hydrology equation in the NCEES reference handbook?

[engineer123]

I'm having trouble understanding the storm return period equation on Page 32 of the NCEES reference handbook. It says:

The probability that a T-year return period event will occur at least once in n years is P = 1 - (1/T)^n

However, in my Intro to Environmental Eng textbook, the risk that the event will be equaled or exceeded at least once in n years is:

R = 1 - ( 1 - 1/T)^n

You get different answers obviously if you plug in the variables, but essentially it seems both are asking for the probability that the event will occur at least once in n years. What is the difference between these two equations? Is the one in the NCEES handbook incorrect?

 

[GirlsCanDesign]

The most current Environmental Reference Handbook has the equation shown as P=1-(1-(1/T))^n. You may be using an older version of the handbook.

 

[engineer123]

@GirlsCanDesignyou're right. looks like they just updated it last month lol thanks!

 

[GirlsCanDesign]

@engineer123You got it! I also noticed it was incorrect a couple months ago and was worried they wouldn't update it, so I feel your pain haha..

When are you schedule to take the exam? I signed up for April 8th but I'm getting worried, it seems like everyone is waiting to take it until the first CBT "victims" post their experience.

 

[engineer123]

@GirlsCanDesignI downloaded the handbook probably back in January so I didn't think they'd update it so fast haha

I started studying last month and nowhere near ready to take the exam due to my work schedule. I definitely need many more months of studying, so I won't know when to take the exam until I feel ready lol

Best of luck to you though! I hope this exam will be "fair" enough with just using the NCEES handbook  Perhaps it might be better than the paper version!

 

[GirlsCanDesign]

@engineer123I certainly hope so! I took the paper exam in October as my first attempt and unfortunately did not pass. I do blame a lot of that on spending a lot of (unnecessary) time "tabbing" and trying to locate solutions to problems rather than actually learning the content. I feel pretty comfortable with the reference handbook for my studying this time, my only concern now is how many theory questions may pop on the exam, which I doubt will be found in the handbook.

Best of luck in your studying, fingers crossed the CBT helps rather than hurts!