The George H. Nichols Multipurpose Dam is one often (10) dams, built between 1962 and 1987, in the Sudbury/Assabet/Concord (SoAsCo) Watershed. The Nichols Dam, which was constructed in 1970 in the Town of Westborough, Worcester County, Massachusetts, impounds flow from the Assabet River. The multi-purpose dam provides flood control and maintains a 380-acre pool for recreation. The contributing drainage area is 6.94 square miles with mixed land use, including forested uplands, open water and wetlands, agricultural, residential development, and industrial and commercial development. Since 1970, urban development upstream of the dam has increased the quantity of stormwater runoff, and predicted hydrologic conditions during design storm events now exceed US Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS) performance and safety standards under current and full build-out watershed conditions. Design of rehabilitation measures were developed and include:1.Relocation and widening of the existing auxiliary spillway;2.Articulated Concrete Block (ACB) protection along the spillway exit channel;3.Reinforced concrete side walls;4.Reinforced concrete cutoff wall at the crest;5.Toe drain replacement; 6.CIP Rehabilitation of the existing CMP drawdown pipe (pond drain); and 7.Extension of the existing earthen dam embankment.Design of rehabilitation measures was completed in August 2010. The project is currently under construction; anticipated to be complete in October 2011. The purpose of this paper is to present the design methodology, procedures, and lessons-learned during construction; particularly as it applies to the ACB.
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