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Off-allocation system components

As stated in Overview, an off-allocation flow sharing system is described by:

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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 Loss(wu, other)	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 Each account at the OAN represents a downstream water user's supplementary entitlement to each owner's off-allocation flow at the node. These accounts are assigned a priority level by the modeller – which effectively prioritises the access of the downstream water user to off-allocation water. The lowest number has the highest priority.	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
Ratio_OffAlloc(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) Usage(sa)	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
Vol_OffAlloc	Total volume of off-allocation water at the OAN remaining to be distributed in the current time step.	volume	Flow
Vol_OffAlloc(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. Note: recall the definition of "water user" in the list of Definitions 521945996. We have to be a little careful here. I couldn't find my comment on being the same thing, but the main difference from a coding point of view between an account a and a water user wu, is that a water user isn't ever an account of an off allocation account type. The supply point is the account. What this means is that a water user can be associated with many accounts. This has ramifications for the way water is allocated to an account. As an example if a water user is attached to 2 supply points, then it will send the same request up both branches of the system. This means that we have to make sure this request is not over fulfilled, so when the off allocation node goes to distribute off allocation allocations to users, it first checks that any requests from associated water users to the account have not already been fulfilled by accounts on other off allocation nodes. Realise this is confusing, so happy to sit down and talk you through it. Generally speaking I think we need to be careful how we use these terms and make sure we only use primarily 1 (prob 'a') unless necessary.	n/a	Configuration, Initialisation, Flow

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Save each owner's request for off-allocation water (the volume at the OAN; i.e. adjusted for losses).
If ownership is enabled and there is more than one owner, the owner loss contribution, Loss(wu, owner), in meeting the request for each water user at the OAN, are determined. Determine the loss contribution of each owner 521945996 describes how this is done.
The volume of off-allocation water that is available, Vol_OffAlloc ,is calculated. See Determine the off-allocation volume below for details.
The off-allocation water is allocated. If ownership is not enabled or there is only one owner, the steps below are only performed once. When there are multiple owners, they are repeated until either there is no off-allocation water to share, or all requests are met, or the system's usage limit has been reached (if there is such a limit).
1. A check is made to see whether there is any off-allocation water to allocate, or not. If there is no off-allocation water (remaining) to share (ie. if Vol_OffAlloc = 0 or Vol_OffAlloc < lowest volume allocation level ), the allocation procedure stops here.
2. How much of the total requested volume at the OAN can be met/supplied is determined.
  
  If met ≤ 0 , the allocation procedure stops here.
3. If there is a usage cap defined for the off-allocation system, a check is made to see if there is remaining usage capacity. This is calculated based on the current usages of all accounts a at every OAN in the off-allocation system:
  
  If LimitUsage(system) = 0 , there is no remaining system cap to share, so the allocation procedure stops here.
4. The off-allocation delivery efficiency is determined for each account using the following equation:
  
  where a is the account for a downstream water user. (Recall that each water user which requires off-allocation flow to be allocated to them from a particular OAN in the river system holds one off-allocation account at that node.)
5. Determine the maximum volume of a request remaining to be fulfilled for each off-allocation account a at downstream water users:
  1. If there is a usage cap configured, it is the smaller of the request and the remaining usage cap
  2. Otherwise, it is the requested volume
  3. If no account has LimitUsage(a) > 0 , the allocation procedure stops here.
6. Off-allocation water is allocated to accounts at the OAN. At every priority level, in order from highest to lowest, the following occurs:
  1. If the equalise shares option has been selected, account allocations/usages at a given priority level are equalised based on their usage to shares ratio. Equalise shares of off-allocation water 521945996 describes how this is done.
  2. Remaining off-allocation water is allocated to accounts at the given priority level according to account shares. Allocate off-allocation water to accounts based on shares 521945996 describes how this is done.
7. At this stage the OAN may have met each of the water user's owner requests and thus supplied more water than the water user requires – as the total request was placed for every owner. The steps that follow check for this and re-distribute any excess allocation – firstly to other water users of the same ownership, then to other water users. The process depends on how many owners there are:
  
  If ownership is disabled or there is only one owner, usage is simply updated:
  
  Otherwise (i.e. there is more than one owner):
  1. Any excess is redistributed according to the method described in Re-distribute off-allocation excess 521945996.
  2. The usage for this round of allocation is updated
  3. Return to step 3. The next round will redistribute any losses met by other owners to water user accounts with insufficient water to meet requests.
Account balances for every account at the OAN are updated

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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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For each off- allocation system configured

Model Element	Parameter	Frequency	Notes	Off-allocation system	Remaining Capacity: Difference between system cap and system usage	time step
Off-allocation system	Usage: System usage	time step	For each off- allocation system configured
Account Type	Remaining Capacity: Difference between account type cap and account type usage	time step	For each off- allocation system account type configured
Account Type	Usage: Account type usage	time step	For each off- allocation system account type configured
Accounts	Remaining Capacity: Difference between account limit and account usage	time step	For each account in an off- allocation system account type
Accounts	Usage: Account usage	time step	For each account in an off- allocation system account type
Water user/Account Holder	Allocation: No sure?	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Constrained Order: Don't know?	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Equalisation Ratio: Ratio between water user usage and total usage for the account type	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Non Debit Balance: Don't know	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Order Volume: Off allocation request volume for the current time step	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Remaining Capacity: Difference between the water user off allocation limit and the water user usage	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Total Volumetric Share: Off allocation share since the start of the water season	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Usage: Accumulated off allocation use since the start of the water year	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Usage Today: Off allocation volume used in the current time step	time step	For each account holder in an off- allocation system account type
Water user/Account Holder	Volumetric Share: Share of off allocation volume	time step	For each account holder in an off- allocation system account type
Off-allocation node	Borrow and Payback	time step	For all off allocation nodes
Off-allocation node	Constituents	time step	For all off allocation nodes
Off-allocation node	Downstream flow>Flow: Downstream flow	time step	For all off allocation nodes
Off-allocation node	Downstream flow volume>Volume: Downstream volume	time step	For all off allocation nodes
Off-allocation node	Mass balance	time step	For all off allocation nodes
Off-allocation node	Off allocation Flow Volume>Volume: Volume of off allocation	time step	For all off allocation nodes
Off-allocation node	Off Allocation Orders Volume	time step	For all off allocation nodes
Off-allocation node	Ordering Network	time step	For all off allocation nodes
Off-allocation node	Rules Based Orders	time step	For all off allocation nodes
Off-allocation node	Storage Volume	time step	For all off allocation nodes
Off-allocation node	Total Inflow Volume	time step	For all off allocation nodes
Off-allocation node	Total Outflow Volume	time step	For all off allocation nodes
Off-allocation node	Upstream flow>Flow: Upstream flow	time step	For all off allocation nodes
Off-allocation node	Upstream flow volume>Volume: Upstream volume	time step	For all off allocation nodes

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Old Version 95

New Version 96

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Document History

Off-allocation system components

Off allocation and storages