Routing through bridge 1

[Crystalct1]

I need help! I'm doing a bridge replacement analysis. I'm familiar with HEC-HMS, but not a whole lot. I need to know where I enter the information I have. I've got design storms. I have geometry. I know storage upstream of the bridge at each elevation. Do I use river reach routing? Or reservoir routing? I was told to treat the reach as a detention basin with the bridge opening as an outlet. But the reservoir editor in HMS ask me for a lot of information about the "outlet". What do I say about crest elevation when the "crest" is actually the roadway above the opening, which is not exactly level? What do I say about the dam when there is no dam but HMS won't compute without dam info if I use reservoir routing?

And if I use river reach routing, I'm getting peak outflows (just slightly) higher than my peak inflows--is this possible? Any suggections?

 

[sam74]

It sounds like you should be using HEC-RAS instead of HEC-HMS for water surface elevation calculations.

 

[Crystalct1]

Sam, I did that already. That's where I got the elevation, storage, flow info. NJDEP permits acquisition requires you to route a certain design flow (usually 100 year storm) hydrograph through both the existing and proposed bridges to see the change in outflow. DEP does not want larger bridge openings to cause too much an increase in outflow for fear of downstream property, etc, etc. So I still need routing info as well as surface elevation info.

 

[sam74]

I've never used HMS before so I'm not sure if you can do that or not. You should be able to try unsteady flow modeling in RAS though. I've only had a chance to try this once on a complicated system and didn't have much luck. If you are only modeling a short piece of channel and one bridge you might have more success than I did.

 

[cvg]

you could do it very easily in HEC1 using a reservoir route. You would need to enter only the stage - storage data and the stage - discharge data which you apparently already have.

 

[ALBUD1962]

I would develop a stage discharge relationship for the bridge.Depending on the size, this can be modeled as some sort of culvert or obtained from Hec-Ras. I am assuming you can calculate the storage behind the structure. I am not sure how you are modeling the flows(ie, scs, rational, etc.) You can model a storm as gage data if you just have Q's. I believe I used a junction or a source node instead of a subbasin when I did this. The stage discharge and storage data input is found under the reservior object. You need to set up your met model as no precipitation. Also, the run won't compute unless you provide the control specification. you could add a reach downstream of the stucture if you want to model the effects of the discharge on the downstream channel.

I put an example of this at

http://penntrout.org/test.zip

 

[Crystalct1]

Wow. Thanks a lot to everyone--especially Albud. This was extremely helpful.