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Notes on Regional and Big River Basin Baseline Values for Fine Sediment

Barnard (1992) measured fine sediment inside and outside coho salmon redds in Freshwater Creek, after the watershed had 40-60 years of rest from logging activities. At ten sampling sites, he found the average fine sediment levels (<1.0 mm) outside coho redds to be 13%, with fine sediment levels less than 10% at 8 of 10 sites (see chart). This study is useful because the geology in the Freshwater Creek basin is especially erodible. Two thirds of the Freshwater Creek basin is in Franciscan bedrock geology, similar to the Noyo, Big and Ten Mile river watersheds. The remaining third is in Wildcat terrain, which is more erodible than prevalent rock types in the Mendocino area basins. Barnard's choice of 1.0 mm instead of 0.85mm for fine sediment and his use of the freeze core sampling method, which is highly effective for collecting fine sediment, most likely biased his samples toward higher values of fines. Therefore, control values for fine sediment for northern California streams is well under the lowest values reported by Burns (1972) or Valentine and Jameson (1994).

Burns (1972) finding of 20% fine sediment (<0.8 mm) in 1966 before logging resumed in the Little North Fork basin probably does not represent baseline conditions (pre-disturbance). The Little North Fork had been railroad logged in a prior era and the roadbed still extended along the active stream channel, providing a source of sediment (Valentine and Jameson, 1994). Caspar Creek, another Burns (1972) study site had been completely railroad logged as well. The North Coast Regional Water Quality Control Board (1998) pointed out that Burns (1972) samples also followed the 1964 storm  which would have elevated sediment levels.