Rossmiller conversion equation 1

[gglaubrecht]

thread162-70645
In his post, LHA listed a conversion equation by Ronald Rossmiller.

I can't seem to find this online. There is a term "I" in the equation which is not defined in his post and I wanted to make sure what this parameter was.

The formula listed was:
C=(7.2*(10)^-7)*(CN^3)*(RI^0.05)*{[(0.01*CN)^0.6]^-s^0.2}*[(0.001*CN^1.48)^(0.15-0.1*[highlight #FCE94F]I[/highlight])]*{[(IMP+1)/2]^0.7}, where RI=return interval(yr), IMP=impervious coverage( decimal)and S=average land slope (whole number percent)

The I in the term (0.15-0.1*I) is what I'm after.

 

[TerryScan]

It appears that is not the only thing that needs more explanation base on a complete article found here:

http://cleveland2.ce.ttu.edu/research/txdot_0-6070/Literature_Archive/rossmiller80/rossmiller80.pdf

 

[gglaubrecht]

Thanks for taking the time to find this for me (How do you guys find this stuff? I looked for a good while and came up empty).

FYI in the paper, the term appears as .15-1I (it should actually be .15-0.1I). If you run the numbers with the former, the result is gibberish.

 

[fel3]

Years ago, a co-worker attended a seminar taught by Dr. Rossmiller. One of the handouts was a 70+page document titled "Some Comments on the Rational Formula," by Dr. Rossmiller (April 1980). My co-worker gave me a copy, which I scanned an am passing along here.

According to p.22 (see attached), "I" is the rainfall intensity in inches per hour.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[TerryScan]

Thanks for taking the time to find this for me (How do you guys find this stuff? I looked for a good while and came up empty).

I did one google search. I think the terms were "Rossmiller rational SCS".

 

[SMIAH]

I prefer this :

CN = 1/0.045*LN(C/0.014)

 

[SMIAH]

For Rossmiller :

If T-r is 10 years, Imp is 0.2, CN is 87, S is 0.04 and i-ave is 1.0 inch/hour, K is 2.2823 and C is 0.41.
Dropping CN to 77, C is 0.31.

 

[gglaubrecht]

SMIAH,
Thanks - do you have a reference for the formula you prefer?

 

[SMIAH]

I don't have the exact reference but I know it was made in Excel using both CN and C values (curve fitting).

But... I'm sometimes using it as a rough guess.