How deep should i install my land drains

[irishal]

Hi,
I intend installing land drains into my back garden as 10 months of the year it is sodden after even a short rain shower. The garden soil is mainly clay with about between 1/2 to 1 foot of topsoil beneath the lawn. The garden slopes down towards the back of my house with other houses behind me. I have a handy connection into an existing access chamber at the lower end of the garden but it is shallow - only approx. 1 foot. To get the drains to feed by gravity into the access chamber would mean having the land drains at a depth of only 1 ft. Would this work?

Or would they be too shallow? The other option is to install the drains deeper with a new deeper chamber with submerisble pump with float switch. This would add to the expense but would be better done now rather than have the cost of having to dig up the newly installed drains. What would be the optimum depth for this type of system?

Thanks
Alan

[Tony McC]

You can, in theory, install land drains with zero fall and rely on hydrostatic pressure to force the collected water towards the outfall. What you mustn't do is have backfall, though.

1ft deep (300mm) is awfully shallow and I'd look at using one of the composite units in place of traditional land drainage. I have a product in mind, but can't reacll the name - I'll have a root through my library later.