wh ich can be used to make obj ec tive decision s as to whether or nor ir should be removed. In addition to rhe habitat considerations, rhe removal of LWD is expensive and ir is surprising that prior co rh e work of Gippel, O'Neill and Finlayson (1992) there had been no rational decision-making procedure available for this purpose. In summary, rhe Tumur River has had its annual discharge increased by 50%, irs seasonal regime reversed, rhe parrern of occurrence of bankfull discharge changed from a frequency of about once every rwo years to continuous bankfull flow each summer for months on end , and almost complete removal of large woody debris in the channel. As is rhe case for the Snowy River, there are no baseline data for the Tumur River against which the impacts of these changes can be measured. The Goulburn River: Irrigation Flows. The Goulburn river in central Victo-
ria has a long history of regulation, the most recent and largest dam , Lake Eildon, having been completed in 1954. Lake Eildon is used as a storage for irrigation water which is used in rhe Goulburn- Murray Irrigation District. Warer released from Eildon is used to generate hydro-electricity and rhe channel of rhe Goulburn River deli vers irrigation water co the major offtake, the Goulburn Weir, 218 km downstream. Discussion in this section will ce ntre mainl y on the effects of Lake Eildon on water quality in rhe Gou lburn River wi th some sugges ti ons on how thi s problem might be addressed. This srrerch of river has been substantially modifi ed by these irrigation flows. Gippe l, Finl ayson and Th omp so n (1991) have analysed the effects of flow regulation on the hydrology of the Goulburn , in particular the frequency of overbank flows and the fill ing of floodplain wetlands. They show rhar close to the dam, wetlands which used to fill annually are now fi lled only three years in ten. This effect declines with distance downstream and little posr-dam change can be detected 200 km from rhe dam. Nathan (199 2) has also reviewed th e imp act of rhe dam on rh e hydrology of the Goulburn River. Erskine et al. (199 3) have reported on rhe impact of Lake Ei ldon on sediment load and channel stability of rhe mid-Goulburn River. They point our rhar channel response below the dam has been limited by the fact that there is less sediment available for deposi rion, flood flows have been red uced and as a result rhe channel has narrowed, bank erosion has been red uced and vegetat ion has increased on channel islands and in-stream bars. As is commonly rhe case in rhe examination of rhe im pacts of dams in Australia, there are no pre-dam water quality data for che Goulburn with which co compare the prese nt situation. Gippel and Finla yso n (1993) have dealt with chi s issue by generating water quality data for a site downstream of che Eildon Dam using observed water quality data in inflow screams. Despite WATER AUGUST 1994
the fact the Eildon is a large , deep re lease rese rvoi r, ir has no observab le impac t on dissolved oxygen levels. The dam does show an effect on pH, electrical conductivity and turbid ity though the effects are not large and probably do nor have any significant environmental impact. The dam does however drastically alter rhe temperature regi me of the river downstream (Fig ure 5). Medi an sum mer water temperatures are depressed by up to 7°C and median winter temperatures raised by up ro 2.5°C. Overall the effec t of the dam is co even our the seasonal pattern of temperature. Figure 6 illustrates the downstream trend in temperature for January and indicates chat the impact of che dam on water temperature has largely disappeared at Seymour, 138km downstream. These temperatures are unsuitable for the spaw ning of Macquarie perc h and river blackfish and rhis explains their absence from rhi s sec tio n of the rive r (Departm ent of Water Resources Victoria, 1989). Even under natural co ndition s ocher nati ve spec ies common in inland waters (Murray cod, silver perch , freshwater catfish, and golden perch) probab ly did nor spaw n in these waters because of low temperatures . The situation now is chat releases from Lake Eildon have rendered the Goulburn between rhe dam and Seymour (138 km of river) uninhabi table by the native species which used co live there, bur favo urable ro introduced spec ies , especially trour. Ic is technically feas ible, though quite ex pens ive, to manage the lake and th e releases so as to favo ur native fish over the introduced species and allow them to return to rhis section of the river. However, trout is a popular fish with recreational anglers , who are prepared to pay for fishing licences to fish for it, and a case can be made for continuing rhe present situation which favours it. Gippel and Fin layson (199 3) point out there are ot her probl ems (not ca used by rh e dam ) further downstream on the Goulburn which need to be addressed to improve native fis h habitat there. They suggest that licence fees from trout fis hing on rhe mid-Goulburn could be used ro defray che cost of improving native fish habitat in the lower Goulburn , a revenue-neutral outcome with benefi ts for rhe environment and for river users with a variety of interests.
Concluding Statement In this brief and limited discussion of the impact of dams on downstream habitat, one issue which has not bee n di scussed is rh e methodology for determining environmental flows. Currently available method s have bee n reviewed by Kinhill Engineers (1 988) All the methods reviewed have been developed overseas and there is clearly a need for serious research on the provision of envi ronmental flows for Australian conditions. Flow releases from dams for environmental purposes need
to provid e appijlpriate in-scream habitat , include floods of appropriate size and frequency to maintain the channel whi le still all owing rese rvoir managers to meet the needs for which the dam was built. Compromises such as rhac suggested above for the Goulburn wi ll no doubt be an increasi ngly important option in thi s area. The capital value of the dam and associated headworks and the retail value of water will be srrong constraints on environmental flow provision. In this context the case for environm ental flow releases will need to be based on strong and defensible evidence. Ir is here tha t rh e limi rations of our knowledge become glaringly apparent. It is possible to reconstruct pre-regulation flows, water quality and channel morphology sufficiently well ro detail the impact of regulation, as ill ustrated by the examples given above. What is not well known are the conditions necessary to maintain important aspects of the natural ecosystem. Since it is not feasible to return regulated rivers to thei r unregulated condition, we need to know the critical charac ter isti cs of flow, water qualit y and chann el co ndition whi ch wil l opt imi se in srream habitat. These are the research issues and their solution requires the genuinely interdisciplinary efforts of engineers, geo morphologisrs , aqu atic eco logists and system managers..
References Acke rman W C, Wh ite G F, and Worthi ngton E B, (Eds), 197.l , 'Man-Made Lakes: Their Problems and Envi ronmental Effec ts' , Geophysical Monog raph 17, American Geophysij;;il Union, Washington, DC. Ai rd WV, 196 1, 'The Water Supply, Sewerage and Drainage of Syd ney '. Metropolitan Water Sewerage and Drainage Board, S)'dney, 24 7pp. Bayley I A E and Williams W D, 1974 , '. Inland Waters and Their Ecolog)'', Longman, Melbourne. Brizga S O and Fin layson BL, 1992, 'The Snow)' River Sed imenr Srudy: Investigation intothe Disrribut ion 1 Transport and Sources of Sand in the Snowy Ri ver Between Lake Jindab)'ne and Jarrahmond '. Department of Water Resourcts Victoria, Water Rtsourct Management Series, Report No 81, 7.lpp. Cadwallader PL, 1978, Some causes of the decli ne in range and abu nda nce of nati ve fish in the Murra y-Darl ing system, Pmc Royal Soc Vic 90, 211-224. Depart ment of Water Resources Vic ro ria, 1989, 'Water Victoria: An Enviro nmental Handboo k', Victorian Govern ment Printing Office, Melbourne, 352pp. Ers kine W D, 1985 , Downst rea m geo morphic im pac rs of large da ms: the case of Glenbawn Dam, NSW. Applied Geography, S, 195-2 10. Erskine W D, Terrazzolo N and Warner R F, 199 1, Downst ream envi ronmental im pacts of the Snowy Mountains H)'d ro-El ectri c Scheme on the Snowy River, Austral ir Mitteil1111gsblatt des Hyd,·ographische11 Da11s tes in Osterreich, 6S/66, 5-6. Erskine, W D, Rutherfu rd, I D, Ladson, A R and Tilleard, J \V/ , 199.l . Flu vial Geomorphology of the Gou/burn River B"sin, Mid-Goul burn Catchment Coordinating Group ln. Gippel C J , Fin layson, B L and Thompson, B A - 199 1. Remote sensing of wetland warer reg imes and vegetation characteri stics Part II of Rapid Techniques fo,· Assessing Wetland Vegetation and Water Regime, Burea u of Rural Resources, Working Papter No . WP/12 /91, pp86- l 29. Gippel CJ , Marchant R, Stewardson MJ , Bri zga S 0 , Campbell I C, Woodfull J , FinlaysonB L and McMahon T A, l 992 . 'A review of environmental fl ow requirements of the Thomso nR iver from Th omso n Dam to Cowwaa r
19