For years, residents of Winchester, Mass., have enjoyed use of the town’s main athletic ground: Manchester Field. When they noticed that the field and adjacent neighborhoods were prone to flooding, engineering firm AECOM Environment came on board to find a solution.
After looking into the existing stormwater conditions, the engineers concluded that the system was undersized and could not collect and discharge even small-scale storm events. AECOM recommended upgrading the system for storms less than and including the 25-year and 24-hour storm.
The $1.2 million, two-phase project proposed the construction of an innovative, integrated stormwater management system, which incorporated underground detention chambers provided by CULTEC Inc.
Before installing the detention system in the basketball courts area during the first phase, the engineers had to solve a significant challenge. The existing drainage system flowed through a siphon that crossed the 48-in. diameter sewer main. The siphon had to be replaced to connect the drainage from the neighborhood streets into the system. The new siphon was installed approximately 10 ft into groundwater using pipe-jacking techniques, which required a significant amount of dewatering.
With the new siphon in place, contractor Green Acres Landscape and Construction began installing 1,356 chambers in three beds fed by two header lines. The system occupies 36,000 sq ft and provides 496,584 cu ft of storage.
Additionally, the footings for the basketball hoops extended 4 ft into the ground right above the chambers, limiting the available space for installation of the subsurface chambers.
The second-phase location has a greater separation to the groundwater, and the engineers selected a high-capacity, 32-in.-tall chamber. Its parameters allow fewer units to be used to achieve the desired storage volume.
The second system will be installed in the summer of 2011. It will offer 527,076 cu ft of storage and will be located under the teacher’s parking lot behind McCall Middle School. The design calls for 556 units arranged in two beds and fed by one header line.
The stormwater system upgrade is designed to reduce the surcharge of catch basins and manholes and the ensuing flooding of the field area. The detention systems play a key role by offering the necessary runoff storage and allowing the aboveground land to be used for the school’s athletic facilities.
Source: CULTEC Inc.