Pacific Southwest

Title: Mapping Prehistoric, Historic, and Channel Sediment Distribution, South Fork Noyo River: A Tool For Understanding Sources, Storage, and Transport

Author: Koehler, Rich D.; Kelson, Keith I.; Matthews, Graham; Kang, K.H.; Barron, Andrew D.

Date: 2007

Source: In: Standiford, Richard B.; Giusti, Gregory A.; Valachovic, Yana; Zielinski, William J.; Furniss, Michael J., technical editors. 2007. Proceedings of the redwood region forest science symposium: What does the future hold? Gen. Tech. Rep. PSW-GTR-194. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 371-382

Station ID: GTR-PSW-194

Description: The South Fork Noyo River (SFNR) watershed in coastal northern California contains large volumes of historic sediment that were delivered to channels in response to past logging operations. This sediment presently is stored beneath historic terraces and in present-day channels. We conducted geomorphic mapping on the SFNR valley floor to assess the volume and location of sediment associated with pre-historic terraces, historic terraces, and the active channel along four 1-mi-long stream reaches. Additionally, we established ten streamflow and suspended sediment sampling locations to monitor water and sediment discharges. We estimate 158,000 yds³ of sediment stored in the active channel, and 68,000 yds³ of sediment stored beneath historic terraces. These volumes are an order of magnitude less than the volumes estimated for pre-historic terraces. The present-day channel sediment is stored presently in large gravel bars and is mobilized primarily during winter flood events.

Based on channel mapping and hydrologic data, we infer that the largest suspended sediment loads are spatially coincident with the locations of the greatest amounts of stored channel sediment. Re-mobilized historic sediment appears to increase suspended sediment load, and may be a significant, previously unrecognized sediment source. Thus, accurately mapping and quantifying channel deposits is a critical step for assessing sediment budgets, especially in Total Maximum Daily Load (TMDL) studies attempting to relate upslope management to suspended sediment production.

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Citation

Koehler, Rich D.; Kelson, Keith I.; Matthews, Graham; Kang, K.H.; Barron, Andrew D.  2007.  Mapping Prehistoric, Historic, and Channel Sediment Distribution, South Fork Noyo River: A Tool For Understanding Sources, Storage, and Transport.   In: Standiford, Richard B.; Giusti, Gregory A.; Valachovic, Yana; Zielinski, William J.; Furniss, Michael J., technical editors. 2007. Proceedings of the redwood region forest science symposium: What does the future hold? Gen. Tech. Rep. PSW-GTR-194. Albany, CA: Pacific Southwest Research Station, Forest Service, U.S. Department of Agriculture; p. 371-382.