Earth Sciences
Permanent URI for this collection
Browse
Recent Submissions
Item Mapping of Major Urban Green Spaces and Study the Accessibility Using Network Analysis in Addis Ababa City, Ethiopia(Addis Ababa University, 2023-06) Lidya Geletta; K. V. Suryabhagavan (PhD); Tibebu Kassawmar (PhD)Cities in developing countries are growing rapidly. As a result of uncontrolled urban expansion and population growth urban green spaces are deteriorating at an alarming rate. The aim of this study is to assess the status of major urban green spaces and to study their accessibility using GIS based network analysis approach. OBIA (Object Based Image Analysis) classification algorithm is used to map and assess LULC (land-use and land-cover) of the study area. Remote sensing indices such as NDVI (Normalized Difference Vegetation index) and NDBI (Normalized Difference Built-up Index) have also been used to depict the vegetation cover and urban expansion rate which has direct influence on the deterioration of UGSs (urban green spaces). The accessibility analysis was carried out to study the spatial distribution and availability of public recreational parks existing in Addis Ababa city. Three accessibility indicator standards are used. The result shows that the accessibility of public parks are inadequate and their distribution are uneven. The central part of city has a little denser park concentration whereas, the eastern and southern part of the study area doesn’t have park facility except the Kality Park located in Akaki sub-city. The network analysis was computed based on residential area coverage and population number enjoying the park facilities. In addition, the current demand of public parks required by the population were assessed. Very low accessibility of parks are recorded for 300 and 800 meter service areas. The 300 m service area serves only 6 % of A.A residential area. Whereas, the 800m SA serves 34 % of the city residential area. Moreover, the population residing in Addis Ababa that enjoys public parks is 7 % for 300 m and 35 % for 800 m service areas. The 300 meter service area refers to 4 minute walking distance whereas the 800m refers to 4 minute walking distance. Therefore, urban residents are forced to walk more than 10 minutes in-order to enjoy park facilities. In addition to the international standards, national accessibility indicators recommended by AACC, is also included in this research. The AACC recommends city parks to be accessed within 10km radius and Sub-city parks in 5km radius. The study finding shows that 70% of residential area access sub-city parks. Moreover, the recorded value of residential area served by city parks is 87 % for all existing sub-cities. In addition, this study demonstrates 72 % of A.A resident’s reside with 5 km radius service area. While the population enjoying 10 km SA of City Park is 80 percent.Item Managed Aquifer Recharge Suitability Mapping in the Akaki Catchment, Central Ethiopia(Addis Ababa University, 2022-12) Hebron Tadesse; Dessie Nedaw (PhD)Groundwater resources in Akaki catchment are under increasing stress due to excessive use and a variety of anthropogenic influences such as population growth, urbanization, and pollution. The intense pumping has caused the water table level to drop quickly. For groundwater resources to be utilized in a sustainable manner, artificial recharge techniques and effective management methods are essential. Managed Aquifer Recharge is an artificial method for replenishing subsurface aquifers utilizing excess surface water, treated wastewater, and stormwater. It could be used as a method to increase freshwater availability and prepare for climate change. Creating a MAR suitability map may be one of the steps to be taken to reach sustainable groundwater management. The present study used GIS multi-criteria decision analysis commonly known as GIS-MCDA method to identify suitable sites for implementing MAR. Utilizing a web-based application called INOWAS, the available MAR techniques are summarized based on the hydrogeologic parameter and the study area's objectives. To create the MAR suitability map, seven contributing factors were employed as criteria: drainage density, land use, slope, soil, geology, water level and rainfall. They were selected based on the objective and the available data. Three steps are performed in order to identify suitable sites for MAR: problem definition, suitability mapping, and sensitivity analysis. Among different criterions, step-wise function was used for standardization, pairwise comparison was used for criterion weighing as well as weighted overlay analysis was used as decision rules. The suitability map divided the study area into highly suitable, suitable, moderately suitable, low suitability, and unsuitable classes. The results show that 71.54% of the area is moderately suitable for implementing MAR. The suitable areas locate in the northern part of the catchment. The majority of areas are moderately suitable and are scattered throughout the watershed. The areas with low suitability are mainly in southern parts of the area. The first MAR suitability map for the Akaki watershed can be used as a guide and screening tool to target site-specific research for MAR implementation in highly suitable regions.Item Crustal Structure of the Northeast African Rift System from Receiver Function Analysis(Addis Ababa University, 2023-05-16) Birhanu Abera; Atalay Ayele (Professor)This study examines the crustal structure in different regions, including Afar, Northwest (NW) plateau, Southeast (SE) plateau, Northern Main Ethiopian Rift (NMER), and Central Main Ethiopian Rift (CMER). High-quality teleseismic data (Mb > 6.0) with epicentral distances of 30◦ to 90◦ were analysed. The data were collected between 2000 and 2013 from 27 temporary broadband stations in Ethiopia and Eritrea, and between February 2015 and October 2016 from 17 stations of the RiftVolc broadband network. The study reveals consistent seismic velocity in the Afar crust, except in magmatic segments. These segments have a shallow layer with fast Vs (4.5 km/s) at depths of 6-14 km. Below this layer, Vs decreases (< 3.2 km/s), and the Vp/Vs ratio increases (2.0) at lower crustal depths (20-25 km). This suggests partial melting beneath the lower crust, particularly in the western Afar region and magmatic segments. The NW Plateau exhibits fast Vs (4-4.7 km/s) in its crust, with some regions showing slow Vs (3.2 km/s) and high Vp/Vs (1.85-2.0) at mid-crustal depths (10-25 km). Partial melt is observed in specific mid-crustal areas, possibly due to the extension of the plateau or melt migration from the rift. The uppermost crust (depth <6 km) in the NMER and CMER has slow Vs due to sedimentary and/or volcanic layers. Crustal Vs exhibits lateral and depth variations. Slow Vs (∼2-3 km/s) is observed beneath volcanic centres in the upper-mid crust, while the lower crust consistently shows slow Vs (Vs < 3.5 km/s). The slow lower crust is associated with high Vp/Vs ratios (1.9-2.0). A low Vs and a small fraction (< 5%) of high Vp/Vs material in the rift system indicate possible partial melt, which is widespread in the rift valley as segmented and localized features. These findings suggest that partial melt in the lower crust beneath active magmatic rifts is more significant than previously thought. The presence of a substantial melt reservoir in the lower crust highlights the role of magmatism in crustal extension and its influence on the evolution of the rift system. In contrast, the Eastern Plateau exhibits uniform and faster Vs, with a distinct velocity contrast between the crust and upper mantle, indicating less deformation compared to the central rift zone. The estimated Moho depth in Afar ranges from 26-30 km, showing a gradual transition compared to other areas studied. Furthermore, the NW Plateau has a Moho depth ranging from 36-44 km, while the SE Plateau has a depth ranging from 36-42 km. These findings have implications for understanding continental rifting mechanisms, magmatic system formation, and long-term lithospheric evolution.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 GIS and Remote Sensing in Land Use/ Land cover Change Detection in Finchaa Valley Area, East Wollega(Addis Ababa University, 2005-06) Kebebew, Zeleleke; Korme, Tesfaye (PhD)This study assessed land use! land cover change of Finchao valley area by integrating GIS and Remote sensing rechniques in Finchaa valley area in belll'een 1973 and 2003, The stud,' comparedfollr different techniques: image differencing, rationing NDV! image comparisons and posl classification Comparisons, Image differencing and rationing proved not suitable fiJr Ihe slwl\' area, SDVI isfollnd belter for visual comparisons with its mean \'{Ilues, Posl classification comparison is proved the best melhodfor Ihe stlldv area, The res lilt of Ihe analysis indicates thai generally \'egetalion cove is decreasing a/lribule ta increase in crop land with accelerated rate of change, Ihe de\'elopment of mechanized slate farm in heMeen 197_' and 1986 and agroindusrial development since! 991 at accelerated rate of change "'ilh ils re 'ated inji'astruclures bUI collapse of slale f arm in the valley. The change is directly related to socia-economic activities, fire and poor elIvironl11enlalll1anagell1ent and inseparably connect"d to one ana/her, From observational the change has negative implications on the environments particularly all land, vegetation and animal diversities, Therefore the ill environmental management strategy should be re evaluated fO pro/eel 10 protect vegetation e'er and to keep the development sustainable,Item Evaluation of Land Degradation and Landsude Using Integrated Remote Sensing and Gis Approach Around Wolayita Sodo-Shone Area, Southern Ethiopia(Addis Ababa University, 2005-06) Teferi, Yodit; Korme, Tesfaye (PhD)In this study two major environmental hazards, namely land degradation and landslide have been investigated. These hazards have clear dynamic relationships given that both are chaotic phenomena that can be trigg~le e9..uilibrium situation occurring drastically and abruptly to the enVironment. ,. Southern Nation's National Peoples Region is one of the most populated regions in the country. The area is situated in the western margin of the Ethiopian Main Rift system and it is structurally controlled and tectonically active. Therefore, the study area is an excellent site where natural and human induced or anthropogenic factors work jointly to result in such a staggering environmental damage. Generally, it is a place where most favorable factors of land degradation and landslide coincide in space. An integrated GIS and remote sensing approach was very helpful to study the intensity and extent of the two environmental hazards. The degradation rate that was calculated in areal base using cross classification of temporal data shows the degradation rate is becoming severe with time. The degradation rate that was 1.8 sq. km/year between 1984 and 1995 has increased in to 3.1 sq. km/year in recent times (till 2001). These figures show that the rate of degradation is increasing at an alarming rate. The amount of soil lost from the study area is estimated using cut and fill technique applied on 5 representative sites. Profiling was done using GPS reading taken at every 5-10m interval and organized in a database. The volume loss calculated shows that 2,485,818 mS amount of soil is lost from 291,241 m'area; with the net lose per area being about 8.53 m~. ~i1 Factors that are found to be significant in triggering the Land degradation in the study area include structure, lithology, landusc/ landcover, slope, soil, drainage, and climate. Similarly these factors with addition of slope aspect play an important roll in aggravating the frequently occurring landslide. The presence of all the factors that are responsible for the staggering environmental hazard and their coincidence in space and time indicate that the area is highly prone to these hazards. Factors that are considered to be responsible for the two environmental hazards were weighted in hierarchical order using the MCE approach to produce susceptibility maps that express the likelihood occurrences of the hazards in the area on the bases of the local terrain condition.Item Application of Remote Sensing and GIS for Geological Investigation and Groundwater Potential Zone Identification, Southeastern Ethiopian Plateau, Bale Mountains and the Surrounding Areas(Addis Ababa University, 2005-07) Rango, Tewodros; Ayalew, Dereje (PhD)The application of remote sensing and GIS has found to be a quick and inexpensive technique in order to obtain the desired output efficiently. For the present study an attempt was made to map dykes, lithology and other thematic maps such as of drainage density, slope, elevation, lineament, rainfall, landcover and burrowing of rodents and then to integrate them in a GIS environment to get information about the occurrence of groundwater and used to select promising areas for further groundwater exploration. The present study was conducted on southeastern part of Ethiopia plateau, the Bale Mountains and the surrounding areas. Satellite image of Landsat ETM+ of all bands except the thermal bands were utilized for lithologic and geologic structures mapping. Topographic map at the scale of 1 :50,000 were used to generate elevation contour at the interval of 20m. Slope map were derived from TIN (Triangulated Irregular Network), which is derived from elevation contour map. Spatial distribution of drainage density was derived by using three softwares AutoCAD map 2000 engineering software, Arcview3 .2 and MapInfo professional 6.0. The burrowing of Rodents were mapped from field Knowledge and using 742(RGB) that shows areas of rodent burrowing activities. Secondary data of landcover, soi l were also utilized. Groundwater potentiality in the area has been assessed through the integration of the different thematic layers that contributes for the natural recharging of aquifer. The predicted groundwater potential zones were divided into 5 classes from very good up to poor. Color composite, ratio and PCA (Principal Component analysis) were made to interpret the lithology of the area. Due to vegetation cover and similarities of reflectance of different rock units it was difficult to separate them. The field knowledge and some petrographic analysis support the identification of the lithology. Key words: dykes, lithology, groundwater potential zone prediction, Remote Sensing and GISItem Assessments of Seasonal Variability of Land Surface Temperature Using Multi-Resolution Satellite Data of the Year 2021 In Case of Tana Sub Basin North West Ethiopia(Addis Ababa University, 2022-02-05) Addis, Yitayih; Kassawmar, Tibebu (PhD)Quantifying Land Surface Temperature (LST) has a great role for biophysical and landscape monitoring like that of hydrology, urban management and environment. LST is a fundamental physical property relevant to many hydrological and atmospheric processes. The objective of this study is to assess the Spatial inter-seasonal variability of LST using Multi-resolution satellite Data of dry and wet (rainy) season of the year 2021 in the case of Tana Sub Basin, North West Ethiopia. Split Window Algorithm (SW) was used to retrieve LST, Mann-Kendall trend test for inter season trend analysis and the Pearson correlation coefficient (r) for correlation analysis. In this study, LST from three satellite images was retrieved and downloaded to see the Spatial and inter-seasonal LST variation. The maximum LST was gained from Sentinel-3 in April with LST 51°C, whereas the minimum LST was 5°C from Landsat 8 during February of the dry season. Similarly, the maximum LST in wet (rainy) season was extracted from Landsat 8 in June with LST 42°C and the minimum was in Sentinel-3 in July with 8°C. Spatially the maximum LST was observed in the periphery of the study area. The minimum LST was observed in central parts of the study area, this is due to Lake Tana. The relationship between LST obtained from Landsat 8, MODIS, and Sentinel-3 and mean temperature shows strong values of r >= 0.5 in dry and wet (rainy) season, except July of Sentinel-3. The correlation result shows a better fit between temperature and LST results obtained from Landsat 8 followed by MODIS in dry season. Similarly, Landsat 8 has a better correlation followed by MODIS in wet (rainy). In general, LST retrieved from Landsat 8 thermal bands shows better than the other two. From Mann-Kendall trend test for both Landsat 8 and MODIS LST there was statistically insignificant increasing, whereas for Sentinel-3 no trend in dry season. While, in wet (rainy) season the Mann-Kendall trend tests for both Landsat 8 and MODIS LST, there was a statistically insignificant decreasing trend. In contrast Sentinel-3 mean LST revealed statistically insignificant decreasing trend. The study result showed that, satellite based LST retrieval is time and cost effective. Therefore, it is recommended to be used with caution.Item Water Pollution/Quality Assessment in Relation to Wet Coffee Processing Plants in Surface and Shallow Groundwater in Sidama and Gedeo Zones (SNNPR)(Addis Ababa University, 2005-06) Gobena, Mesfin; Alemayehu, Tamiru (PhD)The study area located in Southern Nation and Nationality People Region (SNNPR) and encompass Sidama & Gedeo Zones that are among all the coffee growing region of Ethiopia, bounded between 37° 54'N to 39°8 N latitude and 5° 52'E to 7° 13'E longitude in which most part of it situated in the rift valley lakes basin and the remaining part in Genale Dawa basin . The study area has different land form characteristics varied from High Mountain up to low lands: its altitude varies from the highest peak (3000m) up to lowlands (1100 m) High water usage, channeling residual water and the pulp together, in efficiency of the traditional waste disposal pits, absence of monitoring and lack of sustainable wet coffee production strategy and policy are some of the factors that aggravate the impact of the processing plants on the poll ution of water bodies were di scussed in problem identification and analysis. Measured values of physical parameters such as turbidity and pH are out of the range of WHO guideline values and standards. From the Physical observation itself during coffee processing periods rivers and streams have objectionable color odor and taste so that the waters have evil or pungent small and test. TDS and EC values of rivers and streams in particular spring and boreholes in general shows that the water is fresh. Based on the measured value of the total hardness in terms of CaC03 the surface and groundwaters of the study area classified as moderately hard. The limited water chemical analysis fi'om previous representative sources indicated that the river and ground waters are Na HC03 type of water, the dominant cation being Na and anion bicarbonate. The highest value BOD and COD in river water is 8750 and 3120mg/1 that have a potential for decreasing greatly the level of dissolved oxygen in the rivers that reduces the diversity of aquatic life. The maximum COD value of the effiuent obtained from this analysis (24,600mg/l) is 98 times higher than the EPA standard fro effiuent discharges to inland waters. The highest BOD value was 39 times higher than the EPA standard. The bad, evil and pungent smell that can be sensed along the river courses during coffee processing periods were explained by the concentration of Ammonia (NH3) that was ranged from 1.48to 90mg/1 and was much higher than the recommended limits. The highest nitrite (N02-) concentration was 60mg/1 in Melkadimtu Rivers. From the total analyzed samples about 50% of them had their values were nearly I mg/I, which are far higher than levels in unpolluted waters (0.03mg/I). Rural communities that use river water as their source of water supply may expose to carcinogenic effect due to this level of nitrite. Coffee pulp, which is one of the bypro ducts of coffee processing, have some economical applications that may become evident as their use is increased. Compost and fertilization, Pulp beverage, animal feed, fuel wood substitutes are some of the suggested measures to be taken to mitigate the effects.Item Seismic Vulnerability Analysis of Major Ethiopian Dams with Emphasis on Dam Safety Evaluation(Addis Ababa University, 2020-02-01) Aman, Ali; Mammo, Tilahun (Professor)Dams are critical facilities, which require special consideration to ensure their longterm safety. Among the safety concerns for large storage dams, seismic safety plays an important role, particularly for dams located close to the seismically active regions like the East African Rift System. Large dams in such seismically active regions must be capable of resisting severe earthquake ground motion expected at the dam site without uncontrolled release of water impounded in the reservoir. This can be achieved by conducting a comprehensive site-specific seismic hazard analysis, proper seismic design, adequate construction quality control, and appropriate operation and timely maintenance for upgrading any seismic deficiency, particularly for older dams. The main factor contributing to the risk of large storage dams is the water stored in the reservoir. Some of the reservoirs in Ethiopia are very large. In this dissertation, the seismic safety evaluation of large Ethiopian dams is analysed, which includes the review of previous works, site-specific seismic hazard evaluations, seismic risk analysis and detailed seismic safety analysis. A review of the seismic design criteria used for large dams in Ethiopia shows that different criteria were considered and, in some cases, the poorly known seismic activity in the project region was ignored. In some dams, modern design and safety criteria were used whereas in other projects out-dated seismic design guidelines and codes were employed. As a result, the existing, under construction and planned dams require detailed seismic safety reviews to comply with modern seismic safety criteria. The dam sites are located in variable geological and tectonic settings, which are responsible for the spatial variability of the seismicity at dam sites. The main tectonic structure in Ethiopia is the Main Ethiopian Rift (MER), which is characterized by its extensional tectonic nature, seismically active faults and major fractures that affect the safety of dams and may cause water losses from the reservoirs. This requires an extensive geological investigation beyond the footprint of the dam. For the seismic hazard study, the seismogenic source zones were modelled by integrating the information developed from the regional geology, tectonics, seismic energy release map, and observed seismicity. The seismic hazard analyses were conducted based on the probabilistic approach and a seismic hazard map is developed for the horizontal component of the peak ground acceleration (PGA) for a return period of 10,000 years. Six seismic zones are delineated in this map. In addition, for the different seismic zones, an estimation of the future power and irrigation potential of Ethiopia is made. Moreover, the dam sites are ranked according to the PGA-values for return periods of 10,000 years. These results are used as input for the seismic risk analysis. The seismic risk of 30 large Ethiopian dams was evaluated. In the risk analyses, the levels of seismic hazard for which the dam is exposed, the vulnerability of the dam, and the consequences in the case of uncontrolled release of water from the reservoir were considered. Based on the risk analysis results, the following five dams Gibe GERD Saddle dam, Gidabo, Tendaho, and Tekeze dams were selected for detailed site-specific hazard evaluation and seismic safety analysis. In the site-specific seismic hazard analyses, multiple earthquake effects were taken into account. For the nonlinear stress, deformation and stability analyses acceleration time histories were used, which match the acceleration response spectra obtained from the seismic hazard analysis. Gibe III dam is an RCC gravity dam with a height of 243 m. It is the world's highest RCC dam. The dam site is located at the border of the seismically active MER. Seismic stability analyses are carried out to check the response of the dam for the updated ground motion parameters of the safety evaluation earthquake (SEE). The static and dynamic analyses are performed using a two-dimensional (2D) plane stress finite element model of the highest cross-section of the dam. First, a linear-elastic dynamic analysis is carried out followed by the dynamic sliding stability analysis of different detached concrete blocks. The foundation rock is assumed massless, which implies that only the kinematic interaction effects are considered. The hydrodynamic pressure acting on the upstream face of the dam was represented by an added mass according to Westergard, assuming incompressible water in the infinite reservoir. The spectrum-matched acceleration time histories are used as input in the dynamic analysis. All dynamic analyses are done by direct time integration of the equations of motion. Grand Ethiopian Renaissance Dam (GERD) is the largest hydropower station currently under construction in Africa. The main dam is a 145 m high roller compacted concrete (RCC) gravity dam. It will create a reservoir with a volume of about 74 km3. Besides the RCC dam, there is a 5.2 km long saddle dam with a maximum height of 65 m and a volume of 17 Mm3. It is one of the longest concretefaced rockfill dams (CFRD) in Africa. The seismicity in the project area is assumed to be low. However, the information on historical seismicity is scarce in the region. Because of the size and importance of the GERD project, the seismic stability of the saddle dam is checked for the ground motion with a return period of 30,000 years. The dynamic analysis of the saddle dam is carried out by the equivalent linear method using a 2D dam model of the highest cross-section. The results show that the dam is safe under the worst-case earthquake loading and the crest settlement is insignificant compared to the available freeboard. Gidabo dam is a central core earth-fill dam with a height of 27 m. The project includes an intake tower supported by a pile foundation in the upstream part of the dam, which is connected with a diversion conduit laid on a weak compressible foundation passing through the dam body. During dam construction (2016), the conduit that was laid on the soil foundation settled, creating a vertical offset of more than 50 cm at the joint between the pile-supported intake tower and the conduit due to the static loads from dam construction. Moreover, the dam site is located in the seismically active MER with several destructive earthquakes recorded in the past. The seismic stability analysis was conducted to determine the maximum deformation of the dam and settlement of the conduit when it is subjected to the SEE ground motion with 10,000 years return period. The total settlement estimated during SEE is tolerable. The dam is safe against overtopping, as sufficient freeboard is provided. However, cracking of the clay core along the conduit due to differential settlement may lead to internal erosion. Moreover, the offset of the conduit will increase and the conduit may not be adequate for lowering of the reservoir after the SEE. vi Tendaho dam is one of the largest irrigation dams located in a region of high seismicity in Ethiopia. Movements along tectonic faults and other discontinuities in the footprint of the dam that can be activated by strong earthquakes close to the dam are expected to be the worst-case seismic effects for the dam. The present study aimed to check the seismic safety of the dam when it is subjected to both ground shaking and tectonic fault movements. The dynamic analyses were carried out by a 2D model of the highest cross-section using the equivalent linear analysis method. The results of the dynamic analyses show that the maximum loss of freeboard is 1.89 m due to slope movement, seismic densification of the embankment and fault displacement in the footprint of the dam that can be accommodated by the available freeboard of 3 m. Seepage along the fault in the dam foundation due to damage of the grout curtain and erosion along the dam-abutment contact due to seepage are possible. The 188 m high Tekeze dam is the highest arch dam in Africa. The project area is characterized by undulating topography with steep slopes and deep valley, which is different from the other dam sites. Therefore, mass movements into the reservoir that generate impulse waves are possible during strong earthquakes. The seismic stability of the critical slopes is checked for the horizontal component SEE ground motion with a conventional pseudo-static procedure. The landslide is modelled as a solid mass and three-dimensional (3D) free radial propagation of the impulse wave was considered for estimating the wave generation and wave propagation parameters. The parameters controlling the impulse waves on dams were computed and the size of resulting impulse waves in the reservoir was determined. The maximum wave run-up and the possibility of dam overtopping were estimated. The results show that the maximum wave run-up under worst earthquake action can be accommodated by the freeboard allowance of 5 m adopted in the design. As a result, there is no overtopping risk expected from landslides generated impulse waves. However, the overall result of the present study highlights the importance of reviewing the seismic safety of the dam for the increased level of earthquake ground motion.Item Land Suitability and Crop Suitability Analysis Using Remote Sensing and Gis Application. A Case Study in Legambo Woreda(Addis Ababa University, 2010-06) Mulugeta, Henok; Legesse, Dagnachew ( (PhD)The present study was carried out to evaluate the suitability of the land for agri cultural crop prodUction by using Remote Sensing and GIS application The evaluation of land in terms of suitability classes was based on the method described in FAO guidel ine for land evaluation. The factors that were considered for evaluation of the land suitability for crop production were slope, soil drainage, soil texture , soil depth, soil type and the present land use of the study area. Multi-criteria decision evaluation method was used to evaluate the physical land characte ristics of the study area for crop production. The techniques, which were used to weigh and standardized the factors were pair-wise comparison and weighted linear combination . After evaluating the physical land suitability for agricultural crop, land suitability map was developed. This map was classified in to five suitabi lity classes based on FAO guidelines. From the total land of the study area 100 km2 (9 .2%) was very suitable, 257 km2 (236%) was-suitable, 293 km2 (269%) was marginally suitable, 390 km2 (358%) was not suitable and 49 km2 (4 .5%) was permanently unsuitable for agriculture. The land in the study area was also evaluated for suitability of wheat and maize production. In addition to the factors mentioned above, temperature and rainfall of the study area were used for crop suitability evaluation. Suitability maps for both wheat and maize were developed. The crops suitability maps were classified in to five suitability classes. The result shows that 82 km2 (7.5%) was very suitable, 249 km2 (23%) was suitable, 483 km2 (444%) was marginally suitable, 240 km2 (22%) was not suitable and 35 km2 (31 %) was permanently unsuitable for wheat production. Regarding suitability of maize 92 km2 (8.5%) was very suitable, 299 km2 (274 %) was suitable, 321 km2 (294%) was marginally suitable, 262 km2 (242%) was not suitable and 1-14 km2 (105%) was permanently unsuitable. The evaluation of physical land qualities of the study area indicates that the study area has a potential for agricultural crops. Keywords Land suitability; Crop suitability; MCDM; Pair-wise comparisonItem Soil Erosion Modeling Using Remote Sensing and Geographic Information System: A Case Study of Awassa Area.(Addis Ababa University, 2005-07) Hagos, Hamelmal; Korme, Tesfuye (PhD)Land degradation has been a major global issue because of its adverse impact on agronomic productivity, the environment, and its effect on food security and the quality of life. Soil erosion is the major form of land degradation in Ethiopia. This study is done in Awassa Catchment, which is the central part of the Main Ethiopian Rift. Assessment of soil erosion rate in the study area is done using the statistical and relatively simple soil erosion model that is USLE. All factors used in USLE were derived independently, while in reality the factors interact in a dynamic system and several assumptions have to be made to adapt the model to a given set of conditions. Based on the analysis of the data, 97.51 % of the study area is characterized by low to moderate soil erosion rate (0-10.09 t/ha/yr) and 2.49% of the study area is characterized by high to extremely high soil erosion rate (10.09-20\ .79 t/ha/yr). Out of 97.51% of the study area that is characterized by low to moderate soil erosion rate, 88 .05% of it is associated with slope gradient factor less than one. 49.32% of areas with erosion rate greater than I 0.09t/ha/yr (30.92 km2 ) are associated with slope gradient factor greater than or equal to one. And 6.37% (1.97 km2 ) of those areas with erosion rate greater than 10.09t/ha/yr (30.92 km2 ) are related to slope length greater than or equal to 4.5. And areas with high to extremely high erosion rates are associated either higher slope grad ient factor or with degraded bare land and grassland and shrub land cover. Out of the whole catchment, 30.24 km2 lies under high to extremely high soil erosion rate and this requires immediate . conservation measures like planting trees which can hold the soil intact. According to the rates of soil tolerance limits that are developed for tropical soils (0.2 and 11 t/ha/yr), 97.51% of the study area is under tolerable soil erosion rate. But one thing to remember is that the USLE measures only rill and interrill erosion therefore the overall soil erosion rate especially in the Muleti area where ground cracks are observed could be much higher than the predicted by the USLE. Thus, estimation of soil loss from the ground cracks in Muleti area should assessed by other models. Therefore the analysis of high-resolution remote sensing data combined with furth er spatial information in a GIS environment provides an integrated and cheap tool for resource management within the scope of sustainable development.Item Landuse/Cover Dynamics and Selection of Suitable Site for Water Harvesting Structure: The Case of Ziquala Watershed, Wag Himra Zone(Addis Ababa University, 2010-06) Mohammed, Habtamu; Ayenew, Tenalem (Prof.)The study area Ziquala Watershed located at a distance of about 760 km from the capital Addis Ababa city covers an area of about 759 km' . It is one of the drought p;one areas in the country. It is found in drought prone areas of the Wag Himra Zone. The area is charocterized by scarcity of water even during the rainy seasons. Agriculture predominantly animal rearing is the main stay of the area. Water harvesting structures are extremely important to conserve precious natural resource like, soil and water, which is depleting day by day at on alarming rate. GIS offers a powerful tool for mapping potential sites for rainfall harvesting. Selection of suitable sites for artificial recharge and water harvesting structures needs a large volume of multidisciplinary data from various sources. Remote sensing is of immense use for natural resources mapping and generating necessary spatial database required as input for GIS analysis. The most affecting factors on mapping the poten tial sites: landuse, soil, geological formation, drainage density and slope respectively. The main objective of this study is to evaluate the landuse/cover change and select and mop suitable sites for different water harvesting structures tor Ziquala watershed. Landuse/cover was prepared using supervised classification of Landsat imageries of three different years. Post classification analysis was used to reveal the change in landuse/cover during the study periods. During 1988-1999 period more change occur on bareland decreasing by -32.63% and bush land/shrub land increasing by 28.53%. The water harvesting structures considered for this study area are check dam, farm pond, semi-circular bund and contour bund. Multi-criteria evaluation (MCE) method was used to identify suitable sites for WHSs. Weight was given based on their relative importance for individual WHS. Check dam with 48.33% has higher coverage fallowed by contour bund, semi-circular bund and farm pond having 2.8%, 1% and 1% coverage respectively. The remote sensing and GIS technique proved to be effective for generating thematic layers, facilitating, analysing and derivation of database management and results. Key word: GIS, Landuse/cover change, MCE, Remote sensing, suitability, Water harvestingItem A New Approach to Compact Gravity Inversion Algorithm(Addis Ababa University, 2021-06-28) Geletu, Mesay; Lewi, Elias (PhD)The gravity method is one of the geophysical methods that has been used in a wider range of geophysical prospecting and investigations. One of the indispensable steps in this method is the inverse modelling of the measured data to estimate the subsurface density distribution and geometrical properties (e.g. shape and depth) of the causative bodies. Particularly, delineating localized and blocky geologic features, through the inversion of gravity data is an important goal in a range of geophysica l investigations and it is still a subject of interest and concern in the scientific communit y. Most conventional inversion algorithms generally yield smooth models with poor edge definition. These methods have difficulties in recovering non-smooth distributions that have sharp boundaries. The main objective of this thesis was then to develop and implement a gravity inversion algorithm that can produce compact and sharp images, aiming at recovering localized and blocky geologic features with varying geometric representations. In the course of the thesis work, this goal has been achieved by presenting a gravimetric inverse modelling method that has been tested to be effective. At the heart of the developed inversion method lies the usage of the 𝐿0-norm minimization of the objective function, which consists of data misfit and L0-norm stabilizing function, by an efficient iteratively reweighted least-squares (IRLS) algorithm. As a major contribution, the presented method incorporates three novel technical advancements. At first, the method incorporates an auto-adaptive regularization technique, which automatically determines a suitable regulariza t ion parameter, and a modified error weighting function that helps to improve both the stability and convergence of the method. The other advantage of the auto-adaptive regularization technique and error weighting matrix is that they are not wholly dependent on the known noise level. Because of that, the method can yield reasonable results even when the noise level of the data is not properly known. The other major contribution is the use of a new depth weighting function. The advantages of the newly proposed depth-weighting function can be summarized as follows: (I) It properly counteracts the gravity kernel decay, so that the inversion results can provide realistic depth information. (II) It avoids the selection of the depth weighting function parameters through trial and error, which was common in the traditional methods, through the usage of automated parameters selection techniques. Especially, this has a significant advantage when there is no prior depth informa t ion that helps to choose the optimum parameter in using the traditional depth weighting function. Furthermore, to achieve geologically plausible results and also reduce solution ambiguity, a physical parameter inequality constraint algorithm has been developed and employed to constrain the obtained density contrast values. Finally, the implementation of an effectively combined stopping criterion has been used to terminate the iterative inversion procedure, when geologically viable solutions are obtained. The proposed combined termination criteria are shown to outperform traditional termination criteria, used in most iterative geophysical invers ion algorithms, through the modeling of synthetic and published measured data To test the new method, forward and inverse modeling codes were written using Python programming in a Linux environment. The validity of the overall Python codes, and the practicality and efficiency of the presented inversion method were tested by inverting a number of synthetic data sets from geometrically complex bodies and field data sets from different geological settings. The results of the inversion confirmed the capability of the developed inversion method in producing geologically acceptable compact and sharp models that define the shape, location, and density distribution of the causative subsurface bodies. This proves, the reliability and effectiveness of the developed inversion method in practical applications to delineate sharp discontinuit ies and blocky features such as distinct layering or formation of localized bodies in the subsurface.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 Investigations of Landslide Problem Using Geophysical Techniques around Debresina-Armanja Main Road in Tarmaber Woreda, Northern Shewa Zone, Ethiopia(Addis Ababa University, 2013-06) Gebreanenia, Gebreselassie; Haile, Tigstu (PhD)Geophys ical and geo logical in vesti gat ions have been conducted 1'01' land slide problcm characteri zation of the exist ing main road of the study area. The s ite is located in betlle~n Debres ina and Armaniya towns. Tarmaber Wereda. north ern Sheila Zone of Amhara Regiolllce of the problematic main asphalt road. identi fy tri ggering mechani sms of land slide problem. and recommend possible mitigation measures based on the geo-elect ri cal res isti vity stratil·ication of the site and magnetic anomalies obta ined over the survey area. Geophysical investigations using 2D electrical imaging and magnetic methods havc been conducted Il)r the land slide problem of the road located HI kebdc' Dokakitnear Sar Amba Kidan cm hir~tloe al it \ betlleenDebrL' Si na and l\rmania t""lh. 1- 1'0111 the resuhs or the survc). it has been possihk to map thl: ~ Iidillg ;-,tl b:-,u rl ~ ICl: or the g~ologiL' layers, their ve rti ca l and lateral extents. It has al so been poss ible to map areas 01· lIeaknc\S in the subsurlace that could be causing and damaging to the lile of the road. According t" the interpretation of the geophysical result s. the ncar stll·face geolog) of the study area includes fragmented and di sturbed la ye rs togcth er "ith expansive clay soils which have also conside rab l) cause of sliding problem over the area. In profile three the cia) so ils are mueh thicker than the oth er two profil es. In prolile three low res istiv ity deposits are dominant particularl) in the northeastern side of the survey area. These deposits are may be hugc deposits ol· the fragme nt al basalt and expansive clay so ils that arc moved down the slope and accllmulated in location " I' prolile three whic h is jll st do\Vn the road . Based on the joinl interpretation or the result s. the Slirve) ed area has possi ble slide lone II hich " characterized by Ij·agmented and structural I) disturbed po rt ion IIhicl! staib rrom "lnhlSt h,&"Cthe surveyed line to\Vards north cast direc tion . This is interpret ed to be the re'I)(>I"e 01· thL' "'lier saturated, lIeathercd and fractu red ba sa lt rocK . I·here is also l"nlbliLie "rkcted sllbsurillce tltal c.\hibib intermedi ate apparent re~istivit) \alue ~ l.'uillprise~ of thl' ~U Ulll\\t: ~t end or 1il(' ~lInc\l' d proli lcs. This zone consists orsurlitce orllcakncss and some displaced rock units. As conc ili sion I·j·om the work, the aspha lt road para ll el to the stll·ve) proliles has active slidillg problem and cracks espec ially at the two ends or the profi les. The clifterent weak zones. deeph IIcatheri ng cond ition s. ac tion of rain la lL springs and slope nature of th e stlld) arc" lIere the causi ng lactors l'or this sliding problem. Therel'ore. special alieni ion should be given to maintain and protect from further sliding problem.Item The Effect of Land Use Land Cover Change on Hydrologic Response of Wukro-Genfel Catchment, Tekeze Basin, Ethiopia(Addis Ababa University, 2010-06) Melaku, Fitsum; Legesse, Dagnachew ( (PhD)The environment of the northern Ethiopia highlands are seriously affected by land degradation, mainly caused by the combined effects of deforestation, overgrazing, expansion of cropland and unsustainable use of naturaJ resources. These have also a potential effect on the runoff, infiltration, sedimentation and other hydrologic parameters. The main objectives of the current study are to assess land use land cover change that occurred during 1986-2007 and its effect on the hydrologic response of Wukro-Genfel catchment, in Tekeze river basin. The widely used Soil Conservation Service - Curve Number (SCS-CN) method was integrated with Remote Sensing and Geographical Information Systems (GIS) techniques. The analysis revealed an overall decrement of woodland, scrub and grassland by 2.9%, 2.2% and 4.7% respectively and increment of farmland, shrub and bareland by 8.6%, 3.1% and 2.3% respectively over the past twenty one years (1986-2007). Considering Antecedent Moisture Condition (AMC) II which is moderate soil moisture condition and taking 36mm of rainfall event, there was a decrement of runoff depth by 37. 6% for shrub to woodland change, 6.1% for scrub to shrub change and 2.1% for scrub to farmland change with Hydrologic Soil Group (HSG) A, A and B respectively. On the other hand, there was an increment of runoff depth by 30.4% for woodland to farmland and by 3.7% for farmland to bareland with HSG B and C respectively. Out of the whole land uselcover classes, woodland plays significant role on runoff generation and its spatial distribution. Thus, Special attention should be given to sloppy river banks where high nmoff is generated. The total volumetric runoff was decreased on average by 17.6% during the period 1986-2000 mainly due to the increment of woodland. An average increment in the total volumetric runoff was also observed by 13.5% for the period 2000-2007 caused by the depletion of woodland in the area. Key Words: Land use land cover, Runoff, SCS-CN, Hydrologic Soil Group (HSG), Remote Sensing, GISItem 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 Geophysical Investigation of the Crustal Structure Beneath Metehara, Main Ethiopian Rift.(Addis Ababa University, 2010-06) Guta, Addisu; Mammo, Tilahun (PhD)Analysis of the gravity data, with the help of the seismic refraction results (G.D. Mackenzile, H .Thybo and P .K .H .Maguire 2005) and Euler deaconvolution results also produced to simplify the modeling process of the study region and it was done to study the crurtal thickness variation under the subsurface layers of Metehara. Which is located 39° 301 48.34011 to 40° 591 27.60011 E longitude and 8° 481 15.12011 to 9° 28141.26811 N latitude as shown in Fig. I. I.The Bouguer gravity anomaly which shows the area of study relatively higher value with a strongly denser contour at the lower comer of S-E of the anomaly map. The Gravity modeling constrained with seismic refraction and Euler deconvelutivn result, indicates a crurtal thickness of about 34.8 and 36.6km under selected profiles AB and MN respectively. The model also shows two highest dense bodies as mafic intrusions over profile AB.Item Characterization of Embankment Material with Special Consideration to Clay Core a Case Study for Kalid Dijo Dam in Southern Ethiopia(Addis Ababa University, 2021-09-10) Tafa, Yosef; Hailemariam, Trufat (PhD)The research is assessing the quality of construction material of the Kalid-Dijo irrigation dam, located in Southern part of Ethiopia, Silte Zone. It is a zoned rockfill embankment dam designed using multi criteria analysis, to tolerable the high probable seismicity that involves quality clay material for its central core. However, the project investigation reveals that the available borrow sites do not fully satisfy the prerequisite for core material. Thus, this research aims to characterize further the locally available clay core material and attempts to forward experiment-based alternatives to meet the required quality for core material of the designed zoned rockfill embankment dam. The previous studies identified MH core clay materials using USCS near to the dam axis; while in this investigation, the same borrow site classified as CH, to have high compressibility, low dry density, low shear strength, high swell potential and high volumetric shrinkage. It fails to satisfy the general design specification criteria and limits for impervious material. In this research, blending experiments using different ratios are conducted using the available gravelly material to that of the clay from selected borrow sites. Different tests including classification, proctor compaction, consolidation, free swell, volumetric shrinkage, direct shear, dispersion and permeability tests were conducted on the blended ratios to check the improvement on the clay core material. And it is found out that the required improvement was achieved with 50G:50C mix proportions. Based on results, the blended GC material (50G/50C) has an average of 1.6 maximum dry density (MDD), 24% optimum water content (OMC), plasticity index (PI) 24, 52.33KPa cohesion (C) and 29.380 friction angle (Ø), which satisfy the basic requirements of core material. It generally showed shows 40% reduction in PI, 12% improvement in MDD, 5% reduction in OMC, and 18% reduction in compression index. It has also a better shear strength and compressibility characteristics than other mix proportions; however, it needs proper care to manage its segregation potential, likely to be resulted from improper mixing in the field that may lead to continuous leakage path within the core during construction stage. Based on permeability results, all the blended ratios were classed as low to very low permeability (< 10-6 cm/sec). Blended ratio of 40G/80C and 30G/70C is preferable in terms of economy; however, the required engineering properties like compressibility and compaction is relatively low. Therefore, the 50G/50C blended proportion can almost satisfy the standard limits set for design for impervious core material.