Comparison of mudflow simulation models in an ephemeral mountainous stream in Western Greece using HEC-RAS and FLO-2D

Abstract

Mudflows are a class of non-Newtonian flows which can occur naturally in mountainous regions and have also been reported in the Mediterranean region. Even though their occurrence is not frequent, they can cause significant damage to infrastructure. While different approaches for the simulation of mudflows exist, the most common is to include the shear stresses caused by the increased sediment content as an additional friction term in the depth-averaged momentum conservation equation. However, the formulation of the additional term is not a straightforward task, and several models are proposed in the literature which contain empirical and ad-hoc components. In the present work, we compare two commercially available mudflow models, FLO-2D and the recently released HEC-RAS non-Newtonian flow module, by applying them to the Boudava stream in western Greece—a region where such phenomena, which are attributed to intense water loads present in the soil mass due to continuous unprecedented rainfall values antecedent to the event, have occurred in the past. Firstly, we derive theoretical relationships that relate the mudflow parameters of the two models. Subsequently, we run different scenarios and compare the results in terms of flow depth and velocity at critical cross sections as well as the overall flood extent maps. Our results suggest that the HEC-RAS implementation of the additional shear stress model is directly comparable to that of FLO-2D in terms of both physical coherence and numerical application. The proposed methodology provides useful insights to engineers aiming at applying mudflow models in their relative studies. The latter can subsequently be utilized by decision makers to prevent human and economic losses from such phenomena while allowing further steps to be made towards environmental integration.