Runoff from One Watershed for a 100 Year Simulation with SWMM 5 Statistics for the Subcatchment Impervious and Pervious Depth

Introduction:  This set of blogs uses the 1000 year rainfall/runoff/hydraulics model that you can download at http://swmm2000.com/forum/topics/1000-year-simulation-with-rainfall-in-swmm-5 to show the inner workings of SWMM 5 and by extension InfoSWMM and H2oMap SWMM using a QA/QC version of SWMM 5 with extended graphics.   I always hope that seeing the inner workings of a SWMM 5 feature helps to understand the code, sensitivity and importance of a parameter.   It also helps show sometimes when a parameter is not important.  

Discussion:  In this blog we look at the Subcatchment Runoff Depth for the three types of Subcatchment Surfaces in SWMM 5:

1.       Impervious with depression storage
2.      Impervious without depression storage
3.      Pervious area with depression storage

As you can see in the graphs of depth (Figure 1) the pervious depth is often zero as the infiltration is greater than the continuous rainfall.  Of course this depends on the rainfall intensity, infiltration type and infiltration parameters.  If you perform a Statistical Analysis on the pervious depth at a saved time step of 1 hour you will find 2721 events over a threshold of 0.01 feet. 

Figure 1.   Runoff from One Watershed for a 100 Year Simulation with SWMM 5 Statistics for the Subcatchment Impervious and Pervious Depth