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International Institute for Geo-Information Science and Earth Observation (ITC) 2016

Groundwater resources evaluation in Kalahari Karoo basin

Kisendi, E.E. (Emmanuel Ezekiel)

Titre : Groundwater resources evaluation in Kalahari Karoo basin.

Auteur : Kisendi, E.E. (Emmanuel Ezekiel)

Etablissement de soutenance : University of Twente International Institute for Geo-Information Science and Earth Observation (ITC)

Grade : Master of Science in Geo-Information Science and Earth Observation 2016

Groundwater resources evaluation is an important aspect of water resources’ management. It is most important in dry areas where there is no surface water, and hence groundwater becomes the only source of portable w ater . Groundwater resources are optimally evaluated by distributed numerical models which however require accurate definition of external driving forces and good understanding of aquifer geometry and vertical and horizontal heterogeneity of the aquifer sys tems . The main objective of this study was to evaluate groundwater recharge and groundwater resources in the Lokalane- Ncojane Karoo Basin (LN KB). At first, cross- sections over much larger, regional Kalahari Karoo Basin (KKB) were developed to assess the vertical extension of each layer unit. Then, using the RockWorks software, a 3D litho- stratigraphic model of the Kalahari Karoo Basin (KKB) was developed. The cross- sections of that model were first developed for all formations following Smith ( 1984) , and further narrowed down to include only five hydro stratigraphic layers on top of the impermeable rock basement. The five hydro stratigraphic layers included ; 0- 189 m Kalahari Sand saturated/unsaturated zone layer , 0- 329 m Stormberg Basalt aquitard , 0- 230 m Ntane Sandstone aquifer , 0- 282 m Mosolo tsane- Kwetla Mudstone aquitard and 0- 275 m for Ecca Sandstone aquifer . The Kalahari Sand and Ecca Sandstone have spatially continuous extent , while Stormberg Basalt, Ntane Sandstone and Mosolotsane- Kwetla Mudstone are spatially limited . The calculated thic kness es of the five hydro- stratigraphic layers were compared with the known regional geology of Botswana. Once understanding the spatial extent of the KKB layers , an integrated hydrologic steady state model (IHM) of the groundwater prospective LNKB area was created . It consisted of the three aquifers, separated by two aquitards . The simulated period was six hydrologic years. The steady- state model comprised mean measurement of six hydrologic years. The steady- sate model was calibrated by trial and error met hod, using the vertical (VK, VKCB) and horizontal (HK) hydraulic conductivities as calibration variables . After model calibration, the fluxes IN and OUT of the model were calculated. It was observed that, the total inflow components to the model was 194.1 0 mm yr- 1 , out of which, 194.06 mm yr- 1 (99.9%) c a me from the UZF gross recharge component of which 194.03 mm yr- 1 was lost through ET, resulting into only 0.03 mm yr- 1 as groundwater rechar ge through the unsaturated zone .

Mots clés : Kalahari Karoo Basin ; Lokalane- Ncojane Karoo Basin ; 3D Stratigraphy model ; 3D hydrostratigraphy model  ; integrated hydrologic model

Version intégrale (ITC)

Page publiée le 2 avril 2018, mise à jour le 16 octobre 2018