by Ken Muellers
When I started my gardening career on the South Shore of Long Island where I grew up, I never gave drainage much thought. The sandy soils that I was used to didn’t allow puddles to sit very long. When my career path took me to the North Shore, and its heavier clay soils, I suddenly discovered that drainage is an integral part of landscaping. Not only is good drainage important for the survival of most plants and essential for avoiding moss and molds developing, it is actually required by code in many towns.
When I say “drainage” what I am really talking about is controlling and getting rid of excess water from rainfall. The two main strategies for dealing with this water are a) dealing with it on the surface, or b) putting it below ground.
Putting the water below ground usually involves a system of catch basins to catch the water, drain pipes below the surface to direct the water and dry wells to store the water. To know how much of all this you need, calculations are done to figure out the volume of water to be contained based on a determined amount of rainfall. Many towns will require you to accommodate 3 inches of rainfall over any impervious surfaces (areas that don’t absorb water, such as roofs, driveways, walks and patios). All parts of the system, from drain to dry well, have to be large enough to handle the volume of water expected. Catch basins can range from small 4-inch diameter plastic grates to 30-inch diameter cast iron grates on top of a concrete box. Dry wells also can be as small as a 2-foot by 2-foot plastic ring to as big as 12-foot diameter cast concrete rings stacked on top of each other going 20 feet down. Once the water is in the dry well it needs to percolate into the soil around and below it (otherwise it would fill up after a rainfall and that would be it for your drainage system). For this reason dry wells sometimes need to be placed deep below grade where sandy soils exist that will absorb the water.
Some of the drawbacks to putting the water below ground are limited capacity and the fact that catch basins, pipes and dry wells can clog up over time. It can also get very costly to install systems for large volumes of water. For these reasons many designers prefer to handle the water on the surface.
The advantage of controlling it on the surface is that you can see what is happening. If handled correctly, it can also be less expensive. Water is usually directed by creating “swales,” which are shallow valleys in the grade that allow the water to move from where you don’t want it (usually near or in the house) to where you do want it. These swales need to have enough pitch or slope for the water to move and not puddle. A recent trend is to direct this runoff to low areas planted with moisture loving plants. These rain gardens, or bioswales not only help absorb and filter the water, but also can be an attractive solution to the problem.
When done well, a drainage system is something you don’t even see or notice. Some may consider this a waste of money, but in the long run, I’d consider it money well spent. And with a little luck, it will keep your yard as dry as this article.