It's standard in the engineering world to use overland flow no more than 25% of total. This isn't published very often, because the government doesn't like to state what's not in their favor.
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where I work we use a simple program to make sure there is pipe capacity for pipe design, then whenever we need an HWE we just use civiltools program culvert design tab.
Our program does not calculate the HGL inside the manhole like Hydraflow does, just inside the pipes, however the upside is...
5% maximum grade approaching any intersection, but It doesn't necessarily HAVE to be a tangent, as long as 100' up to intersection is less than 5%. If there is a slight curve less than 100' nobody will care if it's less than 5%.
Yes, I like to break the grade before the cross walk also.
I...
