At one time I lived in a cottage halfway down a hillside with meadowland behind. The hill was clay and the water table was higher than the floor level in the cottage which was on a level spot which had been cut into the hillside back in the 1600s. A few years before we moved there the then owners had interfered with the way the land drained by filling in the well and a ditch and building a retaining wall. From then onwards the house was always damp in the winter according to neighbours.
We dug a ditch at the side of the house to drain the pool that gathered at the back of the house ... while doing this an elderly neighbour said that we were simply reinstating what had been there originally ...she said she’d told them that filling in the ditch would lead to trouble.
From there on the water ran down our sloping driveway, across the road and through a culvert into the stream at the bottom of the hill.
It may be that some old watercourses have been neglected over the years and need reinstating.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
We have a large ditch between us and the field at the back - we call it a moat. Unfortunately as we are quite level there is nowhere for the water to be diverted to. It was so bad yesterday that the moat burst its bank... We were told that our excess water went into a nature reserve under the road butRadnorshire wildlife will NOT maintain the ditches their side so we really do have nowhere for excess water to go.
Ok I've got a proper keyboard and mouse now. I've been dealing with a similar problem on a local property here where the fields above were draining down into the garden and the water had nowhere to go so it was creating a temporary lake for the owners. Believe it or not this is how we are told to treat surface water these days. According to the guidance we should collect the water from the roof first in tanks above ground, then deal with any excess on the surface of the ground in ponds and swales, then direct it from there to soakaways and to a watercourse as a last resort.
The problem you have is twofold. The ground's surface layers hold water fine but isn't letting the water dissipate fast enough in heavy rain. The soakaways also don't have enough holding capacity for the amount of water being sent to them and the outflow is slower than the rate at which they're filling up. The water from your roof is mixing with the ground water and making the flooding twice as bad. Do you get any drains backing up during drier weather when we have a lot of rain?
With my client's property we installed a large holding tank and connected that to a fin drain running through the worst of the flooded areas. Fin drains are similar to french drains (which are a gravel filled trench) but they are much deeper and can penetrate through the clay layer and into a more permeable strata. This means they're acting as a soakaway while also carrying water away from vulnerable areas.
I would place a bet that your soakaways are just pits that were dug and backfilled with rubble. This was the old way to do things and was never very effective as the capacity to hold water was bad to start with due to the rubble taking up most of the space and it would have got worse over time as the available voids silted up. What we're using now are hollow plastic crates (see the pre-fabricted cellular crates section on the link below) and these hold almost a thousand litres/m³. You can work out the area of your flooded patio, times by the depth and get a rough idea of how much water holding capacity you need, but assume at least 4m³
for an average size house. You can also help this out by fitting all your water butts with slow release valves to make sure they're empty when you get a storm and then release the water slowly into the drains. I just set the taps on mine to run at a slow trickle and they rarely overflow. It can take a bit of trial and error to get right though. The more water you can store above ground the less you will need to store below ground and it's a much cheaper option if you have the space.
You will need to get someone with a digger to come in and dig some test pits to find out if the ground below the clay allows water to soak away, how deep that layer is and how fast it can let water out. Once you know that then you'll have a better idea of how to size a suitable soakaway. Soakaways should be at least 5m away from the house and roads.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
That's a very interesting and thought provoking post @wildedges so thanks for that info. I'm sure the original poster will be grateful.
We had to have drainage pipes laid all round our new garage which were directed to a new soakaway under the parking area and then to an original drainage ditch under the old hedge. We do still have an intermittent problem with natural springs breaking out in high rainfall times as we are surrounded by fairly high hills but there's not much we can do about that. Interesting that the new guidance states soakaways should be 5 metres away from roads - surely that's not always possible?
Technically a soakaway needs to be 5m from any structure, road or boundary. As you say that's not always possible so sometimes the plastic crates are wrapped in polythene to make them water tight and a valve is used to reduce the outflow rate and the water is directed to a watercourse or even into the mains drains in very extreme cases. You need permission from the mains drainage owners for that and most don't allow it now. I've worked on a bungalow here that has 10m3 of underground storage under the driveway just to slow down the water flow to a stream a couple of hundred yards away. It was a huge cost to the owners for very little gain in flood prevention terms but it was that or no house at all under the current regulations.
One thing I didn't mention with this particular question was what is happening with the foul drainage from the house if the garden is getting flooded so often? If you have a septic tank you may need to check where the outflow from that is going and make sure the soakaways aren't going to prevent it doing its job.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
What a detailed response and thank you so much for all your information. Our 'moat' works quite well at containing water and this was the first time it breached! We have numerous large water butts (2 on most downpipes) but hadn't thought about letting them drip. Some do overflow when we have torrential rain. Will look into what else can be done but really think we ought to get in a specialist and no one can suggest one. I've googled but apart from one that would charge hundreds just to come and look at the problem (which would be taken off the final bill when we employed them) we're stumped. We have a neighbour who works in this kind of field and he suggested a pipe from the field going down deep so that it flows down the other side of the field. Reckons it could cost thousands and can't guarantee success. Our neighbour has the same problem and she had bore holes put in the field which did nothing... Thanks again, let's just hope we get some dry weather and Noah won't be needed with his ark.
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Hopefully he'll pop in and might be able to help in some way
I live in west central Scotland - not where that photo is...
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
Hopefully he'll have a bit of advice
I live in west central Scotland - not where that photo is...
You will need to get someone with a digger to come in and dig some test pits to find out if the ground below the clay allows water to soak away, how deep that layer is and how fast it can let water out. Once you know that then you'll have a better idea of how to size a suitable soakaway. Soakaways should be at least 5m away from the house and roads.
I'm sure the original poster will be grateful.
We had to have drainage pipes laid all round our new garage which were directed to a new soakaway under the parking area and then to an original drainage ditch under the old hedge. We do still have an intermittent problem with natural springs breaking out in high rainfall times as we are surrounded by fairly high hills but there's not much we can do about that. Interesting that the new guidance states soakaways should be 5 metres away from roads - surely that's not always possible?
Thanks again, let's just hope we get some dry weather and Noah won't be needed with his ark.