The Hills Urban Overland Flowpath Mapping

CSS were engaged by The Hills Shire Council to map all urban overland flow path alignments in The Hills Shire Council LGA. The purpose of the study was to help identify all allotments that may be traversed by an urban overland flow path and which may be subject to a flood-related development controls (i.e., flood control lots).

The project was completed using a detailed 2 metre DEM in conjunction with our CatchmentSIM software. Custom CatchmentSIM scripts were developed to determine appropriate initiation points for all overland flow paths based on a minimum peak 100 year ARI discharge value as well as the degree of incision of the terrain to enable areas of sheet flow and concentrated, channel flow to be distinguished.

The overland flow paths were verified by comparing them with allotments where flood complaints had been previously received (refer yellow parcels in image). All flow paths were found to be located within or in close proximity to these lots.  In addition the flow paths intersected allotments that were previously identified as flood control lots and did not pass through allotments that were previously identified as not being flood control lots.