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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

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)
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

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.
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

...

  • Using a matrix to solve the owner's share:


Anchor
Equalise shares of off-allocation water
Equalise shares of off-allocation water
Equalise shares of off-allocation water

This is an optional process that is undertaken only if the modeller specifies that it should be done. The following steps are repeated until either there is no more off-allocation water to assign, or the lowest account usage to share ratios are equal (see step 3).

  1. For a given priority level of accounts, the usage to shares ratio for every OAN account at the current priority level is calculated:


  2. The two accounts at this priority level with the lowest ratios are found


  3. Check to see whether the two lowest ratios are the same:
    1. If this is the case (MinRatio = NextRatio), the equalised allocation process is finished – exit this priority level and move on to the next one.

    2. Otherwise continue on.

  4. For each account a at the current priority level, the following occurs:
    1. If VolOffAlloc = 0 then equalisation ends.

    2. If the account request/usage limit has been reached (LimitUsage(a) = 0), this account is skipped and processing of the next one starts.

    3. The volume required to bring the ratio of the current account up to the second lowest accounts ratio is calculated:








    4. Water is allocated to the account and limits are updated


    5. Reduce the volume of off-allocation water available to share


  5. Return to step 1 to continue equalisation.

Anchor
Allocate off-allocation water to accounts based on shares
Allocate off-allocation water to accounts based on shares
Allocate off-allocation water to accounts based on shares

Firstly, at the current priority level, p :

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  1. Limit the share volume for an account (Note that if LimitUsage(a) is not specified by the modeller its value defaults to a very big number):





  2. Reduce the volume of off-allocation water available to share



  3. Calculate the volume that this represents at the source



  4. Calculate allocations for the account for each user and adjust the usage limits if required.






  5. If a system cap has been specified and would be exceeded by allocations in the current time step, then allocations are reduced to fit within cap (otherwise this step is skipped).

    1. Sum the allocations for each user in the current priority level


    2. Calculate the volume by which the system cap would be exceeded based on potential allocations


    3. Calculate the proportion that each allocation would have to be reduced by to meet the system cap restriction


    4. For each OAS node account at the current priority level allocations are adjusted so that they do not exceed the system cap, taking into account the efficiency factors, then the limits for the adjustment are updated:








Anchor
Re-distribute off-allocation excess
Re-distribute off-allocation excess
Re-distribute off-allocation excess

When there are multiple owners, excess water may have been allocated as the water user's requested volume was duplicated for each owner. This method redistributes the excess, then determines the new excess volume for each owner once losses met by other owners at all water users are taken into account.

...

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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Remaining Capacity: Difference between system cap and system usage

Model Element

Parameter

Frequency

Notes

Off-allocation system

time step

For each off- allocation system configured

Off-allocation system

Usage: System usage

time step

For each off- allocation system configured

Account TypeRemaining 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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