Advice on a soakaway please

[Sprocket*]

We are in the process of putting in a soakaway at one side of the allotment but would appreciate some advice from anyone.

Basically our allotment is at the bottom of a slight incline with about 7 other allotments up the lane from us. When we get any more rain than a shower we end up paddling at one side. The soil on that side is pretty much solid clay which I have been attacking quite successfully with clay breaker in the beds for the last two years.

The plan is to dig a sink hole and run a rubble drain down that side into the sink hole but don't know how deep to dig the trench. We have plenty of rubble to stick in it as the previous occupant seems to have been cultivating bricks and rocks.... The sink hole is about 5ft deep and can't go any further as we have hit a massive sewer pipe but there are a load of lime stone chippings around it. The edge of the sink hole are pure clay.

Any help or suggestions much appreciated.

[HeyWayne]

I know when we had drainage problems in our garden they dug a 6x6x6ft hole in my lawn and carried out a "percolation" test. Basically dug the hole, filled it with water and covered it up. Left it for a week and came back to see how much water - if any, had drained away. This told them if the place was actually suitable for a soakaway (which it turns out it wasn't).

Our garden is very heavy clay - so we ended up having to have a trench dug at the back of teh house and connected up to the surface water drain (you wouldn't believe how many people we had to get involved!).

Are you planning to use the ground above where you intend on placing the soakaway? If not, then it might be a sensible option to create a pond of some sort where the drain ends. Benefits the wildlife, and gets rid of your water.

[jacob marley]

I would fill the sink hole with all the ruble that you can find and hope that the the limestone chipping's act as a drain and take's the water away your own free land drain....jacob

[SarzWix]

The trench my dad had made running to a soakaway was a spade deep gradually descending to 2 spades deep on the way down, the wettest parts were 2 spades. Better to have it too deep than too shallow though

[Paulottie]

I'm not the most experienced land drainage expert as the land here is sand...but being 1/2 Dutch possibly gives me some inheritance?

Anyhow, Wayne made a very sensible suggestion there but one point to stress that your excavations may also act as a land sump...ie the water from the surrounding land`will just seep in turning it to a pond....that is not just the surface water but through the sides of the well and may not improve the land drainage at all....as Sarzwix pointed out wettest part maybe 2 spits down. So don't connect it at first... see if it fills up before you try whether it empties again

[Snadger]

A French Drain is what you are trying to create. French drains are usually quite large affairs and dug out with a back hoe of a JCB. Roughly about 2 foot wide and 2 foot deep filled with very course rubble.

If the soakaway isn't big enough or the ground around it not very permeable what could happen is that in heavy rain the soakaway will overflow and water will run on the surface to the lowest point.

If possible it would be better to position the French Drain to catch the water and funnel it away onto lower wasteland rather than a soakaway!

[HeyWayne]

If possible it would be better to position the French Drain to catch the water and funnel it away onto lower wasteland rather than a soakaway!

That's what I meant in a roundabout way.

[jacob marley]

What i was trying to say is use the limestone chipping's as a type of french drain in a round about sort of way....jacob

[sewer rat]

Righto, here goes.
From my understanding of your post, the problem is that you end up with a lot of surface water on one side of your plot.
As previously mentioned what you need is a french drain to take this water from where it causes the problem on your plot to the main sewer that you have already uncovered.
Fill in the hole that you have dug down to uncover the sewer and it's lime chippings bedding to about a foot above the lime chippings. Use whatever rubble you can find lying about but be a wee bit careful when filling the hole that you don't crack or damage the sewer. From the top of this rubble start to dig a gently sloping (indeed if you so wished it could be dead level) trench to just past the problem area. Fill this trench with the larger rubble at the bottom and trhe smaller stuff at the top.
Voila, un French Drain !
By the time the water filters down to the lime chippings round the sewer, most of the dirt / silt will have been filtered out and it should just run off down the sides of the main sewer.
If you so wished , before filling the trench with rubble, you could lay a length of 4" perforated drainage pipe along the bottom of it - water will flow away quicker with this pipe in place.