Heavy clay drainage help

My garden measures 30ft x 30ft. It is very heavy clay, and currently a waterlogged wasteland. I've literally had standing water for weeks on end now, and even when there is no visible surface water, it is boggy and you sink if you try and stand on it!

I had land drains installed on the 17th December, to hopefully fix the water logging issue. It hasn't. There is still standing water and the ground is still boggy, I'm devastated as it was so expensive and seems like it's been a complete waste of money, which we didn't have much of to start with!

I have no idea how best to proceed now. I just want a garden where my kids can play on the lawn without it being a sinking mud pool that you need wellies for 90% of the time (summer heat bakes the ground rock solid for some of the year) & I want to be able to plant shrubs and plants (unfortunately I adore acers, which hate wet feet!) without them drowning.

From my limited understanding of things I have been considering these 3 options -

1) excavate 12" of clay from the entire garden and replace with 12" of better topsoil, which will then (hopefully?) drain freely into the installed land drains. I'm not sure how trees with deeper roots would fare though?


2) add 10-20 tonnes of compost (and/or grit?) and rotovate into the top 6-12 inches of clay, to hopefully improve the drainage so it can freely drain into the land drains below.

3) raise the entire garden above the waterlogged clay - add a layer of gravel/hardcore straight onto the clay as a drainage course and then add 12-24 inches of topsoil on top. Or can I just add topsoil without a gravel drainage course?

I would love any and all advice and opinions here - which option do you think is best? What are the pros and cons of each choice? Is there an option I've not considered?

Thank you so much for your time.

 

Where do the "land drains" empty into? Are the surrounding gardens similarly waterlogged? Is this a new build?

 

The land drains go straight into the main surface water drain (that our gutter drains into) if that is the right word for it, so the water is completely removed from our garden.

It isn't a new build, it has just been left unattended for years and years by the previous homeowner. There was a solid towering wall of sixteen 35 foot leylandi conifers crammed along the back of the garden which we had felled. The difference in size and light is incredible, but I think the downside is that the vast amounts of water they were drinking is now just pooling in our garden. Both our neighbours to the sides have paved gardens. The garden behind us is slightly higher in elevation and has lots of large 35 foot silver birches etc.

Edit - to clarify - the drains were installed by a professional landscaper on their recommendation after seeing our garden. They are plastic pipes buried in trenches surrounded by gravel and membrane, in a herringbone pattern.

 

You don't say where you're at. Record rainfall has flooded many areas at the moment. Many more areas have the water table at ground level. If this is your issue then only a bilge pump will work. I'm presuming that this isn't the problem though.

Heavy clay doesn't drain well. I'm surprised the people who did your land drains didn't point out the harsh reality, that land drains don't work very well in heavy clay. I hope they didn't just put the clay straight back on top of the pipe when they backfilled the trench?

The clay will eventually seep into the pipe and clog it, rendering it useless.

Personally, I think the first goal is to make the heavy clay less heavy. I had the same issue here when I first moved in. On the recommendation of @Zigs, I used spent mushroom compost. This is dirt cheap compared to regular compost, and in my experience it is better for the job. If you look on eBay you can order pallet loads of the stuff for about £100 (give or take, based on how much you think you'll need).

I'd order that, then dig the lot in. This alone will make a big difference. But then I'd give the intended lawn area a light covering of sharp sand, sow seed onto that, then another light coating of sand, just enough to hide most of the seeds from the birds.

I find that having a lawn on clay also requires a bit of on going maintenance once established. Once a year, I buy 3 or 4 20kg sacks of sand, stand them on the lawn, open them up, then tell the kids to do what they want with it. Within a short time, the lawn is completely covered in sand. When the kids get bored, just rake it about. You could Google the concept of top dressing, but I sometimes think the articles describing how to do it properly are written by people who want you to think it's difficult enough to warrant paying a 'professional' to do it.

 

You have me really worried now, as it was explained to me the pipes were wrapped in membrane to stop anything seeping into them, I'm certain they did just backfill with the clay, is the membrane not enough to stop the clay entering?

I'm near Warrington, I'm not in an area that has flooded, and the water logging has been happening for as long as we have been here (over 3 years now) so is definitely not just due to the recent rains. It isn't a permanent water logging, more seasonal as in summer the surface has a tendency to bake rock hard and develops giant cracks.

Should I phone the landscaper tomorrow and complain? Honestly I'm so upset about all this. They assured me the drains would make an amazing difference and completely fix the problem. I spent a huge portion of our savings trying to get it right. I could honestly cry!

Oh and thank you for the advice, what a fantastic idea about the sand, my kids would absolutely adore that.

 

I'd get the opinion of another Landscaper first, then if they agree it was a pointless job contact trading standards.

I know it's not quite the same thing but I install French drains to take water away from old buildings now and again, this is my idea of a drain...







Certainly wouldn't dream of backfilling with clay

 

Yes, I'd speak to the people that did the drains. I can't think what membrane they might have used, but I think anything that could stop clay particles would also pretty much stop water.

The pipes are supposed to be surrounded by gravel and sand. That acts as a sort of first line filter to catch most stuff, includingthe bulk of the clay particles, although clay will always get through eventually, as its particles are so small. The idea is that most get trapped, and what does get through is sufficiently small amount that it just gets washed away. That said, even a field drain done properly will clog after a few years. It's an on going thing rather than a one time fix.

You might find that the contractor that did the drains will come and sort it without any argument. Word of mouth is their main advertising method, so often they don't want people to be unhappy, so I'd speakto them on civil terms first. If that doesn't work, then I'd base my next action on how likely I felt I was to win, vs how much stress I'd create for myself. If it was a dodgy, mobile number only fly by night, I'd probably cut my losses for the sake of my stress levels. If its an established legit company then I might consider the small claims procedure.

 

Surrounding with membrane is fine, its the backfilling with clay that will have rendered them almost useless.
Ive got major drainageprobs too that will need sorting this year. Have been looking at pavingexpert .co.uk and found all the answers to all my questions. One of the best sites on the net.

 

Thank you so much for all the advice, I really appreciate it so much, I can't even tell you!

The landscaper came very highly recommended from quite a number of neighbours and the company seems well regarded and has lots of positive online reviews so I'm hoping he will be gracious about the problem and it's been a genuine error in judgement on his behalf. Complaining makes me anxious, if you were me what would you be asking him to do to remedy it? Or should I ask for a partial refund to put towards amending the soil? Or ask him to amend the soil himself? I feel bad making a fuss because he did do the work, but it cost me over £1,000 and it hasn't helped and it was done because of his recommendation so I'm not being awful complaining am I?

I had a look and mushroom compost seems roughy £150 for 3 tonnes, is that going to be enough to make a significant difference in drainage or am we talking much larger quantities. like 10 tonnes?

Sorry to be a pain with so many questions.

 

Clay is very slow draining even with land drains,

the drains you put in sounds right, but your neigbours have a paved areas that water may head your way,adding to the problem

one thing with water is that it can come back up the land drains if is pushed by a flow of water from the storm drains if that water can flow away quick enough, but this is me just thinking it may not be happerning i'm just saying that water can flow both ways

we have had a lot of rain being that clay is slow draining it may nead time to drain, you can help by pushing a fork into the ground as far as you can and push the fork back and forth and make holes in the ground over the drains
I've just reread, you had the drains put in on the 17th dec, i think it is possible that it has not had enough time to start working properly

 

@Jiffy thank you for the reply, can I ask in your experience how long do drains like this usually take to work? I was given the impression they should start working pretty much instantly.

 

Your problem reminds me of when I lived in Houston Tx. Heavy black clay soils that when wet, which was most of the time, would literally suck my boots off of my feet. The problem, besides being clay soils was that it was level, no slope of any kind, so the water just sat there and bred mosquitoes. I tried digging drainage ditches but that was a waste of time. Finally the ground dried out enough to work it and what I did to fix the problem was this. I tilled the ground as deep as the tiller would go and then tilled in a LOT of cheap mulch, which raised the area by about 6 inches. Then I moved by wheelbarrow this mulch/soil combo from one side to the other and made a gradual slope of 3 inches per every 12 feet, ending up with the original elevation at the bottom. Then I added good compost about 1/2 inch deep over the whole thing and then put sod on top and rolled it in. I lived there for about 5 years after that and never had the problem again. However, the mulch that I used to mix with the clay finally decomposed but the slope remained. Maybe this will work for you too.

 

There are 2 types of water that cause problems, ground water and surface water. Land drains take away ground water (which includes any surface water that percolates down to them). If those drains were surrounded with gravel, but then backfilled above that free draining surround with clay subsoil, then they would do little to alleviate surface water drainage problems.

 

What should have been done, backfill completely with gravel? You can't lay a lawn over that then though can you?

 

If lateral drainage though the clayey topsoil layer was improved, and something other than clay subsoil was used to backfill trenches, perhaps that land drainage scheme whould have been successful.

So what did your contractors use to backfill above the gravel pipe surround? There needs to be an improved route for surface water to get into those drains.