Assessing sediment stress closures in two-phase sheet flow models

A crucial component of models using a two-phase flow approach to simulate sediment transport is the closure employed to describe the sediment phase stresses. We assess and compare several formulations which have been successfully implemented in simulations of sheet flow sediment transport and in multidimensional studies. To that end, we use numerical results of a two-phase flow model which uses a one-equation granular flow sediment stress closure and which has been extensively validated. We first assess existing empirical parametric sediment stress formulations under steady and oscillatory sheet flow conditions. The numerical results only partially support existing mathematical expressions, and lead to a ratio between normal and shear stresses which is not a constant. We also directly compare the numerical results obtained using three different sediment stress closures against intrawave sediment flux data.