UC Davis

The floodplains of the Sacramento and Feather River support the largest documented population of Bank Swallows (Riparia riparia) west of the Great Lakes region. Bank Swallows depend upon fluvial geomorphic processes to create and maintain their nesting substrate of steep vertical banks and friable soil. These processes also drive the complexity and overall biodiversity of riparian ecosystems. Bank Swallows have declined significantly within the watershed. Conservation efforts call for improved understanding of the distribution and condition of habitat resources, and identification of recovery measures. Here I present a novel analysis that links soil-suitability mapping to a physics-based model of river meander (MeanderJP). I correlated colony locations with key soil characteristics derived from the SSURGO database (USDA-NRCS 2018). I also evaluated the incremental effects of flow impairment and flood control infrastructure on the interactions of river meander and suitable soils. Both soil suitability and river meander extent have extremely limited overlap on the landscape over 50-year modeling scenarios and vary significantly by river reach due to local geology, river planform, levees, and bank stabilization. Dam operation has reduced historical suitable soil-river meander interactions by 24%, and flood control infrastructure has further limited these interactions by 24%, for overall habitat reductions of 48%. Last, I evaluated the return of Bank Swallows at 18 locations where rock revetment no longer remained in place, and in all but 2 instances Bank Swallows colonies were re-established. These findings provide a fundamental understanding of habitat suitability and river process which can be used to prioritize locations where process-based restoration of the Sacramento River and Feather River corridors should occur in order to ensure species persistence and recovery.