As Councils and Water Authorities have increased their understanding and knowledge of flood behaviour in their catchments through flood modelling, their requirements of future developments have become correspondingly rigorous. The type and complexity of issues to be addressed varies depending on the size of the project and whether it is a greenfield or brownfield (infill) development.

Greenfield developments in flood prone areas will require filling to provide the appropriate flood immunity. This requires careful design to maintain the passage of water on the floodplain without causing adverse flood impacts on neighbouring properties. Another consideration is the increase in impervious areas which increases the runoff from the development compared to that from the existing greenfield site. It is necessary to manage this change to ensure there is no impact on neighbouring properties.

Infill development where single or multiple lots are converted into higher density development is typically in older areas where the existing drainage network was not designed to contemporary standards (refer Urban Flood Mapping). The existing lots are often in overland flowpaths and the increased density of development can potentially block these flow paths resulting in flood impacts on neighbouring properties. Other considerations include ensuring that finished floor levels are above the flood level and ensuring the requirements for site safety and safe access/egress are achieved. These constraints can control the location and extent of development of the site and an unoptimised design may not maximise usage of the site.