Stochastic Analysis of Sediment Flux in the Context of River Management

A basin-scale, sediment transport study which models the uncertainty in mainstem flow conditions was initiated along the Sacramento River, California. The study incorporates: HYDROCARLO, a stochastic event-based flow generator; HEC-RAS, a flow-routing software; and the Engelund-Hansen sediment transport equation for total load. Inflow hydrographs from major tributaries were simulated with HYDROCARLO over the desired time period and routed through the mainstem Sacramento using HEC-RAS. Daily stage data output from flow routing were used to calculate water surface slope and velocity at desired cross sections. Stage and velocity were then used to drive the Engelund-Hansen sediment transport equation and predict sediment flux in various grain size classes (determined from field data) and in distinct portions of the channel cross section. The technique was cross-checked against results from statistical models employed to predict suspended sediment flux at the same cross sections. Stochastically-driven sediment transport calculations can be formulated as probabilities thus suggesting a range of uncertainty and a central tendency. Such calculations could provide river managers with constraints on sediment flux estimates in river channels that are undergoing adjustment to natural perturbations or management scenarios.