With the rapid expansion of urbanisation, coupled simulation of stormwater pipe networks and river networks has become crucial for urban flood control and drainage planning. Traditional hydraulic models often employ separate numerical frameworks for pipe and river networks, requiring iterative boundary condition exchanges that introduce numerical errors and increase computational complexity. This study presents a Unified Hydraulic Calculation Model that integrates the governing equations and numerical solution methods for both pipe and river networks into a single computational framework. The model seamlessly handles transitions between open-channel and pressurised flow, ensuring numerical stability and high accuracy across various hydrodynamic conditions. The model is validated through three case studies: (1) a looped river network scenario, yielding average relative flow errors of 0.0402% and 0.0802% compared to reference studies; (2) a stormwater drainage network case, demonstrating strong consistency with Storm Water Management Model (SWMM) and InfoWorks; and (3) a coupled drainage–river network case, where average relative errors of flood peaks remain within 5% compared to MIKE 11 + MIKE URBAN iterative coupling, with computational efficiency enhanced by approximately 30%. By eliminating interpolation-based coupling, this model reduces user workload while offering a robust tool for urban flood management and watershed hydrodynamics.
Wang et al. (Tue,) studied this question.