I have seen a number of questions on in the Discussion Group recently regarding the Hydraflow Storm Sewer Extension and the calculation that do not exactly meet expectations.  There have been some misunderstandings, and some assumptions.  While I am jumping over Intensity, I think this is time to talk about some calculation options because they are connected.

Attached is the Calculation Options available to analyze and design your storm sewer network.  Each set of calculations options are different.  They each have a different role and produce different results.   If you don’t understand each option and the resulting answer, click the help button.

In my practice, I typically run both Options 1 and Options 2.  Option 3 for me doesn’t get a lot of use – Civil 3d tends to do some of the full design, and experience the other.  Option 4 should get more use, but I don’t tend to use it enough.

One typical mistake I see in practice is in using the Analysis and Design option and the assumption of a velocity.  In many cases, the first set of analysis assumes the design pipe velocity to compute the Pipe Travel time.   For some, that might be wholly adequate to establish some pipe sizes or an invert or two or to use the interactive features.  (I like them)

But, Read the yellow highlighted section. 

This is going to make a HUGE difference in your Tc if your velocities exceed your design velocities.  This the analysis that I would submit to your engineer or to the review agency.  If your system includes critical depth, hydraulic jumps or something less than pipes flowing full,  you need to CHECK your output, your assumptions and your options. 

As an aside, AU 2008 registration is open.  I look forward to teaching CV204-4, and I look forward to seeing you in Vegas.