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Gualala River Sediment Source Summary

The quote below is from California Regional Water Quality Control Board (CRWQCB). 2001. Gualala River Watershed TMDL Technical Support Document for Sediment. CRWQCB, Region 1. Santa Rosa, CA. 147 pp.

"Natural sediment yield accounts for approximately 1/3 of the total sediment delivery in the Gualala watershed while human-caused sediment delivery accounts for 2/3 of the sediment delivery in the watershed, or 200% of the natural load. The analysis shows that road-related processes are the dominant source of sediment delivery in the watershed.

It is important to note that although the analysis only estimates sediment delivery that has occurred since 1978, pre-1978 management activities are still causing increased sediment delivery. While conducting the field measurements of random plots, staff observed many legacy problems associated with management practices pre-dating the Z’Berg-Nejedly Forest Practices Act.

The total natural sediment delivery in the watershed is estimated to be 380 ton/sq mi /yr. Regional Water Board staff believes, based on best professional judgment, that 380 ton/sq mi /yr may actually be an underestimate of the true natural yield. In cases of uncertainty, conservative assumptions were made which incorporate a margin of safety in the loading capacity estimate. Section 303(d) of the Clean Water Act requires that TMDLs include a margin of safety to account for major uncertainties concerning the relationship between pollutant loads and in-stream water quality."