EXPLANATION OF RESERVOIR OPERATING CURVES IN PROPOSED DRBC RULEMAKING TO IMPLEMENT THE DECREE PARTIES' FLEXIBLE FLOW MANAGEMENT PROGRAM (FFMP) AGREEMENT

The following example is provided to explain how releases are made from the Cannonsville, Pepacton, and Neversink reservoirs under the FFMP. The analysis illustrated by this example will be undertaken each day.

The assumptions used in this hypothetical example for January 1 are as follows:

• Combined storage in the three reservoirs is 245.828 billion gallons (bg) or 90.8% of usable capacity.
• The individual reservoir usable storage numbers are: Neversink 26.701 bg (76.4% of usable capacity), Pepacton 124.516 bg (88.8% of usable capacity), and Cannonsville 94.611 bg (98.9% of usable capacity).
• There is snow pack in each of the three reservoir watersheds with the following water equivalents: Neversink 8 bg, Pepacton 12 bg, and Cannonsville 2 bg.
  

When snow pack exists in the reservoir watersheds during the October 1 through April 30 period, 50 percent of the water equivalent in the snow pack will be included in the determination of combined and individual usable storage.

In this example, the combined storage in the three reservoirs was 245.828 bg or 90.8% of usable capacity. Combined snow pack in the three reservoir watersheds had a water equivalency of 22 bg; 50% of this number, or 11 bg, is added to 245.828 bg for a total of 256.828 bg or 94.8% of usable capacity (shown in figure 1 above). This storage level falls within the L1 zone (i.e., above the green curve in figure 1).

In order to find out how much water would be released under this program from each of the three reservoirs, one would refer to figure 2 (below). The daily release amount will vary by reservoir depending on how much water is being stored in that reservoir on a particular day, again expressed as a percentage of capacity.  In this hypothetical example, the percentage of usable storage in Neversink, Pepacton, and Cannonsville reservoirs is 76.4%, 88.8%, and 98.9%, respectively. When we add 50% of the snow pack water equivalencies in each of the reservoir watersheds (Neversink 4 bg, Pepacton 6 bg, and Cannonsville 1 bg), the adjusted percentage of usable storage in Neversink, Pepacton, and Cannonsville is 87.9%, 93.1%, and 99.9%, respectively. These percentages are depicted as black dots in figure 2. Based on these adjusted storage percentages, figure 2 tells us that Neversink Reservoir falls in the L1-c zone for that date (i.e., below the yellow curve), Pepacton Reservoir falls in the L1-b zone (i.e., between the red and yellow curves), and Cannonsville Reservoir falls in the L1-a zone (i.e., above the red curve). 

Once the release level (L1-a, L1-b or L1-c) has been determined, Table 3A provides the numerical release rate for each reservoir.  Since January 1 falls in the winter period of December 1 - March 31, the L1-a release rate for Cannonsville Reservoir is 1,500 cubic feet per second (cfs), the L1-b release rate for Pepacton Reservoir is 185 cfs, and the L1-c release rate for Neversink Reservoir is 65 cfs. Since 1 cfs = 646,317 gallons per day, the following reservoir releases would be made under this hypothetical example on January 1: approximately 969 million gallons from Cannonsville, 120 million gallons from Pepacton, and 42 million gallons from Neversink.

Please note: If the combined discharge resulting from uncontrolled spills when the reservoirs are over 100% capacity and controlled Zone L-1 releases appearing in Table 3 exceed 4,200 cfs from Cannonsville, 2,400 cfs from Pepacton, and 3,400 cfs from Neversink, then the controlled Zone L-1 releases will be decreased or eliminated in order to minimize impacts immediately downstream of the reservoirs.

In addition, Zone L1 releases will not be made from a reservoir when the river stage at Hale Eddy below Cannonsville or Fishs Eddy below Pepacton is within two feet of flood stage, or forecast to be within two feet of flood stage within 48 hours of a planned spill mitigation release. Similarly, Zone L1 releases will not be made from Neversink Reservoir when the river stage at Bridgeville is within one foot of flood stage, or forecast to be within one foot of flood stage within 48 hours of a planned spill mitigation release.

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