Flood Frequency Analysis MCQ with answer and solution

Concept

Weibull's Formula for Return Period

Formula

T = (N + 1) / m

Step-by-step solution

1. Identify the total number of recorded years (N) and rank the event in descending order (m). 2. Substitute the values of N and m into the formula T = (N + 1) / m. 3. Divide (N + 1) by m to find the return period (T) in years.

Explanation

Weibull's formula is the standard and most commonly used method in hydrology to estimate the return period of flood or rainfall events. It calculates the return period using the simple formula T = (N + 1) / m, where N is the total number of years of recorded data and m is the rank of the specific event.

Shortcut

Remember "Weibull is Well-used" for estimating return periods: both start with "WE" (Weibull = Well-accepted/Well-used standard).

Common mistake

Students often confuse Weibull's formula with California's formula (T = N/m) or Hazen's formula due to similar empirical plotting position equations, incorrectly choosing California's formula because of its simpler structure.