Land drain pump chamber - What pump housing for storm water?

[Jim S]

Hi
I’ve been looking at many aspects of this site for ages. It is so informative and interesting. This is only my second post.

In heavy rain my garden floods! It was lawn and flower beds, but the water took ages to go away and turned sour and green in places. We have a high wall at the end of the garden and at one time over the wall was an agricultural area with the big house about 100 yards away at the top of the hill. Unfortunately this has been replaced by about 300 houses!

This development, together with the naturally high water level and clay subsoil causes my problem. As we are now “getting on a bit� we decided to go for easy maintenance and also hoped this would alleviate the water problem. I removed part of the lawn to build decking, however the whole area was full of water when it rained heavily. I decided to put in a land drain and did so with 80mm perforated pipe, membrane and gravel. Then I dug a hole approximately 1m x 1m x1m to catch the water for pumping to the storm water drain.

I got hold of two old heavy duty (plastic) gas pipe ends about 1m long by 350mm diameter. I bolted these together and placed in the hole and backfilled with 20mm gravel. The land drain feeds to the first one which I call the silt trap (bucket on string at the bottom), this then feeds the second unit which houses the pump. The first rain showed that it was indeed working, however the rain continued overnight and in the morning the containers had been lifted about 300mm by the water coming in naturally OUTSIDE my containers. So my tanks should be anchored somehow.

I have now removed the tanks and dug out the backfill. The land drain is still working well as there is constant flow into the hole. But also the hole is being filled by natural drainage from the surrounding area.

What I am asking for are comments and suggestions for a permanent collector/pump chamber.

1 - Should I use the “tanks� but anchor them in the hole, and drill holes fairly high to let the surrounding water in also?

2 – Instead of the tanks, should I build a brick unit with a small silt trap?

3 – Can anyone suggest a better method.

Lastly, please forgive the length of my post. I wanted to give a clear description.
Many thanks, Jim

[Pablo]

Stick with what you have but there is no need for the tank to be watertight so drill plenty of holes in it especially at the base so there is no risk of it "floating" out of the soil. Wrap it in geotextile to protect it from silt and it should do your job. Is the pump on a float switch?.

[Jim S]

Thanks for your advice Pablo.
Yes, the pump has a float switch. I worry that there may not be enough space in the tank for it to operate correctly. Tank is about 350mm dia, maker recommends 450mm square.

[flowjoe]

Most float pumps have an adjustable float arm/lead however the shorter that arm the more often the pump activates, and in theory the shorter the life span of said pump.

There is also the chance of the pump arm becoming lodged and not activating or even worse becoming lodged and not turning off and burning itself out.

To be honest 350mm sounds a bit small for a chamber, we always put in as big a chamber as possible and set the pump to its maximum activation point, i would use either 450mm plastic manhole sections (circular) or possibly 600 x 450 x300 concrete sectional manhole rings (square) to build a chamber.



Edited By flowjoe on 1218280867

[Jim S]

Thanks for your reply, flowjoe.

The float switch jamming is my my main concern and really not worth risking , is it?

I'll have a look on the internet to see what manhole sections/rings are available. Should I leave gaps in the sections to allow the surrounding water into the sump?

Many thanks
Jim

[flowjoe]

Most BMs stock plastic manhole sections, so do B&Q, wickes etc..... Build up off flag base, drill a few holes in the rings and surround with granular fill.

Concrete sections are a bit cheaper but obviously heavier to work with, they will not be water tight anyhow but again you can drill a few holes or put spacers between each ring

Either suspend your pump off the base with a chain or sit it on a brick or half flag to keep any silt that gets through to the chamber out of the pump.