Environmental Engineering Reference
In-Depth Information
CHAPTER 3
Characteristics of an urban environment in the
context of diffuse pollution control
R. Hranova
ABSTRACT: Harare, the capital city of Zimbabwe, located in the
Manyame River catchment basin, has been characterized, in terms of
population growth characteristics, land use patterns and the water supply,
sewerage and drainage systems. Specific attention has been given to the
water quality of the Lake Chivero and tributaries, which receive the runoff
from the city. A historic overview of the catchment water quality has been
done, based on published data from previous research projects. Nutrients
variations in urban drainage have been presented, based on data from the
city's monitoring program for the period 1995-2000. Results show a
sustained trend of increase in the concentrations of phosphates and
ammonia. Comparison with earlier studies shows that this trend has been
reported since the 1980's. The existing regulatory instruments and
monitoring practice have been discussed with emphasis and implications
with respect to diffuse pollution control and abatement, and corresponding
recommendations for future development put forward.
1 INTRODUCTION
1.1
Urbanization trends
Throughout most history, the human population has lived in a rural life style, dependent
on agriculture and hunting for survival. In 1800, only 3% of the world's population lived
in urban areas, while in 1950, 30% of world's population resided in urban centers and the
number of cities with over 1 million inhabitants had grown to 83. The world had
experienced unprecedented urban growth in recent decades. In 2000, about 47% of the
world's population, which is about 2.8 billion people, lived in urban areas, and with
respect to developing countries, about 40% of the population resides in urban areas. It is
expected that, by 2030, 60% of the world's population will be living in urban areas with
the most growth occurring in the developing countries (UN Population Division 1997).
In Africa, at the start of the 20
th
century, 95% of Africans lived in rural areas. Even in
the 1960's, Africa remained the least urbanized continent with an urban population of
18.85%. By 1996 this had more than doubled, and by 2010 at least 43% of the population
is expected to live in urban areas. The average annual urban growth rate in Africa during
1970-2000 were the highest in the world at more than 4%, and it is projected to decrease
slightly to about 3% during 2020-2025. In Northern Africa, more than half of the
