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- Order phase - There is a potential to reduce upstream orders through borrowing of tributary inflow. See Ownership at Inflow and Confluence Nodes - SRG for details.
- Flow phase - An owner can have a delivery shortfall as a result of higher than expected losses, lower than expected tributary inflows, or the use of its water by another owner that was planned in the order phase. If there is surplus water in the river at the point where the shortfall occurs, the owner with the shortfall can borrow from other owners.
Input parameters required
BPSystem - The borrow and payback system to use in determining distribution rules and, where relevant, updating accounts. Borrow and payback system(s) are associated with each model node and link during model initialisation.
component - Model component using this borrow method, needed for updating accounts.
Surplus(owner), Deficit(owner) - The current ‘surplus’ and ‘deficit’ volume/capacity for each owner. At a storage node, surplus water is any water that is not required to meet downstream requirements in the current time step. This definition may vary between model components, and between the model phases (order or flow). Refer to the SRG entry for the appropriate model component for more information.
Airspace - Each owner’s share of airspace in the borrow and payback system’s payback storage (when there is one). This is needed to limit lending.
UpdateAccounts - Borrow accounting only needs to occur in some circumstances, as described above. This parameter is set or reset according to whether or not borrow accounts are to be updated.
Output parameters
The borrow method returns the volume each owner borrowed and lent for the time step (OwnerBorrowed(t, owner), OwnerLent(t, owner), OwnerBorrowed(t, owner, other_owner), OwnerLent(t, owner, other_owner)) to the relevant component so that the payback requirement can be adjusted (see examples at the end of this SRG entry). Borrowed volumes are subtracted from, and loaned volumes added to, the requirement.
Steps
The following steps describe how surpluses are distributed within the given borrow and payback system BPSystem. Note that an owner can participate in sharing at a priority level (is in the owner(pl) and other_owner(pl) lists) when BPSystem.Share(pl, owner) = Yes.
- Start with zero borrow between all owners:
- If the borrow and payback system BPSystem is a local system and this method is used in the flow phase to lend water (UpdateAccounts = Yes), limit the surplus amount each owner can lend to their airspace (to ensure payback is possible).