French Drain

[Zak S]

Hi. Due to very clayey soil and high water table with lots of trees in the area, I noticed the house we are buying has an issue of water logging in the far end of the garden and it was literally flooding that corner of the garden. However, Grass across the garden felt drenched in water and has lots of mossy growth. Garden is north east facing but total plot size is 0.38 acre. How best to deal with this issue. Should I go for french drains just the area where it floods and drain the water to other area or to mains? Happy to aerate the garden on regular basis. Would it address the problem on an ongoing basis?

[ProDave]

If the water table has reached the surface, no amount of drains will drain it anywhere.  If it is just one bit, do as we do and avoid walking there in the winter and it dries up in the summer.

 

Moss needs removing with a lawn rake annually, if you actually find a way to stop it, you will probably become a wealthy man.

[Zak S]

 

14 minutes ago, ProDave said:

If the water table has reached the surface, no amount of drains will drain it anywhere.  If it is just one bit, do as we do and avoid walking there in the winter and it dries up in the summer.

 

Moss needs removing with a lawn rake annually, if you actually find a way to stop it, you will probably become a wealthy man.

Does aeration of the soil not help at all?

 

I am not sure if water table has reached the surface as in Dec it was at one meter depth (as the GI) was done. The flooding of the garden on one side might be due to fast rain/storm last Monday. Hence the thought is french drain will resolve the issue?

[Mr Punter]

Could you make a shallow water feature in that area?  If it has soggy grass and moss it may be more suited as a semi wetland with planting to suit.

[JohnMo]

Sharp sand, grass likes the extra drainage, moss hates because it irritates them, so they don't grow.

 

I think you need to use horticultural instead of builders Sharp sand.

[Zak S]

2 hours ago, Mr Punter said:

Could you make a shallow water feature in that area?  If it has soggy grass and moss it may be more suited as a semi wetland with planting to suit.

Great Idea. The grass seems to be very spongy. So basically instead of spending money on Frend Drains make a water feature and suitable plants. Is it because French drain dont work or too expensive?

[Zak S]

28 minutes ago, JohnMo said:

Sharp sand, grass likes the extra drainage, moss hates because it irritates them, so they don't grow.

 

I think you need to use horticultural instead of builders Sharp sand.

Thanks. Just to clarify, are you saying drains would work. Where do the sharp sand come into it. How do I use it? Do i remove top soil and clay and mix with sharp sand?

[Mr Punter]

French drains work really well at directing water elsewhere although they can clog on clay soil.  I just think that if the area is naturally prone to waterlogging and it is not affecting the house you may do better to have it as a wetland and maybe encourage some wildlife as well as it could be a valuable habitat.

[Radian]

What's the topology like in the part that floods? Is there an obvious reason - like being lower than everywhere else?

[Cpd]

Maybe post some photos so people can get a better understanding of the site, I have this problem with an area of lawn and dug it out and it filled with water and made an instant pond,  there are two kids living next to it at 2 and 1 years old so I have drained it until I can re visit the landscaping plan at a later date. 

[Russell griffiths]

Dig a hole 750x750 and 600 deep, look at it every day and work out what is going on. 

If it fills with water when it rains that is ok, but what happens the next day, does it drop or just sit there. 

Look at it for a month working out how long it takes to drain and so on. 

You will work out a pattern. 

[Zak S]

3 hours ago, Mr Punter said:

French drains work really well at directing water elsewhere although they can clog on clay soil.  I just think that if the area is naturally prone to waterlogging and it is not affecting the house you may do better to have it as a wetland and maybe encourage some wildlife as well as it could be a valuable habitat.

I spoke with the landscaping/tree specialist and he said any water feature need to have the water recycling ability to ensure it does not stay stagnant and become smelly. I intend to install a summer house in that corner. He did suggest River Birch but not sure if it would survive in clay.

[Zak S]

3 hours ago, Cpd said:

Maybe post some photos so people can get a better understanding of the site, I have this problem with an area of lawn and dug it out and it filled with water and made an instant pond,  there are two kids living next to it at 2 and 1 years old so I have drained it until I can re visit the landscaping plan at a later date. 

Please see below the topographical survey with flooded area marked out. This corner is also where I intend to install decent size summer house as it gets decent amount of Sun. Any

_2021-20-1 Topographical Survey - with waterlogged area marked.pdf

[Radian]

Looks quite flat overall. Is that a field to the North? Possibility of a broken land drain (ancient) if so. 

[Zak S]

1 minute ago, Radian said:

Looks quite flat overall. Is that a field to the North? Possibility of a broken land drain (ancient) if so. 

No there are house behind the garden. The area was called Coppice with lots of trees which was developed partially in 1950-60s but all the trees have blanket TPO.

[saveasteading]

4 hours ago, Russell griffiths said:

Dig a hole

Agreed. if the water table is permanently high then that is a problem and no amount of drains will help.

 

However if the water table is below the ground then a pond is a likely option. It is somewhere for you to divert the water, has a big ground surface and some head to drain into the ground, and a top surface to encourage evaporation. Plants will help in the summer.

When you dig a pond you get surplus earth, which can be used to raise all or some of the remaining ground above the wet area.

[Zak S]

21 minutes ago, saveasteading said:

Agreed. if the water table is permanently high then that is a problem and no amount of drains will help.

 

However if the water table is below the ground then a pond is a likely option. It is somewhere for you to divert the water, has a big ground surface and some head to drain into the ground, and a top surface to encourage evaporation. Plants will help in the summer.

When you dig a pond you get surplus earth, which can be used to raise all or some of the remaining ground above the wet area.

Thanks. I think I need to test by digging the hole and see what's happening. I think the water only stays there for around 24hrs after the rain and then disappears but slowly. A landscaping contractors suggested to remove the top layer of the garden about 3 to 4 ft and add hardcore and then sand and topsoil to improve it. Given the size of the garden, its going to be significant costs hence thinking if Severn Trent allows to drain the water to mains then we can improve the drainage to an acceptable degree. If the water was to surface level then I agree no point for drainage to improve the situation.  

Edited February 24, 2022 by Zak S

[saveasteading]

4 minutes ago, Zak S said:

if Severn Trent allows to drain the water to mains

They shouldn't. The recent floods are not only climate change, but fast runoff from land and buildings. For a new development the runoff is usually limited to (from memory) 5 litres/second/ hectare, (including the house drains so that would have to be retained too) which for a normal garden is very little. I always aim for zero and you probably can too.

[Zak S]

8 minutes ago, saveasteading said:

For a new development 

Just out of interest if I don't do any other work other than remedial work in the garden for the excess water; would this be classed as 'New Development'? Given the area is marked for a summer house, Ideally I need to find a solution to move the water elsewhere. Another issue is as this particular area in question is adjacent to neighbour I will be bringing their water into my Garden if I divert the water to another place in the garden. 

Edited February 24, 2022 by Zak S

[Zak S]

@saveasteadingWould the improvement in Ground (like pushing stone in the ground) for the summer house result in improvement of ground drainage ie ability of water to be soaked in the ground?

[saveasteading]

Unlikely unless you can break up what is there to become more porous. Digging it over would have more effect but short term.

Another thing that helps is trees and shrubs. They don't drink the water in winter but the roots can make channels for the water to run away to deeper levels. Not scientific though. ie it probably helps but as an extra,

[Zak S]

On 24/02/2022 at 23:59, saveasteading said:

Unlikely unless you can break up what is there to become more porous. Digging it over would have more effect but short term.

Another thing that helps is trees and shrubs. They don't drink the water in winter but the roots can make channels for the water to run away to deeper levels. Not scientific though. ie it probably helps but as an extra,

 

I was thinking of vertical stone columns. I am thinking that it might help to drain the water vertically? Is that possible and if there any issue I might come across with that approach.

 

As I understand there are two water level. First strike was at 1m and second at 6.7m. So not sure how verticle Column work in draining the water vertically. If thats an option, is it commonly used? And if that works would that not be a solution also for storm water drainage instead of soakway or Suds with attenuation tanks?

[saveasteading]

14 hours ago, Zak S said:

verticle Column work in draining the water vertically.

It is used extensively in huge projects such as motorways and estates. However it only works if it reaches another layer that can accept all the water and so this is getting technical and expensive.

Also, they fill with muck and need the gravel replaced every few years.

And there are strict rules to avoid the localised water flow causing sink holes.

 

So not for a little job unless you happen to know that there is a layer of porous ground, not far  beneath the non-porous surface.

[Zak S]

On 24/02/2022 at 22:35, Radian said:

Looks quite flat overall. Is that a field to the North? Possibility of a broken land drain (ancient) if so. 

You are quite right. I had a chat with the previous owners who had some historic survey from 1800s. He said there used to be an old river right on the edge of the garden where it floods. By river he meant water stream. Hence the water level is higher at that end.

Edited March 11, 2022 by Zak S

[Radian]

It may be that you can pinpoint the end of a clay pipe that used to lead to the stream, probably less than 1m or so depending on how it originally terminated. I'd start by estimating the 'epicenter' of the flooded area and have a dig. If you can find a pipe (it often runs in short, disjointed sections) you may be able to trench it out to your rainwater system.