Environmental Engineering Water Use and Population Forecasting

WATER DEMAND Factors Affecting Water Use Many factors affect the amount and timing of water use: population size and character: climate; the types of water uses in the region; the cost of water; public commitment to environmental protection and restoration; public attitude toward conservation and wastewater reuse; water management practices; federal, state, local government laws and ordinances; and tourism. Population. The amount of water used in a locality is directly related to the size, distribution, and composition of the local population. Forecasts of future water use depend,in part, on population forecasts as well. Climate. The amount of water used in a locality is influenced by its climate. Lawn irrigation, gardening, bathing, irrigation, cooling, and many other water uses are directly affected.

WATER DEMAND Types of Water Uses. The type and scale of residential, commercial, industrial, and agricultural development in an area define the levels and timing of water uses. Economic Conditions. Economic health is reflected in all aspects of resource management and development. Inflation and other economic trends influence the availability of funds for water supply, wastewater treatment, and environmental and other programs, and they affect the attitudes of individuals as well. Environmental Protection. Social attitudes toward environmental protection and enhancement strongly affect water allocation and use. Water use forecasts must take into account the amount of water that is to be dedicated to environmental protection and restoration. This quantity can be substantial.

WATER DEMAND Conservation. Attractive alternatives to developing new water supplies are conservation practices and the reuse of wastewater and storm water. These approaches, although not a panacea, can at least delay the need for additional water supplies and/or the development of new facilities. Management Practices. water management practices, including interbasin transfers, saline water conversion, water reclamation and reuse, and many other practices influence water use trends . The impact of technological change on water use can be significant. Tourism. Some states, have annual tourist populations that significantly exceed their resident populations. The impacts of such occurrences must be recognized when forecasting future water demands.

WATER DEMAND Example A reservoir has a capacity of 340 x103 hectare meter. How many years would this supply a city of 100,000 ? Assume a use rate of 680 Lpcd. Solution 1 hectare= 104 m2 340x103 x10,000=340 x 107 m2. m 340x107 m2.m x 1000= 340x 1010 Litre Time = (340x 1010)/(680 x 100,000) = 50,000 days = 137 years

WATER DEMAND Example If the minimum flow of a stream having a 51,800 hectares watershed is 0.38 m3/d.hectare what population could be supplied continuously from the stream? the water use rate is 662 Lpcd. Solution Q = 51,800x0.38 = 19,684 m3/d Population = 19,684x1000 / 662 = 30,000 people

WATER DEMAND Example The population of a state was 7 million in 2000. Consider that by 2015, it is expected to increase to 9 million. Consider that the amount of freshwater withdrawn in 2000 was 9.5x109 LPd. Estimate the amount of freshwater that might be withdrawal in 2015. Assume 15% reduction in per capita use Solution 7/9.5x109 = 9/X X = 9*9.5x109/7=1.22x1010 Lpd Then in 2015, the requirement would be1.22x1010*0.85 = 1.037 LPd

WATER DEMAND Example Compare the annual water requirements of a 809-hectare irrigated farm during growing season and a city with a population of 100,000. Assume an irrigation requirement of 915 x 10-3 hectare .m/yr/hectare and a per capita water use rate of 606 Lpcd. Assume the growing season is 180 days

Calculate the daily water use for irrigation during the growing season.   Convert to L/day = 41,124 x 106 L/day Calculate the daily water use for the city Therefore, the average daily use for the city is larger than the daily irrigation use during the growing season.