Simulation
Simulation is the most common way of performing analysis and design checks. This process, usually in mathematical form, imitates or mimics the behaviour of some real thing or system.
In models such as DRAINS, the behaviour modelled is the passage of storm runoff through a catchment’s drainage system as a result of a storm event. This is done by determining flow behaviour and characteristics (as measured by flowrates, flow depths, widths and velocities, water levels, and hydraulic grade line positions).
A simulation or analysis of flows takes place over time, with a starting point at time = 0 and a calculation of the states of a system at regular time steps thereafter. These 'states' include factors of interest such as flowrates through conduits, HGL or water levels at nodes and storage volumes. The calculations stop when a certain number of time steps pass, or when a key factor such as a flowrate falls below some cut-off level.