Water Journal September 1986

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SEPTEMBER 1986 JOURNAL OF THE AUSTRALIAN WATER AND WASTEWATER ASSOCIATIONwaterISSN 0310-0367Official Journal AUSTRALIAN WATER AND WASTEWATER ASSOCIATIONVol. 13, No.…
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SEPTEMBER 1986 JOURNAL OF THE AUSTRALIAN WATER AND WASTEWATER ASSOCIATIONwaterISSN 0310-0367Official Journal AUSTRALIAN WATER AND WASTEWATER ASSOCIATIONVol. 13, No. 3, September 1986 FEDERAL PRESIDENT A. Lloyd , G.H. & D., GPO Box 668, Bri sbane 4001 .FEDERAL SECRETARY G. Dooley, Bo x A232 P.O. Sydney Sth., 2001.FEDERAL TREASURER J . D. Molloy, Cl- M.M.B.W. 625 Lt . Collins St. , Melbourne, 3000. 'BRANCH SECRETARIES Canberra, A.C.T. M. Sharpin , Willing & Part ., P.O. Box 170, Curtin , A.C.T. 2605. (062) 815 811New South Wales M. Hann on, P.W.D. Sewerage Branch , 74 Philli p St. , Sydney , 2000. (02) 270 4488CONTENTS Viewpoint-R. M. Hillman, Chairman Water Authority of Western Australia . ... .. . ...... . .. . .......................... .. .. .5Association News, Views and Comments . . . .. . ...... . ........... .6IA WPRC News . . .. . .................... ..... ............ .... .12Augmentation of the West Pilbara Water Supply- The Harding Dam Project -R. J. Wark, G. C. Meink and C. R. Tenby ...... .. ...... .... .. .14Industrial Waste Disposal-Victoria -The MMBW Proposal ........ . ....... ....... . ... . .... ... .19Cape Peron Environmental Monitoring -P. N. Cha/mer and L. W. Edmonds20People-Conferences-Courses . .. .......... ....... ........... .26Products-Plant-Equipment .. : . .... ..... .. . ... . . .......... .. .27Swampy Odour in the Drinking Water of Perth, Western Australia -J. E. Wajon, B. V. Kavanagh, R. I. Kagi R. S. Rosich, R. Alexander and B. J. F/eay ............. ..... .28Products-Plant-Equipment . . ............. ... .............. . .34Water Hammer Alleviation - A Western Australian Case Study - Y. H. Ng and A. J. Gale ........ .. ........................ .35Calendar ..... .. ... . . . .... .......... ... ... ............ ..... . .38Victoria J . Park, Water Trai ning Cent re, P.O. Box 409, Werribee , 3030. (741 5844)Qu eensland D. Mac kay, P.O. Bo x 412, Wes t End 4101 . (07 44 3766)South Australia A. Glatz, State Water Labora tori es, E. & W.S . Pri va te Mail Bag, Salisbury, 5108. (259 0319)Western Australia Dr B. Kavanag h, Water Auth. of W.A. , PO Box 100, Leedervi lle 6007 (09) 420 2452Tasmania T. Denne, 675 Nel son Rd ., Mt . Nelson. (002) 23 2267 (A. H.)North ern Territory M. Lukin , P.O. Box 37283 Winnelli e, N.T. 5789.ED ITORIAL & SUBSCRIPTION CORRESPONDENCE G. A. Goffin , 7 Mossma n Dr., Eaglemont 3084 03 459 4346waterCOVER PICTURE The cover photo shows the recently completed Harding Dam and its reservoir, Lake Poongka liyarra. The works were constructed by Leighton Contractors Pty. Ltd. in 1983/84 for the Water Authority of Western Australia. The Dam supplies water to the towns of the West Pilbara region. Front cover photograph, courtesy the Water Authority of Western Australia; cost donated by Leighton Contractors Pty. Ltd.The statem en ts made or opinions expressed in 'Water' do not neces sa rily reflect the views of the Australian Water and Wastewater Association, its Coun cil or committees.WATER September, / 986IAugmentation of the West Pilbara Water Supply T¡he Harding Dam Project R. J. Wark, G. C. Meinck and C.R. Temby ABSTRACT The West Pilbara Water supply is the second largest country water supply in Western Australia. T he stimulus given to the region by the development of the North West Shelf Gas Project required major augmentation of the scheme and planning studies for augmentation of the headworks resulted in the decision to construct the Harding Dam and associated works. The Pilbara is an arid region with irregular rainfall, high evaporation and low topographic relief. The particular form of conj unctive use of the surface and underground resources adopted to overcome these problems is unique in this country. The remote location and the climatic conditions posed a number of problems in the construction of the 42 m high earth core rockfill dam requiring special attention which are described in the paper with the wide ranging environmental and social evaluations undertaken.INTRODUCTION The Harding Dam is located on the Harding River , in the Nort h of Western Australia. The dam, constructed in I 983 and 1984, is the first surface storage to be incorporated into the West Pilbara Water Supply (Figure 1). The original scheme, based on groundwater drawn from the Millstream aquifer, was first constructed in 1969 to meet the needs of the iron ore mining and export trade through the towns of Dampier and Karratha. In 1971 the scheme was expanded to supply water to Wickham and Cape Lambert, and is now the second largest country water supply in the State.R. J. WarkG. C. MeincklC.R. TembyBob Wark, B.C.E., B.App., Sc., M.l.E.Aust. is Principal Engineer Dams and Garry Meinck, A. W.A.l. T., M.l.E. Aust. is Supervising Engineer, Dam Projects, with the Water Authority of Western Australia. Both were involved in the planning and regional investigation phase of the West Pilbara Water Supply augmentation and in the detailed investigation and design of the Harding Dam. Colin Temby, B.E.(Hons.), M.S.C.E., M.l.E.Aust. is Principal Engineer, Water Supply Design of the Water Authority of Western Australia and was the Project Manager for the construction of the Harding Dam.DEMAND FOR WATER Projected Use The major component of water use in the West Pilbara is the domestic demand of the population. Following the initial rapid rise in the demand (Figure 2) which followed the development of iron ore mining and export, the demand remained relatively stab le during the late 1970s . However, in this initial domestic supply phase, the Nort h West Shelf Gas project has caused a marked increase in demand. Development of the export phase of that project in the late 1980s is expected to result in a demand for water of around 15 x 10â&#x20AC;˘ m' per ann um by the mid 1990s.Demand Management One aspect of the water industry in the Pilbara of considerable concern has been the high per capita consumption which approximates around 1500 m 3 /service/yea r - some two to three times the consumption rate in other comparable countr y towns. While recognising the social and recreational benefits derived by the communities from such water use , there is a need to conserve the scarce water resources of the region. Also significant economic and environmental benefits which can accrue as result of reduced need for supply capacity increases. Restrictions on Lhe use of sprinklers during the daylight hours have applied in the West Pilbara since 1974. Apart from an early initial impact, there is no indication that per capita water consumption has been reduced. While the restrictions are remaining in force it is fairly clear that they are not an effective tool for generating long-term reductions in demand. The pricing structure in country areas normally penalizes high water consumers but the problem in the West Pilbara is that many consumers enjoy significant free water allowances, the cost being borne by their employers, the major companies. Water consumption statistics indicate consumers with free water allowances use two to three times the quantity of water consumed by those paying for their own consumption. Changes to the pricing policies are accordingly unlikely to be effective and would unduly penalize those meeting their own water charges. The most effective demand management activities have been those of local committees and the Western Australian Water 14WATER September, 1986~ N IFigure 1. Locality plan.Reso urces Council. This work has shown consumers that it is possibie to generate a pleasant and attractive urban environment\20Year\1975·as'80'E:::, C C"'15.,,,,.-.,,,'Xs//,"';----90%150Q)§100>"OCC.Q"'Io 1oo i---- - - - - t - - - t - - - --E Q)0 Q)1995Conjunctive use with the Harding Dam'"---0' "''905;;;\- --.-- --"<-+-- ------,Decision to take ac tion:';90% Construction & commissioning of Harding Dam1990199510% 150 t--- - - - ~ ~ - - - - ~ - ---+- - ~ - - - - ~ 10%Yea rLEGEND- - Projected aquifer depletion volumes with Harding DamFigure 2. West Pilbara demand projection.with low water use gardens. The local population and the mining companies are now well aware of the economic and environmental benefits of reducing consumption and this is starting to become apparent.- · - · - Projected aquifer depletion volumes without Harding Dam - - - - - - Actual aquifer depletion volumeNOTES 1. Aquifer depletions are maximum va lue in any yea r. 2. Percentiles represent the probability that aquif er depletions would be grea ter than the va lue shown.MILLSTREAM AQUIFER The Millstream aquifer is a basin of calcrete covering a total area of approximately 600 square kilometres. The water surface is 20 to 25 metres below the ground surface and the saturated zone is up to 26 metres thick. The main water bearing calcrete is cavernous and the water flows freely to the extraction bores. Current estimates indicate that the primary calcretes have some 600 x 10• m3 of water in storage and total storage could amount to 1700 x Io• m3 • Due to the high lime content of the rocks forming the aquifer, the water is hard and the total soluble salts (TSS) content of water supplied to consumers is generally in the range of 900 to 1000 mg/ L. The aquifer is recharged naturally by direct rainfall, runoff from the surrounding hills and from flood flows in the Fortescue River, the estimated average recharge rate being 17 x 106 m3 / year. Water from the aquifer discharges through springs on the perimeter . These springs feed several large pools in the Fortescue River . One of the most important environmental issues occurs at Millstream where the flow from springs and permanent water supports a large variety of vegetation formations and their associated ecosystems (Figure 3). Many of these are unique to the area, the Millstream palm is of particular significance as major populations are found only in this locality . The palm together with the sedge and heathlands are among the most importarl1: ecological features. A National Park has now been created over the area of major environmental significance. As water supply extractions increase and water levels in the acquifer fall, natural flows from springs are decreased, reducing the supply of water to the pools and riverine forests. Supplementation of these flows by pumping from the aquifer has been an essential part of aquifer management policy for some time. Thorough understanding of the hydrogeological processes has been a key factor in the management of the aquifer system and has led to the successful development of the hydrologic model of aquifer behaviour. Using this tool it has been possible to predict with confidence the performance of the aquifer under a range of operating conditions, a factor which has been vital in the development of the water management strategies for the region.REGIONAL INVESTIGATIONS OF ALTERNATIVE RESOURCES Planning StudiesBy the late 1970s it was evident that the development of the North West Shelf Gas Project would have a major impact on the future water demand . Studies showed that , without augmentationFigure 3. Millstream aquifer performance.of the headworks, the reserves of storage available in the Millstream aquifer would be rapidly depleted. (See Figure 3) . Collection of the basic hydrological data and the assessment of the underground and surface water resource potential of the region began in the 1960s. Planning studi~s in the early 1970s showed that supply from surface water resources within the region was both feasible and economic. However, this work highlighted the need for a comprehensive review of the engineering (particularly the hydrologic,v factors), economic, environmental and social parameters to permit a multi objective assessment of the relative merits of the various alternatives. This work commenced in earnest in 1974 with engineering investigations of two dam sites on the Fortescue River. Consultants were engaged to investigate environmental aspects and the Western Australian Museum undertook the social assessments. In conjunction a number of public meetings were arranged and discussions held with various community groups. In 1976 the studies were broadened to include a thorough evaluation of the regional alternatives including both surface and groundwater resources . These investigations were completed by late 1977 so that the Government, in making decisions on augmentation the West Pilbara supply, could do so on the basis of firm planning data. Conjunctive UseAlthough development of the known groundwater reserves could double the nominal yield from the Millstream aquifer, to meet the sustained expansion of the region, utilization of the large surface water sources is necessary. Development of the surface water sources was complicated by three factors : • poor storage characteristics of the major dam sites, • high evaporation rates, • erratic stream flows. The combination of these three factors meant that none of the surface storages could supply significant quantities of water if operated as independent storages. These factors together result in rapid deterioration in the quality of water retained to provide drought security . The conjuctive use strategy has been adopted to utilize efficiently the surface resources, and involves top priority to using water from surface storage when water of suitable quality is available . The full water supply demand is drawn from the Millstream aquifer when the surface storage is depleted or contains unusable water. Operating this way, the bulk of the supply is WATER September, 198615drawn from the surface storage with the Millstream aquifer providing drought reserve. Environmental StudiesThe comprehensive environmental work carried out in the region was, in many cases, the first review carried out since the times of early exploration. While the environmental studies generated some very detailed information on the ecology of the region, they were primarily aimed at identifying the broad characteristics of each of the various surface and groundwater alternatives. In general, the surface storage proposals had the largest direct impacts and much of the effort was directed to evaluating these . Social Impact StudiesThe studies fairly quickly identified the impact upon Aboriginal culture of the various alternatives as the most significant aspect. Most of the early investigative work was undertaken by experts familiar with the culture and the traditions of the area. Ir, order to assess the impact of the proposed alternative developments on specific aspects of the culture, direct consultation between the project engineering staff and the local people was necessary. This led to a better understanding of the issues and had a significant bearing on the decision making process. s~Iection of the Harding Dam OptionThe Harding Dam proposal was found to be the most economic soludon of the alternatives studied. The impact on social values is low and the direct environmental impact of the dam and the reservoir was not high in absolute terms. The improved scope for -management of the Millstream aquifer resulting from a dam development was considered to be a more significant environmental consideration. The all groundwater alternative was some 2507o more costly than the Harding Dam, although it has a low direct social and environmental impact. The reduced scope for management of the Millstream environment was considered a serious disadvantage. Also, the average quality of the water supplied from groundwater would be inferior to that supplied from the dams.HARDING DAM In June 1981 the State Government approved in principle construction of the Harding Dam and at that stage, detailed engineering, environmental and social impact studies commenced. These led to the final detailed engineering design and included a review of the system yield and flood hydrology, field investigations and materials testing. The selected arrangement of the works is shown on Figures 4 and 5. Tenders for construction of the major civil works were called in October 1982 after approvals had been obtained under the appropriate environmental statutes. In February 1983 a contract was awarded to Leighton Contractors Pty Ltd for substantial completion by November 1984. The overall cost of the project, including the dam and ancillary works, pipelines and Millstream headworks was $45 million (1985 values) . GeologyFigure 4. Harding Dam -la. out of works.imum rainfall, with appropriate freeboard. The 12 hour duration storm gave the largest peak inflow flood of 24 200 ml/sec from a rainfall of 790 mm. However, peak levels in the storage were generated by the 36 hour duration storms with rainfalls of 1365 mm and a peak inflow rate of 19 200 ml/sec. The large flood surcharge (16 m) and flood storage causes significant attenuation of the flood peak, with peak design outflows amounting to just over 6000 ml/sec on the main spillway and 2300 ml/sec on the auxiliary spillway. EmbankmentsThe 64 x 10' ml capacity storage is formed by the construction of two 45 m high embankment in the river valley and a 15 m high auxiliary embankment closing off a saddle located south of the embankment in the reservoir flood zone. Both embankments have a central impervious core protected on both sides by sand and gravel filters supported by rockfill shoulders .The dam and reservoir are located in a group of pyroclastic rocks including tuffs, agglomerates and interbedded sandstones which have been intruded by a dolerite sill structure known as the Cooya Pooya Dolerite. The pyroclastic rocks occupy the areas of Excavation and Foundation Treatment low relief and the dolerite forms a hilly terrain with extensive scree Excavation for the rockfill foundation involved removal of the slopes. The dam is located in a gorge where the Harding River has scree, slopewash and alluvial deposits, as well as highly and comcut through the dolerite. The river valley is approximately 160 metres wide, with up to 9 pletely weathered rock. This exposed a foundation surface of metres of highly permeable river bed alluvium overlying the moderately weathered to predominantly fresh rock. Some local dolerite bedrock. Tuff occurred as rafted blocks within the excavations were required on the main embankment to remove dolerite sill structure, particularly on the abutments. Some out- deeper pockets of completely and highly weathered dolerite . Moderately and slightly weathered rock was removed during crop was visible but both abutments were predominantly covered with a layer of scree of both rock types, several metres thick, lying excavation of the impervious core and filter foundation, revealing predominantly fresh rock or fresh rock with stained joints. In at close to the angle repose. particular, in the river bed area of the main embankment, very little further excavation was required after removal of the alluvial Flood Hydrology deposits of sand and shingle - an even, flat work surface of fresh The dam is considered to be a 'high hazard' dam as defined in rock being exposed. Curtain and blanket grouting of the impervious core foundathe ANCOLD 'Guidelines on Design Floods for Dams ' and has been designed to pass the flood generated by the probable max- tion was carried out using cement grout. The design envisaged 16WATER September, 1986Filter Materials Maiumum Flood Level AL 76 Om 0 l5l0 !SmCo11st F11!e1 -.... L ..L-â&#x20AC;˘SCALESte-el Mnn P,01ec11onIThe key to the problems of the potentially dispersive core material and the possibility of cracking due to shrinkage and settlement lies in the design of the filters. These consisted of a twolayer system of fine and coarse filters processed from existing river gravel deposits in the Harding River. Following an extensive round of laboratory testing, including tests of the interaction of the cracked core and filter, an effective size
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