2. Introduction
• Primary Source of
Water for our planet is
Precipitation.
• Precipitation : Water
falling from the
atmosphere to the
surface of the earth in
the form of Rain, Snow,
sleet(snow mixed with
rain),hail(frozen dew),
out of this major one is
rain, minor is snow.
• The origin of all sources of
water is rainfall.
• When precipitation occurs, part
of it may evaporate and return
immediately to the atmosphere.
3. • Most of the water obtained through precipitation is
retained in surface depressions, carried away as surface
runoff in natural streams or rivers and percolates into the
ground and joins the groundwater.
• As such the various sources of water available for a water
supply may be broadly classified into the following two
categories.
4. Surface sources : These are those sources of water which are
available at the surface of the earth. The various sources are:
-Rivers and streams
-Lakes and ponds
-Impounding Reservoirs or storage reservoirs
Sub-Surface or Ground Water : These are those sources of
water which exist below the ground surface. The various
sources are
-Springs
-Infiltration works
-Wells and tube wells
5. Streams and Rivers :
Streams:
• Feeds their waters to lakes
• Quantity of water available is small.
• Sometimes go dry
• Not suitable f or water supply schemes
• Large streams may be used as source of water by providing
storage reservoirs, barrages etc.,
Rivers:
• River is a natural channel which carries surface runoff
received by its catchment or drainage basin.
• Rivers are the most important sources of water supply,
several big and important cities of the world are situated
on the banks of the important rivers.
6. • India Cities like Delhi, Calcutta, Ahmadabad are served
water supply from Rivers.
• This is due to availability of large quantity of water from
rivers throughout the year.
• River Water Softer than Ground Water.
• Contains large amount of Organic matter
• It contains Suspended Matter, Clay, Silt etc.
• In Indus River – excess quantity of Harmful Dissolved Salts
like Mica, Magnesium sulphates are present in water.
• Easily accessible, freely used for washing and bathing.
• Rivers are polluted due to Industries.
• River water is thoroughly treated before supply to the
public.
7. • Rivers are two types, they are perennial and non-
perennial rivers.
Perennial
• Water is available throughout the year
• Rivers are fed by rain during rainy season
• They can used as source of public supplies directly
Non – perennial
• Used as source of public water supply by providing
storage on the upstream side of the intake water.
• Not reliable
• Contains large amount of silt
8. Lakes and Ponds:
• Ponds and Lakes A natural large
sized depression formed within t
he surface of t he earth, when
gets filled up with water is known
as pond or lake. Difference
between pond and lake is only
that of size.
• Pond: If the size of depression is
comparatively small, it is termed
as pond.
• Lake: When the depression is
large, it is termed as lake.
• The quantity and quality of water in the lake depends upon
the characteristics of its catchment.
• Thus water in a lake would be relatively pure and of good
quality if its draws from uninhabited upland areas free from
soluble salts.
9. • If the water came from low land areas, the water in the lake
is contaminated with large quantities of soluble salts and
other impurities.
• A ponds containing still water may have plenty of algae,
weed and other vegetable growth imparting bad smell,
taste and colour to the water.
• Thus if sufficient quantity of good quality of water is
available from a lake then it will be a very useful source of
water supply, from which water may be supplied without
any treatment or with some preliminary treatment.
• Ponds are may sometimes man-made diggings, these are
filled up with water in rainy season.
• Pond water is generally not used for drinking purposes and
it can be used for bathing, washing of clothes or for
animals.
10. Storage Reservoirs:
• The flow rate of the river in a
river or stream may vary
considerably during different
periods of a year.
• It may carry little or no water
during dry weather period and
may carry huge amount of
water during rainy season.
• Thus, if the water is drawn
directly from the river then
during extremely low flows it
may not possible to meet the
demands of the consumers,
while during high flows there
may be operational problems.
As such it is essential to
create a storage reservoir
or an artificial lake by
constructing a dam across
river, which can store the
excess water that flows in
the river during the periods
of high flows for use during
the periods of high flows
for use during the periods
of low flows or droughts.
11. • The quality of water in a storage reservoir mainly depends
on the quality of the water flowing in the river on which the
reservoir is created.
• As such the water from a storage reservoir also needs to be
properly analysed and treated before supplying to the
public.
• The storage reservoirs are the main sources of water supply
for big cities.
• These are created not only for water supply but also for
other purposes such as irrigation, hydro-power generation,
navigation, flood control, etc.
• A storage reservoir meant for supplying water for more
than one purpose is termed as multipurpose reservoir.
12. Sub Surface Source:
Springs:
• A spring is natural outflow of
ground water which appears at
earth surface as a current or
stream of water flowing.
• Appeared as small water.
• These are Holes at the foot of
hills/along River banks.
Water Springs may be classified into
1.Those resulting from gravitational
forces
2.Those resulting from non-
gravitational forces
13. Gravity Spring: These are results from water flowing under
hydrostatic pressure. The following are different types of
gravity springs
a. Depression springs:
• These springs are formed due to overflowing of the water
table, where the ground surface intersects the water table
as shown in figure.
14. b. Contact springs or surface springs:
• These springs are created by a permeable water bearing
formation over laying a less permeable or impermeable
formation that intersects the ground surface as shown in
figure.
15. c. Artesian springs:
• These springs result from release of water under pressure
from confined aquifers either at an outcrop of the aquifer
or through an opening in the confining bed as shown in
figure.
• The amount of water available in an artesian spring may be
large if the catchment area is large.
16. Non-Gravity springs:
• It includes volcanic springs and fissure springs.
• The volcanic springs are associated with volcanic rocks and
the fissure springs results from fractures extending to great
depths in the earth’s crust.
• These are usually thermal springs.
• Thermal springs discharge water having a temperature in
excess of the normal local ground water.
• In general springs supplies small quantity of water, it may
supply water for small towns, especially near hills are the
bases of hills.
• The water obtained from some of the hot springs is found
to be useful for the cure of certain skin diseases.
17.
18. Infiltration Galleries:
• An Infiltration Gallery is a a horizontal tunnel usually
rectangular in cross-section and having permeable boundaries
so that groundwater can infiltrate into the same, and hence it
is also sometimes known as horizontal well.
• It is generally provided in highly permeable aquifers with high
water table so that adequate head is available for gravity flow
of groundwater into the gallery.
• It is usually placed near a perennial rivers and hence it is
usually placed along the bank, or under the bed of the river.
• The usual depth at which the gallery is placed ranges from 3
to 10m below the ground surface.
• It is generally constructed by cut and fill method.
• In the walls of the gallery number of openings are provided to
permit the entry of water into the gallery.
19. • The gallery is laid at a slope and the water collected in the
gallery is led to a sump from where it is pumped out and
supplied to consumers after necessary treatment.
• Infiltration rates of 1500 to 7000 m3/day per 100m length of
gallery.
20. Infiltration Wells:
• Infiltration wells are the shallow wells constructed in series
along the banks of a river to collect the water seeping through
the banks of the rivers.
• The wells are closed at top and open at bottom.
• These are constructed with brick masonry with open joints.
• Manhole is provided for the inspection, at the top of the well.
• The water infiltrates through the bottom of these wells and as
it has to pass through the sand bed it gets purified to some
extent.
• The various Infiltration wells are connected by porous pipes to
a collecting sump well-known as jack well, the water flows by
gravity into jack well, from the jack well water is pumped into
the treatment plant and supplied to the consumers.
21.
22. Wells:
• A well is a vertical cylindrical opening which extends from
the surface of the ground down in to the water bearing
formation (Aquifers).
• These are used when large discharges are required but a
thin highly permeable aquifer is available.
• A well consists of a reinforced concrete caisson or well
about 3 to 6m in diameter from which horizontal lateral
screened pipes are projected radially near the bottom.
• The caisson is sunk into the water-bearing stratum by
excavating the earth from the inside and its bottom is
sealed by concrete plug.
• Water wells may be classified as
1. Open wells or dug wells
2. Tube wells
23. Open wells or Dug wells:
• Open wells are the wells which have comparatively
large diameters but low yields and are not very deep.
• The diameter usually vary from 1 to 10m.
• The yield of these wells is mostly 20 m3/hr or less.
• The depths of open wells may generally range from 2m
to 20m.
Open Wells may be further Classified as
1.Shallow open wells
2.Deep open wells
• Shallow open wells are those which rest in the top
water bearing strata and draw their supplies from the
surrounding material.
24. • Deep open wells are those which rest on impervious
strata and draw their supplies from the pervious
formation lying below the impervious strata through
the bore holes made in the impervious strata.
26. Tube Wells:
• A tube well is a long pipe sunk into the ground intercepting
one or more water bearing strata.
• As compared to open wells the diameter of tube wells are
much less and usually vary from 80mm to 600mm.
The tube wells may also be further classified as
1.Shallow wells (depth = less than 30m and yield 20m3/hr)
2.Deep wells ( depth = greater than 30m and maximum depth
of about 600m and yield is more than 800m3/hr)
The tube wells are classified based on construction type
a. Strainer type tube well
b. Cavity type tube well
c. Slotted type tube well
27. a. Strainer type tube well:
• it is the most common
and widely used type of
tube well, tube well
generally refers the
strainer type tube well
only.
• In this type the pipe
introduced into the
ground is an assembly
of strainer pipes and
ordinary pipes which
are alternatively placed.
28. b. Cavity type tube well:
• Cavity type tube well consists of
a pipe sunk into the ground and
resting on the bottom of a
strong clay layer.
• It does not utilise the strainers
and hence it draws its supplies
from the bottom and not from
the sides.
• The principle is similar to deep
open well, but the difference is
deep open well taps only the
water in the first aquifer, a
cavity type tube well may tap
water from any lower strata.
29. c. Slotted type tube well:
• It is consists of a pipe which is
slotted for a part of its length at
one end and for the rest of the
length it is a plain pipe.
• The slotted pipe portion is
usually about 5m long and it
penetrates the water from the
confined aquifer.
• The size of the slots is 25 mm X
3 mm and spacing is 10 to 12
mm.
• The mixture of gravel and sand
placed around the well pipe is
known as shrouding.
30. Comparison of sources with reference to Quality,
Quantity and other considerations : (Quality )
Sl.No Surface water Ground water
1 Consists Low TDS Colour less
2 High Turbidity Less bacterial contamination
3 High Suspended Matter High TDS
4 High Bacterial Contamination High Fluoride
5 More Industrial pollutants High Nitrate
6 More Residential Pollutants High Alkalinity
7 Low Hardness High Hardness
8 Small Reserve
(Less than 1% of fresh, liquid water in
the planet )
Great storage capacity (95% of
the water )
9 Deliver instantly a great amount of
water
Allow pumping from wells
10 Need water treatment before supply Don’t treatment except
Chlorination
31. Selection of Site for a Storage Reservoir
The selection of site for a storage reservoir depends on the
following factors:
• A suitable site for the construction of a dam must be
available where the reservoir is proposed to be created.
• The river valley at the site should be narrow so that the
length of the dam to be constructed is less, but it should
open out on the upstream side to provide a large basin for
the reservoir.
• The surroundings hills of the reservoir should be water tight.
• The reservoir basin should also be reasonably water tight so
that the stored water is not able to escape under the
surrounding hills through cavernous rock or other
continuous rock or other continuous pervious strata.
32. • The site should be such that as far as possible
minimum land and property is submerged in the
reservoir.
• The site should be such that it avoids water from those
tributaries which carry unusually high content of
sediment.
• The site must be such that adequate reservoir capacity
is made available.
• As far as possible a deep reservoir must be formed so
that the land costs per unit of capacity are low,
evaporation loss is less and there is less likelihood of
weed growth.
33. • The reservoir site should be such that there are no
objectionable minerals and salts present in the soil and
rocks at the site, which may get dissolved in water and
deteriorate its quality.
• The quality of water stored in the reservoir satisfies its
intended use.
• The site should be such that the costs of associated works
such as roads, rails, housing colonies for workers and other
staff, etc are not excessive.
Capacity of Storage Reservoirs ,Mass Curve Analysis
• A Reservoir is a storage space for water.
• Storage reservoirs are constructed to store the water in the
U/s side during rainy season and useful to release the water
to the Downstream when it is required.
34. • Reservoir capacity depends up on the inflow available
and demand.
• Reservoir capacity corresponding to a specific yield.
Yield: amount of water that can be supplied from the
reservoir in a specific interval of time.
Safe yield: It is the maximum quantity of water which can
be supplied from a reservoir in a specified period of time
during a critical dry year.
The reservoir capacity can be determined with the help of
1. Analytical methods
2. “mass inflow curve” or “demand curve”
35. Analytical methods
In this method an analysis of demand and inflow of water per
month of the year is made.
• Total inflow of the stream during each month of a critical
low flow year (or dry year) at the reservoir site.
• Total loss of water due to evaporation, percolation, etc.,
during each month f the year.
• Total precipitation during each month of the year.
• Total amount of water required to be released from the
reservoir during each month of the year to satisfy the prior
water right requirements of the residents on the
downstream of the reservoir.
• Total demand of water during each month of the year.
36. The following procedures are adopted to determine the
capacity of the storage reservoir:
1. From the total inflow of the stream during each
month, the total loss of water due to evaporation,
percolation, etc., and the total amount of water to
be released to meet the downstream requirements
during that month are subtracted and the total
amount of precipitation during the same month is
added. This gives the adjusted or net inflow of the
stream for different months of the year.
2. By subtracting the adjusted or net inflow from the
demand the deficiency
37. or the amount of water required from the
storage to meet the demand for different
months is obtained. However, if the demand is
less than the adjusted or net inflow it indicates a
surplus.
3. The total deficiency during the successive months
gives the required capacity of the storage
reservoir.
4. If the provision is to be made for two or three
successive dry years, the capacity obtained in
step 3 is increased accordingly.
40. Determination of Reservoir Capacity
• A mass curve of inflow is prepared from the flow
hydrograph for a number of consecutive years selected
from the available stream flow record such that it
include the most critical or driest period.
• Prepare the mass demand curve corresponding to the
given rate of demand. If the rate of demand is
constant, the mass demand curve is a straight line. The
scale of the mass demand curve should be the same as
that of the mass inflow curve.
41.
42. 3. Draw the lines AB, FG, etc. such that
(i) They are parallel to the mass demand curve, and
(ii) They are tangential to the crests A, F, etc. of the mass curve.
4. Determine the vertical intercepts CD. HJ, etc. between the
tangential lines and the mass inflow curve. These intercepts
indicate the volumes by which the inflow volumes fall short
of demand.
• Assuming that the reservoir is full at point A, the inflow
volume during the period AE is equal to ordinate DE and the
demand is equal to ordinate CE. Thus the storage required is
equal to the volume indicated by the intercept CD.
5. Determine the largest of the vertical intercepts found in Step
(4). The largest vertical intercept represents the storage
capacity required.
43. The following points should be noted.
(i) The capacity obtained in the net storage
capacity which must be available to meet the
demand. The gross capacity of the reservoir
will be more than the net storage capacity. It
is obtained by adding the evaporation and
seepage losses to the net storage capacity.
(ii) The tangential lines AB, FG; etc. when
extended forward must intersect the curve.
44. This is necessary for the reservoir to become
full again, If these lines do not intersect the
mass , the reservoir will not be filled again.
However, very large reservoirs sometimes do
not get refilled every year. In that case, they
may become full after 2-3 years.
(iii) The vertical distance such as FL between the
successive tangents represents the volume of
water spilled over the spillway of the dam.
45. Determination of Yield of a Reservoir
The yield from a reservoir of a given capacity can be
determined by the use of the mass inflow curve.
1. Prepare the mass inflow curve from the flow hydrograph
of the river.
2. Draw tangents AB, FG, etc. at the crests A, F, etc. of the
mass inflow curve in such a way that the maximum
departure (intercept) of these tangents from the mass
inflow curve is equal to the given reservoir capacity.
3. Measure the slopes of all the tangents drawn in Step 2.
4. Determine the slope of the flattest tangent.
46. 5. Draw the mass demand curve from the slope of the
flattest tangent (see insect).
The yield is equal to the slope of this line.
50. Types of Water Bearing Formations
• Groundwater is water that exists in the pore spaces and
fractures in rocks and sediments beneath the Earth’s surface.
• It originates as rainfall or snow, and then moves through the
soil and rock into the groundwater system, where it
eventually makes its way back to the surface streams, lakes,
or oceans.
There are basically four types of geological formations
1.Aquifers
2. Aquitard
3. Aquiclude
4. Aquifuge
51. Aquifers:
• It is defined as geological formation that contains sufficient
permeable material which permits storage as well as
transmission of water through it under ordinary conditions.
• Aquifers may occur at various depths.
• Those closer to the surface are not only more likely to be
used for water supply and irrigation, but are also more likely
to be topped up by the local rainfall.
• Aquifers contains saturated material which will yield
significant quantities of water to wells and springs.
• Unconsolidated sands and gravels are the examples of the
formations which serves as aquifers.
• Also known as Artesian /Pressure aquifers.
53. • Groundwater is confined under pressure greater than
atmospheric by overlying relatively Impermeable.
• In a well penetrating such an aquifer, the water level will
rise above the bottom of the confining bed, as shown by
the artesian and flowing wells of Figure.
54. Unconfined aquifer:
- Water body present in between the Impermeable and
water table known as Unconfined Aquifer.
- Also called as water table,Free,Phratic and non-artesian
aquifers.
- Water table serves as the upper surface zone of saturation .
- Rises and falls in the water table depends on volume of
water stored.
Perched Aquifer
• Special type of unconfined
aquifer.
• Occurs where a ground water
body is separated from the main
ground water by a relatively
impermeable stratum of small
extent.
55. Aquitard:
• A saturated low permeability unit that can restrict the
movement of groundwater. It may be able to store
groundwater.
• Aquitards normally slow down the movement of
groundwater and contaminants. Aquitards can also store
groundwater and contaminants.
56. Aquiclude:
• A geologic formation, group of formations, or part of
formation through which virtually no water moves.
• An impermeable body of rock or stratum of sediment that
acts as a barrier to the flow of groundwater.
• It is a solid, impermeable area underlying or overlying an
aquifer. If the impermeable area overlies the aquifer
pressure could cause it to become a confined aquifer.
57. Aquifuge:
• An impermeable body of rock which contains no
interconnected openings or interstices and therefore
neither absorbs nor transmits water.
58. Determination of Yield of a Infiltration
galleries
• Ground water travels
towards lakes, rivers or
streams.
• This water which is
travelling can be
intercepted by digging a
trench or by constructing a
tunnel with holes on sides
at right angle to the
direction of flow of
underground water.
59. • These underground tunnel used for tapping
underground water near rivers, lakes or streams are
called ‘Infiltration Galleries’.
• Underground water may be allowed to enter these
infiltration galleries from both sides or one side as
desired. The yield from these galleries may be as much
as 1.5 × 104 litres/day/metre length of the infiltration
gallery.
• For maximum yield the galleries should be placed at
the full depth of the aquifer. Infiltration galleries may
be constructed with masonry or concrete with weep-
holes of 5 cm x 10 cm.
60. • Infiltration galleries are surrounded on sides and top
with gravel or pebble stones to increase their intake
capacity. Longitudinal slope is given to the galleries and
at the end sump well is constructed, from where water
is pumped out.
Following assumptions are made while determining, the
yield of an infiltration gallery:
(a) The soil is isotropic and incompressible.
(b) The tangent to the water table line or its slope is equal
to its sine.
(c) The rate of flow of the water into the gallery is
uniform and remains horizontal throughout the depth
of the aquifer.
61.
62. q = yield of the infiltration gallery per unit of its length
= ky.dy/dx
Where, k = coefficient of permeability
Y = the effective height of the ground water table above the soil of the
gallery at point x.
Area of unit width through which the water enters the gallery = y × 1
Slope of the ground water table at point x = dy/dx
... q. dx = ky. dy
Integrating it q.x. = ky2/2 + C
Putting x = L = length of the gallery
y = H
The yield of the infiltration gallery
q= k((H2 – h2)/L)
Where
k = coefficient of permeability
63. H = depth of the permeable stratum above the bottom of the
infiltration gallery.
h = height of the water surface inside the infiltration gallery.
L = distance through which seepage takes place.
Problem :
Determine the yield of an Artesian well with the following
data:
(a) Depth of water before pumping = 50 m.
(b) Thickness of the aquifer = 25.5 m
(c) Depth of water during pumping = 42.0 m
(d) Radius of the circle of influence = 92.0 m
(e) Radius of the well = 10 cm.
(f) Value of constant k’ = 4 x 10-3
66. Introduction
• In any water supply
project the first step is to
select the source of
water from which water
is drawn.
• The device Installed for
the purpose of drawing
water from the source of
water are called Intakes.
67.
68. Intake Structure
• The basic function of intake structure is to help in safely
withdrawing water from the source and then to discharge
this water in to the withdrawal conduit, through which it
reaches the water treatment plant.
• It is constructed at the entrance of the withdrawal conduit
and thereby protecting it from being damaged/clogged by
ice, debris.
• Some times from reservoirs where gravity flow is possible,
water is directly transmitted to the treatment through
intake structure.
• If gravity flow is not possible, water entering intake
structure is lifted by pumps and taken to the treatment
plant.
70. Selecting Location Of Intake Structure
• Site should be near the treatment plant to reduce
conveyance cost.
• Intake must be located in the purer zone of the source so
that best quality water is withdrawn from source to reduce
the load on the treatment plant.
• Intake must never be located in the vicinity of waste water
disposal point.
• Intake must never be located near the navigation channels
so as to reduce chances of pollution due to waste discharge
from ships.
• The site should be such as to permit greater withdrawal of
water, if required in future.
72. Selecting Location Of Intake Structure
• Intake must be located at a place from where
it can draw water even during the driest
period of the year.
• The intake site should remain easily accessible
during floods and should not get flooded.
• In meandering rivers, the intakes should not
be located on curves or atleast on sharp
curves.
74. Intakes for Collecting Surface Water
Types of Intakes
According to type of source
• River Intake
• Canal Intake
• Reservoir Intake
• Lake Intake
According to position of Intake
• Submerged Intake
• Exposed Intake
According to presence of water in the tower
• Wet Intake
• Dry Intake
75. According to position of Intake
(a) Submerged Intake
(b) Exposed Intake
• The submerged Intake structures are those which are
constructed entirely under water. They are less
expensive to construct but are difficult to maintain. Such
intakes are commonly used to obtain water from lakes.
• The Exposed intakes is in the form of well or tower
constructed near the bank of river or in some cases even
away from the bank of river. They are more common due
to ease in operation and maintenance.
76. According to presence of Water in the tower
(a) Wet Intake
(b) Dry Intake
• A Wet intake is that type of the Intake tower in which
the water level is practically the same as the water
level of the source of supply. Such Intakes are also
called as Jack Well and is most commonly Used.
• In Dry Intake There is no water in the intake tower.
Water enters through entry port directly in to
conveyance pipes. The dry Intake tower is simply used
for the operation of valves.
77. Simple Lake Submerged Intakes
• It consists of a simple concrete block or a rock filled timber crib
supporting the starting end of the withdrawal pipe.
• The intake opening is generally covered by screen so as to prevent
the entry of debris, ice etc.. in to the withdrawal conduit.
• In lakes, where silt tends to settle down , the intake opening is
generally kept at about 2 to 2.5m above the lake bed level to avoid
entry of silt.
• They are cheap & do not obstruct navigation
• They are widely used for small water supply projects drawing water
from streams or lakes having a little change in water level through
out year.
• Limitation is that they are not easily accessible for cleaning &
repairing.
81. Intake Towers
• They are widely used on large water supply projects
drawing water from rivers or reservoirs having large change
in water level.
• Gate controlled openings called Ports are provided at
various levels in these concrete towers to regulate the flow.
• If the entry ports are submerged at all levels, there is no
problem of any clogging or damage by ice or debris etc..
• There are two major types of intake towers:
(a) Wet intake towers
(b) Dry intake towers
82. Wet Intake Towers
• It consist of a concrete circular shell filled with water
up to the reservoir level and has a vertical inside shaft
which is connected to the withdrawal pipe.
• The withdrawal pipe may lie over the bed of the rivers
or may be in the form of tunnels below the river bed.
• Openings are made in to the outer concrete shell as
well as, in to the inside shaft.
• Gates are usually placed on the shaft, so as to control
the flow of water in to the shaft and the withdrawal
conduit.
83. • The water coming out of the withdrawal pipe
may be taken to pump house for lift (if treatment
plant is at high elevation) or may be directly taken
to treatment plant (at lower elevation).
• A wet intake tower has entry ports at various
levels and the vertical shaft is filled with water up
to reservoir level.
• It is less costly to construct and is usually not
subjected to flotation and certain other stress
may not be the consideration.
86. Dry Intake Towers
• The water is directly drawn in to the withdrawal conduit
through the gated entry ports.
• It has no water inside the tower if its gates are closed.
• When the entry ports are closed, a dry intake tower will be
subjected to additional buoyant forces.
• Hence it must be of heavier construction than wet intake
tower.
• They are useful since water can be withdrawn from any
selected level of the reservoir by opening the port at that
level.
• Dry Intake tower has a merit that the intake tower being
dry is made accessible for inspection and operation besides
that the water can be withdrawn from any level by opening
the port at that level.
91. Trash Racks
• Trash rack is defined as a screen or grating provided at the entrance
of intake to prevent entry of debris.
• Trash racks usually consists of trash sections 1.5 to 2 m wide and
not too long for handling, made up of mild steel flats on edge 5 to
15 cm.
• Coarse trash racks are provided near the ports to prevent large
drift, such as cakes of ice, roots, trees and timber from being drawn
into the intake.
• In some part of the intake fine trash racks are provided to protect
the machine & machine parts through which water flows.
• In cold region, trash racks is often clogged with fragile ice.
• Electrical heating for small trash racks are provided to prevent ice
formation on the racks.
• The floating debris accumulated, as are denied entry into the
intake, are removed with the help of power driven rack-rakes.
93. River Intake
• A River Intake is located on the upstream side of the
city to get comparatively better quality of water.
• They are either located sufficiently inside the river so
that necessary demand of water can be met in all the
seasons of the year.
• The intake tower permits the entry of water through
several entry ports located at various levels to cope
with fluctuations in the water levels during different
seasons.
• This are also called as penstocks. The penstocks are
covered with suitable design screens to prevent entry
of floating impurities.
94. They can be classified in to two types
(1) Twin well type of intake structure
(2) Single well type of intake structure
Twin Well Type Intakes
• They are constructed on almost all types of rivers, where the river water
hugs the river bank.
• A typical river intake structure consists of 3 components:
(a) An inlet well
(b) An inlet pipe (intake pipe)
(c) A jack well
• Inlet well is usually circular in c/s, made of masonry or concrete.
• Inlet pipe connects inlet well with jack well. It has a min dia of 45cm, laid
at slope of 1 in 200. Flow velocity through it<1.2m/s
• Water entering jack well is lifted by pumps & fed into the rising main Jack
well should be founded on hard strata having B.C> 450 kN/m2.
96. Single Well Type Intakes
• No inlet well & inlet pipe in this type of river intake.
• Opening or ports fitted with bar screens are provided
in the jack well itself.
• The sediment entering will usually be less, since clearer
water will enter the off-take channel.
• The silt entering the jack well will partly settle down in
the bottom silt zone of jack well or may be lifted up
with the pumped water since pumps can easily lift
sedimented water.
• The jack well can be periodically cleaned manually, by
stopping the water entry in to the well.
99. Canal Intakes
• In case of a small town a nearby Irrigation Canal can be
used as the source of water. The Intake Well is generally
located in the bank of the Canal.
• Since water level is more or less constant there is no need
of providing inlets at different depth. It essentially consist
of concrete or masonry intake chamber or well.
• Since the flow area in the canal is obstructed by the
construction of Intake well, the flow velocity in the canal
decreases.
• So the canal should be lined on the Upstream &
Downstream side of the intake to prevent erosion of sides
and bed of channel
101. Intakes for Reservoirs
• When the flow in the river is not guaranteed throughout the year, a dam is
constructed across the river to store the water in the reservoir so formed.
• Reservoir Intakes essentially consists of an Intake tower constructed on
the slope of Dam at such a place where Intake can draw water in sufficient
quantity even in the driest period.
• Intake pipes are fixed at different levels, so as to draw water near the
surface in all variations of water levels.
• An intake structure constructed at the entrance of conduit and thereby
helping in protecting the conduit from being damaged or clogged by ice ,
trash, debris, etc.., can vary from a simple Concrete block supporting the
end of the conduit pipe to huge concrete towers housing intake gates,
Screens, pumps, etc.. and even sometimes, living quarters and shops for
operating personnel.
102. Lake Intake
• Lake Intake are mostly submerged intake. These Intakes
are constructed in the bed of lake below the low water
level so as to draw water even in dry season.
• It mainly consist of a pipe laid in the bed of the lake.
• One end of the pipe which is in middle of the lake is
fitted with bell mouth opening covered with a mesh
and protected timber or concrete crib.
• The water enters in the pipe through the bell mouth
opening and flows under gravity to the bank where it is
collected in a sump well and then pumped to the
treatment plant for necessary treatment.
105. Conveyance of Water
• Water is drawn from the sources by Intakes. After it’s
drawing the next problem is to carry it to the treatment
plant which is located usually within city limits.
• Therefore after collection, the water is conveyed to the city
by mean of conduits. If the source is at higher elevation
than the treatment plant, the water can flow under
gravitational force.
• For the conveyance of water at such places we can use
open channel, aqueduct or pipe line, Mostly it has been
seen that the water level in the source is at lower elevation
than the treatment plant, In such case water can be
conveyed by means of closed pipes under pressure
107. Conveyance of Water
• If the source of supply is underground water, usually
there is no problem as, these sources are mostly in the
underground of the city itself.
• The water is drawn from the underground sources by
means of tube-wells and pumped to the over-head
reservoirs, from where it is distributed to the town
under gravitational force.
• Hence at such places there is no problem of
conveyance of water from sources to the treatment
works.
109. • In case of sources of water supply is river or
reservoir and the town is situated at higher
level, the water will have to be pumped and
conveyed through pressure pipes.
• If the source is available at higher level than
the town, it is better to construct the
treatment plant near the source and supply
the water to the town under gravitational
forces only,
111. Open Channels
• These are occasionally used to convey the water from the
source to the treatment plant. These can be easily and
cheaply constructed by cutting in high grounds and banking
in low grounds.
• The channels should be lined properly to prevent the
seepage and contamination of water. As water flows only
due to gravitational forces, a uniform longitudinal slope is
given.
• The hydraulic gradient line in channels should not exceed
the permissible limit otherwise scouring will start at the
bed and water will become dirty.
• In channel flow there is always loss of water by seepage
and evaporation.
113. Aqueducts
• Aqueducts is the name given to the closed conduit
constructed with masonry and used for conveying
water from source to the treatment plant or point of
distribution.
• Aqueduct may be constructed with bricks, stones or
reinforced cement concrete.
• In olden days rectangular aqueduct were used, but
now a days horse-shoe or circular section are used.
These aqueduct are mostly constructed with cement
concrete The average velocity should be 1 m/sec.
115. Tunnels:
• This is also a gravity conduit, in which water flows under
gravitational forces.
• But sometimes water flows under pressure and in such
cases these are called pressure tunnels.
• Grade tunnels are mostly constructed in horse-shoe cross-
section, but pressure tunnel have circular cross-section.
• In pressure tunnels the depth of water is generally such
that the weight of overlying material will be sufficient to
check the bursting pressure.
• Tunnels should be water tight and there should be no loss
of water.
117. Flumes
• These are open Channels supported above the
ground over trestles etc.. Flumes are usually used
for conveying water across valleys and minor low
lying areas or over drains and other obstruction
coming in the way.
• Flumes may be constructed with R.C.C, wood or
metal.
• The common section are rectangular and circular.
119. Pipes:
• These are circular conduits, in which water flows under
pressure.
• Now a days pressure pipes are mostly used at every places
and they have eliminated the use of channels, aqueducts
and tunnels to a large extent.
• These are made of various materials like cast Iron, wrought
Iron, steel, cement Concrete, asbestos, cement, timber,
etc.. In the town pips are also used for distribution system.
• In distribution system pipes of various diameter, having
many connections and branches are used.
• Water pipe lines follow the profile of the ground water and
the location which is most economical, causing less
pressure in pipes is chosen.
121. • The cost of pipe line depends on the internal pressure to
bear and the length of pipe line.
• Therefore as far as possible the hydraulic line is kept closer
to the pipe line. In the valley or low points a scour valve is
provided to drain the line and removing accumulated
suspended matter.
• Similarly at high points air relief valves are provided to
remove the accumulated air.
• To prevent the bursting of pipes due to water hammer,
surge tanks or stand pipes are provided at the end of pipes.
125. The selection of material for the pipes is done on
the following points
• Carrying Capacity of the pipes
• Durability and life of the pipe
• Type of water to be conveyed and its corrosive
effect on the pipe material.
• Availability of funds
• Maintenance cost, repair etc..
• The pipe material which will give the smallest
annual cost or capital cost will be selected,
because it will be mostly economical.
127. Following types of pipes are commonly Used
• Cast Iron Pipes
• Wrought Iron pipes
• Steel Pipes
• Concrete Pipes
• Cement lined Cast Iron Pipes
• Plastic or PVC pipes
• Asbestos cement pipes
• Copper and lead pipes
• Wooden pipes
• Vitrified Clay pipes
128. • Out of the types mentioned, plastic or PVC
and Asbestos cement pipes, wooden pipes are
not generally used for conveyance of water.
• They are used in house drainage or water
connection within individual house.
129. • Cast – Iron Pipes are mostly used in water supply
schemes. They have higher resistant to corrosion,
therefore have long life about 100 years.
• Cast Iron pipes are manufactured in lengths of 2.5
m to 5.5 m.
• The fittings of these pipes are also manufactured
in sand moulds having core boxes.
• These fittings are also weighed, coated with coal
tar and finally tested.
• Cast-Iron pipes are joined together by means of
Bell and Spigot, Threaded or flanged Joints.
131. Advantages of CI Pipes
• Ease in jointing the pipes
• Can withstand high Internal pressure
• Have a very long design life. (100 years)
• They are less prone to corrosion.
Disadvantages of CI Pipes
• They are heavy and difficult to transport
• Length of pipe available as less (2.5 to 5.5m) so
more joints are required for laying the pipes so
chances of leakage also Increases.
• They are brittle so they break or crack easily.
132. Wrought Iron Pipes
• Wrought Iron Pipes are manufactured by rolling the flat
plates of the metal to the proper diameter and welding the
edges.
• If compared with cast Iron, these are more lighter, can be
easily cut, threaded and worked, give neat appearance if
used in the interior works.
• But it is more costly and less durable than cast iron pipes.
These pipes should be used only inside the buildings, where
they can be protected from corrosion.
• Wrought Iron pipes are joined together by couplings or
screwed and socketed joints.
• To Increase the life of these pipes sometimes these are
galvanized with zinc.
134. Steel pipes
• The Construction of these pipes
is similar to wrought iron pipes,
it is occasionally used from main
lines and at such places where
pressure are high and pipe
diameter is more.
• Steel pipes are more stronger,
have very light weight and can
withstand high pressure than
cast iron pipes.
• They are also cheap, easy to
construct and can be easily
transported.
135. • The disadvantages of these pipes is that they cannot
withstand external load, if partial vacuum is created by
emptying pipe rapidly, the pipe may be collapsed or
distorted.
• These pipes are much affected by corrosion and are costly
to maintain The life of these pipes is 25 to 50 years, which
is much shorter as compared to cast Iron Pipes Steel pipes
are not used in distribution system, owing to the difficulty
in making connections.
• The joints in steel pipes may be made of welding or
riveting, longitudinal lap joints are made In riveted steel
pipes up to 120 cm dia.
136. Concrete Pipes
• These pipes may be
precast or Cast-in-situ
plain concrete pipe may be
used at such places where
water does not flow under
pressure, these pipes are
jointed with Bel &Spigot
Joints.
• Plain Concrete pipes are
up to 60 cm dia only,
above it these are
reinforced.
137. Advantages of R.C.C Pipes
• Their life is more about 75 years
• They can be easily constructed in the factories or at site
• They have least coefficient of thermal expansion than other types
of pipes . Hence they do not require expansion joints
• Due to their heavy weight, when laid under water, they are not
affected by buoyancy, even when they are empty.
• They are not affected by atmospheric action or ordinary soil under
normal condition.
Disadvantages of R.C.C Pipes
• They are affected by acids, alkalis and salty waters
• Their repairs are very difficult.
• Due to their heavy weight, their transportation and laying cost is
more.
• It is difficult to make connections in them
• Porosity may cause them to leak.
138. Various types of Joints which are mostly used, are
as follows
• Spigot and Socket Joints or Bell & Spigot Joints
• Expansion Joints
• Flanged Joints
• Mechanical Joints
• Flexible Joints
• Screwed Joints
• Collar Joints
• A.C. Pipe Joints
139. Spigot and Socket Joints
• This types of joints is mostly
used for cast iron pipes.
• For the construction of this
joint the spigot or normal end
of one pipe is slipped in
socket or bell mouth end of
the other pipe until contact is
made at the base of the base
of the bell.
