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Objects and Methods : Control Point : User Methods : Key Control Point Balancing
Key Control Point Balancing
This method category can be applicable to both operating level balancing and phase balancing approaches for determining flood control releases. The category appears at the selection of the Phase Balancing method under the Flood Control category of the control point, or at the selection of any regulation discharge method under the Regulation Discharge category that appears under the Operating Level Balancing method for the Flood Control category on the control point.
Selection of a method in this category makes a control point a key control point and causes the key icon to appear on the control point in the GUI to identify it as key. Key control point balancing allows for the balancing of storage in associated upstream reservoirs with respect to the control point. Calculations for the key control point balancing methods are actually initiated from a flood control method selected on a computational subbasin that includes the control point.
* Operating Level Balancing
This method is only available if one of the regulation discharge methods is selected under the Regulation Discharge category that appears under the Operating Level Balancing method for the Flood Control category on the control point. The method uses the empty space available in the channel at the control point that is calculated by the regulation discharge method to balance the levels of associated reservoirs over a specified balance period. The empty space is specifically allocated to the reservoirs over the control point’s forecast period. The method populates results into the Balance Level and Share slots on the control point and the Target Balance Level slot on each associated reservoir.
This method also computes a maximum flood control release for each reservoir under its control and stores the result in the reservoir’s slot Max Flood Control Release. This value is used by the Operating Level Balancing flood control algorithm (see Computational Subbasin). The value is a flow, computed as
M = (RSTG /TTLEV) * MEORD
where
– RSTG is the reservoir’s forecast storage at the end of the balance period above the target level, limited by the outflow control points regulation discharge,
– TTLEV is the total empty space volume at this control point at the end of the balance period, and
– MEORD is the maximum empty space hydrograph ordinate at this control point (over the forecast period), a flow.
Note:  Another way to think about this is that there are two ratios that are equal. The first is the maximum release over the total volume above the balance level. The second is the maximum empty space ordinate over the total empty space volume.
Slots Specific to This Method
 Key Control Point Reservoirs
Type: ListSlot
Units: NONE
Description: List of upstream reservoirs associated with this control point for balancing.
Information: Each reservoir in this list gets an associated column in the Share slot.
I/O: Required input
 Balance Period
Type: ScalarSlot
Units: NONE
Description: Single number representing the number of timesteps in the balance period.
Information: The balance period is the number of timesteps including the current simulation timestep that is used in the algorithm for balancing the reservoirs associated with a key control point. This value can be propagated from a computational subbasin of which the control point is a member.
I/O: Required input
 Balance Tolerance
Type: ScalarSlot
Units: VOLUME
Description: In the iterative calculation for determining the balance level, balance tolerance allows the user to specify how close the storage above the balance level in the reservoirs at the end of the balance period must be compared to the empty space available in the channel over the balance period. Balance tolerance is expressed as a difference between these volumes.
Information: The algorithm to find a balance level where storage equals empty space will iterate until the balance tolerance is reached or until the number of balance iterations is reached. These parameters allows the user to control and limit the number of iterations of the algorithm.
I/O: Required input
 Balance Iterations
Type: ScalarSlot
Units: NONE
Description: This parameter is how many times the balance level algorithm is allowed to iterate in determining a balance level where storage in the reservoirs above this level at the end of the balance period equals the empty space available in the channel over the balance period.
Information: The algorithm to find a balance level where storage equals empty space will iterate until the number of balance iterations is reached or until the balance tolerance is reached. These parameters allow the user to control and limit the number of iterations of the algorithm.
I/O: Required input
 Balance Level
Type: SeriesSlot
Units: NONE
Description: Contains the result of the balance level determination for the key control point.
Information: The balance level calculated for the key control point is written to this Series Slot for each simulation timestep. This slot is invisible but can be viewed in the Special Results details on the Model Run Analysis tool; see Model Run Analysis—Special Results Details Dialog in USACE‑SWD Modeling Techniques.
I/O: Output
 Share
Type: AggSeriesSlot
Units: Decimal
Description: Contains the results of allocating the empty space at the key control point to its associated reservoirs. Values are a proportional allocation and will add up to 1 for each timestep.
Information: Each column is a SeriesSlot and represents the allocated space for one of the reservoirs from the Key Control Point Reservoirs list. Space is allocated for the current simulation timestep through the forecast period. When the next timestep executes, the future forecast timestep values are overwritten by the new simulation and forecast values. This slot is invisible but can be viewed in the Special Results details on the Model Run Analysis tool; see Model Run Analysis—Special Results Details Dialog in USACE‑SWD Modeling Techniques.
I/O: Output
Method Details  
The Operating Level Balancing method for the control point executes the following steps.
1. Total the volume of empty space over the balance period at the control point.
2. Find the total storage above conservation level summed for all associated reservoirs at the end of the balance period. Volume contributed by a reservoir is limited to the regulation discharge of its downstream gage control point at the current simulation timestep multiplied by the number of timesteps in the balance period.
3. If there is no storage, or some storage, but not enough to fill the total empty space, set the balance level to the conservation pool level.
4. Otherwise, determine the balance level at the end of the balance period where the total storage above that level equals the total empty space. The volume contributed by a reservoir is limited to the regulation discharge of its downstream gage control point at the current simulation timestep multiplied by the number of timesteps in the balance period. The bisection algorithm to determine balance level iterates until the Balance Tolerance for comparing storage to empty space is reached or until the Balance Iterations limit is reached.
5. Assign the key control point’s balance level to the associated reservoirs. If a reservoir is associated with more than one key control point, the highest balance level of the associated control points is used.
6. Allocate the empty space at the control point to the reservoirs for each timestep in the forecast period. A reservoir’s share for any forecast timestep is its volume above the balance level at the end of the balance period, provided at least part of a release from that reservoir on the current simulation timestep would reach the key control point by that forecast timestep, divided by the total volume above the balance level at the end of the balance period for all reservoirs whose releases would reach the key control point by that forecast timestep. Again the volume contributed by a reservoir is limited to the regulation discharge of its downstream gage control point for the current simulation timestep multiplied by the number of timesteps in the balance period.
* Phase Balancing
This method is only available at the selection of the Phase Balancing method under the Flood Control category of the control point. It instantiates the phase space hydrograph of the control point’s channel used by the Phase Balancing method on the Computation Subbasin. The phase space hydrograph is used to allocate space to the reservoirs in a given phase over the control point’s forecast period and a maximum flood control release value is calculated for each associated reservoir. (See Phase Balancing discussion in the Computational Object for a complete description).
Slots Specific to This Method
 Phase Space Hydrograph
Type: TableSlot
Units: NONE, FLOW
Description: Contains flow capacity limits of each phase for this control point.
I/O: Required input
 Phase Space Tolerance
Type: AggSeriesSlot
Units: FLOW
Description: Contains a series of tolerance values for defining each phase level of the control point.
Information: Each column (SeriesSlot) represents tolerance values for each phase level of the control point. The tolerance value is added to the phase space hydrograph to calculate the flow capacity limits of each phase for this control point.
I/O: Input
 Number Of Phases
Type: ScalarSlot
Units: NONE
Description: The number of phases associated with the all the phase space hydrograph.
Information: Value must agree with slot of same name on the computational subbasin.
I/O: Input
Revised: 08/02/2021