A soggy, wet lawn will attract all sorts of problems from weed outbreaks to lawn disease and, eventually, thin and dying turf. Installing subsurface drainage is the best way to alleviate drainage issues but it must be installed correctly to work properly. There are a variety of methods and materials that can be used for a drainage project depending on the amount of money, time, and labor available. As long as certain principles are adhered to, the project should be a success no matter what materials or methods are utilized.
Every type of drain requires a trench, and every drainage trench must slope away from your garden. A 2% slope is needed to adequately move the water from one place to another. This means that if the drain line is intended to be 100 feet long, there should be a 2-foot drop in the elevation of the bottom of the trench from one end to the other. This will allow the water to move properly through the trench whether it is routed through a pipe or a gravel bed.
Catch basins are often used as the final destination for drain water. They may also be a stopping point to collect debris and slow down the flow of water before it reaches another area like a pond or ditch. If a catch basin is the final destination, it should have holes or perforations throughout to slowly leach water into the ground. It should also rest in a bed of coarse stone or gravel to aid in the dissipation of the water.
Before installing any drain lines, coarse stone or gravel should always be put in the bottom of the trench to a depth of approximately two inches. Once the drain line is installed, coarse stone or gravel should then be put on top of the drain line leaving approximately 3–4 inches for topsoil for the lawn to grow in. If the drainage problem is severe, it is helpful to bring the gravel right to the top of the drain trench and leave it exposed. In time grass will grow over the gravel and the drain should still function normally. The exposed gravel may also be permanently exposed and maintained as an open drain.
Landscaping fabric can be used to line the trench and to cover the stone once the drain line is installed but it is not necessary. In all cases, it is important that the trench is deep enough to both maintain the proper slope and allow for the drain line to be surrounded by gravel.
Two Common Types of Drains
Drains can vary in style and complexity. The simplest drain is a classic French drain, which is nothing more than a trench filled with coarse stone or gravel. A 2–4% slope is adequate to quickly move water away from trouble areas. The drain can be left open or, if aesthetics are a concern, can be covered with a couple of inches of topsoil and sod.
The most commonly used drain pipe or drainage tile is a corrugated, slotted pipe usually four inches in diameter. Commonly called Big O, this pipe is used in the vast majority of drainage systems on golf courses and in the landscape. The pipe is both able to move large amounts of water and receive water from the surrounding soil.
As long as the slope is correct and care has been taken as to what happens to the water at the end of the line, any combination of materials and techniques can be used to construct a drainage system.