Abstract: The need to limit salinity intrusion into the Sacramento-San Joaquin River Delta led California’s Department of Water Resources to install the West False River (WFR) Emergency Drought Barrier (EDB) from spring to fall, 2015. Fish monitoring data indicate that migrating juvenile Winter-Run Chinook Salmon had left the Delta prior to EDB construction, whereas small proportions of Spring-Run Chinook (<20%) and Steelhead (<10%) were in the Delta (juvenile Green Sturgeon are potentially present year-round). Assessment of the proportion of Delta Smelt near the EDB is challenging because of the species’ current low abundance, with the greatest density apparently in the north Delta and a small proportion likely to have been blocked from exiting the south Delta by the EDB. Vibratory pile driving for abutment sheet/king piles limited noise effects. Sediment disturbance during rock placement increased turbidity, but only near the EDB; following barrier closure, turbidity greatly increased in nearby channels in which velocity increased, whereas low flow decreased turbidity in WFR. These differences in turbidity could have affected Delta Smelt habitat suitability. SCHISM hydrodynamic modeling suggested very high flows occurred through the notch in the middle of the EDB before full closure and formed a number of eddies in WFR which could have increased short-term predation susceptibility. High-resolution measurements indicate that over 95% of tidal flow in WFR was blocked by the EDB which, although creating an impingement risk on EDB barrier rocks for larval/juvenile Delta Smelt already in the channel, would have limited additional entrainment into WFR. Leaving the abutments in place for future EDB installations could have created additional low-velocity, eddy habitat (data from SCHISM modeling), but subsequent investigations found that the abutments are no longer necessary. The assessment of EDB effects provides valuable data to aid decisions made regarding future implementations of Delta barriers, should these be necessary.Summary: The need to limit salinity intrusion into the Sacramento-San Joaquin River Delta led California’s Department of Water Resources to install the West False River Emergency Drought Barrier from spring to fall, 2015. There was relatively little spatial and temporal overlap with listed fishes, although potential construction and operations effects occurred.
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