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Overview
Description and rationale
Modelling of ownership at nodes is an essential component of modelling water ownership in Source, as it enables ownership to be tracked at nodes in Source models. The rationale for modelling water ownership, and the overall principles, are discussed in Ownership - SRG. This SRG entry deals with those aspects of ownership that apply to water entering, leaving and residing in a reservoir (storage nodes). Requirements This is the default method used to track ownership shares in storages. The calculations are based on owner continuity equation. The components include borrow and payback, spill calculations, suspension of ownership and outlet path ownership and are explained in further sections. The requirements for the method are summarised in Table 1. Rules-Based Ordering - SRG describes how owner orders are created, adjusted and released at storage nodes. More information on the storage node is available in Piecewise Linear approach to Reservoir Routing - SRG.If an owner wants to exceed its share of storage capacity temporarily using the option 'Use Airspace' , then the 'Owner Working Volume Proportion Method' shall be used.
Table 1. Partner user requirements
| No | Requirement |
|---|---|
| 1 | Ownership of water can be assigned, tracked and reassigned. |
| 1.1 | Ability to specify initial ownership of water at each location (all water must be assigned to an owner) |
| 1.2 | Ability to specify the transfer of ownership at a location, represented as a node in the river network. |
| 1.3 | Borrow and payback is supported, where owners share surpluses to owners that cannot meet their requirements, and can be paid back later. |
| 1.4 | In every model component, ownership is conserved when it is not explicitly transferred or exchanged, i.e. the following volume equation holds for each owner o: ΔStorageo = Inflowo - Outflowo - Diversiono - Losso + Gaino + Borrowedo - Lento |
| 2 | Ownership tracking works for a range of time steps e.g. sub-daily, daily. |
| 3 | Delivery of each owner’s orders may be constrained by their share of inflow and storage volume, and delivery capacity. |
| 4 | The equation governing ownership in storages is for an owner o: ΔStorageo = Inflowo - RegulatedReleaseo - Cededo - FixedLosso - ProportionalLosso - InternalSpillo - ExternalSpillo + Borrowedo - Lento |
| 5 | Owners can cede (give) water to other owners in a storage. |
| 5.1 | The modeller can configure rules that determine when ceding is to take place and how much water to cede from one owner to another owner. |
| 6 | Storage losses and gains (evaporation, precipitation, groundwater infiltration) are shared between owners according to user-configured rules. |
| 6.1 | Storage losses and gains can be shared proportionally, or according to fixed ratio |
| 6.2 | When storage losses and gains are shared proportionally, owners are assigned a share in proportion to the volume of their water in storage. |
| 6.3 | When storage losses and gains are shared in a fixed ratio, the modeller configures each owner’s percentage share |
| 7 | Owners are assigned fixed shares of storage capacity in which to store their water. |
| 7.1 | The modeller can configure each owner’s share of storage capacity. |
| 8 | The modeller can configure whether ‘internal spilling’ between owners occurs within a storage. |
| 8.1 | When ‘internal spilling’ is configured, owners must transfer the volume of their water that is in excess of their share of storage capacity (the internal spill) to all other owners with ‘airspace’. |
| 8.2 | When ‘internal spill’ is transferred from an owner, every other owner receives a share in proportion to their share of storage capacity, but limited by their ‘airspace’. |
| 9 | An owner’s share of external spill (release volume in excess of demand) is determined by their share of start of time step storage volume, inflow, regulated release and storage capacity. |
| 10 | Storage owner shares can be temporarily overridden and restored later (e.g. Lake Menindee). |
| 10.1 | When storage shares are overridden, they are reassigned to a single owner, and all inflows, losses/gains, releases and spills belong to this owner. |
| 10.2 | The modeller can configure the conditions under which the override occurs, and the owner to which shares are reassigned. |
| 10.3 | When storage shares are restored after an override period, the borrow accounts must be restored to their pre-override balance. |
| 11 | Owners are assigned a share of the capacity of each of the storage’s outlet paths according to user configured rules. |
| 11.1 | Outlet path capacity can be shared proportionally, or according to fixed ratio |
| 11.2 | When outlet path capacity is shared proportionally, owners are assigned a share in proportion to the volume of their water in storage. |
Scale
The concept of spatial scale in the context of Ownership relates to the fact that it can apply to all or part of the length of a river system. Ownership status can be updated as often as at every model time step, or less often if required.
Principal developer
This version of modelling ownership at storage nodes has been developed by eWater CRC for Source.
Scientific Provenance
Ownership has been modelled in predecessors to Source, such as IQQM and MSM, for many years. The concepts in these models have been updated and enhanced to suit the needs of Source.
Version
Source v3.8.8.
Dependencies
In addition to the dependencies applicable to storage nodes, the minimum requirement is that there should be at least two water users and an Ownership system in the river system being modelled.
Availability/conditions
Automatically included with Source.
Structure & processes
Assumptions
Table 2. Assumptions and Constraints
| No | Assumption/Constraint |
|---|---|
| 1 | Owners cannot have a negative share of water in storage or transit |
| 2 | The sum of each owners’ share of flow or storage volume at a model component will equal the total flow or storage volume for the corresponding component. |
| 3 | Owners cannot cede more water than the current storage volume. |
| 4 | The direction of flow on a wetland link connected to a storage is the direction of net flow volume over the time step. |
| 5 | All owners in an ownership system possess a share of the reservoir’s storage capacity. |
Definitions
| Airspace | The difference between the current storage capacity and the volume of water in storage. For an owner: The difference between an owner’s current storage capacity and their volume of water in storage. |
| Ceding | Where an owner gives up water to another owner. |
| Dead storage | Capacity of a reservoir that is below the minimum operating level and cannot under normal circumstances be released. |
| External spill | Release from storage in excess of that required to meet downstream requirements. |
| Full supply level (FSL) | The maximum normal operating level of a reservoir behind a dam. Sometimes the FSL may be set lower than the maximum physical capacity of the dam for management reasons. |
| Internal spill | Occurs when an owner’s volume of water in storage exceeds their current storage capacity and the excess is transferred to the other owners possessing airspace. |
| Regulated release | The volume of water released to meet downstream requirements. |
Spiller | Owner whose share of water in storage exceeds their share of capacity to store it. |
| Storage | Volume of water stored in the reservoir (dam or weir). |
| Storage capacity | Volume in storage when the reservoir is at the full supply level. For an owner: The owner’s share of the volume in storage when the reservoir is at the full supply level. |
Ownership continuity equation
Ownership in reservoirs is governed by the continuity equation, in which each owner’s share of water is conserved. Ownership of water is changed only in the following set of cases:
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The modeller may disable internal spills, so this element may be left out of the equation.
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Each owner’s inflow and last time step storage is known at the start of the reservoir ownership calculations. Shares or functions configured by the modeller determine owner fixed losses and volumes ceded or received (noting that owners cannot cede more than the current storage volume). The remaining parts of the equation to be calculated are the owner’s borrow, internal spill (where relevant), external spill and proportional loss.
Borrow and payback
Owners with insufficient water in the reservoir to meet their release requirements can borrow it from other owners with surplus water. Payback occurs in a reservoir only when it has been configured as a ‘payback storage’, i.e. it:
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Using the borrow method described in Borrow and Payback - SRG Bi for each owner can be calculated. Any owner that had to borrow will have Vi2 = 0.
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Equation (6) returns a value of zero for owners that had to borrow water. It is only necessary to calculate the repayment for owners with a positive surplus that have previously borrowed from other owners (Surplusi > 0, |BPSystem.NetBorrow(i, OtherOwner)| > 0 ). Borrow and Payback - SRG describes distribution systems and priority levels.
Payback is done at each priority level in order from highest to lowest:
At a given priority level, pl, for each owner, i, that has a Surplusi > 0, the steps are:
Accumulate amount the owner owes other owners at the priority level:
Equation 7 - If the owner has borrowed from any other at the priority level ( (CanPayback(pl, i) > 0):
Calculate the ratio to limit the owner’s payback to their current ability to repay:
Equation 8 - For every other owner OtherOwner that shares with owner i at the priority level:
Calculate the payback to the other owner using the ratio above
Equation 9 Update the borrow record for the payback to the other owner
Equation 10 Equation 11 Adjust current time step borrow totals for the payback:
Equation 12 Equation 13 Update the surplus remaining to be shared at the next priority level down:
Equation 14
Forfeiture of credit
If a reservoir is a payback storage, a check is made to ensure that no owner’s credit owing to them exceeds their capacity to store it. If any owner has more water owed to them than they have remaining airspace, the excess is forfeited back to the debtors in order of priority. This methodology is similar to that used for calculating payback, but in this case the forfeits run in the opposite direction to the repayments.
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Accumulate the amount owed to the creditor by other owners sharing at the priority level:
Equation 18 - If the creditor has an amount owing at this priority level (Owedi > 0):
Calculate the amount of credit forfeited to each other owner at the priority level - this is proportional to the other owner’s share of the total owed to this owner at the priority level:
Equation 19 Adjust the borrow record for the creditor and their debtors for the amount forgone:
Equation 20 Equation 21 Update the amount left to forfeit at the next priority level down:
Equation 22
Spill calculations
Each owner is entitled to use a fixed proportion** of the storage capacity of a reservoir (ri) which means that at any time its storage cannot exceed:
| Info | ||
|---|---|---|
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| ** Owners that have a share of the reservoir which floats on top of the other owners will have to be dealt with later here. If an owner doesn’t have any storage capacity (ri = 0) then its water will internally spill to those owners that do. |
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For any owner, i, to be spilling Vi2 = Vimax otherwise the owner would still possess airspace and would not be spilling, and also the current storage volume cannot be greater than the maximum by definition.
Identifying spilling owners
Before each owner’s share of spills can be determined, it is necessary to determine which owners will spill. Where the spill calculation returns a negative value, owners can receive internal spill, while a positive value indicates that the owner is spilling (has filled their storage share).
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When the process is finished equation (30) is evaluated for those owners found to be not spilling.
Calculating internal and external spill shares
The calculations in previous sections established which owners are spillers when proportional gains and losses are taken into account. The next step is to determine the internal (between owners) and external (leaving the reservoir) components of the spill. Based on the calculations in the previous sections the total spill is:
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The process from equation (37) to equation (43) is repeated until InternalSpill approaches zero. Once this occurs the values of Esi and ISi will also be known for all owners where Spillj ≥ 0 the value of Vi2 will be Vimax.
Proportional Loss Sharing
If internal spill is active, each spilling owner, k, is required to meet a fixed part of the proportionally shared lateral flows:
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To determine the evaporation, rainfall and groundwater infiltration components of proportional losses for each owner, the owner share of proportional loss is applied to totals for each proportional flux type:
| Equation 50 |
|---|
Suspension of Ownership
Ownership in a reservoir may be temporarily suspended. This occurs when a storage override function configured by the modeller returns a value of “true”. At this point, the owners’ storage shares are saved, and borrow account balance updating is turned off.
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The owners’ shares of the storage capacity (ri) are restored to the values they were before the suspension started.
Outlet Path Ownership
Determining capacity
Outlet capacity is described by a modeller configured minimum and maximum possible release at each storage level in a piecewise relationship. The capacities of outlets on the same outlet path are combined to determine the minimum and maximum release for an outlet path at each storage volume in the relationship. The slopes and intervals of these outlet path relationships are used to calculate the release range for any storage volume, which are adjusted to take into account spill (the minimum release) at the storage level on all other outlet paths. There may be multiple outlet paths for the same storage, with differing priorities. Hence outlet path release ranges are adjusted in each time step for releases on higher priority outlet paths. Further information on outlet path minimum and maximum release calculations is available in Piecewise Linear approach to Reservoir Routing - SRG.
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The total order on each outlet path is the sum of orders on that path for all owners:
| Equation 55 |
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Case where outlet path release ≥ total order
Where any path’s outflow equals or exceeds the total orders on that path (Rp > 0) then the regulated releases do not have to be restricted and each owner’s release can be set equal to their order:
| Equation 56 |
|---|
Case where outlet path release < total order
If the outflow down a path is less than the orders on that path then there is a restriction and the water considered to have been released for each owner has to be scaled back. For each owner, their share of the release capacity is calculated as follows:
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| Info | ||
|---|---|---|
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| Note: When ownership is suspended, the ‘override owner’ is assigned 100% share of outlet path capacity. If there are any orders for other owners at this time, the other owners may still borrow capacity in order to make a release. This situation is unlikely though, as the ordering system should detect that the other owners have no storage share and send their orders elsewhere (where possible). |
Data
Input data
Details on input data requirements are provided in the Source User Guide.
Parameters or settings
Input parameters and setting are summarised in Tables 3 and 4, below.
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| Parameter Name | Parameter Description | Unit type | No. of values | Allowable values & validation rules | Default Value(s) | |
|---|---|---|---|---|---|---|
| Ownership system | Name of the storage’s ownership system | n/a | 1 | An existing ownership system for the scenario. | Default ownership system | |
| Enable internal spilling | Indicates whether owners will transfer water to other owners when they have insufficient capacity to store their water. | n/a | 1 | ‘Yes’ or ‘No’ | 'Yes' | |
| Storage sharing table: Owner | An owner in the storage’s ownership system. | n/a | Number of owners in o.s. | Read only | Each owner in the storage’s o.s. | |
| Storage sharing table: Capacity share | The owners % share of storage capacity. | % | 1 per owner | Real 0-100% | Equal share of 100 per owner. | |
Storage sharing table: Capacity | The owner’s storage capacity. | volume | 1 per owner | Read only | share x Storage Capacity | |
| Storage sharing table: Initial storage share | The owner’s % share of initial storage. | % | 1 per owner | Real 0-100% | Equal share of 100 per owner. | |
| Storage sharing table: Initial storage | The owner’s initial storage. | volume | 1 per owner | Read only | share x Initial storage | |
| Ceding table: From owner | An owner that will cede a volume of water dictated by the ceding function to the ‘To owner’ | n/a | 0 or more | An owner in the storage’s ownership system. | None | |
| Ceding table: To owner | An owner that will receive a volume of water dictated by the ceding function from the ‘From owner’ | n/a | 1 per ‘From owner’ | An owner in the storage’s ownership system. | None | |
Ceding table: Ceding function | Function that determines the volume of water the ‘from’ owner will cede to the ‘to’ owner each time step. | volume | 1 | None | ||
| Rainfall and evaporation sharing method | Indicates how rainfall and evaporation are shared. | n/a | 1 | ‘Fixed Ratio’ or ‘Proportional’ | ‘Proportional’ | |
| Groundwater sharing method | Indicates how groundwater infiltration is shared. | n/a | 1 | ‘Fixed Ratio’ or ‘Proportional’ | ‘Proportional’ | |
| Override owner | An owner that will receive 100% ownership of a storage, its inflows, losses/gains & releases when the override function returns true. | n/a | 1 | An owner in the storage’s ownership system | None | |
| Override function | function that determines when owner shares are to be overridden (when true) | n/a | 1 | Must return true or false value. | 'False' |
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Table 4 — Storage Outlet Path Ownership Parameters
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* Note: The initials o.s. refer to the current storage’s ownership system.
Output data
Recorded variables are summarised in Tables 5 and 6, below.
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