Hydrodynamic analysis of flood wave propagation through rockfill detention dams: a 3D numerical study

The current research presents three-dimensional numerical modeling of the hydrodynamic behavior of flood propagation through rockfill detention dams. Resolution of the Navier-Stokes equations, by the FLOW-3D software, was conducted using the finite volume method and RNG k-epsilon model of turbulence. Simulations were executed on a structured mesh with about 100,000 cells, taking special care with the boundary conditions and sensitivity of the mesh. The porous medium was simulated by 5 and 10 cm diameter spheres, representing the internal flow resistance using the Ergun equation. A total number of 24 models were simulated. The peak discharge reduction through rockfill media was concluded to reach about 40%, while finer material tends to absorb noise more in the output hydrographs. The velocity magnitude results showed an increasing velocity towards the outlet and maximum along the centerline at the exit. That was obtained; the turbulent kinetic energy and its dissipation rate correlate with shear velocity, thus both increased towards the outlet. Streamlines analysis revealed a complex flow pattern of this mixing tank, including generation of clockwise and counterclockwise vortices inside stagnant zones. Based on that, a dimensionless energy dissipation coefficient in terms of particle size distribution was derived: eta = 0.85(d50)-0.3, R2 = 0.92. The result showed that alpha decreases exponentially as porosity increases: alpha = 1.2e(-2.5n) with R2 = 0.88. These findings have significant implications for optimizing rockfill detention dam design. This can contribute to a reduction of erosion downstream by 40%, while a 30% increase in the flood retention time is attainable through optimal shape selection.