When Lynden Pindling International Airport in the Bahamas began a three-phase $400 million expansion and renovation, Stantec engineers came on board to design the airport’s new stormwater management systems. The airport presented significant challenges for stormwater management. The large site featured an exceptionally flat terrain and a high groundwater level — about 6 feet below the finished grade and about 3 feet below the existing ground. The site offered little opportunity for infiltration or for conveying stormwater in piped systems.
For the airport’s landside areas, the engineers found their solution in two underground stormwater systems. The CULTEC Recharger 180 HD unit is 36 inches wide by 20.5 inches high, with a chamber storage capacity of 3.45 cubic feet per linear foot. It provided the largest storage volume and was the best fit in the given depth-restriction scenario.
“CULTEC allowed us to select from nine chamber sizes to accommodate the flat topography and high groundwater, solving our onsite issues,” said Stantec Project Engineer Patrick Clark, who designed the landside stormwater systems.
Designed with HydroCAD modeling software, the stormwater systems can 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, as required by the Bahamas’ stormwater regulations. HydroCAD already included the Recharger 180 HD parameters, so the engineers only needed to specify the 6-inch layers of backfill stone above and below the chambers for both systems.
CULTEC’s chambers have perforated sidewalls and fully open bottoms to 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.
The two specified CULTEC systems offered a combined 42,068 cubic feet of storage. The storage volume was about 35.37 cubic feet per installed chamber, including the storage capacity of the stone. While the systems function independently to distribute and balance stormwater runoff, they are also interconnected in the event that either system reaches capacity or overflows through the outlet control structure.
Moreover, the stormwater chamber systems are connected to several open swales and retention ponds distributed throughout the site to allow for excess storage capacity. The open detention ponds are drained with deep drainage wells for rapid dewatering and provide for infiltration and evaporation.
The use of underground stormwater systems helped solve yet another project challenge: The hard durable rock needed for the installation would have to be imported to the Bahamas. According to CULTEC’s Vice President Fred Dotson, the company’s systems use less stone than other comparable systems on the market, lowering the overall installation costs.
Both CULTEC systems were installed using the company’s internal manifold, which allows manifolding to take place at any point within the stormwater system, thereby condensing the system while decreasing the required footprint. The custom manifold allowed for maximum design flexibility and eliminated the need for costly fabricated pipe manifolds.
According to Clark, the advantages of the internal manifold capability contributed to the engineers’ decision to select CULTEC systems for the project. The underground systems not only solved the issues of high-level groundwater and flat terrain but also permitted the use of space above the systems for parking areas, he noted.
CULTEC chambers meet H-25 wheel load requirements, the company said, and are currently modeled in HydroCAD, Bentley Systems, Inc.’s PondPack, BOSS International's StormNET, and Streamline Technologies' ICPR.
This article was contributed by CULTEC.