Download Flood Protection on Rivers - Water Engineering - Old Exam Paper and more Exams Structures and Materials in PDF only on Docsity!
Cork Institute of Technology
Bachelor of Engineering (Honours) in Structural Engineering - Stage 3
(CSTRU_8_Y3)
Autumn 2008
Water Engineering
(Time: 3 Hours)
Answer five questions in total, a minimum of Examiners: Dr. J. Harrington two questions from each Section Mr. L. O’ Driscoll Use separate answer books for each section Prof. P. O’ Donoghue Programmable calculators are not permitted Mr. P. Anthony All questions carry equal marks Attachments including figures and equations
Section A
Note: Attachments including equations
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. (10 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? (4 Marks)
(b) Water enters a rectangular channel of width 0.3m with a bed slope of 1 in 100 (Chezy Coefficient C = 56) with a depth of 0.15m. Determine the velocity of flow and the flow classification. Under what conditions will a hydraulic jump be formed downstream of this entry section to the channel? What will happen the specific energy if a hydraulic jump is formed? ( Marks)
Q2. (a) Briefly discuss, with the aid of diagrams where appropriate:
(i) Flood protection on rivers (4 Marks) (ii) River discharge surveys (6 Marks)
(b) A river with a low flow of 10 m^3 /sec and 1 mg/l BOD 5 level receives a discharge from a wastewater treatment plant serving an urban area with a flow rate of 0. m^3 /sec, which complies with the Urban Wastewater Directive 25/35 standard. Comment on the ambient river conditions upstream of the wastewater treatment plant discharge. Determine the maximum downstream BOD 5 level. Is the guideline commonly used in practice exceeded in this case? Estimate the population equivalent served by the treatment plant. (10 Marks)
Q3. (a) Discuss Water Quality and Health under the following headings:
(i) Giardiasis (2 Marks) (ii) Cryptosporidium (4 Marks) (iii) Chemical Related Illness (4 Marks)
(b) Estimate the daily flow capacity and transmissivity of a sandstone aquifer of height 18m, width 550m and length 2.1km. The head change over a 2.1km length is 8.5m
(10 Marks)
T = kb
Section B
Q5. A new storm-water sewer is to be designed as shown in Figure B1. The lengths of the pipes and the catchments are shown in Table B1.
Design the sewer in Figure B1, for a return period of 5 years. Indicate the pipe diameters & pipe slopes using the attached Table B1. The downstream end of pipes 1.03 and 2.02 are to be designed to connect with an interceptor sewer at MH 6. The invert level of this interceptor sewer at MH 6 is 39.100mOD. The new connecting sewers 1.03 and 2.02 must have a downstream invert level higher than this.
Design Assumptions
- Assume the ground falls uniformly from manhole to manhole.
- A minimum cover of 1.0m is allowed between cover level, (CL), and top of pipe. Invert Level, (IL) = CL – 1.0m – diameter of pipe.
- Assume Time of Entry of 4 minutes.
- For each pipe, calculate the time of flow from header manhole and add to time of entry, round this value up to nearest ½ minute.
- Use the Dillon equation to establish rain intensity, I = 152.4 T (^) p 0.2^ / t 0. I is rain intensity in mm/hr T (^) p is the return period t is the storm duration in minutes.
- Use the Modified Rational method to establish flow, (^) Q = 2.78 Cv.Cr .I. A Where: Q is the flow in L/s, I is rain intensity in mm/hr and A is the impermeable area in Ha. PR = 80%; Cr = 1.
- Minimum and maximum velocities are 0.5m/s and 3 m/s respectively.
- For pipeline design, see Attachments B1: Colebrook White Chart with Ks = 0.6 and pipe design sheet. (20 Marks)
Figure Q5.
MH GL 45.345mOD Area 1.5 ha
MH GL 45.567mOD Area 0.9 ha
MH GL 44.876OD Area 1.5 ha
MH GL 41.973mOD Area 0 ha
MH GL 42.101mOD Area 1.5 ha
MH GL 42.958mOD Area 0.4 ha
Pipe 1.01 Pipe 1.
Pipe 2.01 Pipe 2.
Pipe 1. Existing interceptor sewer
Q6. A treatment plant is proposed for a town with a population equivalent (PE) of 60,000. Assume for this plant that 1PE equates to 60g BOD/day and 220L/PE/day. Wastewater is to be treated to the 25/35 standard. Suspended solids concentration at the inlet to the works is 220 mg SS/L.
Design a conventional activated sludge system wastewater treatment plant, using the design parameters given in Figure B2. The treatment plant will also include a primary settlement stage. (a) Calculate the plan area and depth of the primary sedimentation tanks and the primary sludge production rate, given the following design parameters:
- Average overflow rate in the range 1-2 m^3 /m^2 /hr
- Peak hourly overflow rate = 4m^3 /m^2 /hr
- Average hydraulic retention time, 2.5 hours
- BOD removal rate = 25%
- Suspended solids removal rate 50%
- Waste sludge concentration 2% solids (4 Marks)
(b) Calculate daily primary sludge production (tonnes/day) (2 Marks)
(c) Calculate the plan area of the aeration tanks, given the following design parameters:
- Sludge depth 4m
- MLSS 3000mg/L (4 Marks)
(d) Design the plan area and depth of the secondary clarifiers, given:
- Average upward flow velocity in the range 0.6-1.3 m^3 /m^2 /hr
- Peak hourly upward flow velocity 2 m^3 /m^2 /hr
- Average hydraulic retention time 3 hours (2 Marks)
(e) Calculate the average volume (m^3 /day) of sludge to be wasted from the system each day, given:
- Qw = MLSS(VA + V (^) C ) / Sludge Age * SW
Where: VA = Aeration tank volume (m^3 ); V (^) C = clarifier volume (m^3 ); S (^) W = WAS suspended solids (mg/L)
- Average sludge age: 10 days
- Waste sludge concentration: 1.5% solids (2 Marks)
(f) Calculate the total weight (kg/day) of dry solids produced in the entire treatment plant each day. (3 Marks)
(g) Describe a number of sludge treatment technologies which could be used to reduce the volume of wet sludge to be removed from the site daily. (3 Marks)
Figure Q6.
Q7. In a sewerage scheme for a town of 50,000 person equivalents, (PE), a pump station is employed to convey the wastewater to the treatment works by rising main.
Q8. (a) Discuss how organic pollution causes water quality problems in surface waters. How does the EU Urban Wastewater Treatment Regulations attempt to solve this problem? (6 Marks)
(b) Describe the primary factors that influence the overall water-balance in a predominantly rural catchment. How does this compare with a predominantly urban catchment? (8 Marks)
(c) Describe how the infiltration capacity of the soil can influence the runoff from a greenfield catchment. (3 Marks)
(d) Describe how the Dunne and Horton runoff mechanisms explain surface runoff. (3 Marks)
