Pacific Southwest Research Station

Methodology to predict total and fine sediment load reductions as a result of channel restoration in Lake Tahoe streams

Restoration of incised streams has been proposed as a way of capturing fine sediments that are degrading the clarity of Lake Tahoe. This project, completed in 2011, proposed to illustrate the differences in fine sediment dynamics in an entrenched versus a nonentrenched stream morphology, and to predict how fine sediment loads could be reduced if streams are restored.

Lead Researchers: Nicole Beck, 2NDNATURE, LLC

Final Report

2NDNATURE Upper Truckee River Floodplain Database

Project Summary

Two stream reaches on the Upper Truckee River (UTR) were instrumented and monitored to obtain continuous site-specific hydrology, in-stream fine sediment particles (FSP) vertical profiles, and floodplain FSP deposition for three consecutive snowmelt events (WY08-WY10). Overbank flow occurred in 2009 and 2010 at the non-entrenched site. The research team applied the FSP concentration data obtained from passive samplers deployed along the upper and lower boundary of the non-entrenched site to estimate an FSP retention coefficient (RFSP) of 0.7 and an estimated FSP mass retained on the floodplain (SFSP) of 20.5 MT and 84.0 MT as a result of the 2009 and 2010 spring snowmelt floods, respectively. This research provides evidence that FSP retention by floodplains does occur and may provide a significant FSP load reduction during overbank flow events. There are a number of critical components yet to be resolved, but the knowledge gained and lessons learned from this research will be applied to the continued development of a Stream Load Reduction Tool by the 2NDNATURE team.