Performance of a shallow-water model for simulating flow over trapezoidal broad-crested weirs

Abstract

Shallow-water models are standard for simulating flow in river systems during floods, including in the near-field of sudden changes in the topography, where vertical flow contraction occurs such as in case of channel overbanking, side spillways or levee overtopping. In the case of stagnant inundation and for frontal flow, the flow configurations are close to the flow over a broad-crested weir with the trapezoidal profile in the flow direction (i.e. inclined upstream and downstream slopes). In this study, results of shallow-water numerical modelling were compared with seven sets of previous experimental observations of flow over a frontal broad-crested weir, to assess the effect of vertical contraction and surface roughness on the accuracy of the computational results. Three different upstream slopes of the broad-crested weir (V:H = 1:Z1 = 1:1, 1:2, 1:3) and three roughness scenarios were tested. The results indicate that, for smooth surface, numerical simulations overestimate by about 2 to 5% the weir discharge coefficient. In case of a rough surface, the difference between computations and observations reach up to 10%, for high relative roughness. When taking into account mentioned the differences, the shallow-water model may be applied for a range of engineering purposes.

Modelling Weirs in Two-Dimensional Shallow Water Models

“…In the same line of development, [13] built a model for the analysis of the hydraulic characteristics over the weir crests. These examples, together with other more recent studies such as [14,15], highlight the remarkable development of 2D shallow water equation (2D-SWE) models in simulating flow over weirs. However, since the first numerical models, the estimation of flow over weirs has represented a challenge for 2D-SWE models due to the violation of the hydrostatic pressure hypothesis [16].…”