Duration of Inundation 1

[KatiLynSki]

I am filling out an Army Corps of Engineers application that asks for the "duration of inundation". I know that this is defined as the amount of time it takes for the water surface elevation to return to it's starting elevation, however what order of accuracy should I be using?

EXAMPLE, 24 hour storm duration:
Starting water surface elevation: el.393.18 @0.0 hrs
Water elevation "sees" the storm: el.393.19 @9.6 hrs
Peak water surface elevation: el. 395.93 @19.8hrs
Tail end of hydrograph:
el. 393.78 (starting+6") @89.8hrs
el. 393.51 (starting+4") @114.8hrs
End of model: el. 393.38 @144.0hrs (note that el. 393.38 starts at 142.2hrs, is definitely trailing off at this point)

What would YOU use as the duration of inundation in this example?

Any rules of thumb as to how to define the tail end of the storm? Is it truly when the water surface returns to delta0.00?

 

[RWF7437]

You may get better answers if you tell us which Corps of Engineers form you are filling out.

If you are working on a project located in a regulatory flood plain that may be a different form than if you are working on a project located in or near a jurisdictional wetland or in a navigable waterway. These things matter to regulators.

How do you know the example you have provided is the appropriate example for your project ?

There is nothing magic, or sacred, about a 24 hour storm.
There is nothing magic about a so called 100 year storm ( 1% Annual Exceedence Probablity storm).

Finally, because regulatory flood elevations are considered accurate to only plus or minus 1 foot this suggest that your duration need only be accurate to a similar range.

good luck

 

[psmart]

KatiLynSki: Are you sure it's the time required to return to the starting elevation, rather than the time that a certain flood elevation is exceeded?

Returning to the starting elevation can take a very long time, especially if the dropping WSE is asymptotically approaching the starting elevation. This would present a real challenge in deciding "how close" you have to get. On the other hand, the (higher) flood elevation is likely to be reached and crossed at a clearly defined time.


Peter Smart
HydroCAD Software

http://www.hydrocad.net