drainage solutions: french drains

To address drainage issues in your yard, an option to include may be a French drain. To determine the best drainage solutions for your property, we can start with assessing the situation, and then select the most appropriate options. See blog regarding Selecting Solutions for a Drainage Problem.

French Drains

Drainage Test: First you could do a low-tech soil drainage test to make sure the French drain will work as infiltration and not require a subsurface drain pipe. Dig a hole that is a cube about 10" to 1 foot length, width, and depth. Fill with water. Time how long it takes to drain into the soil. If a few hours or shorter time, then an infiltration system will be adequate. If it hasn't drained after a day, then an infiltration French Drain system will not function adequately; but a French drain with subsurface pipe may be an option.

A French Drain with a subsurface perforated drain pipe (with the pipe wrapped in the soil separator fabric) at the bottom of the French drain may be an option; if based on existing and surrounding grades, there is a low-enough feasible location for the drainpipe to outfall. French Drain with a subsurface perforated drain typically requires professional design to evaluate volume of run-off, infiltration capability of the existing soil, and determining slope of the subsurface drain and adequacy of outfall.

An infiltration French Drain (if applicable based on drainage test) is an easy DIY project, so is the subject of this blog. Below is a typical detail for installing an Infiltration French Drain. Use a level to ensure that the bottom of the trench is longitudinally flat (since water surface is flat!) so the French Drain may be dug deeper on one end than the other; and often needs to consist of individual French drains that step longitudinally. The visible surface decorative stone (or shredded hardwood bark mulch) of course follows the slope of the grade or as applicable an adjoining walkway. Use Gator soil separator fabric (only available at stone supply centers) and bags of garden gravel. Soil separator fabric is not the same as the landscape weed-control fabric that you can get at hardware stores and garden centers. The French drain will silt-up and not function if you do not use soil separator fabric. If you have a contractor install the French Drain, make sure the materials are listed on the approved contract; and ask to inspect the trench before they add the gravel during installation to ensure that they use the soil separator fabric and that they longitudinally step the French Drain. After installation you should also see the black soil separator fabric below the river stones or thin layer of surface mulch.