Confluence node

A Confluence node represents a natural join in a river system (such as a tributary or reconnection of an anabranch). Both inflows combine into a single effluent without any loss or delay. The behaviour of a confluence node depends on the number of branches that are regulated. You can describe the arrangement of the natural system as one of:

Neither branch is regulated - no configuration is required as there are no orders;
One branch is regulated; or
Both branches are regulated.

Note: The confluence node adds the upstream minimum and maximum constraints together.

One regulated branch

If there is only one regulated branch, the unregulated branch behaves like an inflow node. As there is only one regulated upstream branch, priority setting is not required. In this case, the confluence node can be thought of as acting in a similar manner to an inflow node.

Note: The names in the Link column are those you assign to the upstream links.

As such, the branch which is unregulated needs to have forecasting ability of the inflow arriving, so that orders may be adjusted for the expected inflow. Therefore the confluence node has a forecasting model attached to it (as shown in Figure 1). The forecast model is the same as that available for an inflow node (see Forecasting inflows).

Note: For rules based ordering the confluence forecast model ignores any upstream nodes on the unregulated branch. This means that any upstream inflow node forecast models are ignored in the confluence node forecast calculation in rules based ordering phase. For network LP ordering the unregulated branch may be configured as regulated if processes on the unregulated branch are to be modelled in the order phase.

Figure 1. Confluence node (Single regulated branch)

Both regulated branches

If both branches are regulated, you need to define how orders may be split by choosing one of two methods specified under Regulated Ordering Methodology:

Constraint based (default) - Specify a priority for each branch. Click the cell in the Priority column and edit the value; or
Harmony based - As shown in Figure 2, you must define how the upstream storage volume for each branch is determined using the Function Editor (in the Branch Setup table). You must also specify how to split the upstream orders (under Harmony Ordering Setup) - using either:
- A function that defines the proportion of the total order assigned to the named upstream branch based on model parameters; or
- A table that has the proportional relationship on how orders are to be split upstream based upon the defined volume of water up each branch for each owner.

You can work with the table as follows:

To add a column, right click on one of the column headings and choose Add Volume. The other menu options will change the columns as shown in Figure 2; and
To add a row, click on a cell in the last row to highlight and edit it. Input a value and press Enter.

Figure 2. Confluence node, harmony based

Note: You may have to select the regulated link and then re-select the unregulated link before the forecasting controls become visible.