A situation analysis of the water quality in the Hartbeespoort dam catchment: nutrients and other pollutants' assessment on rivers entering the dam
Date
2008-04-09T12:58:16Z
Authors
Dudula, Maxwell Zanoyise
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Abstract
The water quality study of the rivers in the Hartbeespoort Dam catchment as well as
its outflow has been conducted over a period of 6 months (i.e. from January 2004 to
July 2004). The research effort has focused on nutrient concentrations (i.e.
phosphorus and nitrogen) and their load at chosen points of the catchment. The
occurrence of different phosphorus (P) and nitrogen (N) species as well as other water
quality parameters at the selected points of the catchment have been examined.
Situational analysis of sources of pollution in the catchment has also been carried out.
The load of P and N into the dam was estimated and compared with values computed
from the chosen water quality models. Following the analysis of the data generated in
the research, the Crocodile River was identified as the river contributing the highest
yearly TP load measuring 316.3 t/y into the Hartbeespoort Dam. Of this load, 52% is
from the Jukskei River, 47% is from Hennops River and lastly 1% is from the Upper
Crocodile River catchment. The Magalies and Swartspruit contributed a small
percentage of the load to the Dam. The measured total inorganic nitrogen loading
from Crocodile River was 2 330.2 t/a of which 49% is from Jukskei River, 35% was
from Hennops and 16% from the Upper Crocodile River Catchment. The Magalies
and Swartspruit also contributed a small percentage of the load to the Dam. Natural
runoff from the Dam’s Catchment is approximately 50% of the total runoff and
another 50% is the discharge of effluent from 10 waste water treatment plants
(WWTP) situated in the Catchment. It has also been noted that a large contribution
was runoff from the urban areas. Analysis of data from WWTP’s reveals that most of
the P and N measured in the catchment emanate from these operations in spite of the
fact that most of them comply with effluent discharge standards. Wet season’s runoff
contributes in the nutrient load. Non-point sources have been identified as informal
settlements, cultivated land, developments, urban runoff, golf courses, parks and
burnt pastures.
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The study concluded that despite the implementation of the stricter effluent discharge
standards in the catchment the P load is still very high to maintain the likely mesoeutrophic
conditions in the Dam. In order to maintain the dam in mesotrophic
conditions, the annual load of TP should be kept within the range of 10 to 15 t/a. It is
suggested that abatement strategies to reduce the load into Crocodile River be applied
on the subcatchments.