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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Autumn Examinations 2008/
Module Title: Water Engineering
Module Code: CIVL 8023
School: Building & Civil Engineering
Programme Title: Bachelor of Engineering (Honours) in Structural Engineering – Stage 3
Programme Code: CSTRU_8_Y
External Examiner(s): Mr P Anthony, Prof P O Donoghue Internal Examiner(s): Dr J Harrington
Instructions: Answer Question No. 4 and Two Other Questions
Duration: 2 Hours
Sitting: Autumn 2009
Requirements for this examination:
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination paper. If in doubt please contact an Invigilator.
Q1. (a) A channel with a trapezoidal x-sectional shape is carrying water. It is 4m wide at the base with side slopes of 2 horizontal to 1 vertical. The depth of water is 2.0m. Calculate the volume of water passing per second (Q 1 ) when the depth of water is 2.0m and the bed slope of the channel is 1 in 350. Take the Manning Coefficient n as 0.025. Determine the specific energy of the flow and the flow classification. (12 marks)
What would be the depth of water in the channel to pass twice this volume per second (Q 2 ) if both the slope and the value of n were unaltered? (6 marks)
(b) A channel of rectangular cross-section 12m wide with a slope of 1 in 2000 has a water depth of 3.5m. The Manning roughness coefficient is 0.025. A dam is built downstream. If the depth of water at the dam is 6m, find how far upstream it will be 4.5m. (16 marks)
Q2. (a) Discuss: (i) River water level measurement (7 marks) (ii) Dilution method of river flow measurement (7 marks)
(b) A wide river with a flow depth of 3m, a mean velocity of 1 m/sec and a Chezy coefficient of 50 m1/2^ /sec contains sediments of density 2650kg/m^3. A sample of the suspended sediment load taken at mid depth shows a concentration of 200 mg/l. The sediment has a settling velocity of 3.18 x 10-4^ m/sec. Establish the suspended sediment profile as a function of depth given a k value of 0.4. Also calculate the suspended load assuming a homogenous concentration distribution. (20 marks)
Open Channel Flow
Chezy Eqn.: v = C mS 0
Manning Eqn.: 01 /^2
2 / 3 v = mn S
Backwater Curves
gd
v
s i dl
dd 2 1
Sediment Transport
Vertical Suspended Sediment Profile: (( )) ku^ *
v r
r r
s Y y
Y y y
y C
C (^)
− = −
Shear Velocity: u (^) * = gmS 0
Stoke’s Law: 18 (^ ρμ ρ)
(^2) − vs = gd p
Bed Shear Stress: τ 0 = ρgmS 0 Threshold Entrainment Function: τcr / [(ρs - ρ)gD] = 0.
Well Hydraulics
dx Q =− kAdh T = kb
