Sediment transport, turbidity, channel configuration, and possible effects of impoundment of the Mad River, Humboldt County, California

Sediment-transport conditions were determined at two stations, Mad River near Arcata and Mad River near Kneeland. Using a release-flow model and an empirical equation, the suspended-sediment discharge at Kneeland was estimated to be about 60 percent of the suspended-sediment discharge at the Arcata station. The study of the proposed impoundment determined the effect of discharge on channel configuration and concluded: The reservoir would trap about 60 percent of the potential beach-forming sediments. Release flows could transport'the expected inflow of sediment particles less than 2 millimetres in diameter for the reach of the river downstream from the impoundment site and about 130,000 tons per year (120,000 tonnes per year) of bed material particles less than 3 inches (76 millimetres) in diameter. Release flows could be expected to degrade the channel for about 15.miIes (24 kilometres) downstream from the impoundment, and downstream from that reach artificial adjustments would override most release-flow effects on channel adjustments. Turbidity of release flows could approximate preimpoundment turbidity for an average year.