Need Drainage Help!

jockewing(9a)April 8, 2014

I live in Southeast Louisiana where we get about 60 inches of rain a year, the terrain is very flat, and the soil is heavy and has a lot of clay.

I live in a neighborhood on a relatively small lot. I think it is about 50 x 120. There is a large drainage ditch that runs on either side of the street in the front yard. The house was built up on sandy fill so there is a slight slope from the house to the ditch in the front. The front yard is fine. There was a slight dip between my house and the neighbors that caused pooling. A couple years ago I dug a trench and put in an underground plastic pipe with 2 drains about 10 feet apart that runs out to the ditch. This works great (when the drain isn't clogged by debris) and will drain the area within minutes). Otherwise the front yard is not a problem and stays dry.

The issue is the backyard. It is lower than the front, and water gets trapped back there because it can't clear the raised area where the house is to get to the front yard and ultimately to the ditch. This seems to be a problem with the neighbors as well. I know the people on either side of me have the same issue. What I would like to do is to tie into the drain I built in the front yard so that I can get the water out of the back yard into the ditch along the street as well.

Once I get the trench into the back yard, i want to spilt off into 2 lines - 1 to go along the back fence and another to the low spot nearer the house - which are my 2 lowest spots. I will put drains at the terminus of these 2 lines. My main question is whether or not to go with a french drain with perforated pipe or to go with solid pipe?

In the last 2 weeks we have gotten 2 downpours of probably 3 or more inches on each occassion that flooded streets in town. The ground has not really dried out from the winter yet. I dug a couple of holes and noticed they filled up with water. I removed the water 3 times and they still filled up. I don't know if the closed drain would do anything to help with that subsurface water and might only address the standing water on the surface. I would like to dry out the whole backyard and wonder if the perforated french drain would better accomplish that goal?

What things do I need to consider when deciding whether to go with closed or perforated piping?

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The primary purpose of the pipe is to drain low areas of the back yard. With perforated pipe, you stand a good chance of developing root infiltration if there are any woody plants along the pipe's path (which could include trees many feet away.) To prevent this, it is better to use solid PVC that has glued joints.

The pipe is not going to dry out the soil of the yard. Nothing but a change of soil and regrading will do that.

    Bookmark   April 8, 2014 at 12:22PM
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Thanks Yardvark,

I understand your reasoning, but why do so many people use French drains if they will all eventually fail due to root intrusion?

And I guess clearing off the standing water will help--that is where all the subsurface water is coming from ultimately after all. If it isn't sitting there for days to begin with it wont sink into the groud so much. I have lived in this house for over 10 years and never noticed holes filling with water like this before so it is probably due to the soaking rains we recently got.

Is there any situation where the perforated pipes are truly called for?

    Bookmark   April 8, 2014 at 2:05PM
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"... but why do so many people use French drains if they will all eventually fail ..." Because it's easier or cheaper. Sometimes, people do things thinking that they will be there only a certain amount of time and then it will be the next owner's problem. Or often, they don't know that it won't last.

There seem to be differences here (on this forum) on the definition of "french drain." I think of it as a "dead end" drain with no outfall; water seeps into the ground as if the pipe were an underground detention pond. Sometimes, it's a rock-filled hole in the ground. This type of system is limited to the cavity created by the empty pipe (or rock-filled hole.) Once it's filled to capacity, if water continues to come, it begins backing up and can no longer enter the pipe. Relief only comes proportionate to how fast the water can seep into the ground.

A regular drain has a place downstream (such as the ditch near your street) to where the draining water is piped. As long as water can come out of the pipe at the bottom, it can continue to enter upstream (in your back yard.) If this is the case, there is no advantage to having perforations in the pipe along the way. These are places where roots can grow in and eventually clog it. Without perforations, the water will continue to run through the pipe until it all comes out the bottom.

    Bookmark   April 8, 2014 at 7:28PM
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OK Yaardvark, so it seems like you are saying that when there is an actual good place to direct the water, a closed pipe is preferable. A 'true' french drain is only used where the goal is slow percolation into the surrounding subsoil--is that correct?

I was under the impression that a perforated pipe would not only allow for the water to pass through the drain at the terminus grates to the ditch at the end, I also thought it would allow subsurface water to seep from the surrounding soil and allow it to travel through the pipe to the ditch as well. I was watching a youtube video where a company installed a french drain and they said the homeowner said the french drain was dripping water at the end point for almost 2 weeks from all the hydrostatic pressure of the subsurface water in the soil filling up the french drain from the surrounding soil and draining at the end. I thought maybe if I did that type of drain it might work the same way in my yard.

    Bookmark   April 8, 2014 at 11:23PM
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If you were collecting water at the underground base of a wall, to drain it, You would install a perforated pipe that was enclosed in a filter. The pipe itself would be placed in another more coarse filter, gravel. The gravel also allows water to move within it so as to find a path into the pipe perforations. The purpose of such a pipe is to COLLECT water. All the filtering is so that the pipe doesn't get clogged and stop working. After all, how would you clean the inlets of a buried pipe? It couldn't be done.

Yet in the situation you describe -- collecting water from surface ponding areas -- the goal is not to collect filtered water from underground, but to MOVE surface water as quickly as possible out of the area. If you move the surface water away before it ponds, it's not likely that your back yard will be any more soggy than the front yard after a rain since both surfaces are wet for the same amount of time. It's not practical to use filtered, perforated water-collecting pipe in gravel-filled trenches to drain a yard. Surface grading is the preferred method and where impondment occurs and can't be graded away, catch basins and solid pipe are what to use. (It is better to use smooth pipe over corrugated, even though corrugated is cheaper and easier. The latter tends to collect more silt.)

    Bookmark   April 9, 2014 at 2:41AM
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OK thanks Yardvark. Makes sense. It will be much much cheaper to install a closed pipe system since I won't have to worry about all the gravel and filtering landscape fabric either. And what you say makes sense--if I remove the surface water it wont have a chance to drain into and saturate the soil like it is doing now.

    Bookmark   April 9, 2014 at 9:22AM
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I try to do that occasionally ... make sense. :-)

    Bookmark   April 9, 2014 at 11:01AM
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