Groundwater and surface water interaction in the Uitenhage Artesian Basin, Eastern Cape, South Africa: case study of the Swartkops and Coega aquifer
Nyawo, Bongizenzo Langelihle
The state of water quality in the Swartkops River catchment in the Uitenhage area, Eastern Cape Province, South Africa, continues to be degraded by anthropogenic activities, which include municipal waste water, industrial waste and agricultural runoff. The study area consists of two aquifers (Swartkops and Coega) that are separated by the fault (Coega fault). In the study area there are two main rivers, namely: Swartkops River and Coega River, which are situated in the Swartkops Aquifer and Coega Aquifer, respectively. Most of the degrading anthropogenic activities are situated in the vicinity of the Swartkops River. The focus of the study was on the pollution of the stream water and aquifer (groundwater), with particular emphasis on the groundwater management. The study objectives were to establish the relationship between groundwater levels and surface topography using Bayesian interpolation method and groundwater and surface water interaction using environmental isotope and hydrogeochemical techniques. The bacteriological assessment was also conducted to determine if hydraulic connections exist between groundwater and the polluted streams. The results of the Bayesian Interpolation Method indicated that there was a strong relationship between the groundwater level elevation and surface topography with the correlation coefficient of 0.9953. The results also indicated that the fault is permeable; hence it did not have influence on groundwater circulation; however, groundwater does not flow from Swartkops River to Coega Aquifer due to groundwater flow gradient. The environmental isotope results indicated that both Swartkops Aquifer and Swartkops River were characterised by heavy isotopes signatures, which indicated the correlation between the two water components. The results further showed that the Swartkops River was recharging the Swartkops aquifer. However, no correlation was established between Swartkops River and Coega aquifer due to flow gradient. Although the flow gradient allows the flow of groundwater from Coega Aquifer to Swartkops Aquifer, Coega aquifer is a Government Water Controlled Area, which could have a very low to none impact on the other aquifer. Piper diagram and stiff diagrams indicated one water type found in the Swartkops and Coega aquifers, which was: Na-Cl type. The water in the Coega aquifer indicated high salinity in the chemical properties, which was typical old marine water derived from deep groundwater source. It was noted that the electrical conductivity values in the Waste Water Treatment Work were closest to those of the Swartkops River and Aquifer, which was in central to those of Coega Aquifer. The bacterial analysis results indicated that during the wet season most of the bacterial counts were high as compared to dry season. It was noted; however, that during the wet season the bacterial counts appeared similar in both aquifers. It is unlikely that the similarities emanated from the interaction of the two aquifers as the analysis of the results indicated that the bacterial counts found in the Coega Aquifer emanated from the farming activities. The study concluded that the fault act as a pathway for migration of groundwater flow. It was established that the groundwater only flows from Coega Aquifer to Swartkops Aquifer due to difference in the hydraulic gradient.
Dissertation Submitted to the University of the Witwatersrand in the Fulfilment of the Master’s Degree in Geology (Hydrogeology) Faculty of Science University of the Witwatersrand Date: May 2017
Nyawo, Bongizenzo Langelihle (2017) Groundwater and surface water interaction in the Uitenhage Artesian Basin, Eastern Cape, South Africa: case study of the Swartkops and Coega aquifer, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/23509>