Quick Method for Estimating Flood Discharge Reduction from Dense Water-Blocking Structures

Analyzing the impact of multiple water-blocking structures, such as bridge piers and wharf piles, on flood discharge is challenging due to difficulties in simulating large-scale scenarios and a lack of empirical methods. Based on the increased roughness, this paper presents an empirical approach to quickly estimate the reduction in flood discharge caused by pier groups. The increased roughness arises primarily from two types of water flow energy loss: (1) the loss due to drag force induced by pier groups; and (2) the loss due to the reduction in flow cross-sectional area at the bridge pier locations. The method for estimating equivalent roughness employs the Manning and Chezy formulas and a multiparameter formula, which includes coefficients for resistance, shielding influence, interference influence, and skew. A case study demonstrates that bridge bundling led to a 14.8% decrease in river flood discharge, offering practical insights for improving flood management strategies.