Overview

Annual Accounting is one of three water accounting systems supported by Source. Functionality for modelling water use accounting is needed in any modelling platform intended for reliable modelling of existing regulated river systems. Source provides the following different options for modelling water use: Annual Accounting, Continuous Accounting and Continuous Sharing.

Annual Accounting is undertaken in different jurisdictions across Australia applying many different methods depending on the particular hydrologic and geographic characteristics and management practices of each water resource system. However, there are some general principles which apply in most of these systems.

An available resource is calculated during a defined water year and from that resource allocations are made to different account types, some of which may be used to represent losses or reserve allowances. Each account type’s allocations are then distributed between the accounts that share the same common account type. Any allocated water which has not been carried over at the end of the defined water year will be returned to the available resource for allocation to the various account types in the following water year.

Complexity arises in many aspects of the Annual Accounting process, including:

Calculation of the available resource, due to factors such as the possible linkages between different resource assessment systems, having different owners’ shares (including potential borrow and payback of available resource)
Interdependencies between water account types and how they are treated in resource allocation, and
The necessity in some systems to iteratively calculate allocation through the season based on new estimates of the available resource

The Annual Accounting resource assessment system in Source has been designed to cater for these specialised requirements.

Scale

The allocation to each account type, and to individual accounts within these, are updated each time there is a reassessment. On a spatial scale, an Annual Accounting system can apply to selected water users spread through all or part of the length of a river system.

Principal developer

Several jurisdictions in Australia have developed model representations of Annual Accounting systems, starting from the 1980's with refinements continuing since then in response to evolving water management needs. The representation in Source has been developed by eWater, based on these earlier representations.

Scientific Provenance

A number of permutations of Annual Accounting have been implemented by various Australian states and territories over many years. Within a given jurisdiction it is not uncommon for there to be differences in the way Annual Accounting is implemented between river valleys. The representation of Annual Accounting in Source is designed to replicate these practical implementations and also provide sufficient flexibility to accommodate new changes if required.

Version

Source version 3.8.12

Dependencies

Annual Accounting can be used by any of the following node types which are referred to as "Account Hosts":

Water User Nodes (with attached Supply Point Node)
Environmental Demand Node
Bulk Licensing Node

Exact configuration within each of these Accounts Hosts varying but the underlying Resource Assessment system is consistent.

Assumptions

The assumptions and limitations are summarised in Table 1.

Table 1 - Assumptions and constraints applying to Annual Accounting

No	Assumption/Constraint
1	Resource Assessment systems must have defined water sources which can include: Regulated river flow from a defined list of storages; Regulated off-allocation river flow, defined at one or more locations; Unregulated river flow; Groundwater
2	Resource Assessment system can only utilise water that belongs to the resource owner, which can be: Not specified; An owner in a water ownership system; Another resource allocation system

Assumption/Constraint

Resource Assessment systems must have defined water sources which can include:

Regulated river flow from a defined list of storages;
Regulated off-allocation river flow, defined at one or more locations;
Unregulated river flow;
Groundwater

Resource Assessment system can only utilise water that belongs to the resource owner, which can be:

Not specified;
An owner in a water ownership system;
Another resource allocation system

Annual Accounting

The Annual Accounting implementation in Source follows the same basic concepts as other types of resource assessment systems, namely:

An available resource;
A defined water year;
A set of account types;
Accounts to which water is allocated, and for which usage is tracked; and
Possibly an owner (for example, the state "NSW"), when ownership is enabled.

The modeller is given the flexibility to determine rules such as:

Dates of the water year.
The frequency of the resource assessment and allocation process. By default this occurs annually at the start of the water year.
How the available resource is determined. The main feature of this type of system is that the flexibility of functions is provided within a structure that is common to Annual Accounting methodologies in different jurisdictions.
Rules of allocation.
Usage limits (in addition to the account balance)
Carryover type (spillable or non spillable)

Event Triggers are provided to allow modelling of carryover and other less commonly used methods in Annual Accounting.

There are some features that differentiate Annual Accounting from other types of resource assessment system. In Annual Accounting, a forward projection of usable future inflow to the end of the water year may be included in the available resource and subsequently influence the allocation announcement. Allocations may be reviewed and adjusted throughout the water year, typically as events occur. This type of review looks at the ability of the system to supply the demand for the rest of the water year. There may be some point within the water year when no further allocation announcements are made, typically at the end of the growing season.

To model Annual Accounting, Source performs resource assessment at a user-specified frequency (via the Reassessment Trigger), adjusting the available resource for demands supplied to date. It provides the modeller with a simple mechanism to define the relationship between the resource and allocation - this is Available Resource versus Allocation (ARA) table. At each reassessment this relationship is used to determine the volume of water allocated to each account type represented, based on that time-step’s available resource estimate (See the section on Account Types and the ARA Table). Functions can also be used instead of the ARA table to determine an Account Type’s allocation. In cases where the Account Type has an increase in allocation from the previous resource assessment, the change in allocation (increment) is assigned to its accounts.

Available Resource

The available resource for an Annual Accounting system is calculated as shown in Equation 1.

Equation 1 - Available Resource

Figure 1. Example Resource Calculations for the Goulburn one year planning period and Source configuration comparison

Active Storage

One or more storage nodes may be selected as sources of water for the Annual Accounting system. Each of the selected storages contribute their "Active Storage".

In its simplest form, the Active Storage is a measure of the current volume in the storage minus the dead storage volume.

When ownership is enabled and the Annual Accounting system is linked to an owner, the volume only includes the selected owner’s share of the water in the storage. Meaning that the total volume of Active Storage is scaled by the ownership percentage.

Active Storage can also be affected by the configuration of each of the Storage's "Evaporation To End of Season" and "Minimum Inflow To End Of Season" settings. For each Storage the user can specify a monthly pattern dictating the Minimum Inflow as well as the Evaporation. They can also further control how these patterns are used depending if they want to use the inflow for resource and inflow for evaporation.

Active Storages are summed together and added to the Available Resource during reassessment.

Equation 2 - Active Storage

Equation 3 - Storage Evaporation

Please note that the evaporation as set-up in the configuration is separate to evaporation as specified on the storage itself.

Tributary Inflow

This part of the Available Resource equation represents the Annual Accounting system’s recession tributary inflow volume. One or more Inflow nodes may be used to represent tributary inflows providing water to the system. A recession factor is required for each - the function to calculate this is entered via the Annual Accounting system’s user interface. The function should return a percentage/proportion of the inflow node's outflow volume (on the assessment day) which will be considered the contributing volume available for the remainder of the planning season. The value should, but doesn't need to, relate to the number of days left in the season. The value is likely to be very much greater than one (100%) until the last few days of the planning season.

When ownership is enabled and the Annual Accounting system is linked to an owner and the tributary inflow values used only consist of the selected owner’s share of the total. The volume added to the available resource by each Inflow node in a reassessment is shown in Equation 4.

Equation 4 - Tribuary Inflow
Where "OutflowVolume" represents the Inflow node’s Outflow Volume.

Tip

A method to ensure that only tributary inflows are included for each Inflow node is to disconnect its inlet and outlet, add and connect in a Confluence node in its place in the river network, then connect the Inflow node’s outlet via a "no routing" link to the other (unused) inlet of the new Confluence node. This action will result in the Inflow node’s outflow volume being the same as its tributary inflow volume. The Confluence node then brings the tributary and upstream inflow together.

Tributary Inflows are summed together and added to the Available Resource during reassessment.

Commitments

Commitments are specified via functions and the modeller may specify an arbitrary number of them. They can be used to represent (or reserve water for):

Carryover - An example is the environment’s carry-over volume from the previous water year in the Wimmera / Glenelg system in Victoria. This is the remaining volume after allowing for the environment’s share of storage losses and spills in current allocation year.
Forecast Losses for Remainder of Water Year - There may be several different losses that could all be added into the resource assessment calculation separately. These could include river losses, channel losses and evaporation losses.
Fixed Adjustments - Examples include environmental flows, compensation flows and water quality dilution flows. In the Wimmera / Glenelg system, there is an adjustment for amount of borrowed water returned to the Minister of Environment under sub-clause 6.1(c) of the Flora and Fauna Bulk Entitlement Order.
Reserve - An example in the Wimmera / Glenelg system is the amount of water to be retained in head-works reservoirs this water year to provide for a basic supply next water year.

Some of the above examples could also be represented by Account Types. The volume of water reserved for purposes such as water quality might be independent of allocation, while that required for reservoir evaporation and transmission losses might vary with allocation. The water uses defined under Commitments should generally be those that are independent of allocations within the Annual Accounting system, and for which no water user accounts are required within the system. An example could be water in the system’s storages that is to be managed by another resource assessment system.

Commitments are summed together and the total subtracted from the Available Resource during reassessment.

Other Resources

Other Resources are specified via functions and the modeller may specify an arbitrary number of them. They can be used to add to the available resource a wide range of water resource types and facilitate representation of the following inflow volumes commonly used in Annual Accounting:

Minimum historic usable cumulative tributary inflow volume.
Minimum historic cumulative headwater inflow volume

These volumes are based on historic (rather than modelled) data for each month, and are forecasts of the total minimum inflow volume from the current month to the end of the water year or season.

Other applications include inter-basin transfers and groundwater resources. These resources may be managed by another resource assessment system. An example of an inter-basin transfer is the Wimmera / Glenelg system where water is taken into the Wimmera-Mallee system from the Goulburn-Broken system via the Waranga Western Channel, and water availability is managed via the Goulburn-Broken resource assessment system. Source allows functions to be entered to allow for this linkage between systems, as well as to provide access to relevant model variables.

Other Resource are summed together and the total added to the Available Resource during reassessment.

Usage to date

This parameter represents how much of the water allocated has been ordered or used by Account Hosts in the water year to date. Usage for individual accounts is tracked by Source and may be accounted when water is ordered, delivered, or diverted. The timing of usage accounting depends on whether water order debiting or water usage debiting applies (associated with the resource assessment system).

When the modeller selects the "Usage from Account Host" option, the total of usage in all accounts that has been tracked by Source is used, as in, it uses the value taken from orders made by Account Hosts. Alternatively, the modeller may input an function to determine the usage value (the "Usage from function" option). An example application would be to adjust the tracked value to represent a conveyance loss.

Usage to Date is added to the Available Resource during reassessment.

Spill to date

Spill to date represents water spilled from accounts in the current water year up to date. Spill reduction for each account is tracked in Source, this is the total spill reduction from all accounts within this accounting system from start of water year to date.

Total Spill to Date is added to the Available Resource during reassessment

Adjustment

Adjustments represent changes to the accounts that have occurred via Triggers (not just the "Adjustment" Trigger) Triggers allow changes to Account to occur based on specified Conditions and may result in adjustments to many account properties. When these changes to occur they are tracked to ensure that the modifications are factored into allocation.

Adjustments are subtracted from the Available Resource during reassessment.

Account Types

As with other types of resource assessment system in Source, Account Types in an Annual Accounting system represent a type of water to be allocated or assigned. Some examples are:

Types of entitlement or licence, sometimes referred to as "Products". Examples include High Reliability Water Share (HRWS) and Low Reliability Water Share (LRWS) in Victoria, and High Security and General Security in NSW;
Basic rights, such as stock and domestic rights, and native title;
Environmental allocation;
Reserve. For example, in the Murray, Goulburn, Lachlan and Murrumbidgee systems, water is set aside for following seasons. In the Thomson/Macalister system, allocations are made to a Drought Reserve, which has much the same purpose;
Transmission and operational losses (TOL) in the Lachlan system;
Spill entitlement. An example of where this occurs is the Thomson / Macalister system in Victoria where, if Lake Glenmaggie spills, Southern Rural Water can declare a period that spill entitlement is available and the water delivered to irrigators during this period is not counted as part of their seasonal allocation;
Carryover account types, such as the Spillable Water Accounts (SWAs) in Victoria. Carryover is widely available in annual accounting systems. It allows individuals to carry over part of their unused water allocation (up to a prescribed limit) for use in the following season. It was introduced to annual accounting in northern Victoria in 2006/07 as an emergency drought measure- see DSE (2009), with a limit of 100 per cent of entitlement (ie an individual’s carryover plus allocations cannot exceed 100 per cent). SWAs were introduced on 30 June 2010 to reduce the risk of entitlement-holders losing their carryover in full allocation years. As allocations increase throughout the following season, these are added to users’ accounts until carryover plus allocation equals 100 per cent of the entitlement volume. After this, any additional allocations are credited to the SWA. Throughout the season, the storage manager assesses the risk of the storage spilling during the remainder of the season. Only when the storage manager declares the status of system as "spilling", can the entitlement holders access the water in the SWA;
Bulk entitlements (BEs) in Victoria, and Conveyance licences used in the Murrumbidgee and the Murray in NSW. In Victoria, BEs are issued to Water Authorities to define their respective rights to water (NRE, 1995). The NSW Conveyance licenses are assigned to irrigation companies, which then allocate water to individual irrigators;
Nested or linked resource assessment systems (known in Victoria as allocation groups). One example is the Goulburn system link to the Loddon system. Allocation for the Loddon HRWS account type is calculated firstly based on available resource in the Loddon system and then compared with the Goulburn allocation. The lesser of the two is the final Loddon allocation; and
Off-quota water, or Off-allocation systems (a type of nested resource assessment system).

Some of the above examples could also be represented using the Annual Accounting system’s Commitments or Other Resources functions. An Account Type should be used if its allocation is dependent on allocations to other Account Types within the Annual Accounting system, or usage of the allocation needs to be tracked.

Tip

Percentage based Carryover for any Account Type can be implemented via the modeller creating a Trigger for the Account Type and setting the "Carryover" option for its Action parameter.

The sub-sections below describe the use of Account Type parameters or relationships in relation to Annual Accounting systems.

Priority

The modeller may enter a Priority value for an Account Type to indicate the differences in priority between licence types - for example High or General Security access. In Annual Accounting, Source does not automatically differentiate allocation according to priority, in the interest of flexibility, the modeller may reference Priority in functions that calculate allocation, or simply use this parameter to improve clarity. The ARA Table may also be used to prioritise allocation between Account Types.

Figure 2 and Figure 3 are examples where the ARA table is used to give high security Account Types a higher priority of allocation than general security account types.

Please note that the Account Type priority is not the same as the Account Host priority which is set at the particular Node (e.g., Water User). The Account Host priority is used to determine how orders are handled while Account Type priority is used for determining entitlements. Account Host priority is also used by some triggers (e.g., Transfer) when configured to use an Account Host and deduct from Available Water.

Figure 2 - Example account type v total available resource relationships

Figure 3 - Example account type v total available resource relationships

Unit Shares / Entitlement

The Unit Shares / Entitlement parameter is only used when allocation is assigned in percentage increments using the "Percent (with linked volume)" option described under the sub-section Method to apply for this Account Type in the ARA table, and can only be entered when the modeller does not tick the "Use Unit shares / Entitlement from accounts?" parameter. It represents the volume to assign to the Account Type at 100% allocation. The Unit Shares / Entitlement parameter is designed for use in Account Types without associated accounts - for example, a transmission and operational loss account type. It can however also be used when Accounts are linked to the Account Type.

Accounts without Account Types are referred to in the GUI as "No Account Host" and are displayed as a red icon instead of the standard blue Account icon. These Accounts are not represented outside of the accounting system in any Account Hosts

Allocation Calculation

This parameter determines the mechanism by which the allocation to an Account Type will be made.

The default option is the "Available Resource Allocation Table" entry. When this is chosen, a piecewise relationship must be specified for the Account Type that matches the Account Type’s allocation to a volume of available resource. Example uses of this option are for the Victorian HRWS and LRWS volumetric entitlements.

The other option is "Function", allows the modeller to specify the function by which allocation is calculated. This function may reference a wide range of variables available in the model, including allocations to other account types and resource assessment systems. Example applications of the "Function" option would be for spill entitlement, reserve, carryover, off-quota and nested or linked resource assessment system Account Types.

A function could be used to implement an adjustment to allocations to comply with the Murray Darling Basin cap, such as in the Goulburn-Broken system. In this instance, a relationship of the rolling average "cap" diversions minus modelled diversions versus allocation reduction percentage is applied to reduce LRWS allocations. The function would incorporate:

A time series of rolling average cap diversions;
Comparison of modelled Usage to date and the time series, to determine the difference;
Use of the look-up table determine the reduction amount; and
Application of the reduction to the percentage allocation.

Available Resource verses Allocation (ARA) Table

The ARA table described in the previous sub-section contains a relationship for all Account Types with the relevant Allocation Calculation Method.

Use of the ARA table for multiple Account Types allows the modeller to define the interdependencies between them. One example is the transmission and operating loss account (TOL) for the Lachlan system. At each level of available resource, a volume is reserved for TOL, which cannot be allocated to high and general security account types. An ARA table with TOL and other Lachlan system account types is shown in Figure 4.

Figure 4. Available resource versus allocation table (example only)

Another example is the relationship between HRWS and LRWS account types in Victorian river systems to implement a reserve policy. In this case, the allocation is done according to projections over one year and two year planning periods, as shown in Figure 4.

It can be seen from table that as the resource available increases, allocations increase up to 100% of HRWS entitlements based on the ARA relationship for the one year planning period. There will be no increase in allocation after 100% until enough resource is available to supply 100% of HRWS entitlements in the following season. Then allocations greater than 100% or LRWS allocations can be announced with further improvements in the available resources, using the ARA relationship for the two year planning period. The ARA tables to implement this type of relationship between Account Types in two such Annual Accounting systems (1 year planning, 2 year planning) are shown.

Method to apply for this Account Type in the ARA Table

This parameter caters for the different ways allocations are announced over the water year. The options are:

Percent (with linked volume) - This is designed for cases where allocations are announced as a percentage of the annual volumetric entitlements. This is generally the case in NSW and Victorian systems. The "linked volume" is the total volume of shares for the Account Type - which represents the volume allocated to the Account Type at 100% allocation (see the sub-section on the Shares parameter for more detail). For each ARA Table row, the modeller specifies a percentage which is multiplied by the share volume and included in the (read-only) available resource column total.
Percent (with Function) - Allocations can be announced as a percentage of annual volumetric entitlement. This gives the modeller more flexibility to define percentage by function in ARA Table rows.
Volumetric - used when allocations are announced as a volume. This is the case in the Wimmera / Glenelg system and in the Lachlan for basic rights (native title rights, domestic and stock rights).
Monthly Varying - Volumetric allocations to some Account Types will change over the year. An example is the TOL account type in the Lachlan system. The TOL volume may change each month due to the fact that losses such as evaporation varies according to climatic and other conditions. The modeller can also specify whether the month’s TOL volume should be used for the whole month, or whether it is necessary to interpolate between current and next month values to determine TOL for a particular day.
Function - Allocations are announced through a user-defined function which is fixed and not based upon the Available Resource. Only a single function can be assigned.

A common usage misconception with inputting values into the ARA Table is that the "Resource" field can have values entered. This field is read-only and is calculated based on the Account Type entries.

The Account Type’s allocation entry options are:

Percent with linked volume - The modeller enters a number of shares for the account type. In each row of the ARA table, the modeller inputs the account type’s allocation percentage. Source calculates the account type’s corresponding allocation volume for the row as:

If Use Shares From Accounts is "Yes", the account type’s share volume is derived from its accounts:

If Use Shares From Accounts is "No", the modeller has entered the account type’s share volume:

Volumetric - The modeller enters the account type’s allocation for each table row - ARAAllocation(type,r).
Monthly varying - The modeller enters a monthly time series of allocation volume for each table row - ARAAllocation(type,r,m).

The value shown in the Resource column of the ARA table is the sum of allocation volumes for each of the account types - ARAAllocation(type,r).

Equation 9

Equation 10

Announced Increment and Maximum Announced Percent

Allocation increments are calculated each time there is a reassessment and distributed to accounts. This is to model the "Announced Allocations" made over a season or water year. For example, in the northern Victorian systems (Goulburn and Murray), allocations are announced fortnightly during droughts and monthly in normal and wet years.

When Method to Apply for this account type in the ARA table is "Percent (with linked volume)", the increment is calculated as a percentage. Percentage announced allocations are often made in increments, hence Source rounds the percentage allocated to the nearest value of Announced Increment. To allow for situations where there is a maximum percent allocation allowed, Source allows the modeller to configure a parameter to limit the allocation percentage.

Source does not cater for negative allocations. The lowest value is zero. However, negative adjustments can be made via Triggers.

Carryover

Carryover behaviour is configured on an Account Type bases and affects all the Accounts of this type. This affects the carryover balance and how it is used by the system.

Carryover relies on triggers to move allocation from the Account Balance to the Carryover Balance. It is possible to specify a wide range of events that cause the carryover trigger to execute, however, this is normally done at the end of the Water Year in the Post phase just before Account truncate / write-off. When a carryover trigger is used, the amount to carry over (add to the account type’s entitlement) is calculated as shown in Equation 5.

Equation 5

where:

Carryover_Max(type) is the maximum carryover limit for the Account Type

a is an Account of Account Type

Balance(a) is the balance of Account

Carryover_%(type) is the specified carryover percentage for the account type

type is the Account Type

When Carryover is configured at the Account Type it is only possible to assign water to the Carryover Balance via Triggers. Unless this is done the Carryover Balance will remain 0 even though a separate entry for Carryover will exist in each Account Host which can be separately prioritised.

Maximum effective allocation - a limit to total water availability. If there is a limit, user specifies the maximum proportion of entitlement allocated + carried over to account permitted at any time in the water year. This is to limit volume allocated so as not to exceed a maximum limit and also to ensure that any water that can not be allocated to an individual account will be reallocated to other users.

Carryover Type - user can define whether carryover is spillable or not. If "Non Spillable" is selected, then there is no (zero) spillale water. If "Spillable", source provides two methods for calculating spillable water which is controlled by the Spillable Volume Calculation Method. These are:

Carryover - Use, spillable water is equal to carryover - total usage from carryover - total spill reduction from carry over, which means all the remaining carryover (after any usage or deduction) is spillable. This is taken into account so resolves to be simply the current Carryover
Total water - 100% is for Victoria case. It sums the allocation for each account which have already occurred this Water Year and adds the scaled Carryover entitlement over the whole year. The overall Account entitlement is deducted as is the total SpillReduction so far this Water Year. If the parent Account Type is configured for Water being Available While Spillable then the amount is deducted by the Carryover usage so far this water Year,

Equation 3.1 - Carryover - Use

Equation 3.2 - Total Water - 100%

Do not Carryover Spillable Water - to define whether spillable water can be carried over to next water year.

Spillable Trigger - If carryover is spillable, the user can enter a function to determine if water remains spillable in the current time-step. This will generally be a boolean function of time of year or storage(s) levels. The format of boolean function is "IF A>B,1,0", "1" indicates the action will occur and "0" means action will not happen.

Water Available While Spillable - controls whether water is available while spillable. For most spillable water account, spillable water is not available to the user, however, Victoria Inter-Valley Transfer accounts are useable while spillable.

Basis of Spilling - determines how to calculate spill reduction shared among users, three options are available:

Emptied on spill or pre-release is to totally empty spillable water account if a spill or pre-release occurs.
Reduce Pro-rata is to spill based on proportion (account spillable water / total spillable water) of spill source volume.
Equalise spillable carryover proportions is a rule special for Barmah-Millewa Forest spill. The way this spilling rule works is:
- Spill first from the account with the greatest carryover as a percent of its entitlement.
- When the percentage carryover of the first account reaches the percentage of the second account, spill from the first and second pro-rata until the third highest account is reached,
- Continue on as above until all carryover is spilled or all spill is assigned.

Spill Reduction Priority - to specify priority of spill, the lower the number the higher the priority, for example, an Account Type with "1" priority will spill prior to an Account Type with "2" priority. If different Account Types are emptied on spill and have different priorities, the second priority Account Type does not empty until volume of physical spill after empty on spill triggered exceed the amount written off the first priority carryover account. But if different physical spill sources are used this does not apply. If different Account Types use the same spill source and have the same spill priority, the order to spill for different basis is Emptied on spill first, followed by Equalise Spillable Carryover Proportions and Reduce Pro-rata has the lowest priority.

Priority for Spill Reduction and Account Type priority are not related. The specified priority set in the Carryover tab of the Account Type is independent of the Account Type priority.

Use Account Type Spill Volume - to specify a separate spill volume source for each Account Type. If specified, the volume specified for an Account Type would be used in preference to the allocation system spill source (configured at the System level). This is to cope with Barmah-Millewa water which receives allocation from both the Victorian and NSW allocation systems.

A flow chart is listed below to show how spillable water and spill reduction are calculated in resource assessment post phases.

Figure 5. Spill Reduction Process.

Non-Debit Accounts

Non-debit accounts are designed for New South Wales Murray, Murrumbidgee and Upper Namoi river systems. During wet periods or times of low water demand, natural inflows may result in dams overflowing or significant flows in regulated rivers. When these uncontrolled flows exceed any immediate water needs and any specific environmental requirements as set out in the environmental flow rules they may be made available to licence holders on regulated rivers. Any water extracted is not debited against the licence holders regulated allocation and therefore supplements their normal regulated allocation. Extraction of this supplementary water have been termed "off allocation". To get without debit water to work, user needs to set up an off-allocation system.

The Murrumbidgee limits on the volumes that can be diverted without debit use the term "modified effective allocation" which is defined in Equation 4. The Murrumbidgee water sharing plan limits the total amount of without debit diversion (WDD) that can be taken in a year by an individual.
The Murray water sharing plan limits availability to without debit water based on the announced allocation level which should be less than availability threshold. The Murray water sharing plan limits the total amount of without debit diversion that can be taken in a year by an individual.
The Belubula water sharing plan limits the volume that can be diverted without debit on the basis of available water. Users are also required to repay their without debit use as soon as a subsequent available water determination is made, unlike the Murray and Murrumbidgee where the debit is repaid as the available water determinations and without debit use exceed the upper threshold.

For Upper Namoi river systems, the total amount of Without Debit Diversion that can be taken in a year by an individual. So the remaining off-allocation balance for an individual balance is as shown

When off-allocation balance drops below zero is the point where some of the off-allocation has to be converted to on-allocation.:

Equation 4 - Mod Effective Allocation

Equation 4 - Ratio

Equation 5 - Murray

Equation 6 - Murrumbidgee

Equation 7 - Upper Limit

Equation 8 - Off Allocation

Accounts

Accounts represent an Account Host's entitlement to a type of water. Hence, they are linked to an Account Type and have a number of shares in that Account Type’s allocation. A water user may have more than one account in an Annual Accounting system. For example, Victorian water users may hold both a HRWS and LWRS accounts. In the Thomson / Macalister system, water users may also have a spill entitlement and off-quota account.

Previous usage, usage tracking and usage limits

The modeller can configure the account’s Previous Usage for the water year. Source keeps track of usage over the water year so that it can be taken into account when calculating the available resource (see the Usage to Date sub-section) and allocation (see the Allocation Calculation Method sub-section under Account Type). Account level usage caps may also apply in Annual Accounting systems - this can be implemented by adding a usage limit to the Account.

Unit shares/Entitlement

Although this parameter is expressed as a volume, it usually represents a number of unit shares assigned the account. Parameters for the associated account type determine when Number of Shares represents a volume at 100% allocation:

The Account Type is not in the ARA Table (Allocation Calculation Method is "Function"); or
The Account Type is in the ARA Table, and:
- Method to Apply for this account type in the ARA table is "Percent (with linked volume)"
- Use Unit Shares/Entitlement From Accounts? is "Yes"

Most general security access licences are expressed as a relative unit share of the available water rather than as an annual volume (CSIRO, 2008a).

For calculations relevant to Number of shares / Entitlement, see the sub-section on Allocate to Account Types and Accounts within each Account Type in Model Phase: Resource Assessment and Water Accounting.

Initial Account Balance and Account Balance

This parameter is the starting Account Balance. Account Balance is used in Source to limit to the volume of water a water user may order and/or access using the account. During resource assessment, the Account Balance is credited with the account’s share of the allocation to the Account Type.

Initial Allocation

Allows the user to set what proportion of the Entitlement that is initially allocated.

initial Carryover Scalar

Carryover Scalar initial setting. This controls how much of the Carryover Start of Water Year is assigned to the Carryover Balance so far this Water Year,

Carryover Start of Water Year

This represents the total amount of potential Carryover that can be assigned to the Account based on the Carryover Triggers from the previous Water Year. This is scaled by the Carryover Scalar which controls how much of this total Carryover volume that has been assigned to the Carryover Balance.

Previous Spill from Carryover

Sets-up the previous spill that has been already accounted for in the current Water Year,.

Model phase: Initialisation

Variables are initialised as follows:

The previous allocation to each Account Type (AllocPrevious%(type), AllocationPrevious(type)) is zero for the first time-step;
If the modeller has specified account limitations based on a unit share then the total volumetric limitations for each account are determined; and
Account usage is initialised by evaluating the previous usage settings specified by the modeller and the total accumulated for the RAS.

Model Phase: Time-step Beginning, Time-step End

At the start or end of a time-step, Annual Accounting triggers may be executed, depending on configuration. If the trigger condition returns a true value, the trigger action is executed. By default Annual Accounting systems have a start of water year trigger for reassessment.

Actions at the start of a water year

At the start of each water year the running usage totals etc. are reset to zero.

Model Phase: Resource Assessment and Water Accounting

Figure 5b provides an overview of the Annual Accounting resource assessment method. More detail on the steps involved follows.

Is resource assessment undertaken this time-step?

Calculate available resource. Any functions which are used to define storage, recession factor, other resource, commitments or usage to date are evaluated and then the available resource is calculated as shown in Equation 1.

Set up a version of the ARA table for this time-step

The modeller can opt to use an Available Resource Allocation (ARA) table to calculate allocation for an Account Type, in which case the table must be set up for the current time-step.

The following steps are repeated for each row r in the ARA table:

Initially the resource column has a zero value: ARAResourceNow(r)=0
This time-step’s allocation is calculated for ARA table Account Types:
For each Account Type in the table:
1. The Account Type’s allocation volume for this row in the current time-step is calculated as:
  1. If "Percent with linked volume" or "Volumetric", the allocation percentage/volume entered during model configuration is used
  2. If "Monthly varying", allocation volume depends on the current time-step’s date:
  3. If "Threshold", or the current time-step is the first day in the month, or the current time-step’s month is the end month of the water year, the allocation values for the current time-step’s month m1 are used:
    Equation 10
    Otherwise, interpolation is used to determine allocation at the point for the current time-step that is between values defined for the current month, m1, and next month, m2:
    Equation 11
2. The account type’s allocation volume is added to the resource column:
  Equation 12

Figure 5b. Resource Assessment Flowchart.

Calculate Allocation for each Account Type

Option 1: Calculate allocation using the ARA table

Whenever a resource assessment is made, each row is processed to determine the resources it requires. This is done by calculating how much water is required to achieve the defined allocation level in each account, subject to constraints on the maximum effective allocation and the impact of non debit use. The ARA table is then sorted in ascending order based on the amount of resources required.

1. Two rows r1, r2 are extracted in the ARA table where:

1) the row with the nearest lower required resource than the available resource.
2) the row with the nearest higher required resource than the available resource.

AvailableResource ≤ ARAResourceNow(r1), and AvailableResource > ARAResourceNow(r2)

An interval halving technique is then used in Source to find the actual allocation that can be achieved given the current level of AvailableResource. This approach allows for a segmented relationship between percent allocation and required resource when carryover and non debit use allowances are being truncated as total allocation limits are reached.

- If "Percent with linked volume", this value is referred to as AllocRaw%(type);
- Otherwise, the raw allocation volume is the final one for now - referred to as AllocationNow(type)

2. If "Percent (with linked volume)", allocation rules are applied for the account type to get a final allocation:

a. The percentage allocation is truncated to the nearest value of announced increment, Increment%(type)

Equation 13

b. The allocation is capped to the maximum announced percent specified by the modeller, MaxAlloc%(type):

Equation 14

Equation 15

3. If necessary, the allocation is adjusted to ensure it does not decrease (If the annual accounting RAS is required to cater for a negative allocation increment which would remove water from a water user’s balance, then it will be reviewed for a later phase.)

- If Method to Apply for this account type in the ARA table is "Percent with linked volume"

Equation 16

- Otherwise

Equation 17

Option 2: Forced allocation (via function)

The modeller may "force allocation" by selecting "function" as the Allocation calculation method, and configuring an allocation function. When this is done, the allocation percentage is the result of the function. As for allocation via the ARA table, the allocation must not decrease from the previous assessment, so:

Equation 18

Allocate to account types and accounts within each account type

Water is allocated to account types based on the incremental increase in allocation for that account type since the last resource assessment.

1. The change in allocation from the previous resource assessment is calculated - AIP(type) if the increment is a percentage, or AIV(type) if the increment is a volume. Note that for the first announcement of the water year the increment is equal to the allocation.

2. The incremental allocation is distributed to accounts based on account shares:

a. The amount to credit to each account a is determined in the following way

Equation 19

- - - - If Use Shares From Accounts is "No", NoOfShares(a) is the number of unit shares held by the account and Shares(type) is the volume for the account type at 100% allocation so:

Equation 20

- - - - If Method to Apply for this account type in the ARA table is "Volumetric" or "Monthly Varying":

Equation 21

- - - - Where Allocation Calculation Method is "function", the calculation is the same as for the ARA table’s "Percent (with linked volume)":

Equation 22

b. Each account’s credit volume Credit(a) is added to its AccountBalance(a)

c. Totals allocated to each account type, and to the system as a whole are accumulated for reporting.

Save Allocation for each Account Type

Calculation of incremental allocation requires that the allocation for each account type from the previous resource assessment is saved.

If allocations are expressed in terms of a percentage:

Equation 23

If allocations are expressed in terms of a volume:

Equation 24

Model Phases: Time-step - Order and Flow Distribution

The working of these phases is described in detail in the SRG sections on Continuous Sharing - SRG, Continuous Accounting - SRG and the Water user node SRG.

In summary, at Account Hosts with the "Account Sharing" option selected, every order placed uses an Account. The volume ordered using the Account is limited to the Account Balance. Accounts are debited either for orders placed (if the account is of an order-debit account type), or usage (where the account is of a use-debit Account Type). Water-order accounts are debited in the order phase and the total is re-credited for shortfalls in the flow distribution phase. Account Host Accounts are debited for "usage" in the flow distribution phase.

The Account Hosts perform some complex processing to determine the "usage" to assign to accounts. A running total of usage for the water year for each account is tracked by Source. This total may be referenced by Annual Accounting triggers that cap usage.

Variables used

The variables used by the model are summarised in Table 2.

Table 2 - Variables Used in Annual Accounting

Symbol	Purpose / Description	Units	Usage
a	An account in a resource assessment system (RAS)	n/a	Configuration, Initialisation, Ordering, Flow
AccountBalance(a)	The volume of water available in the current time-step for an account a.	volume	Initialisation, Resource allocation, Ordering, Flow
AIP(type)	Allocation increment percentage: The % change in allocation from previous resource assessment.	%	Resource Allocation
AIV(type)	Allocation increment volume: The volumetric change in allocation from the previous resource assessment.	volume	Resource Allocation
AllocNow%(type)	The percentage of available resource volume to allocate to account type type in the current resource assessment.	%	Resource Allocation
AllocRaw%(type)	The raw value of AllocNow%(type) - that has not been rounded to increments or modified to ensure an increase.	%	Resource Allocation
AllocPrevious%(type)	The percentage of available resource volume that was allocated to account type type in the previous resource assessment.	%	Resource Allocation
AllocationNow(type)	The total volume of resource allocated to account type type in the current resource assessment.	volume	Resource Allocation
AllocationRaw(type)	The raw value of AllocationNow(type) - that has not been rounded to increments or modified to ensure an increase.	volume	Resource Allocation
AllocationPrevious(type)	The total volume of resource allocated to account type type in the previous resource assessment.	volume	Resource Allocation
ARAAllocNow(type,r)	ARA Table - current resource assessment: The volume to allocate to account type type when the available resource volume equals ARAResourceNow(r)	volume	Resource Allocation
ARAAllocation(type,r)	ARA Table - input: The volume to allocate to volumetric account type type when the available resource volume equals ARAResource(r).	volume	Configuration, Resource Allocation
ARAAllocation(type,r,m)	ARA Table - input: The volume to allocate to monthly varying account type type when the available resource volume equals ARAResource(r,m).	volume	Configuration, Resource Allocation
ARAAlloc%(type,r)	ARA Table - input: The percentage of available resource volume to allocate to account type type at the resource level in the current row r.	%	Configuration, Resource Allocation
ARAResource(r)	ARA Table - calculated on input: The volume of available resource for the allocation in row r.	volume	Configuration, Resource Allocation
ARAResource(r,m)	ARA Table - calculated on input: The volume of available resource in month m corresponding to the allocations in row r (including TOL account type).	volume	Configuration, Resource Allocation
ARAResourceNow(r)	ARA Table - current resource assessment: Volume of available resource given the allocation for all account types in row r.	volume	Resource Allocation
AvailableResource	Total volume of water available for allocation in the annual accounting system.	volume	Initialisation, Resource Allocation
Credit(a)	Amount credited to account a.	volume	Resource allocation
dd	Index of the current day in the month.	n/a	Resource allocation
Increments	Number of increments of change in the allocation for account type type in the current resource assessment.	n/a	Resource Allocation
Increment%(type)	"Announced Increment": The unit of change in allocation percentage for account type type (input).	%	Configuration, Resource Allocation
MaxBalance(a)	Maximum volume that can be held in an account at any one time.	volume	Configuration, Initialisation, Resource allocation
MaxAlloc%(type)	"Maximum announced percentage" allocation	%	Configuration, Resource Allocation
m, m1, m2	Index of a month	n/a	Initialisation, Resource Allocation
NoOfShares(a)	Number of shares assigned to an account. If an allocation % function or the Use shares from accounts option is "Yes", it is also a volume at 100% allocation.	n/a	Configuration, Initialisation
r, r1, r2	Index of a row in the ARA table.	n/a	Configuration, Resource allocation
Shares(type)	"Shares" assigned to an account type - entered by the modeller. This is actually a volume at 100% allocation.	volume	Configuration, Initialisation
type	An account type	n/a	Configuration, Initialisation, Resource allocation
fAllocExpr(type)	Function that returns the current allocation for account type type as a percentage	%	Resource allocation
truncate()	Function that truncates a number and returns the integer value	n/a	Resource allocation

Input data

Input data is summarised in the following tables:

Configuration parameters - Table 3;
Allocation parameters - Table 4;
Trigger parameters - Table 5. The parameters listed in this table are a sub-set of those described in Table 8;
Account Type parameters - Table 6;
Account parameters - Table 7;
Per-trigger parameters - Table 8. There is one set of the parameters in this table for each trigger in the Annual Accounting System.

Table 3. Configuration parameters

Parameter	Description	Units	No. of values	Allowable values & validation rules	Default Value(s)
Storage node name	Name of a storage in the river network.	n/a	1 per scenario storage	Read only	n/a
Include storage?	Indicates whether the storage in this row is a resource for this RAS.	n/a	1 per scenario storage	"Yes" or "No"	"No"
Inflow node name	Name of an inflow node in the river network	n/a	1 per scenario inflow node	Read only	n/a
Include inflow node?	Indicates whether the *outflow from the inflow node in this row is a resource for this RAS.	n/a	1 per scenario inflow node	"Yes" or "No"	"No"
Recession factor function	function to calculate recession factor to apply to *outflow at this row’s inflow node.	n/a	1 per selected inflow node	Must return a real number ≥ 0	0
Other resource name	Name of another resource	n/a	1 per other resource	Alphanumeric characters	none
Other resource function	function to calculate a volume of the "other resource" in this row	volume	1 per other resource	Must return a real number ≥ 0.	none
Commitment name	Name of a commitment	n/a	1 per commitment	Alphanumeric characters	none
Commitment function	function to calculate volume of "commitment"	volume	1 per commitment	Must return a real number ≥ 0.	none
Usage to date	Option as to how to determine usage to date.	volume	1	"Usage From function", "Usage From Water User"	"Usage From function"
function	function to calculate usage to date.	volume	1	Must return a real number ≥ 0.	none

*This will be changed to tributary inflow in future versions of Source

Table 4. Allocation parameters

Parameter	Description	Units	No. of values	Allowable values & validation rules	Default Value(s)
Date for resource calculation	Date the ARA table resource and monthly varying account type allocation columns apply to.	n/a	1	Valid date on/after the start of the water year.	Start of the water year
Available Resource versus Allocation Table: Resource	Volume of available resource (on the currently selected Allocation date where relevant)	Volume	1 per table row	Read only (calculated)	Sum of account type allocations
Available Resource versus Allocation Table: <Account type> Allocation%	Percentage of account type’s share volume to allocate	n/a	1 per table row & "Percent (with linked volume)" allocation method account type	Real number between 0 and 100.	0
Available Resource versus Allocation Table: <Account type> Allocation	Account type’s allocation (on the current selected date if monthly varying account type).		1 per table row & "Volumetric" or "Monthly varying" allocation method account type	"Volumetric" account type: Real number ≥ 0 "Monthly varying" account type: Read only (calculated)	0
Monthly Varying Table: Resource	Volume of available resource	Volume	1 per ARA table row	Read only	Same as the ARA table Resource value
Monthly Varying Table: <Month>	The monthly varying account type’s Allocation volume for the month <Month>.	Volume	1 per ARA table row & month in the year.	Real number ≥ 0	0

Table 5. Trigger parameters

Parameter	Description	Units	No. of values	Allowable values & validation rules	Default Value(s)
Name	Name of the trigger	n/a	1 per trigger	Read only	none
Parent	Type of resource assessment system trigger is in	n/a	1 per trigger	Read only	"Annual Accounting"
Type	See Table 8 - this is the Trigger parameter.	n/a	1 per trigger	Read only	"Annual Accounting"
Action	See Table 8 - this is the Action Type parameter.	n/a	1 per trigger	Read only	"Annual Accounting"

A default "Start of Water Year" trigger is created with each new annual accounting system:

Parent: The annual accounting system’s name
Type: "Start of Water Year"
Action type: "Re-assessment"
Execution: "Timestep beginning"
Time-steps from last assessment: "1"

Table 6. Account type parameters

Parameter	Description	Units	No. of values	Allowable values & validation rules	Default Value(s)
Account type name	Name of the account type	n/a	1	Alphanumeric	Account type <seq no.>
Debit type	Indicates whether accounts of this type are to be debited on ordering or use of resource.	n/a	1	"Order", "Use"	"Order"
Entitlement Priority	Determines order in which the account type will be credited during a resource allocation.	n/a	1	Integer ≥ 1	1
Minimum balance type	Indicates whether the minimum balance is specified, and if so, whether it is an absolute volume or per unit share	n/a	1	"Unrestricted" , "Absolute volume", "Per unit share"	"Unrestricted"
Minimum balance	Minimum balance absolute or per unit share volume.	volume	1	Real number ≥ 0	0.01
Maximum balance type	Indicates whether the maximum balance is specified, and if so, whether it is an absolute volume or per unit share	n/a	1	"Unrestricted" , "Absolute volume", "Per unit share"	"Unrestricted"
Maximum balance	Maximum balance absolute or per unit share volume.	volume	1	Real number ≥ 0	0.01
Allocation calculation	Indicates whether account type allocation will be done via the ARA table, or function	n/a	1	"Available resource allocation table", "Percentage function", "Volumetric function"	"Available resource allocation table"
Allocation function	function to calculate allocation for the account type	n/a	1	Result must be a real number, and: if Allocation calculation = "Percentage function" 0 ≤ result ≤ 100. If Allocation calculation = "Volumetric function", result ≥ 0.	none
Method to apply for this account type in the ARA table	Indicates how allocation for this account type will be described in the RAS’s ARA table.	n/a	1	"Percentage: exclude share volume", "Percentage: include share volume", "Volumetric", "Monthly varying"	"Percentage: exclude share volume"
Monthly varying calculation method	Dictates whether to interpolate or use threshold values for allocations at a resource assessment date.	n/a	1	"Interpolate", "Threshold"	"Interpolate"
Announced increment?	Indicates whether new allocations will be given in multiples of an announced increment.	n/a	1	"Yes" or "No"	"No"
Announced increment	Percentage/ratio of available resource that will be allocated in a block to the account type.	% or ratio	1	Real number between 0 and 100.	1%
Announced increment unit type	Indicates whether announced increment is a % or ratio (proportion).	% or ratio	1	"%" or "proportion"	"%"
Maximum allocation?	Indicates whether there is a maximum percentage of available resource to allocate to the account type.	n/a	1	"Yes" or "No"	"No"
Maximum allocation	Maximum percentage/ ratio of available resource that will be allocated to the account type.	% or ratio	1	Real number between 0 and 100.	100
Maximum allocation unit type	Indicates whether maximum allocation is a % or ratio (proportion).	% or ratio	1	"%" or "proportion"	"%"
Use shares from accounts?	Indicates whether to enter shares or accumulate them for all the account type’s accounts.	n/a	1	"Yes" or "No"	"No"
Shares	Volume to allocate to the account type at 100% allocation.	volume	1	Real number ≥ 0	0

Table 7. Account parameters

Parameter	Description	Units	No. of values	Allowable values & validation rules	Default Value(s)
Account name	Name of the account	n/a	1	Alphanumeric	Account <seq no.>
Associated water user node	Water user node associated with the account	n/a	1	A water user node in the scenario.	The first water user node added
Number of shares	The account’s number of unit shares in the account type’s allocation. For percentage based allocation it is the allocated volume at 100% allocation.	volume	1	Real number ≥ 0	0.001
Previous usage	Previous usage of the account’s allocation in the water year at the date when the model run starts.	volume	1	no value or Real number ≥ 0	none

Table 8. Pre-trigger parameters

Parameter Name	Parameter Description	Unit Type	No. of values	Allowable values & validation rules	Default Value(s)
Name	Name of the trigger	n/a	1	Alphanumeric (Read only)	none
Trigger Type	Type of condition that causes the trigger to operate	n/a	1	Specified date, Start of Water Year, End of Water Year, Storage level, Season, Per timestep, Monthly Trigger , function	"Start of water year"
Execution	The part/phase of the timestep in which to perform the action.	n/a	1	"Timestep beginning", "Timestep end"	"Timestep beginning"
Specified Date	The date at which the trigger action is performed.	dd-mmm	1	Day and month within year, format dd-mmm	Today’s day & month
Storage	Name of the storage that the "Storage Level" trigger applies to	n/a	1	Storage in the river network	none
Level change type	Type of level change that causes the "Storage Level" trigger action to occur.	n/a	1	"Rising", "Falling"	"Rising"
Level	The "Storage Level" trigger action will occur when Storage has the Level change type (rises/falls) to reach the Level.	Depth	1	Real number	0
Time-steps	Number of time-steps between a trigger action (if 1, then every time-step.).	n/a	1	Integer ≥ 0	1
Season start date	Date at which the season starts (the season in which the trigger action occurs)	n/a	1	Day and month within year, format dd-mmm	Today’s day & month
Season end date	Date at which the season ends (the season in which the trigger action occurs)	n/a	1	Day and month within year, format dd-mmm	Today’s day & month
Offset from	Defines whether the action date is offset from the start or end of the month.	n/a	1	"Start of the month", "End of the month"	"Start of the month"
Days offset	Number of days the action date is from the start/end of the month.	n/a	1	Integer ≥ 0	0
Action Type	Type of action to perform when the triggered condition is true.	n/a	1	Transfer, Truncate accounts, Write-off accounts, Per-unit share allocation, Assign allocation, Reassessment, Carryover (Read only)	"Transfer"
Account type	Account type action applies to for the following action types: truncate, write-off, per-unit share allocation, assign allocation, carryover.	n/a	1	Account type in the annual accounting RAS	none
Amount	The volume to change/limit account balances to/by for the following action types: truncate, per-unit share allocation, assign allocation.	Volume	1	Integer ≥ 0	0
Carryover%	The percentage of the balances of accounts of the specified type to carryover when action type is "Carryover".	%	1	Integer ≥ 0	0
Re-assessment time-steps	The number of time-steps between each standard resource allocation when Action Type ="Re-assessment"	n/a	1	Integer ≥ 1	0
From account type	Account type to transfer allocation from when Action Type = "Transfer"	n/a	1	Account type in the annual accounting RAS	none
To account type	Account type to transfer allocation to when Action Type = "Transfer"	n/a	1	Account type in the annual accounting RAS	none
Transfer%	Percentage of allocation to transfer between accounts of specified type when Action Type = "Transfer"	%	1	Integer ≥ 0	0

Table 9. Account Type recorded output variables

Attribute	Description	Units	Range
Account balance	The sum of all balances of accounts associated with the account type after the time-step order phase.	volume	Real number > 0
Account balance pre-phase	The sum of all balances of accounts associated with the account type before the time-step order phase.	volume	Real number > 0
Carryover	The carryover volume for the account type (only relevant if a carryover trigger has been configured). For a description of the calculation, see the sub-section Carryover trigger under Account types and the ARA table.	volume	Real number > 0
Change in allocation	The difference between the account type’s total allocation volume in the current and previous time-step, ie the amount credited in the time-step. See AIP(type) and AIV(type) under Allocate to account types and accounts within each account type under Model Phase: Resource Assessment and Water Accounting).	volume	Real number > 0
Order/Use debit	Sum of the "usage" debited from the balance of all the account type’s accounts in the time-step.	volume	Real number > 0
Percent per share entitlement	Only applicable for account types with percentage based allocation (via the ARA table or a percentage function). This value multiplied by a total share volume is used to determine volumetric entitlement for the time-step. (The account type’s total share volume may be specified, or the sum of account shares depending on configuration).	%	Real number > 0
Total Usage Water Year	The sum of usage deducted from all the account type’s accounts over the defined water year.	volume	Real number > 0
Volumetric entitlement	Only applicable for account types with volumetric allocation. It is the account type’s entitlement for the time-step expressed as a volume. If there are associated accounts, it should normally match the sum of account balances. There are instances where this may not be the case, for example if account maximum balances limit allocation, or the available resource decreases over the water year	volume	Real number > 0

Parameters or Settings

When modelling an existing continuous accounting system, the values of parameters adopted will be dictated by rules governing the operation of the system in place. When modelling new systems or modifications to existing systems, it will be a matter of professional judgement and consultation with stakeholders as to reasonable values to explore, combined with "trial and error" solutions, to arrive at acceptable parameter values.

Output data

Output data is summarised in the following tables:

Account Type recorded output variables - Table 10;
Account recorded output variables - Table 11; and
Recorded output variables - Table 12

Results are provided for each time-step, although they are only calculated in resource assessment time-steps.

Table 10. Account type recorded output variables

Attribute	Description	Units	Range
Account balance	The sum of all balances of accounts associated with the account type after the time-step order phase.	volume	Real number > 0
Account balance pre-phase	The sum of all balances of accounts associated with the account type before the time-step order phase.	volume	Real number > 0
Carryover	The carryover volume for the account type (only relevant if a carryover trigger has been configured). For a description of the calculation, see the sub-section Carryover trigger under Account Types and the ARA Table.	volume	Real number > 0
Change in allocation	The difference between the account type’s total allocation volume in the current and previous time-step, ie the amount credited in the time-step. See AIP(type) and AIV(type) under Allocate to account types and accounts within each account type under Model Phase: Resource Assessment and Water Accounting).	volume	Real number > 0
Order/Use debit	Sum of the “usage” debited from the balance of all the account type’s accounts in the time-step.	volume	Real number > 0
Percent per share entitlement	Only applicable for account types with percentage based allocation (via the ARA table or a percentage function). This value multiplied by a total share volume is used to determine volumetric entitlement for the time-step. (The account type’s total share volume may be specified, or the sum of account shares depending on configuration).	%	Real number > 0
Total Usage Water Year	The sum of usage deducted from all the account type’s accounts over the defined water year.	volume	Real number > 0
Volumetric entitlement	Only applicable for account types with volumetric allocation. It is the account type’s entitlement for the time-step expressed as a volume. If there are associated accounts, it should normally match the sum of account balances. There are instances where this may not be the case, for example if account maximum balances limit allocation, or the available resource decreases over the water year.	volume	Real number > 0

Table 11. Account recorded output variables

Attribute	Description	Units	Range
Account balance	The balance of the account after the time-step order phase.	volume	Real number > 0
Account balance pre-phase	The balance of the account before the time-step order phase	volume	Real number > 0
Change in allocation	The amount allocated to the account in the time-step. See Credit(a) under Allocate to account types and accounts within each account type under Model Phase: Resource Assessment and Water Accounting).	volume	Real number > 0
Order/Use debit	The amount debited from the balance of the account in the time-step (the "usage").	volume	Real number > 0
Total Usage Water Year	The total usage deducted from the account over the defined water year.	volume	Real number > 0

Table 12. Recorded output variables

Attribute	Description	Units	Range
Active Storage	Total volume of water in the annual accounting system’s storages minus the system’s total dead storage volume.	Volume	Real number > 0
Available Resources	Total volume of available resource in the system in the time-step - see calculation in the Available Resource section.	Volume	Real number > 0
Commitments	The sum of the time-step’s result for all the system’s Commitments functions.	Volume	Real number > 0
Inflows	Total recession inflow volume for the time-step - which is the sum of recession inflow volumes in the time-step for all the system’s inflow nodes. See the Tributary Inflow calculation in the Available Resource section.	Volume	Real number > 0
Other Resources	The sum of the time-step’s result for all the system’s Other Resources functions.	Volume	Real number > 0
Total Usage Water Year	If the "Usage from water user" option is specified, this is the sum of usage deducted from all the system’s accounts over the defined water year. Otherwise, it is the time-step’s result of the function specified by the modeller.	Volume	Real number > 0

Reference list

CSIRO (2008a) Water Availability in the Lachlan. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project.

CSIRO (2008b) Water Availability in the Murrumbidgee. A report to the Australian Government from the CSIRO Murray-Darling Basin Sustainable Yields Project.

DSE (2009) A Proposal for Future Carryover Arrangements. Northern Region Sustainable Water Strategy

James, B., Erlanger, P. D. and Hansen, W. R. (1993) Modelling a Complex Irrigation Restriction Policy Using a General Simulation Package. Hydrology and Water Resources Symposium, Newcastle, June 30 - July 2.

NRE (1995) The Bulk Entitlement Conversion Process. Bulk Entitlements Report Series No. 2, Department of Natural Resources and Environment, Victoria.

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