Common Drainage Systems

Common Drainage Systems

Drainage swales are often established to channel water to a desired location. A swale is a depression or channel in the soil. A swale can be shallow and covered with grass or whatever surrounding landscaping materials are used. A swale can be deeper and lined with stones, in which case it is sometimes called a dry bed.

Underground drainage systems are sometimes used where drainage swales are impractical or where natural water flow causes erosion, such as on steep hills. Underground drains are sometimes called French Drains. Underground drains for older homes may be constructed using clay tiles. Flexible corrugated plastic pipe, usually 4 inches diameter, is often used for newer homes.

Water entering underground drains may come from several sources. Water often comes from a gutter downspout. Water may be captured above ground in a component called a catch basin or in a hole filled with stones called a dry well. Water may flow from a sump pump or in rare cases from an underground water source. People occasionally connect foundation drains to underground drains. While often not visible, this connection is a significant defect that can cause water to back up into the basement or crawl space.

Water flows inside the underground drain and discharges at an appropriate location such as at the street or into a swale, creek, or drainage easement. The discharge pipe is usually terminated to the open air (sometimes called daylighting). In cases where there is not enough slope for an open air termination a device sometimes referred to as a bubbler is used. A bubbler opens above ground to let water flow out and closes when the water flow stops.

Sump pumps are occasionally used in exterior drainage systems when storm water must be pumped up for discharge. The sump pump is located in a pit or catch basin that receives surface water or water from underground pipes and mechanically discharges the water to an appropriate location.