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Restoring a Sandy Basin with Articulating Concrete Block

Flood control is of great concern for many communities. In Contra Costa County, articulating concrete blocks were integral in the large Upper Sand Creek Basin Restoration Project. The basin works in conjunction with other facilities in the watershed to temporarily hold floodwaters waters from an extreme rainstorm and release them more slowly downstream. This significantly reduces the flood risk for Antioch, Brentwood and Oakley residents living downstream along Sand Creek and Marsh Creek.

The project expanded the basin, built an 1800-foot-long dam, restored Sand Creek, created 10-acres of wetlands inside the basin, and installed a trash capture device to help clean up the creek. It is a major part of the Regional Flood Protection plan as it is designed to weather the 100-year storm. The restoration portion required the use of a hard armoring systems to prevent severe soil erosion, the County selected articulating concrete block mats for the important project.

Open Cell Blocks Provide Protection from the Flood

The Upper Sand Creek is on Deer Valley Road in Antioch, CA. The basin is about 3 miles south of Highway 580 in Contra Costa County. The project required  102,000 sf  (9476.11008 sq. meters) of concrete block that were manufactured locally in Tracy, California.

Open cell blocks were selected and manufactured with dry-cast concrete to meet ASTM D6684, Standard Specification for Materials and Manufacture of Articulating Concrete Block (ACB) Revetment Systems. The open cell blocks were laced in mats 12 to 40 ft long in the plant and shipped to the job site on flatbed trucks. A total of 362 mats were necessary for the project.

The installation of the mats was performed with a crane, using a Spreader Bar (see picture). The site was graded and the mats were set into place over a geotextile and gravel layer by the contractor Top Grade. The installation and details followed industry recommendations that can be found on the TEK 11-13.

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Figure 1. Typical project section showing the geotextile, gravel and ACB mat.

Top Grade installed the 362 mats on the project. The mats ranged in length from 12 feet to 40 feet long. An anchor trench was used to secure the mats following the plans.

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Figure 2. Termination trench detail

After the mats were installed, a 6 inch (15 cm) layer of top soil was placed on the ACB mats and hydroseeded to vegetate the emergency spillway.

The project was completed in fall 2013. Two years later, the basin has been fully covered with grass with its rolling hills disguising the concrete infrastructure underneath.

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Project Owner: Contra Costa County

Designer: GEI Consultants – Oakland, CA

Contractor: Top Grade Construction

ACB Producer: Basalite

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