1. Hydrogeology in the Limpopo Basin
Overview of key hydrogeological units in the Limpopo basin in Mozambique, South Africa and Zimbabwe
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2. Why Hydrogeological Units
Insight into groundwater potential for the basin
In sight of where to apply water conservation
Because water conservation is affected by hydro geological units’ characteristics such as
storage capacity ( porosity related)
residence time (underlying units related)
thickness of the weathered overburden (direct relationship between water yielded to thickness)
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3. Geology of Limpopo basin in Moza
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4. Mozambique Hydrogeology
mostly sedimentary rocks or unconsolidated sediments, with minor hard rock lithologies.
primary porosity aquifers with high groundwater storage capacity.
Coarse grained sediments give abundant groundwater; fine grained sediments are poor aquifers.
Coastal regions and areas along the main river channels are most promising.
Regular recharge is important in terms of ensuring good fresh water quality.
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5. For the unconsolidated sediments:
The Hydrogeology of the Limpopo Basin in Mozambique.
Period
Rock types
Groundwater
Potential
Quaternary
Holocene
Pleistocene
Alluvial
Marine / lacustrine alluvials
Very good
Upper
Tertiary
Lower
Miocene
Palaeocene
Ferrigenous arid sands
Mixed calcareous sands
Cretaceous my
Conglomerates + silts + marine sands.
Conglomerates +
Karoo volcanics
Silts – poor
Sands - good
Good
Jurassic my
Rhyolite, Basalt,alkaline rocks.
Very poor.
For the unconsolidated sediments:
Active recharge will be a very significant factor in determining water quality
Grain size will determine well yields
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6. Geology of limpopo basin in Zim
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7. Zimbabwe Hydrogeology
mostly of crystalline basement igneous and metamorphic rocks. Minor occurrence of sedimentary rocks in the basin.
secondary porosity features such as fracture zones and the weathered regolith.
Small scale water supplies available from granitoid crystalline lithologies; greenstones are more favourable.
Karoo lithologies can provide moderate and occasionally large scale groundwater supplies.
Large-scale groundwater supplies restricted to alluvial aquifers along the major rivers.
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8. Hydrogeological Units – Limpopo Basin Zimbabwe
Main lithologies
Groundwater occurrence
Average range of borehole depth (m)
Average range of sustainable borehole yield (m3/d) 1
Achaean Granite and Gneissose rocks
Principally in weathered and fractured zones m thick
40-50 in African surface.
30-40 on post-African surface
in African surface in post African surface 2
Greenstone Belts - Bulawayan metalavas and Shamvaian metasediments
Associated with weathering of Bulawayan strata to 50m and fracturing in Shamvaian strata
30-50 in Bulawayan
40-60 in Shamvaian
or more in Bulawayan
10-25 in Shamvaian 3a
Karoo Sequence has been divided into 5 sub-units.
Batoka Basalt
Controlled by weathering and fracturing from 30-70m below surface
40-60
20-100 3b
The Forest Sandstone
Saturated sandstone generally confined aquifer
50-100
50-300 3c
The Escarpment Grit
Saturated sandstone and grit. Generally confined except in Zambezi Valley
50-70 3d
The Madumabisa Mudstone
Associated with shallow weathering or sandy intercalations which water strike between 40-70m occur
10-25 3e
The Upper and Lower Wankie Sandstone
Saturated sandstone confined aquifer 4
The Cretaceous Sandstones
Deep zones of primary features possibly shallow weathering along drainage lines
70-100
10-50 5
Kalahari sands
Saturated unconsolidated sands and consolidated pipe sandstone 6
Alluvial Deposits
Primary porosity and permeability in gravel lenses, sand layers
20-70
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9. Geology of limpopo basin in S.A
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10. South Africa Hydrogeology
Geology quite complex.
Quartzites / basal conglomerates (Dominion group) and Karst limestones (Malimani & Pretoria group) at the base of the sequence have high to very high potential.
Crystalline basement complex rocks have low to very low groundwater potential, except Archean greenstones, which have medium potential.
Indurated and metamorphosed sedimentary rock also have low potential. Karoo has generally low potential.
Recent unconsolidated sediments and alluvial material have high potential.
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11. Hydrogeological units of S.A.
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12. Conclusions Very varied hydrogeological units Different GW potential
Implication = Different conservations potential
Need to expand this to assess potential for conserving water
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13. Thank you
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