Abstract
ABSTRACTDams are essential for water resources management but impose notable effects on fluvial sediment transport and downstream river morphology by reducing or altering the timing of sediment loads. We explored the relationship between dam sediment management and downstream sediment dynamics in the context of riverine fisheries management. We quantified the effects of dam sediment management operations on downstream salmonid spawning habitat during two differing water‐level drawdown events: (1) an experimental drawdown leading to various high concentration sediment releases, and (2) a typical slower drawdown intended to minimize release of sediment. The experimental drawdown increased deposited fine sediment and decreased hyporheic dissolved oxygen levels. However, the typical drawdown did not increase fine sediment deposition or decrease hyporheic dissolved oxygen. We quantify the immediate impacts of dam operations using a number of water column and substrate metrics, and demonstrate the potential for sediment flushing operations to have short‐term seasonally persistent effects on salmonid spawning habitat. Common surrogates of suspended sediment concentration (i.e., turbidity) were poor indicators of salmonid spawning habitat, especially when sand was the dominant grain size. Instead, other measures of suspended sediment concentration such as acoustic backscatter and depth‐integrated samples, combined with discharge, appear to be better suited for monitoring and inferring the impacts of sediment releases on salmonid spawning habitat. We demonstrate the importance of understanding sediment particle sizes, monitoring relevant water column conditions in real‐time, and provide options for effectively monitoring the downstream impact of dam operations. This work can help managers balance dam sediment management operations with ecological priorities.
Published Version
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