Discharge Capacity of a Grate Street Inlet in Urban Flooding Based on Experimental and Theoretical Studies

Urban flood disasters have occurred frequently in recent years in China, which cause a serious threat to the safety of people and property. The discharge capacity of a street inlet is very important to the calculation of drainage efficiency in an urban area. Laboratory experiments on the discharge capacity of a specified grate inlet were conducted on a 20 m long and 3 m wide experimental platform, consisting of the upper street layer, the triangular weir tank underneath, and a combination of the grate inlet, catch basin and side connection pipe between those two layers. A total of 78 runs of flume experiments were conducted to obtain the discharges through the inlet under various water depths and corresponding velocities. These results show that: (i) the grate inlet was operated like a weir when the catch basin was not fully occupied by water, while it was operated as a nozzle after the basin was fully occupied; (ii) based on experimental data, the weir and nozzle coefficients were respectively calibrated for the discharge formula of grate inlet; (iii) furthermore, an empirical formula for predicting the discharge capacity of street inlet was innovatively proposed using a dimensional analysis method, and it is found that the relative velocity can be expressed as a power function of Froude number of the incoming flow, where the relative velocity is defined as the ratio of the comprehensive velocity through the inlet to the incoming flow velocity in front of the grate; and (iv) finally, the proposed formula was validated in detail against existing experimental data for real storm inlets. This current study can provide a quantitative basis for refining urban flood management.