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1.
Four major fault systems oriented N–S to NNE–SSW, NE–SW, E–W and NW–SE are identified from Landsat Thematic Mapper (TM) images and a high resolution digital elevation model (DEM) over the Ethiopian Rift Valley and the surrounding plateaus. Most of these faults are the result of Cenozoic - extensional reactivation of pre-existing basement structures. These faults interacted with each other at different geological times under different geodynamic conditions. The Cenozoic interaction under an extensional tectonic regime is the major cause of the actual volcano-tectonic landscape in Ethiopia. The Wonji Fault Belt (WFB), which comprises the N–S to NNE–SSW striking rift floor faults, displays peculiar propagation patterns mainly due to interaction with the other fault systems and the influence of underlying basement structures. The commonly observed patterns are: curvilinear oblique-slip faults forming lip-horsts, sinusoidal faults, intersecting faults and locally splaying faults at their ends. Fault-related open structures such as tail-cracks, releasing bends and extensional relay zones and fault intersections have served as principal eruption sites for monogenetic Plio-Quaternary volcanoes in the Main Ethiopian Rift (MER). 相似文献
2.
Extenuating the parameters using HEC-HMS hydrological model for ungauged catchment in the central Omo-Gibe Basin of Ethiopia 
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下载免费PDF全文 Demisse Habtamu Semunigus Ayalew Abebe Temesgen Ayana Melkamu Teshome Lohani Tarun Kumar 《地下水科学与工程》2021,9(4):317-325
Characteristics of ungauged catchments can be studied from the hydrological model parameters of gauged catchments. In this research, discharge prediction was carried out in ungauged catchments using HEC-HMS in the central Omo-Gibe basin. Linear regression, spatial proximity, area ratio, and sub-basin mean were amalgamated for regionalization. The regional model parameters of the gauged catchment and physical characteristics of ungauged catchments were collated together to develop the equations to predict discharge from ungauged catchments. From the sensitivity analysis, crop coefficient (CC), storage coefficient (R), constant rate (CR), and time of concentration (TC) are found to be more sensitive than others. The model efficiency was evaluated using Nash–Sutcliffe Efficiency (NSE) which was greater than 0.75, varying between ?10% and +10% and the coefficient of determination (R2) was approximated to be 0.8 during the calibration and validation period. The model parameters in ungauged catchments were determined using the regional model (linear regression), sub-basin mean, area ratio, and spatial proximity methods, and the discharge was simulated using the HEC-HMS model. Linear regression was used in the prediction where p-value ≤ 0.1, determination coefficient (R2) = 0.91 for crop coefficient (CC) and 0.99 for maximum deficit (MD). Constant rate (CR), maximum storage (MS), initial storage (IS), storage coefficient (R), and time of concentration (TC) were obtained. The result is that an average of 30 m3/s and 15 m3/s as the maximum monthly simulated flow for ungauged sub-catchments, i.e. Denchiya and Mansa of the main river basin . 相似文献
3.
Mario Boccaletti Roberto Mazzuoli Marco Bonini Teresa Trua Bekele Abebe 《Journal of African Earth Sciences》1999,29(4):315
Deformation and magmatism within the 90 km wide northern Ethiopian Rift system is concentrated along a narrow zone - the Wonji Fault Belt. Two key areas (the Nazret-Dera and Asela-Ziway areas), located along the eastern margin of the north-northeast to northeast trending Main Ethiopian Rift, have been investigated in order to reconstruct the recent tectonomagmatic evolution of the northern branch of the Main Ethiopian Rift. In these areas, Early Pleistocene volcanic products (Wonji Group) overlie Pliocene volcanic rocks (Eastern Margin Unit). Detailed stratigraphical reconstructions have revealed the presence of several tectonomagmatic units which can be correlated between the two study areas. The stratigraphical and petrological study of these units outlined (1) the bimodal composition (basalts-pantellerites) of the oldest and youngest units and the unimodal character (pantellerites) of the products erupted during the intervening period; (2) the mainly fissural origin of the ignimbrites and oldest basalts; and (3) a mafic/felsic volumetric ratio of 1:5.The geological data suggest that, around the Pliocene-Quaternary boundary, a change in the stress field occurred in this Main Ethiopian Rift sector, passing from a direction of extension roughly orthogonal to the rift shoulders, to oblique rifting related to an east-west trending extension. In this framework the change in the style of volcanism observed in the Nazret-Dera and Asela-Ziway areas can be related to the change of the stress field. A new geodynamic model is presented for the Late Pliocene to Recent evolution of this sector of the Main Ethiopian Rift. According to this model, a large volume of rhyolitic products was erupted during an oblique rifting phase, following a previous period of pure extension. The change in the tectonic regime favoured partial melting of the underplated basalts as a decrease in the pressure and an elevation of isotherms occurred. 相似文献
4.
The implementation of laws relating to transboundary aquifers necessitates field knowledge so that the laws can be coincident with reality on the ground. The definition of ‘shared aquifer’ is more complex than the mere physically shared body of groundwater flowing from country A to country B. The border between Ethiopia and Kenya is characterized by low-volume groundwater storage and low transboundary flows. However, groundwater has visible environmental, social and economic functions. The characteristics of groundwater flow and storage in aquifers shared between Ethiopia and Kenya are different from those used in setting the foundation of the international legal framework on shared aquifers. By describing the characteristics of the groundwaters that are shared between Ethiopia and Kenya, this work demonstrates that the international legal framework is inadequate when applied in this region. The main inadequacies are: (1) international law does not specify the minimum volume of transboundary flow in an aquifer for it to qualify to be treated under the law, and (2) the physical aspects of water get more emphasis than the functions of groundwater. A more adequate international legal framework would be one that considers specific types of groundwater and local needs. 相似文献
5.
Assessment of groundwater vulnerability to pollution in Dire Dawa,Ethiopia using DRASTIC 总被引：1，自引：0，他引：1
Assessment of groundwater vulnerability to pollution is an effective tool for the delineation of groundwater protection zones.
DRASTIC approach was used to determine vulnerability zones in Dire Dawa groundwater basin, a semiarid region of Ethiopia.
Maps of the seven DRASTIC parameters were prepared. GIS-ArcView was used for mapping and performing weighted-overlay analysis.
The result of the analysis indicated that eastern part of the study area, in which Dire Dawa town is located, is highly vulnerable.
A low aquifer vulnerability class was determined for the western portion of the study area as a result of greater groundwater
depths, higher relative soil-clay content, and relatively low recharge rates for this area. The area between the two zones
is of medium vulnerability. Observed nitrate concentrations in boreholes are in accordance with the vulnerability map. Some
of the boreholes in the Sabian well field (Dire Dawa area) already deliver groundwater with nitrate levels significantly exceeding
health standards set by the World Health Organization, while boreholes in the western part (low vulnerability zone) contain
almost no nitrate. The result of this study is useful for risk assessments and for the development of effective groundwater
management strategies for this region and others like it. 相似文献
6.
Tatek Abebe 《Geoforum》2012,43(3):540-550
Many programmes for AIDS-affected children pursue resource-intensive and external interventions of care, and often place such children at the receiving end of the care continuum. The aim of this article is to explore from a socio-spatial perspective the capacities of families and children experiencing orphanhood and the policy significance of empowering both to address the growing challenge of orphan care in rural and urban Ethiopia. Drawing on participatory research (involving in-depth interviews, focus group discussions, story writing, photo essays, ranking, observation and household visits), the complex social dynamics of care and spatial diversities in the manifestations of the vulnerabilities, capacities, strengths, and potentials of children and their families are discussed. It is argued that rather than the lack of biological parents it is the combination of the absence of a carer and the presence of acute poverty and economic marginality that explain various forms of vulnerability in orphans and non-orphans. The article further argues that effective and sustainable care needs to be informed by identification and empowerment of ‘family collectives’ as sites of interventions. In doing so, it draws analytical attention to the importance of examining the socio-temporal processes of orphanhood and care, children’s changing circumstances, and family collectives’ variances in the capacity to provide support for them. Strategies for sustainable care should recognise the specific needs of AIDS-affected children and the resourceful ways in which they contribute to enhance the care-giving capacities of family collectives in the light of broader socio-cultural and political–economic contexts. 相似文献
7.
Evaluation of groundwater resource potential by using water balance model: A case of Upper Gilgel Gibe Watershed,Ethiopia 下载免费PDF全文
下载免费PDF全文 Abebe Wondmagegn Taye 《地下水科学与工程》2022,10(3):209-222
Groundwater resource potential is the nation’s primary freshwater reserve and accounts for a large portion of potential future water supply. This study focused on quantifying the groundwater resource potential of the Upper Gilgel Gibe watershed using the water balance method. This study began by defining the project area’s boundary, reviewing previous works, and collecting valuable primary and secondary data. The analysis and interpretation of data were supported by the application of different software like ArcGIS 10.4.1. Soil water characteristics of SPAW (Soil-plant-air-water) computer model, base flow index (BFI+3.0), and the water balance model. Estimation of the areal depth of precipitation and actual evapotranspiration was carried out through the use of the isohyetal method and the water balance model and found to be 1 664.5 mm/a and 911.6 mm/a, respectively. A total water volume of 875 829 800 m3/a is estimated to recharge the aquifer system. The present annual groundwater abstraction is estimated as 10 150 000 m3/a. The estimated specific yield, exploitable groundwater reserve, and safe yield of the catchment are 5.9%, 520 557 000 m3/a, and 522 768 349 m3/a respectively. The total groundwater abstraction is much less than the recharge and the safe yield of the aquifer. The results show that there is a sufficient amount of groundwater in the study area, and the groundwater resources of the area are considered underdeveloped. 相似文献
8.
An isolated block of Precambrian basement rocks and Mesozoic sediments is exposed at Kella along the western margin of the Central Main Ethiopian Rift (MER), surrounded by Tertiary to Quaternary volcanic rocks. Apatite fission‐track thermochronology on two basement samples yielded ages of 7.2 ± 1.0 Ma and 6.7 ± 3.0 Ma and a long mean track length (>14.5 μm). Rapid Late Miocene cooling is attributed to denudation related to rifting. Despite the paucity of data, due to the absence of suitable lithologies in the area, our data confirm that the Central MER is younger than 8 Ma as recently proposed on the basis of field evidence and radiometric dating of volcanics. This implies that the Central MER formed after the Northern MER, indicating a diachronous development of this third arm of the Red Sea–Gulf of Aden–Ethiopian Rift system. Terra Nova, 00, 000–000, 2010 相似文献
9.
Hydrological models play vital roles in understanding and management of surface water resources. The physically based distributed model Soil and Water Assessment Tool (SWAT) was applied to a small catchment in south eastern Australia to determine its ability to mimic low and high streamflows. The model was successfully calibrated using 1993–2002 streamflow data and validated using 2003–2011 data with a combination of manual and auto-calibration techniques for both monthly and daily time steps. Sensitivity analysis indicated that curve number for moisture condition II (CN2) is the most sensitive parameter for both time steps. In general, the model performance statistics indicated “very good” agreement between measured and simulated discharges for both calibration and validation periods. The model was able to satisfactorily simulate both low and high flows of the Yass River. Analysis of water balance components indicated that more than 90 % of the rainfall is lost as evapotranspiration and about 45 % of the streamflow is base flow. The calibrated and validated SWAT model can be used to analyze the effect of climate and land use changes on catchment wide hydrologic process. 相似文献
10.
Sustainable groundwater management requires knowledge of recharge. Recharge is also an important parameter in groundwater flow and transport models. Spatial variation in recharge due to distributed land-us.e, soil texture, topography, groundwater level, and hydrometeorological conditions should be accounted for in recharge estimation. However, conventional point-estimates of recharge are not easily extrapolated or regionalized. In this study, a spatially distributed water balance model WetSpass was used to simulate long-term average recharge using land-use, soil texture, topography, and hydrometeorological parameters in Dire Dawa, a semiarid region of Ethiopia. WetSpass is a physically based methodology for estimation of the long-term average spatial distribution of surface runoff, actual evapotranspiration, and groundwater recharge. The long-term temporal and spatial average annual rainfall of 626 mm was distributed as: surface runoff of 126 mm (20%), evapotranspiration of 468 mm (75%), and recharge of 28 mm (5%). This recharge corresponds to 817 l/s for the 920.12 km2 study area, which is less than the often-assumed 1,000 l/s recharge for the Dire Dawa groundwater catchment. 相似文献