Water Demand and Supply

Water Demand and Water Demand and SupplySupply

CE 370 - Lecture 2CE 370 - Lecture 2

Before designing any water project, the amount Before designing any water project, the amount of water that is required must be determined. To of water that is required must be determined. To obtain such information we have to know the obtain such information we have to know the following:following:number of people that will be servednumber of people that will be servedWater consumption (per capita)Water consumption (per capita)Factors affecting consumptionFactors affecting consumption

Forecasting PopulationForecasting Population

Before a water project is constructed, a decision on Before a water project is constructed, a decision on the the design perioddesign period of the project has to be taken. This of the project has to be taken. This may depend on the amount of fund available for that may depend on the amount of fund available for that certain project.certain project.

Since most of Saudi cities are growing in population, Since most of Saudi cities are growing in population, the design period depends mainly upon the rate of the design period depends mainly upon the rate of population growth. The real problem here is how to population growth. The real problem here is how to forecast, as accurately as possible, the population 10, forecast, as accurately as possible, the population 10, 20 or 30 years in the future. 20 or 30 years in the future.

Present population can be obtained through:Present population can be obtained through: Bureau of censusBureau of census City directoriesCity directories Planning commissionsPlanning commissions Use the ratio of population to the number of Use the ratio of population to the number of

children in schools from previous enumeration.children in schools from previous enumeration. The most difficult part is the estimation of The most difficult part is the estimation of

population in the future. There are two types of population in the future. There are two types of population estimates:population estimates:

• short term (1-10 years)short term (1-10 years)

• long term (10-50 years)long term (10-50 years)

Different mathematical and graphical Different mathematical and graphical approaches are used in order to project approaches are used in order to project population, but there are no exact solutions population, but there are no exact solutions since many factors are included:since many factors are included: city trade territorycity trade territory industrial expansionindustrial expansion rate of development in the surroundingsrate of development in the surroundings location with regard to airport, railroads or ports.location with regard to airport, railroads or ports. sudden events such as discovery of an oil field, sudden events such as discovery of an oil field,

development of new industries will upset all development of new industries will upset all estimates.estimates.

The most widely employed mathematical or graphical The most widely employed mathematical or graphical methods for forecasting population are :methods for forecasting population are : Arithmetical method by adding to the existing population Arithmetical method by adding to the existing population

the same number of people for each future period (of the same number of people for each future period (of limited value and can be used for old and very large cities).limited value and can be used for old and very large cities).

Constant percentage growth rate (must be used with Constant percentage growth rate (must be used with caution because it may produce too large results, especially caution because it may produce too large results, especially if the city is young. The method can be applied to old if the city is young. The method can be applied to old cities not undergoing great expansion). cities not undergoing great expansion).

Logistic method (This method depends upon the fact that Logistic method (This method depends upon the fact that population will grow until they reach a saturation population will grow until they reach a saturation population which is established by limit of economic population which is established by limit of economic opportunity). opportunity).

The ratio method which based on upon the belief that The ratio method which based on upon the belief that populations of cities will have a relationship to the populations of cities will have a relationship to the population in the whole country.population in the whole country.

Graphical interpolation-extension (this method may be Graphical interpolation-extension (this method may be considered the most generally applicable one).considered the most generally applicable one).

Knowledge of the population of a region Knowledge of the population of a region permits estimates to be made of the total permits estimates to be made of the total quantities of water needed. To design quantities of water needed. To design water distribution networks, additional water distribution networks, additional information regarding the spatial information regarding the spatial distribution of the population to be served distribution of the population to be served must also be obtained. Population must also be obtained. Population densities may be estimated from data densities may be estimated from data collected on existing areas. If local data collected on existing areas. If local data are not available, Table 1 can be used as a are not available, Table 1 can be used as a guide.guide.

Table 1: Guide to Population Density.

Area Type Number of Persons per Acre

Residential Single family-units Multiple-family unitsApartmentsCommercial AreasIndustrial Areas

5-3530-100100-100015-305-15

WATER CONSUMPTION

Available water to a city can be classified based Available water to a city can be classified based on its ultimate use. Water is used for:on its ultimate use. Water is used for:

Domestic.Domestic. Which includes water supplied to Which includes water supplied to houses, hotels, etc…Such water is used for houses, hotels, etc…Such water is used for sanitary, washing, bathing, drinking and other sanitary, washing, bathing, drinking and other purposes such as air conditioning of residences, purposes such as air conditioning of residences, irrigation and sparkling of privately owned irrigation and sparkling of privately owned gardens and lawns. The practice of irrigation will gardens and lawns. The practice of irrigation will have a considerable effect upon total consumption. have a considerable effect upon total consumption. Domestic consumption may be expected to be Domestic consumption may be expected to be about 30 per cent of the total.about 30 per cent of the total.

Industrial.Industrial. Which includes water supplied to Which includes water supplied to industrial. The importance of industrial industrial. The importance of industrial consumption depends on:consumption depends on: Size of the industrySize of the industry Whether or not the industry uses the public water Whether or not the industry uses the public water

works.works. The industrial use could range between 15 to 60 The industrial use could range between 15 to 60

per cent of the total, averaging at 32 percent.per cent of the total, averaging at 32 percent.

CommercialCommercial. Which includes water supplied . Which includes water supplied to commercial areas. The quantity of water to commercial areas. The quantity of water required for commercial use is expected to required for commercial use is expected to mount at about 20 per cent of the total. In mount at about 20 per cent of the total. In some cases, water consumption for industrial some cases, water consumption for industrial and commercial purposes was related to the and commercial purposes was related to the floor area of the building served. 300 gallon floor area of the building served. 300 gallon per day per 1000 sq. feet was used.per day per 1000 sq. feet was used.

Public Use. Public Use. Which includes water served to Which includes water served to public buildings such as city halls, jails and public buildings such as city halls, jails and schools as well as public service such as schools as well as public service such as sprinkling and flushing streets and fire sprinkling and flushing streets and fire protection. Such services may consume water protection. Such services may consume water at about 10 to 15 gallons per capita. at about 10 to 15 gallons per capita. Extinguishing very large fires will cause the Extinguishing very large fires will cause the rate of use to be high for short periods.rate of use to be high for short periods.

Loss and Waste.Loss and Waste. This the water which is uncounted This the water which is uncounted for although some of the loss and waste may be for although some of the loss and waste may be approximated in the sense of cause and quantity. approximated in the sense of cause and quantity. Unaccounted-for-waste is due to meter and pump Unaccounted-for-waste is due to meter and pump leakage, unauthorized water connection and leaks in leakage, unauthorized water connection and leaks in the mains. Unaccounted-for water, and also water the mains. Unaccounted-for water, and also water wasted by consumers, can be reduced by careful wasted by consumers, can be reduced by careful maintenance of the water distribution system and maintenance of the water distribution system and metering of the water services. In metered and metering of the water services. In metered and moderately well maintained water system, water loss moderately well maintained water system, water loss may mount to about 15 per cent of the total.may mount to about 15 per cent of the total.

Total water consumption is the sum of the afore-mentioned uses and the loss and waste. Table 1 shows the consumption of water for various uses.

USE gallon/capita/day

Domestic or residentialIndustrialCommercialPublicLoss and wasteTOTAL

55 – 6032 – 5020 – 2110 – 1515 – 22

150568 liter/c/d

The figures, given in Table 1, are not fixed but may vary from one city to another. Each city has to be studied carefully especially the industrial and commercial uses as well as the actual or probable loss and waste.

FACTORS AFFECTING WATER FACTORS AFFECTING WATER CONSUMPTIONCONSUMPTION

The determination of water demand of an area requires The determination of water demand of an area requires knowledge and experience of the social, economic and regional knowledge and experience of the social, economic and regional development. Review of water consumption records showed a development. Review of water consumption records showed a wide range of values. This is due to the following factors:wide range of values. This is due to the following factors:

Climate conditionsClimate conditions. Warm dry regions have higher . Warm dry regions have higher consumption rates than cooler regions. In addition, water consumption rates than cooler regions. In addition, water usage is affected by the precipitation levels in the region. usage is affected by the precipitation levels in the region. Where summer is hot and dry, much water will be used for Where summer is hot and dry, much water will be used for watering lawns. Domestic use will increase by more watering lawns. Domestic use will increase by more bathing, while public use will be affected by much street bathing, while public use will be affected by much street sprinkling and use in parks and recreation fields for sprinkling and use in parks and recreation fields for watering grass and supplying fountains. Higher watering grass and supplying fountains. Higher temperature will also lead to high water use for air temperature will also lead to high water use for air conditioning.conditioning.

Size of the citySize of the city. In small cities, it was found . In small cities, it was found that the per capita per day water consumption that the per capita per day water consumption was small due to the fact that there are only was small due to the fact that there are only limited uses of water in those cities. Small limited uses of water in those cities. Small cities have larger area that is inadequately cities have larger area that is inadequately served by both water and sewer systems than served by both water and sewer systems than larger cities. In the unsewered home, water larger cities. In the unsewered home, water consumption will rarely exceed 10 g/c/d, while consumption will rarely exceed 10 g/c/d, while in sewered home, it will equal or exceed 45 in sewered home, it will equal or exceed 45 g/c/d on the average.g/c/d on the average.

Characteristics of the populationCharacteristics of the population. Domestic use of . Domestic use of water was found to vary widely. This is largely water was found to vary widely. This is largely dependent upon the economic status of the dependent upon the economic status of the consumers, which will differ greatly in various consumers, which will differ greatly in various sections of a city. In high-value residential areas of a sections of a city. In high-value residential areas of a city the water consumption per capita will be high. In city the water consumption per capita will be high. In low-value areas where sewerage is not available or low-value areas where sewerage is not available or where a sigle faucet serves one or more homes, water where a sigle faucet serves one or more homes, water consumption will be very low (15 g/c/d), while it is consumption will be very low (15 g/c/d), while it is about 60 g/c/d in apartment houses located in high-about 60 g/c/d in apartment houses located in high-value residential areas.value residential areas.

Industries and commerceIndustries and commerce. Presence of industrial . Presence of industrial activities has a great effect on water consumption. activities has a great effect on water consumption. Since industrial use has no direct relation to the Since industrial use has no direct relation to the population, great care must be taken when estimating population, great care must be taken when estimating present or future water consumption of a city. present or future water consumption of a city. Information should be collected on existing Information should be collected on existing industries, their actual water consumption and the industries, their actual water consumption and the probability of establishing new industries in the probability of establishing new industries in the future. Commercial consumption is that of the retail future. Commercial consumption is that of the retail and wholesale trade houses and office buildings. and wholesale trade houses and office buildings. Figures on commercial consumption are few and Figures on commercial consumption are few and widely divergent, and if the consumption is desired widely divergent, and if the consumption is desired for any district, a special investigation should be for any district, a special investigation should be made. made.

MeteringMetering. Communities that are metered . Communities that are metered usually show a lower and more stable water usually show a lower and more stable water use pattern. Metering of services consists of use pattern. Metering of services consists of placing a recording meter in the line leading placing a recording meter in the line leading from the water main to the building served. from the water main to the building served. Consumers are then billed for the water they Consumers are then billed for the water they use. Charging flat rates has no relation to the use. Charging flat rates has no relation to the actual amount of water used or wasted. It is actual amount of water used or wasted. It is almost impossible to construct a good system almost impossible to construct a good system of water charges unless they are based upon of water charges unless they are based upon actual water consumption.actual water consumption.

Water qualityWater quality. Consumer perception of bad . Consumer perception of bad water quality can decrease the water usage water quality can decrease the water usage rate.rate.

Cost of waterCost of water. A tendency toward water . A tendency toward water conservation occur when cost of water is high.conservation occur when cost of water is high.

Water pressureWater pressure. Rates of water usage . Rates of water usage increase with increases in water pressure.increase with increases in water pressure.

Water conservationWater conservation. Public awareness and . Public awareness and implementation of water conservation implementation of water conservation programs by utilities tend to have an impact on programs by utilities tend to have an impact on the water usage rate. the water usage rate.

Wastewater reuseWastewater reuse. Wastewater reuse offers . Wastewater reuse offers attractive alternatives to developing new attractive alternatives to developing new supplies. supplies. Municipal reuseMunicipal reuse Industrial reuseIndustrial reuse Irrigation reuseIrrigation reuse Recreational reuseRecreational reuse

Environmental protectionEnvironmental protection.. Thermal water dischargeThermal water discharge The use of scrubbers to remove sulfur dioxideThe use of scrubbers to remove sulfur dioxide

Example: Find the population of City A in 50 years from 1970.

YEAR CITY A CITY B CITY C CITY D

19001910192019301940195019601970

57320682507797590780101765115330128735142325

100750120345132720146355162725178010191820214150

127135146240148150166245177130188320198410220320

135335146120158335171720182345194725207415220330

Example: The following Table shows the water consumption for City A from 1949 to 1969. Estimate the water annual and daily consumption rates for 1970 and 1990.

YEAR

ANNUAL WATER CONSUMPTION

(m3)

YEAR

ANNUAL WATER CONSUMPTION

(m3)

19491951195319551957195919611963196519671969

59962638675806467194072280018378826745298629099194703354107074912612141134142591689161182948

1950195219541956195819601962196419661968

64023813696195717426700112576351849589499061491498966973114684029134768019146443261

SolutionSolution

Q1 = Water consumption in 1949 = 59962638 cubic meterQ1 = Water consumption in 1949 = 59962638 cubic meterQ2 = Water consumption in 1969 = 161182948 cubic meterQ2 = Water consumption in 1969 = 161182948 cubic meterAnnual increase rate = Annual increase rate =

= = but this rate was not stable or constant during the 20-year period. but this rate was not stable or constant during the 20-year period. Based on that the 20-year period must be divided into smaller time Based on that the 20-year period must be divided into smaller time segments each of 5 years (as an example) to come up with a figure segments each of 5 years (as an example) to come up with a figure that is closer to the real one.that is closer to the real one.

11

2 nQ

Q

%5159962638

16118294820

1950 - 19551950 - 1955

Water consumption in 1950 = 64023813 cubic meterWater consumption in 1950 = 64023813 cubic meter


Annual increase rate =Annual increase rate =

1955 - 19601955 - 1960



Annual increase rate = Annual increase rate =

%54.4164023813

800183785

%52.2180018378

906149145

1960 - 19651960 - 1965Water consumption in 1960 = 90614914 cubic meterWater consumption in 1960 = 90614914 cubic meterWater consumption in 1965 = 121411634 cubic meterWater consumption in 1965 = 121411634 cubic meterAnnual consumption rate = Annual consumption rate =

1965 - 19691965 - 1969Water consumption in 1965 = 121411634 cubic meterWater consumption in 1965 = 121411634 cubic meterWater consumption in 1969 = 161181948 cubic meterWater consumption in 1969 = 161181948 cubic meterAnnual consumption rate = Annual consumption rate =

Finding the average of 3 closer annual consumption rates, Finding the average of 3 closer annual consumption rates, it will be 6%. This value will be used to predict future it will be 6%. This value will be used to predict future water consumptions.water consumptions.

%03.6190614914

1214116345

%33.71121411634

1611819484

In 1975In 1975Water consumption in 1969 = 161182948 cubic meterWater consumption in 1969 = 161182948 cubic meterPrediction period from 1969 to 1975 = 6 yearsPrediction period from 1969 to 1975 = 6 yearsWater consumption in 1975 = 161182948 Water consumption in 1975 = 161182948 (1.06) (1.06)66 = 228641000 = 228641000 cubic metercubic meterAverage daily consumption = 228641000/365 = 626400 cubic meterAverage daily consumption = 228641000/365 = 626400 cubic meter

In 1980In 1980Prediction period from 1969 to 1980 = 11 yearsPrediction period from 1969 to 1980 = 11 yearsWater consumption in 1980 = 161182948 Water consumption in 1980 = 161182948 (1.06) (1.06)1111 = 305973000 = 305973000 cubic metercubic meterAverage daily consumption = 305973000/365 = 838300 cubic meterAverage daily consumption = 305973000/365 = 838300 cubic meter

In 1985In 1985Prediction period from 1969 to 1985 = 16 yearsPrediction period from 1969 to 1985 = 16 yearsWater consumption in 1985 = 161182948 Water consumption in 1985 = 161182948 (1.06) (1.06)1616 = = 409461000 cubic meter409461000 cubic meterAverage daily consumption = 409461000/365 = 1121800 Average daily consumption = 409461000/365 = 1121800 cubic metercubic meter




Assuming the maximum daily consumption is at 175%, the results are tabulated as follows:

YEARESTIMATED

TOTAL ANNUAL

CONSUMPTIO (m3)

ESTIMATED AVERAGE

DAILY CONSUMPTION

(m3)

ESTIMATED MAXIMUM

DAILY CONSUMPTION

(m3)

1970197519801985199019952000

170855000228641000305973000409461000547952000733283000981298000

468100 636400 8383001211800150130020090002688500

819200111370014670002120700262730035158004704900

Solution

YEAR CITY A INCREASE %INCREASE

INCREASE CHANGE

19001910192019301940195019601970

57320682507797590780101765115330128735142325

TOTALAVERAGE

10930 97251280510985135651340513590

8500512000

19.114.316.4212.113.311.6510.6

97.4713.9

-1205+3080-1820+2580-160+185

2660443

WATER RESOURCESWATER RESOURCES

Rain WaterRain Water Surface WaterSurface Water Ground WaterGround Water Desalinated Sea-waterDesalinated Sea-water Treated WastewaterTreated Wastewater

VARIATIONS IN WATER VARIATIONS IN WATER CONSUMPTION RATESCONSUMPTION RATES

Seasonal VariationsIn summer, daily water consumption rate may reach 120 to 160% of In summer, daily water consumption rate may reach 120 to 160% of average daily consumption rate throughout the year. In winter, daily water average daily consumption rate throughout the year. In winter, daily water consumption may reach only 70% of average daily use throughout the consumption may reach only 70% of average daily use throughout the year.year.

Daily VariationsWater consumption varies from one day to another. Daily variation could Water consumption varies from one day to another. Daily variation could reach maximum of 130 to 170% of average daily consumption during the reach maximum of 130 to 170% of average daily consumption during the year or may reach a minimum value of 60% of average daily water year or may reach a minimum value of 60% of average daily water consumption during the same year.consumption during the same year.

Hourly VariationsMaximum rate may reach up to 150% of average daily rate, of the same Maximum rate may reach up to 150% of average daily rate, of the same day, at the peak, or may reach 225% of average daily consumption during day, at the peak, or may reach 225% of average daily consumption during one year.one year.

POPULATION FORCASTINGPOPULATION FORCASTING

1.1. Arithmetical MethodArithmetical Method

P = PP = P00 + IT + IT

Population in 1980 = Population in 1970 + IncreasePopulation in 1980 = Population in 1970 + Increase

= 142325 + 12000 = = 142325 + 12000 = 154325154325

Population in 1990 = 142325 + 12000 * 2 = 166325Population in 1990 = 142325 + 12000 * 2 = 166325




2.2. Incremental IncreaseIncremental Increase

P = PP = P00 + IT + IG[(T) + (T-1) + (T-2) +…….+1] + IT + IG[(T) + (T-1) + (T-2) +…….+1]

Population in 1980 = Population in 1970 + Increase + Increase ChangePopulation in 1980 = Population in 1970 + Increase + Increase Change = 142325 + 12000= 142325 + 120001 + 443 1 + 443 1 = 154770 1 = 154770

Population in 1990 = 142325 + 12000Population in 1990 = 142325 + 120002 + 443 2 + 443 [2+1] = 167660 [2+1] = 167660Population in 2000 = 142325 + 12000Population in 2000 = 142325 + 120003 + 443 3 + 443 [3+2+1] = 180995 [3+2+1] = 180995Population in 2010 = 142325 + 12000Population in 2010 = 142325 + 120004 + 443 4 + 443 [4+3+2+1] = 194775 [4+3+2+1] = 194775Population in 2020 = 142325 + 12000Population in 2020 = 142325 + 120005 + 443 5 + 443 [5+4+3+2+1] = [5+4+3+2+1] =

209000209000

3.3. Geometric IncreaseGeometric Increase

P = PP = P00 + (1+IP) + (1+IP)nn

Population in 1980 = Population in 1970 (1+%INCREASE)Population in 1980 = Population in 1970 (1+%INCREASE)

= 142325 (1+0.138)= 142325 (1+0.138)11 = 161966 = 161966

Population in 1990 = 142325 (1+0.138)Population in 1990 = 142325 (1+0.138)22 = 184301 = 184301




Water Demand and Supply

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