Global design of hydraulic structures optimised with physically based flow solvers on multiblock structured grids

This paper presents the numerical studies lead by the Laboratory of Applied Hydrodynamics
and Hydraulic Constructions of the University of Liège (HACH) for the rehabilitation of the 21-meter high Nisramont dam in Belgium. After determination of the up-to-date 1000-year return flood using the hydrological runoff model WOLFHYDRO on the global 74,000 ha watershed real topography coupled with statistical analyzes, and after validation on the existing situation and for extreme observed events, the 2D finite volume multiblock flow solver WOLF2D has been applied to the design of the new stilling basin and to the bottom outlet rehabilitation impact study. The multiblock solver possibilities allow mesh refinement close to interesting areas, such as dam spillway and stilling pool, without leading to prohibitive CPU times, while suitable shallow water equations formulation allows the computation of the flows on the strongly vertically curved bottom of the spillway. In the described simulation, 270,000 structured finite volumes, from .25 to 1 meters long, are used to simulate as a whole the flows in the upstream reservoir, dam, spillway, stilling basin and downstream river, this on a real topography.