Environmental Engineering Reference
In-Depth Information
previous section, where the lack of reliable water quality data has not been mentioned as
a problematic issue by the city of Harare authorities, with respect to diffuse pollution
control. As a result of such underestimation, supply orientated management decisions
could lead to expensive solutions, such as the construction of new technical structures-
dams, long water transportation systems, treatment facilities, etc. In other cases, the lack
of qualitative data regarding the status of water resources could cause severe public
health or environmental problems associated with the polluted water resources.
It was mentioned in Chapter 3 that the monitoring program regarding storm water
quality in Harare has been reduced drastically since 1997 and after the year 2000 is
almost non-existent, due to the political, economic and financial difficulties experienced
during this period. In such conditions, the correct estimation of pollution loads and fluxes
to the Lake Chivero is very difficult and unreliable. The problem is aggravated by the
lack of uniform methodology with respect to the estimation of quantitative and qualitative
data. As a result, the contribution of pollution loads from storm water runoff in Harare
has been estimated at very different scales in different studies (Nhapi et al. 2001,
Magombeyi et. al. in press).
6 CONCLUSIONS
The storm water quality from two major channels in Harare could be classified as diffuse
source of pollution to the watercourses with respect to TP, TSS, TDS, ammonia, COD,
Cd and Pb. No statistically significant spatial variation of pollutants was found regarding
SP1, SP3 and SP4. The highest pollution loads were associated with the industrial area
(SP2), where the risk to the environment could be evaluated as medium to high hazard,
while the rest of the urban areas present a low hazard risk, according to the WWEDR
(2000).
Variation of constituents in a single storm event show that the first flush effect was
associated with contaminants bounded to particulate material and the EMC
concentrations regarding these parameters differ substantially from the mean
concentrations.
The specifics of the control and management of diffuse pollution sources require an
event-orientated water quality monitoring program. The determination of typical storm
events, representative of the case of diffuse pollution transport, with corresponding
hydrographs and event mean concentrations, reflecting seasonal variations could help
significantly the accurate determination of pollution loads and could reduce the need of
monitoring frequency. It could be recommended that such data could be collected by
well-defined and planned research projects, to complement a regular and continuous
monitoring program. The use of automatic samplers at selected locations could improve
the quality and reliability of the results and the cost of the monitoring process.
The lack of a uniform methodology for pollution loads estimation could lead to serious
errors in the process of assessment of diffuse pollution and prioritizing abatement
measures. It could be recommended that:
• A uniform methodology for pollution loads estimation should be developed and
implemented in order to evaluate them more accurately, to compare results from
different spatial and temporal data sets and to support the decision - making process.
