Chapter 1..Water Demand (1) examples.pptx

chapter 1 water demand

1. Chapter -One Water Demand

2. Water Demand Water Demand: the quantity of water required for a purpose. To design a water supply scheme, it is important first to know the amount of water demanded by the user. Importance of demand data: To effectively manage existing scheme, To plan new works to meet future demand,

3. Water Demand Estimation of Water Demand: Accurate estimation of water demand is difficult. The problem of estimating water demand may be tackled by a detail study of the population, per-capita demand and design period of the scheme. Per capita demand --- the average daily water requirement of a person. Per capita demand = yearly water requirement of the city /(365xDesign population)

4. Water Demand Factors affecting per Capita Demand: Size of the city, Climate conditions, Living standard of people, Industrial and commercial activities, Quality of water supplies Pressure in the distribution system, Development of sewage facilities System of supply, Cost of water, Policy of metering and method of charging.

5. Water Demand Types of urban water demand: Domestic Demand, Industrial Demand, Institutional and Commercial Demand, Demand for Public uses, Fire Demand, Demand for Losses, etc.

6. Water Demand Domestic Demand: Includes the water required in private buildings for drinking, cooking, bathing, lawn sprinkling, gardening, sanitary purposes, etc. Domestic water consumption per person vary according to the living conditions of the consumers. According to IS: 1172-1993 = Min. 200 lit/day/person In most countries the domestic demand accounts about 50 to 60% of the total demand. The total domestic water demand shall be equal to the total design population multiplied by per capita domestic consumption

7. Water Demand Industrial and Commercial Demand: This includes the quantity of water required to be supplied to offices, factories, different industries, hotels, hospitals, etc. This quantity will vary considerably with number and type of industries, and number and type of commercial establishments. City with small industries = Average 50lit/person/day Industrial cities = Average 450lit/person/day Less commercialized cities = Ave. 20 lit/person/day Highly commercialized cities = upto 50lit /person/day

8. Water Demand Industrial and Commercial Demand: Major industries use their own supply not to degrade the city's water supply and cost. In supply estimation, to include or exclude industrial demand is a problem: If design includes, the industry later may say that it would have its own, and If it is ignored, industrial development may be discouraged. Hence, on average a margin of 20-25% of the total water demand may be taken for design.

9. Water Demand Public Demand: This is the quantity of water required for public utility purposes such as watering of municipal or public parks, gardening, washing and sprinkling on roads, use on public fountains, waste water conveyance, etc. Usually the demand may range from 2-5% of the total demand (on the average 10lit/person/day).

10. Water Demand Fire Demand: The quantity of water required for extinguishing fire. This demand should be easily available and always kept stored in storage reservoirs. Generally, in a moderate fire break out, three jet streams are simultaneously thrown from each hydrant: One on the burning property One each on adjacent property on either side of the burning property. Discharge from a fire hydrant are usually about 1100 lit/min.

11. Water Demand Example on fire demand: In Addis Ababa (Population = 5 million), if six fires break out at different places in a day and each fire stands for 3hours, What is the total amount of water required to distinguish the fires? What is the amount of water required per person so as to use as a basis for design of water supply scheme. What do you say about the result obtained in (B)?

12. Water Demand Solution: A) V = No. of fires x Discharge x Time of each fire = 6 x (3x1100)x(3x60) = 3,564,000 lit/day B) Per capita demand = V/No. of population = 3,564,000/5000000 < 1 lit/person/day C) The rate of water requirement for fire fighting is large but the total water consumption is less than 1lit/person/day. Thus, the fire demand is thus generally ignored while computing the total per capita water requirement of a city

13. Water Demand Losses and Wastes: These include: the water lost in leakage due to bad plumbing or damaged meters, stolen water due to unauthorized water connection and others. These losses should be taken into account while estimating the total requirements. Losses can be reduced by proper plumbing and careful maintenance Even in the best managed water works, losses may go as high as 15% of the total consumption.

14. Water Demand Example :

15. Water Demand Solution:

16. Water Demand Factors affecting losses and wastes: Loosen joints: due to bad plumbing. Usually joints are leaky. Pressure in the distribution system: Higher pressure in the distribution system leads to higher leakage losses. System of supply: In intermittent system of supplies, the leakage loss is reduced, as it does not occur for the whole daylong. Metering: In metered supply, wastage is considerably reduced because people become more careful in using water as they pay for it. Illegal connections: People connect their personal pipes illegally to the system.

17. Water Demand Time variation of water demand: Seasonal variation: such variation occurs due to larger use of water in dry season, lesser use in rainy season. Daily variation: Day to day variations reflect household and industrial activity. Hourly variation: Hourly consumption usually attains peak value between about 7 A.M. to 11 A.M. and then again from 7 P.M. to 9 P.M.

18. Water Demand Time variation of water demand:

19. Water Demand

20. Water Demand

21. Water Demand Total Average Daily Requirement (m 3 /d) Maximum Daily Coefficient 200 2.00 3000 1.55 40000 1.45 300000 1.35 Maximum daily demand adjustment factor

22. Water Demand Town Population Peak Hour Factor 0-50,000 2 50,001-100,000 1.8 100,000 and above 1.6 Peak Hour adjustment factor

23. Water Demand Group Mean Annual Precipitation (mm) Factor A 600 or less 1.1 B 601 – 900 1.0 C 901 or more 0.9 Climate adjustment factor

24. Water Demand Group Description Factor A Towns enjoying high living standards and with very high potential for development 1.10 B Towns having a very high potential for development but lower living standard at present 1.05 C Towns under normal Ethiopian conditions 1.00 D Advanced Rural Towns 0.90 Socio-Economic adjustment factor

25. Quantity of Water Demand Forecasting: Water resources planning and management is highly dependent on projections of future water needs. Design of water supply scheme need to consider functionality of the various components now and in the future. Therefore, the future water demand is a function of: Population at the end of design period Development plan of the city Variations in the demand or draft should also be generally assessed and known in order to design supply pipes, service reservoirs, distribution pipes, etc.

26. Water Demand Design Period: Design period is the number of years from the date of implementation to the estimated date when the maximum conditions of the design will be reached. Design period is guided by: The length of useful life of the units and structures, Initial cost of components, Ease and difficulty that is likely to be faced in expansions, Amount and availability of additional investments likely to be incurred for additional periods, and The rate of interest on the borrowings and the additional money invested. Rate of population growth However, the design period should neither be too long nor should it be too short.

27. Population Forecasting Population data is important for predicting the population of the city at the end of design period. Methods of prediction: 1 . Arithmetic increase method: Assumes a constant rate of increase of a population. i.e. Where, Pn =population after n decades; Po = population at present; n = no. of decades; K = average rate of increase of population per decade.

28. Population Forecasting 2 . Geometric increase ( Uniform Percentage) method: constant percentage of growth rate is assumed for equal periods of time, i.e. Where, Pn =population after n decades; Po = population at present; n = no. of decades; r = assumed growth rate in percent. r can be computed from the past known population data as: r = average [(increase in population/original population)x100 of each decade]

29. Population Forecasting 3. Curvilinear Method: involves the graphical projection of the past population growth curve, continuing whatever trends the historical data indicate. 4. Decreasing rate of increase (Declining Growth) method: assumes of a changing/declining rate of increase rather than a constant rate of increase. Example: From the given data, calculate the population at the end of the next three decades by a) arithmetic; b) geometric; c) curvilinear; and d) declining growth methods. 1970 ---------- 80,000 1980 ---------- 120,000 1990 ---------- 170,000 2000 ---------- 230,000

30. Population Forecasting Solution: a ) Arithmetic K = [(120000 -80000) + (170000-120000) +(230000-170000)]/3 = 50,000 Therefore, 2010 ------Pn = Po + nK = 230000+1*50,000 = 280000 2020 ------Pn = Po + nK = 230000+2*50,000 = 330000 2030 ------Pn = Po + nK = 230000+3*50,000 = 380000

31. Population Forecasting b) Geometric growth method r = [(120000-80000)/80000 + (170000-120000) /120000 +(230000-170000)/170000]*100/3 = (0.50+0.42+0.35)*100/3 = 42.33% Therefore, 2010 ------Pn = Po (1+ r/100) n = 230000(1+42.33/100) 1 = 327359 2020 ------Pn = 230000(1+42.33/100) 2 = 465930 2030 ------Pn = 230000(1+42.33/100) 3 = 663158

32. Population Forecasting c) Curvilinear

33. Population Forecasting d) Declining growth method Year Popn. Increase % increase Decrease in % Increase 1970 80000 40000 50% 1980 120000 8% 50000 42% 1990 170000 7% 60000 35% 2000 230000 Average for decade 7.5%

34. Population Forecasting Therefore, population at end of: 2010 ------ Pn = 230000 + {(35-7.5)/100}*230000 = 230000+(27.5/100)*230,000 = 293250 2020 ------ Pn = 293250 + {(27.5-7.5)/100}*293250 = 293250+(20/100)* 293250 = 351900 2030 ------ Pn = 351900 + {(20-7.5)/100}*351900 = 351900+(12.5/100)* 351900 = 395887

35. Population Forecasting Population Density: It is information regarding the physical distribution of the population. It is important to know in order to estimate the flows and to design the distribution network. Population density varies widely within a city, depending on the land use. May be estimated from zoning master plan.

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