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At various locations in a river system, whether regulated or unregulated, there can be water demands which could be either volume based or water level based. These demands can be either extractive or ‘in-stream’. Extractive requirements involve water being taken from the river for irrigation, town water, industrial and other uses. ‘In-stream’ demands include environmental, recreational and regulatory requirements, and perhaps hydropower.

In Source a combination of demand models, the water user node and the supply point node are used to model the generation and meeting of these demands. Demands, both extractive and in-stream, are generated by demand models. The water user node is used as an interface for water demand models and it also has one or more supply point nodes associated with it. The main function of the supply point node is to identify a location at which water is to be delivered, and model aspects of delivery of water to that location. The water user node distributes demand between supply point nodes associated with it and, in models of regulated systems, generates orders at each supply point node to meet these demands and uses accounts to track and limit these orders.

If the system is regulated the supply point node can place water orders on storages and determine location dependent features of these orders, such as delivery efficiency and travel time. In unregulated systems, supply points cannot place orders but the volume they extract may be limited by a licence, represented by an account balance. Supply point nodes can be ‘extractive’ or ‘in-stream’.

The supply point may also be used to model supply of water from groundwater. Groundwater supply points do not order (and are therefore always classed as unregulated) but their extractions may be limited through accounts. Groundwater supply points are always extractive.

This section describes how the supply point node is used in modelling the delivery of water to a location to meet demand generated at a water user node, and support water use accounting.

Point scale; calculations are updated at every model time-step.

eWater CRC

The supply point node representation in Source builds on concepts in predecessor models, IQQM, MSM and REALM, and experiences with using these models.

Source version 2.19.1

The supply point node can be used when modelling either regulated or unregulated systems in Source. It requires a water user node to be associated with it.

The supply point node is the point at which the water management functionality in Source connects with a specific location in the river network. Specifically, it is the point where:

• Location dependent parameters, such as estimated order delivery time and operation efficiency are either calculated or specified;
• Orders created by the connected water user node enter the water ordering system;
• Constraints on delivery (determined by the water ordering system) are communicated back to the water user node;
• River supply points: In-bank and overbank ‘deliveries’ (flow rate/volume) for a time-step are recorded, and the amount of flow that can be extracted (In-bank ‘Available flow’, ‘Overbank flow’) is communicated back to the water user;
• ‘Extractive’ supply points: Extractions to meet current water user demand are calculated (subject to availability and other constraints, as mentioned above);
• ‘In-stream’ supply points: The amount of in-stream ‘usage’ to deduct from accounts is determined and communicated to the water user node;
• Unused (not extracted) ordered water becomes unallocated (ie available for other uses). The volume of ‘unallocated water’ is updated.

Refer to Table 24.

At a supply point, water may be sourced from a river or groundwater. Supply points are categorised as follows:

• River - regulated. Upstream storage nodes release water to meet the supply point’s orders.
• River - off-allocation. Off-allocation flow sharing (OAS) nodes allocate unallocated water to owners to meet their off-allocation requests at supply points.
• River - unregulated. This is water in the river not assigned/allocated for use in fulfilling any order or off-allocation request. In regulated river sections this water can be used to fulfil ‘opportunistic’ requirements. In unregulated river sections it is all the water in the river at that location above the ‘diversion threshold’, but diversions may still be subject to licence restrictions. The source of this water is the supply point node itself.
• Groundwater. This is similar to unallocated or unregulated river water in that it is not ordered, and the source is the groundwater supply point node itself. This source is limited by diversion capacity, and possibly also by licence restrictions.

Regulated storage and off-allocation sources are similar in that orders can be placed to them. In reality however, off-allocation orders are ‘opportunistic’ expressions of interest in water that has unexpectedly become available. As such they are referred to as off-allocation requests. These requests may be used to reduce "use-debit" orders. When off-allocation flow begins to occur, orders start to decrease as they pass through the inflow or storage locations where the excess flow occurs. This allows storage releases to be reduced.

Table 25 summarises the water user-supply point configurations that activate ordering and extraction functionality at the supply point. The terms "Account Sharing" and "Non-Account Sharing" in this table are explained in the section on Demand Distribution which follows the table.

Note Although groundwater and unregulated river supply points do not place orders, they can use accounts to keep track of and limit extractions.

In any time-step, the water user’s demand model generates a future minimum requirement and a future ‘opportunistic’ requirement. The water user’s demand distribution component generates orders for the minimum requirement, and off-allocation requests for the opportunistic requirement. It also generates a minimum and opportunistic requirement for the current time-step, and these amounts may differ from those predicted earlier. The modeller specifies the rules as to how these demands are to be distributed when they are configuring the model.

Resource assessment systems (RASs) may be used to manage sources of water (both from the river and groundwater). Every RAS is associated with a water owner. In a scenario with no ownership specified, the ‘not specified’ owner is used for all RASs. Both regulated and unregulated water sources can be managed by a RAS. Off-allocation water is always managed under a regulated RAS via off-allocation account types.

Where one or more RASs have been configured for the modelling scenario, the water user node can be configured to associate a supply point’s orders and extractions with one or more resource allocation accounts. This is known as ‘Account Sharing’. When this type of demand distribution is used, the modeller specifies the priority of accounts to be used, via the RAS or directly at the water user node. Accounts (and hence demand) are associated with an owner via the RAS. The volume of orders and off allocation requests that can be made at the supply point in any time-step is limited by the balances of its accounts at that time-step. A supply point may be associated with multiple accounts, but at most one off-allocation ‘account’ per owner.

The other method of demand distribution is ‘Non-Account Sharing’. When this is selected, the water user’s demand is distributed to each owner at each connected supply point node either (a) on a proportional basis, or (b) using fixed proportions specified for each owner by the modeller.

The account or owner a supply point’s orders are associated with will dictate the water source and delivery path used for the order:

• Account sharing water users: Orders can be supplied from any storage associated with the ordering account’s RAS. The order system determines where to source water from according to storage levels and other constraints at each time-step during the model run. Off allocation requests are always supplied from the off-allocation sharing (OAS) nodes associated with the supply point’s off-allocation accounts (if it has any).
• Non-account sharing water users: Orders can be supplied from any storage the ordering owner has a share of water and outlet capacity in.

When there are multiple supply path options, the water ordering system determines where to source water from according to storage levels and other constraints at each time-step during the model run. For more information on how the water ordering system directs orders to storages:

• See the SRG entry on Rules Based Ordering.
• See the SRG entry on Optimised Multiple Supply Path Modelling for this type of ordering.

Groundwater supply points communicate to the water user each time-step the volume they have extracted. This is limited by the diversion capacity of the supply point.

The river supply point communicates to the associated water user node each time-step the volume of ‘available’ in-bank flow that can be extracted (if extractive) or ‘used’ in-stream, and overbank flow. In-bank flow available for extraction may be limited by physical capacity, and may be subject to a diversion threshold. In calculating the in-bank flow available for extraction, the flow required to meet downstream orders is also considered, so as to ensure the needs of downstream water users are given equal priority to water needs at the current supply point node.

The water user node requires the division of available flow into in-bank and overbank components to update accounts in accordance with the rules of its RAS. At this stage, overbank flow usage can only be modelled as being outside of licence constraints. In future implementations, it may be possible to model licence constraints on overbank flow usage.

The supply point determines the downstream flow volume. At in-stream supply points, this is the same as the upstream flow volume. At extractive supply points, it is the upstream volume less the extraction. There may be a shortage of water, causing the flow available for extraction to be less than that ordered. In these cases, the shortage is shared between owners based on their share of the original order. It is still possible however for owners to be left with a negative share of downstream flow after the extraction. In these cases, the borrow method is used to return the owner’s downstream flow to zero. Downstream of an in-stream supply point, the delivered order volume becomes ‘unallocated’, ie available for other uses.

Regulated Supply Points (River)

The water ordering system maintains a record of the orders and off-allocation requests made using each account at each supply point. As mentioned under the Demand Distribution heading, above, the current time-step’s minimum requirement may be less than the volume ordered/requested for the time-step. This could be due to rain, changes in demand etc in the interval between the time-step when the order/request was generated and the current time-step, where the interval in question is the travel time from the closest upstream storage to the supply point.

A water user’s current time-step minimum requirement is met using all its available flow before any opportunistic requirement is serviced. The current time-step opportunistic requirement can only be met using overbank and ‘off-allocation’ flow.

The volume of in-bank flow that can be extracted or used is divided into two components:

• Off-allocation flow - as determined by the associated off-allocation sharing node.
• Regulated flow - flow that has been ordered by the supply point using its accounts.

At in-stream supply points, only the ‘regulated flow’ ordered at the supply point is charged to accounts. At extractive supply points, the ‘off-allocation’ usage may also be charged to ‘off-allocation’ accounts, if the rules of the RAS require this.

A water user’s off-allocation account is assigned water to meet part or all of its off-allocation request as it becomes available at the associated off-allocation node. This ‘account balance’ (volume assigned) is associated with the time-step in which the water will reach the off-allocation account’s supply point. In that time-step, when the off-allocation water is due to arrive, the supply point may use this water to meet part or all of the time step’s minimum requirement, and if there is excess left over, to meet part or all of the time step’s opportunistic requirement. This effectively reduces the amount of pre-ordered water used. The rules of order-debit accounting require that the ordered amount using these accounts is debited regardless, however, the amount deducted from use-debit accounts is reduced by the use of off-allocation water.

When ownership is enabled the water user node determines the usage per owner. Ownership of overbank flow use is specified at the supply point by the modeller. Ownership of in-bank flow usage is based on how the water user node distributes demand.

Unregulated Supply Points (River and Groundwater)

By definition, there is no ordered water at an unregulated river supply point. If an account is used at this type of supply point, the (in-bank) extraction may be limited by the balance of the account. Otherwise, the amount to extract is the water user’s total requirement for the time step, limited by the total flow available for use at the supply point. Overbank water is used first, then in-bank water if required.

Likewise, there is no ordered water at a groundwater supply point and, if an account is used at this type of supply point, the extraction may be limited by the balance of the account. Otherwise, the amount to extract is the water user’s total requirement for the time step, subject to any pump capacity constraints that may apply (note it is assumed there is infinite groundwater storage available).

When account sharing is used at a water user node, the node has accounts that are debited for water ‘usage’. This usage may be for water extraction or delivery at its supply point(s), depending on whether the use is extractive or not. The timing of debiting an account and the amount debited depends on whether its RAS type is ‘order debit’ or ‘use debit’, and on whether the associated supply point is extractive or not. Note that a groundwater or unregulated river supply point must be extractive and, if it is associated with an account, the account is use-debit.

The method of account balance update is outlined in Table 26 below.

The rationale for allowing the modeller to define an expression for account debiting at in-stream supply points is that these have differing applications. In-stream supply points can be used to place orders to ensure flow for a downstream location, such as a wetland, so account debiting should not necessarily occur at the time the flow arrives at the supply point but perhaps instead when the water arrives at the downstream location. There may also be variations to how accounts are debited - eg in the case of bulk water entitlements.

Details on data are provided in the Source User Guide.

Parameters are introduced in the User Guide. This section outlines acceptable parameter/data ranges and other relevant information. This information is presented in Table 27 and Table 28.

Output may be displayed in the form of graphs, tables and statistics for the variables listed in Table 29.