Pipe spec for field ditch discharge

[JulianB]

Evening All,

 

I'm in the process of my extension project, and given the recent heavy rainfall and subsequent flooding (on site...heavy clay ground), have turned my attention to the storm water drainage. Whilst nothing is connected at present (hence the site flooding which is up to ground floor beam and block level), we have planned for two 100mm flexible land drain pipes to run from our cottage, across the adjacent field and into a nearby ditch (40 odd metres away). One pipe will service the sewage treatment plant, whilst the other will be used for storm water. The question is, given that we are unlikely to connect the pipes this winter, in time for a preview of their performance in these sorts of conditions, would this solution likely be adequate, as I'd prefer to not find out after having decorated and moved back in! 

 

Any thoughts are much appreciated!

 

Julian

[Russell griffiths]

I wouldn’t use flexible, I always found it collects sediment 

i would use a ridged 110mm pipe, the drain around the property can be flexible if wrapped correctly to prevent silt entering the system, but as it flows away if the run is slight you can get a silt build up. 

 

 

[PeterW]

You can’t use flex land drain for sewage treatment pipework - has to be UPVC as @Russell griffiths has said. 
 

You may find the EA need you to install storm water attenuation tanks even if you’re going into the stream - you will need permission anyway so worth asking now.  

[JulianB]

Thanks for the replies.

 

We had spoken to our BCO about it as we had originally gone for an oversized soak away however at the depth that we ended up at, the percolation test numbers weren't representative and we found that we were wasting our time. I had read up on needing premission from the EA and had contacted them etc, however given that the cottage has an existing septic tank and soakaway to an unknown location, the BCO seemed happy enough to let us get on with the laying of the pipe without speaking to the EA? I've currently got two flexible pipes down, but it sounds like I will need to retrench once the weather gets a bit better to lay another 110mm rigid pipe, presumably in shingle? I've seen that they do a twin walled land drain which has a smooth interal bore - not sure if this would be better suited or less likely to get crushed or potentially remove the need for the shingle as I'd need quite a bit to get us the 40m trench length!

 

Regarding the flexible (perforated) pipe around the property, I've read mixed arguments on here in regards to wrapping it in non woven geotexile membrane when in heavy clay areas; some suggest it actually increases the rate at which it will eventually clog up...thoughts?

[joe90]

22 minutes ago, JulianB said:

Regarding the flexible (perforated) pipe around the property, I've read mixed arguments on here in regards to wrapping it in non woven geotexile membrane when in heavy clay areas; some suggest it actually increases the rate at which it will eventually clog up...thoughts?

I too have been told that the membrane will clog faster in clay like I have. 

[JulianB]

25 minutes ago, joe90 said:

I too have been told that the membrane will clog faster in clay like I have. 

 

What did you end up doing may I ask?

 

On a side note, with regards to silt build up in flexible pipes...just a random thought but could there be a likely scenario where the silt fills each trough in the pipe and hence it begins to perform as a 'semi smooth' internal bore? The issue we have with any form of tank or soakaway on our site is that we are very close to the perched water table (despite being on a hill, around 15metres above the canal), which we learnt when digging the last soakaway hole...would a stormwater attentuation tank rely on an electric pump to empty, as if this is not the case and it relied on gravity / a lower outlet, I would imagine that it would be filled up by the surrounding water table pretty quickly.

[joe90]

5 minutes ago, JulianB said:

What did you end up doing may I ask?

 

A local drainage contractor told me to trench min 200mm wide, 100mm of drainage stone, perforated pipe on this and fill above with same drainage stone, topped with membrane and topsoil if required. Theory being clay silt will settle to the bottom of the stone before filling the pipe, should last many years (this is what he does round here and been in business for many years).