Hydrogeological conceptual model of large and complex sedimentary aquifer systems – Central Kalahari Basin

Lekula, Moiteela; Lubczynski, M.; Shemang, Elisha

doi:10.1016/j.pce.2018.05.006

Cited by 31 publications

(40 citation statements)

References 38 publications

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“…The whole CKB study area is covered by a mantle of Kalahari Sand of variable thickness, ranging from a few meters in the west to >60 m in the central and eastern part. In approximately two-thirds of the CKB area, the sand is underlain by rocks of Karoo Supergroup Formation, while the remaining third part is underlain by Pre-Karoo rocks (Lekula et al 2018a). The principal aquifers are Lebung, Ecca, and Ghanzi Aquifers (SMEC and EHES 2006).…”

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

“…The hydrogeological framework of the CKB conceptual model presented by Lekula et al (2018a) consists of six hydrostratigraphic units (HU, Fig. 2), including: (1) Kalahari Sand Unit (KSU); (2) Stormberg Basalt Aquitard (SBA); (3) Lebung Aquifer (LA); (4) Inter-Karoo Aquitard (IKA); (5) Ecca Aquifer (EA); and (6) Ghanzi Aquifer (GA).…”

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

“…The top Kalahari Sand Unit (KSU) is composed of sandy unconsolidated to semi-consolidated deposits with thickness ranging from 6 m in the western part to more than 100 m in the central and northern parts of the CKB (de Vries et al 2000;Lekula et al 2018a). The major part of the KSU thickness comprises the unsaturated zone, while the remaining, thin part at the KSU bottom, is saturated and spatially discontinuous.…”

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

“…Lebung Aquifer (LA) consists of well-sorted, reddish to white, massive, but fractured sandstone, also nonuniformly distributed. Its spatially variable thickness ranges from 0 m in the north-western part of the CKB where it wedges out and in the southern part of the Zoetfontein Fault where significant uplifting has resulted in LA erosion, to~230 m in the northeastern and south-western parts of the CKB (Lekula et al 2018a;SMEC and EHES 2006). The fourth HU, i.e.…”

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

“…Its thickness ranges from 0 m in the north-western CKB where it wedges out towards the Ghanzi Aquifer, to~290 m in the southern part of the Zoetfontein Fault (Fig. 1), where significant uplifting is followed by erosion of the SBA, LA and even IKA, so that EA is directly overlain by KSU (Lekula et al 2018a;Smith 1984). The sixth HU, i.e.…”

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

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Use of remote sensing and long-term in-situ time-series data in an integrated hydrological model of the Central Kalahari Basin, Southern Africa

Lekula

Lubczynski

2019

Hydrogeol J

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Distributed numerical models, considered as optimal tools for groundwater resources management, have always been constrained by availability of spatio-temporal input data. This problem is particularly distinct in arid and semi-arid developing countries, characterized by large spatio-temporal variability of water fluxes but scarce ground-based monitoring networks. That problem can be mitigated by remote sensing (RS) methods, which nowadays are applicable for modelling not only surface-water but also groundwater resources, through rapidly increasing applications of integrated hydrological models (IHMs). This study shows implementation of various RS products in the IHM of the Central Kalahari Basin (~200 Mm 2) multi-layered aquifer system, characterized by semi-arid climate and thick unsaturated zone, both enhancing evapotranspiration. The MODFLOW-NWT model with UZF1 package, accounting for variably saturated flow, was set up and calibrated in transient conditions throughout 13.5 years using borehole hydraulic heads as state variables and RS-based daily rainfall and potential evapotranspiration as driving forces. Other RS input data included: digital-elevation-model, land-use/land-cover and soils datasets. The model characterized spatio-temporal water flux dynamics, providing 13-year (2002-2014) daily and annual water balances, thereby evaluating groundwater-resource dynamics and replenishment. The balances showed the dominant role of evapotranspiration in restricting gross recharge to only a few mm yr −1 and typically negative net recharge (median, −1.5 mm yr −1), varying from −3.6 (2013) to +3.0 (2006) mm yr −1 (rainfall of 287 and 664 mm yr −1 respectively) and implying systematic water-table decline. The rainfall, surface morphology, unsaturated zone thickness and vegetation type/density were primary determinants of the spatiotemporal net recharge distribution.

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Section: Study Area and Conceptual Modelmentioning

confidence: 99%

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

Section: Study Area and Conceptual Modelmentioning

confidence: 99%

See 3 more Smart Citations

Use of remote sensing and long-term in-situ time-series data in an integrated hydrological model of the Central Kalahari Basin, Southern Africa

Lekula

Lubczynski

2019

Hydrogeol J

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Depositional style changes during the Permo‐Carboniferous–Early Jurassic evolution of the Central Kalahari Karoo Sub‐basin, Botswana

Bordy

2020

Geological Journal

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The Permo‐Carboniferous–Lower Jurassic Karoo succession in the Central Kalahari Karoo Sub‐basin of Botswana is largely confined to the subsurface, and contains coal, coalbed methane and groundwater resources, similar to other Karoo strata throughout southern Africa. Characterization of the stratigraphic architecture (i.e., spatiotemporal stacking character of sedimentary facies) is essential for various aspects of subsurface resource prediction (e.g., resource parameters; reservoir architecture; mining feasibility). This study uses sedimentary facies analysis on borehole cores from central Botswana and sequence stratigraphic principles to resolve large‐scale depositional style changes during the evolution of the greater Kalahari Karoo Basin in southwestern Gondwana. The results show that changes in the Karoo stratigraphic architecture define two, large‐scale overall fining‐upward depositional sequences (i.e., Lower and Upper Karoo) that are marked by regional subaerial unconformities. These regionally mappable depositional sequences contain pairs of high‐ to low‐amalgamation units, which are typified by stacked, multistorey sandstone bodies, succeeded by finer grained units that are sometimes rich in coal (e.g., the Dukwi‐Makoro‐Kamotaka vs. the Morupule‐Serowe‐Tlhabala formations in the Lower Karoo; the lower versus upper Mosolotsane‐Ntane formations in the Upper Karoo). The large‐scale depositional style changes, reflecting base‐level fluctuations and variation in the balance between accommodation and sediment supply, resulted from climatic changes (e.g., Permo‐Carboniferous deglaciation), tectonic events (e.g., regional pre‐Mosolotsane uplift event), and marine incursions. The latter is documented, for the first time, via the marine‐influenced ichnofauna in the uppermost Ecca Group. Further refining this initial sequence stratigraphic framework for the Botswanan Karoo will require acquisition of radioisotopic dates (e.g., U–Pb zircon ages) and modern seismic reflection data.

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Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

Smerdon

Gardner

2022

Hydrological Processes

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Synoptic sampling of three rivers for a suite of environmental tracers is shown to be an efficient way to gain an understanding of groundwater flow paths for a previously unstudied large area in Alberta, Canada. For regional-scale characterization, classical hydrogeological techniques are limited by the location and number of groundwater wells. This study demonstrates that rivers can become an easily accessible location to sample the distribution of groundwater flow paths discharging to surface water.Modelling of groundwater discharge to the rivers and groundwater mean age helps generate knowledge of groundwater circulation for a large area, which is useful for conceptual model development and focusing future characterization efforts. Results indicate that the benchland areas in this region, with higher topographic relief, had hydrogeological conditions that favoured deeper groundwater circulation with a modelled mean age greater than 100 years from recharge to discharge. Lower relief areas, which coincide with a transition in bedrock formations in this region, appeared to have much shorter and shallower groundwater circulation. The approach required a field program completed in 5 days and financial budget approximately equivalent to drilling a single borehole and installing a monitoring well. It is concluded that under the right conditions, where few classical observation points exist and knowledge is limited, synoptic sampling of rivers can be used to develop scientifically defensible conceptual models at a comparable scale to regional planning and resource management.

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Hydrogeological conceptual model of large and complex sedimentary aquifer systems – Central Kalahari Basin

Cited by 31 publications

References 38 publications

Use of remote sensing and long-term in-situ time-series data in an integrated hydrological model of the Central Kalahari Basin, Southern Africa

Use of remote sensing and long-term in-situ time-series data in an integrated hydrological model of the Central Kalahari Basin, Southern Africa

Depositional style changes during the Permo‐Carboniferous–Early Jurassic evolution of the Central Kalahari Karoo Sub‐basin, Botswana

Characterizing groundwater flow paths in an undeveloped region through synoptic river sampling for environmental tracers

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