Scott:
Note that the way we compute flood wave arrival time is an approximate method. We record the initial water surface elevation (WSEL) at start up, and then during the routing when the WSEL rises by 1 foot, we record that time. This time is then considered the flood wave arrival time. Unfortunately, sometimes the initial WSEL is not that accurate (since it is an approximate starting value) and this method records an incorrect time.
Sincerely,
Chris E. Maeder, M.S., P.E.
Senior Technical Engineer
chris.maeder@bossintl.com