WSUD in ESD: What Does a 100% Stormwater Score Actually Mean?

Water sensitive urban design strategies

For many planning applications, Water Sensitive Urban Design (WSUD), is assessed through an SDA, SMP or standalone WSUD report.

However, WSUD is often misunderstood. It is not just about adding a rainwater tank or achieving a number in BlueFactor calculator. Good WSUD design helps reduce pollutants, manage runoff, support water reuse and protect downstream waterways such as creeks, rivers and water ways.

For many small-medium developments in Victoria, project teams are asked to demonstrate a BlueFactor score of 100% or above. This is an important compliance benchmark, but it should not be read as “100% of stormwater is treated on site”.

The simple idea

A 100% stormwater score means the proposed treatment strategy meets the Nitrogen removal benchmark in the assessment tool.

Nitrogen is most important for salt water, and reducing nitrogen loads to Port Phillip Bay is a key focus for the greater Melbourne area.

What pollutants are we trying to reduce?

Stormwater runoff can collect sediment, nutrients and litter from roofs, driveways, roads and landscaped areas. These pollutants can enter local drains and eventually reach waterways.

Nitrogen receives particular attention in Melbourne because excess nitrogen entering Port Phillip Bay can act like fertiliser for algae. This is related to eutrophication, where too many nutrients can lead to excessive algal growth and poorer water quality.

Harmful Algae blooms from Nitrogen

Common WSUD strategies for inner-suburban projects

For inner-suburban sites, space is often limited. The best solution is usually a combination of practical measures, including tanks, raingardens, and permeable paving.

Common WSUD strategies

The takeaway

For most inner-suburban projects, WSUD compliance is achievable. The key is early coordination.

A 100% BlueFactor score is not just a calculator result. It depends on whether the roof, driveway, landscape and drainage strategy are designed to work together.

If you are preparing a planning application and are unsure about the most appropriate WSUD strategy, early advice can help avoid Council RFIs and late redesign.