Homework: Digging a drainage trench
When a lawn gets very wet on rainy days or during a snow melt in early spring, you need to use the same engineering technology used for years to collect rainwater from roofs -- a gutter and downspout solution, but inside the soil. Installing a drainage trench in the yard will collect subsurface water and transport it to the lowest part of the land, where it would end up by default. Credit: Tim Carter
1. Rain drain
When a lawn gets very wet on rainy days or during a snow melt in early spring, you need to use the same engineering technology used for years to collect rainwater from roofs -- a gutter and downspout solution, but inside the soil. Installing a drainage trench in the yard will collect subsurface water and transport it to the lowest part of the land, where it would end up by default.
2. Drench trench
Think of land on a big scale. Its slope and that of neighboring land of higher elevation is like a roof. Many thousands of gallons of water could be flowing downslope in the soil toward a property and you need to capture it just like a gutter collects rainwater. You do this with a simple trench that can be anywhere from 2 feet to more than 8 feet deep.
3. Deep seep
The depth of the trench is a function of many things. The most important one is the elevation of the lowest spot on your property. Since you'll rely on gravity to move the water, you need to make sure the water can flow by itself through the trench to the lowest part of your land.
4. Unrolling stones
The trench will have a perforated drainpipe in it and will be filled with clean (washed) stones or gravel that are the size of golf balls or slightly smaller, perhaps the size of a large glass marble. It should be dug so that it protects your yard, your basement, your crawlspace and so forth, like a moat protects a castle.
5. In good shape
The trench may only need to be L- or U-shaped, so that one or both ends eventually poke out of the ground. This happens if you keep the bottom of the trench level or just with a slight slope and the ground falls away. Eventually, just like a cave or mine entrance on a hillside, the trench ends.
6. Dry run through gravel
If you really want to make your yard dry, you should fill the trench up to nearly the top with the stone. This makes for a highly effective gutter in the ground. The drainage system works because water finds it infinitely easier to flow down through the gravel than push its way through the soil. Water always wants to travel the path of least resistance.
7. Dig it (but not too much)
The trench only needs to be 1 foot wide, and even a trench just 6 inches wide can suffice. If you need to use a digging machine, you may end up with a trench 16 or 24 inches wide. There is nothing wrong with this; it's just that you'll end up buying more gravel.
