# Engineering Hydrology Questions and Answers – Raingauge Network

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Raingauge Network”.

1. As per the recommendations of World Meteorological Organisation, the ideal density in flat regions of temperate, Mediterranean and tropical zones is ___________
a) 100 – 300 km2
b) 300 – 500 km2
c) 500 – 800 km2
d) 600 – 900 km2

Explanation: With the help of the optimum density of gauges, important information about storms can be obtained. So World Meteorological Organisation has recommended certain values of densities. For flat regions of temperate, Mediterranean and tropical zones, the ideal density is taken as 600 – 900 km2.

2. As per the recommendations of the World Meteorological Organisation, the acceptable density in mountainous regions of temperate, Mediterranean and tropical zones is __________
a) 500 – 800 km2
b) 25 – 1000 km2
c) 70 – 1200 km2
d) 400 – 800 km2

Explanation: Information about storms can be obtained from the optimum density of gauges. As per the recommendations of the World Meteorological Organisation, the acceptable density in mountainous regions of temperate, Mediterranean and tropical zones is in the range of 25 – 1000 km2.

3. As per the recommendations of the World Meteorological Organisation, the density in arid and polar zones is in the range of ______________
a) 1500 – 10,000 km2
b) 400 – 4,000 km2
c) 450 – 10,000 km2
d) 1,500 – 5,000 km2

Explanation: World Meteorological Organisation has recommended densities of gauges for different types of areas. The density in arid and polar zones is in the range of 1500 – 10,000 km2.

4. What percent of rain gauge stations should be equipped with self – recording gauges for measuring the intensities of rainfall?
a) 5%
b) 6%
c) 8%
d) 10%

Explanation: In a specific catchment area, there are different rain gauge stations. 10% of the rain gauge stations should be equipped with self – recording gauges for measuring the intensities of rainfall.

5. From practical considerations of Indian conditions, which IS code gives the densities of rain gauges for different areas?
a) IS:4567
b) IS:4657
c) IS:4987
d) IS:4345

Explanation: Optimum density of gauges helps in providing information about the storms. From practical considerations of Indian conditions, IS:4987 gives the sufficient densities of the gauges.

6. According to the Indian Standard code considering the practical conditions of India, what is the sufficient density for plains?
a) 1 station per 500 km2
b) 1 station per 520 km2
c) 1 station per 540 km2
d) 1 station per 550 km2

Explanation: The Indian standard code recommends certain sufficient densities of gauges for different areas. Considering the practical conditions of India, the sufficient density for plains is 1 station per 520 km2.

7. According to the Indian Standard code considering the practical conditions of India, what is the sufficient density for areas having an average elevation of 1000 m?
a) 1 station per 200 – 300 km2
b) 1 station per 260 – 390 km2
c) 1 station per 300 – 400 km2
d) 1 station per320 – 450 km2

Explanation: The Indian standard code recommends certain sufficient densities of gauges for different areas. Considering the practical conditions of India, the sufficient density for areas having an average elevation of 1000 m is 1 station per 260 – 390 km2.

8. According to the Indian Standard code considering the practical conditions of India, what is the sufficient density for predominantly hilly areas with heavy rainfall?
a) 1 station per 500 km2
b) 1 station per 450 km2
c) 1 station per 330 km2
d) 1 station per 130 km2

Explanation: The Indian standard code recommends certain sufficient densities of gauges for different areas. Considering the practical conditions of India, the sufficient density for predominantly hilly areas with heavy rainfall is 1 station per 130 km2.

9. The formula for finding out the optimal number of rain gauge stations(N) required for measuring mean rainfall with permissible error is ___________
(Note – CV is the coefficient of variation and ԑ is the allowable percentage of error.)
a) N = (CV / ԑ)2
b) N = (CV * ԑ)2
c) N = (CV / ԑ)
d) N = (CV * ԑ)

Explanation: In a catchment area, there are a few rain gauge stations. The optimal number of rain gauge stations is necessary to maintain the accuracy of mean rainfall obtained with a minimum permissible error. The formula of optimal number of rain gauge stations(N) is given as follows: –
N = (CV / ԑ)2
Where,
CV is the coefficient of variation.
ԑ is the allowable percentage of error.

10. What is the allowable percentage of error for evaluating the adequacy of rain gauges?
a) 8%
b) 10%
c) 15%
d) 20%

Explanation: In a catchment area there are few numbers of rain gauges. The optimal number of rain gauges should be calculated to maintain the accuracy of measured value of mean rainfall. A percentage of error is allowed in this case. This error should not be more than 10%.

11. Calculate the additional number of rain gauge stations required.

 Station A B C D E F Rainfall (in cm) 80.6 100.9 180 110 99 134

a) 3
b) 4
c) 2
d) 1

Explanation:
P1 = 80.6 cm
P2 = 100.9 cm
P3 = 180 cm
P4 = 110 cm
P5 = 99 cm
P6 = 134 cm
Number of rain gauges present (m) = 6
Mean precipitation (M) = (P1 + P2 + P3 + P4 + P5 + P6) / 6
= (80.6 + 100.9 + 180 + 110 + 99 + 134) / 6
= 117.416 cm
Standard Deviation (D) = √(((P1 – M)2 + (P2 – M)2 + (P3 – M)2 + (P4 – M)2 + (P5 – M)2 + (P6 – M)2) / (m – 1))
= √(((80.6 – 117.42)2 + (100.9 – 117.42)2 + (180 – 117.42)2 + (110 – 117.42)2 + (99 – 117.42)2 + (134 – 117.42)2) / (6 – 1))
= 35.25 cm
CV is the coefficient of variation.
ԑ is the allowable percentage of error = 10%
CV = 100 * D / M
= 100 * 35.25 / 117.416
= 30.02
N = (CV / ԑ)2
= (30.02 / 10)2
= 9.01 = 10 (approx)
Additional number of rain gauges = 10 – m = 10 – 6 = 4 numbers

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