Simulation of local scouring downstream of broad crested weirs with variable step angles

Broad crested weirs are hydraulic structures used to control the flow depth and discharge of channels. Structures constructed in rivers and channels are exposed to scour around their foundations as they cause turbulences in uniform flow and sediment transport as a result of increase in flow velocities at downstream. If the scour depth becomes substantial the stability of the foundations endangered with a resultant hazard to the structural failure. In this study the flow field variation and the corresponding scour depth was simulated using three-dimensional hydrodynamic analysis and a bed-load transport model by Flow-3D software. The bed-load transport model in Flow-3D is able to simulate the scour hole development. Four models of perforated hump Step Broad Crested Weirs [A, B, C, D] with different downstream reverse angles (0.0, 4.50, 8.70 ,13.0) respectively are tested under the same flow intensity and the same duration of 6 hours. There was a good agreement between experimental and Flow-3D results. The results showed that, model C reduces local scour hole volume and the maximum depth of scour and also shift the scour holes away from the structure as compared to the other models. The present technique similarly reduces costs and improves the hydraulic performance of broad crested weirs