Jobghost.blogspot.com
provides the Gate-2016 important study materials for Civil engineering for the candidates
who are going to appear for the GATE-2016 examination. Here the “ENVIRONMENTAL
ENGINEERING-Population Forecasting” topic is explained. And also the GATE-2016
practice sets, Example problems, previous year Question papers are available in
jobghost.blogspot.com.
1. Population Calculation:
Population Forecast is the most
important thing in real life. Whenever there is a need of design of sewers or
water supply systems, then the population must be forecasted. And this
population forecast is based on the law of probability. It will not give the
exact population in the forecast, but gives the approximate estimate for the
design. So that the design with the forecasted population will be near to the
exact population. Following forecast methods are used to calculate the
population at any decades or at any year.
a) Arithmetic Increase Method:
This is the simple method of forecast
of population. This gives the approximate population after n decades. In this
method the rate of change of population is assumed to be constant. But this
method is only applicable to old and largest cities with no industrial growth
and which already reached a saturation or maximum development. So there is no
possibility of sudden increase of population. And hence this method is used to
forecast gradual and constant increase of population.
Pn = (P0 + n.X)
Pn ------> Population after “n”
Decades.
P0 ------>Last Known Population.
X
------>Average increase of population for each decade.
b) Geometric increase Method:
Geometric increase methods are most
commonly used for the population forecast. This gives the good results for the
young cities. So this method is used to forecast the young and expanding
cities. The percentage increase of
population for every decade is assumed to be constant. In this method the
forecasted population is added for the next calculation. So it gives the rapid growth
of population.
Pn ------> Population after “n”
Decades
P0 ------>Last Known Population
r
------->geometric mean percentage increase of population
c) Incremental Increase Method:
Incremental increase method is most
reliable method of forecasting. And this method is the combination of
Arithmetic increase methods and Incremental increase method. The incremental
increase average is calculated to find the total population after n decades.
Pn ------> Population after “n”
Decades.
P0 ------>Last Known Population.
X
------>Average increase of population.
Y
------>Average incremental increase of last known decade.
d) Decreasing rate method:
This method is used to find the
reduced population of the cities whose population rate of increase goes on
reduces, as they reach the saturation. It is most commonly used for the smaller
cities with undeveloped area.
e) Simple Graphical method:
This method is not use in recent days
due to its unreliability. In this method the graph is plotted for the known
value of population vs time and it is smoothly extended up to the desired time.
The graph is called logistic curve graph.
f) Comparative Graphical method:
This method is based on the comparison
with same like cities. The city which has the development like existing known
populated cities is considered similar cities. Then the average similar cities
graph value is taken as the required population of new city. This method gives
the reliable and precise results. So using this method forecasting of
population is done by considering the similar cities population which is
developed as same like the required city. Growth curves for the similar kind of
cities are plotted for existing population and the consideration city is fitted
between them.
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