Abstract
The Olifants River Water Resource Development Project (ORWRDP) is a multipurpose project incorporating
both economic and social development objectives to cater for the water demands of commercial and social
users. Phase 2 of the project encompassed the construction of the De Hoop Dam within the Steelpoort River
basin and bulk water transfer pipelines. During this study, various water quality assessment techniques were
conducted along the length of the Steelpoort River from a site situated just downstream of the De Hoop Dam to
a site near the town of Steelpoort in order to determine spatial trends and relate these trends to changes
imposed by the construction of the De Hoop Dam and the bulk water transfer pipeline. A total of four sites were
selected within the Steelpoort River to assess the impacts on water quality as a result of the construction
activities. Chemical water analyses and Physico-chemical Assessment Index (PAI) techniques were employed
to assess the water quality status and to determine the present ecological state of the Steelpoort River.
The water quality results with respect to the different water constituents did not illustrate a distinct change in
water quality over the study period. From the results obtained during this study, it was detected that
concentrations of nutrients such as phosphate, nitrate and nitrite were generally low and similar to the
concentrations recorded prior to construction in the baseline study for the ORWRDP. Mats of filamentous algae
were observed to increase with distance increase downstream of the dam and they may be responsible for the
uptake and removal of nutrients within the river. The highest concentrations of nitrate were recorded at Site 3
(Dwars River), a tributary of the Steelpoort River. Agricultural return flows and pollution such as dumping of
used nappies were identified as the main sources of nutrient inputs within the Steelpoort River. The
concentration of toxic constituents such as lead, cadmium, cyanide, mercury, manganese, zinc and arsenic
were recorded below detection limit at all sites with occasional spikes observed. The most noticeable impact
observed during this study occurred due to the alteration in the flow regime as a consequence of construction
activities. Alteration of flow has resulted in the erosion of stream banks along the Steelpoort River. Pipeline
construction activities have resulted in the removal of riparian vegetation, stream diversions which encourage
erosion and were observed to contribute significantly to the sediment loads entering the river through water
discharges. This may have resulted in high turbidity levels and siltation observed downstream at Site 4.
The eco-classification scores using PAI indicated that the Steelpoort River is a moderately impaired watercourse
in terms of water quality. The main driver components contributing to such a score were excessive
sedimentation and changes in trophic status with distance downstream. Site 3 (Dwars River) a tributary to the
Steelpoort River was still largely natural. The findings of this study indicated that the Steelpoort River is in the
similar ecological class in terms of water quality as prior to construction of the De Hoop Dam and the bulk water
transfer pipeline. The water quality within the Steelpoort River however deteriorated during construction mainly
due to the addition of sediment loads. It was therefore recommended that further studies be carried out within
the Steelpoort River on macro-invertebrate response and the habitat integrity to increase the level of confidence
of results obtained in this study.
M.Sc. (Aquatic Health)