When the water table around your property is high, you will have problems with wet basements or yards that are always soggy. Installing French drains can go a long way in reducing this problem to manageable proportions.
What Is a French Drain
Water always flows from a higher level to a lower level, and this is the basic concept behind French drains. French drains are trenches with slight slopes that are filled with gravel. The gravel is a porous media through which water can infiltrate easily. A pipe that has several perforations all around its circumference is embedded in the gravel, and this allows any water that infiltrates into the gravel to be carried away to drainage or other outlets. This ensures that the groundwater is carried away from the property where the French drain is installed.
Draining French drains
Installing French drains has to start with identifying a low-lying area in your property where the water can be diverted. You can also identify a drainage ditch that can act as a retention pond for the water. You can also look for dry wells in your vicinity, or obtain permission from the authorities to divert the water on to streets so that roadside drains can take care of this water.
Location of French Drains
French drains must extend horizontally across your property and must be uphill of the area that you want to keep free of water. Drains do not have to be very deep and sizes of drains that are two feet deep and one and a half feet wide are acceptable. You then need to find perforated pipes to install within the drain. If you have any trees in your property, make sure that pipe that is close to the roots of the tree is not perforated, else roots can get into the pipes and clog them. Deeper drains with two or three layers of pipes can help you to do a better job of controlling groundwater levels.
The Installation of French Drains
Once the trench is excavated, fill the bottom six inches or so with the gravel. The gravel must be clean and free of debris and fines. The pipe can then be laid with a slope of 1 inch for every 8 feet, as this should be sufficient to create the necessary flow for the water to drain away. Your gravel can be graded and have larger stones which are best placed in the lowest portion of the drain. Pipes can be of metal, concrete or plastic. Plastic pipes are the easiest to perforate and also easy to install. Diameters of the pipes should be a minimum of 4 inches, and 6-inch diameters are ideal. You can even have two pipes laid side by side to increase the water carrying capacity.
The gravel acts as a filter and ensures that the pipe in the French drain carries only water. You can even install drains at deeper levels and the gravel covered over with earth or turf. You can keep your basement dry by installing French drains all around the outside perimeter of the basement.