Design Procedure for Determining Optimal Length of Side-Weir in Flood Control Detention Basin Considering Bed Roughness Coefficient

AbstractSide-weir detention basins have been increasingly highlighted as an alternative countermeasure for decreasing peak flood discharge and have become increasingly adopted as part of an integrated watershed flood protection plan. However, there were few methodologies sufficient enough to quantitatively estimate the decrease of the peak flow by the side-weir detention basin in flood-control measures by fully considering relevant design and hydraulic parameters. Until now, any noticeable standardized design procedure to optimally design the size of a side-weir located at the inlet of a detention basin has not been available. In this study, a generalized design procedure was proposed for determining the horizontal length of a side-weir considering hydraulic parameters, especially for the bed roughness as a major hydraulic parameter, where other hydraulic parameters were assumed to be invariant and restricted by field conditions. The proposed design procedure is exemplified based on a simple numerical model detailed herein. In particular, the design procedure considers complex overflow regimes dominated by free and submerged overflow between the main channel and detention basin through the side-weir. Subsequently, a concept for a flood control performance graph is suggested for evaluating the decrease of peak flow for design and hydraulic parameters of the side-weir, such as the bed roughness and the length of side-weir, respectively. Also, a design characteristic line is also proposed to finally determine the optimal length of side-weir.