Problem

How does the StormCAD (GVF-Rational solver) calculate the velocity at a cross section node element? 

Solution

For a cross section, the velocity corresponds to the downstream end of the upstream channel link, whose shape is determined by the next upstream cross section.

Example:

1. Take the flow reported in the link upstream of the cross section node you want to check the velocity on. In this example that is, 67.53 m^3/s for Channel -1.

2. Locate the bottom width of Channel-1, which is defined in cross sections-0 and is 1.250 m (The upstream node bottom width is used for the channel because channels are assumed to be prismatic in StormCAD). This will be multiplied by the Depth (Out) of Channel -1, which is 6.65 m.

3. Now divide the  flow reported from step 1 by the value from step and that will give you the velocity at the downstream node, which in this example is 8.06 m/s at CS-1.

The  equation looks as follows:

Q=VA

V=Q/A

V = (upstream link flow (Channel-1) \ (bottom width of upstream channel defined  at it's upstream cross section (CS-0) * depth out of that channel (Channel -1)))

V = (67.53 m^3/s \ (1.250 m * 6.665 m))

V = 8.06 m/s