UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING. MSc CIVIL ENGINEERING SEMESTER TWO EXAMINATION 2017/2018 URBAN DRAINAGE SYSTEMS MODULE NO: BLT4022

Transcription

1 [ESS29] UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING MSc CIVIL ENGINEERING SEMESTER TWO EXAMINATION 2017/2018 URBAN DRAINAGE SYSTEMS MODULE NO: BLT4022 Date: Monday 21 st May 2018 Time: 10:00 13:00 INSTRUCTIONS TO CANDIDATES: There are FIVE questions. Answer FOUR questions. All questions carry equal marks. Marks for parts of questions are shown in brackets. This examination paper carries a total of 100 marks. All working must be shown. A numerical solution to a question obtained by programming an electronic calculator will not be accepted. A formula sheet and HRS tables are attached.

2 Page 2 of 11 Question One a) Describe what is meant by integrated catchment modelling and what types of modelling are involved in it? b) Critically explain your understanding of the environmental standards (Urban Pollution Management) and demonstrate their use in achieving compliance assessment of a river reach. c) Fig.Q1 below shows two reaches of a river which serves as receiving water for a nearby town drainage system. The river receives final effluent from the town treatment work (FE), a combined sewer overflow (CSO), a surface water outfall (SWO) and a runoff flow from rural catchment (CFB) at different locations as illustrated in the figure. For a particular moment of time the values of flow and concentrations of the Biological Oxygen Demand (BOD), Ammonia (NH4) & Dissolved (DO) for these inputs, as well as for the upstream end of the river reach at location P1 (RBF), are given in Table Q1.1. The percentage increase or decrease for the concentrations of BOD, NH4 & DO, due to the natural biochemical processes within the two reaches, is given in Table Q1.2. i. Using the principle of mass balance and natural biochemical processes, find the concentrations of BOD, NH4 and DO in the river at locations P1, P2, P3 and P4. (10 marks) ii. Carry out compliance assessment for the two reaches against the UK (UPM) standards for fishery (shown in Table Q1.3) at same locations mentioned in (i). CFB SWO FE CSO RBF P3 P2 P1 P4 Reach Question 1 continues over the page.

3 Page 3 of 11 Question 1 continued. Table Q1.1: Input Data Input Name m 3 /sec mg/l mg/l mg/l River Base Flow (RBF) Final Effluent (FE) Combined Sewer Overflow (CSO) Surface Water Outfall (SWO) Catchment Flow Boundary (CFB) Table Q1.2: Effects of Biochemical Processes Flow CBOD CNH4 CDO Process Reach1 Reach2 DO Percentage Increase by Aeration DO Percentage Decrease by Biodegradation & Nitrification BOD Percentage Decrease by Biodegradation NH4 Percentage Decrease by Nitrification Table Q1.3: Pollution Standards UPM Standards for Fishery Pass Fail DO >=5 <5 NH4 <=4 >4 Total 25 marks

4 Page 4 of 11 Question Two a) Critically discuss the main functions of a Combined Sewer Overflow (CSO). (7 marks) b) Define the term CSO Setting and its importance as part for the hydraulic structure, and the different techniques to determine the setting. (8 marks) c) The population of a catchment is 5000, average wastewater flow is 180 l/c/d. Infiltration is 10% of the domestic wastewater flowrate, and average industrial flow is 2 l/s. (i) Determine the DWF for this catchment (4 marks) (ii) The CSO setting to serve the catchment according to Formula A given below (4 marks) (iii) Express the CSO setting as a multiple of DWF (2 marks) Question Three Total 25 marks a) Explain what you understand by time of entry, time of flow and time of concentration in storm sewer design. Why is the duration of the design storm in the Rational Method taken as the time of concentration? b) A small separate storm sewer network has the characteristics presented in Table Q3 and Fig Q3. Assume sewer gradient are fixed. Sewer Table Q3 Length Sewer Gradient Contributing Area (m) (1:x) (ha) Question 3 continues over the page.

5 Page 5 of 11 Question 3 continues. Design the network using the Rational Method for a 1 year return period storm using a runoff coefficient of 1.0 and a time of entry 4 min. Take pipe roughness, ks, as 1.5 mm. Use the Ministry of Health formulae (given on page 8) to determine the design rainfall intensities. Fig. Q3 (20 marks) Total 25 marks Question Four a) Designing a pumping system presents a different set of challenges from designing a gravity system. Explain why. b) A submersible pumping station is to be designed to be located in an urban area. The station will receive flow directly from a combined sewer overflow which it will then pump to a nearby sewage treatment works. The overflow will serve a population of 12,000 and receive some industrial effluent. Under normal storm conditions the overflow will be designed to pass Formula A (given on page 8) flows to the pumping station at first spill. At peak design storm flow conditions the flow passing to the pumping station will increase by approximately 15% above Formula A flows. Question 4 continues over the page.

6 Page 6 of 11 Question 4 continued. Water consumption G = 220 litres/head/day Infiltration I = 55 litres/head/day Industrial effluent E = 235,000 litres/day Rising main = 230m in length, KS = 1.5mm Ground level at pumping station = 140.7m AOD Invert level of inlet pipe to Pumping station = 137.8m AOD Rising main discharge Invert level = 149.1m AOD Assume pump diameter (in plan) is 0.7m, and concrete segmental rings are available in 1.0m diameter increments with a depth of 1.0m. Roof slab thickness = 300mm. i) Choose the number of pumps for the station. ii) Determine an appropriate size for the sump, and calculate suitable "stop" and "start" levels for the pumps. iii) Choose a suitable rising main diameter and determine the "Total Head" requirement for an individual pump during each operational phase. iv) Sketch a suitable configuration for the chamber construction Total 25 marks

7 Page 7 of 11 Question Five a) Critically appraise the main consequences of flooding and the main objectives of flood risk management (8 marks) b) Discuss the key objectives of inspection at a dam site and the factors that should be considered in determining its frequency. (7 marks) c) A trapezoidal channel with side slopes of 1.5:1, a depth of 2 m, a bottom width of 8 m and a channel slope of carries a discharge of 56 m 3 /s. Estimate the value of Manning s roughness, n. (10 marks) Total 25 marks END OF QUESTIONS

8 Page 8 of 11 Formulae sheet Formula A (l/d) = DWF P + 2E DWF = PG + I + E Ministry of Health Formulae: i (mm/hr) = 750/(D+10) i (mm/hr) = 1000/(D+20) for storms between 5 and 20 min duration. for storms between 20 and 120 min duration. Rational Method: Qp (l/s) = 2.78*C*i*A Manning Equation: Q = 1 n AR2/3 S K 1, K 2 = 2.0 hf = So x L HT = hf + hs

9 Page 9 of 11

10 Page 10 of 11

11 Page 11 of 11