Description and rationale
Modelling of ownership on links is an essential component of modelling water ownership in Source, as it enables ownership to be tracked through links in Source models. The rationale for modelling water ownership, and the overall principles, are discussed in the Ownership Systems SRG entry.
Scale
The concept of spatial scale in the context of ownership on links relates to the fact that it applies to link divisions and these have length, width and depth dimensions (even if they are represented as points for modelling). 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 on links has been developed by eWater CRC for Source.
Scientific Provenance
Ownership on links 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
The requirement is that there should be at least two water users (as well as an ownership system) in the river system being modelled, in addition to at least one link.
Definitions
| Dead storage | The storage remaining in a division when the stream has ceased to flow. This storage is affected by fluxes which are independent of index flow in the division. See the Link Storage Routing SRG entry for more information. |
| Division | In Source, a routing link represents a river reach, which is divided into one or more divisions of equal length. Ownership modelling takes place at the level of a division. |
| Fixed flux | Loss fluxes whose ownership is known a priori because they are shared by fixed ratio or by some other means such as time-series or expression. |
| Flow based flux | Lateral flux in a division whose rate is a function of the division’s index flow rate. |
| General purpose flow based flux | A modeller configured, piecewise monotonically increasing relationship between flux and index flow. See the Link Storage Routing SRG entry for more information. |
| Groundwater flux | A function of head/water level which, in turn, is a function of flow. The flux calculated via a linked groundwater model. See the Link Storage Routing SRG entry for more information. |
| Lateral flux | Flow into or from the division that is not from upstream or going downstream. In Source, this can consist of groundwater infiltration, evaporation, precipitation, time series flux (representing diversions etc.), or flow based flux (general purpose, could be used to represent overbank loss). See the Link Storage Routing SRG for more information. |
| Live Storage | That part of the total storage in a division that is a function of the index flow rate (see the Link Storage Routing SRG for more information). |
| Murray-style loss | Method of sharing the loss (or gain) from a division due to high flow. Losses caused by flows in excess of the regulated flow range are shared to owners in proportion to how far each of them is above their fixed share of the regulated flow range. In Source, the losses to be shared in this way are represented by the flow based flux. |
| Net evaporation | Evaporation less rainfall. |
| Owner | An entity such as a state, country or water user group that has a defined share of water in the river system, where this share is managed completely separately from any other share. |
| Ownership system | A component in Source used to track and manage the ownership of water in a defined section of a modelled river network. An ownership system has a set of owners that share water within the ownership system’s boundaries. Each of these owners may lend water surplus to their requirements to other owners with a deficit via the ownership system’s borrow and payback systems. Lending owners can be paid back some time later at any location within the ownership system boundary. |
| Proportional flux | Loss fluxes that are shared in proportion to the ownership of the water in the division. |
| Storage | Volume of water within a division at a defined point in time. |
| Time series flux | A modeller specified time series used to represent known losses or gains of particular owners from a division. See the Link Storage Routing SRG for more information. |
Other definitions can be found in the eWater River Systems glossary.
Assumptions and Limitations
Table 1. Assumptions and constraints applicable to modelling ownership on links
| No. | Assumption/constraint |
|---|---|
| 1 | Owners cannot have a negative share of water in storage or in transit. |
| 2 | The sum of all owners’ shares of storage in a link equals the link’s total storage volume. |
| 3 | The sum of all owners’ shares of flow in a link equals the link’s total flow. |
Theory
Background
In Source, components that are physically or logically connected are joined using a link. If the connection is significant enough to have an effect on the time that water would take to pass along it then the link is modelled as a routing link. Each routing link is subdivided into one or more divisions.
Figure 1 below shows a single routing division, its storage compartments and fluxes. Each owner’s share of these storage compartments and fluxes must be determined for every division. The principles on which these calculations are based are discussed in the Theory section and the sequencing of the calculations is described in the Methodology section.
Figure 1. Division ownership conceptual model
Definition of terms used in equations
Table 2. Symbols used in equations
| Symbol | Description | Units |
|---|---|---|
| dt | Model time-step | time |
| Deficit(o) | Owner’s deficit to be made up using borrow and payback. | volume |
| fFlowLG(q‾) | Function that returns a lateral loss/gain flux for a given index flow rate . Also referred to as the flow based flux function. | volume |