Source of water Surface source Rivers and Streams

Source of water Surface source Rivers and Streams Sub surface or GW source Lakes Ponds Springs Artesian wells Impounding reservoir Wells Dug wells Shallow wells Infiltration galleries Infiltration wells Tube wells Deep wells Intake works Treatment works Plain sedimentation Sedimentation with coagulation Filtration Disinfection Miscellaneous treatment Distribution system Gravity system Pumping system Service reservoir Dual system Service main Branches Consumer Waste water

Quality of water q Water during precipitation itself it carries some amount Ø Ø Ø of physical, chemical, or biological impurities. During the runoff also it pick up some dissolved particles of soil, garbage, sewage, pesticides, other human or animal waste or chemical. During passage through the soil before joining water table though the water gets filtered out the suspended particles, some mineral may dissolve in it. Note → Lesser amount of iron, calcium, magnesium, fluorine etc. are useful for drinking but larger amount make it unfit for drinking Presence of toxic or poisonous substances such as arsenic, barium, cadmium, chromium, cyanides, lead, etc. →harmful even in very low quantities Brackish water → presence of salts

Quality of water - contd Analysis of water ↕ Physical Chemical Biological Radiological ↕ ↕ Turbidity Total solids Bacteria Radium 226 Colour p. H value Viruses Radium 228 Taste and odour Hardness Plankton Radon Temperature chloride content Algae Uranium Specific conductivity Nitrogen content Fungi Gross alpha activity Metals and other chemical substance Dissolved gases

Quality of wter-contd q Physical impurities v Turbidity →Dispersion of suspended solid particles such as clay, algae, fungi, minerals, organic and inorganic matters Ø Depends on concentration and fineness Ø Though not harmful →aesthetic and psychological effects q Measurements v Equipment → turbidity rod/Turbidimeter Ø Turbidity rod Ø When immersed in sample →Read aluminum rod when the platinum needle ceases to be seen Ø Unit → 1 mg finely divided silica dissolved in 1 litre of distilled water Ø Desirable below 5 units Ø Not objectionable up to 10 units

Quality of wter-contd v Jackson’s turbidimeter (JTU scale) →Light path eg: 10. 8 cm-200 JTU, 21. 5 cm -100 JTU, 72. 9 cm -25 JTU Ø Lake water → 25 JTU Ø Turbid water → 100 JTU Ø Disadvantage → Read up to 25 JTU v Baylis turbidimeter → Comparing sample and standard turbidity water v Commercial form → Nephlometer → NTU scale/FTU(Formazine)

Quality of wter-contd q Colour →Due to presents of colloidal or dissolved organic matter such as coloured soil, micro organism, algae etc. Ø Though not harmful →aesthetic and psychological effects →not suitable for washing industry Ø Unit → 1 mg platinum cobalt dissolved in 1. litre of water (cobalt scale) Ø Measurements → comparing sample with tubes (Nessler tubes) containing standard solutions v For drinking water → Ø Preferable-less than 10 units and maximum up to 20 units Ø Commercial form → Tintometer

Quality of wter-contd v Taste and odour → Due to presents of dissolved organic /inorganic matter (salts) gases such as CH 4, H 2 S, CO 2 etc. combined with organic matter, minerals such as Na. Cl, Iron compound, carbonates and sulphates of other elements, phenols etc. also contribute. v Measurements → By odour intencity Ø Unit → Threshold odour number →Dilution ratio (The number of times the sample is diluted) Ø Eg: 20 ml diluted to 100 ml →Threshold odour number= 5 Ø Max: permissible value → 3

Quality of wter-contd v Temperature →Desirable value = 10°C and Objectionable →Above 25°C v Specific conductivity →The total amount of dissolved salts can be measured by sp. conductivity v Measurements → sp. conductivity can be measured by equipment called dionic water tester v Unit: Micro-Mho → 1 amp. /1 volts Ø Total dissolved salts = A constant (0. 65 –depends on type of salt) * sp. Conductivity AT 25°C

Quality of wter-contd v Chemical analysis Total solids (suspended as well as dissolved solids) v Measurements → Ø Total solids→ evaporating the samples and weighing the residue Ø Suspended solids → Obtained by filtration Ø Dissolved solids → Total solid-Suspended solids Ø Desirable limits → 500 -1000 mg/lit

Quality of wter-contd v p. H value →Negative logarithm of H⁺ concentration v p. H scale → ` p. H =0 p. H =7 p. H =14 ↑ Max: acidity ←neutral water → max: alkalinity H₂O↔H⁺ + OH⁻ HCl ↔ H⁺ +Cl⁻ →Hydrogen ion concentration is more than 10^ - 7→ Acidic Na. OH ↔ Na⁺ + OH⁻ → Hydroxyl ion concentration is more than 7→Alkaline

Quality of wter-contd v Measurements → Colorimetric method → Colour comparator Electrolytic method → PH meter Causes of alkalinity → Bicarbonates of calcium and magnesium Ø Carbonate alkalinity → Carbonate of sodium, potassium, calcium and magnesium Ø Hydroxide alkalinity → Hydroxide of sodium, potassium, calcium and magnesium Ø Causes of acidity→ Presents of mineral acids, free carbon dioxide, sulphate of Iron and Aluminum Ø Ø v Ø

Quality of wter-contd v Hardness of water Ø It is the characteristics which prevents leathering of soap when used with water and usually due to the presence of calcium and magnesium salts. v Causes of hardness → Ø Temporary or carbonate hardness→ Due to the presents of carbonate and bicarbonate of calcium and magnesium → Removed by boiling Ø Noncarbonated or permanent hardness → Due to the presents of sulphate, chloride and nitrates of calcium and magnesium → Removed by special method of water softening

Quality of wter-contd v Classification of hardness→ Ø Up to 75 mg/lit → soft water Ø 75 -200 mg/lit → moderately hard water Ø Above 200 mg/lit → hard water v Desirable limit for drinking water → 75 to 115 mg/lit v Problems due to hardness → Ø Greater soap consumption Ø Scaling of boiler Ø Corrosion and incrustation of pipes Ø Food tasteless

Quality of wter-contd v Chlorides → Chlorides are generally present in water in the form of sodium chloride and may be due to the leaching of marine sedimentary deposits, pollution from sea water, industrial or domestic waste, etc. Ø Determined by titrating against std. silver nitrate solution with potassium chromate as indicator Ø Desirable limit → 250 mg/lit

Quality of wter-contd v Nitrogen → Ø It is the indicates the presents of organic matter in the water and may occur in the following forms → v Free ammonia → Ø First stage of decomposition Ø It indicates recent pollution un (decomposed) Ø Max: limit =0. 15 mg/lit v Albuminoid/organic nitrogen → Ø Second stage of decomposition Ø Free nitrogen is first removed by boiling Ø Then adding strong alkaline solution of KMn. O 4 and boiled to collect ammonia liberated Ø Max: limit =0. 30 mg/lit

Quality of wter-contd v Nitrites → Ø Partly decomposed stage of organic matter Ø Extremely dangerous Ø Presents not desirable Ø Determined by colour matching method → Sulphonic acid and naphthamine colour and is matched with std. concentration v Nitrates → Ø Fully decomposed organic matter Ø Presents are harmless Ø Normal limit = 45 mg/lit Ø Determined by colour matcing method → Phynol-disulphonic acid and potassium hydroxide develop colour and is matched with std. concentration

Quality of wter-contd v Metals and other chemical substances Ø Metals such as iron, manganese, copper, lead, barium, cadmium, arsenic, selenium, fluorine v Desirable limits → Ø Iron = 0. 30 mg/lit Ø Manganese = 0. 05 mg/lit Ø Copper → affects human lungs Ø Sulphate greater than 250 mg/lit → laxative effects on human system

Quality of wter-contd v Fluoride Greater than 1. 5 mg/lit, cause Fluorosis and less than 1 mg/lit, cause dental carries v Dissolved gases Ø Nitrogen, methane, hydrogen sulphide, carbon dioxide, and oxygen Ø Methane and hydrogen sulphide, even in small extent is not permitted Ø Hydrogen sulphide → imparts taste and odour

Quality of wter-contd v Biochemical oxygen demand → Oxygen consumed for 100% oxidation-prolonged process and 5 days BOD is determined v Determination → Ø Mix known volume of sample with known volume of distilled water saturated with known quantity of oxygen Ø 5 days incubation at 20°C Ø Determine the oxygen consumed by deducting the present quantity of oxygen from known quantity of oxygen Ø BOD 5 → Oxygen consumed * dilution factor

Quality of wter-contd q Ø Ø Ø v Ø Ø Ø Living organism in water Bacteria Protozoa Algae Plankton Funki Viruses Types of bacteria → Pathogenic –Disease causing-Harmful Eg: Salmonella typhi - Typhoid Salmonella paratyphi – Paratyphoid Vibrio cholera - Cholerae Mycobacterium tuberculosis - Tuberculosis

Quality of wter-contd v Non pathogenic – harmless - useful –decomposition etc. Ø Aerobic – Bacteria which can survive in presents of oxygen Ø Anaerobic - Bacteria which can survive in absents of oxygen Ø Facultative – Those which can survive with or without oxygen Ø Eg: Cocus → spherical Ø Diplococus → pairs Ø Streptococus → chain Ø Staphilococus → irregular colonies Ø Bacillius → rod like Ø Spirillum → spiral shaped Ø Vibro → curved

Quality of wter-contd v Protozoa → Ø Unicellular animals Ø Eg: Amoeboid – irregular shape, naked or shelled, single or colonial Ø Fagellate – lash like appendages Ø Ciliat protozoa – hairlike appendages v Problems: Form scum, unsightly deposit on porcelain utensils

Quality of wter-contd v Algae → Ø A type of plant, which grows in water and flourishes in presents of sunlight Ø Eg: Asterionella – Diatomaceae group Ø Volvox – chlorophyceae group Ø Anabaena – Cyanophyceae group v Problems: Taste and odour

Quality of wter-contd v Plankton → microscopic plants and animal life that either swim or float in water and serve as food for small sea creature v Problems: Taste and odour, colour, problems on filter bed, stain on porcelain fixtures, dye works, photographic cells etc. v Fungi → Plants which grows without sunlight and live on other plants or animals Ø Eg: Toastools Ø Removal –Chlorine treatment v Viruses →small agents compared to bacteria and some are not visible even under microscope

Quality of wter-contd v Analysis of bacteria → Ø Total count test, membrane filter technique and Bcoli test Ø Total count → Ø Mix 1 ml of sample in 99 ml sterilized water v To diluted 1 ml of sample, add 10 ml of agar gelatin Ø Keep in incubator, 37°C for 24 hrsor 20°C for 48 hrs Ø Count the number of colonies Ø Number of colonies * dilution factor – No. of bacteria per lit. of sample

Quality of wter-contd v Membrane filter technique Ø Sample is filtered in specially designed filter paper (80% porosity, aperture size of 5 -10 mµ) Ø Culture the filter paper with”M Endo’s medium, 37°C for 24 hrs Ø [M. End broth, LES Endo agar, 35°C, 20 hrs – coli form group] and [M-Fc broth, 44. 5°C, 22 hrs – fecal coli form] Ø Count colonies which give the presents of bacteria

Quality of water - contd q. B-coli test → Presumptive and confirmed test v Presumptive test Ø Take diluted sample in standard fermentation tube with “lactose broth” as culture media Ø Keep in the incubator, 37°C-24 -48 hrs Ø If gas produced indicates B-coli v Confirmed test Ø A sample of presumptive test is taken in to another std. fermentation tube containing ‘brilliant green lactose brile ‘as medium Ø Keep in incubator, 37° Ø If colour is formed, confirms-B-coli

QUANTITY OF WATER-MODULE-II Ø Before designing a water supply project, the water work Engineer should Ø Study or Survey about the demand of water Ø Study about availability(source) of water Let, V → Annual vol. of water → Annual avg. rate of draft → V/365 lit/day Annual avg. rate of draft person /service→ Annual avg. rate of draft ÷ (No. of person/services) in lit /day

QUANTITY OF WATER- CONTD Water supply project Survey of availability of water Analysis of demand of water Forecasting future population Analysis of percapita demand Total quantity of water

QUANTITY OF WATER- CONTD q Percapita demand→ It is the annual average amount of daily water required by one person and includes, the domestic use, industrial and commercial use, public use, wastes and theft etc. and is given by→ v Total yearly water requirement of the city in litres ÷ (365 * Design population) v To determine percapita demand we have to find out various purposes for which water is to be used Ø Ø Ø Ø Domestic Industrial Institutional Commercial Public Fire demand Loss & Waste

QUANTITY OF WATER- CONTD q Domestic demand →IS: 1172 -1993 Ø Cooking → 5 lit Ø Drinking → 5 lit Ø Bathing → 75 lit Ø Washing of clothes → 25 lit Ø Washing of utensils→ 15 lit Ø Gardening → 15 lit Ø Washing of room → 15 lit Ø Flushing → 45 lit v TOTAL→ 200 lit/person/ day Ø For low income group→ 135 lpcd Ø For high income group→ 250 lpcd

QUANTITY OF WATER- CONTD q Industrial demand v It depends on Ø Nature & magnitude of Industries Ø Economic prosperity of the city Ø Size of city Ø Future expansion of both the city & industries v On the average→ 50 lpcd v Max → 450 lpcd Ø Note: Some industry may have their own water supply arrangements

QUANTITY OF WATER- CONTD q Institutional & Commercial demand Ø Hospital, College, School, Railway station, Restaurant, Govt. offices etc. Ø On the average→ 20 lpcd Ø Max → 50 lpcd q Public demand Ø The consumption for public parks, gardens, sprinkling & washing of road, Drinking, fountain etc. Ø On the average→ 10 lpcd Or Ø 5% of total demand

QUANTITY OF WATER- CONTD q Fire demand Ø The damages due to fire may depend upon many things such as size of city, commercial establishment, Industrial establishment, population density of the city. Ø A separate service reservoir is required to meet fire demand Ø Fire hydrants are provided in the distribution system 100 to 150 m apart Ø The minimum pressure should be about 10 -15 m of water (100 -150 KN/m²) Ø Minimum 3 water jets are required for a singlefire. → Ø One for jetting on fired property Ø Other two on either sides each Ø the minimum discharge for one jet is → 1100 lit/min

QUANTITY OF WATER- CONTD q Problem: Estimate the quantity of water required for fire fighting for a city of 50 lakhs, if the number of fire per day is 6, with 3 hr duration v Quantity of water→ 6[3*1100*3*60] → 35, 64, 000 lit/day Percapita demand→ 35, 64, 000/50, 000→<1 lit/day Though the percapita demand is negligible, the quantity of water influence the design of distribution system For population above 50, 000→ Water in KL →√P*100 Where, P →population in thousands

QUANTITY OF WATER- CONTD q Thumb rule for determination of fire demand. v Hatchling's formula Ø Q→ 3, 182√P Where, Q →is in lit/min P →population in thousands v Freeman’s formula Ø Q→ 1136 [(P/10) + 10]

QUANTITY OF WATER- CONTD q National Board of fire underwriter’s formula. v When population below 2 lakhs Q→ 4637 √P [1 -0. 01√P] v When population more than 2 lakhs a provision of 54600 lit/minute, plus additional for second fire 9100 -36400 lit/min v For Residential city Ø (a) Small or low building → 2200 lit/min Ø (b) Large or high building → 4500 lit/min Ø (c) High Value apartments → 7650 -13500 lit/min Ø Three storied building in densely built section→ up to 2700 lit/min Ø Three storied building in densely build section up to 27000 lit/min.

QUANTITY OF WATER- CONTD q Buston’s formula Q→ 5663√P Ø Note: →In Indian condition, 2 hr storage is considered in design of standby units Ø All the above formula not consider the type of city (Zoning) Ø Actual , observed in Jabalpur city of India Q = 4360 R 0. 275 (t +12 ) 0. 757 Where, Q → in lit/min Ø R →Recurrence internal of fire(depends on Zoning, min→ 1 year) Ø t →time duration in minute (min→ 30 mints)

QUANTITY OF WATER- CONTD q Problem: The quantity of water required for fighting a fire of duration 2 hr with intervals of 3 years. t → 2 hr → 2 x 60 → 120 min R → 3 Q → 4360 R 0. 275 (t +12 ) 0. 757 → 4360 x 30. 275 (t +12 ) 0. 757 =146. 36 lit/min

QUANTITY OF WATER- CONTD q Demand for loss and waste Ø Normally, this is assumed as 15% of the total consumption q Factors affecting losses Ø Water tight joints Ø Pressure in distribution line. Ø System of supply. Ø Metering Ø Unauthorized connection

Quantity of water - contd q Factors affecting percapita demand Ø Climate condition →In summer season-more water requirements Ø Size of the city→ Cleaning, sewered city requires 5 times, Ind. &Comm. Estt. , affluent rich family etc. Ø Industries →more industries more water Ø Habit of the people →Rich and upper classmore water Ø Cost of water→ High cost-less water

Quantity of water - contd Ø System of supply →continues or intermittent Ø Policy of metering →min. tariff or based on consumption Ø Distribution pressure →High pressure-more loss (20 -30 m pressure→ 20 -30% loss) Ø Quality of water →Best quality-more consumption Ø Sewerage→ more consumption

Quantity of water - contd q Variation in demand v Hourly variation v Daily variation v Monthly variation v Seasonal Variation q Consider average daily demand → (q) Ø Max. hourly demand, 150% of the ave. value Ø Max. daily demand, 180% of the ave. daily→ Ø Max. monthly demand, 140% of the ave. value Ø Max. Seasonal demand, 130% of the ave. value Ø Total / Absolute max →[1. 5*1. 8*1. 4*1. 3] of ave. daily demand (q)

Quantity of water - variation in demand

Quantity of water - contd q Effects of variation in demand on capacity of various components Ø Source of Supply → Max. daily demand Ø Pumping main → Max. daily demand Ø Filter unit → Max. daily demand Ø Distribution → Max. hourly demand Ø Service reservoir → Max. hourly demand

Quantity of water - contd q Problem: A water supply scheme is to be designed for a city having a population of 1 lakh. Estimate the important kinds of draft which may be required to be recorded for an avg. annual consumption of water. Also determine the required capacities of the major components of the proposed water supply projects using river as a source of supply. Assume suitable fig & data required.

Quantity of water - contd v Solution Percaptia demand → Domestic =200 lit /day Industrial =50 lit/day Institutional =20 lit/day Public purpose =10 lit/day Total =280 lit/day Loss and waste → 5% of 280 → 14 lit/day Grand total → 294 lit/day

Quantity of water - contd Ave. daily demand → 294*1, 000 → 29. 4 Mld Max. daily demand → 1. 8*29. 4 → 52. 92 Mld Max. hourly demand → 1. 8*1. 5*29. 4 → 79. 38 Mld v Fire Demand Q = 4637√ P (1 -0. 01 √ P) = 4637 √ 100 (1 -0. 01 √ 100) = 41733. lit/min = 41733 x 24 x 60 = 60095520 lit/day = 60 Mld

Quantity of water - contd v The coincident demand may be taken as the highest of the following → Ø Max. daily demand + Fire demand or Ø Max. hourly demand Quantity → 52. 92 Mld + 60 Mld → 122. 92 Mld Or max. hourly demand → 79. 38 Mld < 122. 92 Mld Ø Coincident demand → 122. 92 Mld

Quantity of water - contd v The capacities of various components are → Ø Intake structures → designed for max. daily → 52. 92 Mld Ø The pipe- mains → designed for max. daily → 52. 92 Mld Ø The filter bed → designed for max. daily or 2 times the ave. daily → Ø That is → 2*29. 4 Mld → 58. 80 Mld

Quantity of water - contd Ø The lift pumps → designed for max. daily or 2 times the ave. daily → Ø That is → 2*29. 4 Mld → 58. 80 Mld Ø If the pumps are operated for 8 hrs Quantity of water → 24 x 58. 80 8 → 176. 40 Mld Ø The distribution pipes are designed for the coincident demand → 122. 92 Mld

Quantity of water - contd q Population forecasting v Design period →The period for which the various components of the water supply schemes are designed is called the design period. v The following factors normally, governs the design period Ø Useful life of the component structures and the chances of their becoming old and obsolete. Ø Ease and difficult with the expansion if undertaken in future – difficult for expansion long design period is considered.

Quantity of water - contd Ø Availability of funds – less fund, design period less Ø Rate of population growth → less rate →design period long. v Note: Normally various components of the system are designed for 20 to 30 years. Dam and reservoir are designed for max. up to 50 years.

Quantity of water – population fore casting q Various methods of forecasting population Ø Arithmetical increase Method Ø Geometrical increase Method Ø Incremental increase Method Ø Decreasing rate method Ø Simple graphical method Ø Comparative graphical Ø Master plan method. Ø The apportioned Method Ø Logistic Method

Quantity of water – population fore casting q Arithmetical increase method dp → C, a constant dt P → population t → time in decades p₁ → population for next decade p₀ → present population n → no. of decades Pn → p₀ + n. C

Population fore casting – Arithmetical increase method q Problem: The following are the senses details for the last few years. Determine the population for 1980, 1990 and 2000. Years Population 1930 25000 1940 28000 1950 34000 1960 42000 1970 47000

Population fore casting – Arithmetical increase method Year 1930 1950 1960 1970 population increase in population 25000 28000 3000 34000 6000 42000 8000 47000 5000 → 22000 Average increase → 22000/4 C → 5500

Population fore casting – Arithmetical increase method v Pn → p₀ + n. C Ø Population for 1980, Ø Population for 1990 Ø Population for 2000 → → → 47000 + (1 x 5500) 52500 47000 + (2 x 5500) 58000 47000 + (3 x 5500) 63500

Quantity of water – population fore casting q Geometrical increase method P₁ → p₀ + p₀ (r/100) → p₀ (1+r/100) P₂ → p₁ + p₁ (r/100) → p₁ (1+r/100) P₂ → P₀ (1+r/100)² v Therefore, Pn → p₀ (1+r/100) n

Population fore casting – Geometrical increase method Year population 1930 1940 1950 1960 1970 25000 28000 34000 42000 47000 Increase in Population % increase or rate 3000 6000 8000 5000 12% 21. 43% 23. 53% 11. 91% ∑ 68. 86%

Population fore casting – Geometrical increase method v Arithmetical growth rate Rate of increase → r₁ = 3000 x 100 25000 Average rate of increase → [r₁+r₂+r₃+r₄]/4 = 68. 86/4 r → 17. 22 v Geometrical growth rate = 4√r₁*r₂*r₃*r₄ Therefore r → 4√ 12 x 21. 43 x 23. 53 x 11. 91 → 16. 38 v when successive population of year by year is not given

Population fore casting – Geometrical increase method v Assumed growth rate r → t [ p 2/p 1 ] - 1 Where r→ Growth rate p₁→ Initial population p₂ →Final population t → number of decades Ø The rate of growth can be determined by arithmetically or geometrically. If we are using rate of growth by arithmetical method, the forecasted population will be more, but always better to use, rate of growth by geometrical method by a conservative value.

Population fore casting – Geometrical increase method Ø P 1980 →p 0 * [1+r/100] = 47000 x [1+ 16. 38/100] = 54700 ====== Ø P 1990 = p 0 (1+ r/100)2 = 47000 (1+ 0. 1638)2 = 63658 ====== Ø P 2000 = p 0 (1+r/100)3 = 47000 (1+0. 1638)3 = 74085 =======

Population fore casting – Geometrical increase method q The population for 1930 & 1970 are available from the survey records as 25000, 47000 respectively. Determine the population 2000 and 2006. v Assumed growth rate, r → t√[ p₂/p₁]-1 =4 √[ 47000] -1 25000 = 0. 1709 → 17. 09% P 2000 = 47000 (1+ 0. 17)3 = 75449. 65 → 75450 P 2006 = 47000 (1+ 0. 17)3. 6 → 82940

Population fore casting v Incremental Increase Method P 1 → p₀ + (¯x+¯y) P 2 → p₁+ (¯x+2¯y) ¯x → arithematical increase ¯y → incremental increase P 2 → p₁ + (¯x+2*¯y) → p 0 (¯x+¯y) + (¯x+2*¯y) → p 0 + (2*¯x + 3*¯y) → p 0 + 2*¯x + 2/2 (2+1) ¯y Therefore, Pn → p 0 + n¯x + n/2 (n+1) ¯y

Population fore casting – Incremental increase method q Determine the population 1980, 1990, 2000 Year Population Increase Incremental Increase 1930 25000 1940 28000 3000 1950 34000 6000 3000 1960 42000 8000 2000 1970 47000 5000 3000 ¯x→ 5500 ¯y → 666. 67

Population fore casting – Incremental increase method Ø P 1980 → → Ø P 1990 → → → Ø P 2000 → → → p₀+¯x+¯y 47000+5500+666. 67 53167 P₀ + 2*¯x + 2/2(2+1) ¯y 47000+ (2*5500) + (3*666. 67) 60000 P₀ + 3*¯x + 3*[(3+1)/2]*y 47000+ (3*5500) +3/2*4*666. 67 67, 500

Population fore casting v Decreasing rate method Ø Since, the rate of increase reduce as the population reaches saturation, a method which makes use of this decrease in rate of increase, gives rational results. The average decrease in percentage increase is worked out. This percentage decrease is deducted from the last percentage increase for the successive decades.

Population fore casting - Decreasing rate method Year 1930 1940 1950 1960 1970 Population 25000 28000 34000 42000 47000 %increase% Decrease in % increase 12 21. 43 23. 53 11. 91 Average decrease→ -9. 43 (12 -21. 43) -2. 1 (21. 43 -23. 53) 11. 62 (23. 53 -11. 91) → 0. 09/3 → 0. 03

Population fore casting - Decreasing rate method Ø P 1980 Ø P 1990 Ø P 2000 → → → 47000 + (11. 91 -0. 03)47000 52579+ [(11. 91 -(2 x 0. 03)]52579 58809+[11. 91 -(3 x 0. 03)]58809 65756 v Simple Graphical Method v Comparative Graph method

Population fore casting - Simple Graphical method Population 47000 Appr. extention 1930 1970 Year

Comparative Graphical method

Population fore casting - Zoning method v Zoning Method Ø The development of the city in a particular zone is a planned one. Ø The growth is planned one, and the future growth can be determined easily. Ø Master plan will give us when and where the development of residential, industrial, commercial etc would develop.

Population fore casting - Apportioned method v Apportioned Method Ø The ratio of local population to national population is worked out for last 3 or 4 decades Ø A graph is drawn with these ratios and the corresponding decades Ø The ratio for the designed decade is taken from the extrapolation of the graph Ø Knowing this ratio and the national population, the population for the city can be determined.