Underground detention relieves under-sized stormwater system

November 2011 » Web Exclusive » PROJECT CASE STUDY

Project
Manchester Field stormwater, Winchester, Mass.

Civil engineer

AECOM Environment

Product application

CULTEC Recharger low-profile chambers provide underground stormwater detention in an area of high groundwater.

For years, residents of Winchester, Mass., have enjoyed use of the town’s main athletic ground, Manchester Field. When they noticed that flooding occurred in the area of Manchester Field and the adjacent neighborhoods, 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 under-sized and could not collect and discharge even small-scale storm events. AECOM recommended upgrading the system to accommodate storms less than and including the 25-year, 24-hour storm.

The $1.2 million, two-phase project proposed construction of an integrated stormwater management system that incorporated underground detention chambers provided by CULTEC Inc. According to Jacob San Antonio, P.E., water resource engineer at AECOM who worked on the project, underground detention was the only suitable best management practice for this four-acre site.

“The site did not have enough space for an above-ground detention solution, so we went underground,” said San Antonio. “We designed CULTEC systems as detention galleys to attenuate peak discharge rates to prevent the existing system’s surcharges and increase storage when the Aberjona River level rises above the low ground areas.”

For the Manchester Field project in Winchester, Mass., CULTEC systems were designed as detention galleys to reduce peak rates of stormwater discharge to the Aberjona River.
Photo: CULTEC.

Before installing the detention system beneath an area of basketball courts during Phase I, engineers had to solve a significant challenge. The existing drainage system flowed through a siphon that crossed the 48-inch-diameter Massachusetts Water Resources Authority sewer main. The siphon had to be replaced to connect the drainage from the neighborhood streets into the detention system. The new siphon was installed approximately 10 feet into groundwater using pipe-jacking techniques, which required a significant amount of dewatering.

With the new siphon in place, contractor Green Acres Landscape & Construction began installing 1,356 CULTEC Recharger 150 HD chambers in three beds fed by two header lines. The system occupies 36,000 square feet and provides 496,584 cubic feet of storage.

“CULTEC was instrumental in helping us launch this project smoothly,” said Anthony Amaral, Jr., assistant project manager with Green Acres Landscape & Construction. “A representative helped us every step of the way, clarifying details and specifications, and answering questions about the system’s installation. He has also been onsite during the installation to assist in any way he can.”

Engineers selected the Recharger 150 HD, a lower-profile, 18.5-inch-tall unit, for Phase I to accommodate the high groundwater level. Additionally, the footings for basketball hoops extended 4 feet into the ground right above the chambers, limiting the available space for installation of the subsurface chambers.

Engineers used CULTEC’s Recharger 150 HD underground chamber to accommodate the high level of groundwater and basketball hoop footings extending 4 feet into the ground.
Photo: AECOM Environment

CULTEC manufactures nine chamber sizes ranging from 8.5 inches to 32 inches to accommodate site parameters. According to the company, 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.

In addition, CULTEC developed an in-line side portal manifold system — which eliminates the need for a conventional pipe header system — and a water quality unit for maintaining the chamber systems. CULTEC products meet H-25 wheel load requirements and currently are modeled in HydroCAD, Bentley Systems Inc.’s PondPack, Autodesk’s Autodesk Storm and Sanitary Analysis, and Streamline Technologies' ICPR.

Additionally, CULTEC said its products can contribute to U.S. Green Building Council LEED rating system credits, when the project is designed per LEED requirements.

The second-phase location has a greater separation to the groundwater, and engineers selected the Recharger V8, a high-capacity, 32-inch-tall chamber. Its parameters allow fewer units to be used to achieve the desired storage volume.

The second CULTEC system was to be installed during the summer of 2011. It will offer 527,076 cubic feet of storage and will be located under the teachers’ parking lot behind McCall Middle School. The design calls for 556 Recharger V8 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 Manchester 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.

This article was provided by CULTEC Inc.


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