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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.
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| Note: Throughout this document, unless explicitly stated otherwise, the term routing means hydrologic routing, not hydraulic routing. |
Using links in Source
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You can configure some aspects of links in a similar way to nodes. Refer to Renaming nodes and links, Searching for nodes and links, Deleting nodes and links, Node and link default names and Copying and pasting
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Adding links to a model
There are two types of links available depending on the nodes you are connecting (refer to Figure 1).
Vertical links are used to connect most nodes. To add this link to a model, first refer to Figure 1 which defines the terminology. To create the link:
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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 previouslyfor vertical links. Figure 2 shows the an example of a horizontal link.
Figure 2. Horizontal link
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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. For more detail on the wetland link, refer to Wetland 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 Types of link routing for more detail.
Editing
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link parameters
To edit link parameters using a feature editor, refer to About feature editors.
Types of link routing
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| Note: You can also toggle the view of specific links that join certain types of nodes. Refer to Schematic Editor options toolbar for more detail. |
Adding notes
You can include a text-based message, or note, for a storage routing link. Refer to Adding notes to nodes and links for details.
Link elevation
You can set the elevation for a link using the Location Control window (shown in Figure 3). Choose View » Location Control to open this window.
Figure 3. Location Control window
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| Note: While it is usual to use zero storage as the reference point for the elevation of a link or node, there is no convention for a link as to whether that should be at the start or end of the reach, or some point in between. Source has no mechanism for indicating the fall across a reach. |
Types of link routing
Source supports three types of link routing. You can either use straight through routing, a lagged routing model or a storage routing model. To enable routing, right click on the link, choose Routing Type, then click on the required link routing. A demand link , 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. They behave exactly like no routing links, and cannot be configured.A wetland routing link interconnects wetland hydraulic connector nodes and/or storage nodes. A wetland link is also known as a horizontal link because it is can only attach to the sides of storage and wetland connector nodes, rather than their upstream or downstream connectors. The presence of a horizontal link at a storage node indicates that the storage is behaving as a wetland. A wetland routing link is represented in the Schematic Editor as a solid green line with an arrow representing the expected direction of flow, which is set when you draw the link.
Figure 3. Project Hierarchy (link models)
Link elevation
You can set an elevation for a link using the Location Control window.
Figure 4. Location Control window
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A demand link 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. They behave like no routing links and cannot be configured.
A wetland routing link interconnects wetland hydraulic connector nodes and/or storage nodes. A wetland link is also known as a horizontal link because it is can only attach to the sides of storage and wetland connector nodes, rather than their upstream or downstream connectors. The presence of a horizontal link at a storage node indicates that the storage is behaving as a wetland. A wetland routing link is represented in the Schematic Editor as a solid green line with an arrow representing the expected direction of flow, which is set when you draw the link.
Figure 4. Project Hierarchy (link models)
Straight through routing
All links are assigned straight through routing by default. All water This link has the following features:
- Water enters and exits such a link in the same time-step
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- There are no configuration parameters associated with straight through routing links; and
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- You cannot configure fluxes, constituents or ownership.
Straight through routing links are represented in the Schematic Editor using black, dashed lines.You can check which routing models are in use in a scenario using the Project Hierarchy. The example in Figure 3 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.
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.
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Lag Time represents the time it takes for water to travel along the link and is a positive real number. This can be expressed in various units shown in Figure 4. Initial Storage is 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).
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- 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.
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 routing equation is shown below and some of its terms are represented diagrammatically in Figure 56:
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where:
S is the storage in the reach,
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Figure 7. Link (Storage Routing), Generic
You can also specify a piecewise relationship (as shown in Figure 8) instead of a generic one.
Figure 8. Link (Storage routing), Piecewise
About dead storage
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The next section provides an overview of the parameters shown in Figure 5.
Initial conditions (flow or storage)
If necessary, one of these parameters may be used to seed a reach with either an initial flow or storage so that reach behaviour is fully defined from the first model time-step.
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Piecewise routing allows you to specify how K varies with flow. If x=1 then K must always be less than or equal to the time-step. In BigMod routing, the highest value of K is found in the travel time relationship, and the reach should be subdivided into sufficient divisions such that the highest value of K for each division is less than half the time-step.
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Rating curves are used to describe the physical characteristics of the reach and convert a flow into a level, ie. they produce an output of level. The piecewise linear editor allows you to define relationships with respect to water level, discharge rate, reach width and dead storage. You can define multiple rating curves for a reach, each scheduled to commence on a particular date.
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- Right click Rating Curve and choose Add Rating Curve;
- Today’s date will automatically be entered for Start Date. To change this, click the calendar on the right side (see Working with date-pickers);
- Enter the water level, discharge rate, reach width and dead storage; and
- Enter an appropriate value for Overbank Flow Level.
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Figure 9. Link (Storage routing, Loss/Gain)
You can enter the relationship manually, or import the data from a .CSV file, the format of which is shown in Table 5. This table shows the data file format for both evaporation and rainfall.
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Choose Evaporation to specify the rate of evaporation per unit of surface area. Typically, this is done using a time series (loaded using Data Sources), the format of which is shown in Table 5. You can also specify the rate of evaporation as a single value, or as an expression using the Function Editor.
Figure 10. Link (Storage routing, Evaporation)
Rainfall on link surfaces
To specify the rate of precipitation per unit of surface area, choose Rainfall. Just like evaporation, this can be specified as a single value, as a time series (format shown in Table 5) or an expression. A time series can have multiple columns containing rainfall data.
Figure 11. Link (Storage routing, Rainfall)
Timeseries Flux
This allows the input of a time series of total water lost or gained on a link. Values can be positive or negative. A negative value denotes water returned to the link (a gain). See also Link losses and gains.
Figure 12. Link (Storage routing, Timeseries flux)
Constituents
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Figure 13. Link (Ordering)
Ownership at links
The intention of ownership at links is to define which owner is responsible for fluxes that occur on links. This is available when ownership is enabled for a scenario. These fluxes are defined as an expression using the Function manager. Refer to Figure 14 for details.