To meet the storm water management requirements for a new addition to the Indian Woods Middle School in Shawnee Mission, Kan., an underground detention system was constructed. The original design called for three storm water treatment units to meet a local ordinance because the 16,000-sq-ft proposed building addition along with sidewalks exceeded the 5,000-sq-ft threshold outlined in the Overland Park (Kan.) municipal code. Also, the system had to meet regional environmental requirements.
Additionally, several area homes were identified in the Indian Creek Watershed Study as being subject to flooding. The municipal code requires storm water detention facilities to be constructed for projects that result in an increase in peak discharge from the site whenever downstream homes or habitable buildings are flooded in a 1% or larger frequent storm, when the homes and buildings would be flooded as a result of future development or when streets are subjected to flooding in excess of the city engineer's standards.
Indian Woods Middle School is part of the Shawnee Mission School District and serves some 624 students in grades seven and eight. The expansion was created due to the closing of another middle school, leading to an increase in Indian Wood's enrollment. Improvements included four new classrooms, a library and an auxiliary physical fitness area.
The final storm water management system measures 130 ft wide by 154 ft long, with 12 rows of 30-in.-diameter corrugated high-density polyethylene (HDPE) pipe from Advanced Drainage Systems Inc. (ADS). A total of 1,440 linear ft of the N-12 watertight HDPE pipe that meets ASTM Standard F2306 was used, along with 103 ft of watertight manifolds. It is designed to hold 7,600 cu ft (60,800 gal) of storm water at a rate of 1.37 cu ft per second. The detained storm water is released into the existing storm sewer system at a controlled rate to minimize the additional storm water burden imposed by the gymnasium addition, impervious roof and sidewalk areas.
“This entire system provides a technological advantage to hold water and trap debris,” said Jim Clemans, vice president of allied products, ADS. “All components are designed and manufactured to provide a long-life, low-maintenance and highly effective storm water management solution.”
Storm water enters an ADS Flexstorm inlet filter with a Nyloplast inline drain basin and exits through a submerged outlet chute located opposite to the direction of the rotating flow. Enhanced vortex separation is provided by forcing the rotating flow within the vessel to follow the longest path possible rather than guiding it directly from inlet to outlet.
Higher flows bypass the treatment chamber to prevent turbulence and washout of captured pollutants. An integral bypass chute conveys infrequent peak flows directly to the outlet chute, eliminating the expense of external bypass control structures. Floatables are diverted from the bypass chute into the treatment chamber.
