Abstract: Golf course areas that cannot be drained with conventional 4″ pipe installed 2-3 feet deep may require slit drainage. These areas are usually flat with heavy soils that perch the drainage water on the surface.
Slit drainage uses 1 1/2″ ID single wall, perforated HDPE pipe covered with a geofabric envelope. Some delete the geofabric. The pipe is installed in a 4″ wide trench , 8-12″ deep, and back-filled with drainage sand that percolates at 40 inches per hour.
The pipe is installed in long lateral lines 6-7 feet apart. The pipe must be sloped, so some field engineering will be required to determine the existing pitch, if any. If the area doesn’t slope, install shorter lines and deepen the trench on the upslope end. Pitched properly, the pipe daylights into larger carrier pipe (usually 4″ HDPE solid). Install the carrier pipe perpendicular to the slit drainage, and connect with 2″ holes bored into the carrier pipe.
Slit drainage can be installed with an trenching machine mounted on the rear of a tractor. A conveyor, attached to the tractor, loads spoils into trailers. Some use a simple trencher and a slope laser to install the pipe.
The sand is installed to the top of the trench. Don’t put sod or topsoil on top of the trench. The slit drain acquires water from the exposed sand on the top and the sides.
Golf course superintendents panic when the slit drainage detail is described. You’ll have plenty of exposed sand trenches before the turf fills in over the exposed sand. After a few months, the trenches will be covered with stolons, and the improved drainage will make you very popular.
Slit drainage is a cheaper alternative to a subsurface rebuild. Winged Foot, and other top courses, have installed this drainage detail.