CS6A - Concurrent Session 06A: Decade Dam Failures - Update on the 2005 Failure of Hadlock Pond Dam, Fort Ann, NY

Abstract Description: The Hadlock Pond Dam is located in Fort Ann, NY, approximately 6 miles east of Lake George. The dam was originally constructed circa 1896 as a timber crib structure approximately 850 ft in length. The dam was raised with embankment fill in 1933 and a new spillway was constructed in 1977. In 2004, a subsequent significant remedial project commenced to bring the dam into regulatory compliance. This work included a new staged auxiliary spillway system comprised of an ogee spillway, fuseplug spillway sections, and reconstruction of portions of the existing embankment. Work was completed in May 2005 and the dam began impounding water with the goal of achieving a full reservoir for the summer recreation season. The reconstructed dam had a structural height of approximately 30 feet and is regulated as a High Hazard structure. The dam subsequently breached during the evening of July 2, 2005. It caused approximately $10 million of damage downstream, but there were no casualties.

Clough Harbor & Associates was retained by the New York State Department of Environmental Conservation to perform a forensic evaluation on the cause of the failure. The evaluation examined six modes of failure considered plausible and concluded that the failure was attributable to internal erosion that developed along potential preferential pathways, most likely at the interface of old and new embankment fill. While this case study was previously presented during the Dam Safety 2015 conference, the current paper and presentation are intended to provide updates to the failure, including the legal ramifications which were not settled until 2017. The current effort also includes the performance of dam breach hydraulic modeling with a 2-Dimensional HEC-RAS model to see how well model results compared with the actual inundation and damage areas. In addition, a LifeSim analysis will be completed to assess how well the life loss and economic damage estimates from that application compare with the real world results.