Lynden Pindling International Airport (LPIA), formerly known as Nassau International Airport, is the largest airport in the Bahamas and the largest international gateway into the country. With two runways, more than 30 gates, and 482,000 square feet of terminal space, the airport sees more than three million passengers per year.
Named after Sir Lynden Pindling, the first Prime Minister of the Commonwealth of the Bahamas, the airport sits just west of Nassau and a short drive from some of the best resorts and hotels in the world. LPIA aims in the near future to accommodate up to five million passengers annually and become one of the top world-class airports in North America. More than 80% of passengers are visitors from the United States.
The airport has completed two phases of a three-phase, $410 million expansion and renovation project that will upgrade the terminal buildings and provide for airport growth and future capacity. Approximately 110 acres of the airport territory were under construction or renovation, including about 60 acres of airside and 50 acres of landside terminal areas. Landside improvements included new and expanded road access, parking facilities, revenue control systems, rental car and airport support buildings, and new utilities infrastructure. The airside improvements included new and reconstructed aircraft aprons, passenger piers, jet bridges, and infrastructure.
While developing the new design for the space, engineers from Stantec Architecture Ltd. faced a number of challenges with the previous stormwater management system. In addition to an exceptionally flat terrain and high level of groundwater, the system did not have any outlets and kept runoff onsite after a storm. This runoff was stored in drainage swales around the existing parking areas until it evaporated or infiltrated, causing the site to flood and impacting surrounding roads and parking areas. The system also included several deep drainage wells, which reintroduced stormwater runoff into the ground approximately 150 feet below the surface.
Because the expansion of the landside parking lot would displace the existing stormwater retention areas, the site required an addition of substantial capacity to store and retain stormwater runoff. Since more storage capacity was needed and there was less area to store runoff without releasing water offsite, the engineers decided that the most practical solution was to use existing real estate and install a subsurface system. New paved parking facilities would be conveniently placed above the system.
Per the Bahamas’ stormwater regulations, the new stormwater system had to be able to handle at least 6 inches of runoff over the entire drainage area or a rain event of 1-inch intensity for a duration of six hours.
Stantec engineers chose to divide the new stormwater management design into three phases. They decided that, given the site constrictions and the regulation requirements, Cultec’s Recharger 180 HD model would provide maximum storage and best satisfy the needs of the project. The unit is 36 inches wide by 20.5 inches high and has a chamber storage capacity of 3.45 cubic feet per linear foot. In light of the high groundwater, it was the best fit for the site and its storage capacity met the Bahamas’ stormwater regulations.
“Cultec offers a variety of chamber sizes and, due to the restrictive nature of this site, we needed one that would maximize the volume despite the limited vertical and horizontal area,” says Pat Clark, senior civil engineer with Stantec. “The Recharger 180 HD gave us this option, and it came equipped with feed connectors, a unique feature, to balance the large systems.”
Cultec chambers can be used as subsurface retention or detention systems and as replacements for ponds, concrete structures, or pipe and stone installations. The company manufactures several chamber sizes ranging from 8.5 to 48 inches to accommodate almost any site parameter. The chambers’ perforated sidewalls and fully open bottoms promote maximum infiltration capability and allow for the transfer of high volumes of water at a low velocity. The units can be installed singularly or in series in single- or multi-layer beds.
A typical underground stormwater system includes the inlet, water-quality filter, conveyance device, and storage chambers. Runoff enters a collective device, generally from a single inlet structure, and passes through a maintenance filter. The filter consists of an HDPE charger with a series of pass-through filter frames to remove debris and silt from the stormwater runoff. The stormwater moves into a manifold system, which is a combination of interlocking plastic chamber sections that store the stormwater until it is either infiltrated or dispelled.
Developed areas with impervious surfaces such as pavement prevent stormwater from naturally soaking into the ground, and runoff can cause flooding, erosion, or infrastructure damage. Implementing a subsurface stormwater management system eliminates these potential complications. When water is handled underground, space for further development such as parking lots, additional buildings, or enhanced landscaping remains.
Installing a subsurface stormwater management system allows for maximum use of the land area and reduces maintenance costs and liability issues on most sites, compared to using aboveground water storage systems. A subsurface system also offers the added benefit of eliminating accessible standing water for breeding insects such as mosquitoes, which can carry the West Nile Virus. Subsurface infiltration systems are specifically designed to address economic concerns, reduce environmental impact, and satisfy EPA requirements. They typically offer a cost-effective installation while providing an environmentally effective stormwater management solution.
As for the systems themselves, most components are relatively lightweight, require less heavy equipment, and are often stackable and easy to ship. The systems also tend to be made with interlocking connections to allow for a quick and straightforward installation process.
To analyze and design the stormwater management system for LPIA, engineers used HydroCAD modeling software. Since the program already included the Recharger 180 HD parameters, they needed only to specify the layers of stone above and below the chambers for the first two systems. Although the stone had to be transported to the Bahamas, Cultec’s systems generally use less stone than other system on the market, reducing overall installation expenses.
Phase two of the LPIA expansion included the installation of two additional Cultec underground stormwater systems in the airport’s landside parking lot areas. These systems join the stormwater chambers that were installed under the paved passenger parking lots during phase one of the project.
The second phase of the LPIA project mirrored the first in that it included the installation of two separate systems made up of four storage beds under the new parking areas. Each phase included approximately 1,100 Recharger 180 HD chambers, which provide about 40,000 cubic feet of underground storage and occupy an area of 23,500 square feet.
To provide additional capacity beyond the Cultec underground chambers, the new system included oversized pipes connecting the systems with little or no slope or pitch. Several small open swales and ponding areas have also been added throughout the site, and all are interconnected with pipes and culverts. Dewatering issues were addressed by installing 12 150-foot-deep drainage wells throughout the site to discharge the runoff deep into the ground. These wells will allow the system to dewater during and between storms and add capacity to handle some of the smaller storms prior to flooding the storage chambers.
At Lynden Pindling International Airport, the Cultec systems were designed to work together with other stormwater management practices such as the open swales, retention ponds, and deep drainage wells to capture and store large amounts of runoff onsite. According to Clark, the underground systems became an ideal solution because they solved the challenges of flat terrain and high-level groundwater and allowed engineers to use the space above the systems for parking areas.