3-D numerical study on the influence of orifice arrangement on sediment transport upstream of a dam

Multiple orifices set on a dam are commonly used for flood discharge and sediment removal. Different arrangements of orifices may lead to different scalar or sediment transport process in the near dam reservoir region. 3-D numerical simulations are implemented to simulate flow and sediment transport near an idealized rectangular dam region with a focus on the influence of orifice arrangement on scalar and sediment transport under a same flow discharge and concentration condition. It is found that the concentration distribution in the near dam reservoir region and the transport flux at the dam-site may change dramatically due to different arrangements of orifices. The effect of orifice arrangement on scalar and sediment concentration distribution in the near dam reservoir region is found to be limited roughly within a range of \((15-20)\sqrt{\sum{A}}\) away from the dam where ΣA is the total area of all opened orifices on a dam. Under the same inlet water flow and concentration condition and at a steady state, for scalar transport, the transport flux at the dam-site may be independent of orifice arrangement; while for sediment transport with considering the settling effect, the transport flux is generally larger in cases with one orifice except when the orifice centroid elevation is sufficiently high. This work may provide guidance for reservoir regulation, e.g., to discharge more sediment downstream a reservoir or adjust local sedimentation distribution near the dam.