This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Design Flood”.
1. What are the main criteria for deciding the design flood magnitude for designing a structure?
a) Cost and importance of structure
b) Economic development of area and cost
c) Importance of structure and economic development of area
d) Cost, importance of structure and economic development of area
View Answer
Explanation: The type and importance of structure and the economic development of the surrounding area govern the selection of flood magnitude for design of these structures. For example, culverts are design for smaller floods, whereas dams require large design floods.
2. Which of the following is not true regarding spillway design flood?
a) Used for the design of a hydrologic structure
b) Maximum discharge that can be passed through a dam without damage
c) Used for the design of spillway of a dam
d) Maximum discharge that can be passed through a dam without affecting its stability
View Answer
Explanation: A spillway is a hydrologic structure present near dams to help with the release of water. Spillway design flood is a quantity that is specially used for the design of spillways. It also signifies the maximum water that a structure can withstand without damage or instability.
3. What is the quantity that considers a severe combination of hydrometeorological factors but excludes very rare combinations?
a) Standard probable flood
b) Probable project flood
c) Mean flood
d) Standard project flood
View Answer
Explanation: Standard project flood (SPF) is reasonably applicable to a region as it formulated from a possible combination of severe hydrometeorological conditions. However, it does not include extremely rare combinations of factors which are highly unlikely to occur in the region.
4. The failure of a hydrologic structure may result in loss of life and heavy damage to property and environment. Which of the following may be used to design such a structure?
a) Mean annual flood
b) Probable maximum flood
c) Standard project flood
d) Maximum project flood
View Answer
Explanation: Probable maximum flood indicates the most extreme flood that is possible in a region, by considering the severe most and rare combinations of hydrological and meteorological factors. It is used in design of structures whose failure would lead to heavy damage and loss of life.
5. Which of the following is true regarding standard project flood?
a) It includes extremely rare hydrometeorological combinations
b) It is not physically possible in the region
c) It is used for structures whose failure causes minor loss or damage
d) It is larger than probable maximum flood
View Answer
Explanation: Probable maximum flood is an extreme case flood which has the largest value and is used for structures whose failure causes catastrophic damage. Standard project flood is physically possible in the region and is used for design of structures whose failure causes less severe damage.
6. Let A be the standard project flood for a region and B be the probable maximum flood for the same region. If A = kB, what is the most suitable value of k?
a) 0.3
b) 0.45
c) 0.8
d) 1.2
View Answer
Explanation: For a given catchment, it is generally considered that the standard project flood is 40-60% of the probable maximum flood. Therefore, a standard project flood value that is 45% of the probable maximum flood is the most likely option.
7. What is the capacity value by which storage structures are divided into separate categories for selecting the design flood, as per CWC?
a) 1 Mm3
b) 30 Mm3
c) 60 Mm3
d) 100 Mm3
View Answer
Explanation: As per the CWC guidelines for selecting design floods, the storage structures are divided into two categories based on their storage capacity. Large dams of storage more than 60 Mm3 have different design flood as compared to dams with capacity less than 60 Mm3.
8. Maximum probable flood cannot be used as the design flood of a structure.
a) True
b) False
View Answer
Explanation: The design flood is the value adopted for the design of a structure based on the hydrometeorological conditions and cost-benefit analysis of the project. The design flood may be spillway design flood, standard project flood or probable maximum flood.
9. A spillway is to be designed for a project with a storage capacity of 2 km3. What is the recommended design for this structure as per CWC?
a) Empirical formulae
b) Rational method
c) Standard project flood
d) Probable maximum flood
View Answer
Explanation: Capacity of structure = 2 km3 = 2 x 109 m3 = 2000 x 106 m3 = 2000 Mm3 > 60 Mm3
As the structure has a capacity of more than 60 Mm3, it should be design using probable maximum flood which is determined from unit hydrograph and the probable maximum precipitation of the region.
10. A dam with a reservoir to store 80 billion litres of water is to be constructed. What is the recommended design flood to be used as per CWC? The precipitation data of the region is not available.
a) Probable maximum flood
b) Standard project flood
c) Flood with return period of 500 years
d) Flood with return period of 1000 years
View Answer
Explanation: Storage capacity = 80 x 109 litres = 80 x 106 m3 = 80 Mm3 > 60 Mm3
The structure comes under major projects and requires the probable maximum flood. But since the precipitation data is not available, probable maximum flood is not applicable. Instead, flood frequency method should be used to find the flood with a return period of 1000 years.
Sanfoundry Global Education & Learning Series – Engineering Hydrology.
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