water supply Project theory

PALPA ENGINEERING COLLEGE
1
WATER SUPPLY AND SANITARY PROJECT 2072
Chapter 1: INTRODUCTION
1.1 Background:
The project is planned to bring water from Sisne Ban
to Padhera 1+264.6 Km pipe line is laid from source to tap5.
The identified project is first studied and feasibility study report
is prepared and then detailed survey detailed survey was
carried out. The survey and measurement was carried during
dry season of 2072 B.S.
1.2 Project objective
The project aims at providing safe water in the adequate
quantity effectively at low cost in Mujhung VDC and
communities of the projects area in order to improve living
standards as well as economy of people.
1.3 Approaches and procedure Adopted in Engineering
Equipments such as Abney level, staff, ranging rod,
measuring tape, tripod stand, pegs, compass, etc. are used in
order to carry out the detailed survey of the project. Watch and
Bucket are specially used for the measurement of discharge of
the source.
Before visiting the project area, selection of route and
the additional information about the project area was carried
out.
Chapter 2: Service Area

2
2.1 Location and Accessibility:
The Mujhung is the VDC of the Palpa district of Western
Development Region of the country Nepal. The district headquarter
is linked by Siddhartha Highway. It takes about one and half hour
from Butwal to the communities of survey area. Local materials
such as stones, aggregates, sand etc. are available from
KaliGandaki and Tinaukhola, and also non local construction
materials are transported from Butwal.
2.2 Topography, Geology and Vegetation:
The project area lies in the Hilly region. The altitude of project
varies from about 1200m to 1300m above mean sea level. The
area has good vegetation with forest,Salla,Pipal, Rododendron,
Katus, Chilaune, sal, etc.
2.3 Climatic Condition:
The climatic condition of this area is cold. Here the climate is
moderate and suitable for all kinds of vegetation as well as human
beings.
2.4 Socio-Economic Structure and Occupation:
Agriculture as well as business and tourism is the occupation of
the people of this area and also the live-stock is closely related and
linked with business. The expenditure pattern is almost equal to
their earning.
CHAPTER: 3 DESCRIPTION OF GRAVITY WATER
SUPPLY SYSTEM
3.1 INTRODUCTION

3
A gravity flow scheme collects water from springs or small
streams. It is then supplied to a storage tank situated above the
community from where it is distributed to public stand stands the
pipe network generally consists of HDP pipes. But in rocky sections
& gully crossing GI pipes are used. Water treatment in the form of
plain sedimentation is provided when the stream source is used.
3.2 UNDERSTANDING TO GRAVITY WATER SUPPLY SYSTEM
In gravity water supply system, the water could be supplied to
community with the use of reservoir tanks or without it technically
we call these as.
A. Open system
B. Close system
A. Open system
A system is designed as an open system when the total
design demand (tap- flow) of community could be met by the safe
yield of the source confirming no need of further storage so an
open type water supply system runs for 24 hours without use of any
faucets at the tap stand.
-Q source peak daily design demand (ltr/day)
-No reservoir required.
B. Close system
When the safe yield of the source for a system is
insufficient (less than the water demand tap flow) to meet the peak
water demand showing the need of storage, then the system is
called as close system.

4
-Discharge on source is less or equal to the average of daily
design demand (ltr/day)
-Reservoir required based on operating system,
Closed system is divided in to two types.
1. Continuous type
2. Intermittent type
1. Continuous type:
The water supply system which is designed to supply the
water throughout the day (24 hours) is known as continuous type
system.
2. Intermittent type:
If the system has been designed to supply the water in the
interval of time like morning, day evening shift that is known as
intermittent type system.
3.3 SAFE YIELD
The safe yield of the source should be sufficient to meet the
total design demand. The measured dry season yield is multiplied
by a factor of at least 0.9 to obtain safe yield. The safe yield should
not less than 0.1 ltr/sec in gravity flow system. The source should
be measured in dry season (March – April) should be done by
measuring the indentified source from (October – June) outside
monsoons period.
Safe source yield = 0.9× measured source yield at the peak of dry
season
3.4 COMPONENTS OF GRAVITY WATER SUPPLY SYSTEM
INTAKE
Intake in a gravity flow water supply system, an intake is the
structure which collects water from the water source and feeds to
transmission pipe.

5
The type of intake depends upon type of source from which
water is tapped. For example of the source is spring the intake
constructed (to tap water) is called spring intake.
The intake is built at the section of maximum water availability
from the source. Spring intake stream and river intake infiltration
galleries.
COLLECTION CHAMBER (CC)
If the intake could not be constructed at the safe place,
collection chamber is provided at the safe place with provision of
minimum of 5 meter static head.
The purpose of collection chamber (CC) are also to collect
from more than one water sources settle course materials and
remove floating material like leaves as well.
INTERRUPTION CHAMBER (IC)
Generally, interruption chamber (IC) are provided in a
transmission line to break pressure and is always without a float
valve (valve maintain constant water level)
Interruption chamber allow the flow to discharge into the open
atmosphere there by reducing its hydrostatic pressure to zero, at
establishing a new static level (TRANSMISSION LINE or in
distribution line) if the static head exceeds 60 meter than
interruption chamber is provided.
However if there is ‘U’ profile zones in the water system,
interruption chamber could not be used. Interruption chamber
maintain the desire residual pressure.Interruption chamber is made
of stone masonry, RCC, ferrocement etc.

6
BREAK PRESSURE TANK (BPT)/ CHAMBER (BPC)
The function of break pressure tank (BPT) is similar to
interruption chamber but generally used in distribution line and
used with float valve (to collect water at the reservoir tank)
 Break pressure tank allow the water to be collected at upstream
structure (for example reservoir tank)
 Any open vessel like storage tank, collection chamber,
distribution chamber may act break pressure tank besides their
original purpose.
 Break pressure tank provide if the static head exceeds 60 meter
even if pipe with a pressure rating of 10 kg per sq. centimeter is
used.
 Break pressure tank is made of stone masonry, RCC, faro
cement.
DISTRIBUTION CHAMBER (DC/DT)
 Distribution chambers (DC) are provided to divide the flow (if two
reservoirs are needed branches of pipe lines for each reservoir
tank can be provided from distribution chamber to reservoir tank.
 Generally these chambers work satisfactory up to 2 to 3 ltr/sec
and gate valves are used in outlet of distribution chamber.
RESERVOIR (RVT)/ STORAGE TANK
 The reservoir tank serves to store water that is provided by the
source during low demand period (night period) and for use
during high demand periods such as in the early morning.
 Reservoir tank balance the variation of water demand in a day.

7
 Reservoir tank should be located at suitable place above the
highest located stand post of the service area so that a residual
head of 5 to 10 meter can be maintained at the stand post.
 Reservoir tank should be designed as it gets just filled during
non-supply hours (overnight within 10 hours). The safe yield it
manages as just filled the reservoir tank.
 If tapped follow > designdemand flow, the reservoir size is small
and transmission pipe diameter is bigger. It would be economical
when transmission is shorter.
 Reservoir tank should be located in average not more than 15
meter above the community and not more than 10 meter above
the topmost tap.
 If tapped flow is equal to the design demand flow, Then the
reservoir size is bigger. It would be economical, transmission
line is long.
 If reservoir tank size calculated greater than 12 cu. meter
(sometimes 20 cu. meter), then number of reservoir tank be
increased. (Reservoir tank calculated 20 cu. meters, we can use
12 cu. meter and 8 cu. meter two numbers of reservoir tank).
PIPE LINE
 Pipe line transfer water from the source to the service area.
 There are various types and sizes of pipes but mostly high
density polythene (HDP) pipes are used in the community water
supply scheme in rural areas. In rocky terrains and when the
static pressure is likely to be very high, HDPE pipes are not
suitable. Galvanized iron pipes and in special cases high
pressure steel pipes may be used whenever static head is
exceptionally high.
6mm……………………...1/4”

8
10mm…………………….3/8” 1/2"………………..15mm
12mm…………………….1/2” 3/4"………………..20mm
16mm…………………….5/8” 1”………………….25mm
20mm…………………….3/4” (1+1/4)”…………...32mm
22mm…………………….7/8” (1+1/2)”……………40mm
25mm...............................1” 2”…………………..50mm
32mm…………………….(1+1/4)” (2+1/2)”……………65mm
40mm…………………….(1+1/2)” 3”…………………..75mm
50mm…………………….2”
1/2”,3/4”,1”,(1+1/4)”,(1+1/2)”,2”,(2+1/2)”,3”,4”,(4+1/2)”,5”,6”
PIPE LINE ARE CLASSIFIED AS
 Designed without considering any peak factor.
 For easy operation and maintenance without should be provided
at about 1.5km interval.
 Transmission main:- The selection of pipe line from source to
reservoir.
 Distribution main:- The selection of pipe line reservoir to
tapstand.
 Distribution pipe sizes are determined by the tap flow rate when
the water is supplied through the stand post.

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SEDIMENTATION TANK
 Water from the stream sources and large springs generally
contains suspended particles as the turbulence of a flow get
clay, silt and even small pieces of gravel. Such particles carried
in the flow can give the water a dirty and unhealthy taste and
also scour the pipe surface. If the water is allowed to stay
relatively quietly in the tank for some time, most of these
suspended particles sink and settled down to the bottom of the
tank. This process is called sedimentation and tank is called as
sedimentation tank.
 Plain sedimentation(Heavy particles settles fast than fine
particles, design seem to be for heavy particles is not able to
remove all contamination).
DESIGN OF SEDIMENTATION TANK
 Detention time (time needed to settle in sedimentation tank).
 Flow velocity in pipe line.
 Type and size of particle in water.
 If detention time is 1 to 2 hours (Coarse materials), then main
velocity in main pipe is 1m/sec.
 If detention time 4 – 6 hours for river carry fine particles
(materials) where the computed velocity, flow velocity is in main
pipes be below 1m/sec.
PIPE CROSSING

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 If the pipe line crosses river, streams landslides a separate
structure constructed called as pipe crossing.
 If such crossing are shorten such as less than 12 meters in
span, suitably anchored GI pipes will used. Dry stone and
Gabion embankments are recommended.
 For longer span water depth in stream, river is sufficient high,
special cables should be provided.
 If the flow dies or goes minimum during the dry season. HDP
pipe line should be buried sufficiently below the ground/bed and
anchored down using stone measuring or gabion or with any
other means.
STAND POST
It is categorized private or public stand post. In rural
water supply is recommended.
 The number of people to be served by a stand post is also
determined by the tap flow rate.
 A stand post should have a maximum 100 users (sometimes
120 also).
3.5 PIPE HYDRAULICS/ FLUID DYANAMICS/WATER
PRESSURE (STATIC PRESSURE)/HEAD
 Static (water) pressure is related only to the vertical distance
from the nearest surface expressed to atmosphere conditions
this distance is referred as head.

11
 STATIC pressure indicates the amount of gravitational energy
available at that point.
 Static level i.e. water level rest.
DYNAMIC PRESSURE (RESIDUAL HEAD)
 Residual head is the excess energy remaining in the system
after the desired flow has reached the discharging point.
 When the water velocity is not zero static conditions no longer
exists or parts of available energy is consumed to make the
water flow the water is moving within pipe, we refer system is
being a dynamic state. The excess residual gravitation energy
remaining at a within the pipe line is define as residual.
 The residual heads can be plotted on profile to construct the
hydraulic grade.
 The HGL represents the residual energy within the pipe line for a
specified.
FRICTIONAL LOSSES
 Losses appear due to roughness in pipe line.
 As the water passes through the pipe it in encounters this
relative roughness energy to be lost. This losses in energy is
referred to as friction losses.
 Friction losses are the primary
 Available heads between points is equal the elevation difference
between the points the residual head.
 Head loss is governed by friction factor.

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3.6 DESIGN CRITERIA
A) POPULATION GROWTH RATE
The scheme is designed for design period. So population
should be found out for the end of design period called as design
population. Present population would be multiplied by the
corresponding district growth factor to obtain design population.
Design Population (P) = p(1+r)^n
Where p= present population
r = annual population growth factor (district wise)
n= design period
B) DESIGN PERIOD
Design period is the time for which a service life of water
supply was assumed. In a rural, water supply system in Nepal
should be planned and designed for design period of 15 to 20
years.
Description Design Period
For the rural area of annual
growth rate less than 2% 20 years
For the rural area of annual
growth rate greater or equal to 2% 15 years
C) WATER DEMAND
Description Per
capita (Demand/day)
 Domestic covering part of animal demand
 Public connection 45LPCD
 Private connection 65LPCD

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 Institutional demand
 For day scholar students 10LPCD
 For hostel students 45LPCD
 Hospital/health center demand
 OPD patients
1000L/Day
 Night staying patients
3000L/Day
 Temple/Church/Gumba
 Outside prayer 25LPCD
 Manks prayer 45LPCD
D) TAP FLOW RATE
Ultimate water demand Peak flow rate Remark
Per tap (ltr/sec) at service life
3400 - 4600 0.15 Small crestal of
house
4600 - 5800 0.20 Village
5800 – 7600 0.25 Bazzar or village
with school/health
post
E) PEAK FACTOR

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Estimated based on average demand critical which meet the
average demand of community however such tap flow should also
meet the demand of community during the peak time which means
the daily ha to be supplied at a higher flow rate of the community.
Thus, this average flow rate needs to be multiplied by a factor
depending on consumption pattern called peak factor.
Description Peak factor
Public connection 3
Private connection 1
School and health post 3
Temple/Church/Gumba 3
F) CONSUMPTION PATTERN (CONTINUOUS SYSTEM)
Time duration Consumption % of total demand
5:00AM - 7:00AM 25%
7:00AM – 12:00N 35%
5:00PM – 7:00PM 20%
7:00PM – 5:00AM 0%
G) RESIDUAL HEAD
Description Residual head (in m)
At CC/DC/IC/RVT/BPT
-Maximum 15
-Minimum 5
Exceptional 3.5
TAP

15
-Maximum 15
-Minimum 5
Exceptional minimum 3.5
Exceptional maximum 3.5
PIPE LINE
-Maximum As desired by pipe series
-Minimum 5
Exceptional minimum 3.5
H) Service Level:
Service level is the service, which a community can get
without paying extra cost. It governed by per capita demand tap
stand spacing, HH per tap, feature extension (if any)
Description criteria
Basic service level tap stand description public tap stand
House hold per tap stand
-Basic 10 household per tap
-Average 7-10 house hold
I) Maximum static pressure for different pipe series
Pressure bearing capacity of pipe depends on the
thickness of pipe. Pipe should be selected to bear the maximum
static pressure at lower end of pipe section.
Description of HDP pipe Maximum static pressure
(m)

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10kg/cm sq 100
6kg/cm sq 60
2.5kg/cm sq not be used
GI Pipe 160
J) Tap stand spacing
Horizontal Desirable In low
density area
(average horizontal carrying
distance from house hold to
round trip)
150 m 250-350mm
Vertical
(average vertical carrying
distance from house hold to
round trip)
50 m 50-80m
Round trip time 15 minutes
K) Velocity limit
Where the water velocity is very high, water hammer in
the pipe line is then developed if valves are closed
instantaneously. Therefore the designer should be aware of
this phenomena and the following velocity of flow in the pipes
for rural water supply system should be adopted.
Description Velocity (m/s)
Generally maximum
10kg/cm sq 2.8
6kg/ cm sq 2.3
Absolute maximum 3.0

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Absolute minimum 0.3
Maximum
Down hill 2.5
Up hill 2.0
Minimum
Down hill 0.4
Up hill 0.5
No of occupants 4 8 24 60
Diameter of
pipe (mm) 12 20 25 32
S.N Community
population
Adopted
LPCD
Remarks
1 Less than 2000 45 Supply through
public tap
2 Less than 20000 70 – 100 Supply through
public tap
3 20000 to 100000 100 – 150 Supply through
public tap
4 Greater than
100000
150 - 200 Private tap
L) Sizing of reservoir Tank
Time need to deliver the design
days requirement (hrs)
Storage need to balance
flows (days demand)
24 50%
18 33%
15 25%
12 15%
9 10%
Example

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Days design demand = 91,000 ltrs
Source yield (rate of flow) = 1.6 l/s
Time needed to deliver day’s demand
91,000 ltrs * 1/1.6 ltrs * 1hrs/3600 sec =15.8 hrs
1.6l – 1 sec
1l – 1/1.6
91,000 – 1/1.6*9100
=56875 sec =56875/60*60 = 150799 ~ 15.8 hrs
Interpolation
18hrs 33% day demand Y-Y1=Y2-Y1/(X2-X1)*(X-
X1)
15.8 hrs 27.1% day demand
15 hrs 25% day demand
Now, for 15.8 hrs the storage reqrement is 27.1% of daily
demand (27.1% of 91,000)lts=24,600 lts so RVT be =2*12 m cube
(2 reservoir required)
NOTES
 The size of pipe be find by d=2 √Q/ Πv
Q = (A*V)
= d²/4 * V
Accuracy limits
 10% elevation difference between two consecutive
surveying along the some alignment for Abney level
survey.
 6% elevation difference between two consecutive

19
surveying along the same alignment for auto level survey.
For example :- If the maximum static pressure, at a
point is 60m then 6Kg/cm² HDPE pipe would be needed.
Unnecessary use of pipes of higher working pressure (e.g.
G.I pipes and 10 Kg/cm² HDP pipe) should be avoided.
 Use of BPT as far as possible should be avoided because
of maintenance reason. However, if the use of IC or other
pressure breaking /reducing means can decrease the
scheme cost by avoiding the use of higher series pipes in
a significant manner.
 Use of Ferro cement technology for reservoir tanks should
be enchorance, as these are cheaper than traditional stone
masonry reservoir (especially for sizes bigger than 6000
liters capacity).
Water demand for
Hotel Urban area Rural
area
1) Without bed 200l/day
200l/bed/day
2) With bed 500l/day 500-
1000l/day
b) Offices
1) Resident 60LPCD
65LPCD
2) Non residental 10LPCD
10LPCD
Use of excessive residental head (more than 15m) at tap

20
stand and other structures should be avoided. It will decrease the
size of pipe thus the cost.
 Ferro cement tanks are extensively used in Nepal because
they have the advantages of low cost and are simple to
construct. Ferro cement consists of a sand and mortar
reinforced by ms bar and chicken wire mesh. The
reinforcement to take core of hoop stress consist of plain
wire with dia. (3-4mm) spaced at a distance 50-120mm. A
layer of chicken wire is placed which is embedded in the
cement sand mortar. In Nepal a temporary inside would is
made of 32mm HDP pipe, which is used later in the water
distribution network.
1) Level Difference = Difference of Reduced level.
2) Maximum Static pressure =(static level – reduced level 2)
3) Total head available = (HGLUP – Reduced level 2)
4) Residual head = (Total head available – total head loss)
5) HGL(Toldown) = HGL (up/from) – Total head loss
Pipes used in transmission/distribution
a) 16mm 10kg/cm²
b) 20 mm 10kg/cm²
c) 25mm 10kg/cm²
d) 32mm 6Kg/cm² / 10kg/cm²
40mm,50mm,63mm,75mm,90mm,110mm,and so on.

21
4.2 RVT Sizing
Rural Water Supply and Sanitation Fund Development Board
RESERVOIR RANK SIZING FORM
(CONTINUOUS SYSTEM: USING CONSUMPTION PATTERN)
Scheme Name: Sisne Drinking Water Supply Scheme
Support Organization: VDC office District : Palpa
Tap stand no:- 5
STORAGE TANK NO: - 1
A. Designation of tap stand supplied through this RVT:
 Available minimum flow from source safe yield = 0.34 * 0.9 =0.31
ltr/sec
B. Flow in transmission line from SOURCE/DC to RVT:
 Adjusted supply to reservior from source = 0.25 l/s = 21600 l/day =
900 l/hrs
C. Flow in the distribution line from RVT :
Average design demand to be supplied through reservior = 0.187 l/s = 16170
l/days
Time Period Suppl
y
Hours
Demand
Water
Consumptio
n
Supply
(Cum.
Litre)
Demand
(Cum.
Litre)
Surplu
s
( Litre)
Deficit
(Litre)From To
5:00AM 7:00AM 2 25% 1800 4042.5 - 2242.5
7:00AM 12:00N 5 35% 6300 9702 - 3402
12:00N 5:00PM 5 20% 10800 12936 - 2136
5:00PM 7:00PM 2 20% 12600 16170 - 3570
7:00PM 5:00AM 10 0% 21600 16170 5430

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Maximum difference between cumulative supply & cumulative demand
= 3570 L = 3.57 m³ = 4m³
Storage Tank Capacity Provided=4 m³
Total design flow of all standpost = 0.76 ltr/sec
4.3 Hydraulic Design
4.4 Septic Tank Design
SEPTIC TANK
A septic tank is a combined sedimentationand digestiontank
which is rectangular water tight chamberconstructed of brick
masonry or stone masonry or RCC built the ground to collect
human excreta.
Purpose
The main purpose is to collectthe sewage settles and create
digestionprocess effectively.Effluentis disposedin the safe way.
Constructiondetails
1) It is rectangular in plan and length is usually 2 to 4 times breath.
2) The depth should be 1 to 1.8 meter.
3) The depth of freeboard should be 30 to 45 centimeter.
4) T- shaped outlet is provided.
5) Baffle wall is provided it is placed 20 to 30 centimeterfrom the
inlet pipe.

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6) Usually RCC slab with manhole are provided.
7) Ventilation pipe having diameter 7.5 to 10 centimeteris provided
Septic tank is made of brick work or stone masonry or
concrete or other suitable materials. The septic tank should be
plastered with rich cementmortar in which some water proofing
material should be mixed up. The floor should be 1:2:4 cement
concrete and given slope 1:10 to 1:20 towards sludge outlet.
Working and Maintenance
Before starting the septic tank, a small amount of digested
sludge,cow dung is put in new tank to seed bacteria inside. Black
scum seenthrough the manhole proves that the septic tank is well
functioning.
No disinfected soap water are allowed to enter in the septic
tank. The digested sludge is withdrawn from the septic tank 6
months to 3 years and in case of exposed portionof the tank
damage by neighbors or with any other reasons these are repaired.
Disposalof septic tank effluent
Effluent from the septic tank should be properly disposedoff to
prevent nuisance and hazard on public health.
The methods are
 Soak pit
 Leaching cesspool
DESIGN CONSIDERATIONFOR SEPTIC TANK
Length width ratio of tank (L:B) = 2 – 4

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Minimum depth (d) = 1m
Minimum width = 0.75m
 Septic Tank designfor a family having 6 person. The rate of
sewage is looped..
Detention Period = 24 hrs
Cleaning of Sludge = 3 yrs
Given;
Number of Users (N) = 6 Person
Rate of Sewage (Q) = 100 lpcd
Detention Period (t) = 3 yrs
Cleaning Period (T) = 3yrs
Then ;
1) Volume of Settling (V1) = Q ×N×t
=100×6×24
= (100/1000)×6×1day
= 0.6 m3
2) Volume of Sludge (V 2) =0.0425 m3
/person×N
=0.0425×6
=0.255 m3
3) Volume forDigested Storage (V3) =Cds×N
= 0.085×6
= 0.51
Total effective volume (V) = V1 + V2 + V3
= 0.6+0.255+0.51
= 1.365 m3
Assumed;
Effictive Depth (d) = 1 m

25
Surface area (A) = [Volume/ Depth]
=1.365/1 = 1.365 m2
Taking;
L/B =2
L = 2B
Here,
Area (A) = L×B
1.365 = 2B×B
2B2
= 1.365
B = 0.83 m2
> 0.75 m2
Hence designis Safe….
L = 2×0.83 = 1.65m
Provide Free Bord (F.B) = 0.4 m
Overall Depth = 0.4+1 = 1.4 m
Thus;
AdoptSize of Septic Tank
L = 1.65 nearly equal to 1.70 m
B = 0.83 m nearly equal to 0.85m
D = 1.4 m nearly equal to 1.5 m

26

27
Chapter: 5 Drawings
5.1 LongitudinalProfile and HGL Plotting

28
5.2 Pipe Flow Diagram

water supply Project theory

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