French Drains

David Beaulieu over at About.com has a new article on Installing French Drains.

His instructions are simple and straight forward. They are the same directions I give to design clients when talking about french drains, with one exception. In step 6, he recommends putting coarse sand with sod on top. Usually, I add a different recommendation. This is a bit old-school, but I find that putting a layer of sod up-side-down, following by sand, followed by a layer of sod right-side-up can be beneficial. It further helps prevent dirt from working it's way into the drain, and thus extends the life of the drain. Also, I often recommend installing direct-line drains that go past the first layer of sod and the sand. This can help because often the water doesn't seep through the top layer fast enough to help.

I should also say, that I usually only recommend French Drains as a last resort. Here's why:

They don't work

On Saturday, I went out on a design consultation to look at a problem yard. One of the problems was bad drainage in the backyard. The client had recently put new sod down in her backyard, and had put in a brand-new french drain at the time. It wasn't working. Water was still pooling. The newly laid sod was rotting out where the water had been standing, so it was clearly not just an instance of "I just watered 5 minutes ago".

I don't doubt that the problem is better than it was before, but French Drains can only handle so much. If the top layers don't allow the water to seep through quickly enough, then the benefit can only be marginial (This is where those by-pass drains can come in). Often, a much easier, much more effective technique is to grade the yard towards a dry pond or streambed filled with cobbles. an above-ground drainage pond has a couple other advantages:

1) It's easier to clean. Yard debris and dirt can be much more easily monitored and corrected when massive amounts of digging aren't involved.

2) More capacity. Since with french drains you're burying them, they have a smaller volume, and so can't handle as much water

3) In a worst case scenario, a dry pond can be pumped out to the street. If more water is coming down than even the pond can handle, rent an electric pump, and send the water to the street, where the storm sewers are designed to handle it. (Double check your local regulations before sending water off your property, but in cities, water is usually supposed to drain to the street when possible.)