Steady State Floodway Analysis Bridge Issue

[Anonymous]

Hello,

I have a steady state model where I’m trying to complete a floodway analysis, however a bridge within the model is causing some issues, showing significant drops in water surface elevation at the bridge and decrease in WSE rise in a few cross sections upstream of the bridge. The bridge cross section has divided flow, with the bridge itself only being over the channel. The channel is disconnected from the floodplain. The model is calculating orifice flow through the bridge and showing a drop in floodway elevation. The model is calculating the water surface elevation at the same elevation as the low chord elevation of the bridge. Has anyone encountered a model with a similar scenario? Seems like the model should still be showing the WSE increasing above the low chord elevation of the bridge.

Thanks for any insight you can give!
Janeen

[Anonymous]

There are situations where constrictions can actually cause the water surface to drop at the constriction.
Is the energy grade rising?

EG = WSE + VelocityHead

If the velocity head goes up more quickly than the energy grade, the water surface can drop. That may be what is happening for your data set.

[Author]

Posts