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Land Drain Yet Soggy Lawn

ghutton14ghutton14 Posts: 4
in Problem solving
Looking for some advice to hopefully stop me going loopy. Our housebuilder installed a land drain to remove rainwater that runs into our garden from higher ground on 2 sides. It's never worked that well with water still pooling in badly areas  and lawn always soggy so decided to take a look myself. I found that the groundworkers had just cut into the top part of a solid pipe every 300mm or so in an attempt to make it perforated. The branches running off the main pipe weren't connected at all, they were just laid beside one of the slits. Total bodge job.

To fix, I dug all the pipework out, cut perforations using a Dremel grinder all around it, connected the branches using Y connectors and laid geotextile fabric into the trench. Fitted perforated pipe covers at the end of each branch to stop stones and mud entering. Cleaned the dirt off the gravel and put it all back in before covering over with the geotextile then topped with soil/sharp sand and turf. Before I put the soil/sand/turf back on I ran a hose at all points round it and made sure it was working perfectly. 

On to my problem. Had some heavy rain over the last week or so and water is still pooling in areas, specifically on top or at the sides of the turf sitting over the land drain. I cut some slits in the turf and filled with sharp sand. It still pools on top and at the sides. I'm so confused as I don't understand why it's not working as well as I think it should - or maybe I am expecting too much. Once the rain stops the rain water does all go from the lawn surface within around an hour so it is definitely working better than it was. However the lawn remains soggy for a good day or 2. I've now read that in certain soils geotextile fabric shouldn't be used in a land drain system so worried that I've made a booboo.

I suppose my question is - even with a drainage system installed should I still get water pooling on the surface and a soggy lawn for a few days? Any advice would be gratefully appreciated :-)

Posts

  • WilderbeastWilderbeast Posts: 1,415
    @ghutton14 where does the water drain too ? clearly you need to have free flow at the outflow end, how deep is the drain ? . I'd have put stone/rubble over the drain as this allows water to drain very quickly (I come from a farming family and spent many unhappy hours digging up drains so well experienced) and gives more room for water to build up while draining away. Even if you have an amazing set up water can only drain at a certain rate, the pipe work really needs to be the proper perforated stuff as these have holes over the entire surface area and speeds up drainage. However if you have lots of rain you will have a period where water will sit while it can soak away 
  • ghutton14ghutton14 Posts: 4
    @Wilderbeast The land drain connects into a gutter down-pipe. There's a rodding point for it from which I can hear water running when I've tested the drain with a hose. The gravel over the drain is around 30-40mm so I imagine that would allow the water to drain pretty quick. I know what you mean about using perforated pipe. I cut 4 slots in every single section of the solid pipework (took so long I wished I had just bought the perforated stuff!) so think it should be okay. Is there anything else you think I could do with regards the turf and sand/soil base that would help drain the water through to the gravel?
  • nick615nick615 Posts: 1,487
    'Proper' land drains, usually black, are slit very inch or so at intervals all round the circumference, thus allowing speedy draining from farmland.  You don't specify 'section' in terms of length but four slots per whatever it is doesn't seem enough.  I think @wilderbeast may also say that larger aggregate infill works better than gravel which clogs up more quickly.  Let's see what he says but I think I'd have had the original installer back.
  • ghutton14ghutton14 Posts: 4
    edited July 2020
    Thanks @nick615. I've attached a photo below showing the pipe with the new perforations cut in. I'd say they are every inch or so. When the drain was covered with the gravel I ran a hose on it for 1 hr (full on, high water pressure) and at no point did it back up. This makes me think that it is the percolation from the turf to the land drain that is the issue. The original installer is the housebuilder who isn't interested as it's past the 2 year warranty that we got with the house. NHBC aren't interested in helping either hence why I've taken it on.

      
  • LoxleyLoxley Posts: 5,698
    If the standing water disappears within an hour after it rains heavily, it should be okay. I have free draining soil but it has struggled to absorb some of the unusually heavy downpours we've been having. 

    You're right that the issue is probably with the water passing too slowly to the land drains via the soil and turf. The cure is closer intervals between the trenches, or additional slit drains which connect to them, or a layer of coarse sharp sand underneath the whole lawn, which connects to the land drains. 
    "What is hateful to you, do not do to your neighbour". 
  • nick615nick615 Posts: 1,487

    @ghutton14 That's the black 'proper' stuff I see the local farmers using, so my thoughts are basically pure observation but somewhere I got the advice that soakaways, not quite the same thing but similar principle, are best filled with big stones.  When I did a couple, I cadged a trailer load of rough quarry material, some as big as I could lift, and filled the trench with them.  I covered them with old coal sacks and a thin layer of soil.  No (apparent) problems since so I assume the smaller the gaps between stones, the more likely they are to stop a piece of detritus and get blocked - but rely on the experts (which I ain't!)
  • cc87cc87 Posts: 17
    Hi,
    Do you have the holes/slits pointing up or down?
    Best practice is for them to be at the bottom of the pipe, water will flow down through the trench and enter the pipe as it rises up to the level of the holes rather than flowing down through the trench and in to the top where slits are there. 
  • ghutton14ghutton14 Posts: 4
    edited July 2020
    @cc87 The slits are all the way around. After reading up on this (way too much :-)) I understand that if the perforations are only one 1 side that it's best if they point down as you say.
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