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Sediment has an important role in the physical, chemical, and biological integrity of aquatic ecosystems. Managing sediment is an international challenge with sediment often being one of the leading causes of water quality impairment. Sediment accumulation behind dams is especially complex as dam operational needs must be balanced with downstream aquatic uses. Dams naturally accumulate sediment behind them and without management this accumulation can impair dam operations, compromise structural integrity, and increase maintenance costs. Sediment releases can harm downstream aquatic life, but quantifying the response is difficult. An understanding of how sediment releases affect downstream aquatic biota, in particular which fish species, life stages, and time periods are most sensitive to sediment releases is important for informing water quality criteria and operating recommendations for dams. Effective sediment criteria must consider natural temporal and spatial variation in sediment, reflect the requirements of the biological communities they are meant to protect, and be attainable for the system.
In Wyoming, operating recommendations for Willwood Dam are based on a severity index (Newcombe and Jensen 1996) developed more than 20 years ago. We will conduct a literature review to update these relationships. Specifically, we will focus on the four key components of a sediment release: sediment concentration, and duration, frequency, and timing of release. Additionally, we will conduct fieldwork at the Willwood Dam to evaluate how the four components of sediment release vary with streamflow and water management activities. We are particularly interested in evaluating metrics that are directly relevant to fish, such as fine sediment infiltration which can have detrimental effects on salmonid redds. To complement the updated severity index and empirical study, we will compile best management practices related to dam sediment accumulation/release to most effectively protect downstream fisheries and aquatic biota during all aspects of their lifecycles. Our results will have direct implications for current management challenges at Willwood Dam, but will also be applicable to sediment management across the state.
As dams age the issue of how to address sediment accumulation will only become more pressing. This research will directly contribute to ensuring management decisions are meeting the needs of stakeholders and dam operational needs while simultaneously protecting and maintaining downstream surface waters. The information will broadly benefit a number of state and federal agencies that are charged with managing water quality, fisheries, and water storage, including Wyoming Department of Environmental Quality, Wyoming Game and Fish Department, and the United States Bureau of Reclamation.