3. Conveyance of water
There are two stages in the transportation of water:
1.Conveyance of water from the source to the treatment plant.
2.Conveyance of treated water from treatment plant to the distribution
system.
In the first stage water is transported by gravity or by pumping or by the
combined action of both, depending upon the relative elevations of the
treatment plant and the source of supply.
In the second stage water transmission may be either by pumping into an
overhead tank and then supplying by gravity or by pumping directly into
the water-main for distribution.
4. Design of pressure pipes
Hydraulics of flow and Design of pressure pipes as Gravity Mains
The pressure conduits are designed in such a way that the available pressure
head is just lost in overcoming the frictional resistance offered to the flow of
water by the pipe.
The velocities generated in these pipes should neither be too small to require
a large size diameter pipe, nor should be so large as to cause excessive loss of
pressure head
The head loss by pipe friction may be found by using either of the following
formulas :
(i) Darcy-Weisbach Equation.
f=co-efficient of friction which is function of
Reynolds number L=length of pipe
V=mean velocity offlow
d=diameter of pipe
Note: The head loss represents the additional height that the fluid needs to be raised by a
pump in order to overcome the frictional losses in the pipe
5. (ii) Hazen-William's formula. This formula is widely used for pipe flows and
states
The head loss by pipe friction may be found by using either of the following
formulas :
V = 0.85 CH R0.63 S0.54
where
CH= Coefficient given by Table 1
R= Hydraulic mean depth of pipe, = (d/4) in
meters.
S = Slope of the energy line.
V = Flow velocity through the pipe in m/sec.
Table 1. Values of CH for Hazen William's
6. Pumping
a. A pump is a device which converts mechanical energy into hydraulic
energy.
b. It lifts water from a lower to a higher level and delivers it at high pressure.
Pumps are employed in water supply projects at various stages for following
purposes:
1.To lift raw water from wells.
2.To deliver treated water to the consumer at desired pressure.
3.To supply pressured water for fire hydrants.
4.To boost up pressure in water mains.
5.To fill elevated overhead water tanks.
6.To back-wash filters.
7.To pump chemical solutions, needed for water treatment.
7. Design of Pumps
Finding the capacity of pump
Pump has to work against a total head of
“H” M
Total Head (H) = Static head + Dynamic head
Dynamic head
Power of pump = ϒw X Q X H in kW
Where ϒw = Unit weight of water
Q = Discharge in m3/sec
H = Total head in m
Static head (Hs) = Suction head and delivery head
Dynamic head (Hd) = Head loss due to friction
Working Horse power (WHP)=
ϒw X Q X H
0.746
Breaking Horse power (BHP)=
ϒw X Q X H
0.746η𝑝
η𝑚
ηp = Efficiency of pump
η𝑚 = Mechanical efficiency
8.
9. The purpose of distribution system is to deliver water to consumer with
appropriate quality, quantity & pressure.
Distribution system is used to describe collectively the facilities used to
supply water from its source to the point of usage
Introduction
10. Water quality should not get deteriorated in the distribution pipes.
It should be capable of supplying water at all the intended places with
sufficient pressure.
It should be capable of supplying the requisite amount of water during fire
fighting.
The layout should be such that no consumer would be without water
supply, during the repair of any section of the system.
All the distribution pipes should be preferably laid one meter away or
above the sewer line.
It should be fairly water tight as to keep losses due to leakage to the
minimum.
Requirement of good distribution system
11. LAYOUTS DISTRIBUTION NETWORK
The distribution pipes are generally laid below the road pavements, and
as such their layouts generally follow the layouts of roads.
There are general, four different types of pipe networks; any one of
which either single or in combinations, can be used for a particular
place.
CLASSIFICATION OF DISTRIBUTION NETWORKS
1. Dead End System
2. Radial System
3. Grid Iron System
4. Ring System
12. DEAD END SYSTEM or TREE SYSTEM
It is suitable for old towns and cities having no different pattern of roads.
13. Advantage :-
Relatively cheap
Determination of discharge and pressure easier due to less number of valves.
Disadvantage :-
Due to many dead ends, stagnation of water occurs in pipes.
DEAD END SYSTEM or TREE SYSTEM
14. RADIAL SYSTEM
The area is divided into
different zones.
The water is pumped into
the distribution reservoir
kept in the middle of each
zone.
The supply pipes are laid
rapidly ending towards the
periphery.
Advantages :-
It gives quick service
Calculation of pipe size is easy
15. GRID IRON SYSTEM
It is suitable for cities with rectangular layouts, where the water mains and
branches are laid in rectangles
16. Advantage :-
Water is kept in good circulation due to absence of dead ends
In the case of break down in some section, water is available from some
other direction.
Disadvantage :-
Exact calculation of sizes of pipes are not possible due to provisions of
valves on all branches.
GRID IRON SYSTEM
17. RING SYSTEM
The supply main is laid all
along the peripheral roads
and sub mains branch out
from the mains.
This system also follows the
grid iron system with the flow
pattern similar in character to
that of dead end system.
So determination of the size
of pipes is easy.
Advantages :-
Water can be supplied to any point from at least two directions.
18. METHODS OF WATER DISTRIBUTION
For efficient distribution system adequate water pressure required at
various points.
Depending upon the level of source, topography of the area and other local
conditions, the water may be forced into distribution system by following
ways –
Gravity System
Pumping System
Combined gravity and pumping system
19. GRAVITY SYSTEM
Suitable when source of supply is at sufficient height.
Most reliable and economical distribution system.
The water head available at the consumer is just minimum required
The remaining head is consumed in the frictional and other losses.
20. PUMPING SYSTEM
Treated water is directly into the distribution main out storing.
Also called pumping without storage system.
High lifts pumps are required.
If power supply fails, complete
stoppage of water supply.
The method is not general
used.
21. COMBINED GRAVITY and PUMPING SYSTEM
Most common system
Treated water is pumped and stored in an elevated distribution reservoir.
Then supplies to consumer by action of gravity.
The excess water during low demand periods get stored in reservoir and get
supplied during high demand period.
Economical, efficient and reliable system.
23. Distribution reservoirs, also called service reservoirs, are the storage
reservoirs, which store the treated water for supplying water during
emergencies ( such as during fires, repairs, etc.) and also to help in absorbing
the hourly fluctuations in the normal water demand.
Function of distribution reservoirs-
a. To absorb the hourly variations in demand.
b. To maintain constant pressure in the distribution main.
c. Water stored can be supplied during emergencies.
DISTRIBUTION RESERVOIRS
24. Location & height of distribution reservoirs
Should be located as close as possible to the centre of demand.
Water level in the reservoir must be at sufficient elevation to permit
gravity flow at an adequate pressure.
DISTRIBUTION RESERVOIRS
25. TYPES of RESERVOIRS
Depending upon the elevation with respect to ground,
It may be classified into...
1. Surface reservoirs
2. Elevated reservoirs
26. Surface reservoirs
These also called ground reservoir.
Mostly circular or rectangular tanks.
Underground reservoir are preferred especially when the size is large.
These reservoirs are constructed high natural grounds and are usually made
of stones, brick, plain or reinforced concrete cement.
The side walls are designed to take up the pressure of the water, when the
reservoir is full and the earth pressure, when it is empty
27. Elevated reservoir
It is also referred to as overhead tanks
are required at distribution areas which
are not governed and controlled by the
gravity system of distribution.
These are rectangular, circular or
elliptical in shape.
If the topography of the town not
suitable for under gravity, the elevated
tank or reservoir are used.
They are constructed where combine
gravity and pumping system of water
distribution is adopted.
These tanks may be steel or RCC.
