How to save $30k on stormwater detention
How to save your client $30K on on-site stormwater detention (OSD).
The average cost of 5 OSD systems is 10-15kl in Sydney, 2022.
The purpose of OSD is to relieve pressure on the council's stormwater system.
In particular, the critical pipes slow down in the catchment.
Here in this example at Avalon Beach, these pipes are around the shopping area and beach.
Diagram 1, Issue 14
Flow for whole catchment(at this location)
Property without OSD
Property with OSD
OSD is making council's problem worse by this amount
Time of whole catchment peak
Diagram 2, Issue 14
OSD reduces the peak flows from each property
Squashing the curve by dragging the flow out over a longer duration
Flow for one property
But for locations low in the catchment, dragging the flow out over time means the flow from the property with OSD coincides with the peak flow of the whole catchment. Or thinking in reverse, we are better off draining the low properties as early as possible in the storm, before the "wave" arrives from upstream.
Regardless of any council stormwater policy, mathematics and physics always make this true.
I estimate that 20-30% of all OSD systems are not only futile but counterproductive to their very purpose.
It's time that we called out this lazy policy-writing. To save cost and space for both our clients and our community.
Prepared for you by Ian 🙂