Storage elevation flow relationships 1

[Crystalct1]

When doing a reservoir routing with Hec Hms, I need a storage-elevation-flow table. I got my stage-flow relationship from my (already modeled) Hec Ras Stage rating curve at the station at the upstream face of the bridge. Is this correct? At each height, I can see a corresponding flow. Can't I use that as my outflow from the bridge?

Also, I wanted to use cumulative storage from HEC RAS as my storage data, but that doesn't seem to be working. I took the total storage at the upstream-most cross section and subtracted (the cumulative storage at the upstream face) from it. I used the total storage from the channel+LOB+ROB. Something must be wrong because when I run those values in HMS, I get an increase in outflow which isn't possible, is it?

What is the best way to obtain the storage upstream of the bridge?

 

[sam74]

I don't understand how you are getting your storage from your RAS sections. If I were modeling a reservoir I would just use the topographic contour lines to come up with elevation/surface area data.

 

[bltseattle]

Your approach appears correct, and I've used the same approach successfully with HEC-RAS & HSPF. Without knowing the HMS model specifics, thinking in terms of HSPF: If the ponded surface area of the reach is substantial, I would check that your model doesn't have redundant rain-on-reach computations that could, in effect, increase your runoff generating area. To say it another way, if the reach is simulated once in a runoff-generation block and once again as a reach that is rained upon, this could result in extra runoff.