The runoff flow loading approach for interim stormwater detention design

ABSTRACT Land development increases urban runoff and pressurizes undersized drainage systems without proper flood mitigation. This study develops the runoff flow loading approach (ROFLA), a design method for interim stormwater detention systems that address these transitional challenges. ROFLA quantifies spatial and temporal variations in runoff flow rates using the rational method, providing a simplified calculation of required detention volume based on changes in imperviousness. In the paper, the case located in the City of Las Vegas, Nevada, the ROFLA suggests that a temporary storage volume of 1.65 acre-ft be provided to reduce the incoming peak flow from 45.6 to 6.0 cfs. Using a roadside shallow basin, a bubble-up overflow system is employed to spill the excessive stormwater into the basin as soon as the downstream sewer line is pressurized. By gravity, the stored runoff volume is gradually released into the downstream sewer line during the flood recession. The proposed ROFLA may directly work with the rational method for small urban catchments (<50 ha) or link to computer simulations for large and complicated watersheds. ROFLA is an effective tool to implement the master regional drainage plan (MRDP) through continuous parcel developments toward the ultimate regional land-use zoning plan.