Post Graduate Admission Test (April- 2021 Semester)
BUET Water Resources Engineering
Duration: 45 Minutes
Total Marks: 50
Question Solved
By DESIGN INTEGRITY
1. Calculate the time required to irrigate the strip of area 0.203 hectare by a stream discharge of 0.043 cumec, to provide an average depth of 6.35 cm to the field. Assume the average rate of infiltration is 5 cm/h.
2. A field sample of an unconfined aquifer is packed in a test cylinder. The length and diameter of the cylinder are 50 cm and 6 cm, respectively. The field sample is tested for a period of 3 min under a constant head difference of 16.3 cm. If the hydraulic conductivity of the aquifer sample is 0.022 cm/sec determine the volume of the water.
3. A trapezoidal channel with side slope 1:1, flow depth of 1 m and bottom width of 2 m, is laid on a slope of 0.001. Calculate the normal discharge if roughness coefficient is 0.02.
4. A rectangular channel of 3 m width carries 4 m3/s of water at a depth of 1 m. If the width to be reduced to 2 m and bed raised by 10 cm, what would be the depth of flow in the contracted section?
5. Water flows in a horizontal rectangular channel of 5 m width at a depth of 0.50m and a velocity of 20 m/s. If a hydraulic jump forms in this channel, determine the sequent depth and energy loss of this jump.
6. Pipe friction factor can be estimated based on flow characteristics in pipes. Most common and widely used formulas are: 1/ = 2 log (d/e) + 1.14 , f=64/R, f= 0.316/R0.25 where applicable. You are asked to calculate the pipe friction loss for a 300 m long and 300 mm diameter pipe. It has also been stated that the mean velocity in the pipe is 2.5 m/s and the equivalent sand roughness is 0.6 mm. Also calculate the total pressure head at the exit point of the pipe if the total head at the entrance of the pipe is 25m of water.
7. Suppose you went to an amusement park and get into a Ferris Wheel (Nagordola). The operator started the wheel and your movement started in a circular path. During the movement it is expected that you always remain oriented in an upright position as you trace out to your circular path. Now, if you are replaced with a fluid particle (assume no distortion of the fluid particle due to size), what will be the flow type: i) Rotational, or ii) Irrotational, why?
Solution:
The flow type is Irrotational Flow motion that of the carriages of the Ferris wheel .
8. Due to surface tension, water from a faucet tapers from a diameter of 12.7 mm to 7.62 mm after travelling 254 mm downward. Determine the average velocity of the water at A and at B. Also draw the energy grade line (EGL) at point A and B.
9.A catchment in the Sylhet division has a runoff coefficient of 0.15, area = 20 hectare with the general slope of 0. Information of the storm for different return period is shown in the Figure. If a culvert for drainage at the outlet of this area is to be designed, estimate the peak flow for designing this culvert for a rainfall duration of 3 hours with a return period of 25 years
Solution:
10. The infiltration capacity (fp, cm/hr) in a basin can be expressed by fp= 4 + e^-kt where t is in hour. If the depth of infiltration is 2.32 cm after 30 minutes then estimate the depth of infiltration from 30 to 45 minutes of the storm.
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Regards
Engr.Towhidul Islam
Upazila Assistant Engineer
LGED, Ministry of LGRD
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