Improving the understanding of on-site stormwater detention performances

On-site Stormwater Detention has been used around the world to reduce stormwater peak flow at lot scale. However, few studies have evaluated its performance as well as its hydrological and hydraulic parameters on a real scale. To evaluate these variables, two OSDs were monitored in Belo Horizonte/Brazil. Based on the analysis of monitoring data, it was observed that: (i) the OSDs average efficiencies in peak flow damping were higher than 50%; (ii) the storage volume per catchment area was close to 25 L/m(2); (iii) the short tubes discharge coefficients were approximately 0.90 and; (iv) the shape of inflow hydrographs were similar to hyetographs. The use of the Unit Hydrograph Modified Rational Method properly represented the rain-runoff transformation. The findings could be used in OSD design to determine the inlet hydrograph, to pre-sizing the storage volume based on contribution area and to use the proper discharge coefficient value for outlet device.