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Do I need a french drain system?  RSS feed

 
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This year, the rainfall is heavy here and my neighbor sits higher than me, so I naturally got a lot of water. There is a shallow 100 feet sort-of-a-swale running along the two properties by grading of the lot, ending in my front yard. It creates a 4-6 feet flooding zone in my backyard, and then distribute all waters to my front yard. However, one part of the "swale", which happens to be the part closest to my house (around 7-10 feet) seems to be a little bit lower, so water stays there for quite a long time, sometimes 24 hours, sometimes 48 hours, sometimes even 3 whole days. Since it is heavy clay here, the soil in the water path (running around 7-12 feet from my house) stays wet sometimes even a week after a heavy rain. What's more is the neighbor catches the community irrigation water and creates "artificial rainfall" to my my yard during the days it does not rain; therefore, my yard has been wet for almost every day.

A naturally remedy pops to my mind is the french drain system, catches the water entering my yard (2 spots only) and pipe them out. However, after reading and reading, it seems that's not how french drain works; it can only catch the excessive runoff water during heavy rains. In light to moderate rain, or in the case of irrigation water, the water will still stay in my yard. The only difference is it used to be on the ground; now it is 2-4 feet underground. Have I missed anything?

My questions are :
1, is the staying water too close to my house to do any damage? I have a slab foundation. The water pond is roughly 5 feet wide x 20 feet long strip, 7-15 feet away from my house, and usually 1 inch water stays after a rain.
2, Will french drain help? My concern is the soil is heavy clay, when the water seeps down to the rocks, it cannot be absorbed by the surrounding soil anyway.
3, If I put better sodding along the water path, especially around the low spot with some new dirt, will that resolve the issue without putting down the french drain?

I hope I have stated clearly about this issue, will upload some pictures later if necessary.

TIA
Chun


 
                    
Posts: 238
Location: AR ~ozark mountain range~zone7a
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I love my french drain I installed across the whole front of my slab foundation building. It is funny but it is located nearly on top of the hill, but because I had made a huge parking lot in front of the building, all the water had to flash flood somewhere! My drain was about 6" deep at one end and nearly 3' deep at the connection to the city storm drain pipe/box. I used 2 lengths run parallel of 4" perforated sewer pipe to quickly remove vast amounts of rainwater. A typical big rain, pushes water thru those pipe and it looks like a twin fire hose when it's at capacity. Originally I placed 'filter paper' over the french drain pipes, as my local friends told me that would keep the sediment from clogging the pipes. But the filter paper quickly clogged with fine driveway run off, and still flooded my building. Once I dug out the paper, the drain worked properly, for 10 yrs now. The pipes are back filled with washed creek gravel, and nothing grows in the french drain except for occasional grasses...I try to keep it clear of vegetation build up. I walk on the gravel sometimes, and it stays loose, some very coarse sands like 1/2" size might firm up the top layer for a walking path, but I wouldn't use dirt, that might clog up and restrict water run off.

james beam
 
Posts: 554
Location: Asheville NC
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As long as you can slope the drain to daylight (further down hill of your slab and problem area) it should work.
 
Chun Zhang
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I just talked to a landscaper and he is kind of against the french drain system. He said the fine clay soil will eventually blocks all the openings between the rocks inside the french drain system, make it nothing more than an underground pipe. Plus tree root can mess up that pipe since the pipe is not solid.

So, he thinks it is better just to lay down a solid pipe with drain boxes.

Is that true? I am a little bit skeptical about this.
 
Brian Knight
Posts: 554
Location: Asheville NC
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Its true Chun. Thats why its important to create a "burrito"; rigid, perforated PVC in the center, surrounded by clean gravel, with the entire thing wrapped in felt fabric which protects the gravel from silt intrusion. Alternatively, the gravel can extend all the way to the surface of the grade to capture surface water. This is going to be more expensive than the method the landscaper recommends but there is a big difference between the two. The burrito will intercept and capture water below the surface(ground water) while the later will only capture surface water(storm drainage). The grates will also clog with debris and need to be cleaned between rain events. You can of course add the grates to the burrito method to get low spots or problem storm areas.

Without much drop in grade, both methods can get clogged with sediment over time. Rigid PVC (lower schedule white stuff) is preferred over the Polyethelene(corrugated black stuff) because sediment or clogs can be snaked out easier.
 
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I am seeing a theme in some of the above posts that may be amenable to a different approach.  The problem I will try to address is wet spots caused by excessive runoff, and a technique that may be very helpful is to consider planting trees that are "heavy water feeders"! But let me start with a strong cautionary note.    Trees that have this reputation can become a problem if one fails to note that generally such trees aggressively seek water, So care must be takento not plant them where they can get into septic drain fields because such trees will have an inclination to find the drain field pipes and invade them with their roots and that is a problem you do not want.    That warning being given! (and better be heeded) It may be necessary to also note that a wet spot beside or under a foundation might also have a similar problem in that invasion of a wet spot extending under a foundation or just too close, might encourage roots of such a tree to invade and then grow and expand to push against the foundation hard enough to disrupt it. So for instance do not plant such a tree close to a foundation or wall.    Uusing such trees will evaporate the water and evaporate such air and reduce or eliminate  the need to move the water across or through the ground.   Such trees are also often fast growing so while it may take time for such trees to grow large enough it may not take all that long for them to become effective.   And I should also point out the obvious, that if a building site should have such trees before construction, that characteristic should be noted and intigrated into planning. 

So what sort of trees am I talking about?  Weeping willow (silax babylonica) comes to mind first.  Naturally found along stream and river banks as well as ponds, its presence along the banks of flowing water attests to its powerful and extensive root system that can stabilize such soil against erosion.   It will grow in non wet soil as well as wet, but as one would expect this is a tree that thrives in wet soil.   KEEP IT AWAY FROM YOUR SEPTIC DRAIN FIELD !!! Other than that, it is a beautiful and graceful tree.   One often encounters concerns about growing it near small ponds as in a drought it still wants water and a small pond may suffer if it has too many of these on the bank. 

Full disclosure:  I only dabble at being a "sort of" arborist and there are many varieties of some trees so do your homework on this approach before planting,  Especially since some variaties can prove to be invasive.   And a variety thiat is well behaved in one place may be invasive in another.
 
gardener
Posts: 2566
Location: Upstate NY, zone 5
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Willow is certainly a heavy feeder, but I would advise black willow (native to the northeast at least, not sure of its whole range) rather than weeping willow which is a Chinese import. Black willow is not graceful in the same way, but can be majestic. It does grow very large, and you might want a shrub-type like pussy willow for restricted areas.
 

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