September 2013

SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.

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Open systems use swales (natural drainage channels covered with vegetation, usually grass) and gutters (paved swales) to divert water away from the field(s). Open systems rely on slope (gravity) alone to move water away. Lawn swales should be sloped to prevent the accumulation of standing water and to avoid erosion. An open system is fairly inexpensive to build if there is room and if the ground is easily workable. Open systems are less practical on sites where space is limited. Closed systems, on the other hand, include pipes so water is collected and transported in a contained system. Trench drains: There are two types of closed trench drains: gravel drains and grated drains. Gravel drains consist of an open trench with a sloping bottom filled with free-draining stone, with or without a pipe. The trench usually is lined with a nonwoven geotextile filter fabric allowing water but not solids to pass through. Next, a porous or perforated pipe is laid along the bottom of the trench on a gravel bed. The remainder of the trench then is filled with gravel to the surface and left open to catch storm water while the pipe at the bottom collects it and carries it away. Similar options include a grated trench drain (commonly called a channel drain), a gutter made of concrete or prefabricated sectional material, or a slot drain consisting of a prefabricated sectional material placed in a narrow trench. Any of these options will include a grate that prevents debris from entering. The advantage of closed drains is their top surface can be set at a uniform grade, eliminating the need for a sloped swale or gutter. The bottom of the trench slopes instead of the surface. This is particularly useful where there is limited area around the field. In addition, it is quite common to use a gravel trench drain to act as both a surface and subsurface drain. Catch basins: Where the presence of buildings, rocks, trees and/or other fixed obstructions, or significant changes in elevation on the site preclude moving stormwater to a storm sewer or appropriate drain field, a catch basin located at a safe distance from the field and from normal foot traffic, may be used. A catch basin is a below-grade structure, typically made of pre-cast concrete, masonry (block) or pre-molded PVC, with a plastic or metal grate on top. Water is directed by swales, gutters or trench drains to the catch basin and from there it is dispersed. If a catch basin is provided with a sump below the invert-out, it promotes water quality improvement by allowing the settlement of silt, soils and other debris. In many cases, it allows water to safely be dispersed into storm sewers, creeks, ponds, wetlands or other environmentally sensitive areas. In other cases, a catch basin is designed with a perforated sump in order to provide infiltration into the surrounding soils. This is done in areas where soils are highly permeable and the water table is deep enough to allow such infiltration. If constructed in this manor, a catch basin is commonly called an infiltration basin or a leaching basin. Area drains, drain inlets and in-line drains also are used to remove water from the surface and direct it into a closed drainage system. In reality, most surface drainage systems are made up of a combination of swales, gutters, trench drains and/or catch basins, known as a combination system. These systems treat only surface water and may be insufficient if the site is low and a large area of land drains onto it, or if there is a large amount of ground water. They are, however, useful to remove water drained off the field or off nearby buildings or pavements. SUBSURFACE DRAINAGE Subsurface drainage addresses the management of water below ground. Water will naturally drain from high areas to low areas both on the surface and underground. Additionally, there may be natural ground water channels within a site. A French drain places an underground barrier between the facility and approaching subsurface water. The most common type of French drain consists of a trench separating areas of ground water accumulation or flow from the facility. The width, depth, location and number of French drains on a site depends on the soil conditions, the water table and the amount of water needing to be captured and relocated. Generally, a French drain consists of a rectangular trench filled with permeable aggregate extending to the surface, allowing the French drain to serve both surface and subsurface flows. The side walls and SportsTurf 31

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