Environmental Engineering Reference
In-Depth Information
The concentrations of TP observed during this study, exceed considerably
observations, reported in literture sources. Finnemore & Lynard (1982) reported TP
concentrations of 0.16-0.4 mg/l in urban storm water, while USEPA (1995) presented
results regarding the water quality of various streams in the US, where TP ranged from
0.011-0.4 mg/l, which are comparable to the control point concentrations during this
study, as well as, to the background water quality concentrations in the Harare area
(Hranova et.al. 2002). The results obtained during this study, show values ranging
between 1 mg/l and 2 mg/l, which is a point of concern, considering the advanced status
of eutrophication of Lake Chivero.
4 ASSESSMENT OF POLLUTION FLUXES ALONG AN URBAN
STREAM
4.1
Pollution loads and pollution fluxes
Pollution loads contributed by runoff are important characteristics to be determined
during the analysis of the status of water quality at catchment level, and the evaluation of
potential risks to public health and the environment. It is an important parameter to be
considered during the process of the development of pollution mitigation programs. The
term is associated mainly with loads from point sources with well-identified quality and
quantity characteristics. It could be applied successfully in cases of runoff pollution loads
contributed by man-made drainage channels, with defined drainage area and discharge
location.
The process of determination of pollution loads is mostly related to the effluent quality
approach of pollution control and regulation. We could consider the pollution load of one
tributary to a river or the load contributed by a river to a lake as well. By definition, it
refers to the evaluation of the combined effect of water quality and quantity
characteristics of a given man-made or natural channel, before its point of discharge to
other water body.
In cases when the water quality objective approach is applied, it envisages the quality
control of the status of natural water bodies - streams, lakes or aquifers. The contribution
of diffuse pollution from runoff to the water body could not be isolated from the
influence of other factors, such as upstream discharges, background pollution, etc. In
such cases the term “pollution load” is not adequate, as we are evaluating the variation of
the water quality status of the body itself, but not specifically a load contributed from
outside. In other words, we are evaluating the effect of a load, which has already reached
the stream. Instead, the term “pollution flux” will be more adequate, as it reflexes the
varying nature of the combined effect of the quantitative and qualitative characteristics of
the water body at the point of consideration. In the case of the monitoring of a given
pollutant constituent, at a given location along a river or a stream, we should bear in mind
that the value of this constituent would be influenced by:
• The background quality of river water;
• The contribution from runoff from the drained area, as well as drained areas upstream
the location;
• The contribution from point sources upstream the location;
