Hydrogeology of Malawi: Difference between revisions

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| [[File: Malawi_Hydrology.png | frame | Surface Water Map of Malawi (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]
| [[File: Malawi_Hydrology.png | frame | Surface Water Map of Malawi (For more information on the datasets used in the map see the [[Surface water | surface water resources section]])]]
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| [[File: Malawi_LandCover.png | frame | Land Cover Map of Malawi (For map key and more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]
| [[File: Malawi_LandCover.png | frame | Land Cover Map of Malawi (For map key and more information on the datasets used in the map see the [[Land cover | land cover resources section]])]]
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!colspan="4"| Cretaceous to Quaternary
!colspan="4"| Cretaceous to Quaternary sedimentary rocks
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|Sungwa, Chiwondo, Chitembe, Dinosauric and Lupata
|Sungwa, Chiwondo, Chitembe, Dinosauric and Lupata
||Cretaceous to Quaternary
||These sedimentary rocks are found in small, narrow, elongated basins in the north of the country, running parallel to the shores of Lake Malawi. They include loosely consolidated sandstones and unconsolidated sands, sandy marls, clays and conglomerates, but are dominanted by aeolian desert sandstones, with abundant evaporite deposits in a limestone matrix (UN 1989).  
||These sedimentary rocks are found in small, narrow, elongated basins in the north of the country, running parallel to the shores of Lake Malawi. They include loosely consolidated sandstones and unconsolidated sands, sandy marls, clays and conglomerates, but are dominanted by aeolian desert sandstones, with abundant evaporite deposits in a limestone matrix (UN 1989).  
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==Hydrogeology==
==Hydrogeology==
This section provides a summary of the hydrogeology of the main aquifers in Malawi.  More information is available in the references listed at the bottom of this page. ''Many of these references can be accessed through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].''
This section provides a summary of the hydrogeology of the main aquifers in Malawi.  More information is available in the references listed at the bottom of this page. ''Many of these references can be accessed through the [https://www.bgs.ac.uk/africagroundwateratlas/index.cfm Africa Groundwater Literature Archive].''
The hydrogeology map on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see [[Aquifer properties| the Aquifer properties resource page]] for more details). ''The map is available to download as a shapefile (.shp) for use in GIS packages.''
The hydrogeology map on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see [[Aquifer properties| the Aquifer properties resource page]] for more details). ''The map is available to download as a shapefile (.shp) for use in GIS packages.''


  [[File: Malawi_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]
  [[File: Malawi_Hydrogeology.png]] [[File: Hydrogeology_Key.png | 500x195px]]
===Summary===
The two most important aquifer systems in Malawi are (Chavula 2012):
; crystalline basement rocks, which cover much of the country, and form a low yielding aquifer; and
; unconsolidated alluvium in the major valleys and lake shore plains, which forms a high yielding aquifer in many areas.




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|Alluvium
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|Karoo sedimentary sequence
|Karoo sedimentary sequence
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||The rocks of the Karoo are generally well-cemented with low porosity and intergranular permeability. Groundwater storage and flow occurs largely in fractures in the rocks. 
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===Hydrogeology: key references===
===Hydrogeology: key references===
Chavula GMS. 2012. Malawi, in Groundwater Availability and Use in Sub-Saharan Africa: a review of fifteen countries. Pavelic P et al. (Eds). International Water Management Institute, Sri Lanka.


UN. 1989. Malawi: Ground water in Eastern, Central and Southern Africa. Natural Resources/Water Series No. 19, ST/TCD/6. United Nations Department of Technical Cooperation for Development.  
UN. 1989. Malawi: Ground water in Eastern, Central and Southern Africa. Natural Resources/Water Series No. 19, ST/TCD/6. United Nations Department of Technical Cooperation for Development.  

Revision as of 15:00, 1 July 2015

Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Malawi

Authors

Author 1, Affiliation

Author 2, Affiliation


Geographical Setting

Map of Malawi (For more information on the datasets used in the map see the geography resources section)

General

Malawi includes four main physiographic zones: highlands or uplands; plateau areas; the rift valley escarpment; and the rift valley floor/plains.

The uplands cover a relatively small area but reach 2000 m to 3000 m in elevation. The plateau areas cover much of the country, and are gently undulating surfaces from 750 m to 1300 m in altitude. They are cut into by wide valleys, or 'dambos', with grassy, swampy bases, which largely drain towards the rift valley floor. The rift valley escarpment consists of parallel faults with the land stepping down to the rift valley floor. The rift valley floor and plains extend along the shores of Lake Malawi and the upper Shire Valley; they have low relief and range from 100 m to 600 m in altitude.

Estimated Population in 2013* 16,400,000
Rural Population (% of total) (2013)* 84%
Total Surface Area* 94,280 sq km
Agricultural Land (% of total area) (2012)* 60.8%
Capital City Lilongwe
Region Eastern Africa
Border Countries Tanzania, Mozambique, Zambia
Annual Freshwater Withdrawal (2013)* 1,357 Million cubic metres
Annual Freshwater Withdrawal for Agriculture (2013)* 85.9%
Annual Freshwater Withdrawal for Domestic Use (2013)* 10.6%
Annual Freshwater Withdrawal for Industry (2013)* 3.5%
Rural Population with Access to Improved Water Source (2012)* 83.2%
Urban Population with Access to Improved Water Source (2012)* 94.6%

* Source: World Bank


Climate

Malawi has two main seasons: a wet season from November to April and a dry season from May to October. Rainfall is influenced by topography, with the highest rainfall in upland areas and on slopes explosed to the prevailing northeasterly wet season winds. Annual rainfall exceeds 800 mm over most of the country. Lake Malawi and the upper Shire Valley receive relatively low rainfall. There are large interannual variations in rainfall.

Rainfall time-series and graphs of monthly average rainfall and temperature for each individual climate zone can be found on the Malawi Climate Page.


Average monthly precipitation for Malawi showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Malawi showing minimum and maximum (orange), 25th and 75th percentile (red), and median (black) temperature Quarterly precipitation over the period 1950-2012 Monthly precipitation (blue) over the period 2000-2012 compared with the long term monthly average (red)

For further detail on the climate datasets used see the climate resources section.

Surface water

Lake Malawi is the largest water body in Malawi, and is the dominant control on the surface water drainage network in the country. The main rivers flowing into the lake are the Linthipe, Bua, Dwanga and Rukuru. These flow from wide 'dambos' that drain the plateau areas, which have steep valley sides tht shallow as they reach the rift valley.

Lake Malawi is drained entirely by the Shire River, which is a tributary of the Zambezi River. The upper Shire Valley has a wide alluvial plain, changing to a narrower valley with gorges and rapids in the lower part.

Lake Chilwa forms an internal drainage basin, mainly draining the northern uplands. Rivers flowing into the Chilwa basin tend to be ephemeral in their lower courses, losing water to permeable valley alluvial deposits.

Surface Water Map of Malawi (For more information on the datasets used in the map see the surface water resources section)

Soil

Soil Map of Malawi (For map key and more information on the datasets used in the map see the soil resources section)

Land cover

Land Cover Map of Malawi (For map key and more information on the datasets used in the map see the land cover resources section)


Geology

This section provides a summary of the geology of Malawi. More detail can be found in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive. The geology map on this page shows a simplified version of the geology at a national scale (see the Geology resources page for more details). The map is available to download as a shapefile (.shp) for use in GIS packages.

Summary

Most of the country is underlain by Precambrian to Lower Palaeozoic crystalline basement rocks. These are unconformably overlain in places, particularly in the north and south, by more recent sedimentary rocks or volcanic rocks. There is extensive Quaternary alluvium in valley bottoms and the rift floor plain.

The main structural feature is the rift valley, which was formed by a subsidence fault during the Upper Mesozoic and Cenozoic, and is still active. Lake Malawi and the Shire Valley lie on the floor of the rift valley (UN 1989).


Geological Environments
Key Formations Period Lithology Structure
Unconsolidated
Alluvium, colluvium, lacustrine deposits Quaternary Clays, silts, sands and occasionally gravels, deposited in the floor of the rift valley, and along the lakes in the major valley floors. They vary in thickness along Lake Malawi, tending to increase closer to the lake shore to a maximum of 60 m. In the centre of the Shire Valley, alluvium is 40 to 80 m thick, and reaches 150 m thick in the lower Shire Valley (UN 1989). The alluvial deposits are faulted, caused by ongoing subsidence of the rift valley.
Cretaceous to Quaternary sedimentary rocks
Sungwa, Chiwondo, Chitembe, Dinosauric and Lupata Cretaceous to Quaternary These sedimentary rocks are found in small, narrow, elongated basins in the north of the country, running parallel to the shores of Lake Malawi. They include loosely consolidated sandstones and unconsolidated sands, sandy marls, clays and conglomerates, but are dominanted by aeolian desert sandstones, with abundant evaporite deposits in a limestone matrix (UN 1989).
Igneous
Intrusive plutonic rocks Jurassic These occur in the Chilwa region in the south, and comprise granitic and syenitic plutonic rocks.
Stormberg volcanic rocks Jurassic A series of basaltic lava flows, interbedded with layers of sandstone and tuff (UN 1989).
Karoo
Karoo sedimentary series Permian-Triassic Karoo sedimentary rocks crop out in the north of Malawi, in north-south trending basins, and also to the southwest of the Shire Valley. They lie unconformably on crystalline basement. The base of the sedimentary sequence comprises conglomerates, sandstones, argillaceous rocks and coal seams; at the top of the sequence are arkosic sandstones, marls and more argillaceous rocks. The rocks are largely well cemented by calcite. They can be over 3500 m thick (UN 1989).
Basement Complex
Crystalline Basement Precambrian to Lower Palaezoic Dominantly gneiss and granulite; also some metamorphic schists, quartzites and marbles (UN 1989). The Mafinga and Mchinjin groups in the north and east comprise mainly unmetamorphosed sandstones and conglomgerates. Across the whole basement complex are outcrops of intrusive igneous rocks, such as the Nyika and Dzanalyama granites, syenites, and pegmatite and dolerite dykes (UN 1989).


Hydrogeology

This section provides a summary of the hydrogeology of the main aquifers in Malawi. More information is available in the references listed at the bottom of this page. Many of these references can be accessed through the Africa Groundwater Literature Archive. The hydrogeology map on this page shows a simplified version of the type and productivity of the main aquifers at a national scale (see the Aquifer properties resource page for more details). The map is available to download as a shapefile (.shp) for use in GIS packages.

 

Summary

The two most important aquifer systems in Malawi are (Chavula 2012):

crystalline basement rocks, which cover much of the country, and form a low yielding aquifer; and
unconsolidated alluvium in the major valleys and lake shore plains, which forms a high yielding aquifer in many areas.


Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Alluvium

Sedimentary - Intergranular Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Cretaceous to Quaternary sedimentary rocks

Igneous Volcanic

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Stormberg volcanic rocks The most porous and permeable parts are in the zones of contact between lava flows

Sedimentary - Fracture Flow

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Karoo sedimentary sequence The rocks of the Karoo are generally well-cemented with low porosity and intergranular permeability. Groundwater storage and flow occurs largely in fractures in the rocks.

Basement

Named Aquifers General Description Water quantity issues Water quality issues Recharge
The basement complex rocks


Groundwater Status

Groundwater quantity

Groundwater quality

Groundwater use and management

Groundwater use

Groundwater management

Groundwater monitoring

Transboundary aquifers

For further information about transboundary aquifers, please see the Transboundary aquifers resources page


References

The following references provide more information on the geology and hydrogeology of Malawi. These, and others, can be accessed through the Africa Groundwater Literature Archive.


Geology: key references

Hydrogeology: key references

Chavula GMS. 2012. Malawi, in Groundwater Availability and Use in Sub-Saharan Africa: a review of fifteen countries. Pavelic P et al. (Eds). International Water Management Institute, Sri Lanka.

UN. 1989. Malawi: Ground water in Eastern, Central and Southern Africa. Natural Resources/Water Series No. 19, ST/TCD/6. United Nations Department of Technical Cooperation for Development.

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Africa Groundwater Atlas >> Hydrogeology by country >> Hydrogeology of Malawi