Promontory Underground Basin: Breaking Tradition

Promontory is coming to Overland Park and bringing exciting opportunities for the future of the city along with it. If you’re not familiar with the development, Promontory is slated to be a $97.5 million mixed-use redevelopment project that combines active lifestyle, leisure and retail into one. Developing in three phases, Phase 1 is well underway and will include 291 apartments and over 28,000 square feet of retail space along 89th Street and Metcalf Avenue in Overland Park, KS. One of the hallmarks of the project is the innovative underground detention basin. Through local partnerships, a solution was created to save approximately $1 million dollars and reduce the structural footprint by nearly 30%.

Creating a New Path

According to Carl Gerlach, Mayor of Overland Park, Promontory is already making waves. He shared with us that people stop by the site frequently to watch construction and find out what is going on. When asked how the project fit into the scope of Vision Metcalf, an initiative that “calls for higher density, mixed use and pedestrian-friendly development,” Gerlach stated,

“Promontory fulfills that emphasis to change from a single-use development to a project that appeals to all ages. Overland Park’s future depends upon developers willing to break from tradition and create a new path. Already the public has shown interest in Promontory, asking questions about what is occurring on site. We look forward to its completion and success.”

BHC RHODES has been involved since the beginning of the development in a variety of capacities including stormwater detention. One landmark of the development that deserves a closer look is the large underground detention basin. Flyover footage from Launch Development shows the progress of the structure.  The underground detention basin measures 374 feet x 105 feet, roughly the size of an American football field. At nine feet deep the structure has the capacity to hold 316,000 cubic feet of water during a rain event and has a release rate of 9.13 cubic feet per second. A very large and costly investment for the development, it’s interesting to consider the benefits of this type of structure over traditional piping.

Breaking From Tradition

Underground detention basins are structures designed to manage high volumes of stormwater runoff at a developed site. Underground detention systems are costlier than surface located stormwater management, but are a necessity in developed urban settings where land is limited. Based on the location of a development, underground detention basins are used as an alternative when there is not adequate space on the site to properly infiltrate the runoff or construct an above ground detention or retention basin. The underground variety is appealing in areas with a small footprint because it can collect a large amount of water quickly and then control the volume at which it drains into other waterways. This helps control flooding and erosion by using a restricted-flow drain and weir to control the output. Local design requirements and permissible construction materials often inform the decision to make a detention basin of this size and material. Common underground detention basins are smaller and use materials such as corrugated metal or plastic pipes to form underground chambers for the storage of stormwater.

Further Reading: Taking a deeper look at stormwater detention options 

For Promontory, pouring the structure into place helped Launch Development, Inc. save nearly $1 million dollars. It was a concept Launch initiated that BHC RHODES helped make a reality. Through partnering with Bob D. Campbell & Company, the structural design was created by Steve Carroll, which ultimately helped reduce the detention basin’s footprint by nearly 30% rather than using piping. According to Ryan Osborn, Project Manager at Launch Development. Inc., this easily seemed like the more economical choice to help solve a major upstream issue.

There are multiple benefits of using concrete for a basin of this size. These include the ability to hold more water, extend the life of the structure, and require less excavated land than pipes allow for. The current structure has multiple vents to air and four access points built-in for ongoing maintenance. During a rain event, water will backfill into the structure where it is held. From there the water is released into public storm lines at a controlled speed to prevent any flooding. Once completed, the detention basin will be covered by one of the development’s parking lots.

Want to stay up-to-date on the progress? Follow @PromontoryKC on Twitter for the latest!

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