As most residents of Alabama are aware, the state has a variety of weather conditions. This summer has been a scorcher across the South, and lately as the temperatures and humidity have set records, the combination has also produced some hefty thunderstorms.
These storms can produce a few inches of rain over a single location, causing localized flooding in some areas. So what can be done to help reduce this occurrence both commercially and residentially? Using more pervious concrete for parking lots and driveways.
Pervious concrete pavement is a unique and effective means to address important environmental issues and support green, sustainable growth. By capturing stormwater and allowing it to seep into the ground, porous concrete is instrumental in recharging groundwater, reducing stormwater runoff, and meeting U.S. Environmental Protection Agency (EPA) stormwater regulations. In fact, the use of pervious concrete is among the Best Management Practices (BMPs) recommended by the EPA—and by other agencies and geotechnical engineers across the country—for the management of stormwater runoff on a regional and local basis. This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices. In doing so, pervious concrete has the ability to lower overall project costs on a first-cost basis.
Pervious concrete is a mixture of cement, water, and coarse aggregate, and little to no sand. It also frequently contains chemical admixtures. Pervious concrete creates a very porous structure that allows water to drain to the underlying soils. It is commonly produced to allow as much as five gal/ft²/min to pass through the body of the concrete.
By allowing rain events to penetrate the pavement to the underlying soils, the first flush of the paved surface is contained on site. The natural infiltration of the area remains unchanged so the water can recharge the water table. This avoids surface runoff that must be held in retention ponds or added to the storm water surface runoff, which must then be treated before it is returned to the local streams. In most cases the pavement will be designed with a layer of coarse aggregate below the pavement to increase the storage potential of the system. This has proven to be an effective tool to increase the area of usable pavement on a project as well as satisfy local water management regulations.
Throughout Alabama, several recent projects have used pervious concrete. In Auburn, a new Student Housing Project used pervious in the driveways of all of the new construction townhouses. With a small footprint site, the developers did not have adequate space for a retention pond. Using pervious allowed for more townhomes on the small site.
Cool Crate Storage, a temperature controlled storage facility, is another large project using pervious concrete. Located in Tuscaloosa near the University of Alabama campus, the business provides rental units that ensure belongings are stored in the best conditions. By using pervious here, it allowed for an underground retention pond, and in doing so an entirely new building was added to the site which created a positive monthly income for the owner.
The city of Birmingham has been faced with several flooding issues during storms, and had to find a better way to manage the issue, as it was affecting the city’s water quality as well.
The Birmingham Post Construction Ordinance was adopted by the City Council on March 26th, 2019 with an effective date of May 1st, 2019. All development projects and redevelopment projects one acre or greater permitted after the effective date are required to comply with the ordinance which states that all projects regardless of size will require a certification and documentation by the owner or engineer that the project will not have an adverse impact of flooding.
All projects regardless of size are encouraged to use Green Infrastructure and Low Impact Design Practices to help abate pollution, control flooding and enhance the living experience in the city. Several projects including Harris Doyle Construction offices (Vestavia) and the East Lake Park project (city of Birmingham) used pervious concrete onsite.
Many cities in Alabama, like Mountain Brook, have a maximum impervious area of 30% on the property. In order to build a building and have a parking lot, builders would need to use a permeable pavement such as pervious.
Most cities have regulations that state you cannot change the flow off of the property, which is why many choose to build retention ponds on site. By constructing a pervious parking area with an aggregate bed below the pervious pavement to store the water, the issue is better managed. The more water that is needed to store, the thicker the aggregate subgrade must be.
Following are the economic benefits of pervious concrete:
Low installation costs: Pervious concrete comes with low installation costs. After installing pavements of this concrete, there is no need of installing storm drains and underground piping.
Increases land utilizations: As this concrete also manages the stormwater, you do not require buying additional land to install large ponds and other filtering systems to retain stormwater.
Low life-cycle costs: This concrete is a sustainable material and has life expectancy similar to the regular concrete. Most of the parking areas if constructed properly may last for twenty to forty years.
These are the economic benefits provided by pervious concrete. In addition to all the economic factors, this concrete provides many environmental benefits. Besides controlling storm water, they reduce the heat in the atmosphere.
This concrete has a light color and open-cell structure because of which they do not absorb heat from the sun. As they do not absorb and store heat, they also do not radiate the heat back into the atmosphere, which reduces heating in the environment.
The open-cell structure of this concrete pavement allows the temperature of earth to remain cool. The light color also is useful from the energy-saving standpoint. As they are reflective, the requirement of lighting is reduced at the nighttime.