A space-marching model to assess the morphodynamic equilibrium behaviour in a river’s backwater dominated reaches

Abstract

A river that is forced by statistically invariant boundary conditions and is notsubject to any forcing with a temporal trend continuously tends to anequilibrium state in which the bed level and texture fluctuate around stable meanvalues. Studying the equilibrium state of a river can therefore help us explainsome of the long-term trends that are observed in natural rivers (de Vriend,2015). A sufficiently accurate solution of the 1D morphodynamic equilibrium statecan be found by running a Saint- Venant-Exner/Hirano model until the long-termaverage morphodynamic state has converged to a stable value. Yet, this oftenrequires hours to days of computation time and it is therefore not suitable fora quick assessment of the morphodynamic equilibrium state. In this research we studythis state using a newly developed numerical spacemarching model (i.e. abackwater-alike solution procedure) that allows us to compute a river’sequilibrium profile in backwater dominated reaches efficiently.