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March 7, 2012 3:16 PM Subscribe
Green thumbs: What type of ground cover provides the best protection against water incursion into a basement?
My basement is surrounded, for the most part, by thickly grassed ground on a gentle grade. However, an area of about 10 square feet is both flat and bare, and once or twice a year, during violent rainstorms, rain water enters the part of the basement directly below this spot. The incursion of water happens only during extremely heavy rainfall, and takes place within minutes, so it's not a ground water issue. Covering the bare ground with tarps has eliminated the problem temporarily, but I'd like to regrade the area and plant it with ground cover. (The bare area is already beneath substantial guttering.)
I'm assuming that the grass in the graded areas keeps the water from seeping downward, either because the roots absorb it or capture it before it can continue its downward trek. Dumb question, but is this really the case? If the answer's "yes," what type of ground cover affords the best protection against water continuing downward to the level of my basement floor, eight feet below the surface?
I'm willing to plant any type of grass, sod, or bush in this area--aesthetics aren't a question--but the catch is, it gets zero sunlight, so the plants have to thrive in the shade.
My basement is surrounded, for the most part, by thickly grassed ground on a gentle grade. However, an area of about 10 square feet is both flat and bare, and once or twice a year, during violent rainstorms, rain water enters the part of the basement directly below this spot. The incursion of water happens only during extremely heavy rainfall, and takes place within minutes, so it's not a ground water issue. Covering the bare ground with tarps has eliminated the problem temporarily, but I'd like to regrade the area and plant it with ground cover. (The bare area is already beneath substantial guttering.)
I'm assuming that the grass in the graded areas keeps the water from seeping downward, either because the roots absorb it or capture it before it can continue its downward trek. Dumb question, but is this really the case? If the answer's "yes," what type of ground cover affords the best protection against water continuing downward to the level of my basement floor, eight feet below the surface?
I'm willing to plant any type of grass, sod, or bush in this area--aesthetics aren't a question--but the catch is, it gets zero sunlight, so the plants have to thrive in the shade.
It's the grading, not the ground cover. I say regrade and tamp down the soil.
posted by bonobothegreat at 3:30 PM on March 7, 2012
posted by bonobothegreat at 3:30 PM on March 7, 2012
tamp down the soil
Depending on your soil type, this may actually compound your problem, as this will compact the soil and decrease the amount of pore spaces available for water to enter, which will decrease the moisture holding capacity of the soil and increase runoff into your basement. Either way, tamping the soil down would generally just increase the drainage gradient into that spot and encourage more water to pool up there.
Your soil type has a huge influence here - are you on a sandier soil or a soil with more clay in it? If you have sandy or stony soil, think about incorporating some organic matter and clay into the soil before you replant it. This will help hold water in the soil column instead of draining it straight through, improving its water holding capacity, and the humus and clay will help hold your aggregates together so that the infiltration paths don't instantly clog up in a big rainfall event. If it's already pretty clayey, my only guess would be that there might be a semi-restrictive clay layer under other parts of the lawn but somehow not under your 10' square, which (depending on the grade) could drain much of the runoff into that one spot. Maybe somebody punched through the clay layer there to install an old septic tank or plumbing line or shed foundation or something - I have no idea. Does water ever pool up in that spot otherwise? Does water pool anywhere else on your property, or are there any wetlands (seasonal or otherwise) near your neighborhood?
I'm assuming that the grass in the graded areas keeps the water from seeping downward, either because the roots absorb it or capture it before it can continue its downward trek
I don't think this is really true, although the grass improves the soil porosity, incorporates organic matter, and keeps the soil from being eroded by rainfall. Grass can't use water anywhere near that quickly in a big rain event, and I don't think many other garden-variety plants can either. However, planting some ground cover will definitely help to dilate the soil and protect those important stabilizing aggregates from being destroyed by raindrops, and that will probably improve your infiltration somewhat. It would be a good step, but it won't solve the problem.
I would also try to investigate why nothing is growing on those ten square feet of soil, if it isn't immediately obvious - if the grass isn't trying to invade that area at all, and you don't have a bumper crop of weeds there every year, you might have other things affecting the soil there that also contribute to the drainage problem.
Bottom line, though, it really sounds like you have an engineering problem more than a soil or vegetation problem, and fixing the grade and resealing your basement will probably yield much better results than trying to find a ground cover that can maximize evapotranspiration in the shade. Depending on the drainage class of your soil (which you can find from a soil survey map), you may need some sort of drainage system installed (in the worst-case scenario). You can do some of the stuff I suggested to improve the soil, and it might help somewhat, but I really wouldn't count on that solving the problem. Anyway, best of luck!
posted by dialetheia at 4:41 PM on March 7, 2012 [3 favorites]
Depending on your soil type, this may actually compound your problem, as this will compact the soil and decrease the amount of pore spaces available for water to enter, which will decrease the moisture holding capacity of the soil and increase runoff into your basement. Either way, tamping the soil down would generally just increase the drainage gradient into that spot and encourage more water to pool up there.
Your soil type has a huge influence here - are you on a sandier soil or a soil with more clay in it? If you have sandy or stony soil, think about incorporating some organic matter and clay into the soil before you replant it. This will help hold water in the soil column instead of draining it straight through, improving its water holding capacity, and the humus and clay will help hold your aggregates together so that the infiltration paths don't instantly clog up in a big rainfall event. If it's already pretty clayey, my only guess would be that there might be a semi-restrictive clay layer under other parts of the lawn but somehow not under your 10' square, which (depending on the grade) could drain much of the runoff into that one spot. Maybe somebody punched through the clay layer there to install an old septic tank or plumbing line or shed foundation or something - I have no idea. Does water ever pool up in that spot otherwise? Does water pool anywhere else on your property, or are there any wetlands (seasonal or otherwise) near your neighborhood?
I'm assuming that the grass in the graded areas keeps the water from seeping downward, either because the roots absorb it or capture it before it can continue its downward trek
I don't think this is really true, although the grass improves the soil porosity, incorporates organic matter, and keeps the soil from being eroded by rainfall. Grass can't use water anywhere near that quickly in a big rain event, and I don't think many other garden-variety plants can either. However, planting some ground cover will definitely help to dilate the soil and protect those important stabilizing aggregates from being destroyed by raindrops, and that will probably improve your infiltration somewhat. It would be a good step, but it won't solve the problem.
I would also try to investigate why nothing is growing on those ten square feet of soil, if it isn't immediately obvious - if the grass isn't trying to invade that area at all, and you don't have a bumper crop of weeds there every year, you might have other things affecting the soil there that also contribute to the drainage problem.
Bottom line, though, it really sounds like you have an engineering problem more than a soil or vegetation problem, and fixing the grade and resealing your basement will probably yield much better results than trying to find a ground cover that can maximize evapotranspiration in the shade. Depending on the drainage class of your soil (which you can find from a soil survey map), you may need some sort of drainage system installed (in the worst-case scenario). You can do some of the stuff I suggested to improve the soil, and it might help somewhat, but I really wouldn't count on that solving the problem. Anyway, best of luck!
posted by dialetheia at 4:41 PM on March 7, 2012 [3 favorites]
Without seeing your home, it's very hard to say, but some reasons I've seen houses have what you're describing...
Your drain tile at the basement footer cannot keep up with the rainfall, probably because you have a sump pump that needs to pump the collected water up to street/drainage level. If it's happening within minutes, as you say, it may be because that drain tile around your footer is also collecting water from your gutters (I think it's a bad idea, for just this reason, but I've seen it done many times...then when the power goes out and the sump pump doesn't work, you really have problems).
Or your drain tile around the footer is broken, and the reason your ground is flat above is because it sank 6 inches when it collapsed into your drain tile. You could also have roots from a nearby tree that have grown into it and blocked/collapsed it.
The ground being flat itself should be built up and tapered away and planted with grass (to prevent soil erosion, not because I think it will stop the water from getting to your basement). While I agree that the soil type matters, unless the ground is already totally saturated, I don't see how water should make it into the basement 'in minutes' just by running down through the soil.
If it were my house, I'd take a closer look at the drain tile situation, and see if you can use a larger sump pump, and/or divert some of your gutter downspouts if possible (if they're contributing to the sump pumps work load). Good luck.
posted by jhs at 5:50 PM on March 7, 2012
Your drain tile at the basement footer cannot keep up with the rainfall, probably because you have a sump pump that needs to pump the collected water up to street/drainage level. If it's happening within minutes, as you say, it may be because that drain tile around your footer is also collecting water from your gutters (I think it's a bad idea, for just this reason, but I've seen it done many times...then when the power goes out and the sump pump doesn't work, you really have problems).
Or your drain tile around the footer is broken, and the reason your ground is flat above is because it sank 6 inches when it collapsed into your drain tile. You could also have roots from a nearby tree that have grown into it and blocked/collapsed it.
The ground being flat itself should be built up and tapered away and planted with grass (to prevent soil erosion, not because I think it will stop the water from getting to your basement). While I agree that the soil type matters, unless the ground is already totally saturated, I don't see how water should make it into the basement 'in minutes' just by running down through the soil.
If it were my house, I'd take a closer look at the drain tile situation, and see if you can use a larger sump pump, and/or divert some of your gutter downspouts if possible (if they're contributing to the sump pumps work load). Good luck.
posted by jhs at 5:50 PM on March 7, 2012
Once you've regraded, you could plant something but most turfgrass won't do wonderfully if it really gets zero sunlight. What part of the country/world are you in?
posted by BinGregory at 5:54 PM on March 7, 2012
posted by BinGregory at 5:54 PM on March 7, 2012
Plus one on the engineering solution.
While "violent thunderstorms" means different things in different areas, but taking your estimate of 10 square feet times an inch of rainfall is over six gallons of water. No ground cover - or even tree - will take up six gallons of water in the couple of minutes you said it takes for the water to start intruding your basement.
We had a similar problem with similar parameters as yours, with good Ohio clay compounding the problem. A professional waterproofing company dug to the base of the foundation, installed three layers of tar and thick plastic sheeting from the base up to the soil line, and installed a proper french drain that daylights downhill to the street. We were out a couple of grand, but it's dry downstairs and I sleep through thunderstorms now.
Bonus tip: Angie's list is absolutely indicated when it comes to basement waterproofers.
posted by OHSnap at 10:50 PM on March 7, 2012
While "violent thunderstorms" means different things in different areas, but taking your estimate of 10 square feet times an inch of rainfall is over six gallons of water. No ground cover - or even tree - will take up six gallons of water in the couple of minutes you said it takes for the water to start intruding your basement.
We had a similar problem with similar parameters as yours, with good Ohio clay compounding the problem. A professional waterproofing company dug to the base of the foundation, installed three layers of tar and thick plastic sheeting from the base up to the soil line, and installed a proper french drain that daylights downhill to the street. We were out a couple of grand, but it's dry downstairs and I sleep through thunderstorms now.
Bonus tip: Angie's list is absolutely indicated when it comes to basement waterproofers.
posted by OHSnap at 10:50 PM on March 7, 2012
Could plant Dogwood (Cornus) - likes moist/damp/soggy soils and would help water uptake...
posted by RollingGreens at 9:33 AM on March 8, 2012
posted by RollingGreens at 9:33 AM on March 8, 2012
Had a similar problem near the base of a downspout, even though the spout itself was successfully moving water away. Basically, an ivy had been cut back and died off, and the root system rotted out, leaving a sort of dry well right next to the foundation. Filling this empty space with gravel did the trick.
I really feel the speed of the appearance of water points to a similar issue. There's a vertical path from the ground to your basement floor level, somehow, and you need to figure out where it is and mitigate it. This might be easy, as it was for me, or you might simply find that nothing will do except digging out the whole wall and applying various standard techniques, ranging from sealing the wall to installing french drain and/or dry wells.
But no, nothing you plant will make that much of a difference. Water flows; it obeys gravity. Plants sip.
posted by dhartung at 1:19 PM on March 8, 2012
I really feel the speed of the appearance of water points to a similar issue. There's a vertical path from the ground to your basement floor level, somehow, and you need to figure out where it is and mitigate it. This might be easy, as it was for me, or you might simply find that nothing will do except digging out the whole wall and applying various standard techniques, ranging from sealing the wall to installing french drain and/or dry wells.
But no, nothing you plant will make that much of a difference. Water flows; it obeys gravity. Plants sip.
posted by dhartung at 1:19 PM on March 8, 2012
Yup, again: you're trying to shore up the dam by changing the plants atop it.
You need a French drain, or a regrade of adjoining soil, or a drainage ditch (which sort-of worked for a farm house I lived at - except for the section of wall facing a NATURAL SPRING!!!).
posted by IAmBroom at 9:36 AM on March 9, 2012
You need a French drain, or a regrade of adjoining soil, or a drainage ditch (which sort-of worked for a farm house I lived at - except for the section of wall facing a NATURAL SPRING!!!).
posted by IAmBroom at 9:36 AM on March 9, 2012
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I would suggest that you need to create something to deal with the massive rain event - something like a french drain along the building, above which you could hide with ground cover.
posted by Big_B at 3:22 PM on March 7, 2012 [1 favorite]