The Brew Cabin

Hi

I stumbled upon this website shortly after purchasing my house. The two big projects I had planned for the new property (laying a new drive and patio) are covered by this site, which has given so much excellent advice that I am now full of confidence to go DIY rather than use expensive contractors. Well done on the sheer usefulness of the site and the abundance of information it contains.

So, drive and patio taken care of. Thank you. My main problem now therefore relates to the waterlogged back garden. The house is built right next to what was an old brick and tile works. So, below the top couple of inches of topsoil in the garden is an indefinite depth of extremely heavy clay. The whole garden remains waterlogged after rain (often for many weeks after the last fall of rain). I have planned the layout for the garden and will replace the top 500mm or so of clay with soil (so I can actually grow something in it). This would be an ideal opportunity to install some land drainage. I plan to use perforated plastic pipe layed in trenches. From your site I have easily been able to work out how to do this and work out a drainage layout. My problem is where to connect the new land drains to. There is a concrete inspection chamber ideally located in the garden. The main channel is about 500mm below ground level. I've checked and can advise that only toilet and kitchen sink waste flow into this system - definitely no surface water. Am I allowed to connect into this with my land drainage and is it an easy task? Other than that, there is a gulley in the corner of the garden/at the corner of the house which takes the surface water from the roof? Again, am I allowed to connect into this and is this an easy task? The trap water in this gulley only appears to be about 250mm below ground level, so I'm not sure it is low enough to connect into to still allow for the gradient of the drainage. I could probably just about manage it, but by only having the plastic pipes a few inches below the top level of the garden - probably not recommended.
I'm almost there (thanks to your website) but just need the last little push in the right direction.

Many thanks in anticipation.

Do you know if you have two separate drainage systems, ie, Foul and Surface, or is it one combined system?

The best option is to connect up to the surface water system, so that you're not sending what is, effectively, clean water to the ETW when it could be dumped into a river somewhere. You're concerned that the Rainwater Pick-up (RWP) you've identified is too shallow to accommodate the gradient of the planned land-drain system. Have you dug down around this RWP to determine just how deep it runs or to where it is connected? You will probably find that it is at least 500mm deep and that you could install an access chamber (AC) at some point which could then be used to connect-up the land drain.

Installing an AC is relatively straightforward and is already shown on the site with an animation. This is, by far, the best and simplest option. However, if you've a combined system, or you have no viable alternative other than to connect to the foul system, then you will need to use a trapped connection. Rather than go into all the detail about just how that is done, check your RWP and see if an AC is feasible. If it turns out that the Foul option is the only option, I'll explain the Foul Water connection method in greater detail at that time.

Hello again. Thanks for the reply. My investigations have been quite limited because of the rain, which as you know leaves the whole back garden waterlogged. Anyway, there is definitely two distinct systems - one for foul water (of which the inspection chamber belongs to) and one for rainwater. I think the rainwater drain pipe from the gulley does run away at around 500mm deep. I think I can therefore just achieve the gradient required. If the new drains will run under just lawn and patio, what would be the minimum recommended depth? I'll try and go for a surface water system connection and install an access chamber following the instructions given on your site.

Once I've connected an access chamber into the existing pipe running away from the gulley, how do I connect into the access chamber with the new drainage? Is it best done with a short rigid section of pipe (bearing in mind that the land drains will be flexible perforated plastic pipe)? Do I need any end cap over the last piece of drain pipe before it enters the access chamber, to stop any small bits of grit etc. entering the main drainage system? Is it necessary to install a trap? Hopefully nearly there now.

Thanks again.

The minimum recommended depth for a land drain varies according to the contractor that laying it, but I would always make sure they are at least 300mm deep, and preferably 450mm, when it's in a private garden. Keep it as deep as possible, even if it means laying it flat with just 25mm or so fall over the last half-metre where it connects to the SW system to reduce the risk of backwash. On such a relatively small system, the hydrostatic pressure generated by water seeping into the system will provide sufficient force to 'push' the water towards the collection point.

When it comes to connecting the land drain to the new AC, then you should use a 'rocker pipe', which is a short length of unperforated pipe, usually around 600mm in length, and then use an adaptor coupling to connect the perforated flexible drain to the rocker pipe. There's no need for a silt trap if you've used a membrane to surround the land drains or if it's only a small system, and any small bits of grit finding their way into the pipework will be flushed along by the water flow. :)