Environmental Engineering Reference
In-Depth Information
unit pollution loads, which are essential in terms of an optimal choice of pollution
abatement measures, and the general assessment, simulation and prediction of the
catchment's water quality status.
4.2
Urban streams
A spatial integration of the results obtained in previous chapters could be done based on
the Marimba River catchment characteristics, flowing through Harare, Zimbabwe. Figure
12.3 shows a scheme of the catchment, which is characterized mainly by medium and
high-density residential developments. The River originates in Mount Pleasant, and in its
upper reaches, collects the runoff from medium density residential areas, including
commercial areas in the form of shopping complexes and schools. This type of
development does not pose a serious danger with respect to diffuse pollution, as the
runoff from roofs is discharged into surrounding gardens and infiltrates, recharging the
ground water aquifer. Large green areas surround the schools and sporting facilities with
a very low runoff potential. The areas, which contribute the major portion of the runoff
from this land use pattern, could be associated with roads and parking slots.
The middle stretches of the River collect runoff from Warren Park and Kambazuma,
as well as from Tynwald, which are high-density residential areas of larger plots than the
original ones, described in Chapter 5. The Tynwald stream collects the runoff from the
Golden Quarry landfill, which has been abandoned as a solid waste disposal site, but is of
concern as a diffuse pollution source with respect to surface and ground water (Chapter
7). The drainage area is not densely populated, with large undeveloped open spaces,
which in many cases are used for informal agriculture, a typical land use pattern for the
low-density areas in the city. This segment of the River collects the runoff from the
Coventry road drainage channel (results presented in Chapter 4). The channel collects
runoff from a mixed land use pattern, including industrial areas, small to medium
business areas, medium-density residential areas and open undeveloped areas. The
downstream part of the River collects runoff from typical high-density areas, described in
Chapter 5, namely Kuwadzana, Crowborough, Marimba Park and Mufacose. The largest
tributary - Little Marimba River, flows mainly through undeveloped areas, but new high-
density developments are expanding in this direction (Kuwadzana, Dzivrasekwa,
Tynwald and Bluff hill). This stretch of the River receives the highest pollution loads due
to diffuse sources (runoff from high-density areas and Crowborough farm), as well as
from a large point source - Crowborough Sewage Treatment Works (CSTW). Chapter 8
has discussed at length the impact of the farm.
The results from the different studies could not be directly compared, as the
observations in the different case studies were made during different periods of time. The
maximum pollution concentrations were measured at Little Marimba River and ware
associated with the runoff from Crowborough farm.
