UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING MSc CIVIL ... · Page 3 of 16 School of Engineering MSc Civil Engineering Semester Two Examination 2015/2016 Urban Drainage Systems Module

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UNIVERSITY OF BOLTON

SCHOOL OF ENGINEERING

MSc CIVIL ENGINEERING

SEMESTER TWO EXAMINATION 2015/2016

URBAN DRAINAGE SYSTEMS

MODULE NO: BLT4022

Date: Tuesday 17 May 2016 Time: 2.00 – 5.00 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.

Page 2 of 16 School of Engineering MSc Civil Engineering Semester Two Examination 2015/2016 Urban Drainage Systems Module No. BLT4022

Question 1 a) Describe the natural purification processes taking place in a river reach and their

contribution in reducing pollution in rivers. (5 marks)

b) Explain your understanding of River Environmental Standards and Compliance Assessment of a river reach and who issue and oversee them (5 marks)

c) The figure 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 Figure Q1. For a particular moment of time the values of flow and concentrations of the BOD, NH4 & DO for these inputs, as well as for the upstream end of the river reach (RBF), are given in Table 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 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 3) at same locations mentioned in (i). (5 marks)

Figure Q1

Question 1 continued over the page

CSO

P1

RBF

FE

P3 P2

SWO CFB

P4

Reach1

1 2

3


Question 1 continued…

Total 25 marks

Please turn the page

Table 1: Input Data

Input Name Flow CBOD CNH4 CDO

m3/sec mg/l mg/l mg/l

River Base Flow (RBF) 2.50 15 5 7

Final Effluent (FE) 0.50 75 30 6

Combined Sewer Overflow (CSO) 0.03 500 50 6

Surface Water Outfall (SWO) 0.04 10 0.5 6

Catchment Flow Boundary (CFB) 0.30 20 10 8

Table 2: Effects of Biochemical Processes

Process Reach1 Reach2

DO Percentage Increase by Aeration 20 15

DO Percentage Decrease by Biodegradation & Nitrification 60 40

BOD Percentage Decrease by Biodegradation 75 65

NH4 Percentage Decrease by Nitrification 10 10

Table 3: Pollution Standards

UPM Standards for Fishery Pass Fail

DO >=5 <5

NH4 <=4 >4


Question 2

a) Explain the principles of sediment transportation. (8 marks)

b) An 18m wide channel has a bed slope of 0.0012. The particles in the channel have a density of 2250kg/m3 and the particle size d50 = 1.30mm. During a storm event the flow in the channel is raised to 5.8m3/s. Assuming uniform flow conditions, and µ: 1.14*10-3ms/kg, determine whether sediment transportation occurs and if so whether particles are in bed-load or suspended load. (17 marks)

Total 25 marks

Question 3 Critically comment upon the shortcomings of conventional approaches to urban

drainage design and outline the alternative sustainable techniques. Comment on the design and other issues that currently prevent their wider use. Discuss what systemic changes may be required to ensure their wider acceptance.

Total 25 marks

Question 4 a) Discuss the parameters that affect catchment response to rainfall in a rural area.

Explain how urbanisation can impact some of these parameters and the

consequence of this impact on the runoff hydrograph.

(10 marks)

b) Discuss the structural and non-structural mitigation measures of urbanisation

impacts on a runoff hydrograph and give two examples for each of these

measures.

(10 marks)

c) Explain your understanding for the concept of catchment modelling and

differentiate between Blackbox, Conceptual and Physically-based mathematical

models.

(5 marks)

Total 25 marks



Question 5 a) For Site A in Figure 5A, provide a preliminary sketch for a storm drainage

design. Assume a 75% runoff rate from grounds. Comment on all assumptions

made.

(9 marks)

Figure 5A - Site A

Question 5 continued over the page

150m

170m

100m

99.8m

99.6m

99.4m

99.54m Building footprint and roof ridges

Site A boundary


Question 5 continued. b) During setting out and construction of the manholes on Site B the original

drainage design was misinterpreted. The storm drains are now required to be connected into the Combined Sewer manhole MH C2, see Figure 5B.

i) Complete the Site B drainage scheme in Tables 5B-1 and 5B-2 by selecting suitable pipe diameters and gradients to accommodate a 1 in 20year storm event. (HRS tables and rainfall charts are provided). (12 marks)

ii) Using Building Regulation Part H, state the bedding and surround

requirements for all pipes in the storm drainage network. (3 marks)

Total 25 marks


Page 7 of 10

Grassed area to drain through infiltration due to very permeable soil conditions

Site B boundary

Building footprint

1.00 1.01 1.02

MHC1 MHC2

52m

36m

MH1

MH2

MH3 MH4

MH5


Site B - Manhole Schedule

Manhole No.

Cover level (m)

Invert level (m)

Ground catchment area (Ha)

Roof catchment area (Ha)

MH1 9.36 8.16 0.000 0.046

MH2 9.30 0.010 0.000

MH3 9.20 0.011 0.047

MH4 9.20 0.002 0.047

MH5 9.12 8.20 0.000 0.047

MTC1 9.30 5.16 n/a n/a

MHC2 9.20 4.89 n/a n/a

Table 5B-1

Table Q5B-1. To be handed in with answer book Candidate ID No .......................................................



Pipe

No

Pipe

Length

(m)

Pipe

gradient

(1 in )

Pipe fall

(m)

Vel

(m/s)

Time

of

flow

(min)

Time

of

Conc.

(min)

Rate of

rainfall

i

(mm/hr)

Imp.

Area

(ha)

Cumulative

Imp. Area

(ha)

Flow

Q

(l/s)

Pipe

dia.

(mm)

Pipe

capacity

(l/s)

1.00 6 150

1.01 30 225

1.02 24 225

2.00 32 150

1.03 26

Table Q5B-2. To be handed in with answer book Candidate ID No .......................................................

END OF QUESTIONS



Formula sheet Formula A = DWF + 1360P + 2E l/d DWF = PG + I + E DMIN = 0.7 QMAX 0.4

Fr = 4.06Q0.5

√gD5

QO = CD x AO x (2 x g x HO)0.5 HO = 1.2D + 0.5DO

CD = 0.61 + 0.1

o

d

o

u

D

db -

D

db

B = 2.5 x DMIN, L = 7 x DMIN s = 0.8D + DO

Q w = C 2/3wLHg2

3

2

Hw =3

2

w

2

2

w

1

3

2

w

C

Q

C

Q

C

Q

C1 =

2

22

3

1

22

2

3

2

dK

tgL2C,

K

sgL2C,Lg2

3

2C

, C

d = 0.7 , K

1, K

2= 2.0

hf = So x L

n=(sinθ)d1/6 , τo = ρgRS

V∗ = √τo

ρ

τ∗ =τ𝑂

ρ(𝑠−1)𝑔𝑑𝑠


d



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UNIVERSITY OF BOLTON SCHOOL OF ENGINEERING MSc CIVIL ... · Page 3 of 16 School of Engineering MSc Civil Engineering Semester Two Examination 2015/2016 Urban Drainage Systems Module