CHANNEL ADJUSTMENTS TO RESERVOIR CONSTRUCTION AND GRAVEL EXTRACTION ALONG STONY-CREEK, CALIFORNIA

Stony Creek (drainage area 1920 km2), a tributary to the Sacramento River 200 km north of San Francisco, has experienced channel adjustments to both dam construction and instream gravel extraction. Black Butte Dam, constructed in 1963, reduced flood peaks and trapped the annual 100,000 m3 of bedload sediment formerly delivered from the upper watershed. The reach below the dam changed from an active braided channel to an incised, single-thread channel shortly after dam construction. About 25 km downstream of the dam, large instream gravel mines annually extract 230,000-580,000 m3 and have induced channel incision of over 5 m, necessitating bridge repairs costing US$1.4 million.