Interpreting Water Control Manuals - Spillway Gate Regulation Schedule

The purpose of this post is to analyze and interpret a specific passage in a water control manual relating to the Spillway Gate Regulation Schedule.

It is important to understand that the interpretation of a specific passage within a water control manual has to be done with consideration of all passages within a water control manual along with the philosophy of reservoir operations.  I have developed a post detailing the philosophy of reservoir operations.  That post is located here:


The passage that will be analyzed in this post is as follows:


This passage directs the real-time reservoir operator to Plate 7-1 when the pool elevation is between 987.5 feet and 990.0 feet.  A portion of Plate 7-1 is shown below.


The portion of the statement regarding that the curves are to be used as a guide only can be subject to misinterpretation.  This statement acknowledges that there should not be an expectation that the real-time reservoir operator will always be making the releases shown on the curve.  This is not due to a high degree of flexibility that the real-time operator possesses, but rather the recognition that the event can have rapidly changing conditions which do not allow for complete and immediate adherence to the values provided in the curves.  

This should not be misinterpreted that the real-time reservoir operator can simply disregard the curves in favor of an alternative release schedule.  Decisions made by the operator are still based on the complete reading of the water control manual along with an understanding of the philosophy of reservoir operations.  

This statement also acknowledges that some discretion can be made by the real-time reservoir engineer.  For instance, in the example shown on the figure above, the combination of the pool elevation and the 2-hour computed inflow leads to a desired discharge of 112,000 cfs.  However, if it appears that the inflow has peaked or is near its peak and the rainfall forecasts are showing little to no future precipitation, it may be desirable to hold the releases at a lower level (if that lower level will also cause the pool to peak soon and at a safe level) to provide a better downstream result.  

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