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