This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Intensity-Duration Frequency Relationship”.

1. Intensity of rainfall is obtained by the slope of which curve?

a) Sag curve

b) Hydrograph

c) Mass curve

d) Summation curve

View Answer

Explanation: The intensity of rainfall is given by the slope of mass curve. Mass curve is the plot between accumulated rainfall and duration of rainfall.

2. The intensity of rainfall given by the slope of mass curve actually varies with duration of rainfall.

a) True

b) False

View Answer

Explanation: The intensity of rainfall is obtained from the slope of the mass curve. Practically, the intensity of rainfall varies with the duration of rainfall. If the total duration of rainfall is divided into small segments then each segment will have different intensity of rainfall.

3. What is the formula of maximum intensity (I_{m}) of rainfall for ‘t’ duration?

a) I_{m} = c / (t + a)^{b}

b) I_{m} = c / t^{b}

c) I_{m} = c / (t – a)^{b}

d) I_{m} = c / (t + a)

View Answer

Explanation: The mass curve can be further analyzed to obtain the variation of intensity with time. The total duration of rainfall is divided into small segments. The maximum intensity of each segment is calculated. Then the maximum intensity is plotted against duration. The maximum intensity (I

_{m}) is given by:

I

_{m}= c / (t + a)

^{b}

Where,

a, b and c are constants obtained from regression analysis.

t = duration of rainfall

4. If ‘I_{m}” is the maximum intensity and “t” is the duration of rainfall then what will be the formula of maximum depth (D_{m}) of rainfall?

a) D_{m} = I_{m} / t

b) D_{m} = I_{m} * t

c) D_{m} = I_{m} * t * t

d) D_{m} = t / I_{m}

View Answer

Explanation: On analyzing the mass curve we obtain the maximum intensity for a specific duration of rainfall. Now the maximum depth of rainfall can be obtained from maximum intensity of rainfall which is given by:

D

_{m}= I

_{m}* t

Where, D

_{m}= Maximum depth of rainfall

I

_{m}= Maximum intensity of rainfall

t = Duration of rainfall

5. The maximum depth – duration relationship can be developed in the same way as maximum intensity – duration relationship.

a) True

b) False

View Answer

Explanation: If the mass curve is analyzed then the maximum intensity of rainfall for a specific duration can be determined. In the same way, the maximum depth – duration relationship can be determined. The total duration is divided into small segments and then the maximum depth for a particular segment is noted.

6. The maximum intensity – return period – duration relationship is expressed by which formula?

a) i = (KT^{x}) / D^{n}

b) i = (KT^{x}) / (D + a)

c) i = (KT^{x}) / (D + a)^{n}

d) i = (KT^{x}) / (D – a)^{n}

View Answer

Explanation: The maximum intensity can be calculated for each year. Then the graph is plotted which marks the variation of maximum intensity with duration. The maximum intensity – return period – duration relationship is expressed by the following formula:

i = (KT

^{x}) / (D + a)

^{n}

Where,

i = Maximum intensity

D = Duration

T = Return period

K, x, a and n are coefficients for area represented by the station.

7. Depth – duration – frequency relationship deals with which parameter?

a) Minimum depth in a specific duration

b) Maximum depth in a specific duration

c) Depth in a quarter year

d) Depth in only one year

View Answer

Explanation: In maximum depth – duration – frequency relationship, maximum depth is plotted against duration with return period as the third parameter. In this relationship, maximum depth is plotted having a specific duration.

8. What are iso – pluvial lines?

a) Lines joining equal elevation

b) Lines joining equal depth of rainfall

c) Lines joining equal intensity of rainfall

d) Lines joining equal duration of rainfall

View Answer

Explanation: The extreme point rainfall values having different durations are marked by IMD. The iso – pluvial lines are also marked on Indian maps. Iso – pluvial lines are the lines having equal depth of rainfall.

9. If the duration of a storm is 30 minutes and the depth of rainfall is 30 cm then what will be the rainfall intensity in cm / hr?

a) 1

b) 30

c) 3

d) 60

View Answer

Explanation: Duration of rainfall (t) = 30 min = 30 / 60 hr = 0.5 hr

Depth of rainfall (D) = 30 cm

Intensity of rainfall = D / t

= 30 / 0.5

= 60 cm / hr

10. Which relationship is defined when the maximum intensity is plotted as a function of duration and return period?

a) Intensity – duration relationship

b) Intensity – duration – frequency relationship

c) Intensity – frequency relationship

d) Intensity – depth relationship

View Answer

Explanation: Maximum intensity is obtained for a specific duration. This maximum intensity is plotted against duration considering return period as the third parameter. This relationship is known as intensity – duration – frequency relationship.

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