Mar 13, 2017 3:28 pm
So the builder has come back to me today to say the council does not recommend soak wells due to the soil type (M5 class) and that we would need to use rainwater tanks instead. Details of the house / property:
Roof area (m2 on the flat): just under 400
Downpipes: 12 - 90x45 zinc
Location: South East Perth - foothills
Would a water tank (or multiple) be enough to handle storm water for this? The council would like to know the size of tank and location, anyone offer ideas on this? I would like it on the side where the proposed water tank is (below site plan), but if this does not work best for the height / fall of land etc then open to suggestions.
Re: Stormwater Requires Rainwater Tank2
Mar 13, 2017 8:35 pm
Is the council requirement just for retention or is there also a detention (mitigation) component? If the tank filled, where would the water go? It is hard to imagine the council not having a detention requirement with a limited drainage capacity but there are options such as overflowing to a second tank. Having detention capacity makes sense.
The roof would harvest about 1,000 lpm during a 1:20 ARI if you are in a 150mm/hr 1:20 ARI region. The 1:20 ARI determines eaves gutter and downpipe compliance.
The council will most probably require a hydraulic assessment.
You will need two separate 100mm DWV pipes if you have just the one tank but the available head will be critical. It is strongly recommended that you fit leaf diverters to the top of each downpipe if you have a wet system and this is mandated in many areas, you need to check if it also your local requirement. Leaf diverters decrease the available head but they do allow low restriction inlets to be fitted and these supplement a wet system's flow capacity amongst other benefits.
It would be economical if you can site a standard 22,500 litre tank (or two) because they are made en masse and would give a good storage reserve during dry weather but you really need to do some homework and check the area's average annual rainfall, determine what the water usage will be and then do usage and storage projections by looking at sites like the Tankulator.
Re: Stormwater Requires Rainwater Tank3
Mar 14, 2017 1:20 pm
So spoke with the council, they say it is for detention only, we are on mains water so it is not required to be the sole water supplier for the property. Also mentioned they would not need to do hydraulic assessment.
Done some research on average rainfall for the area, average per year is sitting on 830mm. Over the last 20 years it has been between 550mm - 1200mm per year, not sure if that helps? The suburb is Darling Downs in WA.
I guess we are trying to balance the cost against what savings we may get. We will have a large swimming pool as well.
Not sure if that makes a difference in deciding what way we should go?
Does anyone have any recommendations on rain water tank suppliers in WA?
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