A swale or French drain channels the water away from the site to an area where it won’t cause problems. You can divert water to another spot on your own property, but, not to the neighbor’s yard, so if you can’t divert the water to a good location, you’ll have to run a French drain to a dry well. A dry well collects water and allows it to seep slowly into the surrounding soil. Look to your local codes for the required dry-well size for your area. The size can be subject to your property’s conditions, or to the neighborhood’s. Even if your yard has no runoff problems, you can avoid creating them by installing a gravel-lined trench around the patio. First, check for the location of underground utility lines before you start installing any kind of drainage system.
