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 - October 2018 (UW); January 2016 - December 2018 (IWMI)
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
During this reporting period the four MSc students who joined the GRECHLIM project in 2016 successfully completed their research and graduated from Wits University.
Field work was conducted in South Africa and in Botswana in support of the two Msc students working in Ramotswa aquifer. Furthermore, infiltration tests were conducted in suitable areas using double ring infiltrometer, soil samples were collected at different depths near sampled boreholes by auguring to determine gain size particle composition and for chloride profiling. The infiltration tests and chloride profiling help to understand the groundwater recharge processes in the study area. Furthermore, boreholes inventory for both monitoring and pumping boreholes was conducted in the area, two rainfall samples were collected for major ions and stable isotope analyses, 37 groundwater samples were collected for stable isotope analyses, 36 samples were collected for major ion analyses and 18 samples were collected for microbial (total and feacal coliforms) analyses.
Rainfall is currently being sampled from 2 station in Johannesburg and analysed for stable isotopes for construction of the Local Meteoric Water Line. The line is being used as a reference point in the basin to characterize groundwater recharge condition by observing its deviation from the line. In the review period, 63 rainfall samples have been collected and analysed for stable isotopes.
In October 2017, field visit to Ramotswa area in both Botswana and South Africa to identify sites for doing infiltration tests. The selection of the sites was based on different soil and geology type and different landcover /use. The infiltration tests are important to identify areas suitable for managed aquifer recharge (MAR) in the Ramotswa aquifer. Areas with high infiltration rates are more suitable than those with low infiltration rates. The infiltration results are also going to be an input the hydrogeological modelling of MAR feasibility by IWMI that will commence in the next quarter. The hydrogeological model will be used to evaluate how the aquifer system reacts to the induced artificial recharge such as building up of groundwater level (mound) and to determine storage capacity of the aquifer for additional recharge through MAR.
Dendron catchment field visit was conducted in Limpopo, South Africa by participants from IWMI and Wits University. Dendron is characterized by low yielding aquifers and huge groundwater demand for commercial farming. The objective of the field trip was to identify and collect water samples for isotope and tritium analyses for understanding of groundwater flux including recharge and groundwater age. These results are required to refine the base flow filter parameter and groundwater model that has been setup for the catchment. The field trip was successful as we managed to build good collaboration with the chairperson of the farmers union in that area who introduced us to the other commercial farmers in the area. During the field trip, a total of 10 samples were collected for stable isotope analyses.
In the next 3-6 months, two GRECHLIM project team members are going to attend a recharge training session for 2 weeks in the US in 2018 to be facilitated by Richard Healy, project advisor from USGS and staff from the University of Texas.
The team will continue to equip monitoring boreholes in Letsitele area, South Africa and collect water sample for isotopes and chemical analysis in all the GRECHLIM sites in both Botswana and South Africa
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