AN INDEX OF STORED FINE SEDIMENT IN GRAVEL BEDDED STREAMS1

An index of sediments less than 0.3 mm stored in the top layer of small streams was estimated by disturbing a fixed area for 2 minutes and catching the resultant sediment drift in downstream traps. The method was used in 24 small northern California streams and was tested by releasing known amounts and sizes of sediments in controlled trails. Field use showed general agreement with an exponential model of decrease in sediment trapped vs. distance. Sites in distrubed reaches (watersheds logged with no streamside buffers or with buffers less than 30 m) had higher indices of stored sediment than control sites. Estimates from controlled trials averaged 7.5 percent higher than actual losses for composite size classes ≤ 0.3 mm, 19.7 percent higher than actual losses for just the ≤ 0.125 mm class, and 15.2 percent for all 14 trials. The method is relatively simple and suitable for remote locations, particularly in studies comparing many small streams.