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Hi everyone, we just moved into a house, surrounded by neigbors' properties on higher ground:
This causes occasional stormwater runoff to our backyard and we are planning to make a swale to carry all those water away from our house to the street:
Why not to use underground drainage system?
Because the system is pretty old and partially compressed by underground rocks , reducing the water flow. We consulted two plumbers, both inspected and said so far the system doesn't have any blockage. It can accomodate the water flow from 4 downpipes without any backflow problems, but the compressed system is already at full capacity , so it wont work to install drainage pits in backyard and connect them to the existing system. Unless we spent $2000 to relay all those underground pipe!
How about AG drain?
Yes, it seems very common, though both plumbers said its not suggested because the soil is mostly clay soil and makes it difficult for the water to get soaked into the AG drain pipe. Another reason is, the rainfall can be so heavy pooling on the surface that AG drain wont be effective enough. And they said we need to focus on surface drainage such as installing drainage channel
What about other solutions?
After some research, its seems SWALE is another good surface drainage solution. We already dug a small trench, and had some success in divert the water from the left (area with most water) to the right side of our backyard.
Some google picture ideas:
What do we need to do?
To turn a Trench -> a Swale
We need to dig wider and deeper.
What are the challenges ?
1) Even we dug a small trench, the weed spreaded like wild fire and often invades our trench , they are so dense and impede the water flow.
2) The soil can be loose and crumble a little bit blocking the trench
Questions:
1) What type and size of gravels do we need to get from Bunnings to put into the swale?
Type: Ideally it can interlock with each other, so probably need something angular, not round pebbles, and this way we can "walk on" the swale.
Size: Seems we need smaller rocks to "support" the swale and prevent soil erosion? But if we its too small , not sure if this can impede the water flow. But if its too big, we cant walk on them stably. We will lay turf around the swale in future.
2) Do we need to lay weed mat or some mulch in the swale first? Or the rocks will be enough to block the sunlight and prevent those weed from growing.
Video showing the direction we want the water move:
https://www.youtube.com/watch?v=dpLj6qWIFx8
(Looks like a mess. We just moved in. But hopefully we will overcome all these challenges and turn it into a nice backyard without water pooling. You might also notice an old concrete slab, we will remove it with our impact driver.)
Thank you so much for any ideas and advice.
Hello @ivanptr
I understand your troubles when the weed grows through the pebbles. It's very frustrating and defeats the purpose of the swale. I suggest digging your swale trench first. Apply some GRUNT 1 x 10m Non-Woven Geo Textile Membrane Drain Mat Fabric. This will stop the weeds, but allow the water to flow through! Then you can put your pebbles at the top. I suggest putting larger pebbles at the sides to serve as a border for the swale. This is to prevent the turf from moving into the swale. It sounds like a great idea. Any updates you can provide would be much appreciated.
If you need more information or advice, please let us know.
Eric
Thanks Eric 
GRUNT 1 x 10m Non-Woven Geo Textile Membrane Drain Mat Fabric will be in our shopping list.
Continuous update of our project (Just to share our the stuff we learnt and challenges we faced for people like us can learn from our mistakes: ) :
So, our swale can be built relatively easily at our backyard because its just involves some digging and the area is also away from underground pvc pipe / power cable.
But it gets much more difficult to built along the side of our house:
Three trees next to the house - the root, and existing pvc pipe in the soil are major problems - we cannot dig deep without extra work and being very careful. But we need the swale to be deep enough because we need the 1% slope to maintain the fall for the "entire" swale. And we also dont want the swale so close to our house.
We posted our situation in a facebook group full of plumbers asking for DIY solution, and to our surprise, an overwhelming amount of plumbers suggested SUMP PUMP SYSTEM. It seems more common for households in America.
And we already purchased Ozito 350W Dirty Water Submersible Water Pump:
https://www.bunnings.com.au/submersible-pumps_p4816179?store=8191&gclid=Cj0KCQiA47GNBhDrARIsAKfZ2rB8...
The water will be discharged through a clear vinyl thick tube, this is just brilliant:
1. It is a thick plastic and durable tube, we dont need to bury it very deep
2. Vinyl clear and transparent, we can check for any blockage
3. Easy to replace. Much better than PVC pipe: a lot of digging , cut, joiner, primer , blue glue..........
For sure, PVC pipe allows higher amount of water flow, suitable for moving huge amount of water collected on roof
On the contrary , the amount of water pooling around our backyard is much smaller. We tested the Water Pump, the power of the pump seems very impressive and more than adequate (at least for our backyard).
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The next challenge:
We are now searching for sump pump basin, after some research the basin would need to have following characteristics:
1) A lid (Only with a hole for the powerline and tube)
2) Enough volume of at least 70 Litre
3) Tall enough to allow the float of the pump to activate
We are thinking to purcahse this:
https://www.bunnings.com.au/everhard-450mm-series-300-deep-stormwater-pit-base_p4771445?store=8212&g...
Capacity of this pit can be found on:
http://www.plumbingplustrade.co.nz/image/files/Dux/dux_trade/Pits%20_Brochure.pdf
This product fulfulls all three requirement except not having a lid
The price is great. Cheaper than a "sump pump pit" that we need to order online. But basically they are very similar.
@EricL
It seems we could only find grates in Bunnings for this kind of rainwater pit instead of lids. We dont want much sand and grit to get in.
Or we could still buy the grate but use some kind of stuff to seal the gaps. Any product receommednation? ; (
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Some thought and ideas:
Ozito 350W Dirty Water Submersible Water Pump is probably for amateurs.
Not sure if it can last for long. Ideally, the pump will only be activated when some level of water is detected. So the engine wont be running all the time.
But we will see. In long run, we will buy a higher level pump.
Hello @ivanptr
The best way to keep the sand and grit from entering the pit is to place the GRUNT 1 x 10m Non-Woven Geo Textile Membrane Drain Mat Fabric on top of the Everhard Class A Galvanised Grate to Suit Series 450 Pit. You must secure it to the sides of the grate using Crescent 150 x 3.6mm Black Cable Ties - 25 Pack. Make sure that the Geo Textile is straight and flat. This will stop the sand and debris from creating sag points and drag the Geo Textile down. Do not place rocks directly over the grill to prevent it from pulling the Geo Textile. Its main purpose is to filter sand and dirt so that only water may enter the pit.
If you need further assistance, please let us know.
Eric
Just a little setback we had. Tonight we just had a downpour so we were able to put our Ozito 350W Dirty Water Submersible Water Pump into the hole we dug. The pump was connected to Holman 25mm x 25m Black Poly Pipe. The problem is the motor of the pump and water pressure were too strong that the water flush away the hose.
The diameter is 25mm. Is there any products in Bunnings that we can use? How about a clamp for 25mm?
Or we should change the hose too?
Hello @ivanptr
If you are using the Vinidex 25mm x 3m PE100 Poly Pipe, the fitting you need to use is the Philmac 25mm x 1" Metric Poly x FI BSP Pipe End Connector. But before that, you'll need to modify the Ozito Universal Pump Adaptor so that you can screw on the Philmac connector. Your other option is to use the Ozito 25mm x 10m Submersible Pump Installation Kit. This would be the easier option as all you need to do is to fit the hose onto the pump outlet and clamp it.
If you need further assistance, please let us know.
Eric
Hi @Ben2065,
Let me tag @ivanptr so they are alerted to your question.
The required dimensions of your swale would be directly related to the maximum amount of water it's intended to capture. You could work this out by determining the expected volume of rainwater that will hit the collection zone in a downpour, but if you add some images of the area and perhaps draw a sketch, I'm sure our knowledgeable members will be able to give you some ideas.
Grassing over your swale is a possibility, though that will inhibit some of the surface water from being captured.
Mitchell
Hi Mitchell @MitchellMc
Thanks for your advice. I have attached a google maps image of an ariel view of my place. Essentially the 2 unit blocks behind my place have large backyards which have run offs in the direction of the red arrows due to their topography. The property beside mine (family relation living there) has managed to redirect the overflow towards my rear lane to avoid excessive flooding in their place. Unfortunately in our torrential rain recently in Sydney the water continued to travel in the direction of the blue arrows and cause some mild flooding in the rear of my house. I am considering if I should cut out a deeper swale in my lane to direct the water flow in a more defined way and/or line the colourbond fence with besser blocks to act as a channel for water flow. I have also wondered if I should put in a french drain with slotted ag pipe under the surface down the centre of the lane or even put in channel/trough drains but not sure if the water flow would over whelm this? I even considered simply trenching a narrow channel either side of the pavers all the way down the lane to act as water conduits? I really would like to keep the pavers as it is much easier to walk down the lane. I have also been considering if I should turf the lane once I have a more defined water flow in the ground topography as it would look so much better and less unkept? The lane is fairly heavily shaded so not entirely sure if turf would cope so it has been essentially weed trimming for the last 10 years. On my recent research it seems something like native violet maybe more suitable than grass as even the mondo grass between the pavers is struggling to grow. I do have a small storm water pit at the end of one of the blue arrows but it gets blocked with leaf litter and topsoil and then this blocks the pit and floods the area. I would appreciate your thoughts
Hi @Ben2065
Looking at the photos you shared, I can see the low sections where the water would have settled. Redirecting naturally flowing water is a tricky thing especially the laws concerning it. Due to the probable size and length of the proposed drain, I suggest engaging the services of registered plumber.
They will be able to make suggestions on how best to layout the drain and they will link your drain to the storm water system. However, before you make any arrangements, I suggest making your own plans first. I recommend thinking about installing a French drain in the lowest sections of the flooding area.
I recommend doing a survey of the area and where the French drain will pass through for maximum effect. Once you've made your plans you can then consult the plumber for their opinion. Make sure it's on paper so that its clear on what you are planning to do.
They may change parts of your plan but at least you'll have a general idea of how it will be laid out. The plumber will probably redirect your French drain towards the storm water drain to make it easy for them to link into.
Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.
If you have any other questions we can help with, please let us know.
Eric
