I take it that you've already inputted the flows in the flow menu (graphical user interface).

What version of HEC-RAS are you using?

Are you running 1D or 2D?

Running steady or unsteady flow?

I found out in ID unsteady flow, the flows can go negative if there are big variations (abrupt differences) between sections.

Jeff Wong Jeff Wong

Dear Sir,

I am used 2D unsteady Hec-Ras

and i was input all the required discharge data.

Hello Mr. Hamdan ... Unfortunately, I don't have much experience running 2D unsteady with sections. I normally use the grid cells in 2D without sections. You may want to increase your timestep and/or flows to see if it makes any difference (stability issue?). Sorry, that I'm not much help. Jeff.