Environmental Implications of a Multipurpose Scheme for Drinking Water Supply and Power Generation
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The influence of man on the hydrological regime with special reference to representative and experimental basins — L'influence de l'homme sur le régime hydrologique avec référence particulière aux études sur les bassins représentatifs et expérimentaux (Proceedings of the Helsinki Symposium, June 1980; Actes du Colloque d'Helsinki, juin 1980): IAHS-AISH Publ. no. 130. Environmental implications of a multipurpose scheme for drinking water supply and power generation H. BANDLER Turramurra, New South Wales, Australia Abstract The Shoalhaven River is a major stream along the southeastern coast of Australia. There is evidence of past extensive Aboriginal tribal life. The Shoalhaven scheme was developed for water supply and power generation. The works incorporate three dams, a small pondage, three pumping stations, some length of pipes above ground, some canals, some pipeline in tunnel and a shaft below ground. Lake Yarrunga created by Tallowa Dam occupies both Shoalhaven and Kangaroo River Valley. Outlet conduits ensure adequate flow downstream which is essential for fish survival. The dam is located in a large National Park. Some problems arise for the Park admini stration from the policy giving the public road access to the dam and picnic ground. Fitzroy Falls Dam and Reservoir is created by a rockfill dam. A bypass in the dam maintains the attractive Fitzroy Falls nearby. Fishing and sailing are permitted on the reservoir, but facilities for visitors are inadequate. Wingecarribee Dam and Reservoir formed by an earth and rockfill dam, has been made attractive by grassing. Displacement of farming families caused some hardship. Recreational activity is not permitted on the lake. Environmental implications of water supply structures should be explored before design is finalized. Effets sur l'environnement d'un projet à buts multiples pour l'approvisionnement en eau potable et la production d'électricité Résumé. La rivière Shoalhaven est un des importants cours d'eau de la côte sud-est de l'Australie. Il reste des traces de vie extensive de tribus Aborigènes. Le projet de Shoalhaven a été développé pour l'approvisionnement en eau et la production d'électricité. Les travaux comprennent trois barrages, un étang de petite capacité, trois stations de pompage, quelques conduites, quelques canaux, des conduites souterraines et un puits sous terre. Le lac Yarrunga créé par le barrage de Tallowa, submerge les vallées des rivières Shoalhaven et Kangaroo. Des conduites assurent un débit suffisant en aval, pour permettre aux poissons de survivre. Le barrage est situé dans un parc national. Des problèmes sont apparus pour l'administration du parc étant donné que le public a accès par route au barrage et au terrain de pique-nique. Le barrage de Fitzroy Falls et le réservoir ont été créés par un barrage fait de remblais rocheux, une prise d'eau dans le barrage préserve les chutes pittoresques voisines de Fitzroy. La pêche et la navigation de bateaux à voile sont permis sur le réservoir, mais les facilités pour les visiteurs ne sont pas suffisantes. Le barrage et le réservoir de Wingecarribee sont formés de remblais terreux et rocheux et rendus plus attrayants par le maintien d'herbes sur la surface. Les déplacements des familles de fermiers ont causé des difficultés. Le public n'a pas accès au lac. On doit étudier la portée de ces effets sur l'environnement avant l'achèvement du projet. THE SHOALHAVEN RIVER AND CATCHMENT The Shoalhaven River is a major stream which flows generaËy northward parallel to the southeast Pacific Ocean coast of Australia south of Sydney until it turns eastwards to the ocean. The river is about 320 km long within a catchment of approximately 7200 km2 where undulating to hilly landforms predominate, with slopes between 3 and 8° occupying about 44 per cent of the total area. Most of the country is timbered and uninhabited. Extensive alluvial flats extend along the lower part of the river near the sea with highly productive agriculture and dairy farming. There are few settlements within the catchment. The largest township is Braidwood with nearly 1000 inhabitants. Kangaroo Valley township, with a population of 340, is closely linked with the dairy ing activities along the Kangaroo River. Major floods are infrequent in the Shoalhaven River. Farm lands affected by irregular flooding lie principally beyond the storage area. The main Aboriginal tribe 195 196 H.Bandler living in the area around the Shoalhaven River and its tributaries before the intrusion of the white man was the Wandandian Tribe (Tindale, 1974). The area along the Kangaroo River had been claimed to be a 'Black Man's Paradise' and the Aborigines are supposed to have used the valley along the Kangaroo River as a game reserve. Some rock paintings have been found in the vicinity of Tallowa Dam on the southern side of the Shoalhaven River above the stored water level. THE SHOALHAVEN SCHEME STAGE 1 The Shoalhaven scheme, stage 1, incorporates three man-made lakes created by one concrete dam and two earth and rock fill dams; three pumping stations, two of them with the dual function of pumping and power generation in a pumped storage scheme; some lengths of open channel and a small pondage area; and many kilometres above- ground pipeline in two separate sections, each with a surge shaft and a section of pipeline in a tunnel and shaft below ground level. KANGAROO P1PEU v . v „ ... , „ , GlENQUARRY CUT ^—- BURRAWANG TUNNEL SURGE TANK-j - BENDEELA PIPELINE ~BENC€ELA POWER STATION FIGURE 1. Shoalhaven scheme stage 1 : sectional profile. The layout of the scheme is presented on Figs 1 and 2 with the principal dimensions and characteristics of the dams and reservoirs given in Table 1. The scheme is the latest addition to the water supply intake works for the city of Sydney. It was built so that water from the Shoalhaven River may be pumped in stages, by three pumping stations, to the Wingecambee Reservoir. From here it can flow to the existing water supply storage reservoirs on either Warragamba or on Nepean River. The Kangaroo Valley— Fitzroy Complex makes it a multipurpose scheme. In this section the hydroelectric capacity of the project is used by pumped storage between Lake Yarrunga and Fitzroy Falls Reservoir, with Bendeela and Kangaroo VaËey Pumping and Power Stations raising the water approximately 607 m in the pumping mode during the night. TALLOWA DAM AND LAKE YARRUNGA Tallowa Dam was constructed 40 km upstream from the mouth of the Shoalhaven River, at the junction with the Kangaroo River. It is a straight concrete gravity dam with a 350.5 m wide spillway between the headwalls. The downstream face of the dam, with a submerged slotted roller bucket at the toe, is shaped to absorb the energy of floods over-topping the dam so that erosion of the valley downstream is kept to a minimum. Lake Yarrunga, created by Tallowa Dam, occupies both the Shoalhaven and Kangaroo River valleys. In the much steeper Shoalhaven the water is banked up for a distance of 12 km while in the Kangaroo River stored water extends 20 km. The level of the reservoir provides adequate draft for Bendeela Pumping/Power Station. Except when the water is over-topping the spillway during flood times, little flow is generated in the river immediately downstream of the dam. Two river outlet conduits are built into the eastern abutment of the dam to ensure adequate flow downstream Environmental implications of a multipurpose scheme 197 FIGURE 2. Shoalhaven scheme stage 1 : plan. required for water supply of Nowra. No provision has been made for fish to pass upstream beyond the dam for spawning in the upper reaches of the rivers. In a recent study of the effects of river flow termination downstream of Tallowa Dam attention was drawn to the rapid fish kill foËowing the cut-off of water (Bishop and Bel, 1978). This was particularly significant as amongst the many types of fishes killed were a fair number of Australian grayling (Prototrocts maraend), a species listed as the Australian fresh water fish most seriously threatened with extinction (Lake, 1971). 198 H.Bandler TABLE 1. Shoalhaven water supply and power generation scheme : principal features and dimensions of dams and reservoirs Description Type Height Length At fuE su pply level of structure [m] [ml Storage Surface capacity area [Ml] [km*] Tallowa Dam Straight concrete 43* 520 gravity 32f Spillway Ungated ogee crest 350.5 Lake Yarrunga 110000 9.3 Bendeela Pondage Earth and rock fill embankment 14 2146 1200 0.2 Spillway Free overfall weir 121.9 Fitzroy Falls Dam Earth and rock fill Main dam embankment 14 max. 1530 Saddle dams 1524 Spillway Side channel ogee crest 61 Fitzroy Falls Reservoir 23 500 5 Wingecarribee Dam Earth and rock fil 1150 Main dam embankment 19 Saddle dam 720 Spillway Gated ogee crest 11 Wingecarribee Reservoir 34 500 7 * at abutment •f at spillway Tallowa Dam is located in the northern part of the extensive Morton National Park (425 km2) which includes wilderness areas. At its northern extremity, Fitzroy Falls is accessible by main road. Management is vested in the National Parks and Wildlife Service (NPWS). The current policy is to allow small pleasure craft on the lake, such as rowing boats, small sailing boats and canoes, but not power-driven boats. Swimming is also permitted. To use the lake for water-based recreation is a desirable development but creates conflict with the normal use of the National Park in this area. The introduction of the dam and its access road brought about alienation not only of the section occupied but also much of the adjoining land. The NPWS was aware of the difficulties which were likely to be created, before Lake Yarrunga was opened to the public.