Western Australia Chapter

Urban Stormwater and Groundwater Management for Water Sensitive Urban Design Outcomes

Bill Till MIEAust CPEng.

The water sensitive approach to stormwater management aims to maintain the pre- development hydrologic regime. The Department of Water is promoting the design of stormwater infrastructure that addresses both quantity and quality management during frequent, low intensity rainfall events. Traditional design of stormwater infrastructure focused solely on quantity management and ‘disposal’ to provide flood protection during infrequent, high intensity events.

The Department of Water is addressing ‘flow rate and volume’ management up to the 1 year ARI event with the introduction of the following criterion for assessment of urban developments: ‘for the critical 1 year average recurrence interval (ARI) event, the post development discharge volume and peak flow rates shall be maintained relative to pre-development conditions in all parts of the catchment’.

The criterion delivers better hydrologic and ecologic outcomes, at a catchment scale, by slowing water flows closer to pre-development rates, thus limiting the transfer and concentration of nutrients and pollutants to receiving water bodies. This requires a rethink of geotechnical approaches in building foundation design as rainfall is being managed ‘at source’, rather than ‘disposed of’ off site. Sub-soil drainage design becomes a critical element in the delivery of this criterion.

The presentation will outline the new WSUD stormwater and groundwater management criterion for urban development and challenges geotechnical professionals to provide innovative solutions to deliver this criterion thus ensuring better water resource outcomes.

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.