Site drainage problems - Gardening Article

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Friday, 5 December 2008

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Site drainage problems

By:Larry Westfall

Site drainage problems

Inspect the grounds of your old house for drainage problems

Observe the drainage pattern of the entire property, as well as that of the properties next door.

The ground should slope away from all sides of the building. Downspouts, drains and gutters, should re-direct water away from the foundation. Check the planting beds next to the foundations.

Planting beds are often mounded in a way that traps water and edging around planting beds acts like a dam to trap water. Most problems with moisture in basements are caused by poor site drainage. The ground also should slope away from window wells, outside basement stairs, and other areaways.

The bottom of each of these should be sloped to a drain. Each drain should have piping that connects it to a storm water drainage system, if there is one, or that drains to either a discharge at a lower grade or into a sump pit that collects and disperses water away from the building. Drains and piping should be open and clear of leaves, earth, and debris. A garden hose can be used to test water flow, although its discharge cannot approximate storm conditions.

Where a building is situated on a hillside, it is more difficult to slope the ground away from the building on all sides. On the high ground side of the building, the slope of the ground toward the building should be interrupted by a surface drainage system that collects and disposes of rainwater runoff.

There are two general types of surface drainage systems:
·an open system consisting of a swale (often referred to as a ditch), sometimes with a culvert at its end to collect and channel water away,
·and a closed system consisting of gutters with catch basins.

Combinations of the two are often used. The locations and layout of culverts, gutters, drains, and catch basins should be such that if they became blocked and overflowed no significant damage will occur and that any resultant ice conditions will not pose a danger to pedestrians or vehicles.

The design of surface drainage systems is based on the intensity and duration of rainstorms and on allowable runoff. These conditions are usually regulated by the local building code, which can be used to check the adequacy of an existing surface drainage system.
In some locations, especially where slopes lack vegetation to slow water flow, it may be possible to reduce rehabilitation costs by diverting rainwater into a swale at or near the top of the slope and thereby reduce the amount of rainwater runoff handled by a surface drainage system.

This swale, of course, must be within the property on which the building is located. The ground beneath porches and other parts of a building that are supported on piers should be examined carefully. It should have no low areas and be sloped so that water will not collect there.

Water from the roof reaches the ground through gutters and downspouts or by flowing directly off roof edges. Because downspouts create concentrated sources of water in the landscape, where they discharge is important. Downspouts should not discharge where water will flow directly on or over a walk, drive, or stairs. The downspouts on a hillside building should discharge on the downhill side of the building. The force of water leaving a downspout is sometimes great enough to damage the adjacent ground, so some protection at grade such as a splash pan or a paved drainage chute is needed.

In urban areas, it is better to drain downspouts to an underground storm water drainage system, if there is one, or underground to discharge at a lower grade away from buildings. Water that flows directly off a roof lacking gutters and downspouts can cause damage below.

Accordingly, some provision in the landscaping may be needed, such as a gravel bed or paved drainage way.
When a sump pump is used to keep a building interior dry, the discharge onto the site should be located so that the discharge drains away from the building and does not add to the subsurface water condition the sump pump is meant to control.

The site should be examined overall for the presence of springs, standing water, saturated or boggy ground, a high water table, and dry creeks or other seasonal drainage ways, all of which may affect surface drainage. It is especially important to inspect the ground at and around a septic system seepage bed, seepage pit, or absorption trenches.

About the Author

Larry Westfall is the owner of
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