Playground Drainage Issues
In order for playground safety surface systems to be durable and perform properly, drainage of water is essential. Whether using loose fill products, such as engineered wood fiber or rubber chips, or using unitary surfaces, such as rubber tiles or poured in place rubber, the playground area needs proper water drainage.
Most people involved in playground design and construction know that water needs to drain away from the playground. However, it is important for designers to understand how a particular drainage system will affect the playground during and after construction.
All drainage is not equal. Drainage for a playground in Las Vegas, Nevada, will have different drainage needs than a playground in Orlando, Florida. A local water expert can ascertain how much drainage is needed for a particular climate and how much water on average will enter your playground surfacing area at any given time. As a drainage system needs to adequately discharge water away from the surface area, a playground in Orlando may require the use of a drain field into the surrounding areas’ drainage systems, whereas a playground in Las Vegas may not need such an extensive system.
Playgrounds should not be designed as water collection points for the buildings or ground water surrounding a playground. The accompanying photo (See Photo 1) shows water from the roof of the school building draining onto the asphalt area, which in turn drains into the playground protective area. It appears that over half the water at this school is being discharged into the playground surfacing rendering the playground unusable at high water. Additionally, it can cause displacement of wood fiber, premature rotting of the wood, and growth of insects and mold in the wood surfacing.
A sump pit inside the playground protective area is a common and economical way to address drainage concerns. A sump pit consists of a hole being dug a certain length, width, and depth. The hole is then covered with a geotextile fabric and filled with drainage rock. To avoid interference with the footing layout provided by the playground equipment manufacturer, designers should place sump pits to be installed in the fall zone area or other location with the footer placement in mind. (See Figure 2)
While designers may add slope to the play area to aid in drainage, slope can lead to concerns for the installer. Modular playgrounds are designed to be installed on level ground, so if the designer intentionally adds slope, care should be taken to make sure it will not create problems for the playground installer to meet equipment height requirements. For example, if there is two feet of slope in a forty-foot long play structure with slides at opposite ends, one slide exit will be on the ground while the other will be too high, making both slide exits out of compliance. Be sure to design slope that takes equipment height requirements into consideration. Manufacturers can adjust for slope if it is discussed and incorporated into the play structure during the design stage.
In the late 1980s, a drainage design consisting of a layer of drainage rock throughout the entire playground protective area was widely used. Without regular surfacing maintenance, geotextile fabric was exposed and ripped in high traffic areas causing the drainage rock to contaminate the loose fill safety surfacing.
A layer of drainage rock used throughout the play area can interfere with the structural integrity of the playground equipment footing. (See Figure 3) For example, a playground contractor can be put in a situation where the playground equipment manufacturer has designed an eighteen inch footing, and the six inches of drainage rock leave only a twelve inch footing. Use of a French drain or trench systems is recommended instead of a layer of drainage rock, which is now virtually obsolete.
In summary, for your drainage system to perform properly, consider the local climate and the playground equipment manufacturer’s installation specs. Remember, do not use the play area as a discharge system for the surrounding water runoff. The goal is to discharge water away from the playground area without compromising the stability of the footings and manufacturer equipment height requirements.
About the Author: Curtis Stoddard has over 25 years’ experience as a playground contractor. He co-founded the International Playground Contractors Association and serves on the Consumer Products ASTM International Committee. Mr. Stoddard manages Playground Professionals LLC (www.playgroundprofessionals.com), home of The Play & Playground Encyclopedia and the Playground Professionals Directory.