Environmental Engineering Reference
In-Depth Information
comprises of residential and institutional single/double stories buildings. It differs from
DA1 because it contains a larger percentage of medium-size residential dwellings and the
area in general has a lower percentage of impermeable surfaces compared to the CBD.
DA 5 has a similar land use practice to DA 4 and was excluded from the study.
Residential areas could be qualified as medium density with plots varying between 500
and 2000 m
2
.
Figure 4.1. Study area and location of
sampling points.
3.2
Methodology
Grab samples for water quality evaluation were collected at the outlet of drainage
channels of the corresponding drainage areas (Fig. 4.1) during and immediately after 7
major rainfall occasions, from November 2002 to March 2003.
SP1 and SP4 collect the storm water from areas DA1and DA4, and discharge into
Mukuvisi River. DR 4 has two discharge points. Samples were taken from the two points
and mixed proportionally to the corresponding area drained. SP2 is a pipeline,
discharging into an open unlined channel, about 4 km long, which collects the drainage
from DR3 and discharges into Marimba River.
The variation of storm water quality during a single storm event was investigated at
SP1 at one sampling occasion during a storm event of 2.5 h duration, where samples were
collected at 30 min. intervals. The conveying structure to SP1 is a trapezoidal concrete
lined open channel. Measurements of the water level were taken simultaneously to the
