The effects of water transfer from Swakoppoort and Omatako Dams on the water quality of Von Bach Dam, Namibia
In the Otjozondjupa Region, Namibia, water is transferred from Swakoppoort and Omatako Dams into Von Bach Dam to limit evaporation losses and bring water closer to the purification plant. There is a gap in the knowledge about the effects on water quality in Von Bach Dam due to water transfer from Swakoppoort and Omatako Dams, as previous studies on such aspects in the area do not exist. The study objective was to; (a) characterise water quality of the three dams, (b) determine whether water transfers affect the water quality of Von Bach Dam, (c) determine if the treatment of water abstracted from Von Bach Dam for potable water supply has been influenced by water quality changes arising from water transfers. Four sampling locations were established in Von Bach Dam, one in Swakoppoort Dam, and one in Omatako Dam. Water samples were collected in these three dams weekly. Two senior officers responsible for water treatment were interviewed about possible water treatment problems arising from the water transfer. Descriptive statistics, ANOVA and correlation were carried out to analyse the data. The results showed that, secchi disk depths, total phosphorus, orthophosphate, ammonia, dissolved organic carbon, chlorophyll a and microcystis were statistically different in the three dams at a 5% significance level. Upstream land uses, geology of the catchment and water stratification are likely to influence the water quality in the three dams. During water transfers into Von Bach Dam, secchi disk depths, turbidity, dissolved oxygen, iron, total phosphorus, ammonia (NH₄-N) and chlorophyll a were statistically different at a 5% significance level at all the four sampling locations within this dam. These differences are due to the influence of water transfers. The influence of water transfers on water quality was localised at the discharge points SL4 (at the inflow of Von Bach Dam) and SL1 (at the outflow of Von Bach Dam). Water treatment problems due to high ammonia, dissolved organic carbon, and turbidity in the water abstracted from Von Bach Dam occurred during water transfers and runoff from the catchment. This view was supported by the study findings.