More Capacity Please! Improvements to Boston's Historic Wachusett Reservoir Dam

The Wachusett Dam stands as one of the most impressive structures built during the early years of the "golden era" of water supply dams (1895 - 1945), and still remains the critical water supply reservoir for the greater metropolitan Boston area. Advances in hydrologic methods helped engineers identify deficiencies in existing spillway capacity under the design flood. The original designers (including the estimable John Freeman and Frederic Stearns) could have never imagined that the revised peak Spillway Design Flood would increase by 230 percent over the original 1903 design estimate. Hydraulic profile simulations in the spillway discharge channel revealed serious flow restrictions which could cause weir submergence and threaten the integrity of this high hazard dam and 10,000 foot long earthen dike. This case study presents the unique history of this 115 high, stone masonry dam and takes us through the engineering analysis and alternatives studies employed by the design team, including the Massachusetts Water Resources Authority (owner/operator), resulting in the construction of a new auxiliary spillway channel and improved operational flexibility through the installation of a 100 foot long, 5 foot high stainless steel, automated bottom hinged crest gate. The project created challenges in efficiently and effectively integrating 21st century engineering techniques into the impressive stone work architecture of this 100 year old structure. These $4 million dam safety improvements, completed in 2008, now prepare this key piece of civil infrastructure for another century of service for the Boston region. 17 pp., 16 figures, 15 references.