Fully Coupled Unsteady Mobile Boundary Flow Model

Abstract

A fully coupled, one‐dimensional river model, capable of predicting sediment‐transport and bed‐level changes under unsteady flow conditions is described. The governing equations for mass and momentum balance of sediment‐water mixture under unsteady flow conditions in natural rivers with irregular geometries, are solved simultaneously using the Preissmann four‐point linear implicit scheme with weighting factors for space and time coordinates. The resulting system of algebraic equations is solved using a solution procedure that bridges upstream and downstream boundary nodal values by successive substitutions. The friction slope is expressed in a consistent form that allows the consideration of the changing alluvial roughness effect. The system of governing equations is explicitly coupled by introducing the term representing the rate of change of bed level. The fully coupled unsteady mobile boundary flow model (FCM) is applied to the classical problem of sediment deposition upstream of a dam with an arbitrary sediment hydrograph at the upstream boundary as well as to some other proof‐of‐concept tests to demonstrate its original features.