Soakaway for lawn on clay


5 May 2012
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United Kingdom
I have a feeling that my project is a bad idea, but I wanted some advice...

I am re-turfing the back garden, and have dug over the old lawn and rotavated. During heavy rain our lawn (before I dug t up!) was quite squelchy, especially at the top end, though there were never puddles. The lawn is approx 8m x 8m.

I am considering using land drainage pipes running to a soakaway along the bottom of the garden, under and at the edge of the lawn. This area at the bottom is walked on less and there is a hedge running along the length of the bottom of the lawn that I hope will help remove the water.

My problem is that there is a clay subsoil. At the top of the garden I have about 40cm of decent topsoil before hitting clay, and at the bottom, where I want the soakaway, there is about 70cm of decent topsoil before I hit clay.

I do not plan on making a typical 1 m³ soakaway, but instead a shallower long soakaway , eg 40cm deep, 50cm wide, 4m long. So this will sit right on the clay, but have decent topsoil to the sides and above.

Waste of time, effort and money?
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I'd dig a trial hole in the proposed position for the soakaway, and do a percolation test. If this doesnt work then scrap the idea!
would it help to trench and french-drain round the edges of the lawn? with a slight doming and no depressions, standing water would be discouraged and would tend to run off.
Consider a sump containing a pump with a float switch then pipe the stuff away.
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Thanks for the input and suggestions.

The percolation test was not promising, however, this is what I ended up doing... since I had the stones already, and I don't mind a bit of hard work, I made a soakaway 3m long, 60 cm wide, 40 cm deep, about 35cm below the surface. I have not installed land drainage pipes at this time, since the soakaway may not work very well. I am going to finish the job of laying the new lawn, and if drainage is a problem, then I will put in drainage pipes... I decided that digging a channel and putting 2 or three pipes in after laying the lawn would not be the end of the world, but I didn't want to dig a soakaway after the turf was down, so I've given myself the option later.

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