Surcharged d/D in InfoSWMM and H2OMap SWMM

The value of d/D in InfoSWMM is calculated as Link capacity or the Midpoint Capacity

Whereas the Surcharged d/D is calculated from the end node depths or
Surcharged d/D = Average depth in the middle of a link or ½ (Upstream Depth + Downstream Depth) / Maximum depth

Midpoint Capacity = the midpoint cross sectional area (based on the average depth) / the full cross sectional area

If you look at the reports d/D or Midpoint Capacity is not quite the same as the Surcharged d/D which is based on the upstream and downstream depths and not the Capacity (a function of Area).  I hope this explains why Surcharged d/D is equal to the Depth and not the same as the d/D or Midpoint Capacity.

Inverse Color Attribute Browser in InfoSWMM and H2OMap SWMM showing various output data.



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