Land-drain depth

[sparrow100]

Thanks to the wonderful Cadders spotting it on freecycle, I am the proud owner of 12m of 15cm diameter land drain pipe as a means of turning my winter swamp into something less boggy.

I have instructions to wrap in weed membrane and cable-tie the ends, which makes lots of sense in terms of keeping soil & critters out.

But, before my back goes into pre-emptive complaint, what's the depth I should be aiming for? Ideally the shallowest without being ineffective...

[Baldy]

My mate put his in at about 4 ft as I recall. Slightly bonkers ex army so he might have overdone it ( or not ). Not much help am I

[Baldy]

Laying a Land Drain and Removing Excess Water from your Garden | DIY Doctor
Pavingexpert - Installing a land drain

Seems he was possibly about right maybe...

[Alison]

I'd always tend to give about 1m cover so 4' to invert sounds about right.

[sparrow100]

Four feet??? Oh help, Cadders, what have you got me into! I thought a foot and a half would do it, just to get the surface water away to the bottom of the plot. My path is only 3ft wide, if I try for 4ft deep I'll be digging a ha-ha. While on a pogo-stick.

[Cadalot]

So Glad you got it

Don't Worry, the idea is to reduce the ground water level and give it a route to drain away, on your particular site gravity and the incline will do the job for you. I would dig down 450 - 600mm at most and butt the ends together, you are giving the water somewhere to live whilst it travels down hill.

The slope of your pipe is going to be greater than what they normally put them into. You have raised beds so actually any depth under the paths you can add another 100mm to. You don't want to drag the water table down too low during the summer months

Bottom line is it can only make things better for you in reducing the flooding that we have seen in your photos and giving a dryer plot earlier in the season.

[sparrow100]

Phew! Thanks, that sounds much more do-able.

[Baldy]

Disappointed sparrow, I was hoping to see a 'mud and gluts' video of you using a mini-digger
https://youtu.be/_PEEYiODk7s

[Nicos]

We put ours in at 2ft depth and they seem to be doing the trick.

[lottie dolly]

maybe the 4ft depth is to avoid hitting it when builders ext start digging,but for the allotment is will be fine,MR dug a small trench the other year on a friends plot,it was in an area not used to grow on,plus it is fairly near the surface,the pipe is the large plastic type that was scrounged,and it has helped wonderful,just needs a very slight gradient.

[Markyw]

Hi there Sparrow. A land drain you are going up in the world. I have put many of these in over the years, A foot and a half to two foot will be fine with the weed block tied around it , If you can add some pea shingle around the weed block as this helps with the drainage, Just a quick question where is it draining to ?

[sparrow100]

I know, I feel a little swanky! Bromley's only just around the corner and along a bit...if you fancied putting in another one.

I potentially have some hardcore from my other task, which is hacking out more of the old bike track that runs along the southern edge of the plot. Would that work?

In theory it will drain down the centre of my path and then hive off to the left where I am digging a gurt big hole ('natural pond') as otherwise I will be drowning my lovely neighbours and that would be a Very Bad Thing. If it just sat in the lower part of my plot I'd be happy too.

[Cadalot]

Hard core and pea shingle or stones extracted from beds would be idea for the bedding and around the pipe, remember you need to make it easy for the water to get to the pipe. The woven weed membrane will help hold back fines, it should be a geotextile but It's an allotment not a major civil engineering works.

Rain water pipe from the end of the land drain and into a silt trap or traps that you can clean out will stop your pond getting too mucky and silted up. You will be able to use the silt in potting mix.

There are lots of ways of making silt traps, a couple of photographs added below, it could be a series of stilling ponds if you want to do it out in the open and plant water loving plants around it, really depends if you want fish in your final pond.

[Snadger]

I would think the field drain only needs to be just below your maximum cultivation level. If all the plots around you are waterlagged after heavy rain you may struggle to clear yours of standing water.
Depending on the frequency and the depth of water, having ultra raised beds with the drainage pipe around the surrounding paths would work. Remember to back fill with pea gravel or prefrably larger gravel right to the surface of the path to let water percolate away quicker.
If the outlet is into a drain or river/beck there needs to be a silt trap before outlet. The silt traps i have dealt with are just a small chamber with an inlet/outlet pipe coming in and out at a reasonably high level to allow silt to drop to the bottom. If the outlet is going to a pond, you have to make allownaces for lots of water flowing and check where the pond will overflow to!

I would think that any form of drainage has to be an improvement on what you have, but its hard to judge without seeing the plot and the standing water.

[sparrow100]

Cheers Snadger.

The big plot is partway down a hill running from SW to NE. I get water from the plots on the upper field too, and am going to dig a trench along the hedge on my south border to divert some of it before it gets to my plot.

The future pond would seep back onto my plot, not my neighbours. I don't mind the lower third being wet/flooded, I just want to have something that is workable a bit earlier than mid-late April.

This is it at pretty wet - it has got worse, with all the paths under water and everything running down across the eastern slope to the cemetery. Video is 2 mins long.

https://mudandgluts.com/2016/01/05/soggy-bottoms/