Editing Hydrogeology of Ethiopia

Jump to navigation Jump to search

Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.

The edit can be undone. Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.

This page supports semantic in-text annotations (e.g. "[[Is specified as::World Heritage Site]]") to build structured and queryable content provided by Semantic MediaWiki. For a comprehensive description on how to use annotations or the #ask parser function, please have a look at the getting started, in-text annotation, or inline queries help pages.

Latest revision Your text
Line 1: Line 1:
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Ethiopia
 
[[Africa Groundwater Atlas Home | Africa Groundwater Atlas]] >> [[Hydrogeology by country | Hydrogeology by country]] >> Hydrogeology of Ethiopia
  
[[File:CC-BY-SA_logo_88x31.png | frame | This work is licensed under a [https://creativecommons.org/licenses/by-sa/3.0/ Creative Commons Attribution-ShareAlike 3.0 Unported License]]]
+
 
  
 
Ethiopia is one of the oldest countries in the world, having existed within similar borders to today for over 2000 years. For most of its long history its governmental system was an independent monarchy, which was overthrown in 1974. The communist military Derg government that followed was itself overthrown in 1991, since when a shaky democracy has seen several contested elections. The African Union is headquartered in Addis Ababa, Ethiopia’s capital.  
 
Ethiopia is one of the oldest countries in the world, having existed within similar borders to today for over 2000 years. For most of its long history its governmental system was an independent monarchy, which was overthrown in 1974. The communist military Derg government that followed was itself overthrown in 1991, since when a shaky democracy has seen several contested elections. The African Union is headquartered in Addis Ababa, Ethiopia’s capital.  
Line 165: Line 165:
 
The geology map on this page shows a simplified version of the geology of Ethiopia at a national scale (see the [[Geology | geology resource page]] for more details).  
 
The geology map on this page shows a simplified version of the geology of Ethiopia at a national scale (see the [[Geology | geology resource page]] for more details).  
  
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Ethiopia geology and hydrogeology map'''].
+
[[File:Ethiopia_Geology3.png | center | thumb| 500px | Geology of Ethiopia at 1:5 million scale. Developed from USGS map (Persits et al. 2002). For more information on the map development and datasets see the [[Geology | geology resource page]]]]
 
 
[[File:Ethiopia_Geology3.png | center | thumb| 500px | Geology of Ethiopia at 1:5 million scale. Developed from USGS map (Persits et al. 2002). For more information on the map development and datasets see the [[Geology | geology resource page]]. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Ethiopia geology and hydrogeology map].]]
 
  
 
{| class = "wikitable"
 
{| class = "wikitable"
Line 270: Line 268:
  
 
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 [[Africa Groundwater Atlas Hydrogeology Maps | hydrogeology Map]] resource page for more details).  
 
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 [[Africa Groundwater Atlas Hydrogeology Maps | hydrogeology Map]] resource page for more details).  
 
[https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html '''Download a GIS shapefile of the Ethiopia geology and hydrogeology map'''].
 
  
 
Other hydrogeological maps from different sources have been produced and are available in different formats. Some can be viewed on the [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=ETH WHYMAP] website.
 
Other hydrogeological maps from different sources have been produced and are available in different formats. Some can be viewed on the [http://www.bgr.de/app/fishy/whymis/index.php?&type=country&id=ETH WHYMAP] website.
  
  
[[File:Ethiopia Hydrogeology3.png | center | thumb| 500px| Hydrogeology of Ethiopia at 1:5million scale. For more information on how the map was developed see the [[Africa Groundwater Atlas Hydrogeology Maps | hydrogeology map]] resource page. [https://www.bgs.ac.uk/africagroundwateratlas/downloadGIS.html Download a GIS shapefile of the Ethiopia geology and hydrogeology map].]]
+
[[File:Ethiopia Hydrogeology3.png | center | thumb| 500px| Hydrogeology of Ethiopia at 1:5million scale. For more information on how the map was developed see the [[Africa Groundwater Atlas Hydrogeology Maps | hydrogeology map]] resource page]]
  
 
====Unconsolidated====
 
====Unconsolidated====
Line 282: Line 278:
  
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality
+
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
 
|Alluvial sediments
 
|Alluvial sediments
||Afar Region - High Productivity. Northern Ethiopia - Low Productivity.
 
 
||Afar Region: alluvial deposits in floodplains have moderate to high permeability, with measured transmissivity from 1-500 m²/day and yields of up to 20 l/s. These aquifers can be unconfined and confined; they vary in thickness from 0 - 400 metres; water table depth is typically in the range 1 to 60 metres; typical borehole depth is 100 m; salinity is very variable.
 
||Afar Region: alluvial deposits in floodplains have moderate to high permeability, with measured transmissivity from 1-500 m²/day and yields of up to 20 l/s. These aquifers can be unconfined and confined; they vary in thickness from 0 - 400 metres; water table depth is typically in the range 1 to 60 metres; typical borehole depth is 100 m; salinity is very variable.
  
Line 291: Line 286:
  
 
Northern Ethiopia: alluvial sediments overlying basement rocks can store appreciable volumes of water and are characterised by high permeability and high water infiltration capacity. They are typically shallow and have limited lateral extent, and form perched aquifers. Springs and hand-dug wells are common, with recorded yields ranging between 0.05 l/s and 0.17 l/s.
 
Northern Ethiopia: alluvial sediments overlying basement rocks can store appreciable volumes of water and are characterised by high permeability and high water infiltration capacity. They are typically shallow and have limited lateral extent, and form perched aquifers. Springs and hand-dug wells are common, with recorded yields ranging between 0.05 l/s and 0.17 l/s.
 +
 +
||Afar Region - high productivity. Northern Ethiopia - low productivity.
 
||Variable salinity
 
||Variable salinity
 +
||
 
|-
 
|-
 
|Alluvio-lacustrine sediments
 
|Alluvio-lacustrine sediments
||Variable productivity, but can be highly productive in places
 
 
||These sediments have highly variable permeability.  Fine sand deposits have the highest permeability, with some boreholes providing more than 10 l/s with minimal drawdown. Transmissivities range up to 700 m²/day and specific yields are of the order of 3.2 l/s/m. In several places higher transmissivities have been noted. For example, a 150 m deep borehole in alluvio-lacustrine deposits at the foot of the southern plateau has a transmissivity of 3012 m²/day. These aquifers can be both unconfined and confined; they vary in thickness from 0 to 400 metres; water table depth is typically in the range 1 to 60 metres; and the typical borehole depth is 100 m.
 
||These sediments have highly variable permeability.  Fine sand deposits have the highest permeability, with some boreholes providing more than 10 l/s with minimal drawdown. Transmissivities range up to 700 m²/day and specific yields are of the order of 3.2 l/s/m. In several places higher transmissivities have been noted. For example, a 150 m deep borehole in alluvio-lacustrine deposits at the foot of the southern plateau has a transmissivity of 3012 m²/day. These aquifers can be both unconfined and confined; they vary in thickness from 0 to 400 metres; water table depth is typically in the range 1 to 60 metres; and the typical borehole depth is 100 m.
  
 
Fine-grained sands interbedded with massive volcanic tuffs and fine ash are known to have low productivity in many places (e.g. in the central Ethiopian Rift). In the eastern part of the country the total thickness of these sediments can reach about 300 m. In most of the outcrops, they consist of conglomerates, sandstone and mudstone, which are gypsiferous and locally bear saline groundwater.
 
Fine-grained sands interbedded with massive volcanic tuffs and fine ash are known to have low productivity in many places (e.g. in the central Ethiopian Rift). In the eastern part of the country the total thickness of these sediments can reach about 300 m. In most of the outcrops, they consist of conglomerates, sandstone and mudstone, which are gypsiferous and locally bear saline groundwater.
 +
 +
||Can be highly productive
 
||Variable salinity
 
||Variable salinity
 +
||
 
|-
 
|-
 
|Quaternary Alluvial Aquifers within Lake Tana basin
 
|Quaternary Alluvial Aquifers within Lake Tana basin
||Moderate to High Productivity
 
 
||These occur dominantly in the eastern part of the basin following the lower Rib and lower margin of Gumera and Fogera plain (East of Lake Tana). They also cover a significant area of the north part of the basin at the lower part of the Megech and Western shore of Lake Tana. However, the distribution of alluvial sediments is limited compared to the volcanic aquifers. The deposits vary in thickness from 1 to 400m. The aquifers can be unconfined or confined. Water table depth is typically in the range 1 to 60 metres, and typical borehole depth is 100 m.
 
||These occur dominantly in the eastern part of the basin following the lower Rib and lower margin of Gumera and Fogera plain (East of Lake Tana). They also cover a significant area of the north part of the basin at the lower part of the Megech and Western shore of Lake Tana. However, the distribution of alluvial sediments is limited compared to the volcanic aquifers. The deposits vary in thickness from 1 to 400m. The aquifers can be unconfined or confined. Water table depth is typically in the range 1 to 60 metres, and typical borehole depth is 100 m.
  
Line 307: Line 306:
  
 
The previous investigation aided with drilling on the lake floor shows the occurrence of indicates stiff clay up to 80 m depth.
 
The previous investigation aided with drilling on the lake floor shows the occurrence of indicates stiff clay up to 80 m depth.
 +
 +
||Moderate to high productivity
 
||Variable salinity
 
||Variable salinity
 +
||
 
|-
 
|-
 
|Wadi bed aquifers
 
|Wadi bed aquifers
||Moderate to High Productivity
 
 
||Although localised, these intergranular aquifers have significant groundwater potential in water scarce arid and desert settings. Wadi bed length exceeds 30 000 km across Ethiopia, and total groundwater storage in these aquifers could be as much as 3 billion cubic metres. The most important wadi aquifers, which support the livelihoods of millions of people living a pastoral lifestyle, include those in Borena, Lower Omo, Ogaden, the Western Lowlands bordering Sudan, and in the Afar depression. The most productive wadi bed aquifers are those dominated by sandy and gravelly sediments with a low proportion of clay.  
 
||Although localised, these intergranular aquifers have significant groundwater potential in water scarce arid and desert settings. Wadi bed length exceeds 30 000 km across Ethiopia, and total groundwater storage in these aquifers could be as much as 3 billion cubic metres. The most important wadi aquifers, which support the livelihoods of millions of people living a pastoral lifestyle, include those in Borena, Lower Omo, Ogaden, the Western Lowlands bordering Sudan, and in the Afar depression. The most productive wadi bed aquifers are those dominated by sandy and gravelly sediments with a low proportion of clay.  
  
 
One of the highest yielding recorded boreholes abstracting from a wadi bed aquifer is the El-Gof borehole, which taps an intergranular sand and gravel aquifer, overlain by lacustrine sediments, and has a yield of 5 l/s. Other boreholes have recorded discharges of 0.5 l/s to 8 l/s.  
 
One of the highest yielding recorded boreholes abstracting from a wadi bed aquifer is the El-Gof borehole, which taps an intergranular sand and gravel aquifer, overlain by lacustrine sediments, and has a yield of 5 l/s. Other boreholes have recorded discharges of 0.5 l/s to 8 l/s.  
  
An important source of groundwater in areas with little surface water
+
||Important source of groundwater in areas with little surface water
 
||Variable salinity
 
||Variable salinity
 +
||
 
|-
 
|-
 
|Talus slope, landslide bodies, alluvial terraces
 
|Talus slope, landslide bodies, alluvial terraces
||Moderate Productivity
+
||These deposits form small outcrops 0.5 to 2 km² in area. Permeability is enhanced in areas where the material is loosely packed. Groundwater from mountain areas flows towards the talus slope and landslide deposits, from where springs commonly emerge. Typical spring yields are 1 to 2 l/s. These aquifers with readily available groundwater discharges support several villages in areas of relatively gentle slopes and good soil development.
||These deposits form small outcrops 0.5 to 2 km² in area. Permeability is enhanced in areas where the material is loosely packed. Groundwater from mountain areas flows towards the talus slope and landslide deposits, from where springs commonly emerge. Typical spring yields are 1 to 2 l/s. These aquifers with readily available groundwater discharges support several villages in areas of relatively gentle slopes and good soil development. Recharged from groundwater flowing from higher elevation.
+
 
 +
||
 
||Variable salinity
 
||Variable salinity
 +
||Recharged from groundwater flowing from higher elevation
 
|}
 
|}
  
Line 329: Line 333:
 
====Igneous - Volcanic====
 
====Igneous - Volcanic====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality
+
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
  
 
|Rift volcanics
 
|Rift volcanics
||Moderate Productivity
+
||Generally low productivity with low borehole yields, from 1 to 5 l/s.  In some conditions the aquifer is confined, leading to artesian conditions.  
||Borehole yields generally from 1 to 5 l/s.  In some conditions the aquifer is confined, leading to artesian conditions. Both direct rainfall and indirect (eg from river beds) recharge is common.
+
||Low borehole yields
 
||High fluoride and salinity, often exceeding WHO limits.
 
||High fluoride and salinity, often exceeding WHO limits.
 +
||Both direct rainfall and indirect (eg from river beds) recharge is common.
 
|-
 
|-
 
|Quaternary plateau basalts  
 
|Quaternary plateau basalts  
||High Productivity
+
||The most extensive occurrence is in the Lake Tana Basin, where these form a highly productive, fractured aquifer, with borehole yields reaching 20 l/s (there are other records of borehole yields of between 5 and 100 l/s), and groundwater discharge to rivers and springs. Elsewhere in Ethiopia the Quaternary volcanics are highly productive but have dual fracture-intergranular porosity.
||The most extensive occurrence is in the Lake Tana Basin, where these form a highly productive, fractured aquifer, with borehole yields reaching 20 l/s (there are other records of borehole yields of between 5 and 100 l/s), and groundwater discharge to rivers and springs. Elsewhere in Ethiopia the Quaternary volcanics are highly productive but have dual fracture-intergranular porosity. Direct and indirect recharge occurs.
+
||Highly productive
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 +
||Direct and indirect recharge occurs.
 
|-
 
|-
 
|Shield volcanics
 
|Shield volcanics
 +
||This aquifer can  be up to 500 m thick. Groundwater discharge occurs through springs, which are common at the foot of the shield areas. The intercalation of volcanic ash with basalt forms a dual porosity and permeability groundwater system: groundwater storage is focussed in ash layers, while  groundwater flow is focussed through fractures in the basalt layers.  Shield areas dominated by acid volcanic rocks show lower groundwater potential (e.g. in the Bale Massif). The aquifer is typically unconfined to semi confined. The depth to water ranges from 5 to 60 m, and borehole depths are typically 60 to 150 metres.
 
||
 
||
||This aquifer can  be up to 500 m thick. Groundwater discharge occurs through springs, which are common at the foot of the shield areas. The intercalation of volcanic ash with basalt forms a dual porosity and permeability groundwater system: groundwater storage is focussed in ash layers, while  groundwater flow is focussed through fractures in the basalt layers.  Shield areas dominated by acid volcanic rocks show lower groundwater potential (e.g. in the Bale Massif). The aquifer is typically unconfined to semi confined. The depth to water ranges from 5 to 60 m, and borehole depths are typically 60 to 150 metres. Recharge occurs through fractures in highland areas.
 
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 +
||Recharge occurs through fractures in highland areas.
 
|-
 
|-
 
|Upper basalt aquifer (Aiba, Alaji and Termaber formations)
 
|Upper basalt aquifer (Aiba, Alaji and Termaber formations)
||High Productivity
 
 
||This aquifer forms the most productive of the volcanic aquifers in Ethiopia. It is typically unconfined to semi-confined and often artesian.  Groundwater discharge occurs to wetlands and to springs on cliffs. The aquifer thickness ranges from 50 to 1000 m. The depth to water table varies from 0 to 250 metres. Borehole depths are typically from 100 to 150 m. Borehole yields are generally up to 20 l/s.  
 
||This aquifer forms the most productive of the volcanic aquifers in Ethiopia. It is typically unconfined to semi-confined and often artesian.  Groundwater discharge occurs to wetlands and to springs on cliffs. The aquifer thickness ranges from 50 to 1000 m. The depth to water table varies from 0 to 250 metres. Borehole depths are typically from 100 to 150 m. Borehole yields are generally up to 20 l/s.  
  
 
The Aiba Formation has dual porosity, with groundwater occurring in joints, fractures and scoriaceous layers. Deep boreholes show the presence of narrow but extensive fracture zones with high permeability and low storage. Transmissivity varies between 0.5 and 1400 m²/day. Borehole yields range from 5 to 150 l/s.  
 
The Aiba Formation has dual porosity, with groundwater occurring in joints, fractures and scoriaceous layers. Deep boreholes show the presence of narrow but extensive fracture zones with high permeability and low storage. Transmissivity varies between 0.5 and 1400 m²/day. Borehole yields range from 5 to 150 l/s.  
  
Pumping test analysis and well logs from the Termaber Formation show that it is dominated by fracture flow. Recharge occurs vertically through the soil zone and fractures in the rocks.
+
Pumping test analysis and well logs from the Termaber Formation show that it is dominated by fracture flow.  
 +
||The most productive of the volcanic aquifers.
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 +
||Recharge occurs vertically through the soil zone and fractures in the rocks.
 
|-
 
|-
 
|Lower basalt aquifer (Ashangie Formation)
 
|Lower basalt aquifer (Ashangie Formation)
||Low to High Productivity
 
 
||These rocks are characterised by rugged topography with dissected and irregular morphology. The rocks are deformed, and in their northern section dip at up to 40°. They are thinly bedded, and in several areas are brecciated. Field evidence shows that the brecciated parts are characterized by lower permeability. The rocks are typically deeply weathered, when they are reddish in colour, but generally have low permeability. Both primary (vesicle) porosity and secondary (fracture) porosity have been modified and reduced by secondary mineralisation (e.g. by calcite, zeolite and silica).  
 
||These rocks are characterised by rugged topography with dissected and irregular morphology. The rocks are deformed, and in their northern section dip at up to 40°. They are thinly bedded, and in several areas are brecciated. Field evidence shows that the brecciated parts are characterized by lower permeability. The rocks are typically deeply weathered, when they are reddish in colour, but generally have low permeability. Both primary (vesicle) porosity and secondary (fracture) porosity have been modified and reduced by secondary mineralisation (e.g. by calcite, zeolite and silica).  
  
Line 373: Line 380:
  
 
The contact between this unit and the upper basalt above is characterised by spring discharge.  
 
The contact between this unit and the upper basalt above is characterised by spring discharge.  
 +
||
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 
||Good water quality: generally bicarbonate type, low salinity, low fluoride.  
 +
||
 
|}
 
|}
  
Line 380: Line 389:
  
 
====Mesozoic Consolidated Sedimentary Aquifers with Fracture and Intergranular Flow====
 
====Mesozoic Consolidated Sedimentary Aquifers with Fracture and Intergranular Flow====
 
 
Notable hydrogeologic and geologic features of Mesozoic sedimentary rocks of Ethiopia are:
 
Notable hydrogeologic and geologic features of Mesozoic sedimentary rocks of Ethiopia are:
  
Line 396: Line 404:
  
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality
+
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
 
|Hamanile, Gabredarre and Antalo formations (Jurassic limestones)
 
|Hamanile, Gabredarre and Antalo formations (Jurassic limestones)
||High Productivity
 
 
|| The '''Gabredarre Formation''' is characterised by karst features, including caves. The limestones of the Sofomar caves region have the highest degree of karstification of Ethiopia's carbonate rocks. The aquifer has moderate permeability and productivity.   
 
|| The '''Gabredarre Formation''' is characterised by karst features, including caves. The limestones of the Sofomar caves region have the highest degree of karstification of Ethiopia's carbonate rocks. The aquifer has moderate permeability and productivity.   
  
Line 405: Line 412:
  
 
In general, these aquifers are typically 500 to 1000 m thick, and are unconfined to semi-confined.  The water table is usually 200 to 400 m deep; typical borehole depth is 300 m.
 
In general, these aquifers are typically 500 to 1000 m thick, and are unconfined to semi-confined.  The water table is usually 200 to 400 m deep; typical borehole depth is 300 m.
 
+
||
In high rainfall highlands, recharge could reach 200 mm/yr. In arid regions it varies between 10 mm/yr and 50 mm/yr.
 
 
||Good quality water generally. However, high concentrations of dissolved salts, including sodium, chloride and/or sulphate, occur due to reaction with abundant minerals in evaporite beds, and salinity can reach 3 mg/l.  
 
||Good quality water generally. However, high concentrations of dissolved salts, including sodium, chloride and/or sulphate, occur due to reaction with abundant minerals in evaporite beds, and salinity can reach 3 mg/l.  
 +
||In high rainfall highlands, recharge could reach 200 mm/yr. In arid regions it varies between 10 mm/yr and 50 mm/yr.
 
|-
 
|-
 
|Adigrat Formation (Jurassic sandstone)
 
|Adigrat Formation (Jurassic sandstone)
||Moderate Productivity
 
 
||The highly cemented '''Adigrat Formation''' has low primary porosity, and the top part has been altered by heating by Cenozoic volcanism.  Fracturing has created secondary porosity and permeability.  The emergence of springs at the contact of the Adigrat sandstone and the overlying volcanic rocks is indicative of the low permeability of the Adigrat Formation.
 
||The highly cemented '''Adigrat Formation''' has low primary porosity, and the top part has been altered by heating by Cenozoic volcanism.  Fracturing has created secondary porosity and permeability.  The emergence of springs at the contact of the Adigrat sandstone and the overlying volcanic rocks is indicative of the low permeability of the Adigrat Formation.
  
 
This aquifer is typically 200 to 1000 m thick and is unconfined to semi-confined.  The water table is usually 200 to 400 m deep; typical borehole depth is 300 m.
 
This aquifer is typically 200 to 1000 m thick and is unconfined to semi-confined.  The water table is usually 200 to 400 m deep; typical borehole depth is 300 m.
 
+
||
In highlands areas with high rainfall, recharge could reach 200 mm/yr. In arid regions it varies between 10 mm/yr and 50 mm/yr.
 
 
||Very good quality water
 
||Very good quality water
 +
||In highlands areas with high rainfall, recharge could reach 200 mm/yr. In arid regions it varies between 10 mm/yr and 50 mm/yr.
 
|}
 
|}
  
Line 423: Line 429:
 
====Precambrian Basement====
 
====Precambrian Basement====
 
{| class = "wikitable"
 
{| class = "wikitable"
|Named Aquifers||Aquifer Productivity||General Description||Water quality
+
|Named Aquifers||General Description||Water quantity issues||Water quality issues||Recharge
 
|-
 
|-
 
|Precambrian basement aquifers of Southern Ethiopia and Northern Ethiopia; Crystalline Basement aquifers of Western Ethiopia
 
|Precambrian basement aquifers of Southern Ethiopia and Northern Ethiopia; Crystalline Basement aquifers of Western Ethiopia
||Very Low to Low Productivity.
+
||
||'''Basement aquifers in general'''
+
 
 +
'''Basement aquifers in general'''
  
 
The productivity of basement aquifers in Ethiopia largely depends of the development of regolith (weathered rock) amd the density of fractures. In turn, these are partly controlled by the type or grade of metamorphic rock that forms the basement. Less important controls on groundwater occurrence are the sustainability of recharge; and topography. Groundwater in the basement aquifers occurs in shallow regolith (weathered rock) basins.
 
The productivity of basement aquifers in Ethiopia largely depends of the development of regolith (weathered rock) amd the density of fractures. In turn, these are partly controlled by the type or grade of metamorphic rock that forms the basement. Less important controls on groundwater occurrence are the sustainability of recharge; and topography. Groundwater in the basement aquifers occurs in shallow regolith (weathered rock) basins.
Line 440: Line 447:
 
:'''Western Ethiopia''': the crystalline basement aquifers of Western Ethiopia have better groundwater storage than in other areas. This higher groundwater potential is related to high rainfall that supports high recharge; to a relatively thick regolith which favours groundwater storage; and to rugged undulating topography which favours accumulation of weathering products in depressions and flat plains allowing groundwater storage and circulation. The average borehole yield is 5 l/s (Bako & Abakoran).  The hydraulic conductivity of this aquifer varies from 0.12 m/day to 2.3 m/day.
 
:'''Western Ethiopia''': the crystalline basement aquifers of Western Ethiopia have better groundwater storage than in other areas. This higher groundwater potential is related to high rainfall that supports high recharge; to a relatively thick regolith which favours groundwater storage; and to rugged undulating topography which favours accumulation of weathering products in depressions and flat plains allowing groundwater storage and circulation. The average borehole yield is 5 l/s (Bako & Abakoran).  The hydraulic conductivity of this aquifer varies from 0.12 m/day to 2.3 m/day.
  
Recharge varies from 10 to 250 mm/yr depending on rainfall regime
+
||Yield is very low in unweathered basement rocks and highest (~0.1 l/s) where weathering and regolith is most developed
 
||Good quality  
 
||Good quality  
 +
||Recharge varies from 10 to 250 mm/yr depending on rainfall regime
 
|}
 
|}
  
Line 554: Line 562:
  
 
No management system exists specifically pertaining to transboundary aquifers. Conflict over water sources in general is common among pastoralists in the border region of Ethiopia and Kenya.
 
No management system exists specifically pertaining to transboundary aquifers. Conflict over water sources in general is common among pastoralists in the border region of Ethiopia and Kenya.
 
==Groundwater Projects==
 
 
Information on particular groundwater projects in Ethiopia, including links to project results and outputs, can be found on the [[Ethiopia Groundwater Projects | Ethiopia groundwater projects]] page.
 
  
 
==References==
 
==References==
  
Many of the references below, and others relating to the hydrogeology of Ethiopia, can be accessed through the [https://www.bgs.ac.uk/africagroundwateratlas/atlas.cfc?method=listResults&title_search=&titleboolean=AND&author_search=&category=&child_category=&country=ET African Groundwater Literature Archive].
+
Many of the references below, and others relating to the hydrogeology of Ethiopia, can be accessed throughthe [https://www.bgs.ac.uk/africagroundwateratlas/atlas.cfc?method=listResults&title_search=&titleboolean=AND&author_search=&category=&child_category=&country=ET African Groundwater Literature Archive].
  
 
===Geology: key references===
 
===Geology: key references===
Line 594: Line 598:
  
 
===Hydrogeology: key references===
 
===Hydrogeology: key references===
 +
  
 
Alemneh S. 1989. Hydrogeology of Yabello sheet (NB37-14). Ethiopian Geological Survey report number 307. Addis Ababa, 40pp.
 
Alemneh S. 1989. Hydrogeology of Yabello sheet (NB37-14). Ethiopian Geological Survey report number 307. Addis Ababa, 40pp.

Please note that all contributions to Earthwise may be edited, altered, or removed by other contributors. If you do not want your writing to be edited mercilessly, then do not submit it here.
You are also promising us that you wrote this yourself, or copied it from a public domain or similar free resource (see Earthwise:Copyrights for details). Do not submit copyrighted work without permission!

Cancel Editing help (opens in new window)

  [] · [[]] · [[|]] · {{}} · · “” ‘’ «» ‹› „“ ‚‘ · ~ | °   · ± × ÷ ² ³ ½ · §
[[Category:]] · [[:File:]] · <code></code> · <syntaxhighlight></syntaxhighlight> · <includeonly></includeonly> · <noinclude></noinclude> · #REDIRECT[[]] · <translate></translate> · <languages/> · ==References== · {{reflist}} · ==Footnote== · {{reflist|group=note}} · <ref group=note> · __notoc__ · {{DEFAULTSORT:}} <div class="someclass noprint"></div> {{clear}} <br>