The challenges and implications of assessing groundwater recharge: A case study – northern Sandveld, Western Cape,South Africa

Abstract

The Department of Water Affairs and Forestry (DWAF) is currently carrying out detailed hydrogeological studies within the northern Sandveld area, Western Cape, South Africa. In addition, preliminary studies funded by DWAF, have also been carried out in the area assessing hydrological, ecological and botanical components. The area is receiving much attention due to its environmental uniqueness (part of the area is a Ramsar site) and its significant groundwater resources, which are being utilised for agricultural purposes and municipal water supply. In certain areas this groundwater abstraction is impacting on surface water flows, groundwater and associated ecosystems.In order to gain an understanding of the systems and their inter-relationships within the area, it is necessary to carry out water balance calculations. In carrying out such calculations, the quantification of the "input" component and associated temporal and spatial variability is important to address. With special emphasis on groundwater recharge, the area may be receiving both direct groundwater recharge, (as a consequence of precipitation), and distant groundwater inflow, via the large faults that transect the area, which may be importing groundwater from the inland recharge areas (i.e. the Cederberg Mountains).Earlier groundwater recharge studies within the area and in geologically similar settings indicate a wide range in recharge values. With special reference to the primary aquifers, earlier conservative recharge values indicate 8% recharge, with values as high as 15% being obtained. The current study indicates direct recharge values in the region of 0.2 to 3.4%. Assessment of water balance calculations indicate these recharge values are more realistic. The groundwater recharge quantification has huge significance for the Resource Directed Measures that are also being carried out in the area, in line with the requirements of the South African National Water Act of 1998. The Resource Directed Measures are aimed at ensuring water resource use and development is balanced by protection measures thereby guaranteeing the sustainable use of the resource.

Estimation of groundwater recharge via percolation outputs from a rainfall/runoff model for the Verlorenvlei estuarine system, west coast, South Africa

“…Previous recharge estimates made by Conrad et al (2004), within the Sandveld used a GIS approach 614 that involved assigning literature estimates of recharge percentages based on MAP across the 615 catchment. In the J2000 method, physical measurements of rainfall from nearby stations are considered, 616 26 and elevation correction factors are used to assign rainfall to each HRU.…”

“…Various approaches can be used to estimate recharge, but essentially 52 they can be grouped into three methods: 1) physical, for example water table fluctuation (WTF) 53 (Crosbie et al, 2005) or channel water budget (Rantz, 1982); 2) chemical, for example chloride mass 54 balance (Ting et al, 1998) or applied tracers (Forrer et al, 1999); and 3) numerical, for example 55 rainfall/runoff modelling (SWAT, Arnold et al, 2000) or variably saturated flow modelling (HYDRUS: 56 Šimůnek et al, 2012). For the physical and chemical methods, some component of climate is compared 57 to a groundwater component, for example the comparison between precipitation volume and 58 7 within the high lying areas, which are dominated by the TMG aquifer (Conrad et al, 2004), similar to 138 other high elevation regions in the Western Cape. 139…”

Disentangling the Complexity of Groundwater Dependent Social-ecological Systems

“…Fourteen different methods applied to the same arid setting in Nevada, USA led to recharge estimates ranging from 1 to 100 mm/year (Flint et al 2002). A comparison of different methods to estimate recharge in another arid setting in the northern Sandveld area, Western Cape, South Africa also showed variability (Conrad et al 2004), with estimates ranging from 0.2 % to 8 % of annual rainfall as recharge. Therefore, adequate description of how recharge was calculated for the IGM-scape is critical for acceptance by others.…”

Groundwater Recharge Assessment in the Karstic Aquifers of North Khorasan, Iran in APLIS Method

“…In the area under study, due to the lack of periodic assessment of the discharge of large springs, such methods produce limitations and problems in calculation of recharge (Guardiola-Albert et al 2015). Recent years showed significant improvements in assessment methods which are in direct relation to GIS software and many researchers have used these methods (Jyrkama & Sykes 2007;Scibek & Allen 2006;Marechal et al 2006;Lee et al 2006;Samper et al 2005;Conrad et al 2004;Tapia Silva & Mora Flores 2004;Peña & Arcos 2004;Bouraoui et al 1998;Burke 1995). These methods make the calculation of groundwater recharge easier through a quicker and more concise analysis (Peña & Arcos 2004).…”