Coastal Urban Waterlogging Simulation and Drainage System Optimization: A Case Study of the Shajing River Drainage Area in Shenzhen
Urban waterlogging, exacerbated by climate change and rapid urbanization, poses increasing risks, particularly in coastal low-lying areas with dense river networks. This study simulated waterlogging in the Shajing River drainage area of the Maozhou River basin, Shenzhen, using the SOBEK hydrodynamic model. Under a 5-year return period rainfall, 47 manholes overflowed and 31.29% of stormwater pipes operated at full capacity. Twelve waterlogging-prone points were identified: eight due to insufficient drainage capacity and five due to river backflow from low elevation. Two optimization schemes were compared: enlarging pipe diameters and implementing Low Impact Development (LID) measures. Pipe enlargement reduced overflowing manholes by 32 and full-flow pipe length by 20%, effectively decreasing surface ponding. LID measures reduced overflowing manholes by only 4 and full-flow pipe length by 1.5%, but decreased maximum flooding depth by nearly 1 m, alleviating drainage system burden. The study highlights the complex causes of coastal urban waterlogging, especially river backflow under tidal influence, and recommends considering sea-level rise and storm surge in drainage design. The findings provide valuable references for attributing waterlogging causes and planning drainage network upgrades in coastal cities.