Hurricane season is not yet over and stormwater detention is top priority for most rebuilding communities. Billions of dollars of damage have been caused by flooding across our nation with the deadly combination of extreme rain events and too much concrete. Detention ponds cannot keep up with the combination of the rain deluge, overflowing bayous and rivers, overwhelmed stormwater systems and the increased runoff from impervious cover from ever expanding developments.
There is a solution that may save many homes and business from flooding. It is an actionable construction method that will save money, enhance aesthetics and most importantly add cumulative detention capacity to help combat large flood events. Add stormwater detention in every new development or redevelopment project with permeable pavers. Paving with permeable plastic grid pavers filled with gravel or grass is the new standard to add detention without adding cost. Furthermore, plastic grid permeable pavers provide opportunity for detention under the paving and is coded as 100 % pervious cover enabling developers and planners to utilize 100% of their land. The TRUEGRID permeable paver system is the permeable paving alternative to concrete and asphalt that can be used for commercial, industrial or residential paving applications including parking lots, storage facilities, bus pens, truck yards, fire lanes, and even driveways. The pavement system is 100% permeable and rain flows through system surface at over 800 inches per hour. Under the grid system a clean rock base serves as a detention pond so effectively you can drive on the surface and store stormwater below.
Plastic grid pavers can vary but the best system has a combination of rigidity and compression strength married with flexural design elements to handle any soil or climate. The grid has over 8000 psi compression strength when filled with gravel. This compares to most concrete paving at 5000psi. Commercial and industrial traffic including fully 18 wheelers can drive on the grid surface without issues such as cracking and potholes found in cement and asphalt. More importantly, under the plastic grid system in the base rock stormwater can be detained in 40% void space between the rock. Most cities and counties recognize this detention opportunity and code 100% pervious cover and 40% storm water detention volume capacity in the installation cross section of base rock and filled grid. A typical coded detention capacity for a plastic grid system with gravel fill and clean angular 57 stone sub-base is 8 to 9 inches per city code.
The traditional method of storm water detention involves digging and construction a detention pond or separate detention area to handle runoff from hardscape and impervious surfaces such as concrete or asphalt parking lots, roadways and of course, buildings. There are many negatives to this methodology. First up is the land use. Instead of utilizing this land for revenue generating purposes, i.e. additional buildings or parking or commercial space, the land now must be used to build a hole in the ground that will need costly construction as well as long term and continuous maintenance. Often in commercial developments as much as 25 % of the land on a site can be required for detention putting a large burden on the remaining usable property. Separate detention ponds can pose safety issues such as drowning hazards. If not maintained frequently the ponds become toxic and breeding grounds for disease carrying mosquitoes.
Putting detention capacity under plastic grid parking surface– drive on surface, detain storm water below- eliminates all these issues. And it performs for the life of the project, 25 to 40 years, virtually without maintenance.
The aesthetic can be important as the cost. Does anyone ever say – “boy I wish we had more concrete paving area!” Not unless they are concrete salesmen. The fact is that concrete is coming up in the conversation from city planners, engineers, architects and residents who are tired of flooding in heavy rain events due to runoff from concrete from over-development. Grass or gravel filled plastic grid with detention underneath results in some beautifully landscaped, natural elements or sites in what would otherwise be an unsightly concrete lot, fire lane or overgrown detention pond. The gravel color and texture can be chosen to fit in with the building and area. Grass filled plastic grid pavers can be used in applications such as fire lanes to and provide detention capacity underneath and act as French drain or a moat or sorts to keep water away from buildings and directed where the designers intend for the water to flow.
This permeable plastic grid paving methodology mimics nature in terms of stormwater management and the way in which rain water is absorbed, detained and released. Natural aquifers are recharged slowly with stormwater that has been filtered free of pollutants such as phosphorous, nitrogen and hydrocarbons by the bioremediation process and the natural microbial action of water flowing into and through the rock and soil before groundwater recharge. Contrast this to heavily polluted runoff from concrete and asphalt. The recent floods form Hurricane Harvey were a huge health hazard to rescuers and residents who had to wade through the toxic runoff.
A site to be developed is prepared by determining the amount of water detention capacity is needed on the site and the impact of the development on the site and the surrounding area. The depth of the excavation- be it six inches or three feet- is calculated over the square footage of the paving. The square footage multiplied by the depth and 40% void space when clean, washed, free of fines base rock is used determines the storage capacity in the cross section. The subgrade is cleared and leveled. A permeable filter fabric is placed between subgrade soil and the sub-base rock to keep separation and maintain capacity in the void space of the rock by preventing intermingling of the soil and rock base. In areas with porous subgrades, stormwater infiltration will occur into the soil through the fabric. In areas with fat clays or solid rock subgrades water will not infiltrate very much. In either instance the site subgrade may be directionally sloped to direct stormwater release slowly. Alternatively, perforated pipe or other drainage elements can be used to collect and channel the detained water towards the city storm water system or other outlet. The key is the detention to increase absorption and slow water movement and release over time so that heavy flash flooding does not occur and damage and endanger property and people.
If every paved developed site in a community – from driveways to strip centers and shopping malls to churches and parks to storage yards to every parking lot you can think of, the list is endless- was paved with permeable plastic grid pavers with detention capacity under the surface the results of heavy rain storms would be less tragic. This methodology mimics nature in terms of stormwater management and the way water is absorbed, detained and released. Natural aquifers are recharged slowly with stormwater that has been filtered free of pollutants such as phosphorous, nitrogen and hydrocarbons by the bioremediation process and the natural microbial action of water flowing into and through the rock and soil before groundwater recharge. Contrast this to heavily polluted runoff from concrete and asphalt. The recent floods form Hurricane Harvey were a huge health hazard to rescuers and residents who had to wade through the toxic runoff. How many homes with six inches or a foot of water have been saved or could be saved from flooding in the next big storm if much of the paving in the city could absorb and detain heavy rains like a sponge soaking up the overflow.
Development is a good thing when done wisely. Over-development with too much concrete and too little planning is not. Stormwater detention planning and low impact development with permeable grid pavers is the way to design and develop responsibly.