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ripgirl2

Retaining wall drainage

D C
February 12, 2019
last modified: February 12, 2019

I have a 60 foot stone retaining wall in my backyard that was built without any drainage behind it. As a result there is constantly water, sometimes several inches deep, pooled in the grass below making it difficult to get to the wall for plant maintenance. I had a french drain installed in that area but it was apparently a waste of money because the water still just sits in the grass and doesn't drain. What's more there is water that also runs over the wall at the top in a waterfall effect adding to the pond below. Nothing I do stops the runoff and lack of drainage. I had received an estimate to properly re-do the french drain below and install drainage above but then I got laid off so anything will now need to be DIY.

Here is a picture. The area that always has standing water is from the loungers to the end and where the catmints are is where the water flows over the wall.



Here is a shot of what I mean about the water:



Its not this bad any longer since we had drainage boxes installed above the wall about 50 feet back but it's bad enough to warrant further remediation.

Any suggestions that don't include tearing down the wall and starting from scratch would be appreciated!!

Comments (25)

  • mad_gallica

    Drystone walls usually don't have much in the way of drainage behind them since they aren't remotely watertight. And this doesn't look like a drainage problem so much as a grading one. Just like ground should be sloped away from a house, the ground should be sloped away from this wall. Just don't end up pointing it back towards the house.

    D C thanked mad_gallica
  • littlebug zone 5 Missouri

    Water has got to go somewhere. Where do you expect to go, if it can't go down toward your loungers? You'll have to give it another path.

  • PRO
    Yardvaark

    Agreed ... from what can be seen, it looks like probably a grading problem. We can't see grade well from a face-on photo. You might take photos where the camera is lined up with the wall, shooting across the slopes, holding the camera level.

    The stone wall should overlap with the curb (2nd photo).

    D C thanked Yardvaark
  • D C

    littlebug - Well it doesnt make sense to have a retaining wall to redirect water around the area so it becomes usable then the water ends up right where you were told it wouldn't go, does it??

    So we put the french drain in front of the wall to sink the water into the soil (give it another path) rather than pool where the loungers are but it doesn't do that at all. It still just sits on top of the grass for days.

    @Yardvaark - The area above the wall is sloped down towards the wall, which I guess is contributing to the run off but that is why we had 2 drainage boxes installed and they do capture a lot of water from further up the sloped yard. It cannot be regraded at this point; that would mean regrading about a quarter of an acre. The entire back yard is about .75 acre sloped toward the house. Behind the planted bed is a trench which carries water down to the end of the wall but in heavy rains the trench fills up faster that it can flow and that is when the water runs through the plants to the soil below an just sits and does not go into french drain.. What can I do to stop that happening? Add more plants above?


    What do you mean by the stone wall should overlap with the curb?

  • engrgirl
    Simply putting in a drainage box or a drainage tube does not mean the yard in that area will drain. Similar to the shower drain in your home, the box/perforate tube will give you a method to collect the water, but from there you have to move it. In a hoouse shower drain this means pipes that slope down into a sewer/septic system that is at a lower elevation than your shower floor. In your yard hopefully you have some place lower at the side or front of your yard that you can extend (with a contiuous slight downward slope) the landscape drainage pipes towards.
    D C thanked engrgirl
  • engrgirl
    Also wanted to add: I agrees with what others have said that boulder/stone walls typically don’t have drainage behind them since water will not get trapped back there weep out the face between the nooks ans crannies. Also- regrading would be another way to deal with this: if the top surface (or underlying clay shelf if you have mixed soils) is sloped to drain away from the area the water shouldn’t be able to pool there to the point thay you see surface water.
  • PRO
    Flo Mangan
    Can you add a swale that splits and directs water sideways and away from house? Can you create a pond where water pools up? Sometimes you have to embrace nature. Maybe a combination of both.
    D C thanked Flo Mangan
  • PRO
    Yardvaark

    "What do you mean by the stone wall should overlap with the curb?" In your second picture, a curb ends and a stone "wall" begins. Between the two is a gap. The stones should have run past the curb/behind the curb a little in order to eliminate the gap.

    We can't see the grade because you are photographing in line with it instead of across it with the camera held level. So it's hard to be specific about what/where you should make a change.

    Saying that the problem is grading is not the same as saying you need to "regrade the yard." You may need to add or remove a little soil here or there in order to eliminate the problem. But we can't be specific because the photos don't SHOW grade. We are merely told about it. Do you have what looks like a low spot at the base of the wall where water collects?

    D C thanked Yardvaark
  • D C

    I should have stated in the original post that none of this water poses a threat to the house. We have spent a small fortune to ensure that. Anything remaining to be done is just to move minor standing water/runoff that makes this part of the yard wet and unusable at times.

    There is no curb here. This is the backyard. Yes, the area below the wall is where water collects, but it does not appear to be any lower that the surrounding area. Directly underneath this area in the french drain that does not work. In addition, there is a drainage trench under the deck (not in picture) that collects water from the deck and adjacent patio, with an underground trench filled with stone that empties into a seepage pit. We seems to have all the necessary drainage items but are still left with standing water and soggy soil.

    We do have pipes that go the length of the backyard downhill to the front yard on both sides of the yard. They drain into an infiltration bed in the front yard with an overflow to the street. This system definitely works to move the water that is directed to it because I can see evidence of overflow at the opening of the pipe. The french drain at the bottom of the wall was connected to this system and also runs down slope, but maybe not enough?

    We had considered a swale well above the wall to catch additional water from uphill and direct to the drainage boxes but since it would have to be diy now it will be quite a while to finish the 110 feet needed.

    I have also considered just making the spot below the wall a sort of vernal pond, although in the recent year's weather it would be an all season pond. But creating anything there in the grass other than grass would make getting a mower in this area difficult.

  • PRO
    Flo Mangan
    Remove grass and create a “pond” with a dry river bed rock base when dry and drained. Make it big enough to provide enough surface for rapid evaporation. Good luck.
    D C thanked Flo Mangan
  • PRO
    Yardvaark

    "There is no curb here. This is the backyard." A curb can occur anywhere there is a one-step elevation change that is protected by a hard edge. It could be made of stone, concrete, brick or even wood (though wood not often.) In your second photograph it looks like a curb at the right side meeting a stone wall at the left side. Another look says maybe what looks like a curb is a stone. It's a mystery. That's the danger of landscape photos that are taken from too close-up.

    "... the area below the wall is where water collects, but it does not appear to be any lower ..." But is it? Did you take a level out there and check it? Since you're not going to show photos across this grade, we're helpless to give input.

    Per the general description of some of the drainage structures in the back yard, it sounds like some overkill of things that don't matter. Description of the problems sound like neglect of things that do matter. Yet we don't have the information to do any more than guess.


  • Dalton the Bengal (Zone 6)

    Experts - Shouldn't the retaining wall be 2 ft higher (guessing from photo) and the garden behind it be graded so the wall is slightly higher than the garden? ? Thoughts?

  • Christopher C Nc

    No. It is completely normal for there to be a slope above the top of retaining walls of all kinds. That is the point of most of them, dealing with the slope above.

    D C thanked Christopher C Nc
  • Dalton the Bengal (Zone 6)

    Thanks CC Nc, I guess that is often the case. When we had a retaining wall redone part of the goal was to redirect stormwater from above so a sort of flat tier was created with a subtle swale at 5 ft out. It has solved the problem. Could this be done here?

    April

    D C thanked Dalton the Bengal (Zone 6)
  • D C

    Unfortunately I cannot take further photos at his time because of the sogginess in the soil. I don't want to walk around out there creating more issues. It literally has not stopped snowing/raining here since Nov-2017. Which of course has worsened the problem. If you click on the second photo you will see a larger shot, it only loaded close up, don't know why.

    I don' think we can flatten the area above since there is a second smaller wall there at this time, 25 feet out . A swale would work, but not 5 feet out because there would be nowhere to direct the water at that point; it would be blocked by a HUGE berm in my neighbors yard that surrounds their entire backyard patio area, which you can see in the first photo above where the spruce tree and rhodos are. That is why I planned a swale about 50 feet out and about 110 feet long. That swale would direct the water to the 2 drainage boxes that are not definitely not overkill. Everything we have done has helped keep water away from the foundation. Now I want to be able to use the yard.

    Was thinking about a large native planting bed about 25-35 feet out (so in front of swale) that would be planted with deep rooted plants, something like this only not built up so high, behind our second smaller wall:



    Would that help at all? I have to think that it would be better at controlling water flow than mere turf grass which is useless. I also thought about extending the bed behind the original wall but a few feet and planting that with some kind of native grass that would eventually grow in much thicker than turf grass forming a sort of mat, like fox sedge or prairie dropseed. I don't think that would completely stop the water flowing through the catmints but might help some.

  • D C

    Here are photos of the second wall and the drainage area to which I referred.

    Wall 2:


    Drainage area covered with stones to left of wall. Swale would end above this and go behind the birch tree in the photo above. A lot of our water run off(but not all) comes out of the woods in the distance and would be caught by swale and\or planting bed:



  • mad_gallica

    Pretend you are a drop of water. You can only move downhill. How do you get off the property? Currently, you flow down from the woods over the lawn, move towards the end of the wall, fall over the wall, and then stop in a low point behind the chaises. A swale behind the wall will move you away from the wall, but towards where? The goal is to end up in the Chesapeake, or Lake Michigan, or the Mississippi River or wherever your watershed goes. How does a drop of water do that?

    Since that is the goal, planting different plants doesn't help. You have to change where the low points are, so the lowest point is somewhere else, like the Atlantic Ocean.

    D C thanked mad_gallica
  • Dalton the Bengal (Zone 6)

    In the photo that shows the 2nd wall being built, it looks like there is a pre-existing drainage swale coming down from the wooded area above, to the left of the backhoe. Or is that a shadow? What's up there? Are the drainage pipes (french drain?) on the left side of the wall? Things to think about - Are the handsome new walls keeping the stormwater in rather than helping escort it on its way? If that is a swale from the woods, can it be tweaked towards the left of the photo? Is the problem water coming from the berm to the left? Can a gentle swale be installed behind your plantings? it might be only a small change needed. Watch it. USe some special leak tracing dye to see how the water runs. You will find the answer.

    D C thanked Dalton the Bengal (Zone 6)
  • D C

    No there are no swales on my property at the moment. There are only pipes where you can see the stone trench to the left of the new wall. I think I mentioned that they go to an infiltration bed in the front yard with an overflow to the drainage ditch that runs the length of the street. My intention is to put a swale up there, behind the second wall, directing water into that stone area where the drainage boxes with pipes are.

    I think both walls do the job of keeping most of the water at bay BUT trapping some where I'd rather there wasn't standing water. That is why I want a swale above the second wall and I already had a pipe installed in front of the old wall. But the water doesn't infiltrate into the pipe, unfortunately. Now I am left with the task of digging that up to see what the issue is and correct it.

    Great idea about leak tracing dye; I didn't know such a thing existed!

    I have to disagree, to a point, about plants not helping. It is becoming increasingly evident that part of a sustainable storm water management plan includes not only swales, drainage pipes/basins and proper grading but also densely native-planted areas that can drastically decrease water flow and increase soil infiltration rates. Plus they have the added bonus of being attractive to look at and helping pollinators. And with less lawn that means less mowing, too.

  • Christopher C Nc

    Very good point that a native wetland planting can be a big help. How close might you be to a larger body of water? You have a lot of water diversion all ready happening. It has been wet that is for sure.

    D C thanked Christopher C Nc
  • mad_gallica

    I have a swamp. I believe the last time it dried out was in the 1960's. It is 'densely planted with native plants' because, well, that's what is down there. The water does not infiltrate because it is past the ability of the soil to absorb more water. That is what is your real problem. You've gone past the soil's ability to absorb more water, so it sits on top. Turf grass is not a terrible plant when it comes to the ability of the soil to absorb water, so replacing it with something else isn't going to cause a drastic increase in the amount of water that is absorbed. If you want to plant a garden because you want a garden, fine. However, simply replacing the grass with different plants isn't going to solve this.

    D C thanked mad_gallica
  • D C

    It has been that wet, as I said, since Nov-2017. The difference for my area is that it isn't a swamp. In normal climate conditions my yard does dry out, usually by early to late May depending on Spring conditions. I do not live that close to a larger body of water. There is a major creek that our street drainage dumps into via smaller waterways but the creek is probably a 1/4 away at its closest.

    Turf grass is fine for flatter yards but not a sloped yard; most lawn grass does not have the height or root/blade structure to hold/slow water. Grassses like dropseed, sedges or juncus actually sink water into the soil and prevent runoff, maybe not all but much more than a normal lawn. Deep rooted prairie type plants actually improve the soil structure so that, over time, the issue lessens. And yes, I would like something more attractive at the same time that will work in conjunction with the structures already in place and planned. In a drier year the native planted area will provide enjoyment beyond the purely practical swales, pipes, drainage boxes and infiltration beds. Actually, moving the proposed swale a little closer to the second wall means that is could be inorporated as a bioswale, instead of just a regular swale, into the plantings I would like behind that wall.


    I'm starting to feel like a spokesperson for why Green Infrastructure works!

  • Christopher C Nc

    Water flow and wet ground can be one of the most difficult problems to solve since water has a mind of its own and can flow in places we can't see below ground. I'm seeing water in places now that have never been wet before. And more rain is coming.


    I'm not a big fan of French drains because they are so quick to get clogged by plant roots and debris and water being water it can just as easily leave a perforated pipe as it can enter it.


    Since you are contemplating digging up the French drain in your lowest lawn pond, is it possible to switch to a catchment basin and solid pipe for its path to the infiltration bed?

    D C thanked Christopher C Nc
  • D C

    True, I wish I knew about french drains in 2017 what I know now because I wouldn't have wasted my money. Not only that but most landscape contractors touting their "drainage" prowess really appear to know absolutely nothing about it. The pipe was installed absolutely wrong based on my extensive research. Check out: https://frenchdrainman.com/

    I have thought about just a catchment basin filled with drainage stone ending in the pipe going down the side of the property to the infiltration bed, yes. That will probably be the solution although the stone will be have to be covered by vegetation in order to make mowing the adjacent areas easy. In fact, The French Drain Man, despite being based in a completely different state, actually emailed me that stone actually moves more water than a pipe and to just fill the trench with more stone. I will need a pipe at the end though to connect to the existing drainage pipe.

    I am soooo over all of this wet weather. If I wanted to live in a rain forest I would move!!

  • PRO
    Flo Mangan
    Sounds like you have a plan. I thought your description of the “French Drain” sounded odd but glad you may have the best solution.
    D C thanked Flo Mangan

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