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.
Issue link: https://read.dmtmag.com/i/92272
From the Sidelines Continued from page 6 A well designed slit drain system in- stalled into a level or undulating surface will overcome drainage problems. False. Surface water must be able to move laterally over the surface to reach slit drains, and there should be adequate gradient in a single cross-fall or on either side of a camber. Average rainfalls of around 13/64" to 31/64" per 24 hour day hardly promote surface movement over relatively flat surfaces, and water will accumulate and be lost only be evaporation. Undulating pitches will pro- mote run-off to depressions. Initially, slit drains will take in the surplus water in these depressions, but the wetter conditions created in these locations will make the surface softer. They will be more subject to deformation from play and prone to collecting silt containing water run-off that, in time, caps off the opening in slit drains and nullifies their effectiveness. French drains or pipe drains, with pea gravel to the surface, will control surface water moving down cut slopes on to the pitch. False. Water run-off moving down a cut slope will always contain silt passing over the soil surface. This continual silt content will eventually blind open drains, tem- porarily sealing the surface. It is just a mat- ter of time before grass growth covers the silt covered aggregate. Furthermore, at times of high intensity rainfall, surface run- off will not stop at drains to gain entry; water flow will simply find its way on to the pitch. A manageable solution is the cre- ation of a shallow, mowable swale at the toe of cut slopes with a pipe drain installed in the invert of the swale. Any local sharp sand covering pea gravel in a pipe drain trench will serve the re- quired need and enable satisfactory water inflow. False. It is vital that the gravel and the sand are chosen with the particle size distri- bution of each material being such that the acceptable bridging factor is attained. Fine particles in the sand moving down into the gravel soon restrict the drainage perform- ance by occupying the voids necessary to enable satisfactory downward water move- ment. Of particular concern is the fine ma- terial content in the sand (less than 1/64") which ideally should be less than 10%. www.stma.org SportsTurf 39 Drainage design must be adequate enough to accommodate all water not retained after high intensity rainfall. False. Only sand pitches can accommo- date rainfall of 1"/hour (considered the max- imum expected intensity over a 20-year period). Heavy clay loam soils on pitches permit infiltration of up to 13/64"/hour. Even the best maintained 1-yard spaced slit drained surface will not permit a drainage rate of much in excess of 9/32"/hour after continual use, even if regular sand dressings are applied. Hence, with rainfall intensity of 1" in 1 hour, over half the water volume will be subject to run-off and this water will sim- ply flow to the lowest areas and off the pitch. Vertidraining or deep aeration into heavy subsoils will improve the drainage of a sports pitch. False. When clay loam topsoil and clay subsoil is loosened by aerating and creating holes, this will only create more water re- tention which will develop into water- logged areas. The main aim in maintaining heavy loam soils in a condition in which to play football must hinge on retaining a firm surface, with adequate removal of surplus water by means of a suitable by-pass sys- tem. Allowing the topsoil to become loose at the onset of winter promotes the devel- opment of soft areas that are prone to dis- placement and the formation of puddles after rain. A slit drainage system without annual sand dressings is still better than no drainage installation. False. The system is entirely dependent on the slit drains being 'open' at the sur- face, and the sand topping remaining un- contaminated with surrounding clay topsoil spread with play activity. The only way this can be achieved is by applying sand dress- ings to create a sandy medium in the short- est period of time to at least 1" thickness over the slit drains, at least with the appli- cation of annual dressings for 5 years or more. Without these dressings, the drains soon become capped with clay loam top- soil, and the installation cost has become a waste of money. ■