Author(s): Cristiana Di Cristo, Andrea Vacca, Michele Iervolino, Tommaso Moramarco
Keywords: Mud flow; Power law fluid; Kinematic Wave Model; Unsteady analysis;
Abstract: The Kinematic Wave Model (KWM), representing a simplification of the Full Wave Model (FWM) under the shallow-water approximation, is still used for predicting flood propagation requiring a reduced computational effort and for being more easily coupled with high-resolution topographic data. It is as suitable approach also for predicting debris and mud-flows. In this work the applicability of the KWM for reproducing the propagation of mud-flows characterized by a power-law shear-thinning rheology is investigated. The power-law model is suitable for fluids with negligible yield stress, named mud-flows, such as fine sediment-water mixtures which are often encountered in natural estuaries or in landsides. For this reason, it is very important to individuate the hydraulic conditions in which the KWM can be safely applied for predicting mud flow propagation. In this study the power-law shallow-layer model of Ng and Mei (1994) is considered for the analysing the applicability conditions of the KWM through an unsteady analysis. Comparing the flow depth profiles predicted by KWM with those of the Full Wave Model the applicability conditions are characterized by evaluating the error on the dimensionless maximum flow depth along the channel. The preliminary results presented herein confirm a strong dependency from the rheology and indicate that criteria for clear-water flows do not apply to shear-thinning fluids. Moreover, the error increases moving in the downstream direction and higher errors pertain to lower wave durations of the discharge hydrograph. Further investigations will provide specific criteria for the applicability of the KWM for predicting mud-flows propagation.