Environmental Engineering Reference
In-Depth Information
CHAPTER 4
Assessing and managing urban storm water
quality
R. Hranova & M. Magombeyi
ABSTRACT: Basic principles and approaches to assess diffuse pollution
from urban storm water have been presented. As an example of a
pollution evaluation procedure, a case study on the storm water of two
major drainage channels in the City of Harare has been done during the
period 2002-2003, and results were compared to previous measurements.
Results show pollution with respect to TP, TSS, TDS, ammonia, COD, Cd
and Pb, and a relatively good correlation has been found between COD
and Zn concentrations as dependant variables of TSS concentrations.
Spatial variations, as a result of specific land use patterns, did not show a
statistically significant difference, except for the contribution from an
industrial area. A single storm event has been studied and results show a
considerable difference between mean values and EMCs with respect to
parameters associated with particulate material only. The development of
an event-orientated monitoring program, which would allow more
accurate determination of site-specific pollution concentrations, and the
need to adopt uniform methodology of pollution loads estimation has been
recommended, as well as the integration of storm water management into
the process of water resources management at catchment level.
1 INTRODUCTION
Urban development can have a significant impact on catchments by increasing runoff and
pollutant loading. When forests and farmlands are converted to industrial and residential
developments, this change in the land use practice leads to increased runoff volumes and
a rise of downstream flood stages, thus increasing the risks of flooding. In addition, the
ground water recharge is reduced due to the increase of impermeable covers of urbanized
areas. Water quality problems have intensified through stages in response to the increased
growth and contraction of population and industrial centres. Often the problems have
been viewed as inevitable consequences of community development and are sometimes
even accepted as evidence of affluence and progress. The recent trends in urbanization, as
discussed in Chapter 3, show that the scenario of increased urbanization rates will
continue during the coming decades, therefore, it is desirable to face the difficulties and
to adopt management strategies, which could lead to the alleviation of the negative
effects of urbanization.
