Surface water issue

[ktp73]

Hi All,

I'm currently in the process of excavating an area of my back garden for a patio. The garden slopes up away from my house and an existing patio. The soil is really poorly drained and I often get pools of water after heavy rain.

After digging the big hole (about 4m x 4m) it has filled almost entirely with water but we have had a lot of rain. I'm concerned that once I put the patio down it will end up flooded after rain. I plan on putting down about 40mm of hardcore before laying the patio but I doubt that will help with drainage.

Do I need to consider a soakaway or French drains? Given the poor drainage of the soil anyway (possibly high clay content) I'm worried that these drainage solutions aren't going to solve the problem because of the clay.

Any advice gladly received.

Thanks,

Kirk

 

[pinenot]

If you surface the patio with porous slabs/blocks and have adequate drainage under this, possibly running off to a suitable rainwater drain/sump! ...pinenot

 

[ktp73]

Sorry being a numpty here - are you suggesting a drain linked into the existing drain system used for taking away rainwater via downpipes?

 

[pinenot]

Yes, assuming you can and building control have no issues.
Permaslab (you may have seen this around trees/shrubs in certain public places) or permeable blocks (fairly common now) developed to provide solutions to urban areas, where run off i.e. not absorption, is a major problem these days. But if you have existing ponding problems, this issue must be resolved first. You could try deep spiking first (must be through any clay area near the surface) which involves using an implement (maybe a hire able unit available in your area?) the rustic thing was a pinch bar, which could be used in conjunction with a post hole digger, getting a deep enough hole that can be screened with some permeable matting available from most local builders merchants...pinenot

 

[r896neo]

If the patio is only to be 16m/sq i wouldn't worry about putting in drains. You can just fall it onto a lawn or flower bed.

If your garden has terrible drainage and frequently has standing water then thats another issue as pinenot has said.

You are absolutely not allowed to pipe into foul sewer. If you have a combined stormwater and foul system you may be allowed to but you would have to prove a soakaway was not viable. A soakaway needs to be at least 5m from any building

As pinenot says you need to dig a deep hole and see if you can get through the clay. 1m minimum.

 

[ktp73]

I can't fall the patio anywhere obvious. The whole of my back garden slopes towards the house. Years ago I dug out the first 3 metres or so and levelled it and had a patio laid.

Now I'm trying to extend that patio into essentially an L shape. I've effectively dug a cheese wedge out of the remaining back garden and will put a retaining wall of sleepers up around that.

We've had loads of rain recently and my excavation currently looks more like a water feature and isn't draining very quickly if at all.

There is a manhole in the old patio, which isn't far away from the new hole, which I assume is for surface water - not sure about waste though.

I don't really want to involve building control if I can avoid it. I was thinking of digging some trenches at the foot of what will be the retaining walls (on 3 sides) and filling with gravel wrapped in landscaping fabric. Not sure if that is going to be enough though.

The area drained ok before I dug it out so I assume the heavy compaction of the soil underneath is what is causing the water to pool?

 

[colin H]

We had a very similar situation to this , with our garden sloping towards the house .

I built a path /patio 2 years ago , which runs from one end of the garden to the other . To help with the drainage , I cut a hole in the side of the storm drain , below ground level and covered it with a 6" plasic grid cover.

It works perfectly , all the surface water runs into this , and I`ve never had a problem since .

Somebody , will no doubt be able to tell us if this contravenes building regulations , but it`s done the job !

 

[r896neo]

You need the permission of your water authority to drain into a combined sewer and they will almost certainly not give it to you.

Unfortunately there is no silver bullet. Naughty people like colin here have been know to break into a gully and connect some linear drains to it. Draining surface water into a storm drain is not that bad but draining groundwater into it is a big no no and also socially irresponsible

 

[r896neo]

You need the permission of your water authority to drain into a combined sewer and they will almost certainly not give it to you.

Unfortunately there is no silver bullet. Naughty people like colin here have been know to break into a gully and connect some linear drains to it. Draining surface water into a storm drain is not that bad but draining groundwater into it is a big no no and also socially irresponsible.