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EFFECT OF HABITAT IMPROVEMENT ON ATLANTIC SALMON IN THE REGULATED RIVER SULDALSLAGEN. A. Lillehammer and J.E. Raastad (Zoological Museum, Oslo), H. Kaasa (Statkraft, Oslo) and J.A. Eie (NVE, Oslo), Norway. River Suldalslagen, which holds a population of large-sized Atlantic salmon has been regulated twice for hydropower production. The first regulation occurred in 1968, and the second in 1980. Some of the present problems have been the reduced density of benthic fauna, the reduced growth of young salmon, the low survival of 0+ and an increase in the length of the time used for smoltification. A restoration program has been established which includes stocking of salmon fry in tributary streams and in rearing channels, and experimental studies of increasing benthic fauna by introducing dead organic material to some habitats. Improvements of physical habitat, that also includes control with the water flow, in rearing channels increased the benthic animals many times, and the survival of 1+ salmon was about 30X. Experiments that included adding of 115 g wheat/m~ gave a three-fold increase in benthic fauna compared to a control area. The largest increase in numbers in August-September came in Chironomidae, while benthic crustacea also had a significant increase. Other groups were found in only small numbers at that time. The increase in benthic fauna in expected to increase the survival of young salmon fry. Ecological Responses to River Regulation: Physical, Phytobenthic, Zoobenthic BEACH EROSION STUDIES UNDER DISCRETE CONTROLLED RELEASES: COLORADO RIVER THROUGH GRAND CANYON NATIONAL PARK. Brian L. Cluer, Larry E. Stevens, Grand Canyon National Park/Glen Canyon Environmental Studies; Stanley S. Beus, Charles C. Avery, Northern Arizona University; Muniram Budhu, University of Arizona; Jack C. Schmidt, Middlebury College, Vermont. Sand deposits in the Grand Canyon have been subjected to controlled daily fluctuating discharges since the closure of Glen Canyon Dam in 1963. Rather than the natural annual flows of about 90,000 cfs with several weeks duration, there are currently daily discharge fluctuations of 5,000 to 28,000 cfs as Glen Canyon Dam produces peaking hydropower for the southwestern electrical grid. This daily "tidal" release pattern has created a novel environment in which substrata as well as the Flora and fauna depending on the substrata face new hydraulic conditions. Since 1974, profiles on sandy beaches have been resurveyed annually. The results have been varied, showing degradation and aegradation, and conclusions are mixed about the release patterns and effects on alluvial deposits. High spills in 1983, 1984, and 1985 further complicated the alluvial studies by reshaping the existing sand deposits. Between June, 1990 and July 1991, a series of discharge tests were conducted by the Bureau of Reclamation, providing an extraordinary opportunity to observe and measure downstream dam effects on riparian substratum. Terrestrial and photogrammetric surveying resulted in over 1500 topographic maps and residual isopach maps of 67 sand deposits located throughout the Colorado River in Grand Canyon. Ground water monitoring at chosen sites along the river corridor measured the movement of water within beaches with respect to river release patterns. A modeling effort is underway that will result is a system-wide numerical tool to predict erosion under various discharge regimes. Preliminary analyses indicate that it is possible to determine the effects of short-term test releases on the stability of deposits. Specifically, releases of constant discharge or limited peak discharge with slow ramping rates are the least erosive. Given the newly acquired data base and the model under development, it may be possible to predict the effects of other release patterns on deposit stability, longevity, and evolution of fluvial sediment deposits. 3