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All questions of Hydrology for UPSC CSE Exam
The shape of the recession limb of a hydrograph depends on- a)basin as well as storm characteristics
- b)storm characteristics only
- c)basin characteristics only
- d)base flow only
Correct answer is option 'C'. Can you explain this answer?
The shape of the recession limb of a hydrograph depends on
a)
basin as well as storm characteristics
b)
storm characteristics only
c)
basin characteristics only
d)
base flow only
|
Zoya Sharma answered |
The climatic factors control the rising iimb and the recession limb is independent of storm characteristics, being determined by catchment characteristics only.
In Synder’s method of synthetic unit hydrograph development, basin lag is taken as- a)the time interval between centroid of the rainfall excess and surface runoff
- b)the time interval from mid point of the unit rainfall excess to the peak of the unit hydrograph
- c)independent of rainfall duration
- d)independent of catchment characteristics
Correct answer is option 'B'. Can you explain this answer?
In Synder’s method of synthetic unit hydrograph development, basin lag is taken as
a)
the time interval between centroid of the rainfall excess and surface runoff
b)
the time interval from mid point of the unit rainfall excess to the peak of the unit hydrograph
c)
independent of rainfall duration
d)
independent of catchment characteristics
|
Shail Rane answered |
The most important characteristic of a basin affecting a hydrograph due to a given storm is basin lag. Basin lag is the time difference between the centroids of the input (rainfall excess) and the output (surface runoff).
If a 4-hour unit hydrograph of a certain basin has a peak ordinate of 80 m3/s, the peak ordinate of a 2-hour unit hydrograph for the same basin will be- a)equal to 80 m3/s
- b)greater than 80 m3/s
- c)less than 80 m3/s
- d)between 40 m3/s to 80 m3/s
Correct answer is option 'B'. Can you explain this answer?
If a 4-hour unit hydrograph of a certain basin has a peak ordinate of 80 m3/s, the peak ordinate of a 2-hour unit hydrograph for the same basin will be
a)
equal to 80 m3/s
b)
greater than 80 m3/s
c)
less than 80 m3/s
d)
between 40 m3/s to 80 m3/s
|
|
Arnab Choudhury answered |
With the reduction of unit hydrograph duration, 1 cm excess rainfall will occur in reduced period. So peak ordinate of UH will increase and time base will decrease. Thus the peak ordinate of 2 hr UH will be greater than 80 m3/s.
An instantaneous unit hydrograph is a direct runoff hydrograph- a)of 1 cm magnitude due to a rainfall excess of 1-h duration
- b)that occurs instantaneously due to a unit rainfall excess of duration-D h
- c)of unit rainfall excess precipitating instantaneously over the catchment
- d)occurring at any instant in a long storm
Correct answer is option 'C'. Can you explain this answer?
An instantaneous unit hydrograph is a direct runoff hydrograph
a)
of 1 cm magnitude due to a rainfall excess of 1-h duration
b)
that occurs instantaneously due to a unit rainfall excess of duration-D h
c)
of unit rainfall excess precipitating instantaneously over the catchment
d)
occurring at any instant in a long storm
|
Deepika Saha answered |
A finite unit hydrograph is indicated as the duration D → 0. The limiting case of a unit hydrograph of zero duration is known as Instantaneous Unit Hydrograph (IUH).
A flood-hydrograph due to an isolated storm consists of- a)surface runoff, interflow, and base flow phases
- b)surface runoff only
- c)base flow only
- d)surface runoff and base flow phases only
Correct answer is option 'A'. Can you explain this answer?
A flood-hydrograph due to an isolated storm consists of
a)
surface runoff, interflow, and base flow phases
b)
surface runoff only
c)
base flow only
d)
surface runoff and base flow phases only
|
|
Sreemoyee Deshpande answered |
The hydrograph is the response of a given catchment to a rainfall implicit. It consists of flow in all the three phases of runoff, viz. surface runoff, interflow and base flow.
The point of inflection on the recession limb of a hydrograph represents- a)the cessation of rainfall
- b)the condition of maximum storage in the catchment
- c)the end of base flow
- d)peak runoff rate
Correct answer is option 'B'. Can you explain this answer?
The point of inflection on the recession limb of a hydrograph represents
a)
the cessation of rainfall
b)
the condition of maximum storage in the catchment
c)
the end of base flow
d)
peak runoff rate
|
|
Rohan Singh answered |
The starting point of the recession limb, i.e., the point of inflection represents the condition of maximum storage.
In an S-curve derived by a unit hydrograph U of D-h duration- a)the equilibrium discharge is independent of D
- b)the time base of U represents the time at which the S-curve attains its maximum value
- c)the equilibrium discharge of an S-curve is independent of the catchment area of the basin
- d)the ordinate is in units of volume
Correct answer is option 'B'. Can you explain this answer?
In an S-curve derived by a unit hydrograph U of D-h duration
a)
the equilibrium discharge is independent of D
b)
the time base of U represents the time at which the S-curve attains its maximum value
c)
the equilibrium discharge of an S-curve is independent of the catchment area of the basin
d)
the ordinate is in units of volume
|
|
Rithika Kaur answered |
Explanation:
S-curve derived by a unit hydrograph U of D-h duration represents the cumulative runoff at the outlet of a catchment in response to a unit depth of excess rainfall that is uniformly distributed over the catchment for a duration of D hours.
The correct option is B, i.e., the time base of U represents the time at which the S-curve attains its maximum value. This can be explained as follows:
- Definition of S-curve: An S-curve represents the cumulative runoff at the outlet of a catchment over time, starting from the time of onset of excess rainfall until the runoff ceases.
- Relationship between unit hydrograph and S-curve: The S-curve is derived by convolving the unit hydrograph with excess rainfall of varying duration and intensity. The unit hydrograph represents the response of the catchment to a unit pulse of excess rainfall, and its time base represents the time taken for the peak of the hydrograph to occur.
- Effect of duration on S-curve: As the duration of excess rainfall increases, the volume of runoff also increases, and hence the S-curve attains higher values at later times.
- Effect of time base of U on S-curve: The time base of U determines the time at which the peak of the S-curve occurs. This is because the peak of the S-curve corresponds to the time when the excess rainfall is fully converted to runoff and is equal to the peak flow rate of the unit hydrograph. Hence, the time base of U represents the time at which the S-curve attains its maximum value.
- Other options: Option A is incorrect because the equilibrium discharge depends on the catchment area, and hence on the volume of excess rainfall. Option C is incorrect because the equilibrium discharge depends on the catchment area. Option D is incorrect because the ordinate of the S-curve is in units of volume per unit area, not volume.
S-curve derived by a unit hydrograph U of D-h duration represents the cumulative runoff at the outlet of a catchment in response to a unit depth of excess rainfall that is uniformly distributed over the catchment for a duration of D hours.
The correct option is B, i.e., the time base of U represents the time at which the S-curve attains its maximum value. This can be explained as follows:
- Definition of S-curve: An S-curve represents the cumulative runoff at the outlet of a catchment over time, starting from the time of onset of excess rainfall until the runoff ceases.
- Relationship between unit hydrograph and S-curve: The S-curve is derived by convolving the unit hydrograph with excess rainfall of varying duration and intensity. The unit hydrograph represents the response of the catchment to a unit pulse of excess rainfall, and its time base represents the time taken for the peak of the hydrograph to occur.
- Effect of duration on S-curve: As the duration of excess rainfall increases, the volume of runoff also increases, and hence the S-curve attains higher values at later times.
- Effect of time base of U on S-curve: The time base of U determines the time at which the peak of the S-curve occurs. This is because the peak of the S-curve corresponds to the time when the excess rainfall is fully converted to runoff and is equal to the peak flow rate of the unit hydrograph. Hence, the time base of U represents the time at which the S-curve attains its maximum value.
- Other options: Option A is incorrect because the equilibrium discharge depends on the catchment area, and hence on the volume of excess rainfall. Option C is incorrect because the equilibrium discharge depends on the catchment area. Option D is incorrect because the ordinate of the S-curve is in units of volume per unit area, not volume.
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