Piers in HEC RAS

[Smoensen]

Hello,

I am currently modelling a river in HEC RAS 4.0 where the bridge (or viaduct) runns over the river over a long distance. If the modelling is done by adding a bridge, the energy losses are calculated by adding the energy losses due to the expansion of the water, the compression of the water and the friction under the bridge. For every bridge a section upstram and downstream has to be defined. In my case, there is no such thing as upstream and downstream cross section, since the bridge is running over the river over a long distance. How would you modell this case?

1. Interpolate cross sections and define for each pier a bridge (piers cannot be modelled without deck...)?
2. Modell the piers as an ineffective flow area (how does HEC RAS handle the energy losses due to the pier)?

Sorry for my english mistakes, I hope you understand my question...

PS: The deck doens't have to be modelled, only the piers must be entered into the modell...

 

[Rye1]

I would think that you would want to add the four required bounding cross-sections. You should have a detailed survey of the area, use the survey to possibly create a TIN and cut sections from there. The piers are solid obstructions - ineffective flow areas, in my opinion would not be the correct procedure.

Simplified approach: cut one cross section for the survey at the bridge location, add the piers in as blocked obstructions.


Robert Billings

http://www.newrivereng.com

 

[gbam]

Please clarify the direction of the viaduct/bridge, is it parallel or perpendicular to the direction of river flow?

Rye1 mentioned the simplified approach by using blocked obstructions; this is a good approach to determine approximate impact from the piers.

You can also hard code the pier geometry in the cross section.