A french drain is a near-surface drainage system that is designed to increase the overall infiltration rate of the surrounding area and is used primarily to fix wet yard problems. The system consists of an excavation approximately 8 to 16 inches deep, a filter fabric lining, a 2-inch base of gravel, a 4-inch perforated pipe with protective fabric, and gravel surrounding the perforated pipe. The french drain can be topped with gravel for a high infiltration rate or with sod to hide it beneath the lawn. The higher the clay content in the soil, the lower the general infiltration rate. Wet yard problems are commonly caused by a combination of clayey soil, a level ground surface, and a high groundwater table. French drains are not meant to handle and are not designed for stormwater drainage.
Preferably with a series of swales and/or berms. A swale is a relatively shallow linear depression in the ground surface designed to direct stormwater away from structures. A berm is a relatively small rise in the ground surface that protects a structure by preventing stormwater from flowing towards it.
Excess moisture in foundation walls is generally cause by one of three things: (1) surface water infiltration, (2) groundwater infiltration, and (3) a broken exterior pipe. Moist walls caused by surface water infiltration can be spotted fairly easily by the staining pattern. In most cases, the water infiltrating down along the foundation wall is coming from a gutter downspout that is dumping water right next to the foundation. The stain pattern in this case is typically a 45-degree downward angle from the water source. The most common misdiagnosed problem is the surface water infiltration problem. Very often we are asked by homeowners to inspect their basement or crawl space after a “waterproofing contractor” has provided them a quote for the installation of an interior perimeter drainage system (sometimes referred to as a “french drain”). In the case of a surface water infiltration problem, this type of solution is not the correct one for many reasons, but mostly due to the lack of understanding of the source of the water and how to deal with it.
A flooded basement is typically caused by a rising groundwater table, severe negative drainage conditions, a clogged or inadequate drain next to a basement door, or a combination of these three. The solutions for each of these are very different and a design professional should analyze your particular situation and prepare a remedial design that takes into account the various water infiltration sources.
Stormwater runoff occurs when rain or melted snow flows over the ground and is not readily absorbed. Impervious surfaces like driveways, sidewalks, and streets prevent stormwater from naturally soaking into the ground. Instead, the water is channeled into our storm drain system; from there, it is carried directly to streams, ponds, lakes and rivers.
So, stormwater runoff is carried through the storm drain system—it gets treated before it’s released into our water resources, right? WRONG! Sanitary sewer systems carry household water to large facilities where it is treated. Water that flows into storm drains and sewers flows UNTREATED, directly to streams, ponds, lakes and rivers. This runoff carries with it pollutants that damage our natural environment and can be harmful to humans, plants and animals.
Stormwater runoff can have many adverse effects on plants, animals, fish and people.
Keeping pollution out of storm drains not only helps the environment, but saves YOU money. Cleanup efforts are big strains on tax dollars. Minimizing pollution means minimizing cleanup costs and saving your tax dollars for other programs in the community.
By making a few small changes, YOU can help reduce stormwater pollution!