Time step

This is the period between the times when the state of a system is calculated in DRAINS. Flowrates and hydraulic grade line (HGL) positions are calculated at each time step.

DRAINS specifies a computational time which can be set in the Project Options property sheet. It is recommended that you use the time step set by DRAINS or a smaller one, since the flows, HGL positions and design pipe sizes calculated by DRAINS can change with the time step. The time step selected by DRAINS relates to the time taken for flows to pass through shortest pipes or channels in a drainage system.

The smallest time step that can be used is 0.001 minute and the largest is 1 minute. For most systems, the results obtained with the recommended time step will be very close to those obtained with the minimum time step. Due to the new 2019 procedures that require significantly greater calculations and handling of data, hydrographs and HGLs are now stored and presented in 1-minute steps.

Storage routing models usually run with a time step of 1 minute, which may cause results to differ from those of RORB, RAFTS or WBNM which usually run with longer time steps.