Adaptive Instream Flow Regulation: A Strategy to Protect Incubating Cedar River Sockeye Salmon against Redd Scour

We buried accelerometer arrays (scour monitors) vertically in Cedar River spawning habitats to verify the results of two previous scour studies that suggested mobilization of spawning gravels occurred between 1800 cfs and 2200 cfs as measrured at the USGS gage near the river mouth.  In addition, we excavated 17 sockeye salmon redds to provide population specific egg pocket depth information to further inform our scour monitor results.  Scour monitors measured timing of streambed scour and duration of sediment mobilization at specific depths in spawning gravels that sockeye salmon are known to use consistently from year to year.  Accelerometer movements during the sockeye spawning period suggested that the vast majority of scour monitors were disturbed by spawning sockeye prior to subsequent peak flow events.  Our results also suggested that spawning substrates were mobilized during peak flow events at similar flow levels to previous studies.  Scour depth data were combined with egg pocket depth data to estimate potential scour impacts to incubating sockeye at varying flow levels.  Results will be used to further refine flow regulation strategies that are designed to improve sockeye egg to fry survival by reducing redd scour.