Determination of the hydraulic efficiency of intake structures like grate inlets and screens in supercritical flow

Regarding the increasing number of extreme rainfall events there is a need of determining the hydraulic efficiency of existing grate inlets and improving these in order to take as much as possible of the storm water ( note: it's not feasible to catch the whole runoff). In order to investigate and improve the hydraulic efficiency of street inlets, several physical and three-dimensional numerical test runs were done. Beside the total opening area of the grate, the shape and arrangement of the bars lead to different hydraulic performances. Within the presented study the bars are positioned in a 90 degree angle to the flow direction. Compared with the performance of coanda screens within supercritical flow conditions the shape of the bars is varied. Typical bar openings of 36 mm and bar widths of 32 mm were considered as well as the number of the bars regarding the total length of the inlet. Different shapes like a triangular or rectangular cross section were tested. In the physical model the bars fixed on a frame were put in an opening in a tilting flume. The discharge characteristics are then described by the Froude number controlled by the discharge and the slope of the flume (longitudinal as well as transverse).