Public health engineering helping notes

1. LECTURE 9

2. • Collection Works
Dams ,Reservoir, Intake, Pumping station, Tube
wells.
• Purification Works
Sedimentation, Coagulation, Filtration, Disinfection,
Storage.
• Transmission Works
Conduits, Valves, Pumping Station, Gravity flow.
• Distribution Works
Pumping Station, Overhead reservoir, Feeders,
Mains, Pipes, Valves, Fire Hydrants.
Components of Water Supply
Scheme

3. Future Water Requirement
• Selection of per capita water consumption(WC)
• Future population forecast
• Design period

4. Economical Period of Design
“Number of years in future for which proposed facility
would meet the demand of the community “
• Length /Life of structure↑ - Design Period ↑
• Ease of extension ↑ - Design period ↓
• First cost ↑ -Design period ↑
• Rate of interest ↑ -Design period ↓
• Economy of scale ↑ -Design Period ↑
• Lead time ↑ - Design period ↑

5. 200 mm diameter water supply pipe 1km long serves 3000 persons;
Cost =Rs 300000 ;Cost/head=Rs100
400 mm diameter water supply pipe 1km long serves 12000 persons;
Cost =Rs 4800000 ;Cost/head=Rs 40
Economy of Scale

6. Design Periods & Design flows for various
Water Supply Facility
Facilities Design Period Design Flow
Large dams, impounding
reservoirs, transmission
main (conduit)
25-50 yrs Design capacity of impounding reservoir
Maximum daily demand
Conduits generally design for Maximum
daily consumption
Tube wells 5 yrs Peak hourly demand( without storage)
Maximum daily demand (with storage)
Water treatment plant 10-15 yrs Maximum daily demand
Pumping station 10 yrs Peak flow,Maximum+fire demand,Average
flow,minimum flow
Distribution system 25 yrs Maximum daily flow+fire demand
Peak hourly demand+ fire demand

7. Design Period
Problem 1 : A small community had a population of
65000 and 85000 in the year of 1995 and 2005
respectively. Assuming a geometric growth rate and
an average WC of 300lit/cap/day. Calculate the
design flow for the treatment plant and the
transmission main from current year. Select an
appropriate value for design period.

8. Design Period
Problem 2: The present population of a community
is 160000 increasing at a geometric growth rate of
0.043 per yr. The present water requirement of the
community are fully met by a number of tube wells
installed in the city. The average WC is 350l/c/d
using a design period of 15 yrs. Calculate the
number of additional tube-wells of 3.4m3/min
capacity to meet the demand of design period.

9. Sources of Water
Rainwater
dissolution of
CO2-H2CO3
Surface water
suspended solids(silt
clay) inorganic salts,
oils, organics,
nutrients, pesticides,
pathogens from
municipal, agricultural
runoff
Groundwater
Depth>35m
safe wrt microbial contaminants
Generally hard water

10. 1.Rain water
• Generally satisfactory
• Dissolution of carbon dioxide(H2CO3)
• Affected by collection system and storage conditions.
2.Surface water
• Include rivers, streams, lakes
• Generally soft water but may contains;
Significant load of suspended solids(SS) from land
erosion.
Color , odour(decaying vegetation)
Sources of Water

11. Heavy metals, inorganic salts, oils, organic
compounds, nutrients, pesticides, pathogens from
municipal, industrial and agricultural runoffs.
Lead, acid deposition from atmosphere.
Surface waters require elaborate treatment for use
as drinking water supplies.
3.Groundwater
•Ground water are generally safe with respect to
microbial concentration.
•Rich in total dissolved solids
•May contains naturally occurring subsoil heavy
metals such as As, F, Fe, Mn
Sources of Water

12. •Ground water may be polluted due to:
 Seepage of agricultural chemicals(NO3, Pesticides,
Insecticides)
Sanitary landfill leachates
Microbial pollution introduced by soakage pit
Industrial waste impounds may increase heavy
metals, salt and organic matter concentrations
•Ground water generally considered as hard water.
•Ground waters mostly require minimal treatment
(disinfection only) for use as drinking water.
Sources of Water

13. Collection of Surface Water
Intake
• Device or structure placed in a surface water
source to permit the withdrawal of water from
that source
Parts of intake: consists of three parts
1. An opening or strainer or grating through which
the water enters
2. A conduit , to convey water to sump
3. A sump or well from where water is pumped to
treatment plant.

14. Types of Intake
1. Single port:
 To draw water from a constant /fixed depth
2. Multi port:
 For selective draft for various depths
Factors Affecting Intake Type
• Source of supply:
 River , lake Single port
 Reservoir Multi port
Collection of Surface Water

15. Factors affecting Intake Structure
Water Availability
Sediment Transport
Environmental Regulation
Climatic Conditions
Initial and Maintenance Dredging
Operation and Maintenance

16. Reservoir intake

17. Lake intake(single port)

18. River intake (single port)

19. Intakes
• To be located away from pollution source
• Adequate submergence of the ports to avoid floating
debris and meet navigational requirements.
• Adequate elevation of conduit from the stream/lake
bed to avoid bed debris
• Entering velocity in conduit not to exceed 0.15 m/sec
to avoid trapping of excessive floating material,
sediment, ice, or fish.
Technical & Environmental Considerations

20. Technical & Environmental Considerations
Dams
• To be constructed at a location with a narrow gorge(narrow
entrance)
• Provision of solid foundation design
• Adequate height to provide required storage to meet draft
requirements at maximum daily flow.
• Upstream area to be free from pollution
• No discharges of industrial , municipal, and agricultural
runoffs.
• Watershed area to be heavily forested to avoid siltation in the
reservoir.

22. Components of Water Distribution System
• Pipes
• Fire Hydrants
• Valves
• Service Reservoirs (OHR)

23. Water Distribution System
Gravity distribution
• Natural slope, spring at peak (Muree, D.G.Khan)
• Economical and easy to install
• Site specific
• For fire protection, generally pumps are used.

24. Distribution by pump w/o storage
(Direct Pumping)
• Not practicable
• High electricity cost
• Operator role important(constant attendance)
• Power /tube well or fire breakdown problem
• Pressure variation
• Pumps are design at peak hourly flow
• Several pumps to conform varying demand

25. Pump with storage
• Excess water pumped during periods of low
consumption stored in OHR
• High consumption periods water drawn out to
augment pumped water
• Constant pumping rate
• Economical as pumping rate max. daily flow
instead of peak hourly flow
• More reliable due to fire fighting reserve

26. Pump with storage

27. Layout water distribution
Dead End or Tree System
• Irregularly developed cities
Advantages
• Easy design
• Less valve to cut off
supplies
Disadvantages
• Stagnation of water at
dead ends
• Large portions of cities for
repairs to be cut off

28. Grid –Iron System
• No stagnation
• More valves(costly)
• Difficult to design
• Expensive option
• More common in developed countries
Layout water distribution

29. Types of water supply
Continuous-fire demand
• No infiltration
• More water use
Intermittent
• Infiltration/Seepage (more chance of contamination)
• Storing water in dirty containers
• Taps carelessly kept open
• Consumers waste stored water to get fresh water
Pipelines are subjected to vacuum condition after supply hours, which can cause groundwater infiltration into the pipelines with
contamination of the supply or pipes deformation

30. Pipe Distribution System
Primary Feeders
• Main skeleton
• Water pumping to OHR and various parts of city
• In cities form loops, about 1 km apart .
• Looping allows continuous flow and adequate fire
flows.
• Provided with air relief valve & blow off valve
• Size >300mm ϕ

31. Secondary feeder
• Carry water from Primary feeder to cater for
normal supplies +firefighting(12”- Lahore)
• Smaller loops within loops of primary feeder
• In cities these are few blocks apart
• sizes are 200mm,250,300mm ϕ
Pipe Distribution System

32. Pipe Distribution System
Small distribution mains/Tertiary Feeder
• Form grid over areas and supply water to
fire hydrant and domestic supply lines (150
mm ϕ)
Domestic supply lines
• Generally the sizes are <100-150 mm ϕ

33. Consideration pipe layout
• Right of way: not intersect private property
• Not on mines/ military remains
• Not damage existing infrastructure(telephone lines,
sewerage pipes etc.
• For high points use air release valves and low points
blow off valve
• Avoid point of inflection
• When crossing river /stream better to attach with
bridge or if passing through stream keep narrowest
section or widest one if u want to bury pipes
• Concrete blocks at point of inflection(thrust blocks)

34. Laying of Distribution System
Excavation
• Min depth :is 1 m to protect the pipe against
traffic load
• Trench width: Sufficient width be provided for
proper laying & jointing of pipes.
Pipe Trench width
2” 1.5’
3” 2’
4” 2’
6” 2’

35. Laying of Distribution System
Laying & Jointing
• This include removal of pipes from vehicle,
conveying it to the storage in a yard or at street &
placing it in a trench & making proper joints.
Thrust blocks
• PCC blocks are provided at all tees, bends & dead
ends to nullify water thrust
Back Filling
• Back filling material should be free from large
stones.

36. OVER HEAD RESERVOIR

37. Terminology
Yield
The portion of precipitation on the watershed that
can be collected for use.
Safe Yield
It is the minimum yield recorded for given past
period.
Draft
It is the intended or actually quantity of water
drawn for use.

38. Capacity of Overhead Reservoir
Objective of storage
• Uniform pumping rate/day or desired
pumping rate
• Equalize demand over a period of high use or
when pumping discontinued
• Emergency(fire,tubewell changes,electrical
breakdown)

39. • Storage capacity=equalizing storage(15-30%
Max day.)+firefighting(2-10hrs)
+emergency(variable)
• Public Health engineering Department (PHED)
recommended storage capacities for
Electric pumps – 1/6 th of avg. daily
consumption
 Diesel Pumps - ¼ th of avg. daily
consumption
Capacity of Overhead Reservoir

40. Determination of Required Equalization
Storage
Mass Diagram
•Graphical representation for finding the storage
in reservoir.
•Also called Ripple diagram
•Mass diagram present the accumulated total
discharge as a function of time.
•For mass diagram records of stream flow for
substantial period of time is required generally
more than 30 yrs.

41. Mass Diagram
Draft

42. Reservoir Storage
Problem 3: From the following record of average monthly stream
flows:
1) Determine the require reservoir size to provide a uniform flow(draft) of
11000 m3 /day
2) What will be the safe yield of the year in with storage reservoir for the
year.
Month Flow(m3X 106) Month Flow(m3X 106) Month Flow
(m3X 106)
1 0.18 8 0.08 15 1.01
2 1.02 9 0.07
3 1.32 10 0.04
4 0.51 11 0.1
5 0.87 12 0.26
6 0.67 13 0.2
7 0.19 14 1.10

43. Mathematical
• Add the highest positive figure to the highest
negative figure, ignoring the sign
Determination of Required Equalization Storage

44. Reversior Storage
Time Consumption
12MN-4AM 1.00
4AM-8AM 3.00
8AM-12N 3.55
12N-4PM 3.25
4PM-8PM 2.50
8PM-12MN 1.50
Problem 4: Water consumption during a typical day in a
city is given below in a table. Determine the equalizing
storage if pumping is uniformly extended over 4AM to
4PM.

45. TYPES OF WATER SUPPLY
PIPES

46. Water Supply Pipes
• Various types of pipes are available for the
construction of water supply network.
• The following points should be considered for
selection;
Carrying capacity
Durability
First cost
Maintenance cost
Type of water to be conveyed

47. Types of Water Supply Pipes
1. Cast Iron Pipes:
• Most widely used for city water supply
• Average life of pipes 100 yrs
• Corrosion (tuberculation)may reduce its capacity by
70%,must be lined with cement or bitumen
• Roughness coefficient (C)for new pipe is 130
• Roughness coefficient (C) for old pipe is 100

48. 2. Steel Pipes:
• Contains less carbon than cast iron pipe
• Average life is 25-50 yrs
• Frequently used for trunk mains
• Difficult to make connections, hence seldom used
for water distribution
• Much stronger and lighter than cast iron pipes
• Cheaper than cast iron pipes
• Cannot withstand vacuum, hence collapse
• Highly susceptible to corrosion, hence high
maintenance charges required.
Types of Water Supply Pipes

49. 3. Ductile Pipes:
• Similar to CI pipes except increased ductility(it is the
property of a metal of being capable to be drawn
out into wire)
• Ductile iron is produced by adding a controlled
amount of Mg into molten iron of low sulphur and
phosphorus content
• Stronger, tougher and more elastic than CI.
• More expensive than CI.
Types of Water Supply Pipes

50. 4. Galvanized Iron Pipes:
• Produced by dipping CI pipes in molten zinc
• Resistant to corrosion
• Mainly used for plumbing
• Maximum dia 6 inches
5. Concrete Pipes:
• Usual size of RCC pipes 400 mm and above
• Not subjected to corrosion
• Manufactured at or near site
• Average life of pipe is 75 yrs
• Roughness coefficient is between 138 to 152
Types of Water Supply Pipes

51. 6. Asbestos Cement Pipes:
• Sizes available between 100mm-600 mm
• Average life – 30 yrs
• Immune to actions of acids, salts, soil, corrosion
• Less pumping cost due to less friction
• Roughness coefficient is equal to 140
7. Poly vinyl chloride Pipes:
• Mainly used for domestic plumbing
• Easy to install , easy to handle
• Cheaper in material cost
• Weak to sustain load, piling
• Only available upto 350mm dia size
• Expected life – 25 yrs
• PVC becomes brittle when placed in sunlight
Types of Water Supply Pipes

52. Valves
Purpose:
1. Regulate flow
2. Regulate pressure
3. Cut off supply for repair purpose
Location of Valves:
• Two valves at each intersection
• One valve at fire hydrant
• One valve after each 400m length of pipe
• On average 8 valves/km of main

53. Types of Valves
1.Gate Valve(sluice valve)
• Used to shut off water supply
mains for repair
• Generally placed at street corners
where lines intersect.
2.Global Valve
• Used in the plumbing system on
smaller pipes.
• They create lot of head loss

54. 3.Check Valve
• Uni-directional flow
• Discharge side of pump to
reduce water hammer effect
(pumping stations)
Types of Valves

55. 4.Butterfly Valve
• Used in filter plants and high pressure distribution
systems.
• Shut off very slowly to avoid water hammer.
Types of Valves

56. 5.Pressure Regulating Valve
• Reduce pressure d/s side to any desired
magnitude(60 psi)
• Spring and adjustable diaphragm in order to increase
or decrease the water pressure within the water
supply service
Types of Valves

57. 6.Air Relief Valve
• It allows the accumulated air in the pipe to escape
• It also allows the external air to enter the pipe to
break the vacuum.
• Placed at high points of the line
Types of Valves

58. 7.Blow off Valve
• Used to drain a line, or to remove
accumulated sediments
• Located at low points.
.
Types of Valves

59. 8. Altitude Valve
• Close automatically a supply line to an
elevated tank when full
• differential in forces between a spring load
and the water level in the reservoir.
• When the force of the spring is overcome by
the force of the reservoir head, the pilot
closes the main valve
• Desired high water level set by
adjusting the spring force
Types of Valves

60. Fire hydrants
• Atleast 2 hose outlets and
larger pumper outlet
• Located at street intersection
1-2 m from the edge of road
1m3/min
0.5 m