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A preliminary analysis of the groundwater recharge to the Karoo formations, mid-Zambezi basin, Zimbabwe

Larsen, F; Owen, R; Dahlin, Torleif LU ; Mangeya, P and Barmen, Gerhard LU (2002) In Physics and Chemistry of the Earth 27(11-22). p.765-772
Abstract
A multi-disciplinary study is being carried out on recharge to the Karoo sandstone aquifer in the western part of Zimbabwe, where recharge is controlled by the presence of a thick, confining basalt layer. The aquifer is geographically extensive, and has been identified throughout the southern part of the mid-Zambezi basin (Fig. 1). The potential for groundwater abstraction seems to be huge. The key issues in this part of the study are the extent of the recharge area and the recharge rates. The direct recharge area has previously been considered to be the area of outcrop of Karoo Forest sandstone, before it dips below an impervious basalt cover. However,, resistivity profiling shows that the basalt at the basin margin is weathered and... (More)
A multi-disciplinary study is being carried out on recharge to the Karoo sandstone aquifer in the western part of Zimbabwe, where recharge is controlled by the presence of a thick, confining basalt layer. The aquifer is geographically extensive, and has been identified throughout the southern part of the mid-Zambezi basin (Fig. 1). The potential for groundwater abstraction seems to be huge. The key issues in this part of the study are the extent of the recharge area and the recharge rates. The direct recharge area has previously been considered to be the area of outcrop of Karoo Forest sandstone, before it dips below an impervious basalt cover. However,, resistivity profiling shows that the basalt at the basin margin is weathered and fractured, and probably permeable, while the basalt deeper into the basin is fresh, solid and impermeable. Field and laboratory analysis of 22 groundwater samples support this extension of the recharge area to include a large area below the fractured basalt. CO2 gas pressures, calculated with the code PHREEQC using field measurements of pH and alkalinity, show that below the fractured basalt the groundwater is an open system in contact with atmospheric CO2. The C-14 and nitrate concentrations in this groundwater also indicate that recent infiltration takes place. The chloride contents of the rainfall and the groundwater in the recharge area have been measured to calculate direct recharge from rainfall. These data indicate that the direct recharge is in the range of 10-130 mm/yr, with an average value of 25 mm/yr. Preliminary results of recharge estimate using Cl-36 data suggests lower direct infiltration rates, but further studies are needed. The combination of hydro-chemical, isotopic and geophysical investigations show that the recharge area extends well beyond the sandstone outcrop area, northwards beneath the basalt some 20 km beyond the basalt margin. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
hydrochemistry, geophysics, recharge, groundwater, Karoo aquifers
in
Physics and Chemistry of the Earth
volume
27
issue
11-22
pages
765 - 772
publisher
Elsevier
external identifiers
  • wos:000179166600009
  • scopus:0036425445
ISSN
1474-7065
DOI
10.1016/S1474-7065(02)00064-5
language
English
LU publication?
yes
id
822cac11-08aa-41f8-b260-53510f62ff21 (old id 323626)
date added to LUP
2007-11-07 16:08:01
date last changed
2017-09-03 03:36:45
@article{822cac11-08aa-41f8-b260-53510f62ff21,
  abstract     = {A multi-disciplinary study is being carried out on recharge to the Karoo sandstone aquifer in the western part of Zimbabwe, where recharge is controlled by the presence of a thick, confining basalt layer. The aquifer is geographically extensive, and has been identified throughout the southern part of the mid-Zambezi basin (Fig. 1). The potential for groundwater abstraction seems to be huge. The key issues in this part of the study are the extent of the recharge area and the recharge rates. The direct recharge area has previously been considered to be the area of outcrop of Karoo Forest sandstone, before it dips below an impervious basalt cover. However,, resistivity profiling shows that the basalt at the basin margin is weathered and fractured, and probably permeable, while the basalt deeper into the basin is fresh, solid and impermeable. Field and laboratory analysis of 22 groundwater samples support this extension of the recharge area to include a large area below the fractured basalt. CO2 gas pressures, calculated with the code PHREEQC using field measurements of pH and alkalinity, show that below the fractured basalt the groundwater is an open system in contact with atmospheric CO2. The C-14 and nitrate concentrations in this groundwater also indicate that recent infiltration takes place. The chloride contents of the rainfall and the groundwater in the recharge area have been measured to calculate direct recharge from rainfall. These data indicate that the direct recharge is in the range of 10-130 mm/yr, with an average value of 25 mm/yr. Preliminary results of recharge estimate using Cl-36 data suggests lower direct infiltration rates, but further studies are needed. The combination of hydro-chemical, isotopic and geophysical investigations show that the recharge area extends well beyond the sandstone outcrop area, northwards beneath the basalt some 20 km beyond the basalt margin.},
  author       = {Larsen, F and Owen, R and Dahlin, Torleif and Mangeya, P and Barmen, Gerhard},
  issn         = {1474-7065},
  keyword      = {hydrochemistry,geophysics,recharge,groundwater,Karoo aquifers},
  language     = {eng},
  number       = {11-22},
  pages        = {765--772},
  publisher    = {Elsevier},
  series       = {Physics and Chemistry of the Earth},
  title        = {A preliminary analysis of the groundwater recharge to the Karoo formations, mid-Zambezi basin, Zimbabwe},
  url          = {http://dx.doi.org/10.1016/S1474-7065(02)00064-5},
  volume       = {27},
  year         = {2002},
}