WATER DEMAND AND POPULATION FORECASTING METHOD

For designing the water supply scheme for any area or city, we must estimate the population in future for which the scheme should be designed.
The scheme once installed must fulfill the demand of projected population up to some pre determined future date.

Design Period:

• As the water supply scheme includes vast costly structures such as reservoirs, dams, pumping units, distribution system, etc. which can not be replaced or modified to increase their capacities easily in later on.
• Almost all components are designed to ensure that the future needs of the community gets satisfied. This future need is called Design Period.
• The design period should be neither too short nor too long.

Three major factors which are responsible for growth or decline in Population are mentioned below:

• Birth
• Death
• Migration

Population Forecasting Methods

NOTE: Generally Decades are taken as the units of Time in calculations.

1. Arithmetic Progression Method

• In this method, the increase in population is assumed to be constant.

2. Geometric Progression Method (Geometric Increase Method)

• In this method, the Percentage Increase in population is assumed to be constant.
• Government of India Manual recommends Geometric Progressive Method because it gives the maximum value out of the other methods.

3. Incremental Increase Method

• It is the combination of Arithmetic and Geometric Increase method.
• Firstly, the actual increase in each decade is found.
• Then,the average increment of increases is found.
• By using above two calculated values, the population after n decades from present is given by:

Government of India (GOI) Manual Recommends..

• Arithmetic Increase Method is used for old cities as growth rate is assumed to be constant
• Geometric Progression method is used for new and younger cities as it give highest value.
• Whenever there is negative rate of increase, Incremental increase method is used. It gives values in between Arithmetic progression method and Geometric Progression Method.

NOTE: There are other methods also for forecasting but this three methods are important for any exam.

Also Read:

• Different type of water demand and per capita Demand

• Physical water quality parameters