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| 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
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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.
| Info | ||
|---|---|---|
| ||
| Note: 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
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.
You can also specify a piecewise relationship (as shown in Figure 4) instead of a generic one.
Figure 4. Link (Storage routing), Piecewise
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