Browsing by Author "Azagegn, Tilahun (PhD)"
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Item Analysis of Inter-Basin Groundwater Flow System Using Hydrogeochemical and Isotope Hydrology (Δ2h Andδ18o) Between Blue Nile and Awash Basins, the Case of Gerado and Borkena River Catchments(Addis Ababa University, 2020-09-09) Ebrahim, Sadam; Azagegn, Tilahun (PhD)Hydrochemistry and environmental isotope techniques has been used to analyze inter basin groundwater flow and hydrodynamic system between Gerado and Borkena River catchments located at the southwestern block of the Afar depression where it occupies parts of the northern plateau in the northwestern part, western Afar marginal area and associated Graben. The sratigraphy of the area is characterizes by volcanic episodes were by the extrusion of flood basalts, with interbeds of pyroclastic rocks of rhyolitic or less commonly trachytic compositions, particularly at upper stratigraphic levels and seismically active right stepping N-S trending step system of discontinuous graben that are tens of kilometers long and 5–15 km wide which follow the curving N-S trend of the western Afar margins. Lithostructurally, Ashange basalt sequence is strongly faulted and tilted by 20° to 30° towards east. The weathering and jointing with the inclined contact is a favorable condition for ground-water flow from highly elevated plateau to the marginal graben. Boreholes and spring in Gerado catchment are characterized mostly by low TDS (< 500 mg/l) and Ca-Mg-HCO3 water type. While the Borkena catchment show a complex groundwater type and variation in TDS (500- 938 mg/l) Based on its flow pattern. The water types in Borkena catchment generally dominated by Na and Ca cations. Based on inverse Geochemical Modeling and ionic ratio calculations dominant reaction happened on the flow paths of Groundwater is likely to be cation exchange which Na is Exchanging Ca and dissolution of silicate minerals. Most of the groundwater samples from Gerado and Borkena catchments have relatively depleted isotopic signature of 18O and D from -2.28 to -6.83 and -2.5 to -7.8 respectively. Isotopically depleted springs found in the adjacent areas of Borkena Catchment while most of the springs found in the Gerado catchment are fall in a line of local Meteoric water. Spring patterns suggest there is an inter-basin groundwater flow between the catchment. The springs have preferential alignment in emerging with a considerable discharge which support inter-basin groundwater flow.Item Assessment of Water Well Drilling Challenges in Ethiopia(Addis Ababa University, 2018-06-30) Simeneh, Gashaw; Azagegn, Tilahun (PhD)The purpose of this study is to identify the main water well drilling and completion problem and explore viable solutions, in Ethiopia. The scope is limited to literature review, data from private and governmental drilling and consulting companies, technical training institutions and discussion with senior drilling professionals.In general 216 selected boreholes with the typical drilling problem were identified throughout the country with their GPS coordinates, target drilling depth and aquifer type. Analysis was made to categorize which kind of structural and hydrogeological setting is most vulnerable for the recorded well drilling challenge. The most prevalent drilling problems happened in Ethiopia include Well caving, drillpipe stacking, lost circulation, hole deviation, drillpipe failures, hole cleaning and personnel and equipment related problems. Among the problems investigated in this paper, the main Ethiopian rift valley and the Tana basin are the areas with highest frequency of drilling challenges are encountered. Among the drilling challenges, well caving stands out as the major drilling challenge with 26.3% of the total occurrence. The frequency of lithology also clearly showed that 45% of drilling problems happening in Fractured and weathered basalt aquifer. Moreover, discussions with chief drillers and hydro-geologists in the field also unveiled the most of the drillers operating in the field lack basic standard training on the drilling of boreholes with various methods of drilling, using appropriate drilling fluids and troubleshooting when the major drilling challenges encountered on the field. Hence, water well drilling crew and supervising hydro-geologists must have a proper acquaintance with different kinds drilling system. Furthermore, typical drilling fluid consumables which are highly recommendable for drilling of wells in different geologic and structural settings must be identified and accepted by the clients. The water well drilling firms and their technical staffs must also be familiar and willing to apply drilling fluids and polymers in order to minimize the risk of abandoning and failure of borehole construction. Selection of quality casings and screens are also crucial to minimize drilling challenges such as casing and well collapse. The technical specifications of drilling projects must also incorporate consideration of local hydrogeology and geological structures to prepare well designs and to select drilling methods and consumables.Item Comparative Study Between South-Jema and Kesum Catchment(Addis Ababa University, 6/6/2020) Ashine, Zekarias; Azagegn, Tilahun (PhD)The study comprises of South-Jema and Kesum catchment, is located in the central highland. It is geographically confined within 38°50´00´´E to 39°00´00´´ E longitude and 8°45´00´´N to 10°00´00´´N latitude covering a total area of 5,683 km2. The study has been conducted with objective to make a comparative analysis of recharge and hydrochemistry. From the hydro chemical data analysis, concentrations of Na and Ca were found to be higher and being the dominant species in both catchment whereby concentration of Na shows an increment towards the downstream part of both catchments whereas concentration of calcium doesn’t shows any decrement towards the downstream part of south-Jema catchment but a decrement in concentration of Ca has been observed in the downstream part of Kesum catchment with rise in TDS. The anion species are dominated by bicarbonates, showing an increment towards the downstream part of both catchments. As evidenced from hydro-chemical Data, there exists a clear evolutionary trend in increment of TDS towards the downstream part of both catchments. Four types of groundwater facies exist in the region ranging from Ca-HCO3 water types mainly concentrated in representing shallow groundwater circulation with relatively short sub-surface residence time to a Ca-NaHCO3/Na-Ca-HCO3 water type representing evolutionary tend of groundwater along its flow path towards the downstream of Kesum catchment. The spatially distributed groundwater balance model, Wetspass has been used in seasonal and annual estimation of groundwater resources, actual evapotranspiration and surface runoff of both catchments. By coupling of physical and hydro-metrological characteristics of the watershed, the wetspass have simulated the average annual long-term groundwater recharge, actual evapotranspiration and surface runoff in South-Jema catchment is found to be 122.02 mm/ year, 380.64mm/ year and 534 mm/year respectively. In the case of kesum catchment, the average long-term groundwater recharge, evapotranspiration and surface runoff is found to be 114.91 mm/year, 455.61mm/year and 410.08 mm /year. The long-term annual precipitation in South-Jema catchment (1023 mm) is distributed as 11.92% recharge, 37.14% evapotranspiration and 52.19% runoff, indicating almost half of the precipitation feeding the watershed is lost due to surface runoff. In the case of Kesum catchment the long-term annual precipitation (973.81 mm) is distributed as 11.8% recharge, 46.7 % evapotranspiration and 42. 11% surface runoff.Item Comparative Study Between South-Jema and Kesum Catchment(Addis Ababa University, 2020-06-06) Ashine, Zekarias; Azagegn, Tilahun (PhD)The study comprises of South-Jema and Kesum catchment, is located in the central highland. It is geographically confined within 38°50´00´´E to 39°00´00´´ E longitude and 8°45´00´´N to 10°00´00´´N latitude covering a total area of 5,683 km2. The study has been conducted with objective to make a comparative analysis of recharge and hydrochemistry. From the hydro chemical data analysis, concentrations of Na and Ca were found to be higher and being the dominant species in both catchment whereby concentration of Na shows an increment towards the downstream part of both catchments whereas concentration of calcium doesn’t shows any decrement towards the downstream part of south-Jema catchment but a decrement in concentration of Ca has been observed in the downstream part of Kesum catchment with rise in TDS. The anion species are dominated by bicarbonates, showing an increment towards the downstream part of both catchments. As evidenced from hydro-chemical Data, there exists a clear evolutionary trend in increment of TDS towards the downstream part of both catchments. Four types of groundwater facies exist in the region ranging from Ca-HCO3 water types mainly concentrated in representing shallow groundwater circulation with relatively short sub-surface residence time to a Ca-NaHCO3/Na-Ca-HCO3 water type representing evolutionary tend of groundwater along its flow path towards the downstream of Kesum catchment. The spatially distributed groundwater balance model, Wetspass has been used in seasonal and annual estimation of groundwater resources, actual evapotranspiration and surface runoff of both catchments. By coupling of physical and hydro-metrological characteristics of the watershed, the wetspass have simulated the average annual long-term groundwater recharge, actual evapotranspiration and surface runoff in South-Jema catchment is found to be 122.02 mm/ year, 380.64mm/ year and 534 mm/year respectively. In the case of kesum catchment, the average long-term groundwater recharge, evapotranspiration and surface runoff is found to be 114.91 mm/year, 455.61mm/year and 410.08 mm /year. The long-term annual precipitation in South-Jema catchment (1023 mm) is distributed as 11.92% recharge, 37.14% evapotranspiration and 52.19% runoff, indicating almost half of the precipitation feeding the watershed is lost due to surface runoff. In the case of Kesum catchment the long-term annual precipitation (973.81 mm) is distributed as 11.8% recharge, 46.7 % evapotranspiration and 42. 11% surface runoff.Item Fluoride Genesis in Groundwater of Butajira _Koshe _Ziway Transects Areas Using Integrated Hydrochemistry and Isotope Techniques, in Central Ethiopia(Addis Ababa University, 2001-06) Admas, Temesgen; Azagegn, Tilahun (PhD)This research is conducted to investigate fluoride problems with it genesis in groundwater of Butajira_Koshe_Ziway transect of central main Ethiopian rift by using integrated hydro chemical and isotope analysis techniques. The hydrochemical analysis result reveals that groundwater type of the area evolves from Ca(Mg)-HCO3water type of early geochemical evolution in the western highlands and escarpments to Na-HCO3 water type of highly geochemical evolution in the rift floor (i.e. towards lake Ziway) of the study area. Groundwater supplied from the highlands is typically characterized by low conductivity, low TDS, and a calcium bicarbonate facies. The water geochemistry (i.e fluoride content) within the study area is widely (extremely) variable due to meteoric water recharge from the surrounding highlands is affected by different degrees of water–rock interaction ,evaporation processes, rock type, depth variation, chemical and physical characteristics of the aquifer and acidity of soil and rock, concentration of ion present in the water. The high F geochemical anomaly is associated with high Na (R2=0.37), alkalinity (R2=0.25), TDS, EC (R2=0.3), shallow depth and low calcium content. In general, from correlation matrix of collected and analyzed water sample, there is a negative correlation between calcium, magnesium and fluoride concentrations and positive correlation between bicarbonate, TDS, EC and fluoride concentration in groundwater. Saturation indices (SI) were calculated (using PHREEQC) for the different water groups, highlighting that the studied waters are super saturated with respect to calcite and under saturated with respect to fluorite. Groundwater is supersaturated with respect to calcite, which promotes the removal of Ca and HCO3 from solution. As a result, groundwater is generally under saturated with respect to fluorite, the mineral that typically controls the upper limit of fluoride concentrations. The stable isotopes result reveals that highly enriched water from hand dug well, few borehole well and lake itself were observed in the downstream part of the study area surrounding the lake Ziway due to evaporation effect and recharged from the lake water rather than precipitation from highlands while the deep ground water located in the highland and escarpment of the study area reveal that slightly to highly depleted due to it recharged at lower temperature/from local meteoric water directly infiltrated rainfall through long subsurface flow from Guragae highland. The general trend for groundwater flow observed from groundwater contour map, hydro chemical evolution and isotopic signature indicates that from western highlands toward the rift floor in the direction of NW to SE of the study area. Keywords: Fluoride genesis; Ground water flow; Hydrochemistry; Stable isotope (δ18O, δ2H)Item Groundwater Dynamics in Tributary Streams of Muger and Holota River Catchments(Addis Ababa Universty, 2016-06) Hailu, Kidist; Azagegn, Tilahun (PhD)Integrated hydogeological study using major ion hydrogeochemistry and environmental isotope tools were employed to characterize groundwater dynamics in tributary streams of Muger River Catchments in the north and Holota River Catchments in the south. Hydrogeochemical study reveals that water types vary from early stage of geochemical evolution (CaHCO3 type) to the highest level of geochemical evolution (NaHCO3) and from low TDS to high TDS and NaHCO3 type are observed only in the downstream part of Holota River catchment. In relation to stable isotopes, highly enriched groundwater from deep wells were also observed in the downstream part of Holota River catchment. Radon concentration has been observed in the main Holota River and low in tributary streams. However, Radon concentration is low in main Muger River but high in its tributary streams that flow through acidic rock units. The stable isotopes signature of the deep aquifer in Holota River catchment illustrates that, the groundwater is recharged through long subsurface path relative to the deep aquifers found in Tributary streams of Muger River catchment. Radon signature shows that main Holota River is recharged from the groundwater at some segments whereas it is not the case for Muger River. And finally, groundwater level map together with isotopic signature show that groundwater divide shifts from surface water divide towards Muger River catchment and the groundwater flow converges towards Holota River flow direction. Key Words: Groundwater dynamics, Muger River, Holota River, Stable isotopes, RadonItem Groundwater Flow Dynamics in the Eastern Upper Jemma River Catchment, Blue Nile Basin, Ethiopia(Addis Ababa University, 2019-06-05) Adimaw, Melkamu; Azagegn, Tilahun (PhD)The present study was conducted in the Eastern Upper Jemma River catchment, which is found in the Northwestern Ethiopian plateau, Blue Nile Basin and has an area of 1255 Km2. The main objective of the study was to characterize the groundwater flow dynamics and the major aquifer systems of the area. By analyzing the available meteorological data, potential evapotranspiration was calculated using penman combined method and the result is 1376.64mm/year respectively. The actual evapotranspiration of the catchment is calculated using Thornthwait and Mather soil water balance model. Thus; annual AET is 799.76 mm/year. The groundwater recharge of the catchment was evaluated by using Water Balance Method (WBM), Baseflow Separation (BFS) method and Chloride Mass Balance (CMB) methods and the results are 100.47 mm/year, 211.84 mm/year, and 559.1mm/year respectively. The area is dominantly covered by fractured, weathered and faulted volcanic rocks with some Mesozoic sandstone and quaternary deposits. Depending on the analysis of pumping test data and qualitative descriptions made, the area is classified into aquifer types of; fissured aquifer developed on basalts on the plateau (moderate to low groundwater potential), mixed aquifer (high permeability and very high productivity), fissured aquifer developed on basalts in deep valleys (high permeability and low to moderate storage), Porous and fissured Sandstone aquifer in deep valleys, and localized aquifer with intergranular porosity and permeability(High permeability and high productivity). From the analysis of water level measurements of 40 boreholes, 26 hand-dug wells, 111 springs, and Physicochemical measurements’ (pH, TDS, EC & T ), the groundwater flow dynamics is controlled by surface morphology and structures and flows from the southeastern, southern and south-southwestern corner towards north and northwestern corner of the catchment.Item Groundwater Recharge Estimation and Aquifer Characterization. a Case Study of Walga Catchment Upper Gibe Basin, Central Ethiopia(Addis Ababa University, 2020-11-24) Wakjira, Tekalign; Azagegn, Tilahun (PhD)Groundwater is mainly used for irrigation and water supply in Walga catchment as other parts of the country. The main objective of this study is to quantify the amount of groundwater recharge using WetSpass model and characterization of aquifers using Aquifer test in the upper Omo-Ghibe basin of Walga catchment. Meteorological data like rainfall, wind speed, temperature, relative humidity, sunshine hours were collected from meteorological stations located within the catchment and nearby area. Potential evapotranspiration was calculated using Penman-Montieth based FAO CROPWAT software. Slope and topography map were generated from Shuttle Radar Topographic Mission elevation data while Land use land cover were prepared from Landsat OLI8 satellite images downloaded from United States Geological Earth Explorer. Parameter table (dbf data) and grid maps were prepared for WetSpass model input with the help of ArcMap 10.4. Using the model the mean annual recharge of the catchment was found to be 7.5% of the precipitation whereas surface runoff was 38.25% of the annual precipitation. The aquifer hydraulic properties were estimated from the pumping test by fitting mathematical models (type curves) to response data (water level changes) through computer software known as AQUIFER TEST. Yield or discharge of bore holes values range from 0.15 l/sec. to 61 l/sec, whereas Transmissivity ranges from 3.5 x10-4 m2/day to 290 m2/day with an average of 50.94 m2/day. Hydraulic conductivity values ranges from 0 to 16.04 m/se with mean values of 1.2 m/s. The sum of the yield from 72 boreholes is 430 l/s (119.4 m3/hr), this gives a total of 37152000 liters per day. 65.8% of Walga catchment coverage is under Satisfactory ground water potential while 0.72% is classified under very good groundwater potential. The mean descriptive statics value of groundwater quality of Walga catchment is below WHO limit and also good for irrigation water quality. The study area is characterized by lowest groundwater recharge relative to surface runoff and actual evapotranspiration due to effect of impermeable soils, morphology of the land and land use land cover of the area. The lowest transmissivity value is indicative of the poor permeability in the pyroclastic lithologic formations and low discharge to wells. It also implies that it will take a considerable time for the aquifers to replace water into wells removed during pumping.Item Groundwater Recharge Estimation for Mullu Catchment in Somale Region, Eastern Ethiopia(Addis Ababa University, 2019-05-06) Gurmu, Naol; Azagegn, Tilahun (PhD)The increasing demand placed on groundwater has encouraged distinguishing of water resource, which would be the foundation of exploration, management, and conservation. In this study, quantitative estimation of groundwater resources of Mullu catchment has been made. Therefore, the main objective of the study is to estimating the amount of ground water recharge for Mullu Catchment using Water Balance Method. And also, the specific objectives are identifying the recharge area and groundwater flow characterization using water level information. The methodology used to estimating the groundwater recharge for Mullu catchment passes through three different stages; desk study, field work, and post field work. The desk study includes literature search and review and/or collection of available data. The sources of data used in this stage comprise published and unpublished reports, both local and international. The field work includes observing the topography and drainage system, Soil type, Land use/cover, geology and hydrogeology of the study area. After field work, data interpretations coupled with thesis writing have been done. Mullu Catchment is situated at narrow valley that surrounded by quaternary volcanic rocks ridges in which the surface drainage out flows towards Afdem area. The area is drain by seasonal streams originating from south, south east and south west high land areas. The flood from high land area is transporting alluvial sediments comprise silt, sand and gravel to vast central plains. The main aquifer of the area is volcanic rocks under laid the alluvial deposits. Particularly volcanic rocks underlying alluvial deposits are considered to be the most potential aquifers of the area. The Groundwater Recharge for Mullu Catchment has been estimating using Water balance method is 73.41mm/year.Item Groundwater Resource Evaluation of the Upper Jemma Catchment Blue Nile Basin Ethioipia(Addis Ababa University, 2022-05-30) Mammo, Yibeltal; Azagegn, Tilahun (PhD)The study was conducted on the upper Jemma catchment, in Blue Nile basin, central highland Ethiopia, Amhara National Regional State, which is located 254 km from Addis Ababa on the way to Mehal-Meda. The study area covered 3250 sq.km and having an average elevation range from 1556m to 3708m above mean sea level. The main objective of the study was to evaluate the groundwater resource potential of the area. This study has also tried to estimate the groundwater recharge of the catchment using the water balance method. Field based physico-chemical parameters have also been used to characterize the groundwater. The annual precipitation of the basin calculated from long term mean monthly rain fall data is 1114.3mm/year. The actual evapotranspiration (AET) and surface runoff (SRO) are 745.77mm/year and 234.23mm/year, respectively. The mean annual groundwater recharge of the upper Jemma catchment is calculated to be 134.4mm/year, which corresponds to 12% of the total annual precipitation. The study area is mainly covered by tertiary volcanic rocks with some Mesozoic sandstone and quaternary deposits. In the catchment highly fractured and weathered basalt, elluvial and alluvial deposits with mixed aquifers have high permeability and productivity for groundwater reservoir. The main recharge area of the catchment is Tarmaber Megezez Mountain, Mezezo, Kobastil, Yegem and other mountain chain in the eastern part of the catchment, which are located at higher elevation. These highland areas get high rain fall compared to the surrounding lowland. Mostly the groundwater movement is parallel and sub-parallel with the surface water flow of the topography and structures of the area. The electrical conductivity and TDS of the catchment ranges from 85.8μS/cm to 334.2μS/cm and from 55.8mg/l to 217.2 mg/l, respectively. This shows that the groundwater quality falls within the freshwater group of the WHO standard.Item Groundwater Resource Potential Assessment in Temcha River Catchment, Upper Blue Nile Basin, Ethiopia(Addis Ababa University, 2020-07-07) Wondemneh, Paulos; Azagegn, Tilahun (PhD)Temcha river catchment is located in central part of upper Blue Nile river basin in North West Ethiopia. The area covers 1979km2 and elevation varies from 4000 to 1400 meter above sea level. The groundwater potential assessment of the catchment has been done by integrated aquifer characterization, hydrogeochemical evaluation and recharge estimation. Lithologic units in the catchment include, Quaternary sediment, Miocene shield volcanic rocks (Choke basalt, trachyte plug, Choke rhyolite, Kutye basalt and Arat Mekeraker basalt rob-Gebeya basalt), tertiary flood basalt; such as Lumame basalt, upper basalt, middle basalt and lower basalt, and Mesozoic sandstone. Lineaments have NE-SW and S-N orientation. Different Volcanic rocks and quaternary unconsolidated sediments countered in the catchment were categorized into high, moderate and low productive aquifer system. Weathered and fractured tertiary flood basalts and thick alluvial deposits are the main water bearing aquifers in the study area. Accordingly, the intermountain areas i.e. sentera and Yewula plains are groundwater potential zones for groundwater exploitation and development. The occurrence of groundwater in the catchment is controlled by the structural and geomorphological setting of volcanic rocks and their associated sediment. Fractured and moderately weathered volcanic rocks interlayered with clay sediments are suitable for groundwater storage. The main recharge source of the area is precipitation and areal depth of precipitation is 1606.6mm/year. The Recharge rate estimated from soil water balance and base flow separation methods are 126.4 mm/year and 147.6 mm/year respectively. From physicochemical analyses of water sample, the dominant water type is Ca-Mg-HCO3 with low TDS value in highland areas (recharge zone) and the water type at a discharge area are Ca-Na-Mg-HCO3 with relative high TDS value compared with the recharge area. Piper Schoeller and pie diagrams have been used to understand the hadrochemical facies. Most of the water samples quality result shows the area is suitable for domestic and irrigation purpose.Item Hydrogeological Assessment on Upper Mille River Catchment(Addis Ababa University, 2020-09-09) Dessalegn, Eden; Azagegn, Tilahun (PhD)The study aims to elaborate and give some detailed picture of the Hydrogeological features of the study area. Mainly by characterization the aquifer, recharge mechanism, groundwater flow conditions and hydrochemistry of the groundwater. The basin is part of the western escarpment of Afar rift and measures about 1367 km². The mean annual precipitation as calculated by Thiession polygon method is found to be 1157. 6mm. The amount of recharge that is contributed to the subsurface as calculated by using Base flow separation, chloride mass balance and SWAT modelling gives a value of 135.9 mm, 115.66 mm and 140.48 mm (after calibration) and 138.5 (after validation) respectively. To describe the aquifer system of the area pumping test data, well completion reports, well logs and geology of the area were analysed. The study area is characterized by deep groundwater systems on average 214 m (depth of the wells) and groundwater reserve of the graben is estimated 3670.24 MCM. Hydraulic characteristics are spatially variable, in the area transmissivity of the valley ranges from 2.4–1580 m²/d.Its hydraulic conductivity ranges from 0.06 –18.1m/d. The Quaternary unconsolidated sediments are the main aquifer units in the area. The general trend for groundwater flow from pieziometric heads is generally from west to east. Piper plots were used to classify the water chemistry of the area. Groundwater type of the area generally evolved from Ca-Mg-HCO3 or Mg-Ca-HCO3 water type in the area closer to western escarpment to Na-Ca-HCO3 water type in the eastern part of the area. The water is also suitable for drinking purpose based on the standards.Item Hydrogeology and Major Ion Hydro-Geo-Chemistry of Borkena River Catchment Awash Basin Amhara Regional State South Wollo Ethiopia(Addis Ababa University, 2021-06-29) Tsegaye, Rigbe; Azagegn, Tilahun (PhD)The study was conducted at Borkena River Catchment 1192km2, in Amhara regional state, south wolo zone, encompasses Dessie, Kombolcha, Harbu and Kemisse towns to characterize the hydrogeology of the catchment by giving particular emphasis to major ion hydrogeochemistry. Data has been analyzed using GIS and remote sensing, Aquachem and Strater softwares. The results indicate that, the highland receives more precipitation than the lowland, the highest rainfall which is 1573.6 mm recorded at 2428m elevation in western part in Albuko station and the lowest rainfall which is 1013.3 recorded in Cheffa station at 1400m elevation. Areal depth of precipitation of the area was estimated by using Arthemetic, Thiesson and Isoheytal methods. All the three methods provide nearly closer value. The analysis result of three methods is used as the annual average rain fall of the study area. Potential evapotranspiration (PET) of the area was estimated using Thornthwaite method. The estimated value of PET is 1462.6mm. Wetspass modeling and baseflow separation was used to estimate recharge. The average annual long term groundwater recharge is estimated using wetspass as 145.95mm of which 110.63mm occurs during wet and 35.329 mm occurs during dry seasons. About75.7% of the annual groundwater recharge of the watershed occurs during the wet season (summer), and the remaining 24.3 % in dry season (winter). The annual average precipitation (1190.1 mm) is distributed as 49% Evaporation, 43.3 %runoff, and 12.26 % recharge. The alluvial deposits in the central part are the major aquifers of the area. The general ground water flow direction is from the northwestern part to southeaster part. The geology, recharge estimation, hydrogeological system and hydrogeochemistry of the study area assessed using respective approaches. Based on test wells and previously drilled wells studied by ADSWE aquifer parameters and qualitative hydrogeological interpretation, the study area is characterized in to high, medium to high, medium, low and very low aquifer productivity. To characterize the aquifer system of the area pumping test data, well completion reports, well logs and geology of the area were analyzed. The pumping test analysis results indicate that the hydraulic conductivity of the area ranges from 0.2 – 20.2m/d and the mean and the transmissivity of the area ris greater than 500. Aquachem software has been employed to identify the different water types. Piper plots and Durov plot were used to classify the water chemistry and evolution of water type respectively. The dominant water type of the area is Ca-Mg-Hco3 .Waters of the area generally has Ca-Hco3 and Ca-Mg-Hco3 in the recharge area with Low TDS to Na-Ca-HCO3 discharge area with high TDS evolutionary trend this is due to the process of hydrolysis silicate mineralsItem Identification of Water Supply Sources Through Physico-Chemical and Environmental Stable Isotopes Characterization of Tap Waters in Addis Ababa(Addis Ababa University, 2021-06-27) Siraj, Abdulhafiz; Azagegn, Tilahun (PhD); Birhanu, Behailu (PhD)This research evaluates the physical characteristics, and the isotopic signature of tap water and the physicochemical characterization of groundwater and surface water to link water users of Addis Ababa city to their respective water supply sources. As a result of the increase in city water demand caused by increasing populations in recent years, many groundwater water supply points (pocket areas) in the city have been drilled and injected into the previous main water supply pipe lines in various areas, resulting in a complicated and unclear distribution of water supply sources. Isotopic signatures (δD, δ18O) and Electrical Conductivity (EC) of tap water samples collected from ten Addis Ababa sub-cities were used to map the spatial distribution of water supply sources. The isotopic signatures and EC measurements indicated Bole, Gulele, Addis Ketema, and Arada sub-cities heavily rely on the surface. Sub-cities such as Akaki, Nifas Silk Lafto, Lideta, Kirkos, and Yeka, on the other hand, rely heavily on groundwater. Kolfe Keraniyo, Yeka, and Kirkos sub-cities get a measurable amount of water from mixed sources (surface and groundwater). Spatial distribution of water supply sources mapped using stable isotope ratios of hydrogen and oxygen (δ2H and δ18O) and EC was overlaid on Addis Ababa city population distribution. The overlay map showed up to 1.9M people in the city depend on the surface water and nearly 1M people consume water abstracted from the groundwater sources. A noticeable number of the Addis Ababa city population (~800, 000) get water from both surface and groundwater supply sources. The results implied, about 50% of the Addis Ababa city population depends entirely on the surface water supply sources which are more sensitive to climate and demographic changes compared with the 25% depending on more climate-resilient groundwater supply sources. Given the current Addis Ababa city surface water supply production which only accounts the 40% of the total Addis Ababa city water supply, the dependence of a significant portion of the Addis Ababa city population may result in a continuous interruption of connectivity for part of the city which are highly dependent on the surface water supply sources. This study demonstrates applications of Physico-chemical and isotopic information to provide more sustainable and resilient urban water management perspectives which should be considered during the design and construction of water supply infrastructure.Item Lake-Groundwater Interaction and Isotope Mass Balance of Lake Ziway Integrated Approach(Addis Ababa University, 2020-09-09) Chande, Chaka; Azagegn, Tilahun (PhD)An integrated approaches based on the application of stable isotope of water (2H and 18O), radiogenic-isotope of Radon (222Rn) and piezometric evidences are employed in this research to determine the interaction between the lake water and the adjacent groundwater and to evaluate the water balance of the lake Ziway particularly for estimating the groundwater inflows and outflows of the lake. The result based on δ18O-isotope mass balance of the lake shows groundwater inflow accounts for about 4% of total inflow and groundwater outflow accounts for about 8% of total outflow. With respect to the lake and groundwater interaction, the analysis of isotopic compositions of groundwaters shows groundwaters located in the south and southwest of Lake Ziway have similar isotopic composition to that of the lake. This demonstrates the lake and groundwater interaction in that sector of the lake. In contrast groundwater located in the highlands and escarpments displays isotopic composition similar to the precipitation, portraying no hydrologic link between the lake and the subsurface waters in these sectors. Radon-222 concentrations in the lake varied spatially from less than 35.2 – 96.6 Bq/m3. Results from 222Rn measurements shows high concentration values of 96.6 Bq/m3 and 78.5 Bq/m3 at the northeast and southeast shores of the lake respectively demonstrating lacustrine groundwater discharges into the lake in that regions from local flow systems. The piezometric evidence is also in support of this observation. In the region between northeast and southeast groundwater level lies above the lake surface level and this indicates the groundwater flow to the lake. In the western and southern sectors of the lake the groundwater level lies below lake level and thus demonstrates groundwater flow direction to the south and southwest. Evidences from various methods clearly proved the presence of lake and groundwater hydraulic link in the south and southwest sectors indicating the lake recharges the groundwater. This work in particular demonstrates the importance of stable isotope of water in defining separately the groundwater flux components of the hydrologic budget of the lake and in determining the lake-groundwater interaction.Item One Layer Transient Groundwater Flow Modeling at Becho Plain(Addis Ababa University, 2019-05-03) Tadeg, Simegnew; Azagegn, Tilahun (PhD)The study focused on assessment of groundwater level responses and its spatial and temporal variability of the Becho plain using transient state flow following from steady state Modeling. Nowadays most of the water for domestic, irrigation and industrial within the study area is from the groundwater. Despite of this, the effect of abstraction with respect to recharge is not well assessed. The groundwater recharge of the study area is mainly from direct rainfall. WetSpass modeling and Base flow separation was employed to estimate the recharge of the study area. The groundwater recharge was estimated with WetSpass modeling and Base flow separation is 120 mm/year and 85.78 mm/year (10.65% &7.8% of the annual rainfall) respectively. The finite difference schematization of the modeled area was discretized into a uniform squared grid size 400m by 400m, comprising 265 rows and 226 columns. The transient model was simulated with MODFLW pm8 for a period of one year for one layer aquifer of 500 meter thickness. The initial aquifer parameters (hydraulic conductivity and initial hydraulic heads) were used from the steady state model. The model was calibrated with trial and error by adjusting hydraulic conductivity and groundwater recharge by comparing the observed and simulated values. In MODFLOW, average groundwater recharge was simulated 97.72 mm/year which is within the range of recharge estimated by WetSpass model and Base flow separation methods. The water budget of the transient model shows that the aquifer storage declines from 148mm/year to 59.8 mm/year. After abstraction of groundwater with 275376 m3day-1 for ten years, the groundwater declines with an average 90.87m.