Selection of the time-step for a catchment depends on the time step of Meteorological data.
The selection of an appropriate time-step for modelling is a compromise between accuracy and run time/computing power requirements. A smaller time-step will require longer computing time, and this may be an issue, particularly when running on slower machines or using Catchment files with many nodes (for more information on managing computing time requirements, refer to Running and Saving music Simulations).
An appropriate time-step will depend not only on the Source Node or overall Catchment size, but also on the size of Treatment Nodes within the catchment. For example, running daily time-step simulations on a 2m wide grass swale of 50m length, will produce unreliable results for both the routing of flows, and the behaviour of pollutants (because the variation in both will occur at time-steps of considerably less than one day).
Therefore, selection of time-steps should be based on the size of the smallest Source Nodes and Treatment Nodes within the overall Catchment, using a simple three-step process:
- Calculate or estimate the time of concentration (tc) of the smallest sub-catchment within the model;
- Calculate or estimate the shortest expected detention time of proposed treatment measures; and
- Select a time-step which is equal to or smaller than the smaller of 1 and 2.
Warm-up period
Not offered at this stage.