CREAMS/WEPP Sediment Deposition Equation: A Semitheoretical Evaluation

Abstract

A semitheoretical evaluation of the sediment deposition equation used in the CREAMS and WEPP models is presented. The original deposition relationship was presented in the CREAMS and WEPP models without theoretical or conceptual justification. In this article, the relationship is shown to be based conceptually on four characteristics: 1) uniform velocity distribution; 2) no lateral sediment inflow; 3) discrete particle settling; and 4) a uniform sediment concentrationall of which are violated under typical field conditions. Why then does the deposition equation work? The deposition equation, as applied to a rill, approximates the trapping that would occur in a fully-turbulent, rectangular reservoir if a rill is discretized into a large number of sections. When only one rill section is utilized, the equation approximates a quiescent reservoir. Since most shallow rills are typically discretized into a number of sections and experience a combination of turbulent and quiescent flows, the deposition equation should provide a first approximation of field conditions.