(A Report Prepared by Dave Smail, GSLA Vice-President and Chair of the GSLA Water Level Committee)
On May 13, 2018, we find the Great Sacandaga Lake level at 767.5 feet, which is approximately 4 inches below the past 88-year average lake level for May 13th and 17 inches above the Target Elevation. The lake level is in good shape for the beginning of the boating season; however, there has been several reports that docks have become adrift.
This raises the question of why the Hudson River Black River Regulating District (HRBRRD) is following the historic water level curve instead of the Target Elevation curve. Most people believe the Regulating District makes releases from the lake to maintain the lake level at or near the Settlement Target Elevation. This is only partly true. In fact, the license (Federal Energy Regulating Commission – Offer of Settlement) under which the HRBRRD operates the Conklingville Dam, requires the district to make releases from the lake to maintain minimum instantaneous flow on the Sacandaga River below the Stewarts Bridge Dam and the Hudson River below the confluence of the Sacandaga and Hudson Rivers. In addition, the Offer of Settlement sets minimum and maximum daily average flows for the Sacandaga River below the Stewarts Bridge Dam and the Hudson River below the confluence of the Sacandaga and Hudson Rivers. Each of these limits varies depending upon the current lake level. Year-to-Date curve for the Great Sacandaga Lake Surface Elevations below shows that the lake level has been as much as seven feet above the Target Elevation.
Multiple Water Storage Requirements of the Offer of Settlement: Aggressive Water Storage is the simple answer to the question of why the Hudson River Black River Regulating District (HRBRRD) is not following the Target Elevation curve. During the development of the Offer of Settlement there were approximately twenty signers of the settlement, each who had a paddle in the water trying to determine how the lake would be controlled. The hydro companies pushed for what is called “aggressive water storage”. Each of the hydro projects downstream of the Conklingville Dam are known as “run-of-river” and do not have the capability of storing water. The projects are not permitted to allow the water level upstream to vary by more than one foot. For example the Curtis Palmer Hydroelectric Project in Corinth has a total of seven water turbine generators whose combined electrical capacity is approximately 60 megawatts. At full power the combined maximum flow through the project is approximately 8,000 cubic feet per second. As flows on the Hudson River varies, the operators varies the number of turbines to match the river flow. When flows on the Hudson River exceed the 8,000 CFS the excess flow bypasses the turbines and the energy is loss. The hydro projects at Sherman Island and Spier Falls have a maximum hydraulic limit of approximately 9,000 CFS. The aggressive water storage requirements establishes limits on the releases from the Conklingville Dam to minimize the amount of water that needs to be bypassed by the downstream hydro projects. To determine the required daily release from the lake the Regulating District must first determine the minimum and maximum daily average flow limits on the Hudson River below the confluence of the Sacandaga River based upon the current lake level and where the lake is compared to the operating curves and a set of limits that are established in a set of a half dozen tables within the Offer of Settlement. For example I have included one of these tables.
Table F: Targeted Maximum Hudson River Below E. J. West
Great Sacandaga Level Maximum Average Daily Flow Target Below E.J. West (CFS)
735.00 – 745.00 2,000
755.01 – 769.00 8,000
776.0 and above 32,000
Note: for those GSL elevations that are not given as a range, the maximum allowed flow should be linearly interpolated.
To determine the maximum average daily release from the lake, the Regulating District must first estimate the average daily flow on the Hudson River upstream of the confluence. That value is subtracted from the smaller limit that is established from Table E or Table F. For example, if the Regulating District estimates that the average daily flow on the Hudson River upstream of the confluence is slightly less than 6,000 CFS and at an elevation of 755.5 feet, the maximum average flow below the confluence is limited to 8,000 CFS the average daily release would be limited to 2,000 CFS. When operating the E. J. West Hydro Project at Conklingville Dam releases approximately 4,000 CFS. To accomplish the average of 2,000 CFS the project would be operated for 12 hours. You should note that the aggressive water storage establishes limits on lake releases that limits flow on the Hudson River in Corinth that should not exceed the Curtis Palmer hydraulic limit if the Great Sacandaga Lake Level is less than 769 feet unless the flow upstream of the confluence exceeds 8,000 CFS.
The Regulating District must also establish the minimum instantaneous and minimum daily average flows on both the Sacandaga and Hudson Rivers using similar methods and tables. The scheduled daily release must be between the minimum and maximum release. For lake levels above the Target Elevation the Regulating District schedules a release near the maximum. If the lake level is below the Target Elevation, the minimum release is scheduled. Note there has been no discussion about the inflow into the lake and the Offer of Settlement technical requirements does not address it. If the release exceeds the inflow the lake level will drop and will go up if the release in less than the inflow.
Does the Great Sacandaga Lake have sufficient storage capacity to prevent flooding during the spring runoff?: The current flow on the Hudson River above the confluence is 5010 CFS which is slightly below the historical average of 5400 CFS. For the past week the flows within the watershed has been more than double the historical average. As a result of the high flows, the Regulating District has minimized the releases from the lake and the lake level increased by approximately 1.5 feet. On May 11th flows on the Hudson River above the confluence decreased below 6700 CFS and the Regulating District was able to increase releases from the lake and the lake level has stabilized. The Regulating District estimates that the flow on the Hudson River will continue to decrease and is expecting to be able to increase the daily releases and slowly bring the lake level closer to the Target Elevation. Unless we have a significant increase in precipitation the lake has sufficient storage capacity to prevent downstream flooding.
The Target Elevation for June 1st is 768 feet. I estimate the level will be near the Target Elevation for the beginning of the boating season.