Cycle 4 (2015 Deadline)
PI: Tamiru Abiye (email@example.com
), 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 the first quarter of 2018, A manuscript was submitted for peer review titled “Characterization of groundwater recharge conditions and flow mechanisms in the crystalline aquifers of the Johannesburg area, South Africa”.
Eleven rainfall samples were collected in Johannesburg and analyzed for stable isotopes. The discharge of a spring was measured weekly while sampling was done once a month in January, February and March 2018. A sample was collected for radiocarbon and tritium from the spring in February 2018 and sent to iThemba Laboratory, Johannesburg for analysis.
Two monitoring boreholes at 50m and 60m depth were drilled for use in application of water level transect method and for isotope and chemical sampling of groundwater. The boreholes were capped with a flush mounted metal cover with a cement seal and lock system for borehole protection and security reasons. The water level data loggers to automatically take water levels in the boreholes have also been purchased. These data loggers will enable the groundwater level changes to be monitored at a fine resolution of hourly time step. The transect method compares the water levels in the boreholes and the river to assess if the groundwater level is higher or lower than the river water level. if the groundwater level is higher than the river water levels, then the groundwater will flow towards the river and vice versa. Furthermore, these drilled boreholes will be handed over to the Department of Water and Sanitation and included in the national groundwater monitoring system of South Africa for improved groundwater monitoring.
River flow measurements at two sections, 3km apart, where water balance calculations are being done to find if the river flow is increasing downstream are continuing on a monthly time step. If the river flow increases downstream, it them means the river is gaining water from groundwater, provided any inflows into the river are accounted for. Collection of rainfall, groundwater (4 monitoring boreholes: 3 are not being pumped, and 1 is being pumped for water supply to a homestead) and river water samples for isotope and chemical analysis from the Letsitele area is continuing on a monthly basis.
A draft report detailing the methods being applied in the Letsitele area and preliminary results is complete and will be updated as more data and results are being collected during the course of the year (2018). Title of the report: Calibration of baseflow separation using Environmental Tracers and Borehole water level Transects: A study in Letsitele area, Limpopo Basin.
In the next 3-6 months, Collection of rainfall and analysis for stable isotopes shall continue as per rainfall event in Johannesburg to continue to investigate the isotopic characterization of rainfall in the area for good assessment of groundwater recharge. Albert Farm spring shall be monitored monthly and assessed for stable isotopes. A manuscript on estimation of groundwater recharge using Precipitation Runoff Modeling System shall be submitted for publication. Continued river flow measurement at the temporal gauge site and permanent gauge site. An additional method known as Bromide tracer dilution method will be applied to assess groundwater-surface water interaction in the Letsitele area, Limpopo, South Africa
A topographical survey will be carried out to assess the ground surface levels at the monitoring boreholes and the riverbed and river water depth. This data will feed into the groundwater level transect method and improve the results obtained using DEM (digital elevation) levels from Aster website.
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