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Time is Running Out
Final Dam Design Must Incorporate Improvements
DCC, Inc. urges Gilboa Dam improvements at October 16th Schoharie County Board of Supervisor's meeting.
The final design for the rehabilitation of the Gilboa Dam will soon be complete. It would appear that scant consideration has been given by the New York City Department of Environmental Protection and their engineering firm, Gannett Fleming, to requests made by the public, in regard to the rehabilitation design: 1) the addition of a passive, low-cost spillway Crest Wall; 2) Conservation Releases; and 3) Flood Mitigation. These modifications to the Gilboa Dam, requested by the Schoharie County Board of Supervisors, should have been a priority. Using computer modeling for the analysis of the potential for flood mitigation and the results of such testing, should have been made public, along with any reasons for objection to a passive masonry Crest Wall. Conservation releases from the Schoharie Reservoir should be made on a continuous basis during times of non-spillage of the Gilboa Dam. This minimal release of water ranging from 50-75 cubic feet per second (cfs) would help restore the Schoharie Creek downstream to some semblance of its former natural state. The amount of this release can vary between 50-75 cfs depending on the amount of water flowing in from the Platterkill, the first tributary to the Schoharie Creek, north of the Gilboa Dam.
What is needed is a more integrated vision of the place of the dam in the watershed. This sort of integrated watershed management is exactly the focus of the emerging Mohawk Basin Management Plan issued in draft form, summer of 2009, by New York State Department of Environmental Conservation. The document laying out the agenda for the upcoming annual meeting and conference of the United State Society of Dams, April 2010, addresses many of the very issues the public has raised since we became aware of the problems at the Gilboa Dam, 4 years ago, October of 2005.
The newly emerging theme of the United States Society of Dams is a new 21st century approach to reservoir and dam management. "The 2010 US Society of Dams Conference theme is 'Collaborative Management of Integrated Watersheds'. The dams, reservoirs, powerhouses, levee and canal systems are sources of reliable green power, flood control, municipal water supply, food production, efficient transportation and public recreation. ...The various interests and segments of today's society can no longer act independently. We must optimize, enhance and integrate water resource developments because opportunities for new locations are limited. Collaborative skills are vital to the introduction of new uses and/or new users for existing water resources infrastructure. Projects may be structural, non-structural or a combination and include non-traditional features". Gannett Fleming, the lead engineering firm for the NYCity DEP in the rehabilitation plan at Gilboa, is a sustaining member of the US Society of Dams and hopefully would adopt this mission statement of the US Society of Dams. Thus, it has been both frustrating and perplexing to have observed, over the last 4 years, the lack of serious consideration given by the NYCity DEP and its engineering firm, Gannett Fleming, for a passive, low cost, spillway Crest Wall. The NYCity DEP has not responded to requests for an analysis of the benefits of a passive Crest Wall addition to the Gilboa Dam, made repeatedly since the summer of 2008.
The second matter of concern is that there appears to be no protocol for the operation of the Obermeyer Gates, although this was the plan expressly stated by former NYCity DEP, Commissioner Emily Lloyd to the Schoharie County Board of Supervisors. The Obermeyer Gates will be installed in the 220' long x 5.5' deep notch on the western side of the 1324' long spillway of the Gilboa Dam by December, 2009. We know from 4 years of experience that the "notch" can spill up to 8600 cfs or 641,088 gallons per second of water before the spillway is “topped” and the reservoir overflows. The “notch” has shown its worth by attenuating or lengthening the time it takes the Schoharie Reservoir to fill and spill with full force over the entire spillway. During this working interval, the notch is spilling water from the reservoir and storms commonly pass across the watershed before the reservoir fills to crest elevation of 1130' and thus flow, through the dam, never exceeds 8600 cfs. Attenuation is beneficial to those residing downstream of the Gilboa Dam, however, we note that operations of the Obermeyer Gates may not be straight forward in terms of operational procedure. The Obermeyer Gates will enable the NY City DEP to operate the Schoharie Reservoir at full pool elevation of 1130' for which it was initially designed and add 2 billion gallons of extra storage capacity. A key point is that during the last 4 years, the Schoharie Reservoir was able to meet both its water supply requirements to the Ashokan Reservoir and its cold water mandates to the Esopus Creek while operating at “notch” level elevation 1124.5'.
Prior to the installation of the Obermeyer Gates, a protocol should be in place that establishes when they should be lowered; pre-emptively before a major storm event. This plan should be developed by a Joint Task Force for Operation of the Obermeyer Gates at the Gilboa Dam comprising NYCity DEP, NYState DEC, the United State Geological Survey (USGS), the National Weather Service (NWS), Schoharie County Board of Supervisors and other appropriate entities. This protocol would include automatic trigger points for the lowering of the Obermeyer Gate system, thus avoiding any danger associated with the failure to lower the gates in a timely manner, resulting in an additional 8600 cfs which would exacerbate an existing flood. As the gates will likely be raised during most of the hurricane season, this is of special importance to the people residing below the Gilboa Dam. If these gates were to fail during a hurricane induced flood, the results would be catastrophic. Dropping the gates in the middle of a storm would be nearly as bad as having them fail.
We strongly suggest that the NYCity DEP heed the recommendation of the US Society of Dams, and anticipate the forthcoming watershed management advocated by the New York State Department of Environmental Conservation. We need the rehabilitation of the Gilboa Dam to be more carefully considered in the context of synergy in the entire watershed. New York City Department of Environmental Protection should: 1) develop a program of collaborative management of the Obermeyer Gates and the Low Level Outlet; 2) install a passive masonry spillway Crest Wall for flood mitigation; and 3) provide a continuous 50-75 cfs conservation release downstream from the Schoharie Reservoir, for agricultural, environmental and recreational purposes. All three of these key requests supported by the Schoharie County Board of Supervisors and Dam Concerned Citizens, Inc. can be achieved without impeding their mandate of providing adequate water downstate via the Shandaken Tunnel as mandated by SPDES permit #NY-0268151.
We are pleased to note that Gannett Fleming is a sustaining member of the US Society of Dams and hope that they urge the NYCity DEP to support the philosophy of the US Society of Dams. The time for development of these procedures is now.
What Does New York City say? "It is fair to say that the City hasn't always been the best neighbors...Over the long term...we will be committed to...a complete reconstruction of the Gilboa Dam, finally one that will provide mechanisms to ensure that there really is flood control including gates and using other mechanisms like creating voids to ensure that we really have the capacity to control floods." The response by New York City to these reasonable, low-cost recommendations will be the test of whether their stated commitment of flood mitigation is sincere, or just empty rhetoric.