Dam Removal in New York - A Case Study in Satisfying Dam Safety and Restoration Needs

The century-old Lower Melzingah Dam was no longer needed for its original water supply purpose, having been replaced by a larger reservoir impounded just upstream. As a result, the embankment dam fell into a state of some disrepair and failed to meet New York State Dam Safety standards. The cost of rehabilitation could not be justified and the decision was made to remove the dam and its associated hazard (a High Hazard Dam in New York).
Initially, a breach of the embankment was designed to convey floods without impounding water in the former reservoir to excessive depths. But as the permitting process began, it became clear that there were more than Dam Safety requirements to be satisfied. NYSDEC regulators expressed concerns with the potential release of sediments. The U.S. Army Corps of Engineers concluded that the removal activity was subject to Section 404 (Clean Water Act) requirements.
The solution to these regulatory requirements was the design of channel restoration and vegetative stabilization in the former reservoir. Restoration of a stream channel through the reservoir pool area enabled the project to use Nationwide Permit 27 for Stream Restoration, providing mitigation on the site rather than elsewhere. The restoration included a channel design incorporating natural stream channel design principles and riparian plantings, while the balance of the reservoir area was stabilized with selected grasses and other native species. Time consuming investigations and discussions around the options of sediment excavation and removal or controlled release of sediment employed in other dam removals were avoided. Sediment controls and bypass piping were used to prevent unwanted sediment releases during construction.