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Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town
Thesis (MSc)--Stellenbosch University, 2020.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2020
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| _version_ | 1867614136351850496 |
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| access_status_str | Open Access |
| author | Harilall, Zita |
| author2 | Miller, Jodie A. |
| author_browse | Harilall, Zita Miller, Jodie A. |
| author_facet | Miller, Jodie A. Harilall, Zita |
| author_sort | Harilall, Zita |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2020. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/108020 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:47:14.760Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/108020 Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town Harilall, Zita Miller, Jodie A. Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. TMG Aquifer Radiocarbon dating Noble gas dating Aquifers -- South Africa -- Western Cape Groundwater ecology -- South Africa -- Western Cape UCTD Water-supply -- Cape Town -- Sustainability Groundwater recharge -- Measurement Thesis (MSc)--Stellenbosch University, 2020. ENGLISH ABSTRACT: The TMG Aquifer is one of the largest aquifer systems in the country and is currently targeted as a potential source of potable water for the City of Cape Town (CoCT) in times of water stress. This study has aimed to provide proper constraints on turnover time of groundwater in the aquifer system before large-scale abstraction takes place, in order to evaluate the sustainability of the resource. This study has used the 3H/3He system to date modern water (<100 years) and 14C to date older groundwater (>500 years). Groundwater residence times were determined for six aquifers in the Western Cape, namely the alluvial, Witteberg, Bokkeveld, TMG, Cape Granite Suite (CGS) and Malmesbury aquifers. Noble gas and radiocarbon dating of the TMG Aquifer range from 0.3 – 44.6 and <70 – 1 626 years, respectively. Residence times calculated for the alluvial aquifer are also relatively young, ranging from 0.0 – 1 783 years. Good correlation between 3H/3He and 14C ages indicate relatively short residence times for the alluvial and TMG aquifers whereas groundwater from the Witteberg (6 699 years), Bokkeveld (58.5 – 6 038 years), CGS (3.7 – 8 648 years) and Malmesbury (45.5 – 11 146 years) aquifers indicate mixing of older water bodies with modern recharge resulting in distinctly different ages derived from the two dating systems. Noble gas recharge temperatures (9.4 – 28.6°C), 3H and 14C activities suggest that groundwater in the region is primarily recharged at high elevations, but also that rainfall events further down the flow path at lower elevations, make substantial contributions to groundwater recharge. Evaluation of isotopic tracers and basic chemistry have led to the identification of potential proxies for residence time, namely pH, HCO3- concentrations and Ca/Mg ratios. These components can be used to make assumptions on groundwater residence times without the costly process of analysis. Residence times indicate short turnover times for groundwater in the TMG Aquifer (typically <130 years) which suggest that the aquifer would be susceptible to climate change. Projected reductions in precipitation and regular occurrences of droughts would likely diminish groundwater supplies in the aquifer system. If large-scale abstraction does commence, this needs to be factored into abstraction regimes as unsustainable abstraction practices could lead to groundwater depletion. AFRIKAANSE OPSOMMING: Geen opsomming Masters 2020-02-23T13:53:23Z 2020-04-28T12:14:44Z 2020-02-23T13:53:23Z 2020-04-28T12:14:44Z 2020-03 Thesis http://hdl.handle.net/10019.1/108020 en Stellenbosch University xii, 134 leaves : illustrations (some color), maps (some color) application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | TMG Aquifer Radiocarbon dating Noble gas dating Aquifers -- South Africa -- Western Cape Groundwater ecology -- South Africa -- Western Cape UCTD Water-supply -- Cape Town -- Sustainability Groundwater recharge -- Measurement Harilall, Zita Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title | Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title_full | Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title_fullStr | Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title_full_unstemmed | Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title_short | Noble gas and radiocarbon constraints on the residence times of groundwater in and around the City of Cape Town |
| title_sort | noble gas and radiocarbon constraints on the residence times of groundwater in and around the city of cape town |
| topic | TMG Aquifer Radiocarbon dating Noble gas dating Aquifers -- South Africa -- Western Cape Groundwater ecology -- South Africa -- Western Cape UCTD Water-supply -- Cape Town -- Sustainability Groundwater recharge -- Measurement |
| url | http://hdl.handle.net/10019.1/108020 |
| work_keys_str_mv | AT harilallzita noblegasandradiocarbonconstraintsontheresidencetimesofgroundwaterinandaroundthecityofcapetown |