Projects
Swinging Bridge Dam (P-10482) Dam Safety Remediation Project
Aquatic Resource Protection at Mirant Projects
During the winter and early spring of 2006/2007, the latter stages of critical dam repair work at Swinging Bridge Dam will necessitate continued water level reductions and variations at Swinging Bridge Reservoir, Mongaup Falls Reservoir, and Rio Reservoir. During this period, fluctuations in reservoir levels, and in flow releases to the Mongaup River, will be necessary to ensure Swinging Bridge Dam’s integrity and to protect public safety.
Since the reservoir drawdowns were first initiated in late spring 2005, no negative effects to reservoir fishes have been reported. The slow drawdown rates that were used likely allowed fish to escape areas of shallow-water entrapment. There were concerns during the summers of 2005 and 2006 that the emergency work would impact water quality downstream in the Mongaup River, where wild trout and other fishes are found, through flow reductions, increases in temperature and decreases in dissolved oxygen. Fortunately, Mirant was able to provide adequate flows for fish protection as the emergency work progressed.
Currently, significant reductions in flow releases from Swinging Bridge Dam have been necessary to complete some of the final repairs there. All reductions in flow releases have been made incrementally (“ramping rates”) to decrease the chances of stranding fish in shallow areas. However, flow reductions at this time of year may impact trout redds (spawning areas) and eggs that may be located in shallower areas, as well as some bottom-oriented fishes and benthic organisms, such as immature insects.
In the coming weeks, the refilling of Swinging Bridge Reservoir may begin. Refilling would likely take several months, and its scheduling and progress would be dependent upon completion of considerable work and the need for constant inspections of the dam structure. During the refilling process, minimum flows released from Swinging Bridge Dam may be reduced or even curtailed for some periods of time. Effects to minimum flows would be dictated by the need to refill the reservoir at a steady rate for safety monitoring purposes, and the availability of natural inflows. High natural inflows into the Mongaup system above the reservoir could allow refilling at the required rates without affecting flow releases from the reservoir. Low seasonal inflows could require flow reductions during the refill period. As alluded to earlier, impacts from reduced flows during late winter and early spring could affect trout redds and eggs, and possibly, to a lesser degree due to their limited mobility, trout fry and juveniles, as well as to some bottom-oriented fishes and benthic organisms, such as immature insects.
Conversely, an advantage to the refilling of Swinging Bridge beginning in the coming weeks would be that the reservoir could be at normal levels by summer 2007, allowing normal releases into downstream river reaches and reduced chances for impacts to river water quality through low flows, elevated temperatures, or low dissolved oxygen.
Mirant is communicating with the resource agencies regarding impacts to aquatic resources during any periods of reduced flows and any practicable ways that such impacts could be reduced, such as the use of ramping rates. Mirant has also worked, at the Commission’s direction, to ensure that all of its temperature and dissolved oxygen monitoring equipment is ready for the next monitoring season, beginning June 1, 2007.
Access to Swinging Bridge, Mongaup Falls, and Rio reservoirs, and downstream areas of the Mongaup River, is discussed in the Commission’s detailed Fact Sheet on recreation and public access at Mirant Projects.
Mirant has established a Toll Free phone number for communication with the public. The number is: 1-888-326-3389. If you leave questions or comments at this number, along with your name and telephone number, someone will get back to you. The contact person at the Commission regarding aquatic resources is B. Peter Yarrington, in Washington, D.C., who may be reached at 202-502-6129.
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Contact Information
Charles Goggins
Regional Engineer,
Division of Dam Safety and Inspections,
New York Regional Office
Telephone: 212-273-5910
Mirant:
Toll-free:1-888-326-3389
FERC:
B. Peter Yarrington
Telephone: 202-502-6129 |
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