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 describes how the ownership of inflows and outflows at inflow and confluence nodes in the flow distribution phase of Source is determined and tracked. Rules-Based Ordering - SRG describes how owner orders are adjusted for future inflows at inflow nodes. More information on the inflow node and confluence node is available in Inflow node - SRG and Confluence node - SRG, respectively.
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 inflow and confluence 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 inflow and confluence 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
Automatically included with Source.
Structure & processes
Assumptions
Table 1. Assumptions and Constraints
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 flow in a node at each model time step equals the node’s total flow volume. |
3 | In the flow phase, the volume of each owner’s total downstream orders due to have arrived is known at every node and link. |
Theory
Inflows are modelled in Source by the inflow node and the confluence node is used to represent locations where two rivers (or a tributary and river) join to form a single river downstream. The ownership of water at inflow locations and confluences must be considered in Source when ownership is being modelled.
A key rule of ownership modelling in Source is that within an ownership system, ownership is conserved unless it is explicitly transferred (see Ownership - SRG). In unregulated systems, ownership of inflow to a location is conserved in that location’s downstream outflow. In regulated systems, ownership of water at a particular location can be exchanged. Source allows owners to share water within an ownership system’s boundaries, and so lend water to each other as required to meet downstream orders (see Borrow and Payback - SRG). Owner borrowing to meet orders downstream of an inflow or confluence node can therefore result in shares of outflow changing. However, to conserve ownership overall within the system, where water is lent, an account is kept in order for it to be paid back later.
Inflow and confluence nodes have no storage, or lateral loss/gain, hence the ownership conservation/ mass balance equation considers only inflow and outflow. At a confluence node, both inlet links must fall within in the same ownership system, so no rules are required to transfer flow between owners. However, at an inflow node, the additional inflow entering the river at the node has no ownership, so rules must be defined to determine how to share this between owners.
This SRG entry describes how sharing rules are configured at inflow nodes, and how, in the flow distribution phase, owner shares of outflow from inflow nodes and confluences are determined. Owner shares of inflow also need to be considered during the order phase of Source. At both inflow and confluence nodes, future inflows can be used as a supplementary source for each owner’s orders, and hence reduce the storage release required. Rules-Based Ordering - SRG describes how inflow is forecast and used in this way. The information for inflow nodes provided here is also summarised in Inflow node - SRG.
Variables used
Highlighting is used to distinguish between variables and procedures/functions/methods in the table below:
Yellow indicates the item is a method (function or procedure), items with no highlighting are variables.
Symbol | Purpose/Description | Units | Usage phase |
---|---|---|---|
conservedO(i) | Inflow/confluence node outflow for owner i when there are no downstream orders to consider. | volume | Flow |
Deficit(i) | The additional outflow volume owner i requires at this timestep to meet their total downstream orders. | volume | Flow |
DSOrder(i, t) | Total downstream order for owner i due to have arrived at the current node in time step t (for the order to be delivered on time). | volume | Flow |
DSTarget(i, t) | If there are any downstream orders due, this is the current node’s target outflow for owner i in time step t, which is DSOrder(i, t) limited by the owner’s share of any overall shortfall in outflow. | volume | Flow |
I1(i) | For owner i, their share of inflow from: -Inflow node: Upstream-Confluence node: The first inlet branch. | volume | Flow |
I2(i) | For owner i, its share of inflow from: -Inflow node: Additional inflow-Confluence node: The second inlet branch. | volume | Flow |
MassBalance(i) | Inflow or confluence node mass balance for owner i | volume | Flow |
O | Total outflow from a node in the current time step | volume | Flow |
O(i) | For owner i, their share of outflow from a node. | volume | Flow |
OwnerBorrowed(i) | The flow that owner i borrowed from other owners in order to meet its downstream orders. | volume | Flow |
OwnerLent(i) | The surplus flow that owner i lent to other owners. | volume | Flow |
owner% | Inflow node: Configured percentage of additional inflow to be assigned to an owner. | percentage | Configuration, Flow |
Surplus(i) | The outflow volume owner i has at this time-step in addition to that required to meet their total downstream orders. | volume | Flow |
TotalDSOrder | Total downstream order due to have arrived at the current node in the current time step. | volume | Flow |
fFlow(t) | Function that returns total additional inflow volume at an inflow node configured by time series or expression | volume | Flow |
fInflow(t) | Function to return the additional inflow volume at an inflow node for owner in time step t. It uses a method dependent on configuration:
| volume | Flow |
Inflow node
At an inflow node, the modeller configures a ‘source’ of flow for each owner, that returns an additional volume of inflow to enter the river downstream of the node. There are three options:
- Fixed ratio: Each owner i receives a specified percentage of the additional inflow volume (as determined by the configured time series or function fFlow(t) in the current time step t): fInflow(i, t) = owner% × fFlow(t)
- Time series: The modeller specifies for every owner a time series of inflow (fInflow(t)).
- Expression: The modeller specifies an expression to calculate inflow for every owner o for each time step (fInflow(i, t)).
There are two categories of inflow node in Source:
- Headwater inflow node: This type of inflow node has no model components connected to its inlet, so the only flow leaving the node is that from the configured inflow source. Ownership is conserved, so at any time step, t, the outflow for owner is: