Water Resource Assessment of a Complex Volcanic System Under Semi-Arid Climate Using Numerical Modeling: The Borena Basin in Southern Ethiopia

The Borena basin is located in southern Ethiopia, in a semi-arid climate, on the eastern shoulder of the south Main Ethiopian Rift (MER). The study area covers 18,000 km2 and is characterized by a lack of perennial surface waters that can be used for domestic and agricultural purpose. As a result, groundwater, which occurs in complex volcanic settings, is the only source for water supply in the study area. This work is focused on the basaltic aquifers, which are intensely fractured, resulting in strong connectivity within the system. All available data (geology, hydraulic head, hydraulic parameters, well inventory and discharge, etc.) were compiled in a GIS database. The overall objective of this work is the assessment of groundwater potential, its spatial distribution and factors controlling its movement using numerical groundwater modeling to enhance groundwater management and use in the Borena basin. The modeling task was conducted at two scales: (i) regional scale; (ii) wellfields scale. The regional steady state model was calibrated using the Pilot points approach, highlighting a strongly heterogeneous system. A significant result of the regional model consisted of estimating the water balance of the whole system. The total inflow to the basin amounts to 542 × 106 m3/year, of which 367 × 106 m3/year are provided by superficial recharge. Groundwater resources are exploited with 7 wellfields. Exploitation of the wellfields was optimized based on the Sustainable Yield concept, which reserves a fraction of natural recharge for the benefit of the environment (surface waters, ecosystems). Each wellfield was extracted from the regional model, refined and used to simulate and optimize pumping scenarios, with the objective of maximizing discharge rates and avoiding over-exploitation of the groundwater. The optimized abstraction at all wellfields amounts to 121 × 106 m3/year, which represents 33% of the natural recharge and fully agrees with the sustainable yield concept.

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Eruptive frequency of the Bora-Baricha-Tullu Moye (BBTM) volcanic system in the Central Main Ethiopian Rift

10.5194/egusphere-egu21-13966 ◽

2021 ◽

Author(s):

Amdemichael Zafu Tadesse ◽

Karen Fontijn ◽

Abate Assen Melaku ◽

Ermias Filfilu Gebru ◽

Victoria Smith ◽

...

Keyword(s):

Late Quaternary ◽

Volcanic Eruptions ◽

Volcanic Field ◽

Tectonic Activity ◽

Explosive Eruptions ◽

Ethiopian Rift ◽

Rift System ◽

Diagnostic Features ◽

Volcanic System ◽

Main Ethiopian Rift

The Main Ethiopian Rift (MER) is the northern portion of the East African Rift System and separates the Eastern and Western plateaus of Ethiopia. The recent volcanic and tectonic activity is largely focused within the rift basin along a 20 km wide zone on the rift floor. Large silicic volcanic complexes are aligned along this central rift axis but their eruptive histories are not well constrained.The Bora-Baricha-Tullu Moye (BBTM) volcanic field is situated in the central Main Ethiopian Rift and has a different appearance than the other MER volcanic systems. The BBTM constitutes several late Quaternary edifices, the major ones are: Tullu Moye, Bora and Baricha. In addition, there are multiple smaller eruptive vents (e.g. Oda and Dima), cones, and domes across the ca. 20 X 20 km wide area. Currently, there is very little information on the frequency and magnitude of past volcanic eruptions. We present a new dataset of field observations, componentry, petrography, geochronology (40Ar/39Ar), and glass major and trace element chemistry. The data are assessed as potential fingerprints to assign diagnostic features and correlate units across the area, and establish a tephrostratigraphic framework for the BBTM volcanic field.Two large-volume and presumably caldera-forming eruptions are identified, the younger of which took place at 100 ka. The volcanic products exposed in the BBTM area show that the volcanic field has undergone at least 20 explosive eruptions since then. The post-caldera eruptions have comenditic (Tullu Moye) and pantelleretic (Bora and Baricha) magma compositions. Other smaller edifices such as Oda and Dima also erupted pantelleritic magmas, and only differ slightly in composition than tephra of Bora and Baricha. Tullu Moye had two distinct explosive eruptions that dispersed tephra up to 14 km away and on to the eastern plateau. Bora and Baricha together had at least 8 explosive eruptions. Their deposits can be distinguished by their light grey color and unique lithic components. Oda had 7 eruptions, the most recent of which generated a pyroclastic density current that travelled up to 10 km away from the vent. Dima experienced at least 3 eruptions, generating tephra with a bluish-grey colour.This mapping and compositional analysis of the deposits from the BBTM in the MER indicates that the region has been more active in the last 100 ka than previously thought, which has implications for hazards assessments for the region.

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Sulfur distribution in five Ethiopian Rift Valley soils under humid and semi-arid climate

Journal of Arid Environments ◽

10.1016/j.jaridenv.2005.01.010 ◽

2005 ◽

Vol 62 (4) ◽

pp. 597-612 ◽

Cited By ~ 35

Author(s):

F. Itanna

Keyword(s):

Rift Valley ◽

Arid Climate ◽

Ethiopian Rift ◽

Sulfur Distribution ◽

Semi Arid

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A geochemical survey of spring water from the main Ethiopian rift valley, southern Ethiopia: implications for well-head protection

Hydrogeology Journal ◽

10.1007/s100400100134 ◽

2001 ◽

Vol 9 (3) ◽

pp. 265-272 ◽

Cited By ~ 27

Author(s):

Jeffrey M. McKenzie ◽

Donald I. Siegel ◽

William Patterson ◽

D. Jonathan McKenzie

Keyword(s):

Rift Valley ◽

Spring Water ◽

Southern Ethiopia ◽

Ethiopian Rift ◽

Main Ethiopian Rift ◽

Geochemical Survey ◽

Head Protection

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Response to comments on an article entitled 'A geochemical survey of spring water from the main Ethiopian rift valley, southern Ethiopia: implications for well-head protection' by McKenzie et al., Hydrogeology Journal (2001) 9:265–272

Hydrogeology Journal ◽

10.1007/s10040-003-0253-9 ◽

2003 ◽

Vol 11 (2) ◽

pp. 316-317

Author(s):

Jeffrey M. McKenzie ◽

Donald I. Siegel ◽

D. Jonathan McKenzie

Keyword(s):

Rift Valley ◽

Spring Water ◽

Hydrogeology Journal ◽

Southern Ethiopia ◽

Ethiopian Rift ◽

Main Ethiopian Rift ◽

Geochemical Survey ◽

Head Protection

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The Challenge in Increasing Water and Soil Resources Resilience by Landscape Restoration: Examples from Southern Ethiopia and Iceland

Proceedings ◽

10.3390/proceedings2019030084 ◽

2020 ◽

Vol 30 (1) ◽

pp. 84

Author(s):

Michaela Hrabalikova ◽

David Christian Finger ◽

Dominika Kobzova ◽

Petra Huislova ◽

Jan Ures

Keyword(s):

Soil Erosion ◽

Water Conservation ◽

Large Scale ◽

High Rate ◽

Soil Reclamation ◽

Southern Ethiopia ◽

Ethiopian Rift ◽

Strong Wind ◽

Main Ethiopian Rift ◽

Special District

Soil degradation and subsequent soil erosion is a major threat to vital ecosystem services, to food production, and finally to human societies. This threat is particularly imminent in subarctic Iceland and tropical Ethiopia. Both countries underwent large-scale deforestation in the past. Especially in Ethiopia, the demand for wood for cooking, heating, and construction is still high, inducing deforestation. On the other hand, Iceland solved the need for wood for energy purposes through the utilization of geothermal energy. Deforestation, overgrazing, and specific climatic conditions resulted in a high rate of soil erosion in both countries. In this study, the effectivity of restoration efforts is mapped in selected areas in Iceland and Ethiopia. Soil-water conservation (SWC) measures mapping was conducted in the Sidama zone and Halaba special district of southern Ethiopia, as well as in Thorlákshöfn, a municipality in southern Iceland. The Ethiopian study area is located in the Main Ethiopian rift valley. The Icelandic study area is in the Mid-Atlantic Rift. Degraded areas and applied SWC were GPS mapped in the field. The erosion agents in both countries are dominated by water erosion. In addition, Iceland has a high rate of soil loss due to strong wind erosion. In order to mitigate erosion, numerous SWC actions were implemented in both countries. In Ethiopia, indigenous SWC techniques have been applied since 400 BC, while the government-driven activities started after 1970. In Iceland, governmental soil reclamation programs started in 1907 through establishment of The Soil Conservation Service of Iceland (SCSI). Usually, all the reclamation program actions involve the closing of reclaimed area for livestock and people so that natural regeneration accompanied by additional measures such as planting seedlings can take place. In Ethiopia, such an area is called an “Area Closure”. The land is owned by the community. The common problem in the restoration of Closure Areas lies in people not respecting the watershed divide. Hence, the approach to land degradation lacks a systematic approach covering the entire watershed. Another issue is the construction of the road and path network, which in many cases acts as ways of concentrate surface runoff. Degraded paths are frequently abandoned, and new paths are constructed. The main difference in Iceland from the Ethiopia case is land ownership, which is private in most cases. The land restoration began 50 years ago by sowing grass. Today the land is slowly being reforested.

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