Israel, S; Kanyerere, T
Globally, surface waters are severely unsustainably exploited and under pressure in semi-arid coastal regions, which results in increasing demand for groundwater resources. Currently, Cape Town and its neighbouring towns along the West Coast of South Africa are facing water shortage related problems. Managed Aquifer Recharge (MAR) is a nature based solution to improve groundwater security in drought prone regions such as the West Coast. The objective of this study was to design a groundwater monitoring network using a hybrid hydrochemical, geophysical and numerical modelling approach to assess and mitigate the potential impacts of MAR for the West Coast Aquifer System (WCAS). An Analytical Hierarchy Process method was used to perform a Multi-criteria analysis employed in GIS (ArcMap 10.3).
The factors of importance for optimized groundwater monitoring network design were based on available data and consultations with hydrogeologists and environmental scientist at stakeholder workshops. The factors which were considered included: elevation (m), geology, density of existing boreholes (wells/km2), electrical conductivity (mS/m), water rise (m), water level decline (m), transmissivity (m/day), saturation indices and lithological thickness (m). Factors were weighted based on their level of importance for the design of the groundwater monitoring network using Analytical Hierarchy Process (AHP). Priorities were calculated from pairwise comparisons using the AHP with Eigen vector method. The Consistency Ratio (CR) calculated was 5.2% which deems the weighting coefficients statistically acceptable. The results show that high priority monitoring areas occurs in the areas where there are fresh groundwater, high borehole density, elevated topography, higher recharge rates and decline in water levels are found. The monitoring network will include boreholes from the low priority areas to ensure that hydrogeological conditions are monitored and impacts are not worsened. Geophysical, numerical and chemical modelling aspects of the methodological approach will be incorporated into the initial groundwater monitoring network design.