Predicting Aquifer Sustainability of the Modder River Catchment Using CARS Model

This paper presents the concepts of CARS methods and the results of its applications for modelling groundwater sustainability of the Modder River Catchments of South Africa. CARS is derived from the combination of important hydrological parameters that impact sustainable use of groundwater resources and it stand for C- climate, A- aquifer sustainability, R- right to resources and S- socio economics including land use practises. The Modder River Catchment is a Tertiary Catchment of the Orange River System which originates from highlands of Lesotho and flows to the Atlantic Oceans through Namibia. In arid and semi-arid areas of South Africa, farmers and communities only have a limited number of water provision points. This has put more pressure on groundwater and increased the number of wells and boreholes being drilled to access groundwater, which is needed for multiple purposes, especially for agriculture and drinking water. The limited resources of water provision have put undue pressure on aquifers such as the aquifers in the C52 Modder River catchment. The net effect has been depletion and prolonged periods of drought. This has created a need for groundwater sustainability methods, models, and indices such as CARS to predict sustainability of aquifers. The CARS concept is based on the interactions of the factors and physical processes governing hydrological cycles with human induced factors in relation to groundwater sustainability. These interactions (climate-land use-groundwater, land use-surface-groundwater, climate-groundwater) connects the CARS parameters interchangeably. The parameters include rainfall, slope, land use/cover, evapotranspiration, climatic zones, water quality, aquifer yields, rock types, aquifer systems, recharge, population, uses, the permit/licence system and groundwater rights. The parameters were ranked and scored in an index format. The ratings considered the assignment of values to the overall elements in factors: factor (C) climate, factor (A) aquifer sustainability, factor (R) rights/equity verse resources and factor (S) socio economics. Score were assigned with the lowest scores of 1 corresponding to poor practices and the highest score of 5 to good practices. Climate (C) and aquifer sustainability (A) factors were assigned total scores of 30 each, while right (R) and socioeconomics (S) have a scoring of 20 each respectively. The CARS sustainability index scores ranged from 19 for the least sustainable aquifer and 100 for a sustainable aquifer 100. The developed CARS sustainability index was applied to 52 boreholes in the Modder River Catchments of South Africa. ArcView GIS was employed in modelling the response of each of the 52 boreholes to CARS aquifer sustainability concepts. Results shows that 9 boreholes are classified as moderate sustainability which means they are on average sustainable while 43 boreholes are of low sustainability index which suggest they are not sustainable. The new methodology of CARS concepts of modelling aquifer sustainability as applied in this paper to the groundwater of the Modder River Catchment will assist in the sustainable management of aquifers.