7.5 Scheme Elements
Artificial recharge began at the site in 1995 and based on initial experience, the CSIR team made some modifications to the design. In line with the small demand, the scheme only has a maximum injection rate of 1 L/s. The basic scheme elements are illustrated in Figures 35 and 36.
Figure 35 – Scheme layout with sand filter – river sand is sieved for the filter (Murray, 2004).
Figure 36 – Sand filter with injection and abstraction borehole (pump house) in the background (Murray, 2008).
Three controlled injection runs from 1999 to 2001 had the effect of reversing the declining water level trend. During the longest test, which lasted for 138 days, 6,567 m3 was injected. This is more than twice the annual sustainable yield of the borehole (2,400 m3/year).
The water quality improved significantly after injecting the clear filtered river water. With three consecutive years of artificial recharge, the electrical conductivity values decreased from over 250 mS/m prior to injection to less than 100 mS/m after injection as shown in Figure 37 (Murray, 2004).
Figure 37 – Water quality at Kharkams abstraction borehole (Water Wheel, 2003).
Even though the scheme is small and relatively simple, basic maintenance is required otherwise efficiency will decline. In the case of Kharkams, the only maintenance required during operation is weekly removal of the fine sediment that settles on the filter since it slows down infiltration.