(‘dran-ij-‘sis-tem) A system of watercourses or drains designed to carry off excess water.
The first step you should take when planning to install a french drain is to identify low spots in the landscape. If obvious low spots exist on the property, the water must have a way to exit those areas. If you don’t install a drainage system, a puddle probably will develop whenever it rains and could backup causing more serious problems.
Types of drainage to know before you install a french drain:
- Gutters… collect runoff from a building’s roof. This runoff is conveyed through downspouts to the roof drain system. Gutters should be kept clear of leaves and other debris so clogging does not occur in the roof drain system
- Catch basins… are connected to storm drainpipes or on residential projects connected to a line of corrugated pipes and releasing the unwanted water to a desired area. Catch basins are plastic structures (either round or rectangular) with plastic grates on top. The grates capture debris that could clog the pipes and are able to be cleaned up, unlike French drains. You can prevent the system from clogging by checking the catch basins during or after a heavy storm. A simple screw driver is all that is needed to remove grate.
- Trench drains… are used to capture storm water flowing over a larger area like a driveway. Trench drains convey heavy rainwater to a storm drain system if possible.
- French drains… can be installed anywhere on your property that collects water. They are constructed of perforated pipe, filter fabric (sock) that surrounds the pipe, and gravel, similar to foundation drain systems.
A French drain is simply a small trench, dug to a gradient that will allow surface water, or the top of the ground to drain away from a building or area that is prone to surface water build up or flooding. The usual reason to install a French drain is to relieve a build up of water in a low spot in the lawn or natural areas.
You can install a French drain anywhere on your property that collects water. Either PVC or corrugated pipe can be used, depending on the amount of weight that will be traveling over the system after completion.
1. Locate an area along the slope on your side of the boundary where excavation would be easiest to install your French drain (i.e., free of obstructions). Grading should be plotted out before you begin digging to install a French drain. You need to create your own mini-slope to carry the water down to its destination. Aim for at least a 1% grade (i.e., a drop of 1’ per 100’) for French drains. Getting the water to go where you wish is essential for improving yard drainage; the grade will facilitate your efforts.
2. Dig a horizontal trench across the length of the slope. This is the most labor-intensive part when you install a French drain. One end of the trench will head in the direction of the spot where you’ve determined the water will be re-routed (if it doesn’t quite reach that spot, you’ll have to dig a connecting ditch down to it). Trench size will depend on the magnitude of your moisture problem –- and on how strong your back is! Small trenches are often dug to a width of 5”-6” and a depth of 8”-12”.
3. Before applying gravel, line the trench with landscape fabric to keep dirt out of the gravel. You want to preserve the porosity of the gravel, which promotes percolation of water through it — one of the underlying principles that make French drains work. Shovel a coarse gravel onto the landscape fabric. Wrap the ends of the landscape fabric over the top of the gravel layer.
4. You now essentially have a tube of landscape fabric filled with gravel. To hide it for aesthetic purposes, shovel a layer of coarse sand over it and lay sod on top. Your French drain is complete!