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- 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.
One example of a vertical link is a demand link, which is created when you connect a water user node to a supply point node, and is represented in the Schematic Editor using dashed red lines.
Figure 1. Node connection terminology
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Horizontal links (or wetland links) are drawn between the Wetlands Hydraulic Connector node (source) and the Storage node (target) only. This process is similar to drawing a vertical link. Note that 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 for vertical links. Figure 2 shows an example 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.
Figure 2. Horizontal link
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Source supports three types of link routing - straight through routing (default), a lagged routing model or a storage routing model. . These are explained in further detail next. You are responsible for ensuring that you use the correct model for each link.
To change the link routing type:
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You can check which routing models are in use in a scenario using the Project Hierarchy. The example in Figure 4 shows that both lagged flow and storage routing are in use. You are responsible for ensuring that you use the correct model for each link.
Refer to Types of links routing for more information.
Figure 4. Project Hierarchy (link models)
Figure 4. Project Hierarchy (link models)
Straight through routing
All links are assigned straight through routing by default. This link has 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.
Straight through routing links are represented in the Schematic Editor using black, dashed lines.
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 that link at some whole number of time-steps in the future. This type of link is represented in the Schematic Editor as a black line, with alternating dots and dashes. Once you have enabled lagged flow routing, double click the link to configure the settings.
Figure 1 shows the feature editor for a lagged flow routing link and Table 1 describes the parameters required to configure this link.
Figure 1. Link (Lagged flow routing)
Table 1. 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). |
Travel time in the reach is computed as follows:
| Equation 1 |
|---|
A link configured for lagged flow routing is treated as a series of sub-reaches of equal length, with the travel time in each sub-division equal to one time-step. Water moves through the link progressively, without attenuation. You cannot configure fluxes, constituents or ownership on a lagged flow routing link. If lateral flows are significant and/or there is dead storage in the reach, you can approximate lagged flow routing using generalised non-linear storage flow routing, as follows:
- Compute the number of divisions, n, by dividing the average wave passage time by the model time-step and round the result to a whole number. The result must be at least one (ie n ≥ 1).
- Configure a storage flow routing reach where:
- n = number of divisions;
- x = 1;
- m = 1; and
- K = model time-step.
- If you need to account for lateral flows where n=1 and the average travel time is a fraction of the model time-step (eg. a reach with a one day lag in a model with a monthly time-step), you can adjust K to a smaller value without affecting the shape of the hydrograph.
Storage flow routing
This type of link is represented in the Schematic Editor as a solid black line. Storage routing is based on mass conservation and the assumption of monotonic relationships between storage and discharge in a link.
The stability criteria must also be satisfied for a model to run correctly. If this is not the case, the following error appears during runtime: Routing parameters have caused instability in storage routing. Refer to Stability criteria for more information.
This is a simplification of the full momentum equation and assumes that diffusion and dynamic effects are negligible. The method uses index flow in flux, storage and mass balance equations. A weighting factor is used to adjust the bias between inflow and outflow rate, hence allowing for attenuation of flow. The storage routing equation is shown below and some of its terms are represented diagrammatically in Figure 2:
| Equation 2 |
|---|
where:
S is the storage in the reach,
K is the storage constant,
m is the storage exponent, and
q‾ is the index flow, which is given by
| Equation 3 |
|---|
where:
I is inflow to the reach during the time-step,
O is outflow from the reach during the time-step, and
x is the inflow bias or attenuation factor.
Figure 2. Prism and wedge storage
Refer to the Source Scientific Reference Guide for more details.
Figure 3 shows the parameters required to configure storage routing on a link.
Figure 3. Link (Storage Routing), Generic
You can also specify a piecewise relationship (as shown in Figure 4) instead of a generic one.
Figure 4. Link (Storage routing), Piecewise
About dead storage
Dead storage refers to the capacity of a storage that is below the minimum operating level. At this water level, there is no outflow. The level of the reach with respect to dead storage at the beginning of the time-step affects its level in subsequent time-steps as follows:
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