|CSS was engaged by Campbelltown City Council to prepare a detailed flood study for the Campbelltown Locality. The purpose of the flood study was to define flood behaviour for existing and future conditions. In accordance with the requirements of the NSW Government's Floodplain Development Manual (2005), both mainstream and overland flooding needed to be considered as part of the study.|
The Campbelltown Locality includes the suburbs of Campbelltown, Bradbury and Leumeah, and occupies a total area of approximately 10 km2 in south-western Sydney. The study area is highly urbanised and incorporates natural watercourses, concrete-lined drainage channels, as well as sub-surface drainage pipes and culverts. A number of significant flow obstructions are also located within the study area, including Main Southern Railway Line.
The movement of floodwaters throughout the study area was defined using a 2-dimensional TUFLOW hydraulic model. The TUFLOW model utilised a 2 metre grid size and extended across the full 10 km2 study area. The TUFLOW model also incorporated major urban flow obstructions (e.g., buildings, fences), as well as over 3,000 subsurface stormwater pipes and over 3,000 pits. Unique inlet capacity relationships were developed to account for the differing inlet capacities of each stormwater pit type.
The TUFLOW model was used to simulate flood behaviour for a range of storm durations. The complete library of flood level surfaces was interrogated to ensure the maximum flood level at each 2 metre grid cell was extracted from the full range of simulated storm durations. This ensured that the 'worst case' flooding conditions were quantified across all sections of the study area (i.e., ensured that both mainstream and overland flooding were accounted for).
In addition to simulating flood behaviour for existing conditions, additional simulations were completed for future conditions. The future scenario accounted for increased runoff, as well as filling of all potentially developable areas above the peak 100 year ARI flood. This allowed verification of the cumulative impact of future filling on flood behaviour as well as the definition of areas that should be preserved for the future conveyance of flood flows.