Vehicular turf (part 1 of 3)
|Turf Road Test|
PLEASE DRIVE ON THE GRASS is not the sign you expect to see, but why not? Florida turf areas are frequently walked on, driven on, parked on, and used for airport runways. Grass parking lots provide water percolation and natural air conditioning, but are often shunned in observance of the adage, "Don't walk on the grass." Although that might be a good rule for temperate areas, warm-season turfgrasses grown in sand tolerate formidable traffic.
The motive for grass parking areas may be economic, "Can't afford asphalt", or last-resort, "Don't have anywhere else to park", but the outcome is an environmental benefit. While high-impact turf areas can succeed by chance, some imaginative Florida designers, contractors, and clients have planned the concept into landscapes that really work.
|Big Top Flea Marke, photo
by Mr. Marvin Gill
Environmental benefits of turf parking were considered for Big Top Flea Market, Hillsborough County, Florida. The developer, Mr. Marvin Gill, undertook focus studies, indicating the importance of clean, convenient parking, and anticipating a pleasant atmosphere from natural turf. Prospective clients disliked a "vast expanse of asphalt", probably because of its discomforting heat. Construction challenges in the 2,500-space parking facility were solved by the right combination of people to make the concept work. Tampa Stadium (opened in 1967, with 10,000 parking spaces) and Pro-Players Stadium (opened in 1987 with 15,000 parking spaces) are other examples of successful turf for parking. This trend throughout Florida includes churches, community colleges, and home lawns. Why should we drive on the grass?
Asphalt and other non-evaporative surfaces absorb heat energy, dissipating it back to people by radiation and air convection. Because of its evaporative cooling, turfgrass reduces soil and adjacent air temperatures so we feel cooler. In one study in Missouri in October, turfgrass was near 38C, compared with 60C for asphalt (12). The daytime air conditioning from green vegetation is estimated by its evapotranspiration times the heat of vaporization (7), or 2.43 kJ . g-1 water at 30C. For turf in Miami transpiring an average 9.71 mm day-1 in August, this would be 6,500 W h m-2day-1, or 32,400 BTU per daytime hour for a 2.6 m X 6.7 m foot parking stall, while exposed to the sun.
Developments in Florida must provide for storm-water retention within their own boundaries. Special impoundments offset impervious areas, allowing percolation, but temporary ponds can occur. Standing water injures turfgrass and other plants, facilitating succession to sedges and other inadequately rooted species. Management of small wet areas is difficult and mosquito problems and other hazards can occur. Florida shopping malls sometimes use long, narrow, ditch-like catchments located between parking ranges. These steep, often wet, areas are hazardous for people to cross, and they can become catchments for shopping carts and trash.
The vehicular turf alternative can increase groundwater recharge efficiency because trafficked areas are used simultaneously for percolation. This also makes it easier to satisfy building code requirements. Vehicular turf provides visually attractive up-close green areas, compatible with softer, more personable architecture. A year-round growing season, such as that of southern Florida, allows vehicular turf to be always green and attractive. Vehicular turf provides valuable alternative uses, present and future. Examples are garage sales, outdoor food festivals, dances, sporting events, camping, and carnivals.