My French Drain - What did I do wrong?


Old 03-31-10, 02:52 PM
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My French Drain - What did I do wrong?

Hello all,

As anyone who ever installed a french drain and / or a drywell before knows, it is alot of hard work. After recently finishing the french drain portion of my project, I was "excited" for rain (and we got plenty in Penna!)

Unfortunately, my french drain did not work as expected. I was careful follow all of the information I could find: 8' deep trench, lined with water permeable landscape fabric w/ pipe surrounded by 2" of 3/4 inch washed gravel on all sides. The holes on the pipe are positioned towards the bottom and properly sloped.

I overlapped the landscape fabric on top of the gravel (most of the top of the trench therefore has 2 layers of the fabric). I put high-quality topsoil (from bags) on top of the landscape fabric and intend to plant grass.

Here's the problem: after the big rain, very little water entered the french drain (I installed a clean-out downstream so I was able to observe this firsthand). Most surprisingly, there were 1" deep puddles right on top of the soil above the french drain! It seems some combination of the landscape fabric and the soil (currently mud) did not allow the water to enter the french drain.

Do I need to add some type of aggregate to the soil to make it resist turning into mud? Will this no longer be a problem when grass roots help hold the soil together?

I was careful to buy the appropriate landscape fabric - it specifically said it was for drywells and french drains.

Again, the problem was that very little water even entered the french drain system (and even puddled above it!). What did I do wrong and what can I do to fix the situation?

Thanks for any advice, I'm confused!
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Old 03-31-10, 03:36 PM
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Not a pro on this but one thing comes to mind. From what I was told, the fabric comes with different properties. Some allows the water to go one way only others allow it to go both. If you have a piece of the fabric, test it to see if it has an up or down position.

May be crazy, but that is what I was told. The mud on top would also seem to me to be a problem. I would think it would quickly block the fabric. An open gravel bed would certainly work better for surface water, but not sure what you should do to allow water down to the gravel and pipe below.

Old 03-31-10, 04:15 PM
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First, get rid of the two layers of fabric. One is enough.

You should have a minimum of topsoil over the fabric. - Just enough to get germination of to get some sod to take.

French drains have been used for decades on golf courses (you never see them). They did not even use perforated pipe or fabric on the very old istallations that still work well. The filled the trench with a rock and very coarse sand and just used an inch or two of top soil over the granular fill.

Much of the bagged top soil is fluffed up clay and peak mixed with sand. Your could have too much clay or the peak has not absorbed enough water (it takes time) to allow the water to drain around it.

Old 04-02-10, 09:21 PM
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4" corrugated sock pipe with gravel bed under it. I own a water management company.
Old 04-22-10, 01:28 AM
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I read a article about french drains in this sites -

There you can find complete details about the french drains, from the creation to maintenance.

It has been very helpful to me. I hope it may help you too!!!
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