# Engineering Hydrology Questions and Answers – Depth-Area-Duration Relationships

This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Depth-Area-Duration Relationships”.

1. The areal distribution characteristics of a storm of given duration is reflected in which relationship?
a) Depth – volume relationship
b) Depth – area relationship
c) Depth – intensity relationship
d) Depth – duration relationship

Explanation: After collection of raw data about the depth of rainfall, the data can be used for different analysis. Considering the analysis, certain curves are drawn. The areal distribution characteristics of a storm is reflected in depth – area relationship for a given duration.

2. For a rainfall of given duration, the average depth of rainfall is directly proportional to area of the catchment.
a) True
b) False

Explanation: For a rainfall of given duration, the average depth of rainfall is inversely proportional to the area of catchment. The depth of rainfall decreases with the increase in area of catchment for a particular duration.

3. For a given duration of rainfall, the depth – area relationship is reflected in which curve?
a) Hyetograph
b) Sag curve
c) Depth – Duration curve
d) Depth – Area – Duration curve

Explanation: The relationship between depth of rainfall and area of catchment for a given duration is given by Depth – Area – Duration (DAD) curve. From the records of rainfall data, the depth of rainfall for severe storms are plotted against area of catchment for a particular duration to obtain the maximum amount of rainfall.

4. What is the nature of the curve showing the decrease in depth of rainfall with the increase in area of catchment for a given duration of rainfall?
a) Straight line
b) Logarithmic
c) Exponential
d) Parabolic

Explanation: Once sufficient rainfall records for a catchment are collected, the raw data is analyzed further for extracting more information about the nature of the storm. The depth – area relationship of rainfall for a particular duration is represented by Depth – Area – Duration curve. In this curve, it is observed that the depth of rainfall decreases with the increase in area of catchment. The decrease in depth of rainfall is exponential against the increase in area of catchment.

5. The depth – area relationship for a given duration of rainfall is represented by which mathematical expression?
a) P’ = P0 exp (- K * An)
b) P’ = P0 exp (- K)
c) P’ = P0 exp (Kn * A)
d) P’ = P0 exp (- K / An)

Explanation: The depth – area relationship for a given duration of rainfall is represented by the following mathematical equation:
P’ = P0 exp (- K * An)
Where,
P’ = Average rainfall depth in cm over a catchment area
A = Area of catchment in km2
P0 = Highest amount of rainfall in cm at storm centre
K and n are constants for a given region.

6. What is the assumption made regarding the highest station rainfall in the analysis of large area storms?
a) The average depth is taken over an area of 20 km2
b) The average depth is taken over an area of 25 km2
c) The average depth is taken over an area of 30 km2
d) The average depth is taken over an area of 35 km2

Explanation: It is unlikely that storm centre coincides with a rain gauge station. So, the highest amount of rainfall at storm centre cannot be determined. In that case, for the analysis of large area storms, the highest rainfall is taken as the average depth of rainfall over an area of 25 km2.

7. The development of maximum depth – area – duration relationship for a region is known as __________
a) Depth analysis
c) Sag analysis
d) Duration analysis

Explanation: In case of severe storms, the maximum rainfall depth is found out having different durations for different regions. The development of this maximum depth – area – duration relationship for a particular region is called DAD analysis.

8. Which of the following is considered for determining DAD curves?
a) Hyetograph
b) Sag curve
c) Isohyetal maps
d) Hydrograph

Explanation: In order to determine Depth – Area – Duration (DAD) curves, firstly the most severe storms are noted for a particular region. Then the isohyetal maps and mass curves of the storms are considered to find out the maximum depth of rainfall for a duration in the same area. Then the depth – area relationship is plotted against a duration. Thus, DAD curves are obtained.

9. Considering DAD curves, for a given area the depth of rainfall is directly proportional to duration.
a) True
b) False

Explanation: The depth – area relationship is plotted for a given duration in DAD curves. It is observed that the depth of rainfall decreases exponentially with increase in area of storm. If the area is fixed then the depth of rainfall increases with increase in duration.

10. Preparation of DAD curves require detailed topographical information about the area of storm.
a) True
b) False

Explanation: The areal characteristics of a storm are represented in a Depth – Area – Duration (DAD) curves. It is the plot of depth of rainfall against area of the region having rainfall. So, a detailed information about the topographical aspect of the region is required.

Sanfoundry Global Education & Learning Series – Engineering Hydrology.

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