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The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley
Dissertation (PhD) -- University of Stellenbosch, 1991.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2012
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| _version_ | 1867613880846385152 |
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| access_status_str | Open Access |
| author | Greeff, Gabriel Johannes |
| author2 | Halbich, I .W. |
| author_browse | Greeff, Gabriel Johannes Halbich, I .W. |
| author_facet | Halbich, I .W. Greeff, Gabriel Johannes |
| author_sort | Greeff, Gabriel Johannes |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Dissertation (PhD) -- University of Stellenbosch, 1991. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/69444 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:43:10.408Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2012 |
| publishDateRange | 2012 |
| publishDateSort | 2012 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/69444 The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley Greeff, Gabriel Johannes Halbich, I .W. Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. Hydrogeology -- South Africa -- Bree River Watershed Salinity -- South Africa -- Bree River Watershed Groundwater -- South Africa -- Bree River Watershed Dissertations -- Geology Dissertation (PhD) -- University of Stellenbosch, 1991. Measurements made since 1960 have shown a steadily rising salt load in the Brêe River, a major Western Cape river from which large agricultural areas are irrigated. Specific tributaries such as the Bossiesiens River were found to contribute large amounts of salt to the Brêe River, and it was decided to evaluate this valley and procure data for use in a mathematical catchment management model. A research program to analyze the surface drainage and groundwater of this catchment and to test the bedrock for its salt potential confirmed the wide contrast between low TDS water within the Table Mountain Sandstone watershed rocks around the catchment and the highly saline condition of the groundwater within the Bokkeveld Group of shale formations in the central part of the valley. Structural and lithological mapping indicated a synclinal fold cut by a major longitudinal scissor fault which controlled the development of the elongated catchment; a number of other faults are present. Good supplies of high quality groundwater are produced by boreholes and fountains from fault breccias in the Table Mountain sandstone formations. The area of the catchment was measured and the mean annual rainfall and its salinity established. This data, together with the annual volume and salinity of the irrigation water input to the valley by the Le Chasseur canal and boreholes established the total annual contribution of salt to the catchment from outside sources. Construction of a permanently equipped gauging weir at the lower end of the catchment by the Department of Water Affairs allowed flow and salinity measurements to be made on a daily basis, and the total annual tonnage of salt leaving the catchment in river water could be established. A salt balance model was drawn up for the valley, the increments being provided by data forthcoming from a percussion borehole drilling program, the chemical analysis of groundwater, pump testing to determine hydrological bedrock parameters, subsurface tracer irrigation tests and leaching of soil and bedrock materials. Extremely heavy salt loads were encountered in irrigation return flow samples, particularly in areas where deep ripping of soils had been carried out as part of the irrigation development. Oxygen isotope analysis revealed that 18O-depleted groundwater in the Table Mountain Sandstone formations is migrating through the Bokkeveld Shale formations, and leaching out salt along the way, before eventually reaching the Joesiesens River mainly through faults and fractures. Black, micaceous shales appear to be the main source of salinity in the valley, especially in their decomposed clay-rich upper profiles immediately below the soil. Very little salt is released from alluvial sands and the underlying gravels which have been irrigated for more than 50 years, during which time most of the salts have been leached out. It is recommended that the Table Mountain Sandstone catchments be drilled with a view to producing additional high quality groundwater for the region; any new irrigation developments on soils overlying Bokkeveld shale should be restricted, and allowed only after thorough chemical analysis of the subsoil and decomposed bedrock layers have proved the existence of a thickness of at least 1.2 metres of leached soil, with a minimum resistance of 300 ohms, overlying clay-rich decomposed shale. Doctoral 2012-08-27T12:27:05Z 2012-08-27T12:27:05Z 1991 Thesis http://hdl.handle.net/10019.1/69444 en Stellenbosch University 265 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Hydrogeology -- South Africa -- Bree River Watershed Salinity -- South Africa -- Bree River Watershed Groundwater -- South Africa -- Bree River Watershed Dissertations -- Geology Greeff, Gabriel Johannes The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title | The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title_full | The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title_fullStr | The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title_full_unstemmed | The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title_short | The geohydrology of a typical catchment in the Cape Supergroup, Bree River Valley |
| title_sort | geohydrology of a typical catchment in the cape supergroup bree river valley |
| topic | Hydrogeology -- South Africa -- Bree River Watershed Salinity -- South Africa -- Bree River Watershed Groundwater -- South Africa -- Bree River Watershed Dissertations -- Geology |
| url | http://hdl.handle.net/10019.1/69444 |
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