XP Solutions

1D & 2D modelling of urban drainage systems using xpswmm and Tuflow

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The release of a revised New South Wales (NSW) Floodplain Management Manual in 2001 established a new direction for urban flood management in NSW. This new direction was created by a redefinition of the floodplain as the area bounded by the Probable Maximum Flood (PMF) – this poses a challenge to estimate PMF flooding in highly urban areas and particularly in piped drainage areas, and the removal of the distinction between “mainstream flooding” and “local flooding” – this poses challenges in defining and mapping flood risk areas in residential areas inundated by the PMF. At the same time the increasing collection of aerial laser scanning (ALS) across whole local government areas (LGAs) is providing detailed survey levels capable of supporting 2D terrain and hydrodynamic modelling and detailed floodplain mapping.

This new direction and the increasing availability of ALS have ramifications for urban flood studies. The trend in NSW and elsewhere has been for the growing adoption of 2D models as the new benchmark for urban flood studies.

Two case studies that demonstrate the new 1D/2D modeling capability of xp2D (TUFLOW) and xpswmm are described. The first case study is of a reach of Prospect Creek in the City of Fairfield. A 2D and a combined 1D/2D models of the floodplain were assembled and run. A comparison of 1D, 1D/2D and 2D results is given. The second case study is of a local drainage subcatchment that demonstrates the interaction between the piped drainage system and 2D surface overland flows.

It is concluded that the 2D hydrodynamic modeling layer in the xpswmm package offers users new opportunities to undertake more detailed investigations of urban drainage systems and of urban waterways and floodplains. It also demonstrates the on-going evolution of the xpswmm package in response to the changing needs of stormwater managers.

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