The Effect of the Hydrology Time Step on RDII Flow

Note: The wet hydrology time step and the report time step should be adjusted together to generate the smoothest RDII flow at your nodes. The three images show below show:

1.If you hydrology time step equals your rainfall time step then the RDII flow will have a step function appearance or your flows in this case will be constant for one hour or the rainfall interval,

2.If you choose a smaller hydrology time step then the flows will be smoother (2nd image), but

3.If the report time step is much less than the hydrology time step then the flows will still be stepwise linear for the hydrology time step size.

When picking a hydrology time step for continuous simulation you should probably pick a value of about 5 minutes so that the generated flows are smooth but not so small that a lot of time is used in the RDIi convolution process to generate the 3 units hydrographs for RDII.