Drainage Network Modelling with a Novel Algorithm for Junction Calculation

Abstract

Most of the existing drainage network models focus on capturing different flow regimes in sewer pipes. Despite being important to produce reliable results of urban flood simulation, the development of robust scheme to describe the coupled conditions at pipe-to-pipe intersections has received less research attention. In this work, the two-component pressure approach (TPA) is chosen to support pipe flow calculation due to its superior capability in simulating complicated transient flow between the free-surface and pressurized conditions in pipes. To avoid the complicated boundary conditions as required by a TPA model to approximate the junction connections, a novel strategy is proposed in this work where the flow at a junction is calculated using the 2D shallow water equations (SWEs). In junctions, irregular grids are created automatically according to the layout of connecting pipes, on which a first-order Godunov-type finite volume scheme is implemented to solve the 2D SWEs to simulate the junction flow. The 2D SWEs model is driven by the boundary conditions provided from the pipe calculations and rainfall input in necessary, which in turn creates boundary conditions for pipe calculations at the next time step. It is expected that the new approach as proposed will support large-scale drainage network modelling with higher efficiency and stability.