Experimental evaluation of design methods for in-site detention ponds

In this study, the detention rate of detention pond was defined to include both reduction and delay of peak flow. Flood routing experiments, with various combinations of inflow hydrographs and outlet devices in an in-site detention pond, were performed to examine the effectiveness of two analysis methods, namely the simplified method and the hydrological routing method; and to compare the detention rate of two types of outlet, namely the rectangular sharp-crested weir and the rectangular orifice. Comparison between predicted results and experimental outcomes show that the estimation errors of maximum storage volume obtained by the hydrological routing method are less than 5%, while those achieved by the simplified method are less than 10%. Hence, the simplified method with easier calculation but poorer accuracy may be employed to estimate the maximum storage volume in the preliminary design stage, while the hydrological routing method, which involves more complicated calculation but gives more precise estimation, is better suited for application in the detailed design stage. Moreover, the maximum storage volume of the rectangular orifice is smaller than that of rectangular sharp-crested weir under the same peak flow reduction, making the rectangular orifice a better choice of outlet design. In addition, inflow hydrograph with a long recession time or a long rainfall duration needs a long delay time to reach the required reduction in peak discharge.