Browse Forums Eco Living 1 Nov 26, 2015 8:47 pm For our new house in Adelaide we are required to have a 10,000L tank set up as detention/retention. The best bet of getting it into the back yard is via the garage. Between the front garage door height clearance of 2370, and the back door width clearance of 2650, I can only just squeeze a tank that size in, so that limits the choice quite a bit, meaning I need a tank that is that high. We have 330m2 of roof, of which 60% needs to be captured, and I'm thinking to use 6 supadivertas over the 9 downpipes in total. One thing I wonder about this is whether I'll have enough head to do it though. The yard level is only about 100mm below floor level, and with eaves at 2400mm that's only giving around 350mm from the standard tank inlet height to the facia. With a bottom tank entry it will still work, but may not fill up fully. Or is it worth looking at burying the tank a bit? The main aim at the moment is to get the tank into the back yard before the garage doors go on. So to order the tank I expect I need to know the inlet details. What sort of size inlet would I have into the tank with this sort of system? A question to SaveH20 is if you get the new diverter produced, what sort of connection would you end up having to the tank using that system? Then for the slow detention drain, would it make sense instead of drilling the tank and running stormwater all the way to the tank, to instead put a drain at one of the downpipes to divert the excess tank water back into the stormwater? Re: Buying a tank 2Nov 27, 2015 3:24 am oneJohn For our new house in Adelaide we are required to have a 10,000L tank set up as detention/retention. Councils usually refer to one tank with specified retention and detention compartment volumes but unless the detention compartment's overflow outlet has a hydraulic head requirement to be at a particular height to compensate for the fall of the land, then you should be able to have separate retention and detention tanks. This might make life easier. What are the required minimum volumes in each compartment? Have they specified an 8,000 litre detention compartment? Also, you need to check as to whether there is a council water tank height restriction. oneJohn We have 330m2 of roof, of which 60% needs to be captured, and I'm thinking to use 6 supadivertas over the 9 downpipes in total. One thing I wonder about this is whether I'll have enough head to do it though. The yard level is only about 100mm below floor level, and with eaves at 2400mm that's only giving around 350mm from the standard tank inlet height to the facia. With a bottom tank entry it will still work, but may not fill up fully. Or is it worth looking at burying the tank a bit? You need to know the council's maximum permissible site discharge (PSD). The average roof area draining to each downpipe is 36.66 sq m but of course the downpipes will not drain equal roof catchment areas. Nevertheless, we will use 36.66 sq m for this example and the guesstimate will be reasonably accurate anyway. The remaining 40% of roof catchment area not required to be detained = 132 sq m. During an Adelaide 1:20 Average Recurrence Interval that the roof drainage gutter and downpipe compliance is based, this is 264 litres per minute (4.4 litres per second). The maximum flow from the detention tank will be factored as being the difference between the PSD and the 40% of roof area not requiring detention. Note that detention tanks also have an additional higher overflow pipe in case the smaller lower pipe blocks (the wire mesh gumming up is common) or there is a prolonged period of constant heavy rain. The Supadiverta operates with a variable head plus it has about a 3.7% to 4% yield loss due to the internal filter. This is actually worlds best, the 3P Technik Rainus was previously considered the best with 10% yield loss but 4% of the required detained roof area (198 sq m) during a 1:20 storm event is an additional 16 lpm going to the stormwater plus the Supadiverta's diversion flow slows as a tank becomes fuller. This is okay when multiple downpipes are harvested to a single tank under normal circumstances but it does not help your situation where the flow rate must be maintained. The other problem is the height of the proposed tank, from your figures, there would be insufficient head and this would result in a lot of water also diverted to the stormwater, something that the detention system is required to prevent. oneJohn The main aim at the moment is to get the tank into the back yard before the garage doors go on. So to order the tank I expect I need to know the inlet details. What sort of size inlet would I have into the tank with this sort of system? If you get the proposed tank, you would need to utilise a 100mm DWV pipe wet system that drained 6 downpipes. The available hydraulic head could be a problem though and it also prevents you fitting leaf diverters. If you were able to fit leaf diverters, you could also fit a low restriction inlet. Because a low restriction inlet operates with greater head pressure than a wet system with a vertical riser, it has priority flow and it also supplements the system's flow rate, this would be very handy for your situation. oneJohn A question to SaveH20 is if you get the new diverter produced, what sort of connection would you end up having to the tank using that system? The diverter will have a round 90 mm outside diameter drain pipe. This allows it to be fitted to a variety of standard 90mm PVC-u stormwater fittings. We have some very high criteria for this product including 500 micron first stage filtration but we would consider having 700 micron first stage filtration if our designed flow rates through the filter are not met. If other overall size criteria are not met, it will not be manufactured. It would supply a wet system with a vertical riser but our recommendation would be to also have a sediment trap and a low restriction inlet to further improve water quality. oneJohn Then for the slow detention drain, would it make sense instead of drilling the tank and running stormwater all the way to the tank, to instead put a drain at one of the downpipes to divert the excess tank water back into the stormwater? You must comply with the PSD and the system usually requires a tick off by a hydraulic engineer. Do you know your PSD? 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Buying a tank 3Nov 27, 2015 1:46 pm Thanks for the detailed responses. I tried asking council about the PSD, but it could take a little while to find someone there who knows anything about it. From indications so far, they may not care too much about it. They require 4500L detention and 4500L retention, which can either be configured as a single tank, or separate tanks. The land is level, with tanks allowed up to 4m above natural ground level, so there's not too much restriction there. I could have separate detention and retention tanks. In that case do you just fill the retention tank, and the overflow from the retention tank goes into to the detention tank? It would still have the same head issues, so I assume the benefit is just that the tanks are not as tall? I prefer the idea of having leaf diverters at the downpipes, but if it's going to end up too problematic or costly, then we'll just go with a simple wet system with riser. At one stage I had in mind to do things right for good quality water, but when the costs mount up too much it doesn't seem worthwhile. In terms of the head with just the single tank, I may have been a little pessimistic. With a 2450mm diameter tank, if it only needs to fill to 9000L, that will rise to about 1900mm. That's 600mm below the eaves if the tank is on natural ground level, with maybe another 100mm if I alter the levels a bit. Re: Buying a tank 4Nov 29, 2015 2:59 pm oneJohn I could have separate detention and retention tanks. In that case do you just fill the retention tank, and the overflow from the retention tank goes into to the detention tank? Yes. oneJohn It would still have the same head issues, so I assume the benefit is just that the tanks are not as tall? The smaller tank's height will depend on the tank's diameter of course. The smaller tanks will be more manageable when locating and installing as well as providing more head if they are lower. oneJohn I prefer the idea of having leaf diverters at the downpipes, but if it's going to end up too problematic or costly, then we'll just go with a simple wet system with riser. The problem with standard wet systems is the amount of sediment that builds up in the below ground horizontal pipes due to the amount of dirt that collects on a house roof. This can lead to anaerobic conditions and blockages. You can overcome this by fitting a DIY sediment trap to a non turbulent section of horizontal pipe to trap and then flush bed load. This simple trap that I came up with a few years ago uses off the shelf parts and is easy to install. The trap is reduced in size and an inline tap is fitted to the end of the smaller pipe/hose and the trap flushed every few weeks or so. It is very effective. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ oneJohn In terms of the head with just the single tank, I may have been a little pessimistic. With a 2450mm diameter tank, if it only needs to fill to 9000L, that will rise to about 1900mm. That's 600mm below the eaves if the tank is on natural ground level, with maybe another 100mm if I alter the levels a bit. The Supadiverta's maximum head height is taken from the top of the internal reservoir wall that also doubles as the filter's support. The usual head loss between the gutter's sole and the top of the reservoir wall when the downpipe is first diverted under an eave is about 500mm as a minimum but a 550mm head loss is more usual. Some of this head loss is made up by the additional distance (head) between the tank's water level when full and the height of the water at the top of a vertical riser used in a common wet system. It must also be remembered that leaf diverters also reduce the amount of available hydraulic head but the Supadiverta is also fitted with a superior 750 micron internal filter. The difference in effective head loss between most commonly available leaf diverters and the Supadiverta is minimally in favour of the leaf diverter after the height difference between the top of the vertical riser and the height below the tank's overflow outlet is factored. Given that you need high volume inflow capacity to the detention tank during heavy rain, I think that your best choice would be to have a standard wet system and not the Supadiverta's syphonic variable flow system that is designed to harvest numerous downpipes but to also reduce the flow rate when the tank becomes full to prevent water tank overflow problems. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Buying a tank 5Dec 01, 2015 9:36 am I heard back from council, and they don't have any particular site discharge requirements. They don't even check it, although say it should be constructed according to the builder's plan's that went through council. That's just a standard wet system, so it favours going that way. Thanks for the extra detail. It sounds like I might just make it on head height with the supadiverta to fill the tank, but the inflow would be more limited as the tank level rises, meaning it doesn't work as well in its detention capacity. It's all compromises. I liked the idea with the supadiverta that any losses at the leaf diverter would go down the stormwater pipe, rather than spilling near the house footings - as we are on reactive soil. Hi guys and girls We are about to do concrete paving (100mm thick) around the house, using 32 mpa, with plans to build a 1.5x2m x0.8m high fish tank on it later. My… 0 13992 18 74679 From what I know about water tanks (I've been working with a client on them for a few years now) is this - The concrete can last a lifetime if they don't crack for some… 2 6475 |