ANSWER TO U.S. CORPS OF ENGINEERS
CONCERN NUMBER 2

Reservoir operation required with this
plan would also likely aggravate
downstream bank caving.

    In 1997, the Corps issued a plan to regulate the reservoir to reduce downstream bank caving. This plan, actually a list of parameters, was implemented during a January 1999 minor flood with the result that the reservoir was depleted to its lowest level in over 11 years. This happened because the parameters conflicted with each other and people implementing the plan did not know what to do. One person with the Corps must have understood how to properly do this. He contributed parameter #16 on page 22 of the plan. In a minor flood, you must initiate regulation for bank caving when the reservoir has been prereleased to its minimum pool and you must control downstream flow with the reservoir rising.

Once everyone understands this, bank caving procedures will work well and they will actually complement efforts to prevent damage in major floods by requiring the people regulating the reservoir to learn how to prerelease in advance of minor storms. These storms could turn into major storms. Regulating the reservoir to minimize flooding during major storms does not conflict with bank caving procedures. The only difference is that the lake will be at extreme heights at the end of a major storm and regulation for bank caving will occur with the reservoir falling.

The following is a summary of the parameters used for the optimized alternative. Pool limits are shown in Figure 19:

1.   Winter Pool Stage = 296.0
2.   Winter Pool Stage Upper Limit = 296.4
3.   Winter Pool Stage Bank Caving Lower Limit = 295.8 until April 1, increasing gradually to 296.0 on May
4.   Winter Pool Stage Prerelease Lower Limit = 295.0 (292.0 for extreme events)
5.   Recreation Pool Stage = 297.4
6.   Recreation Pool Stage Upper Limit = 297.7
7.   Recreation Pool Stage Lower Limit for Bank Caving = ranges from 297.4 on June 1st to 296.9 on November 1st.
8.   Recreation Pool Stage Prerelease Lower Limit = 296.0 (292.0 for extreme events)
9.   Maximum Daily Drop in Reservoir due to Evacuation = 0.50 feet
10. Minimum Outflow = 375 cfs
11. Minimum Forcasted Inflow Before Prereleasing = 30,000 cfs
12. Number of days ahead to forecast = 2 days
13. Flood Control Stage Table:

Flow	Flood Control Stage
30,000 - 40,000 cfs	296.7 (297.6 rec. pool)
40,000 - 50,000 cfs	297.0 (297.6 rec. pool)
50,000 - 75,000 cfs	297.6
75,000 - 100,000 cfs	299.5
over 100,000 cfs	299.8

14. Targeted Daily Rate of Fall of Jackson Gage for Bank Caving = 2.0 feet
15. Maximum Stage at which to Consider Bank Caving = 28.00 feet
16. Maximum Daily Rise in Reservoir for Storage for Bank Caving = 0.50 feet

Figure 19. Ross Barnett Pool Operation - Optimized Alternative

BANK SLOUGHING PROCEDURE

     For a minor flood event (one that does not require use of the reservoir's cajpacity to prevent flood damage) the reservoir should be pre-released (based on rainfall and stream flow data) to its minimum winter pool level (295.8') in the early stages of the flood event. This level should be maintained until approximately 8-1/2 billion cubic feet of runoff remains in the watershed. This will occur when the reservoir inflow equals 25,000 cfs.

     Watershed "run-out" that provides inflow to the reservoir in the last stages of a flood event follows a very consistent pattern. Six floods were measured to determine the amount of "run-out" that occurred after reservoir inflows had decreased to 25,000 cubic feet per second. Notice how consistent the results are in the table below:

     The following procedure will prevent fall opposite downstream channel banks from exceeding two feet per day. The procedure should be instigated when reservoir "in flow" has declined to 25,000 cubic feet per second.

     Following this procedure will require 8.6 billion cubic feet of water. Initiating the procedure when the watershed has not "run out" and approximately 8-1/2 billion cubic feet remain in it assures that the procedure will not run out of water. The procedures require that the reservoir cut discharge back to 18,000 cfc when the inflow is at 25,000 cfs. This results in a filling of the reservoir during the initial phase of the procedure. For this reason it is necessary to begin the procedure with the reservoir at minimum pool (295.8') to allow room for the reservoir rise.

     Following this rocedure, the reesrvoir should respond approximate, according to the following schedule:

     After a major flood event, the reservoir will be in the process of being "let down" form extreme elevations. The bank sloughing pocedure should be initiated when the combined volumes of water form two sources equal 8.5 billion cubic feet. These sources are:

1. The capacity of the reservoir that existes above minimum pool

2. The "run-off" remaining in the watershed

Example: The reservoir has been let down to a level of 297.8' when inflow has dropped to 25,000 cubic feet of water per second.

1. Capacity of the reservoir form 297.8' to 295.8' equals 2.8 billion cubic feet

2. Capacity of the watershed equals 8.5 BCF

3. The total available for discharge is 11.3 BCF

In this instance, continue discharging at a "let-down" rate until the two sums add up to 8.5 BCF. Remember that these two valves are extremely dependable.

     Example: Continued discharge at 30,000 CFS for 24 hours will lower the reservoir approximately 05 feet to 297.3'. also, during this time approximately 2.0 BCF will have flowed out f the watershed. This would leave approximately 2.0 BCF of capacity in the reservoir above minimum pool and 6.5 BCF of "run-out" left in the watershed. Bank sloughing should be initiated at this time.

     Following this procedure, the reservoir should respond approximately, according to the following schedule:

     This procedure is not intended to be exact. It describes a principal to be utilized that will affect a 2' minimum fall in the channel below the reservoir. The procedure can be refined with more study and adjustments to discharge can be made thoughour the procedure as indicated by inflow.

     The Jackson lake weirs automatically regulate steady flow. They prevent sudden rate changes. This would assist the reservoir in regulating for downstream bank sloughing. The following is a chart which shows reservoir discharge and the corresponding discharge that will pass the weir. If the reservoir were to suddenly increase discharge from 20,000 cubic feet per second to 80,000 cubic feet per second and hold this rate for six hours, the reservoir would drop one foot in elevation. The column on the right side of the charge shows that the discharge over the weir would increase gradually over six hours until it reached a rate of 74,000 cubic feet per second downstream. If the discharge were just as suddently cut back from 80,000 cubic feet per second to 20,000 cubic feet per second, the weir would cause the lower lake to fall gradually. It would require over ten hours for the flow over the weirs to return to the 20,000 cubic feet per second rate. The chart is shown to demonstrate what the weir could do in an emergency. The plan does not call for making such sudden changes in the discharge rate at the reservoir.

THESE FLOWRATES WOULD LOWER THE RESERVOIR
ONE FOOT (1.3 BILLION CUBIC FEET) IN SIX HOURS
ASSUMING AN AVERAGE INFLOW OF 20000 CFS.