Long term hydrochemical analysis and quality assessment of five dams in Lesotho, Southern Africa

Abstract

Abstract Lesotho, is a mountainous country located within South Africa. Water is one of the major export earnings. One of the major dams in Lesotho is called Mohale Dam built at a cost of US$1.5 billion. It has five inflow dams at: Bokoaneng, Bokong, Likalaneng, Jorodane and Senquyanne. There is sparse data on water quality of these dams, hence, data were collected between 2009 and 2012 to monitor and assess the water quality for drinking using these parameters: Na, K, Ca, Mg, electrical conductivity (EC), pH, total hardness (TH) and turbidity. These were compared with the WHO standard for drinking water. Data were analysed using these procedures: means (PROC MEANS) and cluster (PORC CLUSTER) of Statistical Analysis Systems, and trilinear plots/Piper diagram. Results showed that across sites, these variables (i.e. pH, EC, Ca, Na, K, Mg, TH, and turbidity fluctuated across sites and years and still far lower than the critical limits of the WHO as drinking water quality. The only parameter that was relatively high, when compared to the stringent water quality of APHA, AWA and WEF [ 25] standard for drinking was the mean turbidity which ranged between 1.32±0.27 (Bokoaneng) and 4.70±1.26 (Jorodane). However, when compared to the WHO [2] standard for drinking water quality of 5.00 NTU [23], it is still acceptable. The Piper diagram classified the water as sulfate-chloride dominated, though when compared to the critical values of WHO limits of 250mg/L (Cl) and 400 mg/L (SO4 2-) it is still very low as these values are still ≤ 5 mg/L. As at the time of data collection, there was no source of contaminants. However, the aforementioned values were the highest for a dam located at Likalaneng. As, such, it is imperative that sources of the “seemingly” high values should be identified as this might build up over the years.