DEVELOPMENT OF A 2D MOBILE-BED DAM-BREAK MODEL

摘要

Sudden and catastrophic dam-breaks exert high bed shear stresses on the alluvial channel and flood plain as the flood-wave propagates downstream. For gravel rivers, the non-dimensional shear stress can be comparable to those typically estimated during the transport of sand. Despite these high shear stresses, standard dam-break modeling typically assumes fixed-bed conditions. To investigate the effects of sediment transport on flood-wave behavior, a 2D mobile-bed dam-break model was developed for gravel-bed rivers using TELEMAC2D (2D hydrodynamic model) coupled with SISYPHE (2D sediment transport model). Capabilities and features incorporated into the coupled model include: (1) individual critical shear stress values for each of 10 sediment size classes; (2) spatial, vertical, and temporal variation in friction coefficients and sediment sizes; (3) combined gravel transport equation; (4) influence of vegetation density on sediment erodibility; and (5) ability to spatially define bedrock elevations. To test this model, the Malpasset (France) dam-break of 1959 was simulated, and sensitivity analyses were performed on the parameters of grain roughness, vegetation density, sediment grain size, and bedrock depth to examine differences in inundation and flood-wave propagation. A second set of sensitivity analyses were performed under a fixed-bed assumption, and the results were contrasted against the mobile-bed sensitivity results. The analysis demonstrated that there is significant morphologic change after the propagation of a dam-break wave through a river and its floodplain. Both the inundation and flood-wave propagation were influenced at varying degrees by all sensitivity parameters except for bedrock depth. When modeling a mean annual flood over the pre- and post-dam-break bathymetry, it was found that there was a significant difference in flooded regions.