Bed Shear Stress Estimation during Flash Flood Flows: a Review of Methods

Bed shear stress is an important hydraulic parameter influencing sediment transport, channel stability, erosion and deposition. While there are various direct and indirect ways to estimate it, the majority were established for steady or quasi-steady open channel flows. In contrast, flash flood flows are very turbulent, rapidly varying, and significantly unstable, making traditional approaches less trustworthy. This review paper summarizes direct and indirect estimating methodologies, flume experimental studies, and limited field investigations for the flash flood flow. It emphasizes the difficulties/limitations while applying the direct, indirect methods, and obtaining accurate measurements under the intense flows. This paper highlights key research gaps, specifically the scarcity of robust models designed for unsteady non-uniform flows and field-based validation. Future initiatives focus the development of new techniques, high-resolution datasets, and integrated modelling frameworks to better quantify bed shear stress during flash flood flows.