Cycle 4 (2015 Deadline)
PI: Tamiru Abiye (firstname.lastname@example.org
), University of the Witwatersrand, with co-PI Karen Villholth, International Water Management Institute
U.S. Partner: Richard Healy, U.S. Geological Survey
Project Dates: November 2015 - March 2019
As groundwater resources are increasingly developed and impacted by human development, understanding the sustainability of their use and renewability is fundamental. Groundwater recharge processes (defined as the downward flow of water reaching the water table) govern the replenishment of groundwater systems (also called aquifers). Recharge is a critical part of the overall water budget and is one of the most difficult components to quantify. The Limpopo River Basin (LRB) counts on a few very high-yielding dolomite aquifers, as well as large tracts of smaller and less productive crystalline aquifers, each having different recharge processes and groundwater management issues associated with them. While emerging research and incipient field evidence in the LRB suggest that recharge in these semi-arid environments is episodic and driven by climate extremes (van Wyk et al., 2011), simplifying assumptions around annual and steady replenishment persist. This misinterpretation implies a false perception of continuous replenishment and resource security, while in reality the renewal is sporadic and dependent on fewer and interspersed (often decadal) extreme rainfall events. Another conventional perception or approximation is that recharge occurs as a uniform and diffuse or omnipresent process in the landscape, while it is often governed by preferential pathways at different scales, e.g. through fractures in the subsurface, through intermittently flooded and inundated areas and flow channels, like rivers, or at mountain fronts. Finally, understanding groundwater renewability and upper limits for exploitation in an environmental/ecosystem context is in a relatively early stage. This project builds on existing research to (1) better determine processes, quantities, and locations of recharge in the LRB, and (2) use this information in groundwater development, use, and management in selected sites.
Groundwater pumping for irrigation in the Dendron area. Photo courtesy of Dr. Abiye
The key development impact of the GRECHLIM Project is to increase the capacity of young scientists, as well as local and national authorities, to assess groundwater recharge from applied field investigations carried out as part of the project and linked to ongoing initiatives. The capacity development will be part of the students’ theses and supported by dedicated and hands-on training at the facilities of the U.S. Geological Survey (USGS).
The other significant strand of development impact will be pursued through strategic partnerships with stakeholders and entities involved in water resources management in the LRB. These range from the transboundary LRB organization LIMCOM (Limpopo Watercourse Commission) to the local farmers and water utilities interested in augmenting their resources and improving their services. Exploring linkages and collaboration with climate/seasonal forecasting entities like the Southern Africa Regional Climate Outlook Forums will be pursued and their capacity to incorporate aspects of groundwater information in their forecasts supported.
Finally, findings will be synthesized as guidelines and tools for managed aquifer recharge, for predicting groundwater availability as a function of climate and land use, and for assessing upper limits for groundwater exploitation based on environmental flow requirements. The tools and guidelines will be developed in partnership with relevant stakeholders and shared as part of consultations and workshops.
Summary of Recent Activities
The project which has ended resulted the presence of variable groundwater recharge rate and processes. The research also helped in the understanding of the effects of changes in climate variables on the baseflow and the relative contributions of natural stream flow versus wastewater. The Johannesburg rainfall consists of different moisture sources from the warmer Indian ocean, cooler Atlantic Ocean, the high latitude Antarctic and the local water bodies. Because of moisture source influence on stable isotope signature of rainfall, this condition gives rise to isotopically different groundwater, which presents challenges in groundwater assessment. Despite the variable signature in Johannesburg rainfall, there is a high isotopic similarity between groundwater and rainfall indicating prevalence of recharge from rainfall through the preferential flow that bypasses the unsaturated zone. Very low recharge occurs through the soil media due to a high influence of temperature on potential recharge. Recharge predominantly occurs in the south of the Upper Crocodile River Basin, where there is lower temperatures and higher rainfall. Recharge in the Upper Crocodile River Basin mainly occurs through the fractures and cavities of the Witwatersrand quartzites and the Malmani dolomites, respectively. This is deduced on the basis of the deduced insignificant recharge through the soil media and the predominant bypass flow. The interaction between groundwater and surface water occurs mainly from surface water bodies that intersect the fractures, faults, dissolution cavities and lineaments. The traces of rainfall amount and temperature effects reveal the high dependence of groundwater recharge on the amount of rainfall in the Witwatersrand aquifer. The simulations for changes in climate variables indicate sensitivity of stream flow components to changes in rainfall and temperature. The increase in rainfall simulates more baseflow increase than the decrease in temperature, while an increase in temperature simulates more baseflow decrease than a decrease in rainfall. With changing climate variables and increase in industries, wastewater will increase while baseflow decreases leading to more polluted surface water resources within the Upper Crocodile River Basin. The outcome of the project was presented during the stakeholder meeting besides scientific publications.
The International Water Management Instiitute applied physico-chemical water quality analysis to give basic information on groundwater, river water and rainfall quality, and multiple groundwater-surface water exchange and recharge methods to estimate the contribution of river surface water and baseflow to the total river flow. The methods applied include water level transect monitoring, baseflow separation by tracers, constraining the baseflow separation algorithm by the tracer methods and river water balance over a river segment and groundwater recharge methods of chloride mass balance (CMB), Water table flcutuation (WTF) and baseflow separation in the Letsitele Catchment. Understanding the interaction between groundwater and surface water in Letsitele Catchment is essential because of large commercial farming, municipal water supply boreholes located near the river and wastewater treatment plant in the upper catchment that pose pollution threat to water resources. Understanding the interaction provides information that facilitates evaluation of the susceptibility and sustainability of the basement aquifer and surface-water resources in the catchment. As water demands from irrigation and domestic uses are projected to continue to increase with more frequent drought years in the future, an understanding of how groundwater sustains river flow during dry periods equips water-resource managers to make informed decisions about future groundwater development and protection.
The PEER team is going to continuously engage the Department of Water and Sanitation (DWS) so that can they can start to use the recharge methods and groundwater-surface exchange methods that they tested in this study. They will also encourage DWS to continue monitoring groundwater for management and planning purposes and policy development
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