Author(s): T. T. H. Le; M. Tomirotti
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Keywords: Dam break flows; Complex topography; Shallow Water Equations; Finite Volume Method; Outflow hydrograph
Abstract: Dam safety is becoming one of the most important issues in the field of water resources management in Vietnam. In this direction the estimation of the flood wave that would result in the event of a dam failure is a necessary requirement for hazard assessment and the development of early warning plans. The mathematical modeling of dam break flows based on Shallow Water Equations (SWE) is the widely accepted approach to face this kind of problems. In this paper Godunov–type scheme based on Finite Volume Method (FVM) is used to solve 2D SWE on structured mesh; HLLC approximate Riemann solver is invoked to evaluate inter-cell fluxes and MUSCL procedure is employed to obtain second order accuracy. A different approach based on Roe scheme is also implemented. The above schemes are validated by reference test cases demonstrating a satisfactory behavior with respect to their effectiveness and robustness. Therefore, the numerical models are applied to study Malpasset case study (France) and total dam break scenario for the first arch concrete gravity dam Nam Chien constructed in Vietnam. Another aspect considered in the paper is the applicability of simplified methodologies that have been recently proposed in the literature to estimate the discharge hydrograph at dam site in both cases of total and partial dam break, thus providing the upstream boundary condition to model the wave propagation in the downstream valley. The advantage of this approach is that it can be used in cases where the reservoir bathymetry is not available, the only required information being the stage-volume curve. The breach hydrographs obtained in this way for some reservoirs in Dien Bien province show satisfactory agreement with those computed through the numerical model based on the 2D SWE confirming that the simplified methodologies considered in the paper provide realistic evaluations that can be used in dam break studies.
Year: 2014