Browse Forums Landscape & Garden Design 1 Apr 28, 2017 3:20 pm Hi guys,
Would love to hear from some landscape gardeners or people who have been through this before. We are 1 week out from site start and I just received an email from my builder saying that the council drainage requirements have just arrived and we require both a 5000L water tank and a rain garden. (Having a larger tank didn't help, we still were required to have the rain garden) The cost they quoted for the tank came in at $5439 (this has a pump system) and the cost for the rain garden was......wait for it......$28,775!!!! So, post contract signing when all bank details have been finalised, 1 week out from site start we are supposed to find another $33,000 from somewhere. The builder said that as they don't do rain garden beds so they had to out source that to a contractor. Are these rain gardens really that much, or am I being played for a fool here?? This is what the builder has emailed to justify the cost: We also investigated further and found that the cost for the drainage system and new stormwater point have been taken into consideration in that price. Our plumbers visited the site and found that the stormwater point also had to be replaced to support the build of the new home. Another reason is there is no fall on your block which means there is no fall for the water discharges points to be drained to the Legal Point of Discharge that is located to your kerb and channel. In a nutshell the tank, drainage and future pool is basically too low which is why we require pump system to push all the water out to the LPOD. Some other works which are included is the following: 1. Supply and install PVC drainage with grated pits as per plan 2. Supply and install rain garden as per plan 8 x 1 x .3 with PVC hardened perimeter 3. Supply and install All-purpose pump well as per drawing and specs 4. All council permits for storm water connection with concrete bay replacement 5. Supply certificate of compliance I have attached our plan for the rain garden if this helps anyone, but some advice here is greatly needed!! HELP! Rain garden runs along the side of the driveway. Thank you Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Rain Garden Cost- HELP!! 2Apr 28, 2017 3:49 pm That sucks, sorry I have never heard of a rain garden before but I would suggest contact the company to see if they can suggest any alternatives. I had a similar issue where they wanted and add extra rain water tanks and that would mean putting them in our court yard area. I researched it more and called the company to discuss it with them and told them I had researched our areas requirements and that I could use an onsite detention area instead. It is basically a bricked wall of a set height that stops water from just flowing to the road and would look like a big pond if it ever filled up but never will. So it will be a grass area with a brick wall around it which we will be using as our front fence and yard. Good luck. Nev _________________ Blog | ( will start once received tender ) H1 thread | https://forum.homeone.com.au/viewtopic.php?f=31&t=77665 Re: Rain Garden Cost- HELP!! 3Apr 30, 2017 9:25 am The plans are difficult to read and there are no hydraulic calculations shown or if they are, I can't read them. If the 5,000L tank is purely for detention, the price is ridiculous and there are no details shown such as the harvested roof area diverted to the tank, pipe lengths and sizes, can't read the head figures (which calculates to the top of the gutter) etc. The cost of the rain garden is also ridiculous but even more so. Pumped systems are not good, what happens if there is a power failure? I would need details before commenting on the possible/probable alternatives. Have you read the Melbourne Water website rain garden info? 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: Rain Garden Cost- HELP!! 4Apr 30, 2017 9:30 am I have read the info on melbourne water site which is what led me to panic about the price! From what I have now gathered, the $28,000 price tag is due to the pumped drainage set up. I would love to hear some alternatives that I can take back to the builder this week. How can I get the plans to you in a way that you can read them properly? PM me your email perhaps and ill send them to you. I would greatly appreciate any help here at all! Re: Rain Garden Cost- HELP!! 5Apr 30, 2017 10:37 am It depends on what the council will accept, a retention and detention system is best but that depends on the site gradient (hydraulic calculations) and then the aesthetics. Given the fall of your land, you would have a retention component anyway. Many councils wisely don't allow pumped systems for the reason I posted earlier. A single pump also needs its flow capacity to match the council's Permissible Site Discharge (PSD) but 95% of Melbourne's 'rain' is drizzle or light showers, this most often causes a large pump to cycle which is bad news (very damaging) and the reason why dual pumps operating in tandem should be used. I would avoid a pumped 'solution' at all costs (please excuse the pun). What is the planned landscaping? Could you incorporate something like thin tanks as a multi purpose solution? http://www.teampoly.com.au/downloads/Ra ... -Flyer.pdf http://www.tightspottanks.com.au/thinta ... ater-tank/ I would seek advice from the council on their PSD requirement and their acceptable solutions as a first step but you need to talk to someone who is knowledgeable in the art and that can be a frustration when dealing with councils. Try to get the message across that you have no confidence in using a pumped system and explain why. If the levels and hydraulics are ok for a detention system, then that is the lower cost solution. 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: Rain Garden Cost- HELP!! 6Apr 30, 2017 10:52 am ayaman In a nutshell the tank, .......................... is basically too low which is why we require pump system to push all the water out to the LPOD. Just saw the edit. Can you post the height difference between the bottom of the gutter and the LPOD? 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: Rain Garden Cost- HELP!! 8Apr 30, 2017 12:42 pm Just measure it, use mortar lines as the line of sight and ask someone to hold a stick with some graduated marks on it at the kerb. The builder has said that the tank is too low but maybe you just need a higher tank. There may be options that don't involve a big bulky tank if that is the case. The link below is to AS/NZS 3500.3. It is the 2003 version which was updated in 2015 but the information relative to your situation is still accurate. Pumped systems are in section 9. https://law.resource.org/pub/nz/ibr/as- ... 3.2003.pdf 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: Rain Garden Cost- HELP!! 9May 01, 2017 11:11 am I have seen on the plans that you sent by PM that you will have two pumps as per Section 9 of AS/NZS 3500.3. Section 9 also has other requirements that includes a warning siren should the pumps fail as also shown on the plans but electrical pumps won't start during a power failure and at some time, you WILL have a power failure during a major storm event. It should be noted that AS/NZS 3500.3.9.4 states: "The pump controls shall be set up to enable alternate pump operation at each start." This is to avoid cycling which is damaging to a pump's motor. I would query whether the plans satisfy this. The plan's design also shows that you will have two big pumps with 5 lps each, this is 600 lpm discharging to the kerb during a heavy rain event!!! There should preferably be a limited detention discharge but as surface drainage also needs to be factored, the system would be following the Moonee Valley Council edict but surely the council would prefer a more suitable alternative or do they want a tourist attraction? If the total roof area drained included onsite detention with limited discharge, then smaller pumps could be used subject to council approval. Your 5,000 litre water tank is a retention tank that will receive a diversion of approximately 400 litres per minute from the 183.29 sq m of harvested roof during your area's 1:20 Average Recurrence Interval (ARI) but this will way exceed the tank's 100mm overflow pipe's discharge capacity. Melbourne's 1:20 ARI is 130 mm/hr, based on a 5 minute average rain intensity of 2.166 mm/min. 183.29 x 2.166 = 397 lpm. A tank's horizontal discharge capacity is calculated by the depth of water above the overflow pipe's invert (bottom of the pipe) using Torricelli's theorem but water tank overflows are also meshed and the mesh typically has an open area of about 55% which presents a flow restriction. If you look at Figure 8.2 in the link below, you will see that an unmeshed 100mm overflow pipe will flow at about 300 litres per minute with approximately 110mm of water above the invert but your overflow will be meshed unless they use an external flap valve. Using an internal bell mouth orifice would be my preferred alternative to increase the overflow rate. https://ia801901.us.archive.org/20/item ... 1.2003.pdf A charged pipe to the water tank is necessary when the tank is remote to the downpipes. To divert water into the tank, the pipes run underground and this requires head pressure to get water into the tank. The head is provided by the downpipes. The reason I asked for site levels was to see whether a suitable retention/detention system could also provide the head to divert stormwater directly to the kerb but as there seems to be no PSD, then the downpipes could do this if the levels were favourable. If so, smaller pumps could then be used for the surface drainage. Thinking outside of the square, I think that an alternative solution could be provided at a lesser cost if my own belief was followed in that every new house site should be required to provide groundwater recharge for environmental reasons. If you were able to have a bore sunk that was also used for onsite discharge, it would be a win-win situation. I don't know what the cost would be but it might be worth passing the idea by the council after assessing the design feasibility, getting some quotes and determining the depth of the water table as doing this would eliminate the need for the very expensive pumping system and maybe even the rain garden as well as eliminating additional stress on the stormwater system...which should please the council. There is information available on the internet about ground water in all areas of Victoria and falling groundwater levels is an environmental concern in numerous areas. You are paying too much for your water tank installation, I can advise on how to save a lot of money if it isn't too late to do so. 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: Rain Garden Cost- HELP!! 10May 02, 2017 7:01 am No it isn't too late to make changes to the water tank. 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