For an annual flood series ordered by magnitude, what is the return period for an event at rank m within a total dataset of size N________________?
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Answer: D. (N+l)/m
Explanation
The Weibull plotting position formula calculates return periods for extreme flood frequency analysis. Rank order and total dataset size determine the statistical probability of exceedance for an event. Dividing total dataset size plus one by the event rank yields the correct return period. Return period represents the statistical average recurrence interval between flood events of specific magnitude. Annual flood series compile the single largest peak flow recorded during each operational year. Plotting position formulas assign empirical exceedance probabilities to ordered historical hydrologic records.
Civil engineers use flood frequency analysis to design bridge clearances, dams, and urban stormwater systems. Estimating the one hundred year flood requires reliable plotting position formulas applied to historical data. Risk assessment in water resource projects depends entirely on accurate return period calculations. Option A inverts the rank and total size parameters resulting in an incorrect return period formula. Option B calculates cumulative probability rather than the statistical return recurrence interval. Option C represents a simplified exceedance probability formula without the Weibull sample size adjustment.
- Subject
- Engineering
- Category
- Civil Engineering
- Topic
- —
- Difficulty
- medium
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