The Alexandra Canal Catchment Flood Study and Floodplain Risk Management Study was prepared by Cardno for City of Sydney Council.  The majority of the catchment is fully developed and consists predominantly of medium to high-density housing, commercial and industrial development with some large open spaces.

A SOBEK 1D/2D floodplain model was established representing the pits, pipes, channels, buildings, ground elevations and landuses.  Flood modelling showed inundation of roads at many locations across the catchment as overland flow is trapped at low points due to topography, blockage of overland flowpaths by buildings, and limited capacity of the drainage network.

The highly developed nature of the catchment limited opportunities to implement stormwater detention facilities to mitigate inundation.  A long-term option comprising substantial additional trunk drainage pipelines required to achieve 20 year ARI capacity in the drainage network across the catchment was examined.  Smaller reaches of the overall system were also examined for application in the short to medium term.

A significant amount of redevelopment is occurring within the catchment, predominantly the conversion of industrial / commercial warehouse buildings into residential apartments.  The catchment-wide flood model has been used extensively for assessment of these developments to satisfy Council’s Interim Floodplain Management Policy, particularly with respect to floor levels, basement entries, and potential impact to neighbouring properties.