Modeling Sediment Transport in the Lower American River, Sacramento, California: Fid-Bau Portal

Modeling Sediment Transport in the Lower American River, Sacramento, California

Shvidchenko, Andrey B. / Hall, Brad R. / Rivas, Todd

This study quantified sediment transport processes and geomorphic trends along the lower American River, California, for evaluating impacts of the Folsom Dam Modification Project on channel morphology. The analysis used a HEC-6T sediment transport model of the 22-mile reach of the American River below Nimbus Dam and the adjoining 32-mile reach of the Sacramento River. Model geometry was based on 1997 and 2006 bathymetric surveys. Bed material characteristics in the model were specified from a surface and sub-surface sampling program and geotechnical investigations of erosion-resistant stratigraphy. The model was calibrated to measured sediment loads and bed profiles. The calibrated model was then used to simulate long-term morphological changes in the lower American River under existing and project hydrologic conditions. The model results obtained for existing conditions indicated active degradation of the American River below Nimbus Dam and predominant aggradation in the downstream reach, which is consistent with field measurements. The project condition results, which include higher flow releases through the new auxiliary spillway, indicated increased channel degradation immediately below Nimbus Dam and showed no significant changes in bed profile in reaches further downstream to the confluence with the Sacramento River.