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 equivalent depth of scour was simulated by means of three-dimensional numerical analysis using a sediment scour model of FLOW-3D program. The sediment scour model in FLOW-3D is able to simulate the scour hole development process, in this study four models of inclined apron of broad crested weirs [A, B, C, D] with different downstream reverse angles (0°, 4.5°, 8.7° ,13°) respectively are tested under the same flow intensity and the same duration, based on experimental study from the literature that has been held for a duration of 6 hours to see if the same behavior will be concluded for scour reduction. Downstream of the first models act as ordinary weir while the other models act as an obstacle toward the flow, the water flows above the sloped downstream bed and dissipates some of its energy. There was a good agreement between experimental and FLOW-3D results. The results showed, that model C reduces local scour hole volume, the maximum scour depth in addition shift the scour holes away from the structure as compared to the other models. The idea is decreasing downstream height of broad crested weir while providing an obstacle in shape of sloped downstream bed toward the flowing water. This reduction gave the weir a new performance by making it as an energy dissipater. The present technique similarly reduces construction costs also improves the hydraulic performance of single step broad crested weirs.

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 equivalent depth of scour was simulated by means of three-dimensional numerical analysis using a sediment scour model of FLOW-3D program. The sediment scour model in FLOW-3D is able to simulate the scour hole development process, in this study four models of inclined apron of broad crested weirs [A, B, C, D] with different downstream reverse angles (0° , 4.5° , 8.7° ,13° ) respectively are tested under the same flow intensity and the same duration, based on experimental study from the literature that has been held for a duration of 6 hours to see if the same behavior will be concluded for scour reduction. Downstream of the first models act as ordinary weir while the other models act as an obstacle toward the flow, the water flows above the sloped downstream bed and dissipates some of its energy. There was a good agreement between experimental and FLOW-3D results. The results showed, that model C reduces local scour hole volume, the maximum scour depth in addition shift the scour holes away from the structure as compared to the other models. The idea is decreasing downstream height of broad crested weir while providing an obstacle in shape of sloped downstream bed toward the flowing water. This reduction gave the weir a new performance by making it as an energy dissipater. The present technique similarly reduces construction costs also improves the hydraulic performance of single step broad crested weirs.