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I have a depression on the side of my lawn where rain and sprinkler water collects. There used to be a plastic lined pond and a lot of rock (for the last 5-8 years) that I suspect blocked the water from draining properly on that side. I'm going to replace that pond with a decomposed granite (DG) patio with a concrete curb separating it from the lawn. Once I compress the patio, I worried that it will cause the same blockage, or it will affect the patio in some way. So my plan is to install a drain under the new patio, with the inlet and dry well under the depression. The only problem is that the depression is almost as low as the side of my yard where the water needs to go.

I think my options are:

  1. build the depression up a little bit so there's a slope
  2. dig the side of the yard down a bit and fill with rocks so it can percolate up or
  3. drain to the other side of the lawn (70 ft) where it appears to be lower.

And are my assumptions about the patio blocking the drainage or being damaged by it correct?

the string represents the proposed drain pipe

The string represents the proposed drain pipe (there's no existing drains or they're hidden very well and clogged). When it is taut, there is no slope.

Clarification: A level DG patio will take up the majority of the dirt area in the photo. That used to be a pond. The orange paint is the path of a proposed concrete curb.

Wider (older) shot of back yardenter image description here

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@webXL, "The string represents the drain pipe", is that an existing drainage pipe or proposed line of a new one? –  Mike Perry Jul 27 '11 at 18:22
    
It's the proposed line. Thanks. –  webXL Jul 27 '11 at 18:51
    
@webXL, is the proposed drainage line going to run underneath the new patio? If yes, why? & please forgive me if you've already said why in your question (currently I don't fully understand what you're doing ie How the finished project will look, fit into, your landscape). –  Mike Perry Jul 27 '11 at 19:25
    
@Mike Yes, under the patio. That's where the water should go. I don't know of a better way to get the water out of the depression. The patio is going to take up the majority of the dirt area in the photo. That used to be a pond. –  webXL Jul 27 '11 at 19:45
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Note: Although the site is technically "Gardening & Landscaping", we haven't really had any questions on the landscaping part of it. This question has been requested from DIY as a test case to gauge community interest in such questions. –  Lorem Ipsum Jul 27 '11 at 20:33
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migrated from diy.stackexchange.com Jul 27 '11 at 20:30

This question came from our site for contractors and serious DIYers.

1 Answer

Taking into account (nearly) all the comments from below the question, I personally would do the following before putting in some substantial drainage system to help drain what happens to be a relatively small area in your lawn:

  • Carefully take up the lawn in the "puddling" (low) area and put it to one-side (stack it properly for reuse). Make sure you remove approximately 2inches (50mm) of soil with the grass.

  • Dig out the soil in that area to a minimum depth of 12inches (300mm), maximum depth of 24inches (600mm).

  • If you don't encounter, see any problems, I would:

    • Back fill the hole with the same material that was excavated from that hole. Back fill in 4inch (100mm) thick layers and "lightly" tamp down each layer.

    • Bring in enough 50-50 mix of "good" quality screened top soil & "good" quality screened compost to level the excavated area into the surrounding lawn area. Finished level should be approximately 1inch (25mm) below new finished lawn level.

    • Lay back the properly stacked lawn (sod), it should be sitting approximately 1inch (25mm) higher than required new finished lawn level.

    • Lay a scaffold-board over the top of the reinstalled lawn (sod). Shuffle along the board a few times, this will ensure you get good contact between the lawn (sod) and the soil underneath. Move the board over the width of the board, repeat "shuffle" process. Repeat, repeat... until you've tamped down the complete reinstalled lawn (sod) area.

    • Water the reinstalled lawn area so it's moist. Repeat this watering daily for a week or so. After that, if there is no rain, water entire lawn as you would normally.

  • If you do encounter, see any problems, I would:

  • Evaluate exactly what it is that you encounter/see, then form a plan of attack based on that.


If you really want to go with some kind of drainage system to take care of the relatively small "puddling" area in your lawn, I would tackle it something like the below.

The following is based on:

  • Limited knowledge of your landscape, based on a couple of photos.
  • Comments from below the question.
  • Comments from below this answer.
  • Your installing a new decomposed granite (DG) patio (slightly lower than the existing concrete patio) with a new concrete edge curb which lines in with the top of the existing concrete patio.

Install a French Drain on the lawn side (ie Not under the new DG patio) that follows the line of the new concrete edge curb.

Q. Why? Just in case the new hard-scape causes water to start puddling where it meets the lawn.

Install a French Drain that "T's" into the above French Drain at the "puddling" area, and run this drain into the middle of your lawn (discharge point).

Q. Why? Unless there is a better discharge point, somewhere that isn't visible on the 2 photos you've posted above, I would keep the excess water within your landscape and use it to water the lawn at a deep level from below.

The discharge point will be in the form of a underground Dry Well (or what we call a Soakaway in the UK). The minimum size of this underground water storage zone needs to be based on at least the amount of water you receive in your area from a really! good days rain fall and the amount of "puddling" water you want to remove from your lawn.

French Drains should be installed a minimum of 18inches (450mm) below the surface to be most effective.

If you decide to backfill the French Drain trenches with crushed stone (best option, but adds additional cost), you will want to put a minimum 6inch (150mm) thick layer of high quality screened top soil on top, so that your lawn has something suitable to sit on (grow into). Anything less than that and your lawn in those area will suffer badly.


Good luck, and please post back here once you decide which way your going to tackle this "puddling" problem, so that we can learn from your experience."

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What sort of problems am I looking for? The problem is that I have the curbing being installed this weekend, and I was going to start on the patio next weekend. We're under a bit of a time crunch. If I need to install a drain pipe, this is the weekend to do it. I suppose I can do what you suggest and just lay a closed drainage pipe under the patio, as long as it slopes properly and the top of it is beneath the lawn. I was thinking of a 4-6" drain tucked a bit under the curb since the curb will but up against that lowest point. The curb should be removable since it will be in sections. –  webXL Jul 29 '11 at 15:57
    
@webXL, "What sort of problems am I looking for?" Example: Foreign objects/materials/etc (maybe leftover "stuff" from when the pond was installed back in the day) that could be preventing water from draining properly. –  Mike Perry Jul 29 '11 at 16:04
    
@webXL, personally I wouldn't run a new drainpipe under a soon to be installed patio area, unless there really was no other option eg New drainpipe couldn't be run in another direction, or the "problem" area ccouldn't be rectified via some other method... –  Mike Perry Jul 29 '11 at 16:22
    
what about a french drain at that spot? aaronsinspections.com/Drainage%20Improvement%20Primer.pdf " Standing water in low spots of yard -> Surface drains.... Standing water in contoured landscape -> Surface drains.... Soggy flat turf areas -> French drains –  webXL Jul 29 '11 at 21:25
    
I'd say the only time I have standing water is a few times a year. The sprinklers make that area soggy. –  webXL Jul 29 '11 at 21:29
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