Browse Forums Landscape & Garden Design 1 Aug 31, 2014 12:46 pm Hi Everyone I have been reading up on the various drainage threads trying to work out how to solve this problem. I have just bought and moved into this new house, and the backyard is made up of clay soil, and when it is raining heavily, the water will pool and not drain away anywhere, and take about a week to fully dry up. I am not quite sure if just installing say 3 surface drains in the backyard will do something to alleviate the mass of water, or if I can put a big long agi pipe in the middle of the backyard, or exactly what I need to do to solve it. Maybe I need to rip the whole grass yard up, get a bobcat in to put a grade in the clay so it slopes into a central drainage area, then put 30cm of sandy soil on top and re-turf the yard, and divert the water into a drainage channel like that? The other problem is water pools right up against the back of the house, I will be ripping out the hot water system and putting a wall mounted instant system in, so that will solve the HWS getting flooded problem. But I think I may also need some channel drains along the back of the house/concrete verandah area to try and get rid of the water pooling up against the house? Or put a path or pavers in at a slope to dry and keep water away from the slab? The next problem I have is how to connect all of this to the stormwater, there is a stormwater outlet at the gutter at the front of the house, which is about 1m lower than the backyard height. I don't know if there is enough fall in what I would be doing in the backyard to get the water from the back to the front? and whether I can simply connect what I do in the back to the stormwater pipe near a downpipe at the back near the drive-thru-garage by digging down to it and adding onto it? This front gutter stormwater is only a small rectangular outlet about the size of a downpipe, is all of this going to be too much for the one small outlet in downpours? I am willing to cut up the concrete path to the LHS of the garage, to dig a new trench to pipe a bigger stormwater pipe down to the gutter if needed. I just replaced the retaining wall at the rear which has agi pipe just behind the sleepers, flowing from the RHS to LHS (direction away from the garden shed) but it connects into nothing at the end). The back neighbour is about 50cm higher but I don't think there is a lot of surface run-off coming from any neighbour. Side neighbours are relatively flat but don't seem to have water pooling like I do. There is a water tank around the back but only 1 downpipe goes into it, then when it is full the overflow connects to stormwater. I have put some pics below in the hope someone can help me find a good solution. I am willing to spend $$ to fix this but obviously want the best cost effective solution Thanks! Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Backyard Flooding and Drainage Problems 2Aug 31, 2014 9:17 pm That's quite a flood u have there ! Whilst I can't help with your problem yet I'm watching with interest as I think I may have a similar problem with my new house . Good luck and keep us posted on how u go . Cheers Re: Backyard Flooding and Drainage Problems 3Aug 31, 2014 10:40 pm It looks like the lawn and some sandy loam or similar has been laid on top of the site cut. In other words...there is very little or no top soil. You have a level issue and a serious issue with the meagre gap between the ground level and the damp proof course. Another serious issue is the water pooling next to the slab...particularly if you are on reactive soil. The site MUST slope away from the house! You need to redo the levels and treat the clay with a lot of gypsum, layers of newspaper and a good sandy loam. Only after doing this can you prepare the area for turf but you need to remove a lot of clay first. Also read some of Fu's threads on soil conditioning and turf preparation. Having the correct levels is vital and the site needs immediate attention. A well prepared turfed area can soak up a lot of water. You should also look at having a 1:20 sloped 1 m wide concrete path laid next to the back of the house and don't re-turf next to the house. You should also post your location so that people know your climate pattern and rainfall intensities etc so that they can best comment further on drainage. 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: Backyard Flooding and Drainage Problems 4Aug 31, 2014 11:22 pm tacet I think you answered your own question here "Maybe I need to rip the whole grass yard up, get a bobcat in to put a grade in the clay so it slopes into a central drainage area, then put 30cm of sandy soil on top and re-turf the yard, and divert the water into a drainage channel like that?" grade the soil into a agi drain in the middle of your back yard with possibly one or two pits where the water ponds a run it into a silt pit that connects to the existing storm water or you may have to run a new storm water down the left hand boundary to your LPOD at the front Re: Backyard Flooding and Drainage Problems 5Sep 06, 2014 11:36 am Thanks so much for the replies and advice. I have a lot more reading and research to do by the look of it. I am located in South West Sydney, Campbelltown area. So if anyone knows of a specialist in this area that I can call in too this would be great to know. With the small gap between ground level and damp proof course, I checked and at its smallest point, it is about 3-4cm from the grass to the damp course in the bricks. This is in the backyard near the BBQ area. At the area near the water tank it is 10cm from the grass to the damp course. I guess this highlights the problem of levels of the backyard. Should I be digging away the grass removing soil height where that small 3cm gap is to lower the backyard ground level to avoid any possibility of water entering the bricks/slab above the damp course? For re-doing the levels of the yard, this is going to be a job for earthmovers/bobcat right? Does anyone know an indicative of what $ cost I am looking at to get this done? Iām guessing to fix this properly the whole yard needs ripping up and a lot of the clay removed, then replaced with good soil and turf. The big question I really have is how do I properly service the area with storm water, how do you select locations to place storm water pits? Would 30cm x 30cm be large enough? Why are they better options to just straight drain openings in the grass area? Would it end up being sufficient to simply select a few good positions for storm water pits and drainage, and hope that this dissipates the majority of the water, instead of going to the trouble of ripping up the whole backyard, removing the clay and re-grading the slope underneath? Re: Backyard Flooding and Drainage Problems 7Sep 07, 2014 1:52 am During August, Sydney had over 200 mm of rain in 2 weeks whereas Melbourne had about 30 mm for the entire month. That's why photos mean little unless the area is known. The damp course should be at least 175 mm above the natural ground level. Only having 30-40 mm is not good. It is best to maintain the correct levels because they are mandated for good reasons. A lot of homeowners who end up having a path installed on raised site levels often end up with the path up to the damp course and sometimes higher. It pays to be aware because you can't always rely on the tradies to know the regulations in the industry that they work in. Plenty of examples in the sub forum threads. The damp course must also be 75mm above paved, concreted or landscaped areas that slope away from the house or 50mm above finished paved, concreted or landscaped areas that are protected from the weather by a carport or verandah etc. Other measurements apply to properties in low rainfall areas. With ag pipes, these cannot drain directly into the stormwater, silt pits are required. It then becomes a matter of levels when draining from the pit. A bobcat is probably the way to go, some of those drivers are magicians! You will still have a bit to do to finish off though. tacet Would it end up being sufficient to simply select a few good positions for storm water pits and drainage, and hope that this dissipates the majority of the water, instead of going to the trouble of ripping up the whole backyard, removing the clay and re-grading the slope underneath? I think that your number one priority is to fix the levels next to the house to stop the ponding. Once you work out what needs to be done in that area, that will dictate what else you then have to do. Well prepared turf soaks up a lot of water plus it filters and returns it to the groundwater. I personally don't like the thought of a pit in the middle of the lawn. If you have a path along the back of the house, a spoon drain along the outer edge should suffice. Site drainage is a very important issue and it is important to protect your house from high subsoil moisture levels. There is a bit more to it than just the DPC height and there are several very informative H1 threads on the subject that are well worth reading. 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: Backyard Flooding and Drainage Problems 8Sep 09, 2014 9:38 pm If I put a concrete path with spoon drain, which way would I slope the spoon drain, towards the water tank/side of the property? Does water then flow along the spoon drain and into a pit or how does it go from the path, into the stormwater?
Is there a chance that all this drainage solution is going to overload the stormwater pipe capacity in times of heavy rain (e.g. downpipes from a ~230m2 roof, plus all these garden drains), going down the one small rectangular outlet in the gutter and probably 90mm pipe? With the yard, is this more important to address the surface drainage, e.g. get the water flowing down into drains and out to the street as it hits the ground, before it seeps into the soil, or more important addressing sub-soil drainage, e.g. agi pipe solution? Re: Backyard Flooding and Drainage Problems 9Sep 09, 2014 10:22 pm the spoon drain should run into a storm water inlet. The yard is about sub surface drainage and you will need a agi connected to a silt pit and then into your storm water.Make sure the agi drain is in your clay layer not just siting in the topsoil layer. Re: Backyard Flooding and Drainage Problems 10Sep 10, 2014 12:26 am tacet Is there a chance that all this drainage solution is going to overload the stormwater pipe capacity in times of heavy rain (e.g. downpipes from a ~230m2 roof, plus all these garden drains), going down the one small rectangular outlet in the gutter and probably 90mm pipe? The above is a worry if in fact there is only a single 90 mm stormwater pipe, in fact, it is a worry even if it is a single 100 mm pipe. tacet I am located in South West Sydney, Campbelltown area. The stormwater pipe size compliance comes under AS2200. The maximum flow rate for a DIN 90 mm PVCu stormwater pipe is 360 litres per minute. The maximum flow rate for a DIN 100 mm PVCu pipe is 450 litres per minute. The stormwater pipe size is calculated by your roof area and the region's 1 in 20 year storm event. This is referred to in AS/NZS 3500.3:2003 as an Average Recurrence Interval (ARI) but a more area specific method called an Intensity Frequency Duration (IFD) has become more commonly used. See link below. http://www.bom.gov.au/water/designRainf ... vised-ifd/ The nearest grid cell Lat & Long is -34.0625 and 150.8125 This brings up the chart linked below. http://www.bom.gov.au/water/designRainf ... lltown+NSW A 1:20 IFD is based on the rainfall intensity over a 5 minute period. If you intersect the 5 minute column with the 5% column, you will see the figure 13.9. This represents 13.9 mm of rain over a 5 minute period to 'qualify' for a 1:20 IFD status. 13.9 mm over 5 minutes is an average of 2.78 mm per minute over the 5 minute rain intensity duration. Your roof area is about 230 sq metres. 1 mm of water on 1 square metre is 1 litre. If we multiply 230 x 2.78, we get 639.4 litres per minute off the roof during a 1:20 IFD, far too much for a single 90 mm or 100 mm pipe as per AS2200. The above is a simplistic example, there is a little more to it than that, for example (amongst other considerations), if there are in fact 2 pipes, then the roof slope has to be factored to allow for wind driven rain. If you have a standard 22.5 degree pitch, the roof area has to be multiplied by 1.21 to allow for different amounts of rain falling on different sides of the roof during wind driven rain. Note that even if there is just the one pipe, the roof area still needs factoring even though there is no actual need (apart from the regulatory requirement to do so). If you have 2 pipes and a 22.5 degree roof pitch, then the roof is factored as 230 x 1.21 = 278.3 square metres. 278.3 x 2.78 = 774 litres per minute. If the two pipes drain equal roof areas then the average per pipe is 387 litres per minute, clearly not compliant for 2 x DIN 90 mm pipes that are only allowed to carry a maximum of 360 litres per minute each. If there is also a potential problem with the existing stormwater drainage, then it is better that you also investigate it now. If you have 2 x DIN 100 mm pipes, then the stormwater drainage, even if draining uneven roof areas (as most do), should be compliant. Non compliant stormwater drainage is not uncommon. 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: Backyard Flooding and Drainage Problems 11Sep 10, 2014 8:10 am I could be wrong about the size and number of stormwater piping. I will try and do some investigations into that to properly work out what the current system is. Should I do some digging in the yard and try and measure the pipes? I know there is more than one pipe in the backyard joining all this up, but the end output, at the gutter on the street, is simply 1 x rectangular outlet, similar size to the metal rectangular downpipes you see. I'll measure it but is that effectively the smallest hole we are working with? If this whole system is in fact underdesigned, once I start adding extra drainage points and trying to get all the water to follow it, will it just back up and then the water will just sit in the yard until there is space in the pipe for it to go? Or will it also block up in the downpipes? Co-incidentally, at the street right in front of my house is one of those big stormwater inlet holes in the gutter ( you know the ones about 1m long), which is about 10cm away from my stormwater 'outlet' that goes to the gutter. I wonder if this is more looking like I need to rip up the concrete path on the LHS of the house, run new 100mm piping and some how connect/incorporate this to flow into this drain (if that is even legal/able to be done). Another question I have, Is there any benefits to concrete path, as opposed to paving? Another option I was contemplating was a paved path, with 400mm pavers so doing 800mm wide. Is this enough/acceptable comparison to concrete? How would I incorporate something like the spoon drain with pavers, install a U channel drain abutting the edge of the pavers instead? Re: Backyard Flooding and Drainage Problems 12Sep 10, 2014 11:11 am Here is some photos of the stormwater outlet from my property when it gets to the gutter (this is the only one everything is connected to). There is one the same as this in the middle of the driveway, which I imagine was not used when the house was built as they might have poured the driveway before the plumber did the stormwater back when the house was built. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Backyard Flooding and Drainage Problems 13Sep 10, 2014 12:27 pm tacet I could be wrong about the size and number of stormwater piping. I will try and do some investigations into that to properly work out what the current system is. Should I do some digging in the yard and try and measure the pipes? I know there is more than one pipe in the backyard joining all this up, but the end output, at the gutter on the street, is simply 1 x rectangular outlet, similar size to the metal rectangular downpipes you see. I'll measure it but is that effectively the smallest hole we are working with? If the only stormwater drainage you have is what goes to the street, then you only have the one pipe. The saving grace is that there is a decent slope. I would measure the pipe for interest sake. The 90 mm PVC stormwater pipe has a 90 mm outside diameter, the 100 mm PVC pipe has a 110 mm outside diameter. Are you sure that there isn't another stormwater connection? There will be a lot of water coming off your roof during a 1:20 IFD. tacet If this whole system is in fact underdesigned, once I start adding extra drainage points and trying to get all the water to follow it, will it just back up and then the water will just sit in the yard until there is space in the pipe for it to go? Or will it also block up in the downpipes? What type of downpipes do you have? If they are metal, then there will be a plastic downpipe adapter at the bottom. The adapter should not be sealed, any back up needs an escape route but sometimes they are sealed. Excess water flooding out of the plastic adapter is bad news in any case. You have a 1 metre height difference between the front and back but you lose some of this with the pipe depth but you still retain a very good slope. The possible problem I see is that if you address the soil height at the back of the house and match the lawn height to suit, how would an ag pipe's pit outlet depth then relate to the stormwater pipe's depth? An unknown factor is the stormwater pipe's current depth in relation to the damp course. It is not unusual for builders to have the soil level too high and this can result in the plumbers coming along and errantly working off that level when laying pipes. You need to determine the stormwater pipe's level as a first step. It is probable that the soil level was raised after handover when the lawn and edging was put in, meaning that the pipes are at the correct depth but you need to check. tacet Co-incidentally, at the street right in front of my house is one of those big stormwater inlet holes in the gutter ( you know the ones about 1m long), which is about 10cm away from my stormwater 'outlet' that goes to the gutter. I wonder if this is more looking like I need to rip up the concrete path on the LHS of the house, run new 100mm piping and some how connect/incorporate this to flow into this drain (if that is even legal/able to be done). I think that once you establish the pipe's depth and size and plan the order of work, you should talk to a drainer. He will know about levels and permits etc. There will still be a lot that you can do yourself. I wouldn't skimp on addressing the ponding, the soil and the future finished concrete levels at the back of the house though. tacet Another question I have, Is there any benefits to concrete path, as opposed to paving? Paving is permeable, concrete is impermeable. A suitably coloured concrete `path' would look a lot better than plain concrete. The stormwater outlet in the photo looks to be 75 x 75 mm or thereabouts. I have no idea why they used metal and not PVC in the concrete. 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Until you find the cause of the flooding you need to take action to mitigate potential damage to your home. Get automatic float pump and dig a pit then connect to power… 2 4851 The bottom of the downpipe has been taped (see the black tape) to seal the necessary gap between the downpipe and the adaptor that would normally prevent the downpipe… 3 9220 Need more photos from around the house including your gutters. We have had 3 of the wettest years in a row for some time so that wouldn't be helping 3 6946 |