# Engineering Hydrology Questions and Answers – Design Flood – 2

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Design Flood – 2”.

1. For a region, the probable maximum flood is 16.8 units and standard project flood is 9.2 units. From frequency study of the region, the 50-year flood was 7.5 units and 100-year flood was 11.7 units. A small barrage (capacity 20 Mm3) is to be constructed in this region. What is the design flood to be considered?
a) 7.5 units
b) 9.2 units
c) 11.7 units
d) 16.8 units

Explanation: Since the project is a barrage (< 60 Mm3), the design flood used should be the standard project flood or 100-year flood, whichever is larger. Since 100-year flood (11.7 units) is larger than the standard project flood (9.2 units) for the region, it is considered as the design flood.

2. A pickup weir is to be constructed in region. The project is classified as a low importance project. As per CWC guidelines, this project should be designed for a flood of what return period?
a) 50 years
b) 100 years
c) 500 years
d) 1000 years

Explanation: According to CWC guidelines, pickup weirs should be designed for floods with a recurrence interval of 50 or 100 years depending on the importance of the project. Since the given project is of low importance, a design flood of 50 year return period is sufficient.

3. For minor dams, the standard project flood is always used as the design flood as per CWC.
a) True
b) False

Explanation: For minor structures (capacity < 60 Mm3), the recommended design flood value is the larger of the standard project flood and flood with a return period of 100 years as found from frequency studies.

4. The water way of an aqueduct is to be designed for a flood with what probability of occurrence as per CWC guidelines?
a) 0.01
b) 0.02
c) 0.98
d) 0.99

Explanation: According to CWC guidelines, the recommended design flood for a water way of an aqueduct should be a flood with a return period of 50 years. So, probability of occurrence = 1/T = 1/50 = 0.02.

5. The foundation of an aqueduct is considered unsafe as per CWC if it is designed for a flood of what return period?
a) 75 years
b) 100 years
c) 175 years
d) 220 years

Explanation: As per CWC guidelines, the foundation and free board of an aqueduct should be designed for a flood of return period 100 years. Designs considering floods with return periods less than 100 years are not recommended.

6. A hydrologic structure is to be constructed in a region with very limited hydrologic data available. What should the design approach be for the project as per CWC guidelines?
a) Rational method
b) Empirical formulae
c) Flood frequency analysis
d) Regional flood frequency analysis

Explanation: As per CWC guidelines, if there is very limited or inadequate data available for a region where a project has to be initiated, empirical formula suitable to that region needs to be used to estimate the design flood.

7. As per Indian standards for design of dams, the dams are classified based on which of the following?
a) Gross storage and cost of project
b) Hydraulic head and weight of dam
c) Gross storage and hydraulic head
d) Cost of project and weight of dam

Explanation: As per IS: 11223-1985, dams are classified as per size on the criteria of gross storage behind the dam and the hydraulic head, which is the difference between the normal flood level on the downstream and maximum water level on the upstream end.

8. As per Indian standard guidelines for fixing spillway capacity, the dams are classified into how many categories?
a) 3
b) 4
c) 5
d) 6

Explanation: As per IS: 11223-1985, dams are classified based on their size into three categories, namely – small, intermediate and large. These are based on the gross storage (in Mm3) and hydraulic head (in meters).

9. A dam with a gross storage of 50 Mm3 and a hydraulic head of 32 m is classified as which of the following, as per IS code?
a) Small
b) Intermediate
c) Large
d) Massive

Explanation: A dam with a gross storage of 10 to 60 Mm3 is classified as intermediate and a dam of hydraulic head greater than 30 m is classified as large dam. Considering the larger size as indicated by the two parameters, the given dam would be a large sized dam.

10. What is the inflow design flood for a small size dam as per Indian standard guidelines?
a) Standard project flood
b) Probable maximum flood
c) 50-year flood
d) 100-year flood

Explanation: As per Indian standard guidelines for fixing spillway capacity, the inflow design flood for safety to be considered for a small dam is the 100-year flood. The corresponding value for an intermediate and large sized dam is standard project flood and probable maximum flood, respectively.

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