilled bores, as the structure of the basin became better understood bores were drilled on higher locations and water distributed by drain systems. Many properties were often served by one bore, with drains over a 100 km in length. By 1915, the flow from the basin peaked at 750 000 megalitres/ year. Although bores continued to be drilled, the reduction in bore discharge capacity resulted in an overall reduced discharge from the basin (Figure 2).

John Hillier graduated from the University of Queensland in 1972, having worked as a technical assistant in groundwater before that. He continued his professional career working throughout Queensland on all aspects of groundwater investigation and assessment. He is currently Manager, Groundwater Assessment, Water Resources Commission, Queensland Department of Primary Industries, Brisbane.

ASSESSMENT OF SUPPLIES The very noticeable reduction in individual bore flows was a cause of concern from an early stage of development. Landholders saw the rapid decrease in the initial large flows and wondered if the basin would soon run dry. Monitoring of flows and pressures has been carried out on a basin-wide scale since 1910, with Queensland completing a major review of the sustainability of the basin in 1954 (Queensland Government, 1954). Some of the major conclusions of this report were: • There appears to be sufficient water available at the intake areas to accommodate adjustments in the hydraulic gradient. • The present annual flow from all bores is equivalent to a depth of about one-fifth of an inch (5 mm) over the assumed intake area, as compared with an average rainfall of some 25 inches (635 mm). • If all properties were served by piped supplies and the artesian discharge could be regulated to the actual requirement of stock, the discharge from bores could be reduced to less than one-tenth of the present flow . . . • • .. . the benefits which would result from a stringent conservation program are not sufficiently great nor sufficiently concrete to justify a recommendation that such a program be undertaken. • . .. there is no fear that the basin will be exhausted. The report concluded with general findings which stated: • The investigation has shown that although artesian diminution in Queensland constitutes a disability, its incidence, particularly from the economic viewpoint, is far less serious than was feared in many quarters when the investigation commenced. The disability should not increase to any great extent in the future if effect is given to the recommendations and suggestions contained in this report. As bores cease to flow, adequate supplies of water can in general, be made available by pumping from the bore which has ceased to flow and by the provision of other artesian or subartesian bores or excavated tanks. The investigation has also revealed that the chief problem for the Government is to ensure that the flowing supplies are utilised in the best interests of all concerned.

WESTERN AUSTRALIA 2000

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DISC HARGE FRO M All FLOWING A RTESIA N BORES

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1500

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Fig. I - The extent of the Great Artesian Basin

42

WATER December 1992

Fig. 2 - Artesian bores in the Queensland section of the Great Artesian Basin


Reviews since this report have tended to confirm the findings. Monitoring has shown the rate of reduction of flows has decreased and the basin is approaching an equilibrium situation. However, large quantities are still being wastect: Surely this water can be more beneficially used.

CURRENT STATE OF THE BASIN As the large flows from bores decrease naturally, it is obvious that the basin is approaching some sort of equilibrium. But is it really an equilibrium? Is recharge actually becoming equal to discharge? The more we learn about the Basin, the more this type of equilibrium can be questioned. Much work has been carried out to increase our understanding since the 1954 report. Within Queensland, the Water Resources Commission, the Geological Survey of Queensland, and the Bureau of Mineral Resources have all contributed significantly. Forty years of monitoring since this report gives an insight into basin performance which was not available to those workers. The work carried out in the last 20 years includes age dating of water, which shows water in excess of 1 million years old (Torgerson et al, 1991), reinterpretation of the geological sequences, petroleum drilling, geophysical logging programs, better mapping and computer modelling. Knowledge has increased dramatically and now is being drawn together. Reassessment now will take considerable manpower and time, but will use much data not previously available and consider aspects not previously considered. Estimates previously used for recharge in intake areas are being checked by drilling and measurements. Assessment is being made of deeper, previously unused aquifers. Water quality will be examined in detail to determine present and past flow patterns. The end result of reassessment, though, appears obvious - a large volume of water exists in storage which is unlikely to be significantly depleted by current practices in the foreseeable future.

developed and improved from existing metftods. Down hole cameras are being used to visually inspect problem areas at depths down to 500 metres. More heat resistant and stronger inert casings are being developed, and better techniques are being used in physically repairing and grouting of bores.

FUTURE SITUATION Every attempt is being made to repair the bores in such a way that they are permanently controllable. The bores will be subject to regular inspections to ensure that they are kept in good condition. A network of bores to be used for monitoring has been established basin-wide. Already the results of rehabilitation can be seen as pressures are increasing in areas where groups of bores have been controlled. Interest is now being shown in many areas in replacing the drain systems with pipelines, tanks and troughs. The benefits are numerous. Wastage would be reduced to a minimum, watering points can be controlled, thus helping to reduce feral animals, and the spread of such weeds as prickly acacia can be slowed. Significant property management benefits also exist in piping the water. These include better stock control, improved water quality as salt concentration by evaporation of water along drains cannot occur, and more efficient land use from distributing water to areas which could not be serviced by drains. As wastage is reduced, the opportunity to use the water for other purposes expands. More water could be used for town supplies, mining and manufacturing purposes. Where the quality is suitable, small irrigation plots can be established to provide fodder in drought times. In a dry continent such as ours and in areas where surface storage sites are virtually non-existant, this water is too valuable to be allowed to run to waste.

ACTUAL WASTAGE

REFERENCES

The total discharges from bores within the basin in 1987 was estimated by a Sub-Committee established by the Australian Water Resources Council (Woolley et al, 1987) as 1220 megalitres/ day, with waste estimated at 1040 megalitres/ day. Although most of the actual wastage is caused by inefficient distribution systems, a high proportion of bores which supply water to these drain systems cannot have their flow controlled and water flows to swamps and creeks. Over much of the basin, the water is corrosive to steel casing, or corrosive water or clays encountered at shallow depths cause corrosion of the casing from the outside. Many bores leak with flow coming to the surface outside the casing or leaking into shallow aquifers. Headworks are often corroded to the extent where they cannot be used to restrict flow. Significant savings in water could be made if bores could be controlled to the requirements of a well maintained drain system.

Hazel, C.P., (1991): Great Artesian Basin Rehabilitation Program. Queensland Government, (1954): 'Artesian Water Supplies in Queensland; Report following First Interim Report (1945) of Committee appointed by the Queensland Government to investigate certain aspects .j'elating to the Great Artesian Basin (Queensland Portion) with particular reference to the problem of diminishing supply, Department of the Co- ordinator General of Public Works Queensland, Parliamentary Paper A56-1955. Torgersen, T., Habermehl, M.A., Phillips, F.M., Elmore, D., Kubik, P., Jones, B.G., Hemmick, T., and Gove, H.E., (1991): Chlorine 36 Dating of Very Old Groundwater, 3, Further studies in the Great Artesian Basin, Australia, 'Water Resources Res., 27, 3201-3213, 1991. Woolley, D, et al, (1987), AWRC-Report to Groundwater Committee of Great Artesian Basin Sub-Committee.

REHABILITATION PROGRAM A program to rehabilitate these uncontrollable bores has been initiated by the Queensland, South Australia and New South Wales Governments in conjunction with the Federal Government, who included it in the Federal Water Resources Assistance Program (FWRAP). Funding is provided for bore investigation and rehabilitation on a 40:40:20 basis by the State and Federal Governments and the Landholders in Queensland and New South Wales with slightly different arrangements in South Australia. The repairs needed to bring bores under control vary from relatively simple headworks repairs to complete .relining. Sometimes it is cheaper to plug old bores and drill new ones. Extensive use is being made of inert casing materials. Fibreglass and various plastics have been used, and recently continuous lengths of polyethylene piping have been used as a liner. However, all these inert casings are more difficult to use than steel in the majority of circumstances. The program has only been operating for a few years and techniques and materials are still being developed. Geophysical methods to better investigate actual down hole conditions have been

Continued from page 38

D.HOPKINS

The source cost of the water using bore clusters and direct injection is 15 c/kL and allows the deferral of capital which would have been required for the next cheapest source. The next cheapest source has a unit cost of 19 c/kL.

URBANISATION The area is partly urbanised with the remainder zoned urbandeferred and full urbanisation is expected to be achieved in about 20 years time. Urbanisation and associated development of shopping centres and commercial areas results in low level pollution of the groundwater. Domestic gardens leach fertilisers to the water table together with low levels of pesticides and commercial centres can discharge a variety of pollutants. The Water Authority has gazetted the area as an Underground Pollution Control Area with associated by-laws to control land use activities. Industries such as intensive animal feedlots and metal plating factories are not permitted. Service stations are required to protect underground storage tanks from leaks, usually through a double lining system. While development of groundwater schemes in urban areas is not preferred, the schemes have a low environmental impact and present a low cost opportunity to harness a water resource which would otherwise be under-utilised .

WATER December 1992

43


MANAGEMENT The Industry Commission Report (July 1992) Water Resources and Waste Water Disposal by Joanne Henshall An occasional series from Ma!lesons Stephen Jaques, Solicitors and Notaries

THE FINAL REPORT Incidents such as the blue green algae blooms of recent years and expanding popu lations have highlighted the limits of water resources within Australia. In this climate, the Industry Commission has issued a final report on 'Water Resources and Waste Water Disposal' in Australia. The report emphasises two main principles: • effective pricing of water, sewerage and drainage services (WSD services); and • increased cost recovery, as the preferred measures for improving the efficiency and sustainability of Australia's water resources. The Industry Commission report states that: 'Reform is urgent. The problems now confronting Australia in the water area demand an end to the political expediency which has so often thwarted worthwhile reforms in the past.' However, the diverse nature of water authorities, difficulties in implementing many theoretical concepts and conflicting priorities and objectives result in the report only making broad recommendations. In many instances, the report considers the various options for reform in a particular area but the suitability of a particular course may depend upon so many variables that the Commission has simply stated that certain options should be explored by the authorities and has refrained from a definitive statement of a correct course. 34 recommendations for reform under six broad headings are made by the report concerning: • the pricing of urban water services; • the pricing of irrigation water and drainage; • general pricing issues; • institutional arrangements; • tradeable water entitlements; • environmental matters.

PRICING REFORMS The report focuses upon appropriate pricing and costing practices as a means of ensuring that the best use is made of present systems and that the timing and nature of any future investments are guided by appropriate costing and pricing. As a general principle, the Industry Commission believes that the WSD service provision should be underpinned by an objective of full cost recovery. The Industry Commission has recommended that:

44

WATER December 1992

'Except where subsidisation of costs is an explicit government policy, investment in new urban WSD infrastructure should be premised onfull cost recovery, including the designated rate of return on capital. The authority concerned should consider whether the willingness to pay of customers who will benefit would be sufficient to permit full cost recovery, if differential charges could be set for those customers.' This policy of full cost recovery requires that prices for urban WSD services include a component for environmental damages or costs. Two approaches to pricing structures are examined in the report - those of marginal cost pricing and two part tariffs. The first structure was considered inappropriate due to practical problems in its implementation. For urban authorities, the report urges authorities to pursue full cost recovery for the provision of water by a two part tariff scheme. This tariff would consist of an access charge plus a usage charge for each kilolitre of water supplied. Authorities would be required to set the usage charge to cover the cost of making additional water available with a loading to ration supply when capacity in the system is scarce. The access charge is a type of residual charge to be set so that the total price achieved is the desired revenue yield over the life of the asset system . Seasonal pricing arrangements and time of day pricing must also be investigated by WSD authorities. The Commission recognised the different circumstances occurring throughout Australia and recommended that each authority consider seasonal water pricing either through seasonal charges or through tiered usage charges. For large centres, time of day pricing is also to be examined. The report also requires WSD authorities to consider charging for sewerage services according to the percentage of water returned to the system and trade waste discharge charges based upon the quantity and strength of the waste discharged. The principle of full cost recovery underpinning many of the Industry Commission's recommendations begs the questions 'What costs should be covered by prices?' and 'What is an appropriate rate of return?'. The Industry Commission recommends that prices for urban WSD services be set at a level sufficient to cover operating, maintenance, administrative and depreciation costs as well as the target rate of return on the asset base. The target real rate of return for investments in urban WSD infrastructure is

set by the Commission at So/o with the rate to be increased if a higher risk is demonstrated for a particular authority or project. Where the costs of environmental damage associated with the use of WSD services can be identified and quantified, these costs are also to be reflected in pricing. Any community service obligations not fu lly government funded or poor investments, are to be written down and capitalised against existing asset values in calculating the asset bases of authorities. The report also emphasises that not only should WSD service providers seek full cost recovery through pricing but also seek to minimise their costs . Thus, the report recommends required annual increases in the rate of return of authorities to be imposed prior to the achievement of the target rate, and that revenue caps be imposed to ensure that costs are reduced and benefits passed on to consumers. Irrigation accounts for approximately three quarters o~ all water used within Australia. Hence, the need for irrigation water resources to be maintained, well managed and priced appropriately is crucial. •· Under the report, public investment in new irrigation schemes would only proceed if an authority could publicly demonstrate that demand for water would support prices sufficient to cover costs including a return on capital. Again, the minimum rate of return to be applied is 5%. Irrigation water supplied from existing bulk water systems is to be priced to cover the irrigator's share of costs of operating and maintaining those systems including dams and storage areas. Where possible, the Industry Commission recommends that a return on capital should be sought and that the costs of environmental damage from irrigation be included in prices. Bulk water suppliers are to immediately increase the price of water to a commercial level and earn a real rate of return of O to So/o p.a. The Commission does recognise that adjustments imposed on the rural sector by the change to full cost recovery pricing will be significant. Hence, in calling for an immediate increase in the price of bulk water to commercial levels, the report envisages that irrigators would be subsidised in the short term by an explicit government payment to the bulk water supplier. A need for further payments to provide incentives to irrigators to privatise and accept ownership of irrigation systems is also envisaged . The phasing out of property-based access charges for water and sewerage which has already begun in some states was approved


by the Commission. Throughout the report, the Industry Commission emphasises the need for the speed of reform to increase and for water services to be charged for at full cost of provision . Any community service obligations imposed on water authorities are to be identified, valued and directly funded by the government concerned, so that the reason for subsidisation of certain facilit ies is clearly outlined and understood . The complex problem of valuation of assets by water authorities is also addressed in the report. The preferred method is that of the AWRC's Modern Equivalent Asset Methodology which would require changes to general accounting requirements in moving to a system of current cost accounting.

INSTI1UTIONAL ARRANGEMENTS To complement and reinforce the pricing and cost reforms, various administrative and institutional changes are proposed by the Industry Commission. The report states that these changes are designed to ensure that costs of providing WSD services are minimised and that WSD providers adopt practices in line with community goals for water quality and protection of the environment. The corporatisation of WSD service providers is not recommended as a blanket reform by the Commission, but rather put forward as a possibili ty to be assessed in each case. Only if gains beyond mere administrative reforms can be made should a WSD service provider pursue corporatisation. The report emphasises the need for a change in the focus of WSD providers to a commercial environment. In the Commission's view, this entails a clear enumeration of the responsibilities of authorities such as clarification of their water management, service provision and regu latory functions and defining a process for resolving conflicts. Accountability of WSD agencies and clear lin es of accountability of governments for the WSD agencies are proposed and performance results are to be made publicly available. To reduce costs, the report argues that WSD service providers should be allowed to use the best value inputs, whether these inputs be external or internal to the agencies. Amalgamation of service providers should be examined to see if economies of size may be obtained . The report also recommends that the management of public irrigation distribution systems be devolved to regional bodies with a view to their privatisation .

TRADEABLE WATER ENTITLEMENTS Until recently, water a llocations were attached to land rather than to an irrigator. Since 1983, various states have introduced transferable water entitlements, and the report adopts this measure and proposes that permanent water transfers be introduced into all irrigation systems both for groundwater and surface water. The Commission also suggests transfers of water

entit lements between water schemes in appropriate circumstances. The Commission¡sees adjustments of the irrigation sector as a necessary outcome of more efficient pricing and allocation of water. Thus, arrangements to allow for the transfer of water from irrigation to other uses are recommended given the environmental damage caused by irrigators and the need for the distribution of present water resources to meet future needs. To reward those who conserve water, the Commission recommends the introduction of continuous accounting of water entitlements wit hin the release sharing system. Where security of supply is an issue, the report recognises that capacity sharing may provide a superior form of ri sk management. Auctioning of new and old water supplies is also encouraged by the report.

the report also prop~ses that some results of the monitoring should be released in a form readily accessible to the media.

SUMMARY Throughou t the report, the Industry Commission emphasises the need for continuing and increased reform of water resource services despite the political pressures which will no doubt flow from the adjustments propo sed. The Indu stry Commission's priority reforms are those of pricing reform, increased cost recovery and increased accountability and commercial orientation of WSD service providers. In the Commission's words 'hard decisions must be taken now to avoid imposing even bigger costs in the future'.

Book Review ENVIRONMENTAL MATTERS The report also addresses concerns for the environment in conjunction with water resource reforms. Both market based measures and continued regulation of water services are proposed by the Industry Commission. Water needed for environmental purposes can vary due to changes in geographical or other features (for example, whether trees are logged or not, the need to flush out a river system), and is often not well defined. Hence, the Indu stry Commission recommends that the States formalise water entitlements for environmental purposes and allow water for the environment to be purchased from licensed holders when systems are fully or near to fully committed. To reduce the cost of meeting environmenta l goals, the concept of tradeable discharge permits is put forward by the Commission. Such permits are not yet used officiall y anywhere in Australia but a system of salinity credits between New South Wales, Victoria and South Australia is thought to be a suitable application of this type of system . The permit system wo uld involve a quality standard for the whole receiving environment being set and the issuing or auctioning of permits entitling discharges of waste or effluent such that the overall standard is met. In some situations, the Commission also considered that pollution taxes may assist to reduce the adverse environmental impact on water use and waste water disposal. The Industry Commission recommended an assessment of benefits and costs including an assessment of a lternative technologies prior to the setting of a standard by regulations. This process is to involve canvassing of consumers' willingness to pay for improved environmental outcomes and consideration of issues such as sustainability and intergenerational equity. To ensure that failures by WSD service providers to meet environmental standards are made public, the report recommends environmental monitoring by an independent body. To try and improve the public's knowledge of water related issues,

Dams and Environment, Socio-economic Impacts ICOLD Bulletin No. 86, Published by the Committee on the Environment of the International Commission on Large Dams Soft Covers, 43 pp, $29.00 Bulletin No. 86, the latest in a series of ICOLD publications on 'Dams and Environment', deals with social and economic problems arising before, during and after the construction of large dams. It is largely based on reports submitted to the 16th !COLD Congress in San Francisco in 1988 on the subject 'Reservoirs and the environment - Experience in the Managing and Monitoring. The Bulletin draws attention to the need to adequately evaluate environmental considerations and especiall y lo cal economic and social impacts during the planning of any large dam. It is necessary to be aware that well balanced successful management of socio-economic considerations requires evaluation in a comprehensive perspective which extends well beyond the immediate project. Hence attention is drawn to the need for public consultation early in the planning process, and for assessment of the effects of rapidly increasing the size of the local labour force and for new skills to be taught to local workers. Resettlement, badly handled at times in the past, must be properly addressed, as must consideration of cultura l landmark s and heritage resources. Other subjects dealt with include impacts in the post-construction phase, health impacts, particularly the need to counteract the effects of water-borne disease, and mosquitos and harmful molluscs eliminated. Extensive references are provided and the publication is a useful guide to the many socio-economic impacts and problems which need to be considered in the development of a large dam project. Copies of the Bulletin No. 86 and other !COLD publications are available from C.D. Sheedy, ANCOLD Treasurer, NSW Department of Water Resources, PO Box 3720, Parramatta, NSW 2124. HANS BANDLER

WATER December 1992

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SEMINARS

COMMUNITY CONSULTATION IN EFFLUENT DISPOSAL the QLD Branch Regional Conference A report by Ian Betts This year's conference was held in Toowoomba on the weekend of November 6-8 . The conference theme was "Community Consultation in Effluent Disposal - Let's Talk About It." The organising committee of Michael Simms, Peter Beavers, Ernst Bruynis, Murray Clewett and Peter Moss performed an excellent job in arranging a wide variety of interesting speakers for the conference. The program was opened by Alderman Clive Berghofer, the Mayor of Toowoomba, who outlined some of the issues his Council faces in providing water and sewerage services in Toowoomba (It is unclear whether the conference had any bearing; however, several days later Alderman Berghofer resigned from Council.) The first keynote address was delivered by Dr Geoffrey Syme. CSIRO, who suggested that current public involvement in matters of effluent management is largely case by case. Dr Syme believes that better planning outcomes would occur if there were greater public involvement in the general policy area as well as in specific projects. In addition, a clearer sense of direction from professionals is required to avoid confusing the public. Finally, there is a need to design public involvement programs with a better understanding of current community knowledge and attitudes toward effluent, and a greater awareness of what the community perceive as sufficient involvement. Dan Owen, Community Projects Pty Ud, proposed that the public will become involved in proposals for change whether they are invited or not. Public involvement provides a route to identify proposals with the public interest. This tack avoids problems and often results in better solutions. Mark Rickets, DEH, discussed the public consultation program conducted by DEH when developing a new program of environmental management for Queensland. The program involved meetings, calling for submissions and using key stakeholder groups to review submissions and assist in drafting the legislation. Mark outlined many DO's and DONT's in conducting a successful public consultation program. Community interaction in the selection of major new dam sites for SE Queensland was described by Ian Pullar, QWRC. Following protracted involvement with local community protest groups, Ian concluded that it was far better to try to manage the community involvement rather than trying to tough it out and cope reactively. Cr Bill Forrest, Redland Shire Council, considered that decisions by Council to install water meters, place the meters above ground within each property and the pricing policy were matters definitely not open to public consultation. There was, however, a need to inform the public on the decision to install meters, on the need for -water conservation and offering water saving advice. Cr R J Gihnour, Chairman, Murilla Shire Council, outlined the lack of public participation involved in the recent State Government decision to site a toxic waste landfill within the Shire. The "tongue in cheek" presentation described how this decision, made without prior consultation, caused considerable trauma within the local community. Paulina Semple, DEH, identified some of the processes currently used for community consultation/ participation and then presented two case studies; the David Gelatine plant proposal and the A J Bush rendering plant proposal, both in the same areas of Beaudesert Shire. Sue Salmon, ACF, opened her address with a gloomy picture of decaying cities resulting from contaminated water supplies. Long term water management planning is needed to avoid this scenario. Sue then emphasised the relative scarcity of water in Australia and concluded her talk with some thoughts of how to establish the community's need by an appropriate degree of involvement in decision making. Brad Farmer, Surfrider Foundation, outlined the background to the formation of the Foundation and the objectives of this organisation. The Foundation has developed a comprehensive set

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WATER December 1992

of coastal protection policies including the replacement of ocean sewer outfalls with total land re-use schemes. Brad concluded by extending an invitation to discuss with the Foundation proposed projects within the coastal zone, so that the concerns of the Foundation can be addressed in detailed studies for the project. Adrian Jeffreys, Wildlife Preservation Society of Queensland, gave some pointers to running successful public consultation programs. In particular: don't proceed with consultation if you are not¡ interested in what the public has to say; treat participants openly and honestly; and don't always expect the public to become involved - several different approaches may need to be made. John Gilmour, DEH, presented an outline of the Government's attitude towards public consultation/ participation in the policy making area. Stephanie Paul, Turnbull Fox Phillips, explained the importance and benefits of community consultation/ participation in the decision-making process. Stephanie then described how to go about getting community involvement and concluded with a case study involving effluent disposal in Maroochy Shire. John Simpson, QWRC and Ross Anderson, Hervey Bay City Council, presented a paper summarising the elements of public participation and the required degree of involvement, especially in wastewater schemes. The paper then described in detail the public involvement in an effluent re-use scheme at Pulgul Creek, Hervey Bay. This resulted in the scheme gaining a high level of public acceptance. Wally Wight, SKP, outlined reasons for hp.ving public consultation and suggested a process for controlling the agenda of a consultation program. A preferred approach involves talking with two streams; the general community and stakeholder groups. Wal's paper concluded with an outline of ho'¼ the preferred approach is best implemented. The formal conference concluded with a workshop session involving the consideration of a hypothetical toxic waste disposal project. The conference participations were divided into three groups with each group split in two; one to act as the bureaucrats proposing the project and the other representing groups affected by the project. The purpose of the workshop was for each pair of groups to commence a public participation program to discuss the proposed project. This workshop was a valuable experience for the participants and reinforced the ideas presented by the speakers during the Conference.

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Water Journal December 1992  

Water Journal December 1992