Jan 19, 2012 9:48 pm
I moved into a new place about 5 months ago and aside from other issues I've found that there are some pretty major problems with the storm water drainage. The main one is that when it rains hard water flows down the backyard (I'm on the side of a hill in the Dandenong Ranges) and soaks into the path beside the house leading to the basement area of the house (it's on stumps) to be quite damp. In fact when I had the termite treatment follow up done the other week the guy commented that there were actually puddles against the wall under the house. This is made worse somewhat because the roof gutters also overflows in heavy rain and floods back against the house. Eventually if it rains hard enough the water actually flows down the side of the house and washes the gravel driveway out into the street. So needless to say I need a major redesign of the existing system including pits and agi drains to remove the water from the soil before it soaks under the house and also to redirect the above ground water into pits and into the storm water system. I also need to do something about the drains blocking thanks to the pine needles that accumulate in my gutters. Anyway I could go into detail about all the changes I'm planning on making to solve these problems once and for all but after a bit of digging I found some evidence of an attempt at an agi drain already.
If you look at the photos you can see a shallow sort of spoon drain next to the path which doesn't actually go anywhere. I suspected there may actually be some sort of agi drain already under the soil and there was but I've no idea how it would have ever worked. The people that owned this house were quite old so this would have been a paid job. Someone has used what looks to be a PVC agi drain which I've never seen before and back filled it with what I'm guessing is blue metal. However I can't imagine that this PVC pipe was ever going to drain much water and they haven't used any kind of geo fabric or sock so that gravel is now a combination of dirt and tree roots. Needless to say it doesn't work. Is this normal practice? Also would this have been up to the job? The photos show part of the yard but as I'm on an acre and the roof is fairly big you can get quite alot of water down that path in a big storm.
So my plan is that I may have to rip this all out and replace with proper agi pipe with a sock and geo fabric either side of the gravel and then run the agi drain into pits at either end of the house which can overflow away from the house. The pits will plumb into the storm water drainage. I then plan on placing a large pit at the front of the house with the downpipe PVC drain plumbed in from either side (which will divide the downpipe drainage into two seperare systems) and then a 150mm PVC pipe from there down to the front. This way the system has more capacity and if it overflows it will do so on the low side of the property draining away from the house.
What I'm wondering is whether an agi drain will be able to cope with flash flooding when the backyard turns into a torrent and the roof gutters overflow. Could I run a spoon drain the whole length (the plastic type with the removable lid like they have in front of garages) on top of the agi system at ground level to take away the surface drainage. This would the be plumbed into the same pit I guess. Alternatively I could run small pits along the top or beside the agi system however I like the idea of the spoon drain as it can't really block and the trench is already there so it will just sit on top of the gravel of the agi system. Last of all is the current agi system deep enough? It's only about 300mm down.
If you managed to get through all of that and leave a comment then many thanks as I really need someone to bounce ideas off. I talked briefly about it with my plumber but he didn't have much to add and I probably can't afford to have him do all the work anyway...
(agi pipe next to the path)
Re: Storm water drainage problems - agi pipe2
Jan 20, 2012 12:46 pm
Why do your roof gutters overflow? Do you have a secondary issue? The channel drain used in front of garages sounds like the best solution to cope with the amount of water you have mentioned.
Built an EB Memphis 28MK3
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