Dear Shiva:
Note that you can export the cross section data from BOSS RMS and RiverCAD, but I don't know what you would need in order to export the storage-discharge relationship from the cross sectional data for your HEC-1 model.
If you could explain more, I can investigate it.
Sincerely,
Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com