# Engineering Hydrology Questions and Answers – Probable Maximum Precipitation

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Probable Maximum Precipitation”.

1. In the design of major hydraulic structures, the failure probability is made virtually zero.
a) True
b) False

Explanation: In the design of hydraulic structures, the probability of failure is made as minimum as possible that is virtually zero. This is done to prevent the loss of property, economy and destruction due the failure of such massive structure like spillways of dams.

2. What is the full form of PMP?
a) Probable Maximum Precipitation
b) Possible Maximum Precipitation
c) Probable Minimum Precipitation
d) Possible Minimum Precipitation

Explanation: In case of many hydraulic structures, the design requirements aim to minimize the probability of failure of the structures. So, it is necessary to estimate the maximum rainfall possible in a given place. This maximum rainfall is known as Probable Maximum Precipitation (PMP).

3. Which one of the statements is correct about PMP?
a) PMP is the maximum rainfall in an area which may exceed
b) PMP is the maximum rainfall in an area producing flood flow which has risk of exceeding
c) PMP is the maximum rainfall in an area producing flood flow which has no risk of exceeding
d) PMP is the minimum rainfall in an area which may exceed

Explanation: PMP is the Probable Maximum Precipitation. It is the maximum rainfall that can occur in a place. It produces flood flow which has no risk of being exceeded.

4. The estimation of PMP involves two methods. The names of the methods are __________
a) Statistical methods and arithmetic methods
b) Statistical methods and frequency analysis
c) Statistical methods and meteorological methods
d) Statistical methods and analytical methods

Explanation: PMP is a very important design requirement for massive hydraulic structures. PMP can be determined in two ways. One is statistical methods and the other is meteorological methods. PMP is estimated to reduce the chances of failure of the hydraulic structures due to heavy rainfall.

5. Which method uses storm models for estimating PMP?
a) Statistical methods
b) Arithmetic methods
c) Frequency analysis
d) Meteorological methods

Explanation: PMP is estimated using two methods. One is statistical methods and the other is meteorological methods. In meteorological methods, the storm models are used obtained from published literature.

6. What is the formula used for calculating PMP by statistical methods?
a) PMP = Mean precipitation + K * Standard deviation
b) PMP = Mean precipitation – K * Standard deviation
c) PMP = Mean precipitation + Standard deviation
d) PMP = Mean precipitation + K / Standard deviation

Explanation: The Probable Maximum Precipitation (PMP) can be estimated by statistical methods. The formula used in statistical approach is as follows:
PMP = Mean precipitation + K * Standard deviation
Where,
Mean precipitation considers the mean of annual maximum rainfall series
K = Frequency factor. The value of K is in the neighbourhood of 15.

7. In the formula [PMP = Mean precipitation + K * Standard deviation], the frequency factor “K” does not depend on which of the following?
a) Return period
b) Intensity of rainfall
c) Number of years of record
d) Statistical distribution of the series

Explanation: In the formula [PMP = Mean precipitation + K * Standard deviation] used for estimating PMP, “K” is the frequency factor of the series. It depends upon the statistical distribution of the series, number of years of record and return period. The value of “K” is in the neighbourhood of 15.

8. What is the range of PMP of North – Indian plains for one day rainfall?
a) 45 – 120 cm
b) 85 – 130 cm
c) 65 – 120 cm
d) 37 – 100 cm

Explanation: Generalised charts for one day PMP are prepared by the statistical analysis of 60 to 70 years of rainfall data for the North – Indian plains. The range of PMP varies from 37cm to 100 cm for one day rainfall for North – Indian plains.

a) Indian Institute of Tropical Meteorology
b) Indian Institute of Technology
c) Indian Statistical Institute
d) Indian Institute of Weather Sciences

Explanation: Maps which depict the isolines of one day PMP of different parts of India are available in the PMP atlas. The PMP atlas is published by the Indian Institute of Tropical Meteorology.

10. Which of the following equations is obeyed when World’s greatest rainfall having different durations are plotted in a log – log graph?
a) Pm = 32.16 * D0.875
b) Pm = 52.16 * D0.875
c) Pm = 42.16 * D0.375
d) Pm = 42.16 * D0.475

Explanation: The world’s greatest observed rainfalls are noted and assembled. When this rainfall data is plotted against their durations in a log – log graph then an enveloped straight line is obtained which obeys the equation as follows:
Pm = 42.16 * D0.475
Where,
Pm = Extreme rainfall depth in cm.
D = Duration of rainfall in hours.

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