Introduction and Basic Assumptions of Unit Hydrograph

Q. A 6-hour Unit Hydrograph (UH) of a catchment is triangular in shape with a total time base of 36 hours and a peak discharge of $18m^3/s$. The area of the catchment (in sq. km) is

1. 233
2. 117
3. 1.2
4. Sufficient information not available

Q.

What do you mean by integral value?​

Q. A 4 h unit hydrograph of a catchment is triangular in shape with base of 80 h. The area of the catchment is 720 $k{m}^2$ . The base flow and $\varphi$ index are 30 $m^3/s$ and 1 mm/h, respectively. A storm of 4 cm occurs uniformly in 4 h over the catchment.

The peak flood discharge due to the storm is

1. $210m^3/s$
2. $230m^3/s$
3. $260m^3/s$
4. $720m^3/s$

Q. A 4-hour unit hydrograph of a basin can be approximated as a triangle with a base period of 48 hours and peak ordinate of $300{\text{m}}^3/\text{s}$. What is the area of the catchment basin?

1. $7776{\text{km}}^2$
2. $5184{\text{km}}^2$
3. $2592{\text{km}}^2$
4. $1294{\text{km}}^2$

Q. If the base period of a 6-hour hydrograph of a basin is 84 hours, then a 12 hours unit hydrograph derived from this 6 hour unit hydrograph will have a base period of

1. 72 hours
2. 78 hours
3. 84 hours
4. 90 hours

Q. A direct-runoff hydrograph due to isolated storm was triangular in shape with a base of 80 h and peak of $200m^3/s$. If the catchment area is $1440k{m}^2$, the effective rainfall of the storm is

1. 20 cm
2. 10 cm
3. 5 cm
4. 2 cm

Q. A 3 hr unit hydrograph $U_1$ of a catchment of area $235k{m}^2$ is in the form of a triangle with peak discharge $30m^3/s.$ Another 3 hr unit hydrograph $U_2$ is also triangular in shape and has the same base width as $U_1$, but has a peak flow of $90m^3/s.$
What is the catchment area of $U_2$?

1. $117.5k{m}^2$
2. $235k{m}^2$
3. $470k{m}^2$
4. $705k{m}^2$

Q. If a 4-hour unit hydrograph of a certain basin has a peak ordinate of $80m^3/s,$ the peak ordinate of a 2-hour unit hydrograph for the same basin will be

1. $\text{equal to}80m^3/s$
2. $\text{greater than}80m^3/s$
3. $\text{less than}80m^3/s$
4. $\text{between}40m^3/sto80m^3/s$

Q. 1 h triangular unit hydrograph of a watershed has the peak discharge of 60$m^3/s$ at 10 h and time base of 30h. The $\varphi$ - index is 0.4 cm/h and base flow is 15 $m^3/s$

The catchment area of the watershed is

1. $3.24k{m}^2$
2. $32.4k{m}^2$
3. $324k{m}^2$
4. $3240k{m}^2$

Q. A $252{\text{km}}^2$ catchment area has a 6 hr UH which is a triangle with time base of 35 hours. What is the peak discharge of the DRH due to 5cm effective rainfall in 6hr from that catchment?

1. 45 cumecs
2. 115 cumecs
3. 200 cumecs
4. 256 cumecs

Q. The ordinates of a 2 h unit hydrograph at 1 h intervals starting from time = 0 are 0, 3, 8, 6, 3, 2, and 0 $m^3/s$. Use trapezoidal rule for numerical integration, if required.
What is the catchment area represented by the unit hydrograph ?

1. $1.00k{m}^2$
2. $2.00k{m}^2$
3. $7.92k{m}^2$
4. $8.64k{m}^2$

Q. 1 h triangular unit hydrograph of a watershed has the peak discharge of $60m^3/s$ at 10 h and time base of 30h. The $\varphi -index$ is 0.4 cm/h and base flow is $15m^3/s$

If there is rainfall of 5.4 cm in 1 hour the ordinate of the flood hydrograph at 15th hour is

1. $225m^3/s$
2. $240m^3/s$
3. $249m^3/s$
4. $258m^3/s$

Q. The peak of a flood hydrograph due to a 6-h storm is 470 $m^3/s$. The mean depth of rainfall is 8.0 cm. If average infiltration loss is 0.25 cm/h and a constant base flow of $15m^3/s$, then the peak discharge of 6-h unit hydrograph for this catchment is

1. $58.25m^3/s$
2. $60.65m^3/s$
3. $70m^3/s$
4. $72.3m^3/s$

Q. The peak of a flood hydrograph due to 2 hour duration isolated storm in a catchment area is $135m^3/s.$ The total depth of rainfall is 54 mm. Assume a constant base flow of $10m^3/s$ and $\varphi -index$ to be equal to 4 mm/hr, then peak of 2-hr UH for the catchment in $m^3/s$ is

1. 25.0
2. 29.23
3. 23.15
4. 27.17

Q. A 2-hour unit hydrograph can be approximated as trapezoidal as shown in figure. The unit hydrograph refers to catchment of area

1. 138.24 $k{m}^2$
2. 0.0384 $k{m}^2$
3. 384 $k{m}^2$
4. 3840 $m^2$

Q. The peak magnitude of a flood hydrograph during 4 hr study duration over a catchment is $300m^3/s$. The total depth of rainfall is 6 cm, and the infiltration loss during the said 4 hr period is 2 cm. A constant uniform base flow of $20m^3/s$ is premised throughout. The peak value of the corresponding 4 hr unit hydrograph is

1. $75m^3/s$
2. $70m^3/s$
3. $50m^3/s$
4. $40m^3/s$

Q. An effective rainfall of 2 hour duration produced a flood hydrograph peak of $200m^3/s.$ The flood hydrograph has a base flow of $20m^3/s.$ If the spatial average rainfall in the watershed for the duration of storm is 2 cm and the average loss rate is 0.4 cm/hour, the peak of 2-hour unit hydrograph (in $m^3/s$ up to one decimal place) is _____

1. 150

Q. The peak ordinate of 4 h unit hydrograph of a basin is $60m^3/s$. An isolated storm of 4 hour duration in the basin was recorded to have a total rainfall of 8 cm. If it is assumed that the base flow and the $\varphi -index$ are $30m^3/s$ and $0.25cm/hr$ respectively, the peak of the flood discharge due to the storm could be estimated as.

1. $210m^3/s$
2. $420m^3/s$
3. $450m^3/s$
4. $240m^3/s$

Q. Which of the following principles relate to a Unit Hydrograph?

1. The hydrographs of direct runoff due to effective rainfall of equal duration have the same time base.
2. Effective rainfall is not uniformly distributed within its duration.
3. Effective rainfall is uniformly distributed throughout the whole area of drainage basin.
4. Hydrograph of direct runoff from a basin due to a given period of effective rainfall reflects the combination of all the physical characteristics of the basin.

Select the correct answer using the codes given below:

1. 1, 2 and 3
2. 1, 2 and 4
3. 2, 3 and 4
4. 1, 3 and 4

Q. A unit hydrograph for a watershed is triangular in shape with base period of 20 hours. The area of the watershed is 500 ha. What is the peak discharge in $m^3/hour$?

1. 7000
2. 6000
3. 5000
4. 4000

Q. Ordinates of a 1-hour unit hydrograph at 1 hour intervals, starting from time t = 0 , are 0, 2, 6, 4, 2, 1 and 0 $m^3/s$

Catchment area represented by this unit hydrograph is

1. 1.0 $k{m}^2$
2. 2.0 $k{m}^2$
3. 4.0 $k{m}^2$
4. 5.4 $k{m}^2$

Q. The following four hydrological features have to be estimated or taken as inputs before one can compute the flood hydrograph at any catchment outlet:

1. Unit hydrograph
2. Rainfall hydrograph
3. Infiltration index
4. Base flow

The correct order in which they have to be employed in the computations is

1. 1, 2, 3, 4
2. 2, 1, 4, 3
3. 2, 3, 1, 4
4. 4, 1, 3, 2

Q. The drainage area of a watershed is $50k{m}^2$. The ϕ - index is 0.5 cm/hour and the base flow at the outlet is $10m^3/s$. One hour unit hydrograph (unit depth = 1 cm) of the watershed is triangular in shape with a time base of 15 hours. The peak ordinate occurs at 5 hours.
For a storm of depth of 5.5 cm and duration of 1 hour, the peak ordinate (in $m^3/s$ ) of the hydrograph is

1. 55.00
2. 82.60
3. 92.60
4. 102.60

Q. A two-hour storm hydrograph has 5 units of direct runoff. The two-hour unit hydrograph for this storm can be obtained by dividing the ordinates of the storm hydrograph by

1. 2
2. 2/5
3. 5
4. 5/2

Q. A peak flow of a flood hydrograph due to a six-hour storm is $470m^3/s$. The corresponding average depth of rainfall is 8 cm. Assume infiltration loss of 0.25 cm/hour and a constant base flow of $15m^3/s$. What is the peak discharge of 6 hour unit hydrograph for this catchment?

1. $60m^3/s$
2. $70m^3/s$
3. $80m^3/s$
4. $90m^3/s$

Q. A rainfall with an intensity of 1.5 cm/h occurred over a catchment area in a 3 hour storm, resulting in a peak discharge of $210m^3/s$ in the river. The base flow and average storm loss $\varphi -index$ were $25m^3/s$ and 8 mm/hour respectively. The peak of the 3-hour unit hydrograph is ______ $m^3/s$. (Upto two decimal places).

1. 88.095

Q. Viewing watershed as a system, which one of the following assumptions is made in the Unit Hydrograph theory?

1. Non-linearity
2. Both linearity and time variance
3. Both time invariance and non-linearity
4. Both linearity and time invariance

Q. The drainage area of a watershed is $50k{m}^2$. The $\varphi -index$ is 0.5 cm/hour and the base flow at the outlet is $10m^3/s$. One hour unit hydrograph (unit depth = 1 cm) of the watershed is triangular in shape with a time base of 15 hours. The peak ordinate occurs at 5 hours.
The peak ordinate (in $m^3/s$) of the unit hydrograph is

1. 10.00
2. 18.52
3. 37.03
4. 185.20

Q. Consider the following steps which are involved in arriving at a unit hydrograph:
1. Separation of base flow
2. Estimating the surface runoff in volume
3. Estimating the surface runoff in depth
4. Dividing surface runoff ordinate by depth of runoff
Which is the correct sequence of these steps?

1. 4, 3, 2 and 1
2. 1, 2, 3 and 4
3. 4, 2, 3 and 1
4. 1, 3, 2 and 4

Q. A 4 h unit hydrograph of a catchment is triangular in shape with base of 80 h. The area of the catchment is $720k{m}^2$ . The base flow and $\varphi -index$ are $30m^3/s$ and 1 mm/h, respectively. A storm of 4 cm occurs uniformly in 4 h over the catchment.

The peak discharge of 4 h unit hydrograph is

1. 40 $m^3/s$
2. 50 $m^3/s$
3. 60 $m^3/s$
4. 70 $m^3/s$