Assessment of the surface water quality of the main rivers feeding at Katse Dam Lesotho

Abstract

Water quality is an essential and critical aspect in meeting basic human and environmental needs. The scarcity of rainfall and water in South Africa prompted the need to augment water supply by transferring water from other catchment areas through inter-basin transfers, such as the transfer of water through the Vaal River system from the Lesotho Highlands. The Katse Dam is the main dam in the Lesotho highlands feeding water into the Vaal Dam, through the Ash River. Five rivers, namely the Malibamatso, Bokong, Pelaneng, Liphofung and Mokhoulane, feed into the Katse Dam. Surface water resources are susceptible to chemical, physical and microbiological contamination, either through human or natural activities. It became important that the raw water flowing from the five rivers into the Katse Dam be monitored to ensure that the dam water be preserved. The aim of the study was to investigate the surface water quality of the five rivers feeding the Katse Dam in Lesotho. The approach was to determine the activities occurring in the catchment area and whether these activities have any effects on surface water resources, and consequently, on the users of the water resources. Also, to examine the historic (2000 to 2011) and current (2012 to July 2014) water quality data to establish if the water quality has changed. To determine the surface water quality, samples were taken from the five rivers respectively. Samples were taken once a month for Study Period A (2000 to 2005), every second month for Study Period B (2006 to 2011) and four times a year for Study Period C (2012 to July 2014). Physical determinants such as temperature, dissolved oxygen, pH and turbidity were measured in situ. Selected chemical, physical and microbiological determinants were analysed at the Rand Water Analytical Services Laboratory. The water quality of the five rivers was relatively good, influenced mainly by both natural processes and human activities occurring within the Katse Dam catchment area. The water quality varied between rivers and over the study periods. The historic water quality data was not compliant with most water quality guidelines whilst current water quality data showed improved water quality. The Bokong River had the highest number of non-compliant determinants with water quality guidelines, especially for the World Health Organisation (WHO) and Department of Water Affairs & Sanitation (DWS) Aquaculture guidelines indicating that the water quality might have been compromised. The Pelaneng River had the least number of non-compliant determinants, thus indicating even better water quality when compared to other rivers. Natural processes such as rock weathering and geological composition of the catchment area influenced chemical determinants such as aluminium, copper, manganese and zinc, as well as physical determinants such as turbidity, total dissolved solids, water hardness, pH and suspended solids being non-compliant with most of the guidelines. Chemical determinants could have been influenced by the mining activities occurring in the catchment area. However, this requires further investigation. Agriculture and human settlements were to a large extent the most influential activities impacting the water quality. Chemical determinants such as ammonium, nitrates, nitrites and microbiological determinants such as Escherichia coli, coliphage bacteria, faecal coliform, Giardia and Cryptosporidium were linked to the application of manure and other agricultural inputs to crop fields, the lack of proper sanitation, and extensive livestock farming. The concentrations of these microbial determinants far exceeded the WHO, South African National Standard (SANS) drinking water and DWS guidelines. The surface water in this catchment area is used for domestic, livestock and farming purposes, therefore a compromise in the quality could have health and environmental effects on the communities living within the catchment area and the aquatic ecosystem at large. On the basis of these findings and conclusions, it is recommended that a long-term continuous monitoring programme be implemented, especially in areas where increased human activities have been observed. Monitoring should be strengthened for the Bokong and Liphofung Rivers since these rivers showed the highest number of non-compliances and microbial contamination. All anthropogenic activities in the catchment areas of these rivers must be monitored and strictly managed to prevent and mitigate their possible impacts. Specific emphasis should be placed on agricultural development, which should be controlled to ensure sustainable livestock and cropping practices. Sanitation facilities, systems and community programmes should be put in place to minimise faecal contamination. It would be beneficial for the Lesotho Highlands Development Authority (LHDA) to establish a central database for all information that will be accessible to both South African and Lesotho citizens.