Browsing by Author "Kebede, Seifu (PhD)"
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Item Aquifer Vulnerability Assessment in Modjo River Catchment (Central Main Ethiopian Rift)(Addis Ababa University, 2008-11) Bedane, Ewnetu; Kebede, Seifu (PhD)The thesis entitled Aquifer Vulnerability Assessment In Modjo River Catchment is a study of the hydrogeological factors pertaining to the DRASTIC system and covers an area of 1527sq km in the Upper Awash River Basin, particularly Modjo River Catchment, northwestern shoulder of the Central Main Ethiopian Rift system bounded in the Zone 37 UTM grids of 930000meter N to 1005000meter N and 490000meter E to 535000meter E. With increasing demand and reliance on groundwater from a growing population and agricultural activity comes the need to increase efforts to protect and manage the resources. Urban, and Industrial development, as well as agricultural activities, are potential sources of groundwater contamination in the study area. The general objective of the research work is to identify and produce aquifer vulnerability map to pollution in Modjo River catchment and to assess the risk for groundwater pollution by adopting Geographic Information System (GIS) based DRASTIC system through producing thematic maps of pertinent hydrogeological factors within the catchment and finally to prepare both Intrinsic and Pesticide Vulnerability Maps and determine aquifer Vulnerability Classes based on DRASTIC Index values. Accordingly, high and very high vulnerable areas are found to occupy most of the gentle and plain terrains in the central and southern parts of the study area whereas low and very low vulnerable area occupy the elevated lands in the eastern, northeastern and northwestern parts of the catchment. Unfortunately the high and very high vulnerable areas occupy also the high and moderate groundwater potential zones identified by Sisay, 2007. This gives additional stimulus to the need to protect the groundwater in the study area. The final use of such a study is to help planners and regulators make environmentally sound decisions regarding land use and groundwater protection. Keywords: DRASTIC Model; Aquifer, Vulnerability; Intrinsic Vulnerability; Pesticide Vulnerability, Modjo River Catchment ;Central Main Ethiopian RiftItem Aquifers developed on basement rocks of Ethiopia: their genesis, properties and classification(Addis Ababa Universty, 2015-02) Deyassa, Gaddissa; Kebede, Seifu (PhD)The basement rocks of Ethiopia were traditionally described as a system of regional aquiclude. This attribution ignores regional differences in aquifer properties, structure and functioning. In contrast, this work presents how the interactions of evolutionary and modern geological processes determine aquifer development and hydrogeological characteristics of the basement terrain of Ethiopia. It specifically addresses the role of geomorphic history (deep weathering and stripping) in affecting aquifer genesis and their control on vertical and spatial heterogeneity. In addition, the study provides field evidences for existing literature based weathering-stripping model previously developed for the country. Detailed examination of geological, hydrological and hydrogeological evidences enabled the understanding of the causes of regional variation in aquifer properties. The aquifers exhibit noticeable regional differences. Thus, conceptual hydrogeological model depicting three coherent categories of aquifers are developed: (a) in western basement terrain, aquifer is relatively extensive in the thick weathered mantle over fractured bedrocks of low to high-grade metamorphic rocks. High groundwater storage but low hydraulic conductivity characterizes this aquifer. (b) in the northern, groundwater occurs in fractures and discontinuities in bedrocks toward the surface and tectonically induced relatively deeper fracture zones. These aquifers have high hydraulic permeability but low storage capacity. (c) in the Borena lowlands of southern basement region, groundwater occurs in wadi beds, fractures, and preferentially weathered mantles. The orientations of wadi beds follow regional fractures, which control groundwater flow regime and enhance preferential weathering of bedrocks. Aquifers are of intermediate type with regard to hydraulic properties. The variations in low-flow indices and shapes of flow duration curves of streams manifest contrast in bulk storage capacity and hydraulic conductivity of catchments in the three basement regions. This contrast has been used as evidences for characterization of aquifers.The implication of these regional differences on groundwater exploration and exploitation has been the subject of this study.Item Assessment on Hydraulic Properties of the Ethiopian Tarmaber Formations(Addis Ababa University, 2010-07) G/Slassie, Abreha; Kebede, Seifu (PhD)The Ethiopian Taber formation represents, Oligocene – Miocene basaltic shield volcanic on the northwestern and southeastern plateaus covering an area of about 47,194Km2 (which is 8% of the total flood basalt aerial coverage in the country). Two types of Taber formations have been mapped. The Taber Megahertz formation (Ntb) with an absolute age of (16 – 13 Ma, Kamikaze, 1979) is transitional to alkali basalt which covers an area of about 22,058Km2 (which is 3.4% of the flood basalts (or traps) aerial coverage in the country). This formation commonly outcrops in the central highland plateau, the escarpments and the rift floor and at some localities in the south western highland plateau part of the country (sees Fig.-2.1 & 2.3). The Taber Guess formation (PNtb), with an absolute age of (26 – 16Ma, Kamikaze, 1979) is alkaline to transitional basalt, often ridge and cliff forming shield volcanoes with minor trachea and phonologist flows. It covers a total area of about 25,136Km2 (which is 4.5% of the flood basalt aerial coverage in the country). This formation dominantly outcrops in northwestern highland plateau part of the country (see fig.-2.1). The Taber shield volcanoes become progressively younger to southeastern and south western part of the northwestern Ethiopian plateaus. Well-log data and pump test database analyses show that, the Taber formations aquifer system can be categorized as consolidated fractured aquifer category where the dominant aquifer types are, confined, double porosity fractured aquifer system and single plane vertical aquifer systems. The double porosity aquifers are related to deeply drilled wells reflecting presence of large and narrow fracture systems with high permeability but lower storage capacity. It also shows that, Taber Megahertz formation (Ntb) has better aquifer productivity than the Taber Guess formation (PNtb) and yet, both formations show decrease aquifer productivity with respect to increased drilled boreholes depth and increased age of the formation. Besides, boreholes drilled within the Taber formations shows that, the wells have high well loss coefficient values, indicating improper well site location, improper well design and construction factors and well yield deterioration with time due to clogging, corrosion and incrustation activities of the well screens. Spatially, the Ethiopian Tarmaber formations show an increasing aquifer productivity trend from the highland plateau areas towards the escarpment and the rift floor areas, and yet, from the north, south, northwest, southwest, northeast, southeast and east- west directions of the highland plateau areas toward the Lake Tana basin areas. Generally, the Taber basalt aquifer productivity is highly controlled by the location and morphological setup of the formation outcrop, nature and degree of weathering, hydro thermal processes and nature, extent, frequency and orientation of the associated structural features and yet, weathering, hydro thermal processes and other volcanic activities tend to decrease aquifer permeability while, fracturing, faulting and other tectonic activities tend to increase aquifer productivity of the Taber formations.Item Baseflow Analysis of Rivers in Lake Tana Sub Basin(Addis Ababa University, 2010-02) Zewdie, Getachew; Kebede, Seifu (PhD)The Lake Tana sub basin is situated on the northwestern plateau of Ethiopia at the headwaters of the Blue-Nile basin, west of the Afar depression. The drainage area of the lake is approximately 15,000 square kilometers, of which 3062 is the lake area. Topographic high surrounding the basin forces the major River systems to drain toward Lake Tana. The altitude of the basin ranges between 1765m to 3000 m a.m.s.l. The climate of the region is 'tropical highland monsoon' with one rainy season between June and September. The rainfall data for 23 long-term records of rainfall stations lying within or around the Tana sub Basin are used for the computation of rainfall. The Tana sub Basin receives an average arulUal rainfall of 1329 mm. The air temperature shows small seasonal changes with an annual average of 20°C. The major geological formations that outcrops in Lake Tana sub-basin and its adjacent areas are Tertiary and Quaternary volcanic rocks and alluvial along the major tributaries of the Lake Tana sub-basin. Alluvial sediments have limited distribution within Lake Tana sub-basin dominant at the eastern and not1hern side of the Lake. The understanding and knowledge of hydrology and hydrogeologic systems is very crucial for every activities involving economic development in the Lake Tana sub basin. Groundwater recharge is one of the most important factors governing the sustainable yield of grou ndwater and surface water exploitation. The recharge estimation of the Lake Tana sub basin was carried out based on the principle of base flow separation using HMS SMA for gauged catchments on daily bases. The hydrological and meteorological data used for the period of 1992 to 2006. StatistiXL Multiple linear regression was used to estimate the runoff for ungauged catchments. A level of significance of 0.05 was used for the forward and backwards stepwise regressions. Climate and physical characteristics of the catchments were used in multiple regression to predict the flow characteristics of ungauged catchments. The amount of rainfall, topographic setting and geology are the main controlling factors of climate and physical characteristics of the catchments. The grow1dwater contribution from gauged catchments is about 161.17mm/yr or 12. I % of the total rainfall of the basin. The ungauged catclm1ents contribute a total of28. 18 mm/yr or 2.28% of the total rainfall of the basin.Item Baseflow Analysis of Rivers in Lake Tana Sub Basin(Addis Ababa Universty, 2010-02) Ethiopia, Eastern; Kebede, Seifu (PhD)The Lake Tana sub basin is situated on the northwestern plateau of Ethiopia at the headwaters of the Blue-Nile basin, west of the Afar depression. The drainage area of the lake is approximately 15,000 square kilometers, of which 3062 is the lake area. Topographic high surrounding the basin forces the major River systems to drain toward Lake Tana. The altitude of the basin ranges between 1765m to 3000 m a.m.s.l. The climate of the region is ‘tropical highland monsoon’ with one rainy season between June and September. The rainfall data for 23 long-term records of rainfall stations lying within or around the Tana sub Basin are used for the computation of rainfall. The Tana sub Basin receives an average annual rainfall of 1329 mm. The air temperature shows small seasonal changes with an annual average of 20˚C. The major geological formations that outcrops in Lake Tana sub-basin and its adjacent areas are Tertiary and Quaternary volcanic rocks and alluvial along the major tributaries of the Lake Tana sub-basin. Alluvial sediments have limited distribution within Lake Tana sub-basin dominant at the eastern and northern side of the Lake. The understanding and knowledge of hydrology and hydrogeologic systems is very crucial for every activities involving economic development in the Lake Tana sub basin. Groundwater recharge is one of the most important factors governing the sustainable yield of groundwater and surface water exploitation. The recharge estimation of the Lake Tana sub basin was carried out based on the principle of base flow separation using HMS – SMA for gauged catchments on daily bases. The hydrological and meteorological data used for the period of 1992 to 2006. StatistiXL Multiple linear regression was used to estimate the runoff for ungauged catchments. A level of significance of 0.05 was used for the forward and backwards stepwise regressions. Climate and physical characteristics of the catchments were used in multiple regression to predict the flow characteristics of ungauged catchments. The amount of rainfall, topographic setting and geology are the main controlling factors of climate and physical characteristics of the catchments. The groundwater contribution from gauged catchments is about 161.17mm/yr or 12.1% of the total rainfall of the basin. The ungauged catchments contribute a total of 28.18 mm/yr or 2.28% of the total rainfall of the basin.Item Carbon Dioxide-Water-Rock Interaction and Hydrogeochemical Evolution of Thermal and Cold Ground Waters in Wonchi Crater Lake and Ambo- Woliso area.(Addis Ababa Universty, 2011-05) Shube, Hassen; Kebede, Seifu (PhD)Isotopic and geochemical data are used to study the hydrogeochemical evolution of thermal and hypothermal ground waters and CO2-water-rock interaction of ground waters around Wonchi, Woliso and Ambo area. Geochemical data are classified by Q-mode hierarchical cluster analysis in to objective groups in order to identify ground waters that have the same hydrogeological and chemical nature so that to conduct inverse geochemical modeling. HCA classified the water in to two major groups of high and low TDS and six sub-groups. The waters in the classified subgroups are similar in chemical composition, geology and the depth in to shallow and deep aquifer. Hydrogeochemical evolution of ground waters of the study area is highly influenced by two regional structures like YTVL and Ambo-Wonchi-Butajira faults that cut across this region. Thermal and gaseous ground waters of the study area are particularly aligned along these structures. The CO2 influx to ground waters of the area is due to the deep seated faults that bring this gas from deep source of metamorphic decarbonation or mantle gas origin. The source of CO2 gas is suggested by using δ13C isotope indicates high values are in thermal and gaseous mineral waters of the region. High TDS thermal and gaseous ground waters are characterized by NaHCO3 in Wonchi and Woliso area while Ambo area is characterized by NaCaHCO3 type waters. Low TDS ground waters are suggested as shallow and cold ground waters of recharge area that undergone less water-rock interaction and characterized by δ18O enrichment and CaHCO3 and CaMgHCO3 water types except in some mixed ground waters. Stable isotope data indicates that thermal and gaseous ground waters are depleted in δ18O except in Wonchi area ground waters that shows δ18O enrichment due to hydraulic connection with Lake Wonchi. The effect of the influx of CO2 to ground waters of this region plays a major role in CO2-waterrock interaction to be significant and silicate hydrolysis like dissolution and precipitation of silicate minerals during ground water chemical evolution. Trace element mobility is observed in high TDS thermal and gaseous ground waters due to strong CO2-water-rock interaction. Heavy metals that are harmful to the human and environment like Sr, Ba, Mn,Fe and Al are observed in some thermal and mineral waters of the study area above the permissible concentration of WHO drinking water standard. Key words: hydrogeochemical evolution, thermal, gaseous, CO2-water-rock interaction, trace element mobility, Ambo, Woliso, Wonchi Crater LakeItem Comparative Study of Nitrate levels in Groundwater’s of Addis Ababa and Dire Dawa(Addis Ababa Universty, 2017-05) Tsegay, Tsnat; Kebede, Seifu (PhD)Nitrate is the most frequently introduced pollutant in the groundwater’s of Addis Ababa and Dire Dawa city. This study was conducted to compare the level of nitrate pollution of the major cities Addis Ababa and Dire Dawa. The study tries to identify different source of nitrate pollution for both cities by revising of previous works and literatures on geological, hydrogeological and hydrochemistry of both areas. The possible sources of nitrates are city sewage, defective septic tank effluents, municipal waste, industrial waste, wastes from livestock and chemical fertilizers containing nitrogen. In Addis Ababa the mean concentration of nitrate is 7.9 and the standard deviation is ±14.96 and in Dire Dawa the mean concentration is 37.27 and the standard deviation is ±51.4. The spatial plot of nitrate of the study areas shows that the nitrate level of Dire Dawa is higher than Addis Ababa. The lowering of nitrate level in Addis Ababa is as a result of low nitrification process. The nitrate level in Dire Dawa becomes high because of shallow groundwater level depth which varies 9.3-93.5 meter whereas, in Addis Ababa it varies 0-260 meter, the main aquifer is sandstone, sandy soil and agriculture is dominant. Therefore, integrated waste management strategy and proper groundwater management should be practiced to provide safe drinking water with sufficient quality and quantity in both cities. Key word: Addis Ababa, Comparison, Dire Dawa, NitrateItem Estimation of Evapotranspiration for Irrigation Performance Assessment Using Satellite Remote Sensing at Kobo Valley Irrigation Project, Northern Ethiopia(Addis Ababa Universty, 2009-06) Molla, Tegegne; Kebede, Seifu (PhD)This paper describes the use of a remote sensing technique, the Surface Energy Balance Algorithm for Land (SEBAL), to assess actual evapotranspiration across Kobo valley irrigation project. The SEBAL model was applied to the Landsat 7 ETM+ image corresponding to December 05, 2003 to produce estimates of ET at 30×30m resolution. The actual evapotranspiration (ETa) was integrated for 24 hours on a pixel-by-pixel basis from the instantaneous evapotranspiration (ET). SEBAL ETa estimates vary from 0 to 4.86 mm/day over the image. Lowest ETa was observed for barren fields and highest for water bodies. ETa for vegetative areas ranges 3.5 to 4 mm/day. Irrigated areas, drip and sprinkler irrigation systems, appear to evaporate with average rate of 1.8 mm/day. Penman-Monteith reference crop evapotranspiration ET0 on the same day was found to be 4.5 mm/day at the meteorological station. During the dry season, actual evapotranspiration increases with the availability of moisture in the soil instead of the temperature gradient. The performance of the irrigation system for the command area (September to January) was determined according to 5 indicators, namely overall consumed ratio (OCR), relative water supply (RWS), depleted fraction (DF), crop water deficit (CWD), and relative evapotranspiration (RET). Potential and actual evapotranspiration parameters used in determining these indicators were estimated according to the SEBAL (Surface Energy Balance) method using Landsat ETM+ image. Seasonal averages of the irrigation project calculated from the results were 0.55, for OCR; 1.23 for RWS; 0.29 for DF; 42.44mm/month for CWD; 0.43 for RET. According to the seasonal average values of all the performance indicators, the irrigation performance of the area is usually poor and only the overall consumed ratio indicator is within the range of acceptability. Thus, performance indicators showed that less irrigation water was supplied to the area than was needed. Keywords: Performance indicators, performance assessment, evapotranspiration, SEBAL, remote sensingItem Evaluating the Source and Fate of Nitrate in Surface and Ground Waters in Addis Ababa Area: Geochemical Approaches(Addis Ababa Universty, 2016-06) Kifle, Ruhama; Kebede, Seifu (PhD)This study was conducted to evaluate the source and fate of nitrate in surface and ground water. The characterization of nitrate (NO3) in major rivers and aquifers of the Addis Ababa area were investigated by Isotopic and geochemical conditions. And an overall understanding on the sources and fate of NO3 in the surface water and the groundwater was obtained. The NO3 concentrations in both surface and ground water were very low and no samples exceed the WHO standards while concentration of other nutrients such as PO4-, Cl- and NH4+ were higher on surface waters. The Redox condition estimated based on measurements of redox parameters of Eh, The analysis revealed that most of the surface water had anaerobic condition and presence of strong reducing conditions in the surface water and the recharge ground water. The anoxic condition is provided by high organic matter content in the surface water and result depletion of oxygen’s. Here the δ2H_H2O and 8δ18O_H2O result shows that the source of ground water in the city is heavy rain fall of different regime and shallow ground water recharge hypostasis is from rain fall. The recharge of surface water is from dam reservoirs and mixing between tap waters and ground waters. This study brings some clear evidences that unwanted anthropogenic nutrients can be released in both surface waters and shallow groundwater from rapidly growing cities. In addition, these polluted waters can create a serious treat for the downstream populations, with the need to implement expensive tertiary treatment plants to remove nitrate. The chemical data shows that the concentrations of nutrients other than nitrate were higher and shows the pollution of surface waters but low nitrate. From the correlation of nitrate specious with other geochemical parameters reveals that the source for nitrate and other nutrients were the same such as wastes from manure, septic systems, fertilizer and industries.Item Geochemical Evolution if Groundwater from Plateau to the Rift Floor in Shinile Area, Eastern Ethiopia(Addis Ababa University, 2012-03-03) Mengesha, Diriba; Kebede, Seifu (PhD)The objective of this study was to assess geochemical evolution of groundwater from plateau to the rift floor in Shinile area and to identify geochemical processes responsible for evolution by analyzing hydrochemical data using conventional graphical methods and multivariate statistical methods. For this purpose water chemistry data of eighty seven water samples from the area are analyzed and interpreted. Q-mode Hierarchical cluster analysis (HCA) is used to classify the eighty seven water samples in to five distinct hydrochemical groups. The results of this analysis revealed that in general salinity and concentration of the groundwater increases from highland areas to the rift floor and water type in the study area evolves from Ca-HCO3 and Ca-Mg-HCO3 dominated type on the highlands to Na-HCO3 and Na-HCO3-SO4 dominated type on the escarpment to Mg-Ca-SO4-HCO3, Ca-Na-SO4 and Na-Cl-SO4 types on the rift floor following the direction of the ground water flow. Principal component analysis, another multivariate statistical method, is employed to analyze the water samples to identify geochemical processes that are responsible for the observed variation in hydrochemistry of the area. The first three principal components accounted for 72.85% of the total variance in the hydrochemistry. The first principal component which explained 46.99% of the observed variance most probably represents dissolution reactions of carbonates and evaporite sediments; the second principal component which explained 15.29% of the observed variance in hydrochemistry most probably represents silicate hydrolysis reaction and the third principal component which accounted for 10.58% of the variance in hydrochemistry most probably represents addition of contaminants to the ground water from anthropogenic sources based on their factor loadings for the different hydrochemical variables. The relationship among the major ion compositions of the water samples are also analyzed to determine if the geochemical processes suggested based on the PCA results are responsible for the observed variations in hydrochemistry of groundwater in the study area. The results of this analysis clearly indicated the occurrence of dissolution reaction of evaporite deposits and carbonate sediments as well as silicate hydrolysis reactions in the study area confirming the PCA results. Finally water quality of the study area is assessed from domestic use and agricultural point of view and distribution of fluoride and SAR of the area are mapped.Item Ground Water Resource Evaluation and Management Practices in Gilgel Abay Catchment, Tana Basin(Addis Ababa Universty, 2010-01) Abel, Beruke; Kebede, Seifu (PhD)Groundwater resource is the most important natural resource in the study area. The rapidly increasing agriculture, industry and domestic water supply requirements in the study area meet mainly from groundwater. Groundwater is usually protected against contamination from the surface by soils and covering rock layers. This why most drinking water in many areas of the world is groundwater. Due to steep increase in population along with the associated activities, the water demand for groundwater in the study area is maximized from time to time. However, water can be constraint if not properly managed and developed. Even though the water supply coverage of the study area is increases, a significant number of the water supply schemes in the catchment are non functional due to different reasons, which implies that no effective system of groundwater management practices in the area. The main objective of the present study is to evaluate the groundwater potential of Gilgel Abay catchment and to assess management issues in the catchment. To achieve this objective recharge to the groundwater was estimated based soil-water balance method and a value of approximately 489mm annual recharge to the catchments’ aquifer was obtained. In the catchment two aquifer systems were identified based the available well log data and pumping test data namely: Quaternary vesicular basalt and Tertiary scoracious basalt. The groundwater flow direction, recharge area, and discharge area were identified using chemical plotting of trends of major ions, TDS and EC. As the groundwater moves from recharge to discharge areas along its path it evolved from Ca2+- HCO3 type to Na+-HCO3 type. Concerning the management practices, five representative woredas with their respective PA which can characterize the whole water supply problem of the catchment were chosen for house hold water economy analysis. Findings of the study reveal that there are about 354 water supply points, out of which 94 non functional. Lack of skilled manpower, poor construction and maintenance, poor planning and management practices, low community participation are the main problems regarding the water supply schemes. Findings of the study also indicate high community participation, wide investment opportunity for private sector, capacity building of professionals and accountability and transparency of government officials are the main factors to sustain water supply schemesItem Groundwater Recharge Estimation in Ethiopia(Addis Ababa University, 2020-12-17) Degu, Yohannes; Kebede, Seifu (PhD)Understanding the rate of groundwater recharge is crucial to studies of water availability, wellhead protection, contaminant transport, ground-water and surface-water interactions, effects of urbanization, and aquifer vulnerability to contamination. The aim of this study was to determine the rate of groundwater recharge in the study area at long term monthly temporal and 250-meter spatial resolutions by applying the WetSpass-M model, recursive digital filter base flow separation, and chloride mass balance methods, and by developing a groundwater conceptual model before implementing the recharge estimation methods. The multi criteria decision analysis (MCDA) combined the rainfall, soil texture, land use/land cover (LULC), lithology, lineament density, drainage density, and slope factors in the GIS environment to develop a conceptual model of groundwater recharge to the study area and evaluate the appropriateness of the recharge estimation methods selected for the estimation. The WetSpass-M model requires the land use/land cover (LULC), slope, soil texture, depth to groundwater, and climatological variables (rainfall, temperature, potential evapotranspiration, and wind speed) for the estimation of physically distributed groundwater recharge in the study area. The base flow separation, on the other hand, used river flow data on 18 river gauge stations located at the outlets of the major rivers of the study area. The chloride mass balance method requires precipitation amount, chloride concentration in rainfall, chloride concentration in groundwater as input datasets. The MCDA result showed that both the spatial and temporal characteristics of the groundwater recharge potential in the study area was highly controlled by the rainfall characteristics in the study area. Similarly, the highest estimations of WetSpass-M and base flow separation methods were observed in months and areas that receive the highest rainfall. Accordingly, the long term average estimation to the rainy months in the study area (June to September) by WetSpass-M model was found to be 10.5 mm, 18 mm, 15.7 mm and 10 mm, but by the base flow separation method, it was 3 mm, 5.5 mm, 10.9 mm, and 14.2 mm. Some particular areas such as Goro in the western part of the study area, due to their higher and extended rainfall characteristics, receive higher amount of groundwater recharge almost throughout the year. In Goro, groundwater recharge reached up to 400 mm/yr which was around 20% of the average rainfall in that particular location. The long term annual average groundwater recharge in the study area from WetSpass-M, Base flow separation, and chloride mass balance were found to be 73 mm (81 BCM), 63 mm (40 BCM), 65 mm (72 BCM) respectively. The outputs of this study, due to its finer spatial and temporal resolution, can be very useful to better understand the characteristics of rate of both the spatial and temporal groundwater recharge in the country as well as to studies related to groundwater management, contamination susceptibility, landslide, and subsidence.Item Groundwater Resources Evaluation and Management in Woliso Woreda, Central Ethiopia, Southwest Shoa Zone(Addis Ababa University, 2012-06-06) Fekadu, Frezer; Kebede, Seifu (PhD)This study covers two parts where the first part deals with groundwater potential assessment of Rebu river catchment and the second part which is the main focus of the study deals with assessment of sustainability problems of developed water supply schemes in Woliso woreda( i.e part of Rebu river catchment). Rebu river catchment is found at the margin of Main Ethiopian Rift. The average monthly Maximum and minimum temperature of the area are 25 0C and 11.29 oC, respectively. Its mean annual aerial depth of precipitation is 1207mm. Potential evapotranspiration for the area is calculated using Penman and Thornthwaite gives annual potential evapotranspiration value of 952.49 mm/year and 807.3mm/year, respectively. Actual evapotranspiration for the area estimated, from Turc method gives a valueof 806.98mm.While actual evapotranspirationusing Soil-water balance (Thornthwaite and Mather) method is 733.2 mm. The overall water balance of the study area wascomputed with an aim of estimating the amount of annual recharge to the groundwater. Accordingly; annual recharge to the ground water of the study area is approximated to be 244.2mm. The sustainability challenge of developed water supply schemes is conducted in Woliso woreda. The woreda have Thirty Seven PA’s and the total PA’s found in the woreda were surveyed. The main source of drinking water for the woreda is groundwater. Currently there are two hundred sixty five functional water supply schemes were found in woreda; where, 122 hand dug wells fitted with hand pump, 81 shallow wells, 5 deep wells and 57 on spot capped springs and 30 water supply schemes are non-functional;where, 11 Shallow wells, 8 springs, 7 hand dug well and four deep wells are failed to meet their objectives. Findings of the study reveal that Poor quality (high fluoride concentration), management problem, Lack of training for the professionals, water managers, community and local operators is other reason for sustainability problem of the woreda. Result of the study shows that almost al of the interviewed technical staffs clarify that the existing training and staff mobility strategy doesn’t allow professionals to improve their skills. In addition there is high shortage of skilled human resource, budget, and logistics in the rural water supply office of Woliso woreda. There is no clear system for monitoring and supervision of schemes by the office. Little role of local communities was seen during water supply development activities; besides Women participation at the time of development of water supply schemes and after development is completed is insignificant. All the above mentioned factors plays significant role for the failure of the developed water supply schemes. A finding of the study also show investing on knowledge of professionals is first priority of beneficiaries to minimize the rate of failure of water supply schemes.Item Groundwater Resources Evaluation and Management in Dugda Woreda, Central Rift Valley, Ethiopia(Addis Ababa Universty, 2007-12) Kassa, Netsanet; Kebede, Seifu (PhD)This study covers two parts where the first part deals with groundwater potential assessment of Meki river catchment and the second part which is the main focus of the study deals with assessment of sustainability problems of developed water supply schemes in Dugda woreda( i.e part of Meki river catchment). Meki river catchment is found with in the Main Ethiopian Rift in the northern sector of the Lakes region. The average monthly Maximum and minimum temperature of the area are 25.8 oc and11.4 oc, respectively. Its mean annual aerial depth of precipitation is 992mm. Potential evapotranspiration for the area is calculated using Penman and Thornthwaite gives annual potential evapotranspiration value of 1242.8 mm/year and 827mm/year, respectively. Actual evapotranspiration for the area estimated, from Turc method gives a valueof 754mm.While actual evapotranspiration using Soil-water balance (Thornthwaite and Mather) method is 732 mm. The overall water balance of the study area was computed with an aim of estimating the amount of annual recharge to the groundwater. Accordingly; annual recharge to the ground water of the study area is approximated to be 116.7mm. The main aquifer formations of the boreholes are lacustrine deposits, weathered and fractured Basalt, ignimbrite, and welded tuff. The general trend for groundwater flow observed from pieziometric heads is from western highlands toward the rift floor in the direction of NW to SE of the study area. Groundwater type of the area evolves from Ca-Na HCO3 water type in the western highlands and escarpments to Na-HCO3 water type in the rift floor (i.e. towards lake Ziway) of the study area. The sustainability challenge of developed water supply schemes is conducted in Dugda woreda. Five representative PA’s which can characterize the whole water supply sustainability problem of the woreda were chosen. The main source of drinking water for the woreda is groundwater. Currently there are seventy-five developed water supply schemes; where thirty-eight point eight percent are boreholes, thirty-four point six percent are windmills and twenty-six point seven percent are hand pumps. Twenty-six point six percent of these developed schemes have failed to meet their objectives. Local community in the study area also develop 2162 dug wells individually which could result in depletion of the resource. Findings of the study reveal that Poor quality (high fluoride concentration) of water is the main cause for ninety-one percent failures of developed water supply schemes. Findings of the study reveal that ninety-five percent of the water supply schemes are managed by water committees. Lack of training for the professionals, water managers, community and local operators is other reason for sustainability problem of the woreda. Result of the study shows that ninety-four percent of interviewed technical staffs clarify that the existing training and staff mobility strategy doesn’t allow professionals to improve their skills. Eighty-five percent of respondents explain, they didn’t obtain any kind of training. In addition there is high shortage of skilled human resource, budget, and logistics in the rural water supply office of Dugda woreda. There is no clear system for monitoring and supervision of schemes by the office. Little role of local communities was seen during water supply development activities; besides Women participation at the time of development of water supply schemes and after development is completed is insignificant. All the above mentioned factors plays significant role for the failure of the developed water supply schemes. A finding of the study also show investing on knowledge of professionals is first priority of beneficiaries to minimize the rate of failure of water supply schemesItem Groundwater-Surface Water Interaction Along the Main Course of Awash River; Integrated Approach(Addis Ababa University, 2018-05-12) Aregu, Tsedenya; Kebede, Seifu (PhD)In river basin hydrology the role of groundwater for being an integral part of the river basin water resources is often unrecognized. This is true in Ethiopia. Groundwater has multiple roles in river basins. It serves as source of water for socioeconomic activity, it maintains river flows during dry seasons and it could be the main pathway for solute and heat migration. In existing Awash Basin Master Plan groundwater is not accounted as one of the factor for increasing and imposing stress on existing surface water resources. There is increasing discussion among policymakers to learn more about the role of groundwater in the Awash Basin Hydrology. Through multiple methods, namely stable isotope of water (2H and 18O), isotope of Radon (222Rn), piezometeric evidences as well as field physico-chemical characteristics, investigation of groundwater surface water interaction along the main channel of Awash River has been carried out. The analysis of isotopic compositions of groundwaters from Upper Awash generally signifies, the groundwaters have similar isotopic composition to that of the present day rainfall. Whereas from middle and Lower Awash groundwaters here are mostly of older origin- because of lack of 14C data estimating the age of groundwater in the lower Awash Basin was not possible. From 222Rn measurements groundwater discharge into the river is observed, in Upper Awash, in the lower and middle Awash. There are some specific spots where groundwater discharge is noticed in the lower and middle Awash (e.g. around irrigation areas of-Wonji, Metahara and Amibara; and along thermal spring discharge zones downstream-e.g. Meteka). The Pizeometeric evidence also supports this observation. In which Upper Awash is generally a gaining river and the downstream river segments are generally loosing. Most of groundwater loss that occur in the lower part of Awash, takes place between Amibara and Mile and groundwater flows towards North Easterly direction and probably discharges into Lake Abe or into the sea or into other lower areas in Ethiopia. Evidences form various methods clearly indicate the presence of aquifer hydraulic link in the basin. This work generally showed that deep groundwater in the middle and Lower Awash can be considered as separate water resources, whereas, deep groundwaters in Upper Awash are hydraulically connected to Awash River. Therefore, areas where this interaction taking place is mapped based on the obtained results. This has a practical implication in finding way for water resource management, which can solve the current unbalanced usage of water resource.Item Hydrogeochemial and Isotope Hydrology in Investigating Groundwater Recharge and Flow Processes; Lower Afar, Eastern Ethiopia(Addis Ababa University, 2012-06) Deressa, Addisu; Kebede, Seifu (PhD)The research area includes the eastern part of the lower Awash Basin and Aysha Basin located in the eastern part of Ethiopia (South Afar). The areas have two physiographic regions the Rift and the Eastern Escarpment. Stable environmental isotopes (δ18O and δ 2H) and hydrogeochemistry of precipitation and groundwater are used for the eastern lower Awash basin. However, only hydrogeochemistry is used for Aysha basin due to unreliability of isotopic laboratory results. The main objective of this research is to investigate groundwater recharge and flow processes in the area. The integrated application of hydrogeochemistry and stable isotope of water (2H and 18O) for investigating the recharge and flow processes is a new approach for the area under consideration compared to the previous works in the area. The methodologies applied to achieve the objectives set are sampling and analysis, hierarchical cluster analysis (HCA), inverse geochemical modeling, the plot of δ18O vs δ 2H and chloride mass balance (CMB). Analyses of the water samples collected for physico-chemical and isotope were conducted at the laboratory of Water Works Design and Supervision Enterprise (WWDSE) and Addis Ababa University (AAU) respectively. Prior to using the water chemistry results for the intended application, charge balance evaluation is done and those with an error greater than 10% are rejected from the data set. Then hydrochemical facies analysis was conducted to identify the major water types. Accordingly, four major water types in the eastern lower Awash Basin: Ca-Mg-HCO3, Na-HCO3-, Na-Cl-SO42-, or Na- SO42-Cl and Ca-Mg-Cl-SO4 or Ca-Mg-SO42-Cl and two major water types in the Aysha Basin: Ca- (HCO3)2, and Na-Ca- SO4 or Cl were identified. Bicarbonate type water represent recharge area groundwater in topographically higher areas and fast moving discharge area groundwater in the rift. However, as groundwater moves toward rift it evolves to chloride or sulfate water type. HCA also classified the groundwaters of eastern lower Awash basin in to two major groups and eight subgroups and that of Aysha basin in to two major groups and five subgroups. The spatial distribution map of HCA in the basins clearly indicated the groundwater flow directions. Based on the clustering results inverse geochemical modelings are carried out along five selected flow paths in the Awash Basin and along one path in the Aysha Basin. Accordingly, the results indicate dissolution of halite, anhydrite, silicate minerals, consumption of CO2 during silicate hydrolysis, cation-exchange, and precipitation of calcite and clay minerals along the flow path toward the rift. For the eastern part of lower Awash Basin, the plot of δ18O vs δ2H for groundwater identified three recharge mechanisms using local meteoric water line (LMWL) derived from Addis Ababa rainfall: recharge from local rainfalls, recharge from evaporated flood waters or mixing, and regional groundwater which are most likely recharged by lateral infiltration of meteoric water. The integrated analysis of salinity (TDS) and δ18 Keywords: Groundwater, recharge, flow processes, hydrogeochemistry, environmental isotopes O also identified two major processes for the origin of salinity: evaporation and dissolution. The annual recharge rates computed using CMB method for the eastern lower Awash and Aysha Basins are 29.15 and 58.24 mm/year respectively. However, the figure is extremely over estimated for the Aysha Basin due to fast selective recharge. The average annual rainfall amount and average Cl concentration in rainfall accounted for the CMB method are 662.81mm/year and 0.91 mg/l respectively. Ninety nine (99) groundwater Cl concentrations (93 from Awash and 6 from Aysha basin) are used Keywords: Groundwater, recharge, flow processes, hydro geochemistry, environment isotopesItem Hydrogeochemical and isotope hydrology in Investigating Ground Water Recharge and Flow Processes; Borena Lowlands, Southern Ethiopia(Addis Ababa Universty, 2012-06) Fanta, Likissa; Kebede, Seifu (PhD)Hydrogeochemistry and isotope hydrology were used to investigate groundwater recharge and flow processes in Borena lowlands. The study area is characterized by semi-arid and arid climate. Surface water flows are intermittent. The available water resource, therefore, restricted to groundwater. Precambrian basement, Tertiary and Quaternary basalt, and recent alluvial and elluvial sediments are major geologic units. Fractured and weathered basalt is the principal aquifer. The hydrochemical analysis shows that Borena groundwater varies in type over a wide range even within few kilometer intervals and broadly distributed rather than forming distinct clusters. However, three major water types can be distinguished depending on their position on a Piper diagram. These are Ca-Mg-HCO3, Na-HCO3 and Ca-Mg-SO4- Cl/Na-Cl/SO4 water types. In most cases Ca-Mg-HCO3 type waters occur in areas of recharge and Na-Cl/Na-SO4 type waters in rift/lower lying section. The intermediate water types are mixed and lay between these two end members. Ten subgroups were examined from the hierarchical cluster analysis in which distinct hydrgeochemical processes were clearly observed. The dissolution of minerals like olivine, pyroxenes, plagioclase, anhydrite, halite and CO2 gases are deriving the observed natural groundwater chemistry, which are in most cases, balanced by the precipitation of calcite minerals and weathering/formation of clay minerals like Ca-montmorilonite, chalcedony, illite, and K-micas. Cation exchange reactions, particularly in Sarite lower plains, were also controlling chemical composition of the groundwater. The isotopic composition of _18O and _2H in groundwater varies from -5.080/00 to 0.080/00 and from -290/00 to -2.40/00 respectively. In this work the altitude effect on _18O composition shows a depletion of -0.10/00 per 100m elevation rise. Three recharge mechanisms; direct precipitation, regional groundwater and/or fast selective and flash floods recharge mechanisms were known from the groundwater isotope interpretation. The hydrogeochemical and environmental isotope analysis result clearly indicates regional groundwater flows from elevated sections for instance; Elwaya, Yabello, Utalo, Gololcha via the middle Gelchet plains to main Ririba fault. A flow from Mega and Megado escarpments to megado/Biloko lowlands is also identified. For the sub basin recharge rate was estimated using chloride mass balance method and is 28mm/yr. The recharge rate shows variations mainly with topography, groundwater chloride content and annual rainfall amounts. The northwestern (Mermero), northeastern (Yabello) and eastern (Mega) parts receives highest recharge where as the southwestern and southern sectors get the lowest groundwater recharge rates. Keywords: hydrogeochemistry, environmental isotopes, groundwater recharge, semi-arid, Borena lowlandsItem Hydrogeological System Analysis of Allydegi Plain and its Surroundings Using Geochemical Modeling and Isotope Techniques(Addis Ababa University, 2013-06-06) Tadesse, Ephrem; Kebede, Seifu (PhD)Allydegi plain and its surrounding, which is located in the middle Awash river basin of the Main Ethiopian Rift has lack of water supply problems. Hydrogeochemistry and isotope techniques were used to study the groundwater system of the area. Tertiary and Quaternary volcanic rocks with recent alluvial and elluvial sediments are major geologic units. Fractured and weathered volcanic rocks and unconsolidated sediment aquifers are the key aquifers. Hydrochemical study result reveals that the area is characterized by four major water types. Water group of Ca-Mg-HCO3 and Na-Ca-HCO3 types are characterized by recharge area waters. Na-HCO3 type waters are an evolved water types from highland and escarpments of Ca-Mg-HCO3 and Na-Ca-HCO3 water types located in the center of the study area whereas highly concentrated Na-HCO3-Cl and/or Na-HCO3-SO4 type waters are characteristics of discharge area water types. The result of inverse geochemical modeling depicts that dissolution of silicate minerals, calcite, anhydrite and halite minerals, cation exchange, precipitation and/or weathering of clay minerals with a consumption of CO2(g) as a heat from deeper source through fractures control the groundwater chemistry of the area. Beside these, from the correlation of δ18O as a function of chloride content of the groundwater implies that rigorous evaporation and dissolution can be discriminated as salinity sources without ignoring the impact of Beseka Lake after draining in to Awash river. The estimated groundwater recharge of the area using CMB method is 98.11mm/yr and the roughly estimated ground water flow velocity using stable isotope monitoring results is about 5.6x10-3 m/sec. Stable isotopes study result illustrates that the ground water system is recharged from the combination of direct recharge from precipitation, from highlands that bounds the study area through fractures and from Awash river. Isotope monitoring result of Boreholes in Allydegi plain and Awash river also testifies that Awash river recharges the Allydegi plain. The hydrochemical and water level monitoring of reservoir and borehole at dam axis shows that the source of leakage at the left abutment is from reservoir rather than the groundwater system.Item Numerical Groundwater Flow and Solute Transport Modeling of Dire Dawa Groundwater Basin(Addis Ababa University, 2013-06-06) Desta, Zelalem; Kebede, Seifu (PhD)The study focuses on defining the flow of groundwater through the Dire Dawa upper sandstone and limestone aquifer system and migration of high concentration nitrate (NO3-) plume to the Sabian well field which is the main source of water for the town water supply. Groundwater extracted from the aquifer under research concern is the only available source of water in the area. Within the study, the hydrogeology has been investigated, conceptual groundwater flow model has been developed and numerical groundwater flow and solute transport model produced from this. Examination of boreholes lithology logs confirms that the upper sandstone and limestone aquifer beds have complex orientation in space with varying thickness from place to place, especially the upper sandstone. The major cause of this is the rift forming normal fault displacement and volcanic plugs through it. In some boreholes thickness of sandstone penetrated is as small as 10m while in others thickness of 100 to 150m is penetrated before reaching the lower limestone. The groundwater system in Dire Dawa town and surrounding area has been categorized in to two, (WWDSE-BECEOM, 2004). i.e the Escarpment and the Rift floor. The rift forming fault system divided the area in to two topographic pheatures, the up thrown (Escarpment) and down thrown (Rift floor) plain. Dire Dawa town is located in the rift floor. In the escarpment outcrops, basement rocks of granitic composition, limestone and sandstone. Limestone and sandstone on the escarpment are fractured and the limestone especially karestified forming good potential area for groundwater recharge from direct percolation of the rainfall. In the rift floor, the upper sandstone and limestone (major aquifer) are overlaid by tertiary volcanic (basalt and andesite) and quaternary alluvial deposits. In Dire Dwa town, the major aquifer, upper sandstone and limestone is overlaid by course to medium grained alluvial sediment dominantly of sand along Dechatu and Legehare seasonal rivers. These sediments originate from the escarpment where, outcrops basement rock of granitic composition. Two hydrostratigraphic units identified: the alluvial unconfined aquifer along Legehare and Dechatu seasonal rivers, and the upper sandstone-limestone complex aquifer (major aquifer). The upper sandstone and limestone even though, have different composition form one complex aquifer system due to hydraulic connection through their fractures. Poor design of wells during their construction and improperly abandoned wells let groundwater contaminants enter to the underlying confined major aquifer. This is either through forming hydraulic connections between the upper unconfined alluvial aquifer which is vulnerable to pollution and the lower confined major aquifer, or being direct source of contaminants to the major aquifer in the case of improperly abandoned wells. Addis Ababa University, 2013 Zelalem Desta Page viii A single layer groundwater flow and solute transport model using MODFLOW, MT3D and PM path was developed for the upper sandstone and limestone (major aquifer). The model was calibrated using automatic model calibration technique under steady state condition. Simulated and observed head has been compared having good agreement with correlation coefficient of 0.91. This showed the aquifer parameters were estimated honoring the measured (observed) head within the given boundary conditions. Predictive simulations with various annual abstraction scenarios prevails that a total of 1773 l/s of groundwater enters the rift floor aquifer of upper sandstone and limestone as a subsurface, mountain front groundwater recharge assigned a flux (general head) boundary at the southern edge of the rift. Concentration of nitrate (NO3-) within boreholes in Sabian well field was simulated for the future 10 years. The concentration-time curve showed currently water from many boreholes do not meet WHO standard limit for their NO3- content. And groundwater from some of other boreholes will fail to meet the upper limit of NO3- content (45 mg/l) set by WHO within few years after now unless proper remedy be taken there off.Item Origin of High Groundwater Salinity in the Omo Delta and its Surroundings (Southwestern Ethiopia) Hydrochemistry and Isotope Approaches(Addis Ababa University, 2020-09-23) Tadesse, Abebayehu; Kebede, Seifu (PhD); Asrat, Asfawossen (Professor)The groundwater of the Omo Delta is characterized by the presence of fresh and saline groundwater side by side and the success of having fresh water is well below 50%. Therefore, most wells are abandoned due to elevated salt content. However, research on the origin of groundwater salinity and salinization processes, detail hydrochemical and isotopic composition of the Delta groundwater are lacking. The main objective of this work is to characterize the source of salinity and mechanism(s) of salinization in the Omo Delta (Southern Ethiopia) groundwater giving special emphasis on characterizing various morphological units and depositional environments recognized in the area and their implication on groundwater salinity. To achieve the objectives converging pieces of evidences from the conventional hydrogeological investigation, litho-hydrostratigraphic relationships, water chemistry, and isotope hydrology were used to elucidate the cause of groundwater salinity. The geochemical dataset and isotope were analyzed using different but complementary, approaches that allowed for insights into the process of salinization of groundwater in the study area. The correlation matrices of major anions, cations, and physical parameters of water indicate that elements chloride, sodium, fluoride, sulphate, and bicarbonates contributed from mineralization processes. The dominant effects of rainfall, rock weathering, and evaporation play a major role in the geochemical evolution of groundwater. Rock weathering was the main mechanism controlling the chemical compositions of the Hammer basement groundwater whereas; evaporation–crystallization is in the Delta aquifer groundwater system. The saturation index of anhydrite, aragonite, calcite, dolomite, gypsum, and halite shows that the groundwater in the study area was below the saturation with anhydrite, gypsum, and halite, indicating that these minerals are anticipated to dissolve. Moreover, groundwater samples were saturated to over-saturated with aragonite, calcite, and dolomite, implying that the three major carbonate minerals may have affected the chemical composition of groundwater in the study area. The variation of the hydraulic parameters at different locations and layers have been resulted from aquifer materials formed under different depositional environment. These deposits represent different aggradations and degradation phases that were usually accompanied by lake level changes. Groundwater movement and recharge are highly dependent on geomorphic features and depositional environments. Groundwater that is close to surface water sources ii (River and Wadies) is fresh relative to other farther away from it, in the alluvial fan geomorphic feature, the fan apex is characterized by fresh groundwater compared to fan toe, which is more saline. The thickness of clay layers significantly affects the salinity of groundwater as it acts as the adsorption media and filtering membrane for groundwater in the Delta. The isotopic composition of most groundwater samples from sediment plot slightly far from the Global meteoric water line (GMWL) compared to the waters from the Hammer basement indicating that evaporative fractionation before recharge the sediments. The increase in groundwater salinity due to evaporation has resulted in a simultaneous isotopic enrichment. Both hydrochemical and isotope techniques indicate the dominance of local recharge and flow systems. The radon-222 concentration in groundwater samples showed a very wide range from 58.7 to 982.5Bq/m3 compared to the River and Lake Water samples that are range from 18.65 to 105.2Bq/m3 and 10.49 to 10.85Bq/m3 respectively. The highest concentration was found in the samples that were collected from wells close to the Omo River. From converging evidence of geology, hydrogeology, hydrochemistry, and stable isotopes of water, three processes are responsible for the salinization of groundwaters in Omo Delta: salinity originated from water-rock interaction, evaporation at or near the surface, and clay membrane filtration. The results of this study will also be useful to the development of a sound management plan for water resources and the direction of further research in the study area.