Golf putting greens and sports fields that are designed to use a geotextile to retain a sand-based root zone mixture atop a drainage layer are an alternative to the popular design recommended by the U.S. Golf Association (USGA) where the root zone mixture is placed directly atop gravel (USGA Green Section Staff, 2004). The geotextile-based design allows use of drainage layer materials with pores that are too large for the root zone mixture to support itself atop by self-bridging the drainage layer voids as happens when a USGA-recommended (USGA Green Section Staff, 2004) root zone mixture is placed atop gravel with a USGA-recommended particle size distribution. In this respect, the geotextile-based design puts less restriction on the particle size distribution of gravel that can be used and it allows the use of synthetic drainage structures designed to transmit more water per unit depth than does gravel. Although use of geotextiles offers this and other advantages (McInnes and Thomas, 2011), there has not been widespread acceptance, in part because of the possibility that geotextile pores, generally being smaller than that of gravel, could clog with particles eluviating the root zone and consequently restrict drainage and lead to poor performance or failure of the putting green or sports field. This nagging concern continues although extensive research has been conducted on appropriate choices of geotextiles to minimize clogging when they are used to retain soil for engineering purposes (e.g., Koerner, 1998; Koerner et al., 1993; Mlynarek et al., 1991) and the research of Callahan et al. (1997a) more than a decade ago that demonstrated long-term successful use of geotextiles to retain a turfgrass root zone above gravel.
Numerous commercially available geotextiles have sufficient strength and resistance to stretching necessary to support a sand-based root zone atop large pores in a drainage structure, even pores that exceed 50 mm width such as those found in AirDrain (a 25-mm deep highly porous polypropylene geogrid; AirField Systems, Oklahoma City, OK), so choice of a geotextile in a putting green or sports field would be based on cost of the textile and on its ability to transmit drainage water along with particles eluviating from the root zone. Pore sizes of geotextiles are commonly reported by the manufacturer as apparent opening size (AOS), the diameter where 95% of the pores in the geotextile are smaller (ASTM, 2004a; Sarsby, 2007). Apparent opening size essentially gives an estimate of the size of the largest particle that can pass through the geotextile. Clay, silt, and very fine sand are known to migrate in sand-based root zone mixtures (Callahan et al., 1997b; Whitmyer and Blake, 1989; Wright and Foss, 1968). Limiting the available geotextiles to those with AOS larger than very fine sand (150 μm or greater) still leaves plenty whose reported permeability is high enough not to initially limit flow of water from a root zone with USGA-recommended hydraulic properties. The purpose of this study was to evaluate the hydraulic and particle-sieving effects of such geotextiles in various sand root zone–geotextile combinations.
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