Land Drain Advice

[humble_beginnings]

Hi there,

Yesterday we commissioned a well established landscaping company to install a land drain around the internal perimeter of a retaining wall. From what I have read in my research leading up to this, the trench should ideally be 750mm deep for a 100mm pipe.

The company finished the installation whilst I was at work, but when I came home, it looks as though the trench is only about 200mm deep. I queried this with the owner of the company and he said that they typically dig down to about a foot for similar installations (the area doesn't usually become waterlogged, but never dries out).

I am concerned that due to the shallow trench, the effectiveness of the drain will be reduced, but also (and more importantly), the stability of the area when the lawn is relaid - are these valid concerns?

Cheers

Tim

 

[r896neo]

It depends on the function of it? Is this designed to take away surface water from weep holes etc or to reduce groundwater pressure coming from the slope?

A shallower wider drain will be more effective at collecting surface water but be useless at collecting/relieving groundwater etc.

I have dug deep 900mm trenches 6'' wide or shallow 200mm blanket type drains 2 feet wide.

 

[humble_beginnings]

Hi @r896neo,

Thank you for the reply. It is more for surface water really (I think). The lawn area is on a reasonably shallow bed of topsoil (~8") and the area where we have had the drain installed never really dries out.

Cheers

Tim