The time step critical elements in the SWMM 5 report text output file tells you which elements were controlling the time step during the simulation. If no element was controlling the time step then the program will just use the maximum time step. For example, if the maximum time step was 10 seconds and the average time step was 9.8 then only a few time steps were set by a link or node that needed a smaller than maximum time step (Figure 1). If the maximum time step for the same simulation was 30 seconds then many links and nodes will set the time step (Figure 2).
Figure 1. Most of the time the simulation used the maximum time step of 10 seconds so only a few links were time step critical.
Figure 2. Most of the time the simulation used less than the maximum time step of 30 seconds so many links were time step critical.
