Microburst Software
Why WSUD?
Water sensitive urban design (WSUD) provides a range of benefits:
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Healthy waterways
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Reduced flood risks
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Better amenity
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Efficient use of resources
Stormwater retention guideline
Compliance targets
The Stormwater Retention Guidelines use the following terminology to define measures of runoff volumes from impervious surfaces:
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MARV - The Mean Annual Runoff Volume is the average volume of runoff off impervious surfaces over the course of any year.
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FERV - The Flood Event Runoff Volume (FERV) is the volume of runoff from impervious surfaces during a flood causing burst of rainfall.
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Once these are calculated, site retention systems can be sized to retain a proportion of these volumes on site. The percentage retention targets, %MARV and %FERV are set by the catchment manager.
Existing compliance targets
The new requirement to retain a proportion of the runoff from impervious surfaces on a property is in alignment with existing regulations:
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Rainwater tanks are commonly used to meet NSW BASIX water efficiency targets. The new requirements for stormwater retention contributes towards meeting BASIX requirements for potable water use reduction, through the use of roof water harvesting.
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Currently, many catchment managers require stormwater discharge from developments to meet pollution reduction targets for runoff from the developed site – representative pollutants are typically sediment, phosphorous, nitrogen, and gross pollutants. Stormwater retention systems such as raingardens provide pollution reduction benefits which help to meet these requirements.
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On-site detention of peak flows is often required to mitigate potential downstream flooding. Retention systems can reduce the required size of these systems as both act to reduce the frequency and severity of flooding at critical points within the downstream catchment.
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Satisfying the Stormwater Retention Guideline requirements acts as an alternate pathway to meeting these water quality, flooding and water saving targets.