Rossmiller conversion equation
Rossmiller conversion equation
(OP)
thread162-70645: Convert CN's to Rational C's
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*I)]*{[(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.
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*I)]*{[(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.





RE: Rossmiller conversion equation
http://cleveland2.ce.ttu.edu/research/txdot_0-6070...
RE: Rossmiller conversion equation
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.
RE: Rossmiller conversion equation
According to p.22 (see attached), "I" is the rainfall intensity in inches per hour.
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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill
RE: Rossmiller conversion equation
I did one google search. I think the terms were "Rossmiller rational SCS".
RE: Rossmiller conversion equation
CN = 1/0.045*LN(C/0.014)
RE: Rossmiller conversion equation
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.
RE: Rossmiller conversion equation
Thanks - do you have a reference for the formula you prefer?
RE: Rossmiller conversion equation
But... I'm sometimes using it as a rough guess.