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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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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 Feature Editor 1 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).
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 Travel time in the reach is computed as follows:
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. Refer to the Source Scientific Reference Guide for more details.
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The next section provides an overview of the parameters shown in Figure 5.
Figure 7. Link (Storage Routing), Generic
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.
Reach length
The Reach Length is not used in computations and is only for documentation purposes.
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This parameter is used to calculate travel time for orders in the ordering phase. It is not used in the flow distribution phase.
Number of Divisions
Conceptually, this parameter describes the number of times that a reach is replicated. The effective length of a reach is determined from its behaviour, which is controlled by the combination of the storage exponent m, the inflow bias x and the storage constant K. Specifying multiple reach divisions implies applying the same set of behavioural parameters multiple times. In other words, if the effective length of a single-division reach is 500 metres (as derived from its behavioural parameters), changing the # Divisions parameter to 2 implies a combined effective length of 1000 metres. If you want to sub-divide a 500 metre reach into two 250 metre sections, you must also change the behavioural parameters to achieve this.
Inflow bias
The weighting factor x is used to adjust the bias between inflow and outflow rate and allows for flow attenuation. A recommended starting value is 0.5.
Storage exponent
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 m≠1 and x=0, in which case the storage routing equation simplifies to:
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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:
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