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Case Histories Within and Between Whole Catchments CHANGES IN PHYSICAL RIVER CONDITIONS AND THE ENVIRONMENTAL EFFECTS IN FIVE NORWEGIAN CATCHMENTS FOLLOWING HYDROPOWER DEVELOPMENT. Arve M. Tvede, Norwegian Water Resources and Energy Administration, and Svein Jacob Saltveit, Freshwater Ecology end Inland Fisheries Laboratory, Zoological Museum, University of Oslo, Norway. This paper is mainly based on a project entitled "Follow-up Studies of Water Regulation Schemes," carried out within the program "Environmental Effects of Water Regulations Schemes," under the auspices of The Norwegian Council for Scientific and Industrial Research during the period 1982-89. The project is now being continued by The Norwegian Water Resources and Energy Administration. The conclusions made are mainly based on published reports documenting the situation in the catchments before and after regulation. Special attention has been given to studying the relative validity of predictions made before the regulation license was given. In general, the predictions were valid although it was not possible to reach conclusions for all the relevant fields of study. This is either because documentation is lacking or because mitigations or changes in the power plans altered the final scheme compared with that initially proposed. The five catchments under study were Hallingdalselva, Suldalslagen, Aurlandeselva, Laerdalselva and Orkla. The power schemes are all large-scale, representing a total power production of 13.5 Twh, or more than 12x of Norway's total power production. The physical changes studied were ice conditions, water temperature, floods, and erosion/ sediment transport; while the environmental effects were local climate, water quality, fish growth, density and yield. HISTORICAL CHANGES RELATED TO FLOW REGULATION OF THE RIVER HURRAY, SOUTH AUSTRALIA. I. THE PHYSICAL ENVIRONMENT. M.C. Thoms and K.F. Walker, River Murray Laboratory, Department of Zoology, University of Adelaide, South Australia 5000. A complex series of river channel adjustments have occurred along the "lower River Murray" as a result of flow regulation by 10 low level weirs, constructed between 1922-35. The form and timing of these changes are variable. There are two distinct "environmental units" along the lower river, each with different geomorphologies thus adjustments are dependant partly upon position along the lower river. Studies of the physical response to flow regulation have occurred at various spatial scales. The average bed gradient of the lower river has increased over the 83y period. Changes in bed elevation range from -lOm to +lOm. Channel capacities have also changed by up to 100 percent in reaches immediately downstream of the weirs. In the upper reaches cross sections have stabilised whilst those in the lower reaches aze still adjusting some 54 y after weir construction. Distinct deposition and erosion zones now exist between each set of weirs. Modifications to current operational procedures are suggested which may reduce the physical impact of flow regulation in the lower river. Projections for stabilisation are presented and the river should complete adjustment in 60 years if the present flow and sediment regimes are maintained. Increased water demand will alter this senario and the form and timing of adjustment may be further modified. 11