Q1: A storm with a recorded precipitation of 11.0 cm, as shown in the table, produced a direct run-off of 6.0 cm.
The ϕ-index of this storm is ____ cm/hr (rounded off to 2 decimal places) (2024 SET-2)
Ans: 0.64 to 0.65
Sol: Assume ϕ ≤ ilowest
Assume 0.625 < ϕ ≤ 0.8
Q2: The ordinates of a 1-hour unit hydrograph (UH) are given below.
These ordinates are used to derive a 3-hour UH. The peak discharge (in m3/s ) for the derived 3-hour UH is ______(rounded off to the nearest integer). (2024 SET-1)
Ans: 86 to 88
Sol:
Maximum ordinate of 3HUH is 86.67 m3/s
Maximum ordinate is 87 m3/s (to nearest integer)
Q1: Which one of the following options provides the correct match of the terms listed in Column-I and Column-II? (2023 SET-2)
(a) P-IV, Q-V, R-III
(b) P-III, Q-IV, R-I
(c) P-IV, Q-III, R-II
(d) P-III, Q-I, R-IV
Ans: (a)
Sol: Horton's equation is used to calculate total infiltration.
Muskingum method is used in flood response analysis in channels.
Penman equation is used to calculate potential evapotranspiration.
Q2: In Horton's equation fitted to the infiltration data for a soil, the initial infiltration capacity is 10 mm/h; final infiltration capacity is 5 mm/h; and the exponential decay constant is 0.5 h. Assuming that the infiltration takes place at capacity rates, the total infiltration depth (in mm ) from a uniform storm of duration 12 h is ____. (round off to one decimal place) (2023 SET-1 )
Ans: 69.7 to 70.1
Sol: f0 = 10 meter
fc = 5 meter
K = 0.5hr−1
At capacity rates i.e. t→∞
f = 5 + 5e−0.5×∞
= 5 meters
Infiltration in 12hr. = 5 × 12 = 60 mm
If above is not the case :
then
Infiltration = ∫ fdt
= 60 + 10 (1 - e0.5 x 12)
= 69.795 mm = 70 mm.
Q3: A 12-hour storm occurs over a catchment and results in a direct runoff depth of 100 mm. The time-distribution of the rainfall intensity is shown in the figure (not to scale). The ϕ-index of the storm is (in mmmm, rounded off to two decimal places)_____ (2023 SET-1)
Ans: 3.6 to 3.6
Sol: D = 12 hrs.
Direct runoff (R) = 100 mm = 10 cm
P = total rainfall
P = Area under above diagram
P = (1/2)×(12+2)×20
= 14 × 10 = 140 mm = 14 cm
Total Infiltration = Total rainfall − runoff
=140 − 100 = 40 mm
Assuming infiltration rate as x mm/hr.
x/y1 = 20/4
y1 = x/5
y2 = x/y2 = 20/6
y2 = 3x/10
Total Infiltration
= Area under rainfall intensity duration curve Area of same curve below ϕ-index line.
⇒x2−48x+160=0
⇒ x = 3.6 and x = 44.39 [Discarded]
⇒ ϕ = 3.6 mm/hr.
Q4: The ordinates of a one-hour unit hydrograph for a catchment are given below :
Using the principle of superposition, a D-hour unit hydrograph for the catchment was derived from the one-hour unit hydrograph. The ordinate of the D-hour unit hydrograph were obtained as 3 m3/s at t = 1 hour and 10 m3/s at t = 2 hour. the value of D (in integer) is _____ (2023 SET-1)
Ans: 3 to 3
Sol: Clearly seen
The duration D = 3 hours
Q1: A two-hour duration storm event with uniform excess rainfall of 3 cm occurred on a watershed. The ordinates of streamflow hydrograph resulting from this event are given in the table.
Considering a constant baseflow of 10 m3/s, the peak flow ordinate (in m3/s) of one-hour unit hydrograph for the watershed is ________ . (in integer) (2022 SET-1)
Ans: 12 to 12
Sol: C1 = Time
C2 = Ordinates of 2hr DRH
C3 = Ordinates of 2hr UH = (Ordinates of 2hr DRH)/(Rianfall excess of 3cm)
C4 = S-curve lag by 2hr
C5 = S-curve ordinates S2
C6 = S1 curve
C7 = Ordinates of 1hr UH = (S2−S−1)/1/2
Q1: The hyetograph in the figure corresponds to a rainfall event of 3 cm.
If the rainfall event has produced a direct runoff of 1.6 cm, the ϕ-index of the event (in mm/hour, round off to one decimal place) would be (2021 SET-2)
Ans: 4.2 to 4.2
Sol: Total rainfall = 3 cm
Total runoff = 1.6 cm
∴ Total infiltration = 3 − 1.6 = 1.4 cm
∴ W-index = Total infiltration /Total duration of storm
= 1.4/(210/60) cm/hr
= 0.4 cm/hr = 4 mm/hr
As ∅-index > W-index
Hence storm of intensities 4 mm/hr and 3 mm/hr will not produce rainfall exam.
ϕ -index = Total infiltration in which rainfall excess occur / Time period in which rainfall excess occur
= Total infiltration − Infiltration in which no rainfall excess occur / Texcess
= 4.2 mm/hr
Q2: A 12-hour unit hydrograph (of 1 cm excess rainfall) of a catchment is of a triangular shape with a base width of 144 hour and a peak discharge of 23 m3/s. The area of the catchment (in km2, round off to the nearest integer) is _______ (2021 SET-2 )
Ans: 595 to 598
Sol: Area of hydrograph = Total direct runoff volume
⇒ (1/2) × 23 m3/sec × 144 × 3600 sec= Area of catchment × Runoff depth
⇒ (1/2) × 23 x 144 x 3600 m3 = A x (1/100) m
A = 596.16 x 106 m2
∴ Area of catchment = 596.16 km2
Q3: The value of abscissa (x) and ordinate (y) of a curve are as follows:
By Simpson's 1/3rd rule, the area under the curve (round off to two decimal places) is ______ (2021 SET-1)
Ans: 20 to 21
Sol: d = 0.5 unit
A = d/3 [(y1 + y5) + 4(y2 + y4) + 2y3]
= 0.5/3 [(5 + 17) + 4(7.25 + 13.25) + 2 × 10]
= 20.67 unit2
The infiltration capacity at the start of this event (t = 0) is 17 mm/hour, which linearly decreases to 10 mm/hour after 40 minutes duration. As the event progresses, the infiltration rate further drops down linearly to attain a value of 4 mm/hour at t = 100 minutes and remains constant thereafter till the end of the storm event. The value of the infiltration index, ϕ (in mm/hour, round off to 2 decimal places), is _______ (2019 SET-1)
Ans: 7 to 7.3
Sol: P = (4 + 8 + 15 + 10 + 8 + 3 + 1) × (20/60)
= 16.33 minute
= 4mm
Since, ∅ ≥ W
Assume, ∅ = 5.28 mm/hr
⇒ Corrected, ∅ =
= 7.2475 mm/hr
Q1: The total rainfall in a catchment of area 1000 km2, during a 6 h storm, is 19 cm. The surface runoff due to this storm computed from triangular direct runoff hydrograph is 1 × 108m3. The ϕindex for this storm (in cm/h, up to one decimal place) is ______ (2018 SET-2)
Ans: 1.5 to 1.5
Sol: Surface runoff = 1×108m3/1000×106m2 = 0.1 m = 10 cm
Total rainfall = 19 cm
Rainfall intensity = 19/6 = 3.167 cm/hr
w-Index = P − Q/t = Total Infiltration/Total duration of storm
∴ w−Index = (19-10)/6 = 1.5 cm/hr
As intensity of rainfall > w-Index
And rainfall intensity is uniform therefore ϕ-index = w-Index = 1.5 cm/hr.
Q2: The infiltration rate f in a basin under ponding condition is given by f = 30 + 10e−2t, where, f is in mm/h and t is time in hour. Total depth of infiltration (in mm, up to one decimal place) during the last 20 minutes of a storm of 30 minutes duration is ______ (2018 SET-1)
Ans: 11 to 12
Sol: Infiltration rate f(t) = 30 + 10e−2t
Total infiltration depth in time 10 min. to 30 min.
i.e., 0.166 hour to 0.5 hour
1. What is infiltration and how does it affect runoff in civil engineering? |
2. What factors influence the rate of infiltration in a given area? |
3. How can hydrographs be used to analyze runoff from a watershed? |
4. What is the difference between direct runoff and baseflow in hydrology? |
5. How can land use changes impact infiltration and runoff patterns in urban areas? |
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