Decreasing Flood Arrival Times

[sshand]

I have noticed, while analysising a "Sunny Day Failure" (ie piping failure), in the flood crest summary output, that for the last few cross section locations that the flood wave arrival time is decreasing.

For example:

At 5.5km Flood wave arrival time is 1.80 hrs
At 5.9km Flood wave arrival time is 1.94 hrs
At 6.0km Flood wave arrival time is 0.57 hrs.

My time to breach is 0.36 hrs.

Assuming my input is correct, why would this be occuring. It does not seem to occur for a flood induced failure (ie overtopping).

Scott Shand

[Chris Maeder]

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