Hydraulic Engineering

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Establishing Water Release Rules for Koka Reservoir for Wet Seasons.
(Addis Ababa University, 1998-12) Shemeles, Paulos; Seleshi, Yilma (PhD)
Koka is the only single Reservoir found in the Upper Awash River Basin being utilised both for Hydropower and Irrigation uses. The current maximum capacity of the reservoir is estimated at 1,000 million rrr'. Up to the inlet to the Reservoir, the Upper Awash River Basin drains a catchment area close to 11,300 Km2. A number of important schemes found at the flood prone areas, downstream of the reservoir, are in need of a workable operation rule for Koka which can give them some protection against flooding during wet seasons. In this research an operation rule curve is established. The operation rule curve is established in such a way that all important variables for the hydropower operation and flood control are optimised subject to the constraints. Linear programming in MS-FORTRAN language is used to develop the optimisation model for Koka reservoir operation. The dry season water requirements of downstream irrigation schemes are implicitly guaranteed since the optimised rule curve will ultimately lead to a full storage at the end of every wet season which is desirable by those schemes. Emphasis was also given on the flexibility of the model to allow adaptive operation rules responding to the changing constraints and boundary conditions which are quite noticeable in the Koka reservoir system. The Real-Time operation procedure is formulated to be used in conjunction with the established rule-curve to enable the reservoir operators to make decisions, regarding releases for various purposes, in a considerably shorter period of time (e.g.,daily) using the current hydrometeorological information. The most important component in Real-Time reservoir operation is the Rainfall-Runoff model. These models enables, for a known rainfall, to predict the expected runoff which is an important information for the Real-Time operation of the reservoir and for assessing the possibility of flood hazards well in advance of its catastrophic consequences. It is, however, unfortunate that most models are data intensive that the scarcity of data is the major bottleneck in using them. In this research, a rainfall-runoff model is established employing the SCS
Stream flow Simulation for The Upper Awash Basin.
(Addis Ababa University, 2004-07) Behailu, Shimelis; H. Seid, Abdulkarim (PhD)
The Awash Basin is the most utilized and most developed basin in Ethiopia. After the construction of the Koka dam the feature of the basin is changed in large extent. Heavy rainfall in the upstream catchments causes large inflow discharges to Koka Lake. At times where the water level is already close to the maximum water level, the excess water must be discharged through the spillways in order to prevent overtopping of the dam. The discharge through the spillway, together with the water discharged through the power plant turbines, has in the past caused flooding in the downstream areas, most notably in August 1996. To prevent the downstream areas from flooding, the water level in the lake could be lowered in advance provided the inflows could be forecasted. For this reason, the FEWS-SFM was calibrated for the Upper Awash Basin using five years (1991-1995) of stream flow and rainfall records. The model was verified using another five years data (1996-2000). Ground observed data were used for the calibration for both the physical characteristics of the basin and the dynamic inputs: rainfall and potential evapotranspiration. Simulation was done in three scenarios of defining the basin. First the basin is defined to have a single outlet at Melka Hombole hydrologic station. The second scenario divided the basin into six subbasins and the last scenario is made by dividing the catchment to thirty five subbasins. It is seen that the second scenario represented the rainfall runoff to an acceptable range both visually and statistically. The Nash and Sutcliff goodness of criteria (R2) was used for testing the model performance. R2 = 0.63 was obtained for the calibration and the verification yield R2 = 0.6. The simulation of the basin has underestimated the peak summer (July – August) and overestimated flow from March to June. The dry period flow is underestimated. However, further refinement of the DEM and investigation on the DEM and investigation on the way soil properties influencing the rainfall runoff process in the model may improve the model main rainy period flow and overestimation of the small rainfall period. From the results obtained further investigation on the way soil properties influencing the rainfall runoff process in the model is necessary. Key words: Awash, calibration, DEM, FEWS-SFM, flood, Koka, rainfall runoff, simulation, verification.
Rainfall Variation and its Effect on Crop Production in Ethiopia
(Addis Ababa University, 2004-08) Admassu, Seifu; H. Seid, Abdulkarim
Agricultural production in Ethiopia is predominantly rainfed. Variation of rainfall in space and time affects the agricultural production system in the country. This needs accurate measurement of rainfall and close study of rainfall variation. Therefore, the objective of this thesis work is to study rainfall variability and its impact on crop production in Ethiopia. For such type of study and other study in the country, accurate rainfall measurement over wide spatial area extent is required. NOAA provides satellite rainfall estimate in Africa since 1995. The comparison of monthly satellite estimate obtained by CPC (Climate Prediction Center) technique with 37 numbers of rain gauges data show significant correlation (R = 0.77) but generally underestimation over the period of 1996-2002. And the root mean squared error (RMSE) is 68mm in average. With better calibration of the CPC method, better estimation would be obtained. Rainfall variation called trend has been assessed for total annual, Kiremt (June-September) and Belg (February-May) rainfall using 10 selected stations over the period of 1973-2002 in Ethiopia. Trend-free Pre-whitening Mann-Kendall statistical test at the stations show that Belg rainfall totals don’t show significant trend while Kiremt rainfall totals on Gore (-7.75mm/year) and Jijiga (-5.87mm/year), Sep-Nov total rainfall on N.Borena (-3.25mm/year) and annual rainfall totals on Gore (-12.2mm/year) and N.Borena (-11.11mm/year) show significant decreasing trend during the period. It is recommended to extend the study on more number of stations to conclude at regional level. Finally, in the thesis, total annual, Kiremt and Belg areal rainfall are regressed with main cereal production of Teff, Barely, Wheat and Maize on selected study areas over the period of 1994- 2001. The result shows no significant correlation between total annual, Kiremt and Belg rainfall, and production of those cereals. This analysis, however, includes small number of sample data and thus doesn’t include drought years occurred in the country. In addition, in the analysis, other agronomic factors are ignored. Therefore, large number of sample data and consideration of other factors should be used in future studies.
Flood Modelling Using 2D Hydrodynamic Model In the Fogera Flood plain
(Addis Ababa University, 2005) Dejenne, Wondwosen; Yonas
Flood occurs repeatedly in Ethiopia and cause tremendous losses in terms of property and life, particularly in the lowland areas. The majority of flood disasters’ victims are poor people living in nearby stretch of floodplain. Therefore, the study was carried out to perform floodplain analysis and risk assessment of Fogera and near by areas. This research involves application of 2D Hydrodynamic Modeling System with Geographic Information Systems (GIS) to develop a regional model for floodplain determination and representation. The study describes the Velocity mangitude ,innudation depth in the area for different flow conditions derived from the historical flow data of the Gumera River. Flood frequency analysis is used for prediction of peak flow for daily time series data and Gumbel and Log pearson Type III is used and Gumbel Distrubution is adopted with( R2 =0.994) and peak flow of the River for return periods of 2,5, 10, 25,50 and 100 years. boundary condition for upstream and downstream were defined. Similarly, flood discharges for different return periods were also inputted as inlet boundary and steady flow analysis was done for the results. The result of Gumbel Distrubution shows a flow value of 233m3/s,281 m3/s,312m3/s,352m3/s,382 m3/s,and 411 m3/s for return periods of 2,5, 10,25, 50 and 100yr respectively. Detailed topographic maps collected from various utility organizations and CCHE2D hydrodynamic models were used for simulations. Model results were evaluated for six different scenarios varying return period 2,5, 10,25,50 and 100yr. Finally, flood map was created. Based on the study the following conclusions were drawn: to represent river flood modelling , we need Good mesh generated based on bathzemeteric data high resolution inculding both river geometry as well as flood plain is very important to get meanigful innduation depth and velocity mangitude map on flood plain. Key words: CCHE2D, GIS, DEM, Flood Map
Reservoir Operation And Establishment Of Operation Rules For Lake Tana
(Addis Ababa University, 2005-01) Amare, Melkamu; Hussein, Abdulkerim (PhD)
Lake Tana, naturally existed reservoir, located in the northern portion of the Abbay river basin is the largest lake in Ethiopia with an average water surface area of 3110 km2 and estimated drainage area of 15340 km2. It is fed by four major tributaries all of them rising in the highlands surrounding the Lake. One regulation weir, Chara-Chara, is constructed at its out let to regulate the lake water for hydropower productions from two existing plants (Tis Abbay I and II) and for the realization of the envisaged development works both in the Tana and Beles Basins. With an estimated mean annual inflow of 12051.5MCM, water resources of the Lake is currently utilized only for hydropower generation at Tis Abbay I & II, local transport from Gondar to Bahir Dar, largely traditional level fishing and for tourist attractions at Tis Esat fall. Recently conducted Abbay river irrigated master plan project studies (BCEOM and associates, 1999) has indicated that the Tana and Beles basins all together have irrigation potential of more than 268,000ha out of which more than 145,000 ha is identified in the upstream reaches of the Lake Tana reservoir. At times of realization of the envisaged development works, irrigation and hydropower development works are, thus, becoming competing demands in the basin. Envisaged development works in the Beles basin are also competing with those in the Tana basin. This situation reveals that planning and reservoir operation in the basin is a serious issue that needs great attention, one of the principal reasons for this research work to be thought. Establishing the water balance of the lake on a monthly time scale is a prerequisite to effect reservoir operation. This activity is performed applying the continuity equation. Final result of the water balance simulation for the lake has shown that 69.2% of the inflow is lost through reservoir losses and 31% lost as an outflow. Currently the reservoir is operated at some operation rule that satisfies the demand from the existing hydropower plants and minimum requirements of the Tis Esat fall. Reservoir operation in this research work is simulated based on deferent envisaged and existing development scenarios that bear different magnitude of demands to the reservoir. Including the existing condition the research work
Interbasin Groundwater Transfer in Upper Rift Valley Lakes and Upper Awash River Basins
(Addis Ababa University, 2005-06) Ayalew, Bisrat; Mohammed, Mebruk (PhD)
Groundwater models are used to predict the groundwater flow processes using mathematical equations based on certain simplifying assumptions. Numerical modeling method is used to investigate the possibility of groundwater transfer (interbasin groundwater flow) between Upper Awash River basin and Upper Rift Valley Lakes basin. Within the study the hydrogeology is investigated from previous studies, a conceptual groundwater model is produced and the numerical model is developed from this. The model conceptualization is done by idealizing the study area into three models related to the surface water divide and the main perennial Rivers and lakes. For these three basins the boundary conditions are identified and incorporated into the models. The boundaries are Upper Awash River, Meki River, Ziway Lake, and Koka Lake in addition to bottom and top surface of the aquifer in concern. The models are three dimensional steady state by finite element method. All the study basins are discretized according to finite element method into equal element dimensions. The elements are three dimensional. The finite element model used in the study was TAGSAC. The modeling process was towards estimating the hydraulic head in the model basins of the study area by a means of finding the hydraulic conductivity of different geological classifications and estimating surface recharge in terms of some percentage of the rainfall of the study area. Finally the models are calibrated with the measured hydraulic head for each model basins. The models results show that the groundwater divide and the surface water divide are not coincident. There is a clear hydraulic head difference which can make groundwater to flow from Upper Rift Valley Lakes basin towards Upper Awash basin in the middle of the study area, along Ziway- Koka Lake and from Upper Awash to Rift Valley Lakes basin at west and east part of it. Key Words: Upper Awash River basin, Upper Rift Valley Lakes basin, Interbasin flow, Groundwater flow Modeling, Hydraulic head, TAGSAK
Evaluation of Technical Sustainability of Rural Water Supply Projects in The Amhara Regional State Case Study in South Wollo
(Addis Ababa, 2007-02) Assefa, Selamawit; Seleshi, Yilma (PhD)
The objective of this study is to evaluate the technical sustainability of rural water supply situation in South Wollo zone in the Amhara Regional State. The evaluation of water supply in selected rural areas is based on desk study of relevant literature and findings of the field assessment on the performance of the water supply systems . The study is carried out in two Woredas of south Wollo zone by visiting 29 water supply schemes. The three types of water supply technologies studied in the thesis are hand dug wells, spring development, and shallow borehole. Inadequate delivery of rural water supply system services, due to so many, difficulties are inhibiting the access of communities to basic Water Supply System infrastructure services. Existing facilities are often poorly constructed and insufficiently maintained, and do not adequately provide urgently needed basic services. The major problems, which are noticed in the sample water supply projects, are structural defects, quality, quantity, non reliability, inconvenience, too much user, lack of maintenance and repair, lack of trained person, attitudinal problem etc. Among the numerous factors that contributed to the poor performance of the schemes, the two key reasons are technical and institutional problems. Poor facilities design, poor construction, and lack of provision for system management and operation and maintenance, Limited policy implementation, Lack of capacity to keep the system running after project completion, poor cooperation between the water agent and users, lack of involvement of the community in the planning and construction process have also compounded the problems In the paper different kinds of water technologies suitable for small villages are discussed as options, by giving attention to VLOM Hand pumps and renewable energy IE solar and wind pumps. The recommendations stress on the need for proper and routine O&M program, need of quality checking and control, importance of cooperation between different water supply implementing agencies, need for encouraging community involvement as the key to ensure project sustainability and reduction of costs, and on implementing systematic and decentralized management and monitoring system of water supply schemes at the village level.
Impact of Land use Land cover change on Stream flow (CASE STUDY GILGEL GIBE III)
(Addis Ababa University, 2007-12) Nigussie, Assefa; Sleshi, Yilma (PhD)
The population growth and construction of hydropower generation dam caused changes in land cover of the OMO River basin, Gilgel Gibe III sub watershed and this changes have impacted on the stream flow of the watershed by changing the magnitude of stream flow. This study is mainly focusing on the assessment of the impacts of the land cover changes on stream flow through satellite Remote Sensing (RS) and Geographic Information System (GIS) integrated with the SWAT model. ArcGIS used to generate land use and cover maps from Land sat TM,ETM+ and Ls8 acquired, respectively, in 1987,2003 and 2013. The land cover maps were generated using the Maximum Likelihood Algorithm of Supervised Classification. The result of this analysis showed that the cultivated land has expanded, forest land decreased, range grass land decreased and water body has increased during the study period of 1987-2013. Using the three generated land cover maps, three SWAT models set up were run to evaluate the impacts the land use and cover changes on stream flow at the watershed. The performance of the SWAT model was evaluated through sensitivity analysis, calibration, and validation. eleven flow parameters were identified to be sensitive for the stream flow of the study area and used for model calibration. The model calibration was carried out using observed stream flow data from 01 January 1989 to 31 December 2000 and a validation period from 01 January 2002 to 31 December 2007. both the calibration and validation results showed good match between measured and simulated stream flow data with the coefficient of determination (R2) of 0.72 and Nash-Sutcliffe efficiency (ENS) of 0.67 for the calibration, and R2 of 0.86 and ENS of 0.6 of the validation period. Because of change in land use land cover mainly decrease in forest land by 24.03 %, increase in cultivated land by 30.146 % and decrease range-grass land by 6.846 % from year 1987 to 2013 stream flow has increased by 37.13 m3/s,60.92 m3/s and 98.05 m3/s from 1987-2003,2003-2013 and 1987-2013 Land use Land cover respectively. Key words: Geographic Information system (GIS),Gilgel Gibe III Watershed, Land use and cover change, Remote sensing, Soil and Water Assessment Tool (SWAT),Surface runoff.
Regional Flood Frequency Analysis For Upper Awash Sub- Basin (Upstream of Koka)
(Addis Ababa University, 2008-05) Demissie, Mengistu; Michael, Yonas(PhD)
The conventional and L-moment method of flood frequency analysis are applied in determining flood magnitude of defined return periods by selecting the best-fit theoretical probability distribution. The most important part of the distribution is the tail as far as extreme flooding phenomena. These phenomena of floods are of utmost concern in water resources development and management. In most cases the central part of the theoretical distribution fits satisfactorily with the empirical points. In FFA the objective is to estimate flood magnitude (Q) corresponding to any specified recurrence interval of (T) years. The estimation is complicated due to lack of a physical basis for determining the form of the underlying flood frequency distribution and the necessity of evaluating flood event for return periods that exceed the observation period (Leulseged, 2002). Regionalization is generally accepted term to explain the transfer of information about flood peak at one catchment derived from other catchments with similar characteristics. The advantage of such procedure is particularly great in the estimation of frequencies for higher flood magnitudes with limited at site data do exist and inference in the tail of probability distributions makes the stabilization of the estimators difficult. It is quite clear that regionalization is most viable way of improving flood quantile estimation. Although there remain researchable topics in development and application of regionalization method. The performance of regional Extreme value and LN distributions are found to be highly satisfactory and can be widely applied in this paper. More attention is given to at-site homogeneity test to group stations in the upper Awash sub-basin (u/s koka) in to two regions after checking them for the consistency and independency testes and estimation of standard error. The upper Awash sub-basin (u/s of koka) has 10-selected gauged stations consisting of stream flow record varying from 12 to 37 years, out of which 6 stations are found in the upper region and 4 of the stations are found in the lower region. An Extreme value EV1, GEV and Lognormal LN2, LN3 distributions are selected as the best fit distribution for the stations in the sub-basin. The sub-basin has been divided into two regions the upper and lower region, the upper region covers 18.46% of the sub-basin and the lower region covers 81.54% of the sub-basin.
Study of Index Properties and Shear Strength Parameters of Laterite Soils in Southern Part of Ethiopia the Case of Wolayita - Sodo
(Addis Ababa University, 2008-05) Tibebu, Hanna; Haile, Mesele (PhD)
Most geotechnical problems such as bearing capacity, lateral earth pressure and slope stability are related to the shear strength of a soil. The shear strength of a soil can be related to the stress state of the soil. The stress state variables generally used for an unsaturated soil are the net normal stress (_ –ua) and the matric suction. (Ua- Uw).The index properties of soils are also essential parameters for soil classification as well as for indirect estimation of its potential strength. Because of climatic conditions, ground water tables in tropical and subtropical regions are often depressed. Evapotranspiration often exceeds infiltration. This leads to deep desiccation of the soil profile. Therefore, residual soils frequently exist in an unsaturated state with continuous air in their voids. The pore air pressure will usually equivalent to atmospheric pressure, but the pore water pressure will be sub – atmospheric, i.e. negative due to capillary effects in the small pores of soils. This negative pore water pressure or suction produces an additional component of effective stress, or in other words: the effective stress becomes greater than the total stress. The extended Mohr Circle failure envelope defines the shear strength of unsaturated soil. Identifying the soil characteristic is essential to determine the type of test and test procedure that is applied during sampling, sample preparation and testing. In this thesis, several tests have been conducted to understand the effect of unsaturated soil mechanics on the determination of shear strength parameters and comparison of the result with tests on saturated samples. To this effect the geotechnical and geo-chemical characteristics of soils sampled from Wolayita – Sodo have been investigated. For shear strength parameters determination, undisturbed soil samples were collected and unconsolidated undrained tests and unconfined compression tests were carried out because of the triaxial machine’s limitation to suction measurements. Both saturated and unsaturated tests were conducted to make systematic comparison of the test results. xi Moisture content determination, using oven temperatures of l05°C, 50°C and 35°C were carried out on the soil samples to investigate the variation of structural water. Atterberg Limits were investigated for different testing procedures on the soil samples to evaluate the effect of test manipulation on cement bonds between clay clusters. The liquid limit tests were carried out on soil specimens mixed for 5 minutes and 30 minutes durations. From the test results, the soil under investigation has been affected by manipulation. Specific Gravity Test, Particle Size Distribution, Atterberg Limit Tests and Free Swell Tests were conducted at three different test temperatures (as received moisture, air-dried and oven dried at a temperature of 105°c). These tests were conducted in order to understand the behavior of the soil in the area and classification. According to the result of this research, Moisture content ranges between 26 - 41%, Plasticity Index ranges between 19 – 30%, Clay fraction ranges between 48 - 70, Shrinkage limit ranges11-22, Free swell ranges between 28-38% and Specific Gravity ranges between 2.61- 2.97. The shear strength parameters(C - _ value) as determined from UU Test ranges between 150-173 Kpa and 12 º -20 º for unsaturated sample respectively. For saturated soil sample, the C- value obtained is 118Kpa and unconfined compression strength (qu) ranges from 215- 385 Kpa. Laterite soils are characterized by high concentration of Iron Oxide, Aluminium Oxide (Sesqueoxide) and Kaolinite minerals. The soils samples subjected to tests fall below A-line under MH (inorganic clay with medium strength) and contain Kaolinite mineral. The activity number which is the ratio of plasticity index to the percent of clay –size friction by weight, is below 0.75, confirming that the soil is inactive.
Hydrological Models Comparison for Estimation of Floods in The Abaya-Chamo Sub-Basin
(Addis Ababa University, 2008-06) Ayka, Abyot; Sileshi, Yilma (PhD)
Nowadays the major environmental disasters in Ethiopia are recurrent droughts and floods. Their socio-economic and ecological impacts are devastating to the entire country, because most of them do not have real time forecasting technology or resource for post disaster rehabilitation. The Abaya-Chamo river basin is located in the southern part of Ethiopia. The extensive and attractable areas of this region, apart from being densely populated and extensively used for agriculture are also considered as a flood prone. Since most of the rivers in the basin are ungauged, it is essential to now the flow characteristics of the rivers in order to mitigate flooding effects in the basin. The aim of this study is to test the three conceptual hydrological models and propose suitable model for the estimation of floods in the ungauged catchments of the basin. Two catchments; Kulfo catchment from medium sized and Bilate catchment from large sized catchments, are selected for the analysis. Model approaches selected are: Soil Moisture Accounting (SMA) model which is embedded in the HEC-HMS software suite. SMA is a lumped, event, conceptual approach that allows continuous stream flow simulation and a number of model parameters are estimated. The other two models RRL SMAR & RRL TANK models are conceptual continuous daily time series models. Default values of all the parameters are used and then calibration has been made manually and automatically. V Using various models performance evaluation criteria; Nash-Sutcliffe efficiency, NSE (Coefficient of efficiency), Index of agreement d, Coefficient of determination R2 , index of volumetric fit IVF and The relative error of the peak, the output of each models was evaluated. HEC-HMS SMA model performed well compared to the other models especially with the objective of capturing the peak flow and volumetric fit IVF in the two catchments. Thus, the HEC-HMS SMA model can be used for the estimation of peak floods in the two catchments and in the ungauged catchments with or without regionalization. Model uncertainties due to various sources such as improper data input, incorrect model parameterization are also highlighted in the end of this study. Keywords: Ungauged catchment, floods, HEC-HMS SMA, RRL SMAR, RRL TANK, Abaya-Chamo river basin.
Flood Frequency Analysis For Lower Awash Subbasin [Tributaries From Northern Wollo High Lands] Using Swat 2005 Model
(Addis Ababa University, 2008-06) Argaw, Yidenkachew; Seleshi, Yilma (PhD)
Flood frequency analysis provides vital information for the planning and design of many hydraulic structures and risk assessment in flood plain use. The objective of flood frequency analysis is to estimate a flood magnitude corresponds to any required recurrence interval. The resulting relation between flood magnitudes and return period is referred to as Q-T relation (Flood Frequency curve). This study is based on peak discharge, in particular the annual maximum flood Flood frequency Analysis, the determination of flood flows at different recurrence interval, is a common problem in hydrology. The standard procedure to determine probabilities of flood flows consists of fitting the observed stream flow record to specific probability distributions. However, this procedure only works for basins: That have ‘long enough ‘stream flow records to warrant statistical analysis (gauged catchments) because a reliable estimates of the Q-T relationship cannot be obtained from small samples of at-site data because of the high variability involved and where flood flows are not appreciably altered by reservoir regulation, channel improvements (levees) or land use change. The majority section of this study contains the procedure of generating stream flow data for Mille and logiya watershed using rainfall –runoff model approach for use in flood frequency analysis. This thesis describes a spatially distributed watershed model of Lower Awash basin (Mille and Logiya watersheds) that has been developed using SWAT 2005 to describe stream flow generation for Mille and Logiya watershed at Mille station (Gauge033021) and Logiya, (Gauge033027). The Soil and Water Assessment Tool 2005(SWAT2005) was developed by the Agricultural Research Service of the United States Department of Agriculture and distributed by the US Environmental Protection Agency for watershed management. SWAT2005 Simulates through time the daily soil water balance. XII The spatially distributed nature of SWAT 2005 means that the hydrological surface runoff processes are represented independently in different regions across the basin. There are 52 and 29 different regions called HRU (hydrological response units) for Mille and Logiya river watershed respectively in this modeling application (shown at Appendix G and H for Mille and Logiya watershed respectively). A set of SWAT2005 input representative of the basin has been developed from a wide array of data and the flow simulation is successfully tested against measured flow data. For the Mille and Logiya river basin, SWAT2005 model was calibrated and validated over a four year on a daily time base for daily peak surface runoff from January 1990 to December 1994 for calibration and January 1995 to December 1998 for validation period. Sensitive model parameters were adjusted within their feasible ranges during calibration to minimize model predictive error for daily peak flows. Model performance testes were evaluated to test the model accuracy during the validation and calibration period .These measures included percent differences, coefficient of correlation (R2) and Nash-sutcliffe measures (ENs). A summery of the statistical results for hydrological calibration and validation of Mille and Logiya watershed at Mille and Logiya stations is summarized in table5.9 and table5.11 for Mille and table5.10 and table5.12 for Logiya. The daily ENs , R2, and the percentage difference values range from 0.69 to 0.79 , 0.71 to 0.83 and 15.8% to 27.5% respectively for both watersheds at the gauging stations during the calibration and validation period. These hydrology performance test results ranges indicate the model is effectively simulating in the watershed. The results fulfilled the requirements suggested by Santhi et al. (2001) for R² >0.6 and ENS > 0.5. Continuous hydrologic simulation is a valuable tool to determine flood frequencies in Ungauged watershed and in gauged watersheds that have short stream flow records or are heavily regulated. Since hydrologic simulation models the rainfall-runoff relationship in the basin, it can also be used to check the validity of the probabilistic distribution selected for gauged unregulated watersheds with long stream flow records. XIII Stream flow records, if available at all, are often much shorter and most of the sub watersheds are unguaged. The SWAT2005 continuous hydrologic simulation was used the monthly metrological data as an input for weather generator input file (.wgn file) that contains the statistical data needed to generate representative daily climate data for the sub basins and soil, land cover and DEM data layers for simulation and extend the existing short stream flow records form a few years to 50 years data for the watersheds. The objective of the research is to use the watershed (Mille and Logiya) SWAT2005 model generated Annual maximum flow data for determining the best fit distribution for each watershed and Comparative analysis of flood frequency results. The extended records were fitted to a probabilistic distribution using “Easyfit” Statistical application Software and the Gamma three parameter distribution was the best fit distribution for both Mille and Logiya watersheds among many distributions presented within the softwar
Technical Performance Evaluation of Domestic Roof Water Harvesting Schemes (The Case of Minjar and Shenkora Woreda Schemes)
(Addis Ababa University, 2008-07) Kassahun, Befekadu; Michael, Yonas(PhD)
The objective of the study is to diagnoses the technical performance of DRWH schemes implemented by Water Action (an indigenous NGO) in Minjar and Shenkora Woreda, Amhara Regional State. The key selected technical performance evaluation indicators are reservoir capacity, capacity of gutter and down pipes and water quality. The study is conducted on all of the DRWH schemes implemented by water Action in the woreda. The study methodologies employed are literature review, semi-structured interviews, questionnaires, PRA and RRA has been employed to probe more information on the grass root level. The mass curve technique and the SIMTANKA software are also used to establish optimal tank/reservoir/ size. Traditionally excavated pounds, River and deep wells are the major sources of water supply for human being and livestock watering in the woreda. As compared to other water sources traditional excavated ponds are the most reliable sources of water supply though exposed for various contaminants and serves for a few months. Rainwater harvesting is back after having been ignored for decades. For arid and semi-arid regions, DRWH has proven track-record of providing safe water next to the house. The increased interest has been facilitated by a number of external factors among others includes the shift towards more community based approaches, the decrease in the quality and quantity of ground and surface water, the failure of many piped water supply system due to poor O & M, etc. viii The study reveals that, in general, lack of awareness, policy issues, poor system operation or management; lack of regular monitoring and maintenances are among the main technical performance problems on the promotion and implementation of the technology.
The Dynamics of Land use Land cover change on the Stream Flow in Fincha Amerti Neshe Sub-basin: Abay basin, Ethiopia.
(Addis Ababa, 2009) Habte, Taye; Mengiste, Yenesew(PhD)
Fincha Amerti Neshe sub-basin is densely populated causing various effects on resource bases because of deforestation, expansion of residential area, and agricultural land. The sub basin is also facing high erosion by the effects of intense rainfall of the watershed which aggravates the land cover change of the watershed. The objective of this study was to evaluate the dynamics of land use land cover change and its effects on stream flow using SWAT model in Fincha Amerti Neshe watershed. The land use land cover change analyses were performed using ERDAS Imagine 2014 which was used for an input in analysis of SWAT. Land use land cover changes for three different years of 1990, 2000 and 2015 land use scenarios were used for estimation of stream flow. During the study period most parts of the grassland and shrub land were changed to cultivated land. An increase of cultivated land by 18.57% over 25 years period (1990 – 2015) resulted in an increase of stream flow by 13.39m3/s. In Amerti, there was also an increase of cultivated land and wet lands by 15.57%, 15.27% for the periods 1990 – 2000 to 2000-2015 years respectively. On the other hand grasslands were decreased by 10.44% within 10 years period and 11.78 for the 15 year’s period. Moreover, shrub lands and forest showed a significant decrease through the period. i.e Shrub lands showed a higher decrease during the second period from 2000_2015 by -11.13% than the first period from 1990_2000 by -0.84%. The water body becames increased through the decades to promote Fincha reservoir through the tunnel for adding the efficiency of Fincha hydropower. The Nash Sutcliff efficiency, coefficient of determination (R2) and RSR were used for evaluating the model performance. The model results showed a good agreement and correlation with the observed data with NSE > 0.65, R2> 0.84, and RSR < 0.6 values. Key words: Fincha Amerti Neshe watershed, land use change, stream flow, Rainbow, SWAT, ERDAS Imagine.
Groundwater potential assessment and characterization of Genale-Dawa River basin
(Addis Ababa, 2009) Kassahun, Nebiyou; Kemal, Asie(PhD)
Genale-Dawa River Basin is one of the largest basins in Ethiopia. It is one of the most drought prone regions in Ethiopia. As a result a search for alternative source of water has always been a major issue in the region. This study therefore, aims at characterizing and evaluating the ground water potential resource of Genale-Dawa basin. The results of this research ultimately contribute to development of better water resources potential management. Delineation of the Genale-Dawa River basin was carried out first in order to define the problem domain of the model. This has resulted in 17860km2 area of the basin. This area was discretized to form a three dimensional. The discretized region has 19620 nodes, 17862 equilateral triangular elements of varying sizes with a maximum of 5km edge dimension and 2500km model thickness. The conceptualization of the model was done by grouping the discretized region in to 56 geological classes based on previous geological survey of the basin. The equivalent porous medium modeling approach was used to represent the different geological classes in the basin. Moreover, 23 rain gauge stations were used to determine the areal precipitation over the basin. The model takes perennial rivers as constant head boundaries, the side and bottom geometric boundaries of the model as no flow boundaries and the recharge due to precipitation as specified flow boundary. After conceptualization of the flow system was complete and numerical model developed, TAGSAC model manual calibration was done by seating hydraulic conductivity and percentage recharge as calibration parameters when calibration is complete. The result was evaluated quantitatively using average indicators (AM, RMS, MAE) and qualitatively by comparison of groundwater contour maps generated with recorded and simulated hydraulic head data. The calibration model was then used to determine monthly groundwater table fluctuation which eventually enabled the estimation of groundwater recharge potential of the basin. Additionally, base flow separation of perennial rivers was done to determine the monthly excess flux from the aquifer system. By adding these two values the total replenishable groundwater was estimated to be 2.78BMC. Hydro-geological map was also prepared based on hydraulic conductivity values obtained from model calibration. Identification of major groundwater recharge and discharge areas have also been done as an attempt towards basic groundwater flow system characterization.
Dechatu Catchment (Dire Dawa Town) Flood Study
(Addis Ababa, 2009-04) Habte, Tesema; Michael, Yonas (PhD)
Nowadays, extraordinary floods are common to many parts of Ethiopia every year causing a lot of losses to human lives as well as damage to property. However, the researches and studies related to this problem are not as intensive as the damage. Historically, Dire Dawa has been vulnerable to flash flooding from rainfall, in particular of the ungaged Dechatu catchment which passes through the centre of the city. The tributary rivers are originating from the southern highlands of Kersa, Lange and Dengego catchments. Some organizations have tried to estimate the amount of flood and recommended the mitigation measures previously. Traditional flood design methods are increasingly supplemented or replaced by risk-oriented methods which are based on comprehensive risk analysis. Besides meteorological, hydrological and hydraulic investigations such analyses require the estimation of flood impacts. Hence, this thesis is to identify peak flood and delineate risk areas that can be affected by extraordinary floods and to recommend mitigation measures. This thesis tries to consider more options and fills the gaps not covered by others adopting more than seven application softwares like GIS, ArcView, Global Mapper, HEC-HMS, HEC-GeoHMS, HEC-RAS and HEC-GeoRAS. Specially, delineation of the flood area and recommended mitigation measures selection method believed to be the gap not properly covered in the previous Dire Dawa flood studies which I have seen. The data usage for this thesis tried to make very intensive by considering different data options like gridded (DEM and contour), digitized (soil, land use and 1:50,000 scale map) and text (rainfall and discharge) type. For precipitation modelling, ERA Intensity-frequency-duration curve is used for frequency storm and for the gage weights annual maximum daily rainfall for 24 hours and 6 hours duration storm are used since the concern is flood that uses more than one nearby metrological stations. For geographic and terrain data, 57m resolution DEM for catchment, 4m contour interval for the town part and 0.5m contour interval for the Dechatu Stream cross section are used. In this thesis, the flood magnitude estimated, flood area delineated and mitigation measures selection method recommended. The potential vulnerable areas for the 50 years return period flood are Kefira, Gende Gurage, Dechatu Kebele, Coca Cola factory areas, Ashewa Tera, Number one and Half-Cat. Dire Dawa Administrative Council (DDAC), Organizations, engineers and planners who are involved in the study and management of the Dire-Dawa town flood are the direct beneficiaries. Others who are engaged in similar flood related problems believed to be benefitted from this thesis. Now on ward, this will contribute to change the traditional trend of flood damage analysis which is found to be the outstanding problem by now.
Daily Rainfall-Runoff Modeling for the Beles River Catchment.
(Addis Ababa University, 2009-05) Hailemariam, Woinishet; Sileshi, Yilma (PhD)
For an effective and sustainable water resource planning and management, the need for complete and reliable hydrological and meteorological data is unquestionable. To get such data there is a need to develop and maintain hydrometric stations in proper networks. Presently in Ethiopia most of the available gauging stations are located nearby access roads. Because of this situation, most of the rivers which are inaccessible to roads are not gauged. Beles River basin, a sub-basin of the Abay basin, is a basin whose vast area is ungauged, as there are only two gauging stations on its upper part and all its lower parts are ungauged. In this research hydrological models are used to solve the above indicated problem on the Beles sub-basin. Three Rainfall- Runoff Models are tested on the upper Beles catchment, namely the RRL SMAR, RRL Sacramento and RRL Tank models. For all these models calibration and validation are done using the required input data. Evaluation and selection of suitable model for the catchment is carried out following the objective criteria: Nash-satcliffe efficiency (Reff); Efficiency using ln(Q) (logReff); and Coefficient of determination (R2). The RRL Sacramento Model scored the best result among the three Models for all objective functions, and therefore it is selected. Since upper and lower Beles are hydrologically homogenous, the calibrated RRL Sacramento model for the upper Beles are used to the ungauged catchment of Lower Beles without changing its parameter. However, the Sacramento Model result by itself is not found satisfactory, since there is no meteorological station on the Beles catchment and the data used for this study is by transferring data from nearby station, considering the distance between the station and the catchments area. This kind of transferred data can not be the same as the real station data, creating low performance the model. vi Keywords: unguaged, Beles, model, gauged, RRL SMAR, RRL TANK, RRL Sacramento, catchment, Calibration, Validation.
Stochastic Simulation of Streamflow and Hydrologic Drought Analysis (Case Study: Upper Blue Nile Basin
(Addis Ababa University, 2009-06) Hagos, Yohannes; Ayalew, Semu(PhD)
This thesis is concerned with the problem of stochastic simulation of streamflow and hydrological drought analysis in the upper Blue Nile basin ( Abbay).Thirteen stations with long record period ranging from 35 to 45 years were used for the analysis. Two sets of time series models named PARMA (p,q) and Thomas-Fiering were tested and inter-compared for the stochastic simulation of monthly streamflow , and a suitable model were selected. PARMA models of low order are found to be most appropriate for all stations than Thomas –Fiering model. The performance of the model ranges from R2 value of 0.893 at Gilgel Abbay near Merawi station to 0.33 at Abbay near Bahirdar station. The Thomas-Fiering model gives similar results; its R2 values ranging from 0.87 at Gilgel Abbay near Merawi station to 0.32 at Abbay near Bahirdar station. But both models did not give acceptable results for the gauging station at Abbay near Bahirdar .In general, best fit PARMA (p,q) models was found to perform better in most of the gauging stations than Thomas-Fiering model considered in this study. Therefore, long sequence of synthetic flow used for drought analysis in the study were generated using PARMA (p,q) model. Hydrological drought parameters namely, drought duration (D) and drought severity (S) were derived and analyzed from historic and long sequence of synthetically generated data at Gilgel Abbay near Merawi and Guder near Guder stations. The threshold method has been used to identify drought parameters in the streamflow series. Both drought severity and duration were found independent without a trace of trend within it. Accordingly the important drought characteristics were determined and the suitable probability distribution for each parameter was arrived at after studying different probability models. The use of the probability curves thus derived has been also illustrated. It can be concluded that the duration and severity of drought in the basin doesn’t show any trend of increasing or decreasing. However, in the event of other circumstances like climate change, the trend may evolve differently. Future studies may investigate the impact of climate change in the severity and duration of drought.
The Impact of Land Use/ Land Cover Change on Catchment Hydrology and Water Quality of Legedad‐Dire Catchments, Ethiopia
(Addis Ababa, 2009-10) Aduna, Taye; Sileshi, Yilma (PhD)
The main objective of this study was to assess the impact of the environmental changes on the hydrology and water quality of the Lege Dadi-Dire catchments. More specifically, the study analysed the land cover change scenarios that were assumed would have taken place in the catchments, and the effect these changes have had on the hydrology and water quality of the catchment. The Soil and Water Assessment Tool (SWAT) model was used to investigate the impact of land cover change on streamflow, sediment, nitrate, phosphorous, and other considered water quality variables yield of the study area. The model was set up using readily available spatial and temporal data, and calibrated against measured values. There was good agreement between monthly estimated and simulated variables for the calibration and validation periods. The simulation of sediment was slightly underestimated but overall, the agreement between the estimated and simulated variables was acceptable. Two approaches have been taken to conduct the study. First, historical land use/cover data of 1960, 1980, and 2008 were taken and the impact of land use/cover change over the period was analysed. Second, the 1990 land use/cover data was used as a base data and scenarios of the future land use/cover were developed. Taking both cases, impacts of land use/cover and their scale were identified in this study. Accordingly, there has been close correlation between land use/cover, stream flow and turbidity. There has been a considerable increase in runoff of about 8.3% in Lege Dadi catchment which is attributing to land use/cover effect. Without climate change, land cover changes considered in the scenarios account for an increase in runoff of about 3.4-49.9% and 14.9-15.3% for Lege Dadi and Dire catchments respectively. Similarly, the sediment yields have also increased more closely with agricultural land use intensification. In relation to the increase in agricultural land, nitrate, phosphorous and other considered variables have shown considerable increase through the application of agricultural inputs such as fertilizers. This will further escalate the problem of water quality and treatment cost of Lege Dadi water treatment plant. Remedial measures have also been recommended
Computer Program for Optimal Design of Low Head Diversion Structures
(Addis Ababa University, 2009-10) Tilaye, Robel; Hailu, Habtamu(PhD)
A computer program named HelaFlow is developed for optimal design of low-head diversion structures using visual basic.Net programming language. The program calculates the parameters of a diversion structure’s components that are set in consideration of surface flow, subsurface flow, nature of foundation soil, structural stability and economy. It solves the uplifting pressure head distribution on the structure using finite difference technique, allowing for accurate design of structures built on anisotropic and/or shallow as well as isotropic and deep permeable media. It also optimizes the parameters of components for least cost design using cost of construction of components as input. The effects of anisotropy and variation in depth of permeable media were analyzed and found to affect the magnitude and distribution of uplifting pressure head on the apron of structures. Sample designs are presented to demonstrate the capability of the software program. This study equips the design engineer with a convenient decision tool for optimal design of low-head diversion structures. Key words: diversion structure, subsurface flow, hydraulic jump, finite difference method, Anisotropy, optimization

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