Drainage Correction Terms

COLLECTION BOXES

Typically 9″X9″ or 12″X12″ drains that are set in the ground. The top of the drain (grate) is located slightly below ground level. Surface water enters through the grate and collects in the box. A pipe is connected to the collection box below ground which directs the water away. Also referred to as Catch Basins.

COMBO DRAIN

A French drain and surface drain used in conjunction with each other in the same trench to remove excessive ground and surface water from around a foundation.

DISCHARGE

Refers to the disposal of the water collected by a French or Surface drain.

FRENCH DRAIN

This is a trench covered with gravel or rock that redirects surface and/or groundwater away from an area. A French drain has a perforated hollow pipe along the bottom to capture water that seeps down through the upper gravel or rock. French drains are common drainage systems, primarily used to prevent groundwater from migrating under the foundation. Groundwater under a foundation can cause movement beyond seasonal norms. French drains are also used behind retaining walls to relieve hydrostatic pressure.

GRADE

A grade (also called slope, incline, gradient, pitch or rise) of the area around a foundation refers to the inclination of the ground from the horizontal. Negative grade means the slope is towards the foundation. Positive grade, or sloping away from the foundation, is desirable to help prevent unwanted foundation movement.

POP UP VALVE

Sometimes act as the discharge point of a drainage system, opening easily when needed to allow water to flow freely from the pipe and away from structural foundations. The patented spring-loaded cap opens with the hydrostatic pressure of water flowing through the drainpipe, then closes as the flow diminishes.

RETAINING WALL

A wall designed to hold or retain soil. It is typically used in home construction where large quantities of fill dirt are used to “level” a construction pad site. Without a retaining wall to support the fill dirt, the foundation would be undermined by soil erosion or slumping. The addition of a French Drain at the base of a retaining wall is often necessary to reduce hydrostatic pressure on the wall system.

ROOT BARRIER

The act of cutting off the roots of trees that are growing near a foundation and installing a barrier to prevent their reestablishment in the area where they are not desired is called installing a root barrier. Theoretically, a root barrier can minimize the amount of moisture loss from the soil to the root system.

SUMP PUMP

This is a pump used to remove water that has accumulated in a water-collecting sump. Sump pump systems are used when a drainage system (French or Surface) is unable to be discharged with gravity alone. In that case, water is channeled to a collection area known as a sump. Once the collection water reaches a certain volume a submersible pump is used to pump the water away.

SURFACE DRAIN

Surface drains consist of a series of collection boxes or catch basins and a solid pipe. They are designed to collect and transmit water that is accumulating on the surface (around a foundation.)

SWALE

Drainage swales also play a role in residential rainwater, directing water from downspouts or driveway run-off to a yard drain or street storm drain. Like agricultural ditches, drainage swales not only safely control water flows, but carry with them fertilizers and other pollutants from your roof, lawn, and gardens.