5.3 Aquifer Hydraulics

The topography is dominated by the underlying geology (Seyler, et al., 2016), with sand dunes along the coastal areas reaching elevations up to 100 m, relatively flat-lying sandy plains across most of the inland area especially in the flood plain of the Berg River, and intrusive granite plutons forming hills reaching elevations up to 500 m in the area. The dominant land uses in the study area are cultivated land (dryland), shrubland as well as low and high fynbos (a biome of the South African southern coastal region, characterized by a diverse richness of endemic plant species).

The area is composed of two paleochannels: the northern Langebaan paleochannel and the southern Elandsfontein paleochannel (Woodford et al., 2003). These paleochannels coincide with thick water-bearing sedimentary sequences. The sediments attain a thickness of nearly 80 m and are characterized by varying permeabilities and semi-confining peat and clay layers (Timmerman, 1985). A clay several meters thick, extending over a large part of the area, effectively separates the sediments into an unconfined and a confined aquifer (Timmerman, 1988). Significantly, the clay distribution is discontinuous and in particular, west of Hopefield, a “clay-missing window” exists. Fractures in the Malmesbury Shale or Cape Granite bedrock yield water and thus the bedrock itself is also considered to be an aquifer (Seyler, 2016). Figure 21 presents a conceptual model of this aquifer environment developed by Tredoux and Engelbrecht (2009), as modified by Jovanovic and others (2019).

Figure 21 – Conceptual model of lithological layers showing upper and lower aquifer units and discontinuous clay (Jovanovic et al., 2019).