Hydrogeology of Lesotho

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

Authors

Mr Khahliso Leketa, Department of Water Affairs, Lesotho

Mrs Matsolo Migwi, Department of Water Affairs, Lesotho

Emily Crane & Brighid Ó Dochartaigh, British Geological Survey, UK

Geographical & Political Setting

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

General

Estimated Population in 2013* 2074465
Rural Population (% of total)* 73.729%
Total Surface Area* 30360 sq km
Agricultural Land (% of total area)* 75.27%
Capital City Maseru
Region Southern Africa
Border Countries South Africa
Annual Freshwater Withdrawal (2013)* 43.8 Million cubic metres
Annual Freshwater Withdrawal for Agriculture* 8.676%
Annual Freshwater Withdrawal for Domestic Use* 45.66%
Annual Freshwater Withdrawal for Industry* 45.66%
Rural Population with Access to Improved Water Source* 76.7%
Urban Population with Access to Improved Water Source* 93.2%

* Source: World Bank


Climate

Climate classification of Lesotho. Spatial variations in annual average rainfall and temperature.

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


Average monthly precipitation for Lesotho showing minimum and maximum (light blue), 25th and 75th percentile (blue), and median (dark blue) rainfall Average monthly temperature for Lesotho 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

General information about Lesotho surface water – perennial/ephemeral – major rivers – discharge points.

The Hydrology Division of the Department of Water Affairs is responsible for river flow gauging and data management.

Rivers that form part of the Lesotho Highlands Development Authority (LHDA) are gauged by the LHDA. The resulting data is held by the LHDA.

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

Soil

Soil Map of Lesotho (For more information on the datasets used in the map see the soil resources section)
General information about Lesotho soils.

Land cover

General information about Lesotho land cover.
Land Cover Map of Lesotho (For more information on the datasets used in the map see the land cover resources section)


Geology

The following section provides a summary of the geology of Lesotho. More detailed information can be found in the key references listed below: many of these are available through the Africa Groundwater Literature Archive.

The geology map below was created for this Atlas. It shows a simplified version of the geology of Lesotho at a national scale. The map is available to download as a shapefile (.shp) for use in GIS packages. TO BE REPLACED BY SLIGHTLY REVISED MAP

File:Lesotho Geology.png

Geological Environments
Key Formations Period Lithology Structure
Igneous - volcanic
Lesotho Formation (Drakensberg Group) Jurassic Massive basalts which overlie the sedimentary rocks of the Karoo Group. Reaches thickness of 1600m at Mount-aux-Sources in the north of Lesotho (Schmitz and Rooyani 1987).
Igneous - intrusive
Dolerite intrusions Jurassic Numerous dykes cross the country in two dominant directions: NW-SE and NNE-SSW. Most dykes are near vertical, plate-like bodies, but some dip as shallowly as60° (Schmitz and Rooyani 1987). Some dykes cut across all geological formations and others die out within the basalts. Sills (plate-like, near-horizontal intrusions) occur in older Karoo sedimentary strata, especially in the southwest of Lesotho. Maximum thickness of 1600m.
Sedimentary – Karoo
Clarens Formation (Cave Sandstone) (Stormberg Group) Late Triassic to Early Jurassic This is the youngest sedimentary formation underlying the basalts of the Jurassic Lesotho Formation. It occurs across the central and eastern parts of Lesotho, but crops out only in central Lesotho and in major valleys within the Lesotho Formation. The sandstones are of aeolian origin. Generally pale white and cream coloured, although darker beds occur. The formation can be subdivided into three zones:
  1. Zone I: thickly to very thickly bedded, light brown and light red, very fine grained sandstone, silty sandstone and sandy siltstone.
  2. Zone II: alternating beds of massive and cross-bedded sandstone.
  3. Zone III: massive to very thickly bedded, very fine grained sandstone to massive silty sandstone, sandy siltstone and siltstone.
Thickness from 15 to 250m. Outcrops in the form of plateaux in the lower foothills and as cliffs overlooking the lowlands.
Elliot Formation (Red Beds) (Stormberg Group) Late Triassic to Early Jurassic Underlies the Clarens Formation and characterised dominantly by red and purple mudstones and shales and medium to fine grained sandstones.

The strong red and purplish coloration differentiates it from the underlying Molteno Formation and from the white and cream coloured overlying Clarens Formation. The transition from the underlying Molteno Formation to the Elliot Formation is gradual, indicating continuous sedimentation.

Thins from a maximum of 250m in the south to 15m in the north.
Molteno Formation (Stormberg Group) Late Triassic to Early Jurassic White arkosic grits and gritty sandstones, mainly pebbly, with occasional thin shaly sandstones and bluish mudstone (Schmitz and Rooyani 1987). The Molteno Formation underlies the whole of Lesotho and outcrops in the lowlands, where it comprises up to 50m of massive, coarse sandstone. Thins out northwards (Schmitz 1984): from 35m in the north to 150m in the south.
Burgersdorp Formation (Beufort Group) Mid Permian to Lower Triassic Green, purple and red shales and mudstones with some buff sandstone; occasional carbonaceous shales with thin coal seams; some ferruginous concretion beds. Only the uppermost part of this formation is exposed in Lesotho, with its maximum exposed thickness in the Mohokare (Caledon) River Valley in the extreme western part of Lesotho (UNDP 1984). Maximum exposed thickness of 200 to 250m

Hydrogeology

The following section provides a summary of the hydrogeology of Lesotho. More detailed information can be found in the key references listed below: many of these are available through the Africa Groundwater Literature Archive.

The hydrogeology map below was created for this Atlas. It shows a simplified version of the hydrogeology of Lesotho at a national scale. The map is available to download as a shapefile (.shp) for use in GIS packages. TO BE REPLACED BY SLIGHTLY REVISED MAP. A more detailed hydrogeological map is produced by the Department of Water Affairs (Arduino and Del Sette 1994).

Aquifer properties

File:Lesotho Hydrogeology.png

Igneous - volcanic

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Lesotho Formation Generally of low permeability due to the massiveness of the basalt rocks. Drilling evidence supports this. Numerous springs occur at almost all levels, originating from weathered sections of the basalt near dykes, interflow zones and at the contact zone between the basalts and the metamorphosed top of the underlying, very low permeability Clarens Formation.

They have low sustainable yields. However, in higher permeability weathered zones near dykes, sustainable borehole yields can reach 1.5 l/s (DWA database).

The aquifer is semi-confined. Boreholes are typically drilled up to 80m depth.

Small yields. Bypass flow through fractures may be a significant proportion of recharge.

Igneous - intrusive

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Dolerite dyke-related aquifers The wider dolerite dykes (wider than 50m) have significant gabbro content below a depth of about 10m, which can act as a barrier to groundwater flow. This can also be the case for narrower dykes which have a massive fabric. Many dykes are 2 to 20m wide, comprising basalt or dolerite, and some of these may be fractured to depths of 30m to 40m and consequently have high permeability compared with surrounding strata. These may form localised aquifers (Schmitz and Rooyani 1987).

The most hydrogeologically significant feature of the dykes is the contact zone between dyke and parent rock. This is because the intrusion of the dykes caused some induration and fracturing of the surrounding country rock along the contact zone. This is known as the “baked zone”, which is highly permeable and forms dyke-related aquifers. The extent of the "baked zone" depends on the intrusion temperature, thickness and dip of the dyke and on the nature of the country rock at the contact (Schmitz and Rooyani 1987).

Boreholes can give blowout yields of up to 10 l/s and sustainable yields of up to 4 l/s. Numerous pumping test results have shown that, although dykes are very permeable, their storage capacity is generally low. Good yields are usually found within 0.5m from the dyke (Schmitz and Rooyani 1987).

Dyke-related springs are usually perennial and strong, frequently discharging at the lowest topographical outcrop of a dyke, such as a stream bed. Discharges of up to 2 l/s (DWA) have been measured. The dissolved solids content can be as much as 350 mg/L (Schmitz and Rooyani 1987).

This aquifer is semi-confined. Boreholes are drilled up to 80 m depth.

Sustainable borehole yields up to 4 l/s; springs yield up to 2 l/s. Springs can have relatively high dissolved solids content (up to 350 mg/l)

Consolidated Sedimentary - Fracture Flow

The Clarens, Elliot, Molteno and Burgersdorp Formations form sedimentary rock aquifers. The sandstone layers within these formations are the key aquifers. These sandstone layers vary in grain size, shape, packing and degree of cementation and, therefore, vary in their permeability. The primary porosity, storage and transmissivity of groundwater in the sedimentary rock aquifers is generally relatively low. Secondary porosity (fracturing) created by igneous intrusions has improved permeability (Lesupi).

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Clarens Formation This is a minor aquifer due to fine grain size and correspondingly low porosity, which averages 2.5% (Schmitz and Rooyani 1987). Groundwater discharge occurs via many seasonal springs at the base of the cliffs, derived from groundwater flows through fractures in the Clarens Formation that emerge at the junction with the shales and even lower permeability sandstones of the underlying Elliot Frmation.

Boreholes drilled in this formation, if not dry, have low yields of ~0.1 l/s (DWA Database).

The Clarens Formation is confined in some areas where the Lesotho Formation overlies it, but elsewhere it can be said to be semi-confined.

Boreholes drilled in this formation, if not dry, have low yields of 0.1 l/s (DWA Database) The low permeability metamorphosed top of the Clarens Formation does not favour recharge to the aquifer. Recharge occurs through fractures.
Elliot Formation This Formation is not a particularly good aquifer. A critical factor appears to be the sandstone/shale ratio, which must be approaching unity for a good supply borehole.

There is a reported porosity of 25% (Bonny 1975). Tests show that many boreholes drilled in this formation yield from 0.1 l/s to 0.2 l/s, with specific capacity values close to 0.05 l/s/m after 1 hour and 0.02 l/s/m after 24 hours (Schmitz and Rooyani 1987). Very few springs occur in this formation, and any springs have low yields: wet season spring discharges may be 0.05 l/s (Lesupi).

This aquifer is semi-confined.

Molteno Formation This formation is regarded as the best aquifer in Lesotho. The base of the Molteno Formation forms a spring line, and within the formation, stratified variations in permeability produce additional springs, some of which are perennial and high yielding.

Boreholes drilled in this formation have safe yields that vary from 0 l/s to 1.6 l/s with specific capacity values averaging 1.9 l/s/m after 24 hrs (Schmitz and Rooyani 1987). During the dry season, spring yields of 0.5 l/s can be obtained.

This aquifer is semi-confined.

Burgersdorp Formation This formation is not a good aquifer. The sandstone/shale ratio is very low.

Boreholes drilled into this formation are usually dry. Boreholes close to dykes or cut through dykes, which are weathered and more permeable, have a mean yield of 1.16 l/s and a mean specific capacity of 1.12 l/s/m after 24 hrs (Schmitz and Rooyani 1987).

This aquifer is semi-confined.

Unconsolidated

Named Aquifers General Description Water quantity issues Water quality issues Recharge
Alluvial deposits There are a small number of unconsolidated aquifers in Lesotho in which boreholes can yield from 10 l/s to 40 l/s (Arduino et al. 1994). They consist of gravelly to sandy ancient alluvial deposits and are usually found at the banks of major rivers or on a former river course. One well known is the Maputsoe-Nyenye aquifer in the north of Lesotho.


Groundwater Status

According to TAMS (1996) the total renewable groundwater resource in Lesotho is 10 m³/s. This information has not been updated since.

Key groundwater quality issues in Lesotho are naturally occurring contamination by iron, manganese and fluoride.

There are plenty of wetland areas on the Mountain plateaux of Lesotho which form small bogs also known as sponges. The bogs have diameters ranging from 50 to 250 m. they occupy surface depressions and therefore accumulate water where underground is impermeable. They are major sources of rivers in Lesotho.

Groundwater use and management

Groundwater use

The institutions responsible for water supply in Lesotho are:

  • Department of Rural Water Supply (DRWS) - rural areas
  • Water and Sewage Company (WASCO) - urban areas

The major uses of groundwater are industrial, and domestic use in the rural communities. Towns and cities that depend entirely on groundwater resources include: Maputsoe, Roma, Mapoteng, Peka, Thaba Tseka and Morija. Other cities, such as Quthing, Mafeteng, and Maseru, entirely depend on surface water resources.

Groundwater use facts

  • 11.4% of Lesotho's water supply is from groundwater (information from WASCO and DRWS databases).
  • Estimated groundwater abstractions for domestic use are 22,552,662 m³/year
  • Estimated groundwater abstraction for industrial use (including mining) is 473,040 m³/year


Groundwater access
Types of systems Number of systems
Gravity Systems 2768
Diesel Pumping/ Borehole 40
Diesel Pumping/ Spring 45
Electrical Pumping/ Borehole 106
Electrical Pumping/ Spring 38
Solar Pumping/ Borehole 94
Solar Pumping/ Spring 305
Water Point (captured and taped spring) 635
Hand Pumps 831

NB: A gravity system consists of a captured spring upslope of a community, from where water is piped to an outflow downslope. A water point consists of a captured spring, usually downslope of a community, where a tank is constructed at the spring and fitted with a tap. This is usually done where there is no power to pump water upslope to the community.

Groundwater management

The key groundwater management institution in Lesotho is the Department of Water Affairs (DWA). The DWA's Groundwater Division is responsible for assessing and managing groundwater resources, through hydrogeological surveys, borehole construction, aquifer tests and monitoring.

The Water Act 2008 provides for the management, protection, conservation, development and sustainable utilisation of water resources. Permits are required for drilling a borehole (Construction Permit) and for using groundwater (Water Use Permit); these are granted by the Water Rights Division of the DWA.

Transboundary aquifers

Lesotho shares an aquifer with the Republic of South Africa. There is no joint groundwater monitoring of this aquifer.

The Lesotho/South Africa Karoo Aquifer was used as an example of transboundary aquifers in a paper by Cobbing et al. (2008): A critical overview of transboundary aquifers shared by South Africa.

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

Groundwater monitoring

The Groundwater Division of the DWA monitors groundwater levels in 72 boreholes and flows at 162 springs. These are monitored on a biannual basis, in dry and wet seasons. There are also selected key springs and boreholes in each district which are monitored on a monthly basis. The data are stored in the Departmental database.

References

Geology: Key References

Lesotho Government. 1982. Geological Map of Lesotho, Scale: 1:250 000. Government of the United Kingdom (Directorate of Overseas Surveys) for the Government of Lesotho.

Schmitz G and Rooyani F. 1987. Lesotho: geology, geomorphology and soil. National University of Lesotho

UNDP. 1984. Geology and Mineral Resources of Lesotho. Exploration for Diamonds (phase 1) and Exploration for Minerals (Phase 2). Technical report DP/UN/LES-71-503/8 and DP/UN/LES-73-021/9. For the Government of Lesotho.

Hydrogeology: key references

Arduino G, Bono P and Del Sette, P. 1994. Hydrogeological Map of Lesotho, Scale: 1:300 000. Government of Italy General Directorate of Development Cooperation MOLISV-Groundwater Project and Government of Lesotho Ministry of Natural Resources Department of Water Affairs, Groundwater Division.

Schmitz G and Rooyani F. 1987. Lesotho: geology, geomorphology and soil. National University of Lesotho

Lesupi MJ. Hydrogeology of Lesotho. ISARM 1. Unpublished article

TAMS. 1996. Water Resources Management: Policy and Strategy

African Groundwater Literature Archive (AGLA) references

For more references for the hydrogeology of Lesotho please visit the African Groundwater Literature Archive's Lesotho page.

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