Anyone written a Sprdsht to complete TR-55 Worksheets

[PFV]

I'm in the process of creating an Excel spreadsheet for TR-55 Worksheets 2, 3 and 4 (Runoff CN, Time of Concentration and Peak Discharge, repspectively). When done by hand, the process requires a lot of nomgraph input, which can be time consuming.

I've been able to enter most of the formulas that solve the nomographs in the spreadsheet except for one of the last items needed on Worksheet 4, the Unit Peak Discharge (qu). It's been a few years since college, so I'm not sure exactly how to solve for qu and I'm not sure I've entered the formula into Excel correctly. The formula given in Appendix F of the TR-55 manual is:

log(qu) = c0 + c1 log(tc)+ c2[log(tc)]^2

My Excel spreadsheet has:

=LOG10(((J4)+(J5*LOG10(F5))+(J6*(LOG10(F5))^2)))

J4, J5 and J6 are the C constants and F5 is the Tc. The formula is returning an answer, just not the right one according on the nomograph. Part of my problem is solving the oringinal formula for qu. Maybe I need a refresher in high school algebra.

Any help would be greatly appreciated. Thanks

 

[bltseattle]

Seems to me that-

If Log(qu)=f(Tc) then
10^(log(qu)) = qu = 10^(f(Tc))

because 10^x is the antilog, but your formula uses another LOG10, so try changing your first LOG10 to 10^