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ParameterTypeDefinition
Lag timeTime

This represents the time it takes for water to travel along the link and is a positive real number. If the specified lag time is not an integer multiple of the model time-step, it will be rounded to the nearest time-step.

Initial StorageVolumeThe 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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Tip

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titleModelling lagged flow routing with storage routing

Anchor
ModellingLaggedWithStorage
ModellingLaggedWithStorage

A link configured for lagged flow routing is treated as a series of sub-reaches or 'divisions' of equal length, with the travel time in each 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 model lagged flow routing using storage routing and the generalised non-linear storage option, as follows:

  1. Compute the number of divisions, n, by dividing the dividing average travel time (ie. wave passage time

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  1. ) by model time-step and round the result to a whole number. The result must be at least one (ie. n ≥ 1);
  2. Configure a storage flow routing reach where:
    • n = number of divisions;
    • x = 1;
    • m = 1; and
    • k = model time-step.
  3. 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

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  1. the smaller time step value without affecting the shape of the hydrograph.

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  1.   For stability K ≤ dt/x and in this case x = 1.