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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 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. 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.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.
Figure 5. Link (Lagged flow routing)
Lag Time represents the time it takes for water to travel along the link and is a positive real number. 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).
Travel time in the reach is computed as follows:
| Equation 1 |
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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 6:
| Equation 2 |
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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 |
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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 6. Prism and wedge storage
Refer to the Source Scientific Reference Guide for more details.
Figure 7 shows the parameters required to configure storage routing on a link.
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
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)
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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If m=1, linear (Muskingum) routing is implied, otherwise non-linear routing is implied. A recommended starting value for non-linear routing is m=0.8. Laurenson routing is obtained when m≠1 and x=0, in which case the storage routing equation simplifies to:
| Equation 41 |
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Storage constant
When using linear routing (m=1), the units of the storage constant K are in seconds. For models using daily time-steps, the recommended starting value is 86400 (the number of seconds in one day). When using non-linear routing (m≠1), the recommended starting value should be calculated as follows:
| Equation 52 |
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For example, if the reach length is 1000 metres, the time-step is one day, and m=0.8:
| Equation 63 |
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The parameters for storage flow routing are summarised in Table 1.
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| Note: In the Flow vs Loss/Gain table, flow cannot be negative. Additionally, the values for Loss/Gain Qloss must be increasing (as shown in Figure 95). |
Figure
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5. 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
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6. 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
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7. 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
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8. Link (Storage routing, Timeseries flux)
Constituents
Before you can configure constituents for a link, you must define them first for the scenario using Refer to Links.
Ordering at links
Figure
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9. Link (Ordering)
Ownership at links
Ownership must be enabled at the scenario-level (using Edit » Ownership) prior to configuring ownership at storage routing links. Refer to Ownership for details.