Pacific Southwest Research Station

Potential of engineered floodplains and wetlands as fine particle BMPs: case study of Trout Creek and the Upper Truckee River

Principal Investigators:
Geoff Schladow, University of California-Davis
Fabian Bombardelli, University of California-Davis
John Reuter, University of California-Davis

Proposal [pdf]

Final Report [pdf]

Please contact Dr. Geoff Schladow with questions regarding the final report.

Project Summary

This study sought to quantify the deposition and retention of fine suspended sediment on a floodplain of Trout Creek (South Lake Tahoe, CA) using a two-dimensional numerical model. Estimating and determining methods of increasing floodplain sediment deposition in the South Lake Tahoe area is important because of the large detrimental effect fine sediment loads from this area have on Lake Tahoe clarity.

The 2D hydrodynamic flooding model BreZo was chosen for this study, and the model was applied to a previously restored reach of Trout Creek, between Pioneer Trail and Martin Avenue. Modifications were made to BreZo to improve the model's treatment of scalar dispersion, turbulence, hydrology, and bottom boundary friction. Sub-modules were added to simulate water temperature and suspended sediment. The model was calibrated on a snowmelt pulse from the spring of 2003, for which inflow condition data was known. The calibrated model indicated that, of the physical mechanisms leading to fine sediment removal considered, flocculation was the largest, with gravitational settling and sediment stranding by infiltration also being significant.

This strongly suggests that floodplains have great potential for removing fine sediment, as these sediments are the ones most prone to removal by flocculation. Floodplain modification simulations indicated that changes made to the floodplain vegetation and the addition of small backwater depression areas will have minimal impacts on overall sediment retention.

By contrast, small weirs placed in the channel during flooding will have large effects on fine sediment removal, with increases in sediment retention of 20%, if weir placement results in the flooding of previously dry areas. The testing of the ideal placement and sizing can be readily achieved using BreZo. Weirs, through their low costs and low planning demands, may have value as an interim floodplain BMP while more extensive and more broadly beneficial stream/floodplain restoration projects are being developed.