Constructing a soakaway

I thought all rainwater collected by the roof guttering, went into the main sewer.

So I knew there was going to this thing called a "soakaway" dug into the garden, but I hadn't really realised what it was for, or how big it was going to be.

The reason for it existing, is to capture all the rain water - which is collected from the roof by the guttering and downpipes - and allow it to "soak away" naturally into the ground. Originally I just thought it would all be sent down into the main sewer pipe, but logically it makes sense to let nature deal with it on-site. Otherwise there would be millions of extra gallons of processing required, for all the rain water captured by all the roofs in the country!

How big?

Apparently for our size of roof, we'd need approx 2 cubic metres of capacity, to process a downpour of heavy rain. It should then soak-away naturally within a day or two, depending on how wet the ground is already.

How is it made?

To create this kind of void in the ground, the hole they dug was much bigger indeed. The plan originally was to buy special plastic 'crates' which clip together to form a soakaway chamber. However, upon investigation, they proved to be too expensive at about £30 each. We would have needed 20 of them so it starts to get quite expensive. So, thanks to a mis-delivery of some lightweight concrete building blocks earlier in the month, by one of the builders merchants, we made use of these and loosely constructed a chamber in the hole. This was then filled with random rubble from around the site and covered over with polythene.

The drainage piping had already been laid a couple of weeks ago, so it was just a case of adding another small length of pipe to direct the water into the hole itself.

Et voila! One rain water soakaway. The whole lot was covered up again with soil from the site. One day our lawn will sit above it.