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# Rainfall Intensity Equation Coefficient outside of Denver

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## Rainfall Intensity Equation Coefficient outside of Denver

(OP)
I'm trying to develop an IDF curve for Craig, Colorado. I'm using the UDFCD Rational Method spreadsheet and have the appropriate 1-hour rainfall depths but I can't seem find the appropriate coefficients for the Rainfall Intensity Equation (a, b, and c). Is there an adjustment factor or a table somewhere based on zone?

### RE: Rainfall Intensity Equation Coefficient outside of Denver

(OP)
thanks beej67. I used these depths to develop an IDF curve that I can use. I was hoping to be able to come up with an equation for use in our spreadsheets. I did some more research and realized that the coefficients from the equation were derived from the curve using Excel Solver, which I don't have the time to learn how to use so I'll just use the curve for now.

### RE: Rainfall Intensity Equation Coefficient outside of Denver

one mouse click and the equation is solved
create a x,y (scatter) chart
add a trend line
display the equation on the chart

ok, 3 mouse clicks

### RE: Rainfall Intensity Equation Coefficient outside of Denver

Yr, a0, a1
1, 0.103903, 0.313687
2, 0.128763, 0.305261
5, 0.177688, 0.291029
10, 0.226557, 0.279501
25, 0.307198, 0.264093
50, 0.379736, 0.253163
100, 0.462293, 0.242978
200, 0.555014, 0.233734
500, 0.694905, 0.222314
1000, 0.807472, 0.215545

DDF Coefficients calculated using PDF from NOAA for Craig, CO (ID 05-1928)
Inch = a0 x (minutes ^ a1)
Where a0 and a1 are the coefficients for year yr

Please verify before use.

See http://www.hydrocalc.com/beta/rain_ddf/main.html#
You can also convert the DDF to either IDF or to Hyetograph.
Thanks

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