Let’s Talk About Drainage
Editor’s Note: This article was written by Greg Johnson, general manager at ForeverLawn Southwest Florida in Naples, and addresses increasingly more common drainage questions.
We have designed all our ForeverLawn synthetic grass products and our base layers to give a minimum percolation rate of 30 inches per hour; however, the sub-base percolation rates vary. Here are a few of the primary issues that can affect site drainage:
Soil Make Up
Typically, southwest Florida soils are considered sand to sandy loam. Due to the excessive amount of natural rainfall Florida receives during the rainy season, we need coarse, sandy soil to allow all that water to move rapidly through the ground to help mitigate flooding. Most of our native, sandy soils have a percolation rate of between two and eight inches per hour. We have no control over the sub-base material make-up as most is trucked in during the site development process.
Fill brought in from off site quarries can vary greatly based on the location of the quarry and the depth they are digging. Recently, I’ve been seeing a very white, extremely fine sand that the site contractors refer to as “white sand”. This comes from a layer in the soil directly above the cap rock layer. At first glance, it would seam this would have a high percolation rate because it appears to be beach sand. Unfortunately, upon closer inspection the grain size is so small, angular and irregularly sized it actually compacts tightly and becomes virtually impervious.
There is also another fill product made from recycled concrete — all of the houses being torn down are crushed into a 1” or less material used for inexpensive fill. Site contractors love these materials for two reasons: it’s cheap and it compacts easily. This makes passing compaction tests a breeze, so they use it for house pads and to back fill stem walls. It’s a win-win for them and, consequently, a big headache for us.
Existing Site Drainage
At many locations, site drainage is already in place to help evacuate water from areas like roadways, parking lots, sidewalks, and outdoor amenity areas to storm water retention areas or ponds. In many cases, we can take advantage of existing site drainage and tie our drainage directly into that. All developments in south Florida are under the control of the South West Florida Water Management District (SWFWMD) so storm water retention is part of the engineering and permitting process.
Location of Artificial Turf
If there are obvious signs there may be a drainage issue where the turf is to be installed, we’ll bring it to the attention of the owner immediately and make recommendations accordingly. Because of other factors, including time of the year (rainy/dry), unknown sub-base conditions and adjacent site run off/drainage, it may not be obvious that there may be a drainage issue.
So, with all this knowledge, it’s time to make some decisions. Do we call an engineer in to do a soil analysis and percolation test to make sure water not only flows through our turf and base but also flows through your existing sub-base material? Do we automatically install drainage under the turf area and allow the water to move laterally through the soil and into an area away from the turf? Do we ignore the issue altogether and hope everything drains as it should when we’re done?
Chances are the correct answer is a combination of all three. Based on the initial site analysis, we can generally see if there are ongoing drainage issues and make recommendations to correct them prior to installing our base. Again, wherever possible, we’ll make the owner aware of obvious site drainage issues at the initial sales visit, during the quote process or during the installation process itself.
There a couple of options in regard to improving existing site drainage:
- The simplest solution would be re-grade the area adjacent to the turf and channel water away via a simple swale to a lower area or storm drain. Depending on site elevations and the proximity of an existing storm drain, this would be the least expensive solution.
- Install French drains from the turf area to existing site drainage or a storm water retention area. To accomplish this, we would dig a trench about 10” deep by 10” wide, add 4” perforated drainpipe and then back fill the trench with drain rock. This trench would give the water a path to existing site drainage or a retention area and allow the water to percolate down through the sub-base throughout the entire length of the trench. The pipe itself and the rock filled trench will also store a certain amount of run-off before it reaches its destination