This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Precipitation – Data Preparation”.

1. What do you mean by normal rainfall?

a) Average rainfall measured at a specific time, date or month over 20 year period

b) Average rainfall measured at a specific time, date or month over 30 year period

c) Average rainfall measured at a specific time, date or month over 40 year period

d) Average rainfall measured at a specific time, date or month over 50 year period

View Answer

Explanation: The normal rainfall is the average value of rainfall measured at a particular time, date or month over a specified 30 year period. These annual normal rainfall are calculated every decade. So, the normal annual precipitation of a specific area is the annual average rainfall over a 30 year period.

2. If the normal annual precipitation values of different stations in a catchment area are within 10% of the normal annual precipitation of station X then what method is followed to calculate the missing precipitation data of station X?

a) Normal ratio method

b) Geometric mean method

c) Arithmetic mean method

d) Exponential mean method

View Answer

Explanation: If the precipitation data of a station is missing in a particular catchment area then its value can be calculated using the precipitation data of other stations in that catchment area. The normal annual precipitation values of all stations are also considered in this method. If the normal annual precipitation values of the stations are within 10% of the normal precipitation value of station X then the arithmetic mean method is used to calculate the missing precipitation data of station X. Otherwise, the normal ratio method is applied for calculating the missing data.

3. If the normal precipitation values of different stations vary considerably then the missing precipitation data is calculated by weighing the precipitation values of other stations over the ratios of normal annual precipitation values. What is the name of this method?

a) Arithmetic mean method

b) Normal method

c) Mean ratio method

d) Normal ratio method

View Answer

Explanation: The missing precipitation data of a station can be calculated with the help of normal annual precipitation values of other stations present in that catchment area. Missing data can be calculated either by normal ratio method or arithmetic mean method. In normal ratio method, the missing data is calculated by weighing the precipitation values of different stations over the ratios of normal annual precipitation values of other stations. Therefore this method is known as normal ratio method.

4. Inconsistency of record observed during recording rainfall data is not caused due to which of the following?

a) Shifting of a rain gauge station to a new location

b) The neighbourhood of the rain gauge station undergoing a marked change

c) The occurrence of irregular rainfall

d) Change in the ecosystem due to calamities

View Answer

Explanation: Inconsistency of record arises when the conditions relevant to the recording of rainfall data in a particular rain gauge station undergoes a change. Inconsistency is marked from the time the rain gauge station is subjected to that change. Some causes of inconsistency include shifting of a rain gauge station to a new location, the neighbourhood of a station undergoing a change, observational change at the time of recording data and change in the ecosystem due to calamities like forest fires, landslides, etc. The occurrence of irregular rainfall is not responsible for inconsistency of record.

5. Which technique is applied to check the inconsistency of record of rainfall data?

a) Depth curve technique

b) Double mass curve technique

c) Sag curve technique

d) Intensity curve technique

View Answer

Explanation: The inconsistency of record is caused due to certain changes in the conditions relevant to the recording of rainfall data. The inconsistency of record is checked by double mass curve technique. This technique involves the principle which suggests that when recorded data comes from the same population then the data is said to be consistent.

6. What is the formula for the correction ratio used for correcting the inconsistency of record of rainfall data?

a) Correction ratio = Corrected slope of double mass curve/Original slope of double mass curve

b) Correction ratio = Corrected slope of depth curve/Original slope of depth curve

c) Correction ratio = Corrected slope of intensity curve/Original slope of intensity curve

d) Correction ratio = Corrected slope of double summation curve/Original slope of summation curve

View Answer

Explanation: The inconsistency of record of rainfall data is checked by the double mass curve technique. The double mass curve is plotted between accumulated annual rainfall at the inconsistent station and accumulated annual rainfall at other stations included in the group. The formula for correction ratio is as follows:

Correction ratio = Corrected slope of double mass curve/Original slope of double mass curve

7. What is the formula for calculating the missing precipitation data at a station by using the normal ratio method? (Symbols have their usual meaning)

a) P_{X} = N_{X}(P_{1}/N_{1} + P_{2}/N_{2} + …… + P_{M}/N_{M})

b) P_{X} = N_{X}/M(P_{1}/N_{1} + P_{2}/N_{2} + …… + P_{M}/N_{M})

c) P_{X} = (P_{1}/N_{1} + P_{2}/N_{2} + …… + P_{M}/N_{M})

d) P_{X} = N_{X}/M(N_{1}/P_{1} + N_{2}/P_{2} + …… + N_{M}/P_{M})

View Answer

Explanation: The missing precipitation data is calculated by normal ratio method when the normal annual precipitation values of the other stations in that catchment area are beyond 10% of the normal annual precipitation of the station having the missing data. The formula used in normal ratio method is as follows:

P

_{X}= N

_{X}/M(P

_{1}/N

_{1}+ P

_{2}/N

_{2}+ …… + P

_{M}/N

_{M})

8. In a catchment area, the precipitation data of a particular station is missing. To calculate that missing data normal ratio method is used. The formula for the normal ratio method is given below-

P_{X}= N_{X}/M(P_{1}/N_{1}+ P_{2}/N_{2}+ …… + P_{M}/N_{M})

What does “M” specify?

a) Total number of stations in the catchment area

b) Total number of known stations in that catchment area

c) Total number of unknown stations in that catchment area

d) Total number of rain gauges

View Answer

Explanation: The formula for normal ratio method for calculating missing data is as follows:

P

_{X}= N

_{X}/M(P

_{1}/N

_{1}+ P

_{2}/N

_{2}+ …… + P

_{M}/N

_{M})

Where,

N

_{X}= Normal annual precipitation value at the station having unknown precipitation data.

P

_{1}, P

_{2}, …, P

_{M}= Precipitation data at the respective stations.

N

_{1}, N

_{2}, …, N

_{M}= Normal annual precipitation value at the known stations.

M = Number of known stations.

9. The normal annual precipitation at stations A, B, C and D in a catchment area are 81, 68, 72, 90 cm respectively. In the year 2010, station B was inoperative and the stations A, C and D recorded annual precipitations of 90, 73 and 78 cm respectively. Estimate the rainfall at station B in that year.

a) 60.23 cm

b) 65.48 cm

c) 67.81 cm

d) 69.89 cm

View Answer

Explanation: As the normal annual rainfall values vary more than 10% so, normal ratio method is used

N

_{1}= 81 cm

N

_{2}= 68 cm

N

_{3}= 72 cm

N

_{4}= 90 cm

The precipitation values in the year 2010 are

P

_{1}= 90 cm

P

_{3}= 73 cm

P

_{4}= 78 cm

No. of known stations(M) = 3

By normal ratio method,

Missing data (P

_{2}) = N

_{2}/M(P

_{1}/N

_{1}+ P

_{3}/N

_{3}+ P

_{4}/N

_{4})

= 68/3(90/81 + 73/72 + 78/90) cm

= 67.81 cm

10. What is the formula used for calculating missing precipitation data such that the normal annual precipitation values of other stations are within 10% of the normal annual precipitation of the unknown station? (Symbols have their usual meaning)

a) P_{X} = N_{X}/M(P_{1}/N_{1} + P_{2}/N_{2} + …… + P_{M}/N_{M})

b) P_{X} = 1/M(P_{1}/N_{1} + P_{2}/N_{2} + …… + P_{M}/N_{M})

c) P_{X} = N_{X}/M(P_{1} + P_{2} + …… + P_{M})

d) P_{X} = 1/M(P_{1} + P_{2} + …… + P_{M})

View Answer

Explanation: When the normal annual precipitation values of other stations are within 10% of the normal annual precipitation value of the unknown station then the missing precipitation data is calculated by arithmetic mean method. The formula of this method is as follows:

P

_{X}= 1/M(P

_{1}+ P

_{2}+ …… + P

_{M})

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