civil vi environmental engineering i [10cv61] notes

8/16/2019 Civil Vi Environmental Engineering i [10cv61] Notes

1/142

Environmental Engineering – I 10CV61

SJB Institute of Technology, Department of Civil Engineering Page 1

ENVIRONMENTAL ENGINEERING-I

Subject Code : 10CV61

Part - A

Unit - 1

INTRODUCTION: Human activities and environmental pollution. Water for various beneficial

uses and quality requirement. Need for protected water supply.

2 Hours

DEMAND OF WATER : Types of water demands- domestic demand indetail, institutional andcommercial, public uses, fire demand. Percapita consumption – factors affecting per capita

demand, populationforecasting, different methods with merits &demerits- variations indemand

of water. Fire demand – estimation by Kuichling‟s formula,Freeman formula & national board of

fire underwriters formula, peakfactors, design periods & factors governing the design periods

6 Hours

Unit - 2SOURCES: Surface and subsurface sources – suitability with regardto quality and quantity.

3 Hours

COLLECTION AND CONVEYANCE OF WATER : Intake structures – different types ofintakes; factor of selection and location of intakes.Pumps- Necessity, types – power of pumps;

factors for the selectionof a pump. Pipes – Design of the economical diameter for the risingmain;

Nomograms – use; Pipe appurtenances.

6 Hours

Unit – 3

QUALITY OF WATER : Objectives of water quality management.wholesomeness&

palatability, water borne diseases. Water qualityparameters – Physical, chemicalandMicrobiological.Sampling ofwater for examination. Water quality analysis (IS: 3025 and IS:

1622)using analytical and instrumental techniques. Drinking waterstandards BIS & WHOguidelines. Health significance of Fluoride,Nitrates and heavy metals like Mercury, Cadmium,

Arsenic etc. andtoxic / trace organics.

6 Hours

Unit – 4WATER TREATMENT: Objectives – Treatment flow-chart. Aeration - Principles, types of

Aerators.

2 Hours

SEDIMENTATION: Theory, settling tanks, types, design. Coagulantaided sedimentation, jartest, chemical feeding, flash mixing, and clariflocculator.

4 Hours


2/142



Part - B

Unit - 5

FILTRATION: Mechanism – theory of filtration, types of filters, slowsand, rapid sand and pressure filters including construction, operation,cleaning and their design – excluding under

drainage system – backwashing of filters. Operational problems in filters.6 Hours

Unit - 6

DISINFECTION: Theory of disinfection, types of disinfection,Chlorination, chlorine demand,

residual chlorine, use of bleachingpowder. UV irradiation treatment – treatment of swimming pool water

4 Hours

SOFTENING – definition, methods of removal of hardness by limesoda process and zeolite

process RO & Membrane technique.

3 Hours

Unit - 7

MISCELLANEOUS TREATMENT: Removal of color, odor, taste, useof copper sulfate,

adsorption technique, fluoridation anddefluoridation.

4 Hours

DISTRIBUTION SYSTEMS: System of supply, service reservoirs andtheir capacity

determination, methods of layout of distribution systems

Unit - 8

MISCELLANEOUS: Pipe appurtenances, various valves, type of firehydrants, pipefitting,

Layout of water supply pipes in buildings.

TEXT BOOKS:

1. Water supply Engineering – S.K.Garg, Khanna Publishers

2. Environmental Engineering I – B C Punima and Ashok Jain3. Manual on Water supply and treatment – CPHEEO, Minstry ofUrban Development, New

Delhi.

REFERENCES1. Hammer, M.J., (1986), Water and Wastewater Technology – SIVersion, 2

ndEdition, John

Wiley and Sons.

2. Karia, G.L., and Christian, R.A., (2006), Wastewater Treatment – Concepts and DesignApproach, Prentice Hall of India Pvt. Ltd.,New Delhi.

3. Metcalf and Eddy, (2003), Wastewater Engineering, Treatmentand Reuse ,4th Edition,

Tata McGraw Hill Edition, Tata McGraw HillPublishing Co. Ltd.4. Peavy, H.S., Rowe, D.R., and Tchobanoglous, G.,(1986),Environmental Engineering –

McGraw Hill Book Co.

5. Raju, B.S.N., (1995), Water Supply and WastewaterEngineering, Tata McGraw Hill Pvt.Ltd., New Delhi.


3/142



Table of Contents

Unit – 1 (06 – 25)

INTRODUCTION 1. Human activities and environmental pollution.

2.

Water for various beneficial uses and quality requirement.3. Need for protected water supply.

DEMAND OF WATER 1. Types of water demands- domestic demand in detail, institutional and commercial, public

uses, fire demand.2. Per capita consumption – factors affecting per capita demand,

3. population forecasting,

4. different methods with merits &demerits- variations in demand of water.

5. Fire demand – estimation by Kuichling‟s formula, Freeman formula & national board offire underwriters formula,

6. peak factors,

7.

design periods & factors governing the design periods

Unit – 2 (26 – 49)

SOURCES 1. Surface and subsurface sources

2. Suitability with regard to quality and quantity.

COLLECTION AND CONVEYANCE OF WATER :1. Intake structures – different types of intakes;

2. factor of selection and location of intakes.3. Pumps- Necessity, types – power of pumps; factors for the selection of a pump.

4. Pipes

5.

Design of the economical diameter for the rising main;6. Nomograms – use;7. Pipe appurtenances.

Unit – 3 (50 – 69)

QUALITY OF WATER 1. Objectives of water quality management.2. wholesomeness& palatability, water borne diseases.

3. Water quality parameters

Physical

Chemical andMicrobiological.4.

Sampling of water for examination.

5. Water quality analysis (IS: 3025 and IS: 1622) using analytical and instrumental

techniques.

6. Drinking water standards BIS & WHO guidelines.7. Health significance of Fluoride, Nitrates and heavy metals like Mercury, Cadmium,

Arsenic etc. and toxic / trace organics.


4/142



Unit – 4 (70 – 99)

WATER TREATMENT 1. Objectives2. Treatment flow-chart.

3. Aeration - Principles, types of Aerators.

SEDIMENTATION 1. Theory

2. Settling tanks, types, design.

3. Coagulant aided sedimentation4. Jar test

5. chemical feeding

6. flash mixing

7. clariflocculator.

Unit - 5

FILTRATION (100 –

118) 1. Mechanism – theory of filtration2. Types of filters, slow sand, rapid sand and pressure filters including construction3. Operation, cleaning and their design

4. Back washing of filters

5. Operational problems in filters.

Unit – 6 (119 – 132)

DISINFECTION 1. Theory of disinfection

2. Types of disinfection

3.

Chlorination, chlorine demand, residual chlorine4. Use of bleaching powder.

5. UV irradiation treatment – treatment of swimming pool water

SOFTENING 1. Definition

2. Methods of removal of hardness by lime soda process

3. Methods of removal of hardness by zeolite process

4. Methods of removal of hardness by RO &Membrane technique.

Unit – 7 (133 – 137)

MISCELLANEOUS TREATMENT 1.

Removal of color, odor, taste2. Use of copper sulfate, adsorption technique3. Fluoridation and defluoridation.

DISTRIBUTION SYSTEMS 1. System of supply

2. service reservoirs and their capacity determination

3. methods of layout of distribution systems


5/142



Unit – 8 (138 – 142)

MISCELLANEOUS 1. Pipe appurtenances2. Various valves

3. Type of firehydrants

4.

Pipefitting,5. Layout of water supply pipes in buildings.


6/142



Unit1 - INTRODUCTION

Water is a chemical compound and may occur in a Liquid solid gaseous form. All these

three Forms of water are extremely useful to man, full filling his basic necessities of life.No life

can exist without water since water is as essential for life. It has been estimated of water is

absolutely essential not only for survival of human being but also for animals, plants and all

other living creatures further it is necessary that the water required for their needs must be safe in

all respects and it should not contain unwanted impurities or harmful chemical compounds or

bacteria‟s in it therefore in order to ensure the availability of sufficient quantity of good quality

water it becomes imperative in modern society to plan and build suitable water supply schemes

which will provide potable (safe for drinking) water to the varies sections of community in

accordance with then demands and requirements.

The provision of such a scheme shall ensure a constant and a reliable water supply to that sectionof the people for which it has been designed such a scheme shall not only help in supplying safe

whole some water to the people for drinking cooking, bathing, washing, etc.., so as to keep the

diseases away and there by promoting better health, but would also help and thus helping in

maintaining better sanitation and beautification of surroundings. Besides promoting overall

hygiene and public health it shall ensure a safety against fire by supplying sufficient quantity of

water to extinguish it. The existence of such a water supply scheme shall further help in

attracting industries and thereby helping in industrialization and modernization of the society and

consequently reducing unemployment and ensuring better living standards such schemes shall

therefore help in promoting health wealth and welfare of entire community as a whole.

Various important and pathogenic organisms (disease causing organisms) due to these diseases

like typhoid Asiatic cholera Amoebiasisgiavdisis etc..may spread. These diseases are called

WATER borne DISEASES and therefore it will be harmful to health.

The pathogenic organisms (pathogens) do not multiply in water like that in milk but they

do survive i.e water may be considered as a carrier for bacteria and not multiplier thus the control

of pathogens is possible by simple disinfection principles (process). (If we control the purity of

H2O completely, the chances of outbreak water borne communicable diseases will be much less).

Besides communicable diseases certain other diseases like goiter, dental flourosis and skeletalflourosis are attributable to chemical impurities present in water.


7/142



HUMAN ACTIVITIES AND ENVIRONMENTAL POLLUTIONIncreasing human population numbers are putting great pressure on many of these limited

resources and deplete those resources which cannot be renewed. Many different natural

processes occur within those ecosystems influencing humans. Some of these processes includeatmospheric quality. soil generation and conservation, energy flow, the water cycle, waste

removal and recycling. Human activities are altering the equilibrium involved in these natural processes and cycles. If these changes due to human activities are not addressed, the stability ofthe world's ecosystems may irreversibly affected. Humans damage ecosystems by harvesting

trees that are homes to hundreds of different organisms. We damage the atmosphere by releasing

greenhouse gases when we drive cars or use electricity. We pollute water with chemicals and

waste products from factories. We can't reverse the damage, but we can help prevent newdamage by changing our lifestyles to be less wasteful and more conservative with our resources.

I'd love to tell you all about it(I live very green) but it would take a long time. Basically, just

remember Reduce, Reuse, and Recycle. Any little change you can make does help the problem,

even if it's just a minor change like switching to energy saving lightbulbs.

POINTS TO BE CONSIDERED FOR A PROTECTED WATER SUPPLY

SCHEME (WSS)The following factors should be kept in view in water supply for particular place.

i) THE SOURCE: Source should be selected which may sufficiently provide the water

in all the seasons. The sources may be wells steams, natural lakes, deep ponds in

rivers, reservoirs, perennial rivers etc…

ii) QUANTITY OF WATER : It can be estimated by considering need for present

population and future population growth during the design period also some quantity

of water will be required for fire fighting, public conveniences street washings and

horticultural purposes. In addition to these some water is usually wasted by theconsumers. Thus the total quantity way of water may be estimated for a particular

locality considering all the above factors.

iii) CHECK CALCULATION: After the above calculations are completed, designer

should again confirm whether the source of water will provide the required amount of

water especially in summer season of the driest year.

iv) DISTANCE AND DIFFERENCE IN ELEVATION: The designer should see

distance and difference in elevation in a town with respect to source of water. As far

as possible the water should be under enough pressure in service pipes so that it mayreach upto 10-15m.

v) IMPOUNDING RESERVOIR : May only be provided if its provision at higher

elevation is not economical.

vi) QUALITY OF WATER : After this the quality of water should be tested the

treatment units should be installed according to degree of pollution in the source.


8/142



vii) METHODS OF PURIFICATION: The methods of purification of water for

drinking purposes may be divided into 5 parts viz.

a) SCREENING: in which the fine and coarse particles, rags, papers, etc… are

separated through fine and coarse screens. b) PLAIN SEDIMENTATION: in which the sedimentation of set liable solids in

large tanks is affected.

c) COAGULATION OR CHEMICAL PRECIPITATION: This is adopted whenthere is much turbidity. The alum solution is generally mixed in water and the

precipitation is formed which is later separated.

d) FILTRATION: in which water is passed through layers of stones and sand.

e) DISINFEC TION: in which the pathogenic bacteria are destroyed.

NOTE: In addition to these some special methods like softening, aeration, iron removal

etc….. are also resorted to remove colour, bad taste smell etc….

viii) SERVICE RESERVOIR : Pure water may be stored at a higher elevation in the town

which is called a service reservoir. From these reservoir the water may be supplied in

the hours of peak demand

ix) DISTRIBUTION SYSTEM: the water from the service reservoir is served to

consumers through a network of mains, sub mains, laterals called as distributionnetwork system.

ARRANGEMENT OF WATER SUPPLY (FLOW CHART OF WATER SUPPLY

SCHEME)

1- Intake structures

2- Pumping station

3- Screens

4- Coagulants dosing tank

5- Sedimentation tank

6- Filters

7- Chlorine dosing tank

8- Clear water reservoir

9-

Pumping station10- Overhead tank

11- Distribution network systems.


9/142



DEMAND FOR WATER

VARIOUS TYPES OF WATER DEMAND

Which planning a water supply scheme, it is necessary to find out not only the total yearly

water demand but also to assess the required average rates of flow (or draft) and the variations inthese rates. The following quantities are therefore, generally assessed and recorded.

i) Total annual volume (V) in liters or million liters.

ii) Annual average rate of draft in liters per day, i.e V/365

iii) Annual average rate of draft in liters per day per person i.eliters per capita per day orlpcd called PER CAPITA DEMAND (q) or RATE OF DEMAND.

iv) Average rate of draft in liters per day per service i.eV 1

×365 Noof services

v) Fluctuations in flows expressed in terms of percentage ratios of maximum orminimum yearly, monthly, daily or hourly rates to their corresponding average

values.

It is difficult to precisely assess the quantity of water demanded by the public, since there are

many variable factors affecting water consumption certain thumb rules and empirical formulas

are therefore generally used to assess this quantity, which may give fairly accurate results. The

use of a particular method or a formula for a particular case has therefore, to be decided by theintelligence and fore sightedness of the designer. The various types of water demands, which a

city may have, may be divided into the following classes.

i) Domestic water demandii) Industrial and commercial water demand

iii)

Demand for public usesiv) Fire demandv) Water required compensating losses in wastes and thefts.

As correctly as possible the total water demand of a particular section of the community, allthese demands must be considered and suitable provision made depending upon the needs of

those people for whom the water supply scheme is to be designed.

DOMESTIC WATER DEMAND: This includes the water required in private buildings for

drinking, cooking, bathing, lawn sprinkling, Gardening, sanitary purposes etc….

This amount varies according to the living conditions of the consumers on an average thisdomestic consumption under normal conditions in a Indian city is expected to be around 135

litres /day/person as per Id:1172,1971. The total domestic consumption generally amounts to 50-

60% of the total water consumption.


10/142



AVERAGE DOMESTIC WATER CONSUMPTION IN A INDIAN CITY

USE CONSUMPTION IN LPCD

Drinking 5

cooking 5

Bathing 55Washing of clothes 20

Washing of utensils 10

Washing and clearing of houses

and residences

10

30

TOTAL 135 lpcd

INDUSTRIAL AND COMMERCIAL WATER DEMAND

This includes the quantity of water required to be supplied to offices, Factories, different

industries, hospitals, hostels, etc…. This will vary considerably with the nature of the city andwith the number and types of industries and commercial establishment there is no direct relation

of this consumption with the population and hence the actual requirements for all industries

should be estimated. The water requirements for buildings other than residences as per isstandards are as follows.

Type of building Age consumption in

lpcd

1.Factoriesa) where bathrooms are required to

be provided b) where no bathrooms are required

to be provided

45

30

2.Hospitals (including laundry) per bed

a) Number of beds < 100

b) Number of beds > 100

340

450

3.Nurse homes and medical quarters 135

4.Hostels 135

5.Hotels (Per bed) 180

6.Restauvants (Per seat) 707.offices 45

8.Cinemas, Auditoriums and theatres (per

seat)

15

9.Schools

a) Day schools b) Residential school

45135


11/142



DEMAND FOR PUBLIC USES (MUNICIPAL CONSUMPTION)

This includes the quantity of water required for public parks, gardening, washing and

sprinkling on roads, use in public fountains etc…..

A nominal amount not exceeding 5% of the total consumption may be added to meet this

demand on an arbitrary basis or else the consumption of water for municipal purposes as given below may be considered.

PURPOSE WATER CONSUMPTION

Public parks 1.4 litres/m /day

Road watering 1-1.5 litres/m /day

Sewer cleaning 4.5 litres/head/day

Extinguishing for is very small in a year but the rate of consumption is large. The scheme should

provide the necessary peat demand of water for firefighting (although fire hydrants with separate

water mains at about 100-150m apart are provided) The water requirements for extinguishingfire depends on bulk, congestion and fire resistance of buildings. Indirectly we can say, it ,mainly

depends on the population. The minimum limit of fire demand is the amount and rate of supply

that are required to extinguish the largest probable fire that may occur in a town.

Which designing public water supply schemes the rate of fire demand is sometimes treated as afunction of population and is worked out on basis of certain empirical formulas which are as

follows.

EMPIRICAL FORMULAS FOR FIRE DEMAND

A) KULCHILING’S FORMULA : It states that

Q 3182 p

(at a demand rate to be maintained at hydrants of 1-1.5 kg km2 lasting

For 3 hrs) where

Q = amount of water required in litres/minP = population in thousands.

B) FREEMAN FORMULA : It states that

Q=1136.5 1010

2.8

p and

y p

Where

y = period of occurrences of fire in years

Q and „p‟ are same as above


12/142



C) NATIONAL BOARD OF FIRE UNDER WRITER’S FORMULA FCPA central congested high valued city

i. When population is 2,00,000

Q = 4637 1 . 1 p D D p

ii. When population is > 2,0,000 a provision for 54600 litres/ min may be made with an extra

additional provision of 9100 to 30400 litres/min for a second fire.

For a Residential City

1. Small low buildings = 2200 litres/min

2. Large and higher buildings = 4500 litres/min3.

High value Residences apartment and tenements = 7650-1350 litres/min4.

Three storeyed buildings = 27,000 litres/min

D) BUSTON’S FORMULA - It states that

Q = 5663 p All the above formulae suffer from the drawback, that they are not related with the type

of area served. These formulas therefore give equal results for industrial and non industrial areas,although the possibility of occurrence of a fire with of given duration is more for an industrial

area as compared to the non-industrial area.-

WATER REQUIRED TO COMPENSATE IN THEFTS, WASTES, etc..

It includes the water lost in leakage due to bad plumbing or damaged meters, stolen water

due to unauthorized water connections and other losses and wastes, etc…. These losses should betaken into account while estimating the total requirement. These losses can be reduced by careful

maintenance and universal metering. Even in the best managed water works this amount isusually taken as 15% of the total consumption.

DESIGN PERIOD

A Water supply scheme includes huge and costly structures like dams, reservoirs, treatmentworks, penstocks etc…., which cannot be replaced or increased in their capacities, easily and

conveniently for example. The water mains including distribution pipes are laid underground and

cannot be replaces or added easily without digging the road or disrupting the traffic. In order to

avoid these future complications of expansions, various components of w.s.s are purposely madelarger, so as to satisfy the community meets for a reasonable years to come. The future period or

the number of years for which a provision is made in designing the capacities of the various

component of the w.s.s. is known as DESIGN PERIOD. It should be neither too long nor shouldit be too short. Normally 20-30 years is considered for distribution system.

PER CAPITA DEMAND (RATE OF DEMAND) (Q)

It is the annual average amount of daily water required by one person and includes thedomestic use, industrial and commercial use, public use, wastes, thefts, etc…


13/142



=Total yearly water requirement of the citty in Litres

Per capita Demand in litres/day/head =365 Design population

365

V q

P

For an Average.Indian town. As per I.S recommendations the per capita demand may be taken as

given in table below.

USE CONSUMPTION (LPCD)

Domestic use 135

Industrial use 50

Commercial use 20

Civic or public use 10

Waste, theft. Etc… 55

Total 270 lpcd

The above figure or 270 lpcd when multiplied by the population at the end of the design periodshall give the total annual average water requirement of the city/day. When multiplied by 365

will give the volume of the yearly water requirement in litres.

Generally the per capita demand valuesranges between 10-300 lpcd. These variations in

total water consumption of different cities or towns depend upon various factors.

FACTORS AFFECTING PER CAPITA DEMAND

1. Size and type of city

2. Climatic conditions3. Class of consumers

4. Quality of water

5. Pressure in the distribution system6. Sewerage Facilities

7. System of supply

8. Policy of metering system

9.

Cost of water

PROBLEM ON RATE OF DEMAND

Work out the rate of demand of water for an average Indian city. Make your ownassumptions wherever necessary.

Soln: The total requirement of water for various purposes is worked out separately as under.


14/142


15/142



TIME IN HOURS.

Daily and hourly Fluctuations depend on the general habits of people, climatic conditions etc…

more water demand will be on Sundays and holidays due to more comfortable working, etc…. as

compared to other working days. Peak hours may be 6 a.m to 10a.m and 10a.m to 4.p.m

minimum flow and between 10.p.m to 4.a.m it is very less. The above graph shows the hourlyvariation in demand of water or rate of consumption 20% of average hourly demand

ASSESSMENT OF NORMAL VARIATIONS

The maximum demands (monthly, daily or hourly) are generally expressed as ratios of their

means. The following figures are generally adopted.

1. MAXIMUM DAILY CONSUMPTION is generally taken as 180% of the average,

thereforeMaximum daily demand(MDD) = 1.8 Average daily demand (^DD)

= 1.8 q

2. MAXIMUM HOURLY CONSUMPTION is generally taken as 150% of its average

hooray consumption of maximum day, there fore

Maximum hourly consumption = 1.5 (150%) Average hourly consumption

of the maximum day or of the maxm. Day.(Litres/day)

peak demand

1.5 (Litres/hr)24

1.81.5 (Litres/hr)

24

2.7(Litres/hr)

24

MDD

q

q

Therefore,

Maximum hourly consumption of the maximum day

= (2.7 Annual Average hourly demand)

The formula given by GOODRICH is also used for finding out the rather of peak demand

rates to their corresponding average values.

GOODRICH FORMULA P=180 0.10t

Where, P = % of annual average draft for the time„t‟ in days

T = Time in days from1

24 to 365


16/142



When t= 1 day (For daily variations)

P = 1800.10

1

P = 180%

180%

MDD

ADD

When t = 7 days (For weekly variations)

P = 180 (7)-0.10

P = 148%

148% MWD

AWD

T = 30 days (For monthly variations)P = 180 (30)

-0.10

P =128%

128%

Maxm monthly Demand128%

.

MMD

AMD

Avg MonthlyDemand

PROBLEMS

1. The design population of a town is 15000 Determine the Average daily, Maximum hourly

demand under suitable assumptions

Soln: Assuming Average percapita demand as 270 Lpcd

i. ADD = design population Avg. per capita demand

= 1500 270

= 4050000 Litres/dayADD = 4050 m

3/day

ii. MDD = 1`.8 Average daily demand

= 1.8 4050MDD = 7290 m

3/day

iii. Maximum hourly demand of maximum day= 2.7 Annual Avg. hourly demand

= 2.724

q


17/142



= 2.74050

24

= 455.625 m3/hr or

= 10935 m3/day

EFFECTS OF VARIATION

1. The sources of supplies such as wells etc… may be designed for MDD

2. The pipe mains taking water from the source upto the service reservoirs may be designedfor MDD.

3. The filter and OTHER UNITS at water treatment plant may also be designed for MDD.

Sometimes an additional provision for reserve is also made for break down and repairs

therefore they may be designed for twice the ADD instead of MDD.

4. The pumps may be designed for MDD plus some additional reserve (say twice the ADD)

When the pumps do not work for all the 24 hrs such as in small town supplies, thedesign draft should be multiplied by

24

Number of hours in the day foe which the pumps are running

5. The distribution system is generally designed for the maximum hourly demand of themaximum day or coincident draft whichever is more.

6. Service reservoirs are generally designed for 8 days consumption.

COINCIDENT DRAFT

It is extremely improbable that a fire may break out when water is being drawn by the consumers

at maximum hourly draft. Therefore for general community purposes, the total draft is not takenas the sum of maximum hourly demand and fire demand but is taken as the sum of MDD and fire

demand ort the maximum hourly demand whichever is more. The MDD when added to fire

demand for working out TD (Totaldraft) it is known as coincident draft.

COINCIDENT DRAFT = MAXM DAILY DEMAND (MDD) + FIRE DEMAND (FD)

Problem1.A water supply screen has to be designed for a city having a population of 1,50,000 Estimate

the important kinds of drafts which may be required to be recorded for an Avg. consumption of250Lpcd. Also record the required capacities of the major components of the proposed waterworks system for the city using a river as the source of supply. Assume suitable figures and data

where needed.

Soln:

i. Average daily demandADD = (per capita Avg consumption in Lpcd) population

= 250 150000


18/142



= 37500000 Litres/day= 37.5 10

6Litres/day

= 37.5 Million Litres/day or

ADD = 37.5 Mld

ii.

Maximum daily draftMay be assumed as 180% of annual average daily draft.

MDD = 1.8 37.5MDD = 67.5 Mld

iii. Maximum hourly demand of maximum dayMay be assumed as 270% of annual average daily draft.

MHD= 2.737.5

2424

MHD = 101.25Mldiv. Fire demand

Using national board of fire under writer‟s formula, when population isless than or equal to 2 lakhs we have

Q 4637 1 0.01

4637 150 1 0.01 150

49835.92 / min

71763724.35 / min

671.76 10 / min

71.76 .

p p

Litres

Litres

Litres

Q Mld

COINCIDENT DRAFT = MDD + Fire draft= 67.5 + 71.76

= 139.26Mld.

CAPACITY OF VARIOUS COMPONENTS

1. The intake structure for fetching water from the stream may be designed for MDD i.e for

67.5Mld.

2. The pipe mains carrying the water from the intake to the treatment plant and then to

service reservoir. May be designed for MDDRequired capacity = MDD (67.5 Mld)

3. The filters and other units at the treatment plant may be designed for MDD plus somereserve (say twice the ADD)

Required capacity = 2 ADD

= 2 37.5

= 75 ld.


19/142



4. The Lift pumps may be designed for twice the ADD = 2 37.5 = 75 Mld (Assuming pumps are operating for all the 24 hours)

5. The distribution system including the pipes carrying water from service reservoir to thedistribution system may be designed for coincident draft with fire or maximum hourly

demand, whichever is more.

The required capacity = 139.26 Mld.

POPULATION FORECASTING

When the design period is fixed, the next step is to determine population in various periods because the population of the towns generally goes on increasing. The population is increased by

births, decreased by deaths, increased or decreased migration. The correct present and past

population can be obtained from census office. The WSS are not designed for the present

population the future population expected by the end of the design period may be estimated byvarious methods. The method to be adopted to a particular town or city depends on the factors

discussed in these methods.

The various methods of forecasting the population are

1. Arithmetical increase method

2. Biometrical increase method

3. Incremental increase method

4. Decreasing rate of increase method or decreasing rate method

5.

Simple graphical method6. Comparative graphical method

7. Master plan method or Zoning method

8. Ration method or Apportionment method

9. Logistics curve method.

ARITHMETICAL INCREASE METHOD

This method is based upon the assumption that the population is increasing at a constant rate,ie. The rate of change of population with time is constant.

If the present population of a particular town is „P‟ and the average increase in population for

past decade „Ia‟ the future population „Pn‟ at the end of „n‟ decades will be

Pn = P+ nIa

This method gives low results for developing areas, which develop faster than the post this

method of limited value may be useful for smaller design periods or for old and very large cities


20/142



with no industries and which have practically reached their maximum development orapproaching saturation

GEOMETRICAL INCREASE METHOD

This method assures that the percentage increase in population from decade to decade isconstant. This method gives high results for young cities expanding at faster rates and useful forold developed cities. If the present population of the city is „P‟ and the Average percentage

increase/ decade „Ig‟ then the population „Pn‟ at the end of “n‟ future decades will be

Pn =100

n Ig

P I

INCREMENTAL INCREASE METHOD

This method is a combination of the above two methods and therefore gives the advantages

of both arithmetic and Geometric increase methods and hence gives satisfactory results. In thismethod the Average increase is first determined by the arithmetical increase method and to thisadded the average of the net incremental increase once for every future decade.

( 1)

2

n n p p nI L

n o a i

PROBLEMS

1. Estimate the population by 2001 by Arithmetic and geometric progression method using

the following census, which method is ideal and why?

YEAR 1951 1961 1971 1981POPULATION 19800 42000 75000 110000

Soln:

YEAR POPULATION INCREASE PER

DELADE

% INCREASE

PER DECADE

1951 19800 22200 112.12

1961 42000 33000 78.57

1971 75000 35000 46.67

1981 110000Ia = 30067 Ig = 79.116

I) By ARITHMETICAL INCREASE METHODThe population by 2001 is given by

P2001 = P1981 + nIa


21/142



n= 2 decadesIa = 30067

P2001 = 100000 + 2(30067)

P2001 = 170134

II)

By GEOMETRICAL INCREASE METHODThe population by 2001 is given by

P2001 = P1981 = 1100

n Ig

2

79.116110000 1

100

P2001 = 352908

In this case AIM is ideal because, GIM gives very high results.

2. The census record of a town is as follows

YEAR 1940 1950 1960 1970 1980

POPULATION 81420 125000 170000 220000 230000

Workout the populationafter three decades by AIM, GIM, and IIM

Solution:

YEA

R

POPULATIO

N

INCREASE/DECAD

E

%INCREASE/DECAD

E

INCREMENTA

L INCREASE

1940 81420 43580 53.52 1420

1950 125000 45000 36 5000

1960 170000 50000 29.41 40000

1970 220000 10000 4.55

1980 230000

Ia = 37145 Ig = 30.87 Ii = -11194

I) By ARITHMETICAL INCREASE METHODPopulation after 3 decades i.e by the year 2010

P2010 = P1980 + nIa

= 230000+3(37145)P2010 = 341435

II) By GEOMETRICAL INCREASE METHOD populationafter 3 decades

P2010 = P1980 = 1100

n Ig


22/142


23/142



227.056

100 1100

P2011 =258.29(In Thousands)

III) By INCREMENTAL INCREASE METHOD

P2001 = P1991 +Ia +Ii= 160+26.667-12.5

P2001 =174.167(In Thousands)

P2011 = P2001 +Ia +Ii= 174.167+26.667-12.5

P2011 =198.334 (In Thousands)

IIM is IDEAL because GIM and AIM have lorger values. IIM gives a constant value.

SIMPLE GRAPHICALMETHOD

In this method a graph is plotted from the available data, between time and population thecurve is then smoothly extended up to the desired year. The method, however, gives very

approximate results, as the extension of the curve is done by the intelligence of the curve is done

by the intelligence of the designer.

PROBLEM:

1.

Calculate the population at various decades like 2000, 2020, and 2040.

By GRAPH population in the year,

2000 = 603002020 = 65750

2040 = 70000

Comparative graphical methodIn this method the cities having conditions and characteristics similar to the city under

consideration are selected. It is assumed that the city under consideration will also develop in

similar fashion of the selected cities. The population growth curve of the city under consideration

is drawn using the available data as shown in the figure.

Decrease in sale of increases method or decreasing sale method

Simi rate of increases in poplin goes on reducing as a city reaches towards etc. saturationvalue this method which makes use of decreases in the % increases is wed & gives a rational

result in this method the average decreases in the increases is worked out & then subtracted from

the latest increases for each successive decade.

YEAR 1900 1920 1940 1960 1980

POPULATION 35000 40000 44000 49000 55000


24/142



10 10

( 10)

100n n n

Ig n Id P P P

Master plan or zoning method

By & metropolitan cities are generally not allowed to develop in a haphazard &

natural way but are allowed to develop only in planned ways The master plan prepared for suchcities, divides the city into zones & thus to separate the residential, commend & industrial area‟s

from each atThe poplin densities are also fixed. It is very easy to calculationdesign poplin using master

plan because it will give us as to when & where the given no of houses, industries etc..Would be

developed.

Ratio method & apportion method

In this method the cities poplin record is ex as %age

of poplin of the whole country.

At the feat, the rations of local to national poplin are worked out for past 4-5 decades. Agraph in plotted l/w tone & there ratios to design period to calculation future population.

Graph

If the poplin of a town is plotted w.r.t time, the curve so obtained under normal condition are beas in figure & is called as ideal growth curve or logistics curve

The rarely growth of the city is shown by IK & is an increasing rate ofdp

P dt

The growth l/w K

& M followsdp

dt = const

This transitional curve „KM‟ also pass through the point of inflection „L‟ Later the growth from

M to N shows the decreasing in rate ie sdp

P P ds where „P‟ is the poplin of town @ T from J

& Ps value of saturation

The „S‟ shaped curve JKLMN is logistic curve

10

0

0

0

1

log

1 log

s

se s

s

s

s

e

P P

P P H KPt

P

Now let

P P m

P z KP n

P P

m nt

Which is the required eq…


25/142



If 3 pairs of char values 0 P , 1 2& P P @ time 0 1 2, ,t t t which extend over the range of

0 1 2 10, & 2t t t t are known as the saturation value Ps

M & n can he found

2

0 1 2 1 0 22

0 2 1

0

0

0 5 1

10

1 1 0

2 ( )

2.3log

s

s

s

P P P P P P P P P P

P P m

P

P P P n

t P P P

2. The details of a town‟s population are given below.Find its population in 2001

Year 1961 1971 1981

Population 35000 78000 115000

sol0

P =35000 1 P =78000 2 P = 115000

0t =0 1 10t 2 20t

2

0 1 2 1 0 2

2

0 2 1

0

0

0 1

1 1 0

1

2 ( )138271

2.9506

2.3log

0.1338

1961 2001

40

1 log

136364

s

s

s

s

s

e

P P P P P P P

P P P

P P m

P

P P P n

t P P P

t

t

P P

m nt


26/142



UNIT 2 - SOURCES OF WATER SUPPLY

CLASSIFICATION OF SOURCES OF WATER SUPPLY

The various sources of water available on earth can be classified into the following two

categories

PRECIPITATION

Surface sources such as Sub surface sourcessuch as

1.

Lakes(natural) 1.Springs2. Streams and Rivers 2.Infiltration galleries

3. Storage(impounded)reservoir 3. Infiltration wells4. Oceangenerally not used for water supplies at present 4. Wells&Tubewells(Borewells)

SURFACE SOURCES are those sources of water in which water flows over the surface of theearth and is thus directly available for water supplies

NATURAL PONDS AND LAKES: The quantity of water available from pond or lake is

however generally small though they are not considered as principal sources of water supply. Itdepends on the catchment area of the Lake Basin, annual rainfall and geological formations.

The quality of water in lake is generally good and does not need much purification.Larger and older lakes however provide comparatively pure water then smaller and new lakes.

Self purification of water due to sedimentation of suspended matter bleaching of colour, etc…makes the lake water pure and better when compared to stream or river waters.

STREAMS AND RIVERS: The quantity or discharge of the streams is generally low,sometimes even go dry in summer season. Therefore they may be considered as source of water

supply only for small villages. The quality of water in streams is normally good except the first

runoff. But sometimes runoff water while flowing over the ground is mixed with silt, clay, sandand other mineral impurities. This can be removed in a sedimentation basin upto certain extent.

(Rivers are formed when the discharge of large number of springs and streams. Combine

together. Rivers (Perennial) are the most important sources of water for public w.s.s. Thereforemost of the cities are situated on the banks of the rivers the rivers may be perennial or non- perennial (seasonal). Perennial rivers flow throughout the year getting their waters during

summer from snow and from rain in winter. Perennial rivers may be considered as water supply

sources directly where asnon perennial rivers can be used as public water supplies by providingstorage barriers across these rivers.


27/142



IMPOUNDED RESERVOIRS: During summer the water which is flowing in the river may not be sufficient to feed the town and on the other hand during rainy season it may be difficult to

operate due to flood waters. Therefore hydraulic structures are constructed across these river

valleys forming impounded reservoirs.

The quality of water in these reservoirs is not much different from that of lake water while

top waters prove to develop algae, bottom layers of water may be high in turbidity Co 2, iron andmanganese and on occasions H2S.

UNDER GROUND SOURCES (OR) SUB-SURFACE SOURCESThey are nothing but sub-surface sources with regard to their quantity and quality aspect

rainwater percolating into the ground and escaping beyond the reach of vegetation and eithercollecting in underground basins or flowing underground in sub-surface streams constitutes a

ground water source. Generally ground water is clear and colorless but is harder than the surface water of the

region in which they occur. In lime stone formation, ground water is very hard and dispositivenature in pipe lines. In granite formations, they are soft. The water as it seeps down comes in

contact with organic and inorganic substances during its passage through the ground andacquires chemical characteristics representative of the starter it passes. Bacteria logically, ground

water is much better than surface water except where sub-surface pollution exists.

FACTORS” GOVERNING THE SELECTION OF A PARTICULAR SOURCE OF

WATERThe following important factors are generally considered.

1. The quantity of water available

2. The quality of water available3. Distance of the source of supply

4.

Elevation of source of supply5. Cost.

1. QUANTITY OF WATER AVAILABLE = Quantity of water available must be

sufficient to meet the various demands during the entire design period. If the availablesource found is not sufficient. The additional source which is available in the nearby

(vicinity) is considered.

2. QUALITY OF WATER AVAILABLE = water available must not be toxic, poisonous

or in any other way injurious to health.) It should contain minimum impurities so that

their removal does not require costly treatment processes.

3.

DISTANCE OF THE SOURCE = The source of supply must be near to the town in

order to minimize the length of conduits required to transport water.

4. COST = The selection of source should be such that the overall cost of water supply project is brought down to the minimum.


28/142



VARIOUS FORMS OF UNDER-GROUND SOURCES INFILTRATION GALLERY

Infiltration gallery or horizontal or nearly – horizontal tunnels constructed at shallow

depths (3-5m) along the bank of the river through the water bearing strata as shown in the figure.

They are sometimes called as horizontal wells.

These galleries are constructed of masonry walls with concrete roof slab and derive their

water from the aquifer by various drain pipes. These pipes are generally covered with gravel so

as to prevent the entry of sand particles into the pipe. These tunnels are laid at a slope and water

collected in them, is taken into a sump from where it is pumped to the treatment plant and

distributed to the public. These are very helpful when sufficient quantity of water is available just

below the ground level or so.

In order to obtain large quantity of water, a series of shallow wells are sunk in the banks of the

river. The wells are constructed of brick masonry with open joints and are closed at top and open

at the bottom. The water infiltrates through bottom sand bed and gets purified to some extent.For inspection a manhole cover is usually provided in roof slab.

These various infiltration wells are connected to a common sump well by porous drain

pipes. This sump well is called JACK WELL. The water from this jack well is lifted to the

treatment plant.

SPRINGS

A natural outflow of ground water at the earth surface is said to form a spring a perviouslayer sandwiched between two impervious layers gives rise to a natural spring. The springs are

generally capable of supplying very small quantities (amounts) of water and therefore generally

not regarded as sources of water supply.

FORMATION AND TYPES OF SPRINGS Springs are usually formed under 3 general conditions of geological formations

They arei. Gravity springs

ii. Surface springs

iii. Artesian springs.

YIELD AND SPECIFIC YIELD

The volume of ground water extracted by gravity drainage from the saturated water

bearing material is known as YIELD and when it is expressed as the ratio of the volume of water

that can be drained by the gravity to the gross volume of the soil then it is known as SPECIFIC

YIELDA Therefore

volume of water obtained by gravity drainageSPECIFIC YIELD=

gross volume of the soil.

Values of specific yield are dependent on soil” particle size, shape and distribution of pores and

degree of compaction of the soil.


29/142



SPECFIC RETENTION OR FIELD CAPACITY

The quantity of water retained by the materials against the pull of gravity is termed as

specific retention or field capacity. This is also expressed as the percentage of total volume of

materials drained.

AQUIFER AND THEIR TYPES

AQUIFER = An Aquifer is an water bearing stratum or formation capable of transmitting water

in quantities sufficient to permit development.

AQUICLUDE = It is an impermeable stratum that may contain large quantities of water but

whose transmission rates are not high enough to permit effective development.

AQUIFUGE = It is a formation that is impermeable and divide of water.

AQUIFERS may be considered as falling into two categories.

i. Unconfined or Non-Artesian Aquiferii. Confined or Artesian Aquifer, depending on whether or not the water table or free

water surface exists under atmospheric pressure.

i. UNCONFINED AQUIFER OR NON ARTESIAN AQUIFERThe top most water bearing stratum having no confined impermeable over burden

(Aquiclude) lying over it, is known as an unconfined aquifer or non-Artesian aquifer.

The ordinary gravity wells of 2-5m dia which are constructed to tap water from the top mostwater bearing strata i.e from unconfined aquifer are known as unconfined or Non Artesian wells.

The water levels in these wells will be equal to the level of water table. Such wells are thereforeknown as water table wells.

ii. CONFINED or ARTESIAN AQUIFERS

When an aquifer is confined on its upper and under surface by impervious rockformations and is also broadly inclined so as to expose the aquifer somewhere to the

catchment area at a higher level for the creation of sufficient hydraulic head, it is called a

confined or an artesian Aquifer. A well excavated through such aquifer yields water thatoften flown out automatically under the hydrostatic pressure thus even rise or gush out of the

surface for a reasonable height.

PERCHED AQUIFERIt is a special case which is sometimes found to occur within a confined Aquifer. If

within a zone of saturation an impervious deposit is found to support a body of saturated material

then this body of saturated material which is a kind of Aquifer is known as perched Aquifer. Thetop surface of the water held in this perched aquifer is known as perched water table.


30/142



SPECIFIC CAPACITY = Specific capacity of a well is the measure of the effectiveness of thewell and is defined as the yield of the well per unit draw down. Therefore

SPECIFIC CAPACITY =draw down

Q yield

L

Specific capacity of a well is not constant but decreases as discharge increases

WATER TABLE:- The uppermost layer of soil or top soil at ground level is generally pervious.

The rainwater which is directly percolated through this top soil is contained by it. The uppersurface of free water in top soil is termed as water table or ground water level. The water table is

the surface of a water body which is constantly adjusting itself towards an equilibrium condition.

If there were no recharge or outflow from the ground water in a basin, the water table would

eventually become horizontal.

WELLS

CLASSIFICATION OF WELLS The wells may be classified as

i. Open wellsii. Tube wells

i. OPEN WELLS or DUE WELLSSmaller amount of ground water has been utilized from ancient times by open wells.

They are generally open masonry wells having compensatively higher diameters and are suitable

for low discharge (18m3/hr). The dia of open wells may be 2-9m and they are generally less than

20m in depth. The walls of an open well may be built by brick or stone masonry or precast

concrete rings.

The open wells may be classified into the following 2 typesi. Shallow wells

ii. Deep wells

The nomenclature of shallow and deep is purely technical and has nothing to do with the actual

depth of the well. A shallow well might be having more depth than the deep well.

YIELD OF AN OPEN WELLThe term yield of the well is used to indicate the rater of with drawl of water without causing

failure of well. It is the rate at which a well can supply the water.The factors which influences the yield of an open well are:

1. Well dimensions

2. Location of nearby wells

3. Porosity of aquifers4. Quantity of water available in aquifers

5. Slope of water table


31/142



6. Coefficient of permeability of soil.7. Rate of pumping water.

CO-EFFICIENT OF PERMEABILITY (k)

It is defined as the velocity of flow which will occur through the total cross sectional area

of soil (or Aquifer) under a unit hydraulic gradient.

CO-EFFICIENT OF TRANSMISSIBILITYIt is defined as the rate of flow of water in m

3/day through a vertical strip of the aquifer of

unit width and extending the full sanitation height under unit hydraulic gradient at a temperature

of 600F.

T = BK

Where

B = Aquifer thickness

DARCY’S LAW

The percolation of water through soil was fist studied by darcy(1856) who demonstratedexperimentally that for laminar. Flow conditions in a saturated soil, the rate of flow or the

discharge per unit time is proportional to the hydraulic gradient.i.e Q = Ki.A

QV = = Ki

A

WHERE,Q = Discharge

K= Darcy‟s Co-efficient of permeability

i = hydraulic gradient

A = Total C/S area of soil

V = Flow velocity.

EXPRESSION FOR YIELD OF AN OPEN WELL OR DISCHARGE FROM AN

UNCONFINED AQUIFER

Let,H= depth of water before pumping

h= depth of water after pumping

i = slope of hydraulic gradient - dydx

r = radius of wellR = Radius of circle of influence

K= coefficient of permeability

S = draw dawn at the well.

Consider any point „P‟ on the draw down curve (cone of depression) whose co-ordinatesare(x,y). THEN from DARCY‟S law

Q = KM.Ax ix


32/142



WhereAx = Area of C/S at the saturated part of Aquifer at „P‟

Ax = (2 x)y = 2 xy

Ix = hydraulic gradient at „P‟ = dydx

Substituting „Ax‟ and „ix‟ in the above eqn. dy

Q = K.2 y .

dx2

ndx

Q k y dy x

Integrating between the limits „r‟ & „R‟ for „x‟ and (H,h) for „Y‟ we get.

2

2 2

2 2

10

dx2

log2

log ( / )

1.36

log ( / )

R H

r h

H

R

e r

h

e

Q k y dy x

yQ x R k

k H hQ

R r

k H hQ

R r

If there are two observation wells at radial distances „r 1‟ and „r 2‟ and if the depths of water in

them are „h1‟ and „h2‟respectively then

2 2

2 1

10 2 1

1.36

log ( / )

k h hQ

R r

YIELD OR DISCHARGE FROM A CONFINED OR ARTESIAN AQUIFERLet

B = thickness of the Aquifer in „m‟

2.72

log ( / )e

bk H hQ

R r

TEST FOR YIELD OF A WELLThe yield of an open well can be found or tested by the following methods

1. Constant level pumping test

a. Pumping in test b. Pumping out test

2. Recuperation test.


33/142



CONSTANT LEVEL PUMPING TESTIn this test the rate of pumping is so adjusted that water level in the well remains

constant. As and when the condition is reached the rate of inflow will be equal to the rate of

pumping since it is difficult to maintain constant level in the well this test is generally not

adopted to determine the yield.

RECUPERATION TESTIn the Recuperation test the water from the well is pumped at a faster rate and its level is

depressed to certain level is depressed to certain level pumping is then stopped. The time taken

for the water to come to its normal level (Recuperate) is recorded.Let,

H1 = initial depression head after pumping stopped (in m)

H2 = depression head in the well at a time(T) after pumping stopped(in m)

A = Sectional area of the well (m2)

C = specific capacity of the well in m3/hr/ m

2 of the area under in depression head

3 2110

2

2.303log m / hr / m(m )

A H C of Area

H T

Yield of the well Q = CH

PROBLEMS

1) During the recuperation test, the water level in an open well was depressed by 2.5m after pumping and is recuperated by 1.6m in 70mins. Calculate the specific yield of the well. Also

determine the yield from the well of 3m diameter under a depression head of 3.5m

Solution:

2

10

1

210

3

3 2

3

2.303C = log

2.303 2.54 log70 0.9

60

6.191 m / hr / m (m )

yield Q = ch

= 6.191 3.521.67m /

A H H T

C of area

Q hr

2) A 30cm dia well penetrates 25m below the static water table (SWT). After 24hrs of pumpingat 5400 lit/min, the water level in a test well at 90m is lowered by 0.53m and in a well 30m

away the draw down is 1.11m. What is the transmissibility of the aquifer.


34/142



For an unconfined aquifer, discharge2 2

2 1

2

10 1

2 2

2 1

210

1

2 2

10

2

1.36 ( )Q =

log

But, T = kh or k =

1.36 ( )=

log

1.36 (24.47 23.89 )25

5.490log

30

2.5762538.146

1.69 / min.

K H h

r

r

T H

T h h H

Qr

r

T

T

T m

3) Design an open well in fine sand for a yield of 0.004 cusecs under a depression head of 3.5m.

the value of „C‟ is 0.5m3/hr/ m

2 of area/m drawsone.

Solution:

Q = 0.004 m3/sec

Q = 14.4 m3/hr

C

A = 0.5 m

3/hr/m drawdown.

We have for the discharge,Q = CH

Q = C A H A

2

2

14.4 0.5 3.54

10.477

3.24

3.25

d

d

d m

d m

4) A 20cm well penetrates 30m below SWL. After a long period of pumping at a rate of

1800lit/min, the drawdown‟s in the observation wells at 12m and 36m from the pumped well

are 1.2m and 0.5m respectively.

i) Determine the transmissibility of aquifers

ii) The drawdown of the pump well assuming R = 300m.iii) Specific capacity of the well.

Solution:


35/142


36/142



Solution:

We have for an Artesian Aquifer.

10

10

10

3

10

2.72 ( )Q =

log

where

2.72 ( )

log

2.72 35 30 30 27

300log0.1

2464.11 /

102677.14 /

1

log

T H h

R

r T Kb

kb H hQ

Rr

Q m day

Q lit hr

Q R

r

(other things remaining the same)

„Q‟ be the yield of the doubled well „r‟ be the radius of the doubled well = 0.2m

110

1

10

10

1

10

1

log

log

300log102671.140.2300log0.1

112402.31 /

RQ r

RQr

Q

Q lit hr

PERCENTAGE INCREASE IN THE YIELD1

100

112402.31 102671.14100

102671.14

9.48%

Q Q

Q


37/142



COLLECTIONAND CONVEYENCE OF WATER

INTAKE STRUCTURES

Intakes or intake structures are masonry or concrete structures whose function is to

provide calm and still water, free from floating matter for water supply.Intakes consists of the opening, strainers or gratings through which the water enters and the

conduit for conveying the water, usually by gravity to a sump well. From the well the water is pumped to the treatment plant.

SELECTION OF A SITE FOR INTAKE CONSTRUCTIONWhile selecting a site for intakes, the points to be kept in mind are.

i) Intake work should provide good quality water so that its treatment may become less

exhaustiveii) Heavy water currents should not strike the structure directly

iii)

Approach to the intakes should be easyiv) As far as possible intakes should not be selected in the vicinity of sewage disposal

v) Selection of site should be nearer to the treatment plant so that it reduces the cost ofconveyance of water

vi) They should not be located in navigation channels

vii) In meandering rivers, the intakes should not be located on curves or at least on sharpcurves

viii) Intake must be located at a place from where it can draw water even during the driest

periods of the year.

ix) Site should be such as to permit greater withdrawal of water, if required of a futuredate.

TYPES OF INTAKESDepending on the source of water the intake works are classified as follows.

i. Lake intake

ii. River intakeiii. Reservoir intake

iv. Canal intake

For obtaining water from lakes mostly submersible intakes are used. These intakes are

constructed in the bed of the lake below the low water level so as to draw water in dry seasons

also. It consists of a pipe laid in the bed of the river, one end of which is provided with bell

mouth opening with fine screens. The water enters through the bell mouth opening and flowsunder gravity.

ADVANTAGESI. No obstruction to navigation

II. No danger from floating bodies

III. No trouble due to ice.


38/142



RIVER INTAKE

It is a circular masonry tower of 4 to 7 meter in diameter constructed along the bank of

the river at such place from where required quantity of water can be obtained even in the dry

period. The water enters in the lower portion of the intake known as sump well from penstocks

the penstocks are fitted with screens to check the entry of floating solids and are placed on thedownstream side so that water free from most of the suspended solids may only enter the lack

well. Number of pen stock openings is provided in the intake tower to admit water at differentlevels. The opening and closing of penstock values is done with the help of wheals provided at

the pump-house floor.

RESERVOIR INTAKE

It is mostly used to draw the water from earthen dam reservoir. It consists of an intake

tower constructed on the slope of the dam at such place from where intake can draw sufficientquantity of water 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 level. These all inlet pipes are connected to onevertical pipe Indies the intake well screens are provided at the mouth of all intake pipes to

prevent the entrance of floating and suspended matter in them. The water which enters thevertical pipe is taken to the other side of the dam by means of an outlet pipe. At the top of the

intake tower sluice values are provided to control the flow of water. The value tower is

connected to the top of the dam by means of a foot bridge gangway for reaching it.

CANAL INTAKE

Canal intake is a very simple structure constructed on the bank. It consists of a pipe placed in a brick masonry chamber constructed partly in the canal bank on one side of the

chamber an opening is provided with coarse screen for the entrance of water. The end of the pipeinside chamber is provided with a bell mouth fitted with a hemispherical fine screen. The outlet pipe caries the water to the other side of the canal bank

From where it is taken to the treatment plants one sluice value is operated by a wheel

from the top of the masonry chamber provided to control the flow of water in the pipe.

PUMPS AND PUMPING STATIONS

PURPOSE

I.

To lift the water from source to the treatment plant which is at higher level comparedto the source

II. To lift the treated water to the elevated tanks

III. To increase the pressure in the distribution system.

IV. To lift the water at the treatment plant if sufficient natural ground slope is notavailable as to cause gravitational flow between different units of treatment plants.


39/142



Classification of pumps

Based on their Principal of Based on the type Based on the type of operation

of power required service

i. Displacement pumps i.Electrically driven pumps i. Low lift pumps

ii.Centrifugal pumps ii. Gasoline pumps ii.High lift pumps

iii. Airlift pumps iii. Steam engine pumpsiii.Deep well pumps

iv. Impulse pumps iv.Diesel engine pumps iv. Boosters

v. Stand by pumps

Under most of the situations in water supply scheme, displacement and centrifugal pumps are

commonly used.

Displacement pumpsi. Reciprocating pumps

ii. Rotary pumps

PUMPING STATIONS

The location of a pumping station is primarily governed by the place where it is to recerive

water. The points to be kept in mind while selecting a suitable site are.

i. The site should be away from all the sources of contamination or pollution

ii. The site should be above the HFL of the river.

iii. Its future growth and expansion is easily possible

iv. Possibility of fire hazards is also to be considered

FACTORS AFFECTING THE SELECTION OF A PARTICULAR TYPE OF PUMP

1.

Capacity of pumps

2. Importance of WSS

3. Initial cost of pumping arrangement

4. Maintenance cost

5. Space requirements for locating the pumps

6. Number of units required


40/142



7. Total life of water required

8. Quantity of water to be pumped.

HEAD POWER AND EFFICIENCY OF PUMPS

The total head against which a pump works is made up of

i. The suction Head(Hs)

ii. The Delivery Head(Hd)

iii. The Head loss due to friction entrance and exit in the rising main(Hf )

The suction HEAD is the difference in elevation between the low water level and center line of

pump.

Delivery HEAD is the difference in elevation between the pump center line and point of

discharge

Total HEAD (H) =Hs+Hd+Hf The work done by the pump in lifting „Q‟ cumecs of water by a head(H) =WQH kg-m/sec.

Where,

W = Specific weight of water, 1000 kg/m3

Q = discharge to be pumped, m3/sec.

The water horse power of the pump is given byWHP(out put) = WQH/75

If „n‟ is the efficiency of the pump then

BRAKE HORSE POWER of the pump is given byBHP(INPUT) + WQH/75n

ECONOMICAL DIAMETER OF THE RISING (PUMPING) MAINThe economical diameter is a particular size of the pumping or rising main which while

passing a given discharge of water gives the total annual expense to be minimum.

If the diameter chosen is more than the economic dia, it will lead to higher cost of the pipe lineon the other hand, if the dia of the pipe is less than the economical dia, the increased velocity

will lead to higher friction headless and require more HP for the required pumping and the cost

of pumping shall be much more than the resultant saving in the pipe cost.

LEA FORMULAAn empirical formula given by LEA

Connecting the dia and discharge is given by

D = 0.97 to 1.22 Q

Where

D = economical diain‟m‟ Q = Discharge to be pumped in „cusecs‟


41/142



This relation gives optimum flow velocity varying between 0.8 to 1.35m/sec

FOR RIGOROUS ANALYSIS The total cost of pipe and pumping should be woeked out at

different assumed velocities (b/w 0.8 to 1.8m/sec) and a graph plotted between the annual cost

and the size of the pipe. The economical size is one which gives the least annual cost.

PROBLEMS

1. Determine the capacity of pump required for the following data

Population = 3lakhs

Daily demand of water = 140lpedWater level in the source = 100m

Level of the treatment plant = 125m

Pumping hours = 24hours a day

Dia of the Rising main = 90cmDistance between the source and

Treatment plant = 2kmCoefficient of friction = 0.01

Solution:

Total daily demand = 300000 140

(TDD) = 42000000 lit/dayTDD = 42000m

3/day

Discharge =42000

24 60 60

Q = 0.486m3/sec

Static head(Hs) = 125-100=25m

Head loss(Hf ) =

2

53

FLQ

d

2

5

0.01 2000 (0.486)

3 (0.9)

2.67 F H m

Total head = 25+2.67

H = 27.67m

BHP 75

1000 0.486 27.67

75 0.75

BHP 239.07

WQH

n

HP

2. A town with prospective population of 60000 is to be supplied with water from a river

4.8km away and 30.5m below the level of town. Design the economical section of rising


42/142



main and pumping unit where electrical power is available. Take water supply rate as150lped and f=0.01. Assume other relevant details.

Solution:

Total daily demand = 60000 150

(TDD) = 9000000 lit/day

= 9000m3

/dayTDD = 0.1042m

3/sec

Assuming 18hrs of pumping is done a day

3

0.1042 24

18

0.1389 / secm

The economical dia of rising main using LEA FORMULA

1.2

1.2 0.1389

0.4470.45 dia rising main

Q

mm

STATIC HEAD = 30.5M

Head loss(Hf ) =

2

53

FLQ

d

2

5

0.01 4800 (0.1389)

3 (0.45)

16.728 F

H m

Total head = 30.5+16.728Total head = 47.23m

Assuming efficiency of motor (nm) as 90%

Assuming efficiency of pump (nP) as 80%(Since electrical power is used)

Capacity of the pump required75

1000 0.1389 47.23

75 0.9 0.8

BHP 121.49

m p

WQH

n n

HP

3.

A centrifugal pump is to lift 4m

3

of water per sec to a height of 10m. Assuming total lossof head in pipes as 0.5m calculate the H.P of driving engine to run the pump it itsefficiency is 75%.

Solution:Q = 4m

3/sec

Total head = H = 10+0.5 = 10.5m


43/142



Assuming that the efficiency of driving engine is 90%

BHP75

1000 4 10.5

75 0.75 0.9BHP 829.63

P m

WQH

n n

HP

HYDRAULIC DESIGN OF PRESSURE PIPESDETERMINATION OF LOSS OF HEAD IN PIPES

The head loss in the pipe can be determined by the following formula:

a) MANNING‟S FORMULA This formula is usually used in determining the loss of head in the gravity conduits

2 2

4/3H

L

n V L

R

Where

n = Manning Rugosity (roughness) coefficientL = Length of pipe

V = Velocity of flow in pipeR = Hydraulic mean depth(HMD)

R =Wetted area

wetted perimeter

A

P

When circular pipe flowing full = A =2

4

d

P = d

R =

2

44

d

A d P D

When circular Pipe flowing halffull = = A =2

8

d

P = 2d

R =

2

8

42

d d

d

B) HAZEN WILLIAM’S FORMULA V= 0.85 CH R

0.63 S

0.54

CH= Hazen – william‟s coefficient (100 -140)

S = Slope

c) DARCY – WEISBACH FORMULA


44/142



2 2

5

4

2 3 L

FLV flQh

gd d

F = dimensionless friction factor, varies between 0.0075 to 0.03G = acceleration due to gravity

The appropriate value of „F‟ can be determined by the following empirical formula

a)FOR NEW PIPES

1 0.02 1

35d

b)FOR OLD PIPES

1 0.04 1

35d

WHERE, d = diameter of pipes

4.

A town population 1.5 lakh is to be supplied with water. The water works to be located ata lower elevation of 10m than the water level of the source. Find the size of the gravity

main to convey the water from the source to the water works which is located at adistance of 30km. The per capita demand of water is 150lit/day.

Solution:Qty of water required by the town = 150000 150

(TDD) = 22500000 lit/day

= 22500m3/day

TDD = 0.2604m3/sec

Assuming 12hrs of pumping per day

3

0.2604 24

12

0.5208 / secm

We haveDischarge = Area * Velocity

2

2

0.5208

4

0.663

Q AV

QV A

V d

V d

Using Darcy – Weis bach formula


45/142



Hf =

24

2

FLV

gd

Assuming of = 0.0075

22

2

2

5

0.6630.075 30000 ( )

H3 9.81

114.68 0.663

5.04

F

F

F

d

d

H d d

H d

Cosidering all the available head lost in overcoming the friction

5

5.04100

0.55d

d m

5. Determine the size of water main required to carry water from a source 2.15KM away from

the town the yield from the source is 1500lit/min Head lost in friction is 50.50m. Assume F =0.01

Solution

Discharge = 150Lit/min

= 1.5m3/min

Q = 0.025 m3/sec

We haveQ = AV

2

2

0.0254

0.0318

d V

V d

By, DARCY – WEISBACH FORMULA

HF =

2

42

FLV gd


46/142



2

2

5 5

0.03184 0.01 2150

50.502 9.81

8.77733 10

0.15441

15.44

16

d

d

d

d m

d cm

d cm

6. Water is to be supplied to a town of 3laks population from a source 2km away. Percapitademand of town is 180lped. If the town is situated at a higher elevation than the source and the

difference in elevation b/n the lowest water level in the source to the point of inlet at the water

war‟s is 30m, Determine the size of rising main and HP of the pump, The value of

Solution:Quantity of water required by the town = 500000*180

= 90 *106

litres/dayQ = 90MLDQ = 1.042 m

3/sec

V = 0.85 CHR 0.63

S0.54

2

0.630.54

3

1.042 1.2 1.0514

1.0542 0.85 110 5

4

1.495 10

688

Q AV d

S

S Lin CH - 110 and the pump works for 18hours

Solution:Qty of water required by the town = 300000 180

(TDD) = 54000000 lit/day

= 54000m3/day

Q = 0.625m3/sec

The discharge required for 18 hours of pumping per day

3

0.625 24

180.833 / sec

Q

Q m

Assuming the velocity of flow through pipe as 1.2 m/sec


47/142



2

0.833The c/s area of pipe (A) =

1.2

0.694

Q

V

A m

Dia of the rising main2

0.6944

0.94

d

d m

Using Hazen – William‟s equation

0.63 0.54

0.63 0.54

0.63 0.54

0.85

0.94

0.2354 4

0.85 110 0.235

1.2 0.85 110 0.235

1 587.84

H V C R S

Where

HLS

L

d R

V S

S

S in

1

587 2000

3.41 L

HLS

L

HL

H m

The head difference between LWL to water works point of inlet = 30m (static head)

Total head = 30 + 3.41 = 33.41m

Assuming the efficiency of the pump 75%

75

1000 0.8333 33.41

75 0.75

494.94

P

WQH BHP HP

n

BHP HP


48/142



CONVEYANCE OR TRANSMISSION OF WATER

VARIOUS TYPES OF PRESSURE PIPES

Depending on the construction material the pipes are of the following types

i.

C.I pipesii. Steel pipes

iii. RCC pipesiv. Hume steel pipes

v. Vitrified clay pipes

vi. Asbestos cement pipesvii. Miscellaneous pipes such as wrought iron pipes, PVC pipes.

PIPE JOINTS

For facilitating in handling transporting and placing in positions pipes are manufactured insmall lengths of 2-6m. These small pieces of pipes are then joined together after placing in

position, to make one continuous length of pipe the design of these joints mainly depend on the pipe material, internal pressures and the condition of support.

VARIOUS TYPES OF JOINTS are

i. Bell and spigot joint

ii. Expansion jointsiii. Flanged joint Mechanical joint

iv. Mechanical joint

v. Flexible joint

vi. Screwed jointvii. Collar joint

BELL AND SPIGOT JOINT

Design of pipes using monogramsFor the known design discharge. The pipe dia are assumed in such a way that the velocity of

flow varies from 0.6 to 3m/sec smaller velocity is assumed for pipes of smaller dia& larges

velocity for pipes of larger dia. The loss of head in the pipe is then cal using hydraulic formulas.

Out of these formulas Hagen – William formula is more commonly used. The use of Hagen

Williams formula however involves trial & error sol & in order to avoid this monogram of

Hagen Williams formula has been developed. These are in all four variably1.

Discharge Q in m3/min or lit/sec

2. Dia of pipe in mm

3. Loss of heat in m/1000m light of pipe

4. Velocity of flow in m/sec


49/142



If out of 4 quantities any 2 are known. The other 2 can be found from the monogram. Themonogram should in fig is valid for a value of roughness co-eff. C4 = 100. For any other value

of CH the head loss obtained from the monogram is multiplied by the factor CH/100

For example

Let the flow rate he 10m3

/min & the dia of pipe he 400mm. It is required to find the head fora pipe of 800 m length.

Mark a point A corresponding to Q = 10m3/min discharge line & point B corresponding to dia =

400m the dia line from point A & B by means of straight be prolong the line AB to cut the head

loss line

civil vi environmental engineering i [10cv61] notes

Documents