"not physically possible"!!

[manza]

Hi,

First, sorry for my english, I don't speak it very well.

I have a little problem: an error message that says: "For the final momentum answer at the bridge, the upstream energy was computed lower than the downstream energy. This is not physically possible, the momentun answer has been disregarded".

I have tried to do many different options to avoid this message, but it's always there. I think geometry data are good.

Does anyone know something about it?

Thanks a lot.

Manza

[Jack Schaller]

What percentage of the flow upstream is between the bridge abutments versus outside the bridge abutments? If the vast majority of the flow is located between the bridge abutments you might want to look at using a different method for analyzing the bridge losses. If there is no chance of pressure flow and there is only a small loss due to contraction, you might want to see what the losses would be from friction only (the normal bridge method in HEC-2). I do not have the HEC-RAS manual readily available to see which method that is in HEC- RAS. You have the option to allow HEC-RAS to solve several methods and select the highest loss method. You might run that option to allow a quick comparison of the bridge loss methods.