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Trench will solve yard's drainage problem

This trench is nearly 5 feet deep. The coarse gravel allows water flowing through the soil to fall rapidly to the bottom and flow into the drainpipe.

Tim Carter | Special to the Times

This trench is nearly 5 feet deep. The coarse gravel allows water flowing through the soil to fall rapidly to the bottom and flow into the drainpipe.

Q: I live on a slight grade. My yard is very wet when we get days of rain. I sometimes wonder if there's a spring in my yard. Is there an affordable way to dry out my yard so it becomes something other than a mud pit? Why are some yards well drained and others are not?

A: First, let's explore what's happening in the ground. Think of soil as a giant sponge — and I mean giant. If you have a dry or slightly damp sponge sitting on a dry countertop and drip water into it, the water drop will disappear into the sponge. If the sponge is really dry, the water will never make it to the countertop. It is absorbed into the dry sponge matrix. The same thing happens in dry soil when it rains.

However, when soil starts to get too much water, the weight of the water and gravity act to pull water through soil. Because this is happening below the surface, it's invisible. Believe me, water is on the move through soil, and it can happen for days or for months after a rain. This is what causes actual springs to produce water 24 hours a day.

Some soils have a clay component or a dense, hard clay deep in the soil called hardpan. Clay and hardpan block water from moving down deeper into the earth. This is one reason clay is used to line pond bottoms.

Most soils also have a vertical profile that changes the deeper you go into the soil. The very spongy topsoil is the part that really absorbs water. However, below it, the soil becomes denser, and water can have a very hard time traveling through it if there's a lot of clay. If there is clay or hardpan present, the water moving through the soil starts to travel sideways along the border between the topsoil and the denser zone. If the ground is sloped, the water moves sideways and downslope.

This undoubtedly is what's happening in your yard. I happen to know the soil profile where you live. It was affected by one or more continental glaciers that left layers of clay behind many feet thick.

To solve your problem, you need to use the same engineering technology that we've used for years to collect rainwater from our roofs. You need a gutter and downspout solution, but inside your soil. You're going to install a drainage trench in your yard that collects the subsurface water and transports it to the lowest part of your land, where it would end up by default if you didn't live there.

Think of your 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 your 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 8 feet or more deep.

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.

This trench will have a perforated drain pipe 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.

The trench should be dug so that it protects your yard, your crawl space and so forth. The trench may only need to be L- or U-shaped so that one or both ends eventually daylight. 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.

Have a question for Tim Carter? Go to his Web page, askthebuilder.com, which also features numerous videos. You can also sign up for his free newsletter.

Trench will solve yard's drainage problem 12/31/11 [Last modified: Saturday, December 31, 2011 3:31am]

    

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