This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Floods – Data for Frequency Studies”.

1. The amount of data to be considered to obtain satisfactory results in frequency analysis depends on which of the following?

a) Mean of data

b) Standard deviation of data

c) Variability of data

d) Length of data

View Answer

Explanation: The outcome of frequency analysis depends on the length of data. However, the correct length of data to be considered depends on how much variation is there in the data and hence, on the characteristics of the catchment.

2. What is the minimum number of years of record below which frequency analysis should not be considered?

a) 5

b) 10

c) 20

d) 30

View Answer

Explanation: It is better to have large number of data available to proceed with frequency analysis. However in unavoidable cases, smaller lengths may be used. The minimum length below which frequency analysis should not be adopted is considered as 10 years.

3. What is the minimum length of data necessary for conducting reliable flood frequency analysis of a catchment?

a) 10 years

b) 30 years

c) 60 years

d) 75 years

View Answer

Explanation: Other than exceptional cases where long records are not available, it is absolutely necessary that a minimum of 30 years of records are available before conducting flood frequency analysis of a catchment.

4. In an annual series, if events identical to those that are considered are likely to occur at all times in the region, what is the series called?

a) Identical series

b) Variable series

c) Regional series

d) Stationary series

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Explanation: An annual time series (flood series) is classified as time-homogeneous or stationary, if identical events to those considered in the series are likely to occur at all times in the catchment.

5. A 200-year flood series in considered for frequency analysis of a region. What should the series be checked for before beginning the analysis?

a) Homogeneity

b) Standard deviation

c) Difference between highest and lowest values

d) Sample size

View Answer

Explanation: For some catchments, very long annual series, of more than 100 years, are available to be used for frequency analysis. For such cases, the homogeneity of the series needs to be checked to make sure that there is no significant change in the major causative hydrological processes of the considered events, over the span of the series.

6. Which of the following can be used to detect any potential non-homogeneity regions in a time series?

a) Mass curve

b) Flow duration curve

c) Depth-area-duration analysis

d) Hydrograph

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Explanation: Changes in homogeneity of a time series can be identified from the trend or periodicity of a variable over time. Any potential non-homogeneous set of data in the series can be found out with the help of mass curve or by moving average of the variable.

7. Which of the following statistical tests are used to identify non-homogeneity in a flood time series?

a) F-test and z-test

b) Z-test and t-test

c) F-test and t-test

d) F-test, t-test and z-test

View Answer

Explanation: Statistical tests can also be used to detect non-homogeneous regions in a time series. F-test is used to check the equality of the variances and t-test is used to check if there is a significant difference in means.

8. Flood frequency studies are most suited for regions where the climate varies significantly every year.

a) True

b) False

View Answer

Explanation: Areas in which the climate changes every year may result in non-homogeneity in the hydrologic time series for the region. Therefore, flood frequency studies are most reliable in regions where the climate remains uniform every year.

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