RAS - Storage Area

[SMIAH]

In HEC RAS, I am using a stage Hydrograph uptream as a boundary condition in a unsteady flow analysis.

I am wondering, if I want to perform a dambreak study of a dam located just downstream of this boundary condition, do I have to add a storage area upstream?

 

[Drew08]

Depends on what you mean by "just". You need at least 2 cross-sections between a structure and the upstream boundary, regardless. If those cross-sections adequately represent the storage volume in the reservoir, then no. If they do not, then yes. Either way, you need to define the volume of water that gets release.

HEC-RAS only uses the upstream boundary condition for super-critical flow, if the upstream boundary is at a reservoir, super-critical flow won’t occur, so it really doesn’t matter what it is set as. In a sub-critical condition, the upstream boundary is defined by backwater.

 

[SMIAH]

Thanks for the answer.

On my model, the cross-sections upstream of the dam don't represent the storage volume in the reservoir.

I though that I would define the volume of water released by the lake with the stage hydrograph?

I'm performing a unsteady flow analysis (need a upstream flow/stage hydrograph).