Document History
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Symbol | Purpose/Description | Units | Usage |
|---|---|---|---|
a | A water user account at the OAN. | n/a | Initialisation, Flow |
AccessRatio(a,owner) | Ratio of allocation to request volume for an account (representing a water user and owner). Indicates whether there is an excess to reallocate to other owners and/or water users. | n/a | Flow |
Allocated | Total volume allocated to all accounts at the current priority level, p. | volume | Flow |
Allocation(a) | The volume of water allocated to an account | volume | Flow |
Balance(a,t) | Balance of a water user account in a time step, t. This is the volume of off-allocation water assigned to the associated water user and owner that is expected to arrive at the water user's location (e.g. Supply Point Node) in the time step. | volume | Flow |
Cap(a) | Account cap for an account a – representing the maximum usage permitted for the account in the water year. | volume | Flow |
Cap(type) | Cap at the OAN represented by the account type, type, representing the maximum off-allocation usage permitted at the OAN in the water year. | volume | Flow |
Cap(system) | Cap for an off-allocation system, system , representing the maximum usage permitted for the off-allocation system in the water year. | volume | Flow |
DeliveryEff(a) | Factor that represents the efficiency of delivery of water requested using water user account a. | n/a | Flow |
Excess | Total volume allocated that is in excess of the system cap | volume | Flow |
Flow | The volume of flow in the river at the OAN for the current time step | volume | Flow |
InitialUsage(a) | The initial usage figure set by the user for the account a. | volume | Initialisation, Flow |
LimitUsage(a) | Maximum remaining usage for the water user account a in the current time step. This may be the total remaining request. If the account's usage is capped, the remaining usage will be limited by the remaining usage under the cap. | volume | Flow |
LimitUsage(system) | The maximum volume of water left to be allocated to accounts in the OAN's system in the current water year. This limitation only applies to systems with a usage cap. | volume | Flow |
Loss(wu, owner | An owner's share of the estimated volume of loss that will be incurred in delivering a water user's request leaving the OAN this time step. | volume | Flow |
MaxQ | Maximum flow threshold, used for defining off-allocation events (see Figures 1 and 2) | volume | Flow |
MinRatio | Minimum usage ratio for all OAN accounts at the current priority level. | n/a | Flow |
NextRatio | Next lowest usage ratio after the minimum for all accounts at the current priority level | n/a | Flow |
OrderDue | Total volume of order due at the OAN in the current time step. | volume | Flow |
OrderDue(owner) | Volume of order due at the OAN in the current time step for owner. | volume | Flow |
OrigRequest(a) | The saved value of Request(a) before the allocation process begins. | volume | Flow |
OrigRequest(a, owner) | The saved value of Request(a, owner) before the allocation process begins. | volume | Flow |
owner | A water owner at the OAN | n/a | Configuration, Flow |
other | A different water owner to owner at the OAN | n/a | Flow |
p | The current priority level | n/a | Flow |
Proportion | Proportion by which allocations at the current priority level in the current time step need to be reduced so that they fit within the system cap. | n/a | Flow |
RatioOffAlloc(owner) | An owner's share of the total off-allocation volume remaining to be allocated this time step at the OAN. | n/a | Flow |
Request(a) | The volume of off-allocation request placed for account a of water user wu up-scaled for loss to the total required at the OAN. | volume | Flow |
Request(a,owner) | The volume of off-allocation request placed for a water user and owner up-scaled for loss to the total required at the OAN. | volume | Flow |
RequestAtSource(a) | The volume of off-allocation request placed for account a of water user wu at its location (e.g. at a Supply Point Node). | volume | Flow |
ReserveProp(type) | Configured proportion of off-allocation flow reserved (not available for allocation) at the OAN (represented by account type type ) | n/a | Configuration, Flow |
sa | A water user account in a given off-allocation system | n/a | Flow |
ShareVolume(a) | The volume of off-allocation water to be shared to account a in the current time step. | Flow | |
ShareVolumeAtSource(a) | The volume of off-allocation water to be shared to account a in the current time step, reduced for delivery efficiency so that it is the amount available at the water user's location (e.g. at a Supply Point Node). | volume | Flow |
system | An off-allocation system | n/a | Configuration, Initialisation, Flow |
t | Index of the current time step | n/a | Flow |
tdelivery(a) | Estimated number of time steps to deliver water from the OAN to the water user's supply point for account a . | n/a | Flow |
type | The account type which represents the OAN in the off-allocation system. | n/a | Flow |
TotalUnitShare(p) | The total number of specified unit shares for all OAN accounts at a priority level p . | n/a | Configuration, Flow |
UnitShare(a) | The number of specified unit shares for a water user's account a at the OAN. | n/a | Configuration, Flow |
Usage(a) | The usage to date (in the water year) for a water user account which includes undelivered off-allocation water. This value is reset at the start of a water year. | volume | Flow |
UsageRatio(a) | The usage to shares ratio for an account a - this is used to equalise allocations between accounts at the same priority level. | n/a | Flow |
VolOffAlloc | Total volume of off-allocation water at the OAN remaining to be distributed in the current time step. | volume | Flow |
VolOffAlloc(owner) | Volume of an owner's off-allocation water at the OAN remaining to be distributed in the current time step. | volume | Flow |
wu | A water user with an account at the off-allocation node. | n/a | Configuration, Initialisation, Flow |
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Each OAN processes the orders for its direct users downstream (including the next downstream OAN) and passes the combined orders up to the next OAN (if there is one). This means that it is possible to share off allocation water between multiple downstream reaches.
In the example illustrated in Figure 6, below, OAN3 has a share component in OAN2 which also has a share component in OAN1. This means that the off-allocation requirements of water user 3 and 4 are accumulated up the system and are reported as the off-allocation requirement of OAN2. This means that the allocation of off-allocation water to reach 1 takes into consideration the downstream requirements. It is possible to give priority access to downstream requirements by assigning the highest priority to OAN2 in the OAN1 allocation table.
Note that while OAN1 assigns a volume of off-allocation water to OAN2, the processing of OAN2 may result in a change in the volume of off-allocation water available to that reach as the rules specific to OAN2 are used to calculate the available water. 
Figure 6 — Example of multiple off allocation reaches
Off allocation and storages
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