FISH WEIR TO FLOOD CONTROL: RECONSTRUCTION OF AN HISTORIC NEW ENGLAND DAM

摘要

The majority of the nearly 3,000 dams in Massachusetts were originally constructed during the industrial revolution and in some cases during colonial times for the purpose of providing hydropower. Many of these dams are currently in poor or unsafe condition. In some cases, dams are in such disrepair that partial rehabilitation is not practical and complete reconstruction is necessary. The Hemlock Gorge Spillway Dike is located along the Charles River within the Hemlock Gorge Reservation in Newton, Massachusetts. The Dike, along with the adjacent Metropolitan Circular Dam, is used by the Massachusetts Department of Conservation and Recreation (DCR) for the purpose of flood control, recreation, and environmental benefit. The Dike is within a listed historic district and is also an integral feature of a beloved State Reservation. The 1906 Dike is believed to have been just one of a series of structures in the same general location, with earlier structures including mill dams and Native American fish weirs. The 1906 Dike was recently found to be in poor to unsafe condition. Leakage was observed to flow directly through large voids in the concrete structure. The Dike was observed to have overtopped during flooding in 2010. Also, flow could no longer be managed at the Dike as the stop logs had been completely silted in and could not be removed. The objective of the rehabilitation design was to completely remove the existing Dike and construct a new Dike within the existing footprint that would improve the operability of the dam for flood control and meet current dam safety standards. The new Dike would also need to preserve the historical integrity of the site. To accommodate these goals, a new concrete gravity structure was designed. The total structural height of the Dike ultimately measured in at 24 feet, which was surprising because the hydraulic height was closer to 12 feet. A pre-design soil boring revealed bedrock to be much deeper than anticipated. As a result, post-tensioned anchors were included in the new design. The project was designed, permitted, and constructed on an accelerated schedule. The Dike was successfully brought into service in October 2012.