Feasibility Study of laying Trunk & Gravity main, design and costing

A. Plans and long sections (including the HGL) of all routes considered

B. Design calculations

C. Cost spreadsheets

D. Information relevant to pump selection

E. Information relevant to pressure surge protection

1) Introduction:

The design is provided a trunk main route from Borton PS 59.45m AOD to Lambert’s Hill (155.7m AOD) reservoir and a gravity distribution main from Lambert’s Hill to Poundbury 110.0m AOD because the problem with the existing Dorchester water tower is at a lower level 108mAOD compared to Poundbury. The new water pipe system will be able to supply drinking water to the community and sustain the booming economy for decades to come. The design will be in line/according to the Wessex-water standards and should also be able to cater for future extension in it.

Project objective:

The aim is to provide a feasibility study on the pumped trunk main design and the gravity main design from the two proposed materials that is cast iron DI pipe and UPVC PE pipe. The proposal will access the flow rate, pipe selective diameter from industry, maximum pressure in the system, head loss in pipe and pipe design arrangement by using the following methods.

Method 1: Darcy equation and Moddy Diagram

Method 2: C-W equation and H-R walling ford look up tables.

Project will incorporate the best suitable route design trunk main from the pump station to the reservoir and gravity main reservoir to Poundbury along with advice on the need for pressure protection in the piping system. The feasibility study will provide the most cost-effective solutions and economical design to that the project if it will be feasible prior before the approval and implementation.

2) Route Investigation:

When planning pipe layout there are several constraints that must be assessed and considered as a form of site investigation. The site feasibility will evaluate the ground condition and geological factors of the surrounding are.

Ground condition:

Trunk main design:

Eq.1:

Head-loss of pipe(hf), friction factor(f), length(l), diameter (d or D), velocity(V) & acceleration due to gravity(g).

1st Method: Darcy Equation & Moody Diagram

Max pressure of total 10.71bars should be less than 16bars according to Wessex-water standards. 10.71

(Where 1m=0.098041bars)

Pressure check : For min pressure in the system

Min pressure in the system should be equal least 6m

Min pressure = 6m everywhere, therefore will be installing pressure sustaining valve (PSV) closers to end point of the Reservoir where the risks is higher to experience pressure less than 6m.

2nd Method: C-W Equation & H-R Wallingford look up tables

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Colebrook-White equation (0939) (C-W) (Refer to Appendix B)

Eq.9

Velocity(V), Pipe diameter(d), Hydraulic gradient(S), Effective roughness(K) and Kinematic viscosity (

(1) Step 1 : Repeat 1st step from method 1:

(2) Step 2: Repeat 2nd Step from method 1: and Pipe Diameter: 350mm

· Gravity Main Design

The objective is to design and select the appropriate pipe size for each selected gravity main routes from Lambert’s Hill to Poundbury to minimise the frictional head losses (hf).

Calculate frictional losses (hf) in pipe flow design (trunk pumped main) by use of 2 methods:

· 2ND METHOD : C-W Equation & H-R Wallingford look up tables

For selection of the appropriate pipe size the following values should be available as followed

a) Design flow rate Q=120 l/s

b) Length of pipe L(km) and type of material: DI; Galvanised iron (normal condition) and PE; UPVC

c) Start point Lambert’s Hill SR 155.70m AOD and end point at Poundbury 110.00m AOD

d) Lambert’s Hill SR – (Poundbury max elevation + required delivery head) =

Assume hf = 155.7 – (110.0 + 20) = 155.7 – 130 = 25.7m

e) Assume velocity in pipe flow 1.0m/s according to Wessex-water standards ()

Gravity main design:

Eq.9: Gradient

Head-loss of pipe(hf) and length(L)

DI and PE PIPE: Gravity Main

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Darcy Equation (Refer to Appendix B)

Pressure check :

a) At area where pipe from ground elevation has troughs. The lowest trough: risk of high pressure 35m(standard) therefore it is recommended to install Pressure reducing valves (PRV). 3

b) There is highest risk to have max pressure to the downstream end of pie, in times of very low flow, therefore it is recommended to stall Pressure reducing valve (PRV) at the downstream end of the pipe.

c) At area where pipe from ground elevation has peaks. Highest peak, risk of low pressure or even negative ones, therefore it is recommended to install pressure increasing valves at this point.

· Pipe elements required for the routes; Calculating fitting losses: Refer to Appendix B: Table 3.

Types of fittings:

· Pump manifold: Roughness value for 1 manifold is K1= 1.

· Swabbing chambers: ; Swabbing chambers @ every 2.5km of pipe length

· Long radius bends:

· In line valves: In line valves every 2km of pipe length

· Air valves: one air valves needed

· Isolating valves for each crossing:

· In line tees for future expansion plans:

· Wash outs: to clear out sediment and prevent discoloration

4. Costs:

(refer appendix D)

The capital expenditure calculation for CAPX and OPEX are based on input costing data available from Baro Happold. The calculation expenditure is covered for 60 years project life cycle with net present value of £1 at 6%.

Trunk main/Gravity main:

The cost expenditure for pipe design are from the same size and the change in project cost are affected by the length of the pipe, pipe passing through sensitive area and road/river crossing because they have a high rate £/m compared to pipe lay in field area. From the capital expenditure total cost, it clearly shows pipes which are shorter in length cost less and are more cost economic provided that the meet the design requirement with a low operation cost.

· Trunk main DI pipe route 1 has the maximum CAPEX and OPEX cost of £5,930,207/- compare to route 4 which has the lowest CAPEX & OPEX cost of £5,580,854/-

· Gravity main PE pipe route 1 has the lowest CAPEX and OPEX cost of £1,205,788/- compare to the same route 1 with DI pipe which has the CAPEX & OPEX cost of £1,240,733/-. Base on the analysis it more feasible and cost economic to select PE pipe material for the gravity main

5. Pump Selection:

Pump type: 5no 200x290x280 – 81/75x5x18.5=100HW as per appendix D

· The primary reason for not choosing less pump is that at the beginning the cost of installation will be less but the power out put is high, thus it will cause a high operation cost as it require more energy to operate. That is why it is not feasible to consider series 3no to 4no and any formation with high power output. It is more advisable to consider a more cost economic pump installation in series like 5m pump or 6pump which has the lower power output of 100KW but if there are less pump in series that produces the same power out put of 100KW or less it might be considered in the design. As a result, it is more economical to select the 5m.200x290x280 – with power output of 100KW.

Pump selection: by appendix D

The selected type of pump that will be used is an Armstrong 4300 pump with specific spec.

Curve no: PT113-1-1-1500

Series: 4300 Starline

Size: 200-290

RPM: 1500

Power: 81/75x5x18.5=100KW

Efficiency: 85%

Pump in series: 5no.200x290x280.

The operating pump: The pump system in series have been designed in by using the system curve and by looking at the point where the performance curve and system curve intercept. This is the point that define that the pump are suitable for the design. (Operating point is the point where system curve and operating curve cross.)

6. Pressure surge: (Refer to appendix E)

Is the sonic velocity, stiffness and fluid in the piping system which the roughness depends on time and the materials used. If the materials have more resistance to velocity, therefore any change in pressure and that will create a pressure surge in the pipe. Pressure surge consequence are fitting failure, pipe bursting and pump damage.

The graphs in appendix E represent pressure in pipe from two pipe size 350 and 400mm and from two different materials (D1 and PE).

· D1 pipe: Pressure surge: 350mm pipe (ps-sr)

Node1: The closer the water nears a valve changes the stronger the pressure surge and it happens along the full length of the pipe. The pressure rises from 90(m) up to 184(m) then, down to 40(m). This happens consistence across the internal length of the pipe when the pressure surge phenomenon to place. More protection will be need to Node1 than to Node10. Node1 is more likely to be from pump to reservoir and vice versa.

Node3 & 6: The pipe system exerts pressure surge phenomenon but not as intense as in Node1. In Node3 the pressure rises up during a period of time until it reaches 162max and drop to near zero, where as in Node 6 its maximum rise is 130m then it drops to 60 and stable for a period of time until it drop to -20.

Node 10: The pressure changes but does not happen through the entire length of the pipe. It happens as a spick as the pressure rise up from 10(m) to 90(m). It only happens at a single point (Need less protection than Node1). In Node 10 the pressure takes longer period to form compared to Node 1.

· D1=400mm: Model: Has similar effect as in D1350mm (the maximum pressure is near 150m and minimum is around -30(m).

Node3 & 6: Both pipe system in general experiences pressure surge. Node 3 rise up to nearly 140(m) and has a minimum pressure loss below -40(m) which equal to -3.9 bar which is below ˂6m. Node 6 has similar effect. Therefore both pipe system will require pressure increasing valves at the lowest point.

Node 10: Same pressure surge as the Note 10 exert in D1 350m only difference is the maximum and minimum.

· General:

The D1 350mm experience high pressure surge than in D1 400mm at different flow rates while D1 400mm experience lower pressure surge than in D1 350mm. That means that the size of pipe with different flow rates will experience pressure surge differently but the comparison between D1 pipe with PE pipe is that the PE has a high resistance to pressure surge due to its elastic and plasticity of UPVC.

7. Conclusion

To conclude the design analysis using 2nd Method: C-W Equation & H-R Wallingford look up tables to assess the flow rate, gradient, pipe size, frictional loss and maximum powers between DI and PE pipe along with capex and opex cost expenditure:

Trunk main pipe analysis shows that the pipe with the shortest length and less crossing are more feasible and economically viable to be used for this design.

Trunk main route selection are mostly similar, but its advisable to select the less cost effective that have less crossing and bending to minimize frictional head loss.

Gravity main: These two types of material DI and PE does not have much difference in comparison, when analysing route with the same length the only issue that differs is the velocity and retention time between them. PI material is more cost economic and durable. In additional it has a greater resistance to pressure surge compared to DI pipes. More thorough studies are needed to determine the best optimal design for route selection.

On a final note, the feasibility assessment will help to identify the best route that is more cost effective and sustainable and environmentally friendly. The pipes should be laid and tested in accordance with the manufacture’s instructions and the Town and Country Planning Regulations.

8 Appendix A: Plans and long section

Trunk Main

Fig3: Route 3. Photo from Google Earth@2021 Google

Fig4: Route 4. Photo from Google Earth@2021 Google

Fig5: Route 5. Photo from Google Earth@2021 Google

Gravity Main

Fig6: Route 1. Photo from Google Earth@2021 Google

Fig7: Route 2. Photo from Google Earth@2021 Google

Fig8: Route 3. Photo from Google Earth@2021 Google

Appendix B. Calculation

Pump Trunk Main

Eq.1:

Head-loss of pipe(hf), friction factor(f), length(l), diameter (d or D), velocity(V) & acceleration due to gravity(g).

DI Pipe: Trunk Main Route 1

1st Method: Darcy Equation & Moody Diagram

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Darcy Equation

1) Step 1 : Design flow rate; Convert

Eq.2:

2) Step 2 : Assumed velocity in pipe 1m/s; Calculate area of pipe and pipe diameter

We must assume the velocity because we have not designed the trunk-main and we do not have all the value in the system.

i) Eq.3: Area=Flow rate/Velocity,

Pipe Area(A)=

ii) Pipe Diameter: Eq.4:

Pipe diameter=

The possible D=0.321m = 321mm

From industry DI pipe : Possible pipe 300mm DI pipe or 350mm DI pipe

Repeat Step 2:

Pipe Diameter: 350mm

Real Velocity(V): Eq.2

3) Step 3 : Calculate Reynolds number (Re)

Kinematic viscosity (=1.14 (at typical value )

Eq.5

4) Step 4 : Table 38. Recommended roughness values (K).

i) Galvanise iron-good condition K=0.06

Eq.6 K/d=0.06/350=

ii) Use Moody diagram to find friction factor(f) from k-value

Moody diagram F=0.0044

iii) Therefore, frictional head losses (hf).

Eq.1

The total hf losses due to pipe flow are hf=12.047m when selecting DI pipe d=350mm.

Disregard the DI pipe d=300m has it has a higher frictional head loss of hf=13.416m.

Route checks

Last checks to make sure the route is a good design:

(1) Velocity check : Fist assumed V=1m/s but re-calculated V= 0.842m/s

Check V=0.842m/s against Wessex-water standards

V=0.842m/s is less than 2m/s

(2) Retention time (RT) . Calculate as followed:

Pipe Area (A), Length of pipe (L)=6630m and Velocity (V)=0.842m/s

Eq.7 RT = L/V = 6630/0.842 =

Check RT=2h19mins against wassex-water standards. RT should be less than 12hours

(3) Pressure check : For max pressure in the system.

Calculated Max pressure by summing up the following values:

i) Static lift = 155.70 - 59.45= 96.25m

ii) Freeboard= 0.5m

iii) Fitting losses = 0.398 (see appendix xx)

iv) hf calculation from Darcy Method or C-W and look-up tables. hf=12.047m

v) In total; Max pressure : Eq.8 Max pressure= Static lift+ Freeboard+ Fitting losses+ hf

Max pressure of total 10.71bars should be less than 16bars according to Wessex-water standards. 10.71

(Where 1m=0.098041bars)

(4) Pressure check : For min pressure in the system

Min pressure in the system should be equal least 6m

Min pressure=6m everywhere, therefore will be installing pressure sustaining valve (PSV) closers to end point of the Reservoir where the risks is higher to experience pressure less than 6m.

DI Pipe: Trunk Main Route 1

2nd Method: C-W Equation & H-R Wallingford look up tables

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Colebrook-White equation (0939) (C-W)

Eq.9

Velocity(V), Pipe diameter(d), Hydraulic gradient(S), Effective roughness(K) and Kinematic viscosity (

(3) Step 1 : Repeat 1st step from method 1:

(4) Step 2: Repeat 2nd Step from method 1: and Pipe Diameter: 350mm

(5) Step 3:

(a) Table 38. Recommended roughness values (K).

Galvanise iron-good condition K=0.06

(b) Table 15 – HR Wallingford table for K=0.06, Pipe size 350mm and Q=0.081

Q1=0.079, HG1=0.00160…………………………….. (V=0.819m/s)

Q2=0.081, HG2=0.00170…………………………….. (V=0.846m/s)

Real: Q =0.081, HG = …………………………….. (V=0.842m/s)

Linear interpolation gives following equation: Eq:10………..

= 0.0017

Energy losses per meter length of pipe(hf) where then length. Therefore, total losses hf = 6630 x 0.0017 = 11.271m

Route checks

Last checks to make sure the route is a good design:

(1) Velocity check : Fist assumed V=1m/s but re-calculated V= 0.842m/s

Check V=0.842m/s against Wessex-water standards

V=0.842m/s is less than 2m/s

(2) Retention time (RT) . Calculate as followed:

Pipe Area (A), Length of pipe (L)=6630m and Velocity (V)=0.842m/s

Eq.7 RT = L/V = 6630/0.842 =

Check RT=2h18mins against wassex-water standards. RT should be less than 12hours

(3) Pressure check : For max pressure in the system.

Calculated Max pressure by summing up the following values:

i) Static lift = 155.70 - 59.45= 96.25m

ii) Freeboard= 0.5m

iii) Fitting losses = 0.398 (see appendix xx)

iv) hf calculation from Darcy Method or C-W and look-up tables. hf=11.271m

v) In total; Max pressure: Eq.8 Max pressure= Static lift+ Freeboard+ Fitting losses+ hf

Max pressure of total 10.63bars should be less than 16bars according to Wessex-water standards. 10.63

(Where 1m=0.098041bars)

(4) Pressure check : For min pressure in the system

Min pressure in the system should be equal least 6m

Min pressure=6m everywhere, therefore will be installing pressure sustaining valve (PSV) closers to end point of the Reservoir where the risks is higher to experience pressure less than 6m.

Gravity Main Design

Eq.9: Gradient

Head-loss of pipe(hf) and length(L)

DI PIPE: Gravity Main Route 1

2nd Method: C-W Equation & H-R Wallingford look up tables:

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Darcy Equation

i) Step 1 : Design flow rate; Convert

ii) Step 2 : Assumed velocity in pipe 1m/s; Calculate area of pipe and pipe diameter

a) Eq.3:

b) Pipe Diameter: Eq.4:

Pipe diameter=

The possible D=0.391m = 391mm

iii) Step 3 : Gravity Main Route 1: From industry DI pipe : Possible pipe 350mm, 400mm or 450mm

Table 38. Recommended roughness values (K)=0.06 good condition

a) Pipe length L=3040m, hf=25.7m, Real: Q= , HG=0.00845 & D=0.391m

(c) Table 15 – HR Wallingford table. D:350mm

Q1 = 0.118, HG1 = 0.00340

Q2 = 0.121, HG2 = 0.00360

Real: Q = 0.120, HG = …

Linear interpolation gives following equation:

Eq:10………..

= 0.00352

(The actual Q=0.120 and actual HG=0.00352 is less than the initial assumed HG=0.00845)

Energy losses per meter length of pipe(hf) where then length 3040m

Therefore, total losses hf = 3040 x 0.00352 = 10.70m

Route checks

Last checks to make sure the route is a good design:

(1) Velocity check : Fist assumed V=1m/s but re-calculated Vm/s

Check Q=0.120/s and D=0.350m

; V=1.25m/s is less than 1.5m/s

(2) Retention time (RT) . Calculate as followed:

Length of pipe (L)=3040m and Velocity (V)=1.25m/s

Eq.7 RT = L/V = 3040/1.25 =

Check RT=1.06hrs against Wassex-water standards. RT should be less than 12hours

(3) Pressure check :

5 At area where pipe from ground elevation has troughs. The lowest trough: risk of high pressure 35m(standard) therefore it is recommended to install Pressure reducing valves (PRV). 3

6 There is highest risk to have max pressure to the downstream end of pie, in times of very low flow, therefore it is recommended to stall Pressure reducing valve (PRV) at the downstream end of the pipe.

7 At area where pipe from ground elevation has peaks. Highest peak, risk of low pressure or even negative ones, therefore it is recommended to install pressure increasing valves at this point.

PE PIPE: Gravity Main Route 2

2nd Method: C-W Equation & H-R Wallingford look up tables:

Calculation of frictional (head) losses hf in an existing pumped main pipe flow by use of Darcy Equation

(1) Step 1 : Design flow rate; Convert

Eq.9: Gradient =

(2) Step 2 : Assumed velocity in pipe 1m/s; Calculate area of pipe and pipe diameter

a) Eq.3:

b) Pipe Diameter: Eq.4:

Pipe diameter=

The possible D=0.396.9m = 396.9mm (from industry)

(3) Step 3 : Gravity Main Rout 1: From industry PE pipe : Possible pipe: 396.9mm

Table 38. Recommended roughness values (K)=0.03 good condition

From Table 14: K=0.03, Q=, HG=0.0082 and range 375mm & 400mm.

Eq.9: Gradient = 25.7/3140 = 0.00818

b) Pipe length L=3140m, hf=25.7m, Real: Q= & HG=0.00818

c) From Table 2: HR Wallingford table

(d) Eq:11………..

(e) HG1 = 0.00180: Q1 = 0.103, Q2 = 0.122: E Eq:11 Q=0.1196

HG2 = 0.00190: Q1 = 0.106, Q2 = 0.126: E Eq:11 Q=0.1235

(f) Cal for HG value for D:396.9mm

Q1 = 0.1196, HG1 = 0.00180

Q2 = 0.1235, HG2 = 0.00190

Real: Q = 0.120, HG = …

Linear interpolation gives following equation:

Eq:10………..

= 0.00181

(The actual Q=0.120 and actual HG=0.00181 is less than the initial assumed HG=0.00818)

Energy losses per meter length of pipe(hf) where then length 3040m

Total losses hf = 3140 x 0.00181 = 5.68m

Route checks

Last checks to make sure the route is a good design:

(1) Velocity check : Fist assumed V=1m/s but re-calculated Vm/s: Check Q=0.120/s and D=0.3969m

; V=0.97m/s is less than 1.5m/s

(2) Retention time (RT) . Calculate as followed: Length of pipe (L)=3140m and Velocity (V)=1.25m/s

Eq.7 RT = L/V = 3140/0.97 =

Check RT=1.06hrs against Wassex-water standards. RT less than 12hours

(3) Pressure check :

8 At area where pipe from ground elevation has troughs. The lowest trough: risk of high pressure 35m(standard) therefore it is recommended to install Pressure reducing valves (PRV). 3

9 There is highest risk to have max pressure to the downstream end of pie, in times of very low flow, therefore it is recommended to stall Pressure reducing valve (PRV) at the downstream end of the pipe.

10 At area where pipe from ground elevation has peaks. Highest peak, risk of low pressure or even negative ones, therefore it is recommended to install pressure increasing valves at this point.

Calculate of frictional losses in pipe fitting

Table3: Fitting Losses for Trunk Main and Gravity Main

Appendix C: Cost spreadsheet

Capital Expenditure Pump Main

Appendix D: Information for PUMP Selection

Pumps for UK civil engineering application licensed to be used to pump portable water: 4300

Fig10: From lecture: Selected pump: 5 no. 200 x 290 x 280

Appendix E: Pressure surge protection:

Fig11.a: From lecture

Fig11.b: From lecture

Fig11.c : From lecture

Reference: