Continuous accounting

A continuous accounting resource assessment system can be created in Source to replicate the resource assessment system used in the Gwydir and Namoi in NSW. There are a number of defining features of a continuous accounting system which differentiate it from continuous sharing and annual allocation systems:

• Assessments of whether a new allocation can be made occur intermittently (based on triggers defined within the plan) with a new allocation resulting in an additional volume of water added to user’s accounts. With continuous accounting, there is no end of year forfeiture of allocation. There are, however, limits on the volume that can be held in a general security account at any one time and usage limits may also apply;
• An account is maintained for the system as a whole to meet transmission and operation losses (TOL) for delivery of regulated water. An accounting process is followed to determine whether any of the available storage volume is unallocated. The unallocated volume remains after the following have been deducted from the active storage volume:
  • reserve required for storage losses;
  • reserve required for high security uses including an allowance for transmission losses to deliver these supplies;
  • existing volume allocated to the generic system share/s;
  • existing volumes allocated to general security entitlements in this system; and
  • the volume required to be held in the system’s transmission and operation loss account.
• High security accounts are assigned an allocation based on a defined relationship between percentage of the high security reserve met and allocation to accounts. The reserve set aside for high security uses is generally greater than the volume that is allocated to the high security accounts. Whilst the full reserve volume is set aside at each resource assessment prior to making an additional allocation, the accounts are only assigned an allocation on an annual basis.

The enhancements to continuous accounting in Source over IQQM are:

• Ability to simulate more than one type of resource allocation and accounting method in the one scenario and to link one system to another;
• Ability to specify data to calculate the initial balance of the usage limit;
• Better simulation of management during dry periods including the ability to:
  • Restrict allocations to high security accounts during dry periods where the required reserve cannot be met;
  • Define the TOL factor as a variable depending on account balances. This allows a higher factor to be defined when balances are low, as a higher proportion of the allocations will be required to cover transmission losses; and
  • Represent the rules which may reduce the required high security reserve.

System configuration

A continuous accounting system can be added to a particular scenario in a project using the Resource Assessment Explorer (Edit » Resource Assessment...). Right click on the scenario and choose Add Continuous Accounting from the contextual menu (as shown here). The parameters to configure are described in Table 1. Note that the Resource Allocation Table defines the allocation priority when there is more than one account type. It also defines the TOL allocations for each eligible system account type.

Figure 1. Continuous accounting (Configuration)

Table 1. Continuous Accounting, Configuration parameters

Account Type

Lists the account types available by default in a continuous accounting system.

Allocation Priority

Determines the order in which account types will be credited during a resource allocation.

When you add a continuous accounting system, the following account types are automatically loaded:

• Storage Loss Reserve - define the reserve required for evaporation and seepage losses from storage;
• High Security Group 1 - define the reserve required for high security users. Also allows you to define accounts which relate to this reserve and the method for allocating water to these accounts;
  • Trigger Write-Off
• High Security Group 2 - same as for High Security Group 1 but relates to a separate, lower priority group of high security users;
  • • Trigger Write-Off
• Generic System Share 1 - used to allocate water to another Resource assessment system;
• General Security 1 - allows you to define accounting rules and shares for general security accounts;
  • Usage Limit One Year; and
  • Usage Limit Three Years.

Accounts

The Accounts tab (Figure 2) provides a summary of the accounts that have been added to the system. A description of the parameters in this tab are provided in Table 2.

Table 2. Continuous Accounting, Accounts parameters

Trigger Priority

The Trigger priority tab (Figure 3) shows how triggers have been prioritised in the system.

Figure 3. Continuous Accounting, Trigger Priority

Storage Loss Reserve

The storage loss reserve (Figure 4) is a volume which is required to account for expected evaporation and seepage losses from the storage. The reserve is debited from the available resource prior to making any other allocations. It may be made a function of the current storage volume or area, which can be specified using an expression. A minimum percentage of the required reserve that must be maintained can also be specified; restrictions are applied to general security accounts (or lowest priority account type) to achieve the required minimum reserve.

The following parameters must be specified:

• Minimum to cover storage losses - Defines the percentage of required reserve below which borrowing occurs. This parameter is not available in IQQM, so it must be set to zero; and
• Storage Loss Reserve Requirement - the reserve required to cover storage evaporation and seepage losses. Note that in IQQM, this requirement is defined through the number of months that evaporation is take into account. In some cases the storage loss is combined into the carryover reserve.

High Security Groups

High Security Groups (Figure 5) define the reserve which is required for high security users (may also be referred to as essential supplies). The high security reserve requirement may be defined using two groups - a higher and lower priority group. In the case where only one group is required, you can delete the other by right clicking on the item and choosing Delete. Additional groups may also be added (right click on the Continuous Accounting system and choose the desired system to be added). This can be specified as a fixed value or as an expression. The latter can be used where there are rules that vary the high security reserve requirement.

High Security accounts are treated as annual accounts with no carryover. In other words, at the start of a water year (as defined at the system level page), all accounts have their existing balance deleted and a new allocation is made. Allocation to high security accounts can be defined using a time series file or simulated based on whether or not the reserve requirement has been met. The Allocation Rules table allows you to define restrictions on allocations to high security accounts if the reserve requirement has not been completely met. The high security shares held by each water user is defined in Accounts. For example, if 1ML is the total reserve, and only 20% of the required high security reserve has been met, then high security accounts will only be given 0.3ML per entitlement share. Table 3 describes the parameters that must be specified.

Generic system share

The generic system share (GSS) is used to allocate water to another resource assessment system. Water user accounts cannot be added directly to the GSS account from within the Resource Assessment Explorer. The accounts associated with the GSS are configured as part of the linked system. The GSS is credited as part of the continuous accounting allocation method and is debited when accounts in the linked Resource assessment system are debited. If an allocation is made to the GSS, this volume is distributed to users as part of the resource assessment phase of the linked system. The configuration dialog is shown in Figure 6.

The following parameters must be specified for a GSS:

• Time Series Allocation - Enables the entry of a function for allocating to the GSS;
• Simulate Allocation - Define an expression to allocate to GSS. The value of the expression is treated as a volume to be added to the GSS account subject to available water limitations; and
• Total Volume Initial Balance - Initial balance in the GSS account.

GSS is generally used with resource assessment system linking to an annual accounting system where a portion of the resource assessment system is determined by the output of another system.

TO BE CHANGED:

In the Resource Assessment Explorer, when you choose to the Function Editor dialog allows you to link two resource assessment systems using the Time of Evaluation tab. Normally, fields in the function editor are lagged by a time-step (that is, they get their value from the last time-step to use in the current time-step). Enabling the During Resource Assessment checkbox results in the resource assessment system linked parameters being executed within the current time-step. As long as the resource assessment system appears above another resource assessment system in the hierarchical list, the values will be up-to-date in the time-step. Conversely, if one resource assessment system appears below a linked resource assessment system, its values will be lagged by a time-step.

General Security

This item (Figure 7) allows you to define accounting rules for accounts. The general security shares held by each water user is defined using the Accounts tab. The parameters that must be specified are described in Table 4. In the example shown in Figure 7, allocations have been defined to general security account should be simulated using the in-built continuous accounting functionality. There has been no restriction set on the minimum or maximum balance volumes. If, for example, there is a maximum balance of 2ML per entitlement share. This means that if a water user has an entitlement of 200 shares, their maximum account balance is 400ML. Two usage limits have been defined. The first says that no more than 1.25 ML can be used per entitlement share in any water year. The second says that no more than 3ML can be used per entitlement share in any three consecutive water years. These rules replicate the conditions for the Namoi river system.

Table 4. Continuous Accounting, General Security parameters