# Engineering Hydrology Questions and Answers – Design Storm

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

1. Which of the following is an example of a design storm?
a) Standard project flood
b) Design flood
c) Maximum probable precipitation
d) Spillway design discharge

Explanation: To determine the flood discharges to be used for design, one needs to first obtain the design storm and unit hydrograph. The standard project storm is used for standard project flood calculations and the probable maximum precipitation is used for estimating probable maximum flood.

2. In the estimation of design storm in India, which of the following represents the critical rainfall duration in a catchment, if the flood peak is required?
a) Basin lag time
b) Duration of longest storm
c) Duration of largest storm
d) Monthly storm duration of month with longest storm

Explanation: The first step involved in the procedure of design storm estimation adopted in India is the selection of the critical duration of rainfall in the area If the flood peak is of interest, this duration will be the basin lag of the catchment.

3. Which of the following is an important step in the process of determining design storm for a catchment?
a) Flood frequency analysis
b) Depth area duration analysis
c) Regional flood analysis
d) Partial duration series analysis

Explanation: The catchment is studied with past records and the major storms are selected. Depth area duration plots are drawn for these storms, and the curve which represents the maximum depth-duration relationship for the catchment is determined.

4. The critical sequence of rainfall increments should result in what after applied to the unit hydrograph of a catchment?
a) Maximum flood discharge
b) Maximum flood duration
c) Maximum flood peak
d) Maximum flood area

Explanation: Rainfall increments corresponding to some convenient time intervals of a storm are obtained from the enveloping curve. These values must be arranged in a critical sequence, which when applied to the unit hydrograph gives the maximum flood peak.

5. Rainfall increments values are arranged alongside UH ordinates such that the highest increment is against the highest ordinate, second highest increment is against the second highest ordinate and so on. If the sequence of increments hence obtained is A, B, C, D and E, what is the critical sequence for the design storm?
a) A, B, C, D, E
b) E, D, C, B, A
c) C, B, D, A, E
d) Cannot be determined

Explanation: The method of obtaining the critical sequence of rainfall increments is started by arranging the increments alongside the unit hydrograph ordinates as mentioned in the question. After the sequence is obtained, it is reversed such that the first value is last and the last value is first. This new sequence is the critical sequence for design storm.

6. If flood volume is required, the duration of critical rainfall is equal to duration of longest storm in the catchment.
a) True
b) False

Explanation: The duration of critical rainfall depends on whether the quantity of interest is the flood peak or flood discharge. In case of flood discharge it is the duration of the longest storm, and in the case of flood peak it is the basin lag.

7. After obtaining the critical sequence of design storm, it is combined with which of the flowing to plot the rainfall excess hyetograph?
a) High initial loss and high infiltration rate
b) High initial loss and low infiltration rate
c) Low initial loss and high infiltration rate
d) Low initial loss and low infiltration rate

Explanation: The rainfall abstractions which are more likely to result in higher runoff are combined with the design storm values to get the rainfall excess hyetograph. These conditions are that of low initial loss and low infiltration rate.

8. The 2-hour rainfall increment values (in cm) of a 10 hour storm in a catchment is 9, 11, 7, 7.5 and 3. The 2-hr UH values (in m3/s) are given as 0, 14, 38, 60, 72, 77, 75, 71, 68, 54, 32, 21, 11, 5 and 0. What is the critical rainfall increment sequence for this catchment?
a) 11, 9, 7.5, 7, 3
b) 9, 7, 11, 3, 7.5
c) 7.5, 11, 9, 7, 3
d) 7, 9, 11, 7.5, 3

Explanation: Tabulating the hydrograph values and arranging the increment values accordingly,

Hydrograph ordinates Remarks Rainfall increments order
0
14
38
60
72 Third highest 7.5
77 Highest 11
75 Second highest 9
71 Fourth highest 7
68 Fifth highest 3
54
32
21
And so on…

Therefore, the critical sequence is 7.5, 11, 9, 7 and 3.

Sanfoundry Global Education & Learning Series – Engineering Hydrology.

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