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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).
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