Stochastic predictions of sediment yields from small coastal watersheds in Oregon, U.S.A.

Abstract

For many streams in the Pacific northwestern U.S.A., nearly all sediment is transported during brief, distinct runoff events. The event sequence can be stochastically described by combining a Poisson process, a flow frequency analysis, and a sediment rating curve. The model is used to predict long-term distributions of annual suspended-sediment yields from two small watersheds in the Oregon coast range. For these watersheds, observed annual yields appear to be less variable than would be predicted from random sums of individual storm event yields. The discrepancy between synthetic and observed yields is probably due to the controls imposed by sediment sources.