Stormwater and Wastewater Design for Residential Development

A proposed residential development site within a high-priority catchment was facing a real challenge with their stormwater & wastewater management.

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Due to the catchment’s priority status, it is crucial to appropriately assess any new proposed development. Therefore, the council had requested the client to demonstrate that the site’s Stormwater Management System (SWMS) and the Onsite Wastewater Management System (OWMS) to are able to meet the following requirements and prove that the development will not cause any risk of harm to the receiving environment.

Specifically, the proposed SWMS needed to:

retain rainwater runoff from the impervious areas of the development,
provide treatment for tank overflows using soakage or raingardens.

The existing OWMS was undersized and was no longer compliant with current regulations.

The client needed a solution that would meet these council requirements, manage potential interactions between stormwater and wastewater systems, and provide a reliable, long-term servicing solution for the development.

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Morphum approached the project in two stages, beginning with a desktop review of all available site information to understand the constraints for both stormwater and wastewater.

The stormwater system design began with a catchment analysis, a hydrological assessment of the area to estimate runoff volumes and overland flow paths. This informed the sizing of retention tanks and the design of treatment systems, with performance verified using Blue Factor (formerly known as STORM Calculator), a tool published by Melbourne Water.

Once the stormwater design was confirmed, Morphum turned to the wastewater system. The team assessed wastewater generation, daily flows, and treatment options based on site characteristics, before sizing and designing the effluent dispersal field. This process prevented any design constraints between the SWMS and OWMS and ensured a seamless and efficient design process.

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At each stage, findings and design outcomes were documented in technical memoranda with marked-up site plans, giving the client a clear, practical solution with evidence to support it.

With Morphum’s engineering team designing both the stormwater and wastewater systems together, the development was able to meet council requirements and also provided the client with a robust hydrological solution for the development that reduced its impacts on the local communities and the sensitive catchment environment.

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