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The total working volume for all owners is:
Equation 2 | 
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where:
W Ti- Total working volume.
The proportional loss attributed to owner i is Pi and is given by:
Equation 3 | 
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where:
P is the total proportional loss, negative if a gain (rainfall).
If the storage working volume is less than or equal to ownership tolerance level (0.0001 m3), then proportional loss Pi becomes:
| Equation 4 |
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where:
ri - Owner i’s ratio share of the reservoir’s storage capacity.
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Ri - Volume of regulated water released this time step for owner i.
ISi - Net internal spill of owner i, negative if spill into owner’s share.
ESi - External spill for owner i.
The final storage volume is updated after calculating the internal and external spills. The changes in the spill calculations are illustrated in the later sections.
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The total external spill by all owners is known and is given by total outflow minus the total release of all owners as in:
Equation 7 |
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Spill by individual owner
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The internal spill by 'Use Airspace' owner can be negative when there are internal spills to it. The airspace owner does not internally spill to other owners but can receive internal spills from other owners if it is under its capacity share. Therefore, the spill amount is the minimum of it's calculated spill and the total external spill of the storage.
The external spill of the 'Use Airspace' owner when its spill is greater than zero is given by:
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The internal spill of the 'Use Airspace' owner when its spill is greater than zero is given by:
| Equation |
| 10 |
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Calculating internal and external spill shares for the owners
The calculations in the previous sections established which owners are spillers when working volume based proportional losses are taken into account. The next step is to determine the internal (between owners) and external (leaving the reservoir) components of the spill by the owners. The determination involves several steps included and are explained below.
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1. Firstly, the total of all spills greater than zero is calculated as:
| Equation 11 |
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2. If the spill by 'Use Airspace' owner is greater than zero, then it is calculated first before other steps:
a) The external spill of the 'Use Airspace' owner is:
| Equation 12 |
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b) The total spill by the remaining owners is given by:
Equation 13 |
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c) The external spill by the remaining owners is given by:
Equation |
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14 |
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3. The internal and external spill shares of the remaining total spill (as in Equation 13) are calculated as in steps below (noting that the total spill and external spill amounts do not include the airspace owner if it has already been externally spilled as above).
a) Case when internal spills are disabled:
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The internal spill is
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Equation 11
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:
| Equation 15 |
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The external spill is:
| Equation 16 |
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It is to be noted that the TotalSpill in Equation 16 is the total spill calculated as in Equation 11.
b) Case where internal spills are enabled
When internal spills are enabled, the equations 33 to 43 are followed as in the previous version of SRG with no changes.
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It is to be noted that if there is a 'Use Airspace' owner and it's spill is greater than zero, then the TotalSpill and ExternalSpill for the remaining owners in Equations 33 and 34 would be calculated as in Equations 13 and 14 respectively.
Furthermore, the equations 44 to 50 in the previous version of SRG are made redundant due to the adoption of the new method of proportional loss calculation as in Equation 3 above.
The remaining is the same as in the previous SRG version.