# Engineering Hydrology Questions and Answers – Unit Hydrograph

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

1. Which of the following is a method used for predicting flood hydrographs?
a) Hyetograph
b) Unit hydrograph
c) Normal hydrograph
d) Crest method

Explanation: It was problematic to determine flood hydrograph of a known storm. So, many methods have been found out of which unit hydrograph method is most commonly used. It was first suggested by Sherman in the year 1932.

2. Which of the following is not correct with reference to unit hydrograph?
a) Unit hydrograph obtained due to direct runoff
b) Unit hydrograph obtained due to unit rainfall excess
c) Unit hydrograph has no specified duration
d) In the determination of unit hydrograph, the rainfall occurs uniformly over the catchment

Explanation: Unit hydrograph is defined as the hydrograph obtained for direct runoff due to unit rainfall excess. Unit hydrograph is plotted such that the rainfall occurs uniformly over the catchment and the storm should have specific duration.

3. What does the term “unit” mean in unit hydrograph?
a) Unit width of catchment
b) Unit area of catchment
c) Unit volume of base flow
d) Unit depth of rainfall excess

Explanation: The unit hydrograph is obtained due to unit rainfall excess. So, the term “unit” refers to unit depth of rainfall excess which is generally taken as 1 cm.

4. The duration of unit hydrograph is written in the suffix.
a) True
b) False

Explanation: The duration of hydrograph is very important. The storm should be of uniform duration and the rainfall should be uniform over the catchment area. The duration of unit hydrograph is written in the prefix of the unit hydrograph notation.

5. In a D-h unit hydrograph, what does “h” signify?
a) Hydrograph
b) Half
c) Hyetograph
d) Hour

Explanation: In D-h unit hydrograph, “D” refers to duration of the storm of which the direct runoff is obtained and the unit hydrograph is plotted. The term “h” refers to hours. So, a D-h unit hydrograph refers to a hydrograph of D hours duration storm.

6. The unit hydrograph relates the direct runoff with the rainfall excess.
a) True
b) False

Explanation: The unit hydrograph depicts the lumped response of the catchment to the rainfall excess which results in direct runoff hydrograph. So, the unit hydrograph relates the direct runoff with rainfall excess in this way.

7. The area of catchment considered in unit hydrograph is equal to which of the following?
a) Volume of water under unit hydrograph
b) Duration of unit hydrograph
c) Area of the whole catchment
d) Total volume of baseflow

Explanation: As the direct runoff is only produced due to rainfall excess so, the volume of water under the unit hydrograph is equal to the area of the catchment considered in the unit hydrograph. As 1 cm of rainfall excess is assumed in the calculation of unit hydrograph so, the direct runoff produced is also equal to the rainfall excess.

8. What will be the average rainfall intensity for excess rainfall of D-h unit hydrograph?
a) 1 cm/hr
b) 1 m/hr
c) 0.1 cm/hr
d) 1/D cm/hr

Explanation: The average intensity of rainfall for rainfall excess of D-h hydrograph is 1/D cm/hr. The rainfall excess for a unit hydrograph is considered to be 1 cm.

9. Which of the following are the basic assumptions of unit hydrograph theory?
a) Linear invariance and time response
b) Non-linear response and time variance
c) Linear response and time invariance
d) Non-linear invariance and time response

Explanation: The unit hydrograph theory is based on two basic assumptions. They are as follows:
i) Time invariance – It means the particular component does not change with time.
ii) Linear response – It means that the particular component varies linearly with respect to another component.

10. What does the time invariance refer to in case of unit hydrograph theory?
a) Direct runoff is same as rainfall excess invariant to duration of storm
b) Direct runoff is same as base flow invariant to duration of storm
c) Direct runoff is same as rainfall excess variant to duration of storm
d) Direct runoff is not same as rainfall excess invariant to duration of storm

Explanation: Time invariance is one of the basic assumptions of unit hydrograph theory. It suggests that the direct runoff is same as the rainfall excess and does not depend on the duration of storm. So, the direct runoff is always equal to effective rainfall for any duration of storm.

11. The direct runoff response to the rainfall excess is considered to be linear.
a) True
b) False

Explanation: Linear response is one of the basic assumptions of the unit hydrograph theory. It refers that the response of direct runoff varies linearly with the rainfall excess. If for an input of “a” the output produced is “c” and for an input of “b” the output produced is “d”. Then, for an input of “a+b” the output produced will be “c+d”.

Sanfoundry Global Education & Learning Series – Engineering Hydrology.

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