In article ,
says...

On Friday, 19 February 2016 17:55:54 UTC, Mathew Newton wrote:

(Full thread for reference: https://groups.google.com/d/msg/uk.r...0/TEiobQMVAgAJ)

I plan on looking at drainage too and will post back tomorrow with a drawing
to get thoughts from the panel!

I have done this now and would be grateful to hear what others think of me taking advantage of a rainwater sewer inspection chamber that I happen to have under my decking...

A picture speaks a thousand words:

http://www.newtonnet.co.uk/permanent...ge%20Ideas.pdf (3.2MB)

The decking sits in a recess (to minimise the step up from the lawn) and so as a result I am assuming it is well located for draining the whole garden.

The easy (lazy) option (Option A in the drawing) would be for me to perforate the chamber walls - perhaps to nearly full height - however I am mindful that this could cause silting up of the outflow pipe over time?

Option B would be to dig around the top 250mm or so (access isn't all that easy given the surrounding decking hence not doing this for the full height), wrap it with permeable weed-stop fabric and infill with gravel. Only this section would then be perforated and this ought to cause less issues with silting due to the fabric mainly only allowing water through.

Any thoughts on this idea? I recognise that the ideal (aka 'should have done this in the first place'!) option would be to provide channels from across the lawn to the chamber as the clay subsoil might not allow free levelling/distribution of the water without these however I am mindful that I don't have a confirmed drainage issue and also want to minimise effort by not digging the whole lawn/soil up if at all possible!

Mathew

I can't tell if there's any slope towards the colelction chamber; if
not I'm not sure it will drain the lawn much.

I strongly recommend you ask some advice from Tony at his website
here
http://www.pavingexpert.com/

Tony used to be a regular poster here, and he really is an expert,
not just on paving but also drainage; so tell him you came from urg and
Janet says hello. He's helped a lot of people here and gave me a lot of
advice when we were draining out garden.

Janet.