Groundwater recharge influenced by ephemeral river flow and land use in the semiarid Limpopo Province of South Africa

Determining the sustainability of groundwater use in drylands with high climate variability is complex. Central to this determination is an understanding of groundwater recharge and associated processes and controls. Groundwater recharge in drylands can occur by diffuse and focused recharge (focused recharge being associated with intense episodic rainfall events and ephemeral river flow, predicted to increase and intensify with climate change). This study evaluated the relative significance and dominant controls on these two recharge processes. Ten groundwater hydrographs with multidecadal observations were collated from the Limpopo Province, South Africa, based on their proximity to river channels and rain gauges, representing diversity in local climate, landscape, vegetation, and hydrogeological conditions. The hydrographs showed that groundwater-level rises are sensitive to rainfall intensity during the rainy season, with generally larger increases after years with large episodic rainfall events, which disproportionately contribute to groundwater replenishment. Recharge processes and annual recharge volumes were quantified using the water-table fluctuation method and the numerical model HYDRUS-1D. This allowed for the inference of additional recharge contributions from focused recharge in proximity to ephemeral rivers, up to a factor of five relative to diffuse recharge. The analysis revealed synchronicity and linear correlation between annual river discharge and recharge close to the river, substantiating the importance of focused recharge close to the river network. The study showed that recharge in drylands is subject to large spatial and temporal variation and that consideration of focused and episodic recharge is critically important for managing groundwater resources at various scales in these regions

Modelling groundwater systems : understanding and improving groundwater quantity and quality management; Dissertation, UNESCO-IHE Institute for Water Education, Delft.

Groundwater is an essential natural resource. It is the main source of water supply for domestic consumption, agriculture, and industrial development in many parts of the world. Besides that it is of vital importance for securing biodiversity of ecosystems. Yet, the resource is threatened by excessive over-exploitation and by contamination mainly resulting from industrial activities and agricultural practices. Increasing demands due to an increase in population and climate change further exacerbate the problem, and hence further development of groundwater resources and efficient protection against over-use and contamination remains a practical concern for water resources managers. In order to properly manage this vital resource, understanding its behaviour when subjected to external stresses is of significant importance. This thesis explores several specific groundwater management problems related to contaminant migration, groundwater-surface water interactions and managed aquifer recharge, using a variety of simulation methods and combined simulation-optimization modelling approaches. The capabilities and limitations of these approaches for evaluating groundwater quantity and quality management options are explored. Case studies were performed on field applications in Belgium, Germany and Oman. The results of these studies demonstrate that better insights and improved groundwater resource management can be achieved through a combination of different simulation and optimization methods that take into account data availability and specific site conditions

Modelling groundwater systems: Understanding and improving groundwater quantity and quality management

Groundwater is one of the most important natural resources. It is the principal source of drinking water in rural and many urban cities, and widely used for irrigation in most arid and semi-arid countries. However, recently it has become apparent that many human activities are negatively impacting both the quantity and quality of groundwater resources. In many parts of the world, groundwater resources are under increasing threat due to contamination and depletion by excessive pumping.Hydraulic EngineeringCivil Engineering and Geoscience