K19
The Widowmaker
- Joined
- Feb 21, 2012
- Messages
- 84
- Reaction score
- 6
Hello Friends,
I'm using the CERM 12th Edition (1st printing), and believe that Equation 20-11 (Hydrology - Time of Concentration from Watershed Lag Method) is correct in it's original form and that the following erratum posted on PPI's website is wrong.
The expression for tlag in hours presented later in the chapter (Equation 20-23) is correct - I consulted the NRCS National Engineering Handbook to confirm this.
Hence the 100 coefficient (1.67 x 60) in the numerator of Equation 20-11 converts tlag in hours to tc in minutes.
Is this (and the equation as written) correct, or am I missing something?
Thanks,
K
I'm using the CERM 12th Edition (1st printing), and believe that Equation 20-11 (Hydrology - Time of Concentration from Watershed Lag Method) is correct in it's original form and that the following erratum posted on PPI's website is wrong.
The equation is for tc (Time of Concentration) in minutes, which is empirically correlated to lag time by tc = 1.67 tlag.Change "100" to "(60 min/hr)", since the NRCS Lag Equation determines the time of concentration in hours.
The expression for tlag in hours presented later in the chapter (Equation 20-23) is correct - I consulted the NRCS National Engineering Handbook to confirm this.
Hence the 100 coefficient (1.67 x 60) in the numerator of Equation 20-11 converts tlag in hours to tc in minutes.
Is this (and the equation as written) correct, or am I missing something?
Thanks,
K