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- 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.
Lagged Flow when Fluxes are Significant or there is Dead Storage
If lateral fluxes (reach processes) are important, or there is dead storage in the reach, or both, and it is desired to lag flows without attenuation then it is necessary to use a Storage Routing link to do this. The approach that should be adopted uses generalised non-linear routing and is as follows:
- The lag is converted to the number of model time-steps, n, by dividing average travel time (ie. wave passage time) by the model time-step, and rounding off the result. However, the minimum value of n is one (i.e. n ≥ 1);
- Set up a routing reach where the number of divisions, ndiv = n, x = 1, m = 1 and K = dt (recalling dt is the model time-step). However, if ndiv = 1 and the average travel time is much less than the model time-step, and it is required to account for lateral fluxes but not otherwise change the hydrograph shape, then set K = travel time (recall that for stability K ≤ dt/x). For example, this would provide a means of adjusting for fluxes in a reach in a monthly model, where travel times are very small relative to the model time-step.
The solution process is the same as for other applications of storage flow routing.