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
Step 2: Calculate mean annual runoff volume (MARV)
The Mean Annual Runoff Volume (MARV) from impervious surfaces on a property, and the proportion of the MARV that is retained on site, is calculated using continuous simulation modelling. MUSIC is an industry standard software tool used in Australia for this.
For simple stormwater connection systems, pre-developed design aids provided by the catchment manager may be used.
For more complex systems, MUSIC will be required to model the system and calculate retention volumes.
Simple systems
The proportion of MARV retained in the example below is determined by the relative values of the impervious surface area, retention storage volume, and average daily outflow. The typical chart below illustrates this relationship for western Sydney.
The volume and outflow are scaled relative to the size of the contributing impervious surface area - expressed in terms of mm/m2 (millimetres depth of storage per square metre of impervious area) and mm/m2/d (millimetres depth of storage per square metre per day) respectively.
Example application
House roof to rainwater tank
Applying the chart for the example stormwater connection diagram roof area connected to a rainwater tank, 48% of the roof MARV is retained:
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5,000 litre rainwater tank collects runoff from 207 m2 of roof –>
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storage volume = 5,000 / 207 = 24 mm/m2
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Connected to residential hot water, toilet flushing, outdoor irrigation and laundry for 4 people –> demand volume ratio = 414 / 207 = 2 mm/m2/day
Rear shed to lawn area and raingarden
Water infiltration into the soil through a lawn buffer and small raingarden retains 49% of the MARV from the rear shed roof
Other impervious areas direct to drainage
Other impervious areas on the site (189 m2) are not connected to a retention system and none or 0% of the MARV from these areas is retained on site.
These are combined to calculate an area weighted average MARV for the entire site of 30%.
