Ownership - SRG

Ownership functionality is required in Source for modelling river systems that span multiple states, countries or types of users, and also systems using capacity sharing schemes. Terminology related to ownership is defined in the list of definitions under Structure and Processes, below.

The Murray River and Border Rivers (on the border between NSW and Queensland) are examples of systems where water is managed and tracked on a state basis. In the case of the Murray River, water is shared between NSW and Victoria until it reaches the South Australian border where it then belongs to South Australia. In the Border Rivers, water is shared between NSW and Queensland with complex rules for access to regulated and unregulated supplies. The Blue Rock system in Victoria is an example of a system where the water resource is shared between seven different types of user groups.

Source can model water ownership throughout river systems, allowing modellers to track how much water a particular owner has in a system and where that water is located. Source also models cases where the ownership of water is exchanged. An example of this is when one or more owners have insufficient water to meet requirements, and so "borrow" water from one or more other owners that have water surplus to requirements. The volume borrowed/lent is tracked in a set of accounts and may be paid back later, either within a specified reservoir, or anywhere in the river system. Owner borrowing/lending is central to water ownership modelling in Source to ensure the optimum use of available water. The ownership functionality interacts with other water management features available in Source, such as Resource Assessment Systems.

Scale

On a spatial scale, ownership applies to a river system or defined section of a river system. Source utilises the concept of an ownership system, which covers the section of a river system where the same set of owners share water in the river. It is possible for one modelling scenario to include multiple ownership systems. Ownership of water at each modelled location can be tracked at every model time-step.

Principal developer

This version of Ownership modelling has been developed by eWater CRC for Source.

Scientific provenance

Ownership has been modelled in predecessors to Source, such as IQQM, MSM and REALM, for many years. The concepts in these models have been updated and enhanced to suit the needs of Source.

Version

Source (2.19.1)

Dependencies

Ownership must be enabled for the modelling scenario.

Assumptions and limitations

The following assumptions are applicable to modelling Ownership:

• Owners cannot have a negative share of water in storage or in transit
• The sum of all owners’ shares of flow or storage volume at a model component equals the total flow or storage volume for the corresponding component.
• Each Resource Assessment System is associated with an owner, and can only allocate that owner’s water to the system’s accounts.
• Orders for water are associated with an owner
• Mass balance is assumed to be preserved if the difference is less than 0.0001 cubic metres.

Theory

The Murray River and Border Rivers systems are the two major capacity sharing schemes currently in use in Australia: these schemes operate at the interstate level. The functionality for modelling ownership of water in Source is intended to meet the requirements for modelling these two schemes. There are three key documents describing the capacity sharing arrangements, and these are:

• Murray Darling Basin Agreement (Commonwealth of Australia, 2007)
• Border Rivers Intergovernmental Agreement (NSW and Queensland Governments, 2008)
• Border Rivers Bulk Water Sharing Plan (Dumaresq-Barwon Border Rivers Commission, 2007)

In both systems, the participating States (as discussed in the Overview, above) are entitled to a defined portion of the inflows to the system. The Murray has a system for water accounting explicitly defined that allows for ownership to be accounted over an arbitrary time period. In contrast the Border Rivers system does not have an explicitly defined accounting system, instead an approach is used that accounts for ownership in retrospect.

The main properties of ownership described in the Murray Darling Basin Agreement have been incorporated into the design of the functionality for modelling Ownership in Source. It is expected this functionality can be adapted to modelling the Border Rivers System (but not replicating the current approach, for which modelling of ownership would not be needed).

Enabling and disabling of ownership functionality

Tracking water ownership enables modelling of the sharing of a common water resource between two or more independent entities. Not all river systems require this level of complexity when being modelled; consequently, a mechanism for enabling and disabling ownership for a whole scenario has been provided in Source.

Source models ownership using the concept of an "ownership system". If ownership is enabled for a modelling scenario, the scenario will have one or more ownership systems. Each ownership system consists of a set of owners (with each owner having its own Resource Assessment Systems and water use accounting systems), and Borrow and Payback systems (allowing borrow and payback between owners). The rules associated with these entities apply within the physical boundaries of the ownership system.

The physical boundaries of an ownership system are represented in a modelling scenario’s schematic by nodes at the upstream and downstream "edge" of the river network. Where two ownership systems meet, the boundary between them is represented by the "Transfer of Ownership" node. This node may also be used to change the owner shares within the same ownership system. When the Transfer of Ownership node is representing an ownership system boundary, model components upstream of node belong to one ownership system, while those downstream belong to the new ownership system.

Orders are placed at various locations in the model network for a particular owner’s water. When the ordering system examining the model network encounters an ownership system boundary marked by a Transfer of Ownership node, it will either: not pass orders upstream of that point, or transfer orders between the downstream and upstream owners, according to rules defined at the node.

Ownership tracking

When ownership is turned on (enabled) for a modelling scenario, Source tracks and reports owner shares of flow and storage volume throughout the river system.

The initial ownership of water at each node and link is specified by the modeller as data input, noting that owner shares must add up to 100% of the water at each location. Throughout a model network, ownership of water is in general conserved, unless it is explicitly transferred via user settings (available at some node types). Ownership transfer may also occur via borrow and payback, or in special cases within reservoirs, for example when owners have insufficient capacity to store their water.

To track ownership, Source creates a number of control volumes around nodes and routing links. An "ownership continuity equation" accounts for the volumes of ownership entering, leaving, and residing within the control volumes. The general form of the equation for a given owner, o , is:

Some terms in this equation are not relevant at all model nodes, and can be replaced with zero. The storage node, representing a reservoir has a modified equation that splits outflow into spills and releases, and includes some extra terms (see the entry in this guide for Ownership in Reservoirs).

While ownership is continuous and conserved, an owner’s proportional share of water at a location will change due to the effects of the various fluxes. For example, at a Supply Point node, different diversion volumes may be assigned to each owner, changing the respective owners’ downstream shares of flow. Specific forms of equation 1 and its application to each model component are discussed in detail in specific sections relating to their ownership in this guide.

In some cases, both the flux and each owner’s share of it can be specified by the modeller via time series input, a fixed percentage or a function. Examples include the inflow flux at an Inflow node, the routing link’s "Time Series Flux", and Supply Point node diversions (extractions) when connected to a "Non-Account Sharing" water user (see the eWater glossary). Alternatively, the Diversion_o flux can be specified indirectly by the modeller using a Resource Assessment System, as is the case for extractive supply points connected to "Account Sharing" water users.

Some owner fluxes result from physical limitations. For example, at a Storage node, each owner owns a fixed share of the total storage volume they can fill with their water. Once an owner’s share of the storage volume is fully utilised there can be "internal spilling", where the owner’s excess water is distributed between other owners. This is treated as a flux in the ownership continuity equation.

In Source, ownership can be transferred at specified locations according to user configuration. This type of exchange may occur:

• At a "Transfer of Ownership" node. Owner shares of water are reassigned at this node according to rules specified by the modeller. If the node is used as an ownership system boundary, a new set of water owners is introduced, and rules are specified dictating what happens to orders that reach this point.
• At a Storage node where the modeller defines ceding rules so that an owner gives up a specified volume of inflow to another owner.
• At a Gauge node, where the modeller resets owner shares of flow volume.

To ensure the maximum use of the water resource available, Source may automatically transfer water ownership using Borrow and Payback systems. If one or more owners has surplus capacity or water, they can lend this to owners with a deficit. This "borrow" of water can occur at any node where there is a loss or gain, and results in the ownership of the borrowed water being transferred from the lender. If multiple owners need to borrow, and there is insufficient water or capacity to meet their combined requirement, a configured Distribution System is used to determine priority of access.

All borrow is tracked using a set of accounts in a Borrow and Payback system. Borrowing owners may payback their debt by transferring their water to the other owner, either in a specified "payback" storage or indirectly via Resource Assessment Systems. When this happens, the accounts are updated. Payback can either occur immediately or at a later time. This process is described in more detail in the Borrow and Payback - SRG section of this guide. Borrow and payback is applied in a range of situations - from sharing outlet or channel capacity so orders can be met, to maintaining fixed owner shares of reach dead storage.

Model phase: configuration

The modeller configures ownership systems via the Ownership Explorer interface. When a modelling scenario is first created, ownership is disabled. Water ownership is only tracked and recorded once the modeller enables ownership . When ownership is first enabled, a default system with the owner "owner1" is created. Initially the default owner owns 100% of the water in every node and link. Every ownership system is created with a global borrow and payback system, and a default distribution system. If ownership is disabled after it was enabled earlier, ownership system(s) are disabled but not deleted.

Owners may have one or more Resource Assessment Systems (RAS) managing their water. RAS must be explicitly created by the modeller (they will not be created by default), as there are widely varying types of these systems, and they are not necessarily associated with any owner. RASs must be created and configured via the Resource Assessment Explorer. The Ownership Explorer may be used to view ownership details of RAS associated with an owner.

Source automatically assigns each node and link to an ownership system when these items are added to a modelling scenario. The exception is the Water User node, which can have multiple supply points that may be located in different rivers and hence different ownership systems. At a Transfer of Ownership node, the upstream ownership system is auto-assigned, and the downstream ownership system user configured (by default it is the same as the upstream one). Each link’s ownership system will always match the one for the upstream connected node. Overlap of ownership system boundaries may occur as a result of nodes being added to or removed from the model network. The Ownership Explorer prompts the modeller to correct these invalid boundary configurations.

When ownership is first enabled, the whole modelling scenario falls within the boundary of the default ownership system - so every node and link will belong to this system. When another ownership system is created, it will not initially cover any of the scenario’s nodes or links. To associate a new ownership system with the modelled river network, the modeller must create a Transfer of Ownership node and set the downstream ownership system to the new ownership system. Source will automatically assign any connected nodes and links downstream of the new Transfer of Ownership node to the new ownership system.

The list of owners to be configured at each node and link is associated with the ownership system it falls within. Features to be configured will include each owner’s share of:

• Initial volume/flow of water at the node/link
• "Fixed" fluxes each time-step, that are to be shared in a predetermined way. (Other fluxes will be "proportional", ie shared in proportion to the owner’s existing share of water at the link/node).

More information regarding ownership configuration for nodes and links is given in this guide’s sections on Ownership at nodes and links - SRG. Details of data requirements are given in the Source User Guide.

Model phase: Initialisation

During the model initialisation phase a full check for ownership system consistency for the entire model network is undertaken, which entails examining every node and link. The rules of ownership consistency are as follows:

• Transfer of ownership nodes: (Rules also enforced at configuration)
  • The upstream ownership system must match the inlet link’s ownership system
  • The downstream ownership system must match the outlet link’s ownership system.
• Water user nodes: These can have multiple ownership systems, that are set at connected supply point nodes. No consistency checks are required.
• Other nodes
  • For every connected upstream link: The upstream link’s ownership system must match the current node’s ownership system.
  • For every connected downstream link: The downstream link’s ownership system must match the current node’s ownership system. (This rule is also enforced at configuration).

If an inconsistency is found, an error message is generated and the model run is stopped.

Model phase: Ordering

In the ordering phase for systems with ownership, orders and off-allocation requests for each owner are placed. These orders and requests may be limited by the owner’s ability to deliver (ie their share of storage, release capacity, losses and other constraining factors).  More information on the ownership calculations for this phase is available in Rules-Based Ordering - SRG.

Model phase: Flow distribution

Ownership calculations are performed in each time-step at each modelling element (node or link division) at the end of the flow distribution phase, once the calculation of total flow volume and constituent concentrations are complete. Details of the ownership calculations for this phase are discussed in Ownership at nodes and links - SRG.

Model phase: Resource assessment

When ownership is enabled and an accounting system is linked to an owner, only the selected owner’s share of the water in the storage will be considered available for distribution.

Example

The example is a river system with six ownership systems: Border Rivers, Darling River, Murrumbidgee River, Goulburn River, Upper Murray, and Lower Murray. A simplified Source schematic of this system is shown in Figure 1.

A global borrow and payback system and default distribution system was automatically created when each ownership system was defined. Local borrow and payback systems have also been configured for the Upper Murray Ownership System (Hume Dam, and Lakes Menindee and Victoria). Lake Victoria is the "payback" (or reconciliation) storage for this ownership system.

The NSW and Victorian Resource Assessment Systems are used to allocate their owner’s water resources to their respective licence holders within the boundary of the Upper Murray Ownership System.

Input data

Details on data requirements are provided in the Source User Guide.

Parameters or settings

Ownership System parameters and settings are summarised in Table 2.

Table 2. Ownership System parameters

Notes:

1. This is a loss sharing method used in the Murray river where below a threshold losses are shared according to fixed ratio, and above the threshold they are shared proportionally. For more information see the section on Ownership at nodes and links - SRG and the entry on the Splitter node - SRG.

2. For more information see the section on Ownership at nodes and links - SRG.

3. For more information see the section on Ownership at nodes and links - SRG and Gauge node - SRG.

4. This is the amount of water in excess of orders and off-allocation requests required to meet downstream requirements, due to the physical limitations of each channel at an anabranch (represented by the Splitter node - SRG).

The parameters in Table 3 must be configured for every owner in the ownership system. They apply to nodes and links throughout the ownership system.

Reference list

Dumaresq-Barwon Border Rivers Commission (2007, with draft revisions November 2007). Border Rivers Bulk Water Sharing Plan.

Commonwealth of Australia (2007) Water Act 2007 (Act No 137 of 2007 as amended, including amendments up to Act No. 46 of 2011 and SLI 2008 No. 106 (as amended by SLI 2011 No. 117)). Part 1A - The Murray Darling Basin Agreement. Available at www.comlaw.gov.au/Details/C2011C00621/Download

NSW and Queensland Governments (2008) New South Wales - Queensland Border Rivers Intergovernmental Agreement 2008. Available at www.derm.qld.gov.au/wrp/pdf/border/intergovt_agreement_2008.pdf and at www.water.nsw.gov.au/Water-management/Law-and-policy/Intergovernmental-agreements/Intergovernmental-agreements/default.aspx