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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 1 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. Peter Anthony, Prof. P. O’Donoghue Internal Examiner(s): Dr. J. Harrington
Instructions: Answer Question No. 4 and Two Other Questions
Duration: 2 Hours
Sitting: Winter 2008
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 rectangular channel of width 1m and slope of 2 in 1000 conveys water at a rate of 3 m^3 /sec. Determine the depth of uniform flow for a Chezy Coefficient of 56 and the flow velocity. Determine the flow classification. What is the equivalent Manning roughness coefficient? (18 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) Reasons for increased incidence of flooding in Ireland (8 marks) (ii) Global warming impacts on river flow rates (8 marks)
(b) Use the Muskingum Flood Routing Equation to find the peak outflow within a river reach for the following inflow hydrograph.
Day Time Inflow (m 3 /sec) 1 Midnight 1. 2 Noon 1. Midnight 3. 3 Noon 8. Midnight 13. 4 Noon 18. Midnight 19. 5 Noon 18. Midnight 16. 6 Noon 11. Midnight 8. 7 Noon 5. Midnight 5. 8 Noon 4. Midnight 3. It may be assumed that X = 0.25 and K = 27 hours. Plot the appropriate inflow and outflow hydrographs. Comment on these results. (18 marks)
Q4. (a) A water treatment plant supplies a community of 50,000 with water. It receives its supply from a nearby river where eutrophication is not a problem. The river water quality is generally good. A raw water storage tank providing 12 hours supply is required. Outline a suitable treatment process sequence, size the main elements of the treatment plant and quantify the daily amount of the different chemicals used.
Element Design Parameter Design Parameter Value Radial Flow Tank Retention Time Loading Rate
2 - 4 hours 1 – 1.5 m/hour Upward Flow Sludge Blanket Tank
Retention Time Loading Rate
1 – 2.5 hours 2 – 2.5 m/hour DAF Unit Retention Time 30 mins. (Floc. Tank) 20 mins. (Flotation Tank) Slow Sand Filter Filtration Rate 0.1 – 0.2 m/hour Rapid Gravity Filter Filtration Rate 5 – 20 m/hour
Chemical Dosage Conc. (mg/l) Chemical Dosage Conc. (mg/l) Activated Carbon 5 Chlorine 0. Soda Ash 1 Fluoride 0. Alum 25 Lime 5 Polyelectrolyte 0.
(18 marks) (b) In the context of the design of water distribution systems:
(i) Discuss the primary considerations involved in the siting of a service reservoir (5 marks) (ii) Identify the primary pipe materials used, their application and the advantages and disadvantages of each. (9 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
Flood Routing
Ot (^) +∆ t = C 0 It +∆ t + C 1 It + C 2 O t
C (^) 0 = − KKX − KX −^0 +.^50 ∆. 5 t ∆ t
C (^) 1 = (^) KKX − KX +^0 +.^50 ∆. 5 t ∆ t
C (^) 2 = (^) KK −− KXKX +− 00 .. 55 ∆∆ tt
C 0 + C 1 + C 2 = 1
