About links
Links connect nodes in Source - they link, store and route water passing between nodes. Nodes are connected using links only, and two links cannot be connected to each other without an intervening node.
A reach refers to a stretch of river, or physical section, between an upstream and downstream location. A link, on the other hand, is a logical connection within a river systems model. Routing describes the change in timing and shape of flow as water moves down a river.
Links (or reaches) can have routing configured on them. For links (or reaches) that do not have routing configured, they are used to define the order of execution in the model.
Links are categorised as either:
- Vertical - used to connect most nodes. The first four types of links in Table 1 are all vertical; or
- Horizontal (or wetland links) - used to connect the Wetlands Hydraulic Connector node (source) and the Storage node (target) only. The presence of a horizontal link at a storage node indicates that the storage is behaving as a wetland. Figure 2 shows an example of a horizontal link.
The Node Connection Matrix shows the types of links created when you connect different nodes; these are summarised in Table 1.
Table 1. Link types in Source
| Type of link | Used to connect | Representation in Schematic Editor | Example |
|---|---|---|---|
| Demand link | Supply point (source) and water user (target) nodes only | Red, dashed line |  |
| Lagged flow routing | Various nodes | Black line, with alternating dots and dashes |  |
| Storage routing | Various nodes | Black, solid line |  |
| Straight through routing | Various nodes | Black, dashed line |  |
| Wetland link (Horizontal) | Wetlands Hydraulic Connector node (source) and the Storage node (target) only | Green, solid line | Shown in Figure 2 |
Using links in Source
Once links have been added a model, you can edit several attributes in a similar fashion as for nodes:
- Node and link default names;
- Renaming nodes and links;
- Configuring node and link parameters;
- Adding notes to nodes and links (only for lagged flow routing and storage routing links);
- Searching for nodes and links;
- Deleting nodes and links;
- Node and link default names; and
- Copying and pasting.
Adding links to a model
To add a link to a model, first refer to Figure 1 which defines the terminology. To create the link:
- Position the mouse cursor over the upstream node;
- Click and hold on one of its downstream connectors and start dragging;
- When you start dragging the mouse cursor, candidate targets are displayed (as large icons) for the upstream connector of a downstream node; and
- Release the mouse and the link will ‘snap’ into place.
Figure 1. Node connection terminology
For horizontal links, the node connectors appear on the left and right side, instead of above and below the nodes. Click and drag these connectors together as described above. You can also drag the link vertically once it has been created by clicking on the red dot. This appears in the centre of the link when you click on the link.
Figure 2. Horizontal link
Dragging links
You can disconnect and reconnect a link between nodes rather than having to delete and re-add it using the Allow Link Dragged button in the Schematic Editor options toolbar. Note that not all links can be connected to all types of nodes, and specific nodes require certain links. Refer to /wiki/spaces/SD520/pages/55214309 for more detail.
Link elevation
You can set the elevation for a link using the Location Control window.
Types of link routing
Source supports three types of link routing - straight through routing (default), a lagged routing model or a Storage routing model. You are responsible for ensuring that you use the correct model for each link.
Note that you can configure constituents, ownership and ordering for a storage routing link only.
To change the link routing type:
- Right click on the link to display the contextual menu;
- Choose Routing Type; and
- Finally, click on the required link routing.
You can check which routing models are in use in a scenario using the Project Hierarchy. The example in Figure 3 shows that all three types of links are in use - straight through routing, lagged flow and storage routing.
Figure 3. Project Hierarchy (link models)
Straight through routing
All links are assigned straight through routing by default and have the following features:
- Water enters and exits such a link in the same time-step;
- There are no configuration parameters associated with straight through routing links; and
- You cannot configure fluxes, constituents or ownership.
Lagged flow routing
Lagged flow routing only considers the average travel time of water in a river reach. It does not consider flow attenuation. The flow entering a link exits at some whole number of time-steps in the future.
Figure 4 shows the feature editor for a lagged flow routing link and Table 2 lists the associated parameters.
Figure 4. Link (Lagged flow routing)
Table 2. Parameters for lagged flow routing
| Parameter | Type | Definition |
|---|---|---|
| Lag time | Time | This represents the time it takes for water to travel along the link and is a positive real number. |
| Initial Storage | Volume | The amount of water deemed to be in the link on the first time-step. For example, if there is a lag of two days, and there is 10ML in the link at the start of the run, then 5ML is deemed to be flowing out each day (total initial storage divided by lag). |