water supply project theory

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

PALPA ENGINEERING COLLEGE

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


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.


-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 YIELDThe 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.


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.

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.

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 > design demand 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”

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.

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

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.

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.

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

Institutional demand

For day scholar students 10LPCD For hostel students 45LPCD


Hospital/health center demand

OPD patients1000L/Day

Night staying patients3000L/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

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

-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)

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 maximum10kg/cm sq 2.86kg/ cm sq 2.3Absolute maximum 3.0Absolute minimum 0.3Maximum Down hill 2.5Up hill 2.0Minimum Down hill 0.4Up hill 0.5


No of occupants 4 8 24 60Diameter 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

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 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 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.

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 Supply

Hours

Demand Water

Consumption

Supply

(Cum. Litre)

Demand

(Cum. Litre)

Surplus

( 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

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 sedimentation and digestion tank which is rectangular water tight chamber constructed of brick masonry or stone masonry or RCC built the ground to collect human excreta.

Purpose

The main purpose is to collect the sewage settles and create digestion process effectively. Effluent is disposed in the safe way.

Construction details

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 centimeter from the inlet pipe.

6) Usually RCC slab with manhole are provided.

7) Ventilation pipe having diameter 7.5 to 10 centimeter is 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 cement mortar 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 seen through 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 portion of the tank damage by neighbors or with any other reasons these are repaired.

Disposal of septic tank effluent

Effluent from the septic tank should be properly disposed off to prevent nuisance and hazard on public health.

The methods are

Soak pit

Leaching cesspool

DESIGN CONSIDERATION FOR SEPTIC TANK

Length width ratio of tank (L:B) = 2 – 4

Minimum depth (d) = 1m

Minimum width = 0.75m

Septic Tank design for 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)×6×1 day

= 0.6 m3

2) Volume of Sludge (V 2) =0.0425 m3/person×N

=0.0425×6

=0.255 m3

3) Volume for Digested 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

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

2B 2 = 1.365

B = 0.83 m2 > 0.75 m2 Hence design is Safe….

L = 2×0.83 = 1.65m

Provide Free Bord (F.B) = 0.4 m

Overall Depth = 0.4+1 = 1.4 m

Thus;

Adopt Size 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


Chapter: 5 Drawings

5.1 Longitudinal Profile and HGL Plotting


5.2 Pipe Flow Diagram
