An Introduction to Landscape Drainage

Good drainage in the landscape is as important as proper irrigation. Too much water in landscaped areas can result in numerous plant diseases and can even kill sensitive plants like expensive evergreens. Overly wet turf areas are prone to soil compaction and scarring from footprints and mowing equipment.

In addition, drainage around buildings is important to prevent leaky basements, crawl spaces, and moisture intrusion into building foundations and walls.

Drainage systems can use a variety of techniques to remove unwanted water from an area, whether on a residential, commercial, or golf course site.

Surface Drainage Systems

Surface drainage systems aim to collect excess surface water from hardscaping, planter beds, window wells, and specific turf areas where water tends to collect. Water enters a surface drainage system through catch basins, which have a sump area that collects debris to prevent clogging of the piping.

Catch basins and the drainage grates that go on top of them are available in a variety of sizes and styles depending upon the application.

Round drainage grates are used in turf areas.
Square drainage grates are used for hardscaped areas; walkways, driveways, parking lots, around swimming pools, etc.

Atrium drainage grates have a raised "domelike" design to prevent debris from building on top of the grate openings. These are used in window wells, planter areas, and other applications where bark mulch, stone, or landscape debris would tend to cover drain openings.

The size of the catch basin should be sized to the anticipated volume of water to be collected. In addition the pipe carrying the water from the catch basin should be properly sized to carry water from all catch basins to which it is connected. Always size a little larger than necessary for safety. The additional material cost is minimal and mistakes can be costly. If the drain will be exposed to weight or traffic from above, you may need to consider a concrete catch basin and/or a metal drainage grate. The drainage line connecting the catch basins should be of a solid (non-perforated) design. Both solid PVC and corrugated plastic piping are acceptable.

Another form of the surface drainage system is the channel drain. Channel drains are frequently used in paved areas to collect water. They are essentially an extended trough or catch basin covered by a long grate. Typical channel drains can be 10 long and 4" wide. Channel drains are also connected together with solid piping.

Sub-Surface Drainage

The most frequently used form of sub-surface drainage is the French Drain or underground collection drain. This drain collects underground water from saturated soils and carries it to a desired destination. Sub-surface drains help carry water away from low spots and can protect drainage sensitive plant material. For information on how to construct a French Drain from standard corrugated perforated drain pipe, see the section entitled Constructing a French Drain.

Downspout Drainage

Drain lines can be used to carry roof water from downspouts away from buildings and planting beds. Downspout drain lines can be especially helpful if the natural grade around a building does not cause water to move away from the foundation. Downspouts can be connected to solid PVC or corrugated plastic drain pipes to carry roof water away from the building.

If you have questions about the usage and application of drainage equipment, we encourage you to contact your nearest Transitions Landscape location. Our advisors can explain to you the wide variety of equipment that is available from Transitions Landscape to meet all of your landscape drainage requirements.

Constructing a French Drain

French Drains collect sub-surface water from poorly drained areas and carry it to a main drainage line, dry well, ravine, or the street. French drains can intercept water that is draining from adjacent properties and carry it away before it enters your landscape.

A French Drain is constructed using simple materials; pea gravel or crushed rock, woven landscape fabric, and a perforated drainage pipe (usually the corrugated variety).

To create a French Drain, dig a trench that will carry water away from the area to be drained. Ideal places to put French Drains are the bases of slopes, along retaining walls, or any other area where water tends to collect. Make certain that your trench is well sloped so that water is encouraged to move through the drain to the desired destination.

Line the trench with landscape fabric. Install a 4" or 6" perforated drain line at the bottom of the trench, and backfill with gravel. The landscape fabric should be wrapped all of the way around the gravel to prevent mixing of the surrounding soil into the gravel. This will keep the porous spaces in the gravel open for the water to flow through.

In areas with severe drainage problems, multiple perforated lines are used as water collectors or interceptor drains. Water enters the perforations in the drain lines when the surrounding media is saturated and can be carried away more quickly than just by percolating though the gravel.

If desired can connect the french drain perforated lines into a main, non-perforated header line to collect and carry the water to its intended destination.