Water Resource Engineering

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Comparison of Pseudo-Static and Dynamic Response Analysis of Sibilu Dam
(Addis Ababa University, 1979) Getachew, Fantahun; Haile, Messele(PhD)
Dynamic loads induced by earthquakes are often major factors in the design of earth dams. Earthquake induced stresses are major factors in determining the angles of the dam slopes and significantly influence the selection of materials, the zoning of the dam, and the construction method. Awareness about more rigorous seismic stability analysis is also growing during recent years. In Ethiopia dams are being constructed for various purposes. The analysis and design of dams has been carried out by taking many factors in to account. Among these factors earthquake effect is considered mainly for major dams. One of these dams is the Sibilu Dam, which is under design for the Addis Ababa water supply. Until the present, in Ethiopia, seismic effect is commonly considered by the pseudo-static analysis method. But representation of the complex, transient and dynamic effects of earthquake shaking by constant pseudo-static forces is obviously not accurate. In this thesis an attempt was made to compare the pseudo-static and dynamic response analysis by taking the Sibilu Dam as a case study. The main purpose of the study is to show the shortcomings of the pseudo-static analysis method as compared to the dynamic response analysis when applied to the analysis of earth/ rock fill dams. The thesis is organized as follows: initially a background is given on seismicity and seismic hazards in general and Ethiopia in particular. The second chapter covers summary of previous works related to this study. In the third chapter some description is given about the Sibilu Dam, the dam under the case study. In chapter four, the definition of the expected seismic excitation for the dam site is presented. The historical records of earthquake events are collected and geotechnical data of the dam site are reviewed 2 paying special attention to the location of active faults. The obtained data set is analyzed to give the required earthquake parameter for two different return periods. In fifth chapter, the pseudo-static slope stability analysis is done with the conventional limit equilibrium method by using the design ground motion as an input. The analysis is performed for the upstream and down stream slopes of the dam by varying the possible critical cases. In chapter six, analysis and design is done based on permissible deformation. The dynamic response analysis is done by varying the material behavior. Non-linearity is considered by the Equivalent Linear Method. Finally, comparison of the different analysis methods is made and conclusions and recommendations are drawn.
Development of Synthetic Unit Hydrographs for Watersheds In The Upper Awash and Upper Tekeze Basins
(Addis Ababa University, 2004-10) Azeze, Mulugeta; Seleshi, Yilma (PhD)
Hydro-meteorological data are very indispensable for the assessment and development of water resources. However, most catchments in Ethiopia are ungauged and direct streamflow observations are not available at most sites for which rainfall–runoff relationships are required. Therefore, if there are no flow data from a catchment, a technique is needed for estimating the required design parameters, which do not require the availability of hydrological records. One option is to develop models for gauged catchments and link their parameters to physical characteristics, so that the approach can be applied to ungauged basins in the region, whose physical characteristics can be determined. Usually, one resorts to Synthetic Unit Hydrographs (SUHs) if there are no observed discharge hydrographs. This requires that the catchment characteristics be obtained or determined which are then used to adapt the SUH to suit a particular catchment. In this research work coefficients required for the construction of synthetic unit hydrographs using Snyder’s method for watersheds, which have areas in the range from 59.8km2 to 2449km2 in the upper Awash and Tekeze basins, have been determined. Moreover equations for estimating the lag time coefficient (Ct) and peak discharge (qp) from watershed characteristics were also developed. Thirty concurrent rainfall-runoff events from six gauaged watersheds, four in the upper Tekeze and two in upper Awash, were used to estimate the coefficients and develop the equations. 27 rainfall-runoff events were used for calibration and three were used for verification. Due to the lack of getting watersheds with adequate rainfall and runoff records in Tekeze basin two watersheds that have almost similar hydrological characteristics were used to produce a reasonable and largely reliable estimate. Lag time coefficient (Ct), peak discharge coefficient (Cp), unit hydrograph widths coefficients (Cw) at 50% and 75% of the peak and base time coefficient (Cb) were determined by calibrating Snyder’s equations with the available rainfall- runoff data. The mathematical relations for lag time coefficient (Ct) and peak discharge (qp) with watershed characteristics were established by using regression analyses. xiii Lag time coefficient (Ct) for the gauged watersheds range from 0.362 to 0.736 with mean value of 0.542 and a standard deviation of 0.157. The peak coefficients of the unit hydrographs of the gauged watershed range from 0.064 to 0.346 with mean value of 0.180 and a standard deviation of 0.112. Coefficients for the base time (CB) and for the widths of unit hydrograph (Cw) at 50% and 75% of the peak discharge of the gauged catchments are found to be 1.006, 0.20 and 0.108 respectively these values are recommended to construct UH for an ungauged watershed in upper Awash and upper Tekeze basins. Lag time is an essential input for Snyder’s synthetic unit hydrograph model. Strong correlation with R2 = 0.90 is seen between Lag time coefficient (Ct) and slope of a watershed. And hence the equation Ct = 0.032*S-0.597 is recommended to estimate lag time coefficient (Ct) for an ungauged watershed in the upper Awash and Upper Tekeze basins. In addition to this lag time can be estimated directly from the physical characteristics of the watershed by using the equation tp = 0.127*(LLc/S0.5) 0.352. Strong correlation with R2= 0.92 is seen also between qp (in m3/s) and the variable Z = A/tl and hence the formula qp = 8.71*10-3 *(Z) 1.78 Can be used to estimate the peak discharge. Therefore, applying the equations and the coefficients give an estimate to the required UH characteristics, which might serve the intended purpose, as long as the hydrometeorological and physical characteristics of the watershed under consideration are with in the range of those characteristics for the watersheds in this study.
Remote Sensing Based Assessment of Water Resource Potential for Lake Tana Basin
(Addis Ababa University, 2007-04) Daniel, Yohannes; Hussien, Abdulkerim (PhD)
1. Remote sensing techniques have been applied to augment estimation of hydrologic variables. Thus rainfall, evaporation, flooded zone delineation and runoff estimation has been carried out. TRMM monthly rainfall products were employed in rainfall gap filling techniques, the satellite estimates were first validated against observed ground station records and results indicated good correlation, average of 81%. Combination equation (Energy balance-mass transfer) is used to determine gridded potential evapotranspiration from the sub-basin by making use of MODIS 16 days Albedo products. Spatial extent and amount of water on flood plains during wet seasons of the year has also been determined by making use of spot NDVI temporal images through calibrating with high resolution SAR and optical images. Furthermore, land use/land cover information is extracted from Landsat imagery and existing data of land cover has been updated. Using the update land cover information spatial Curve Number (CN) map was developed. Runoff estimation, using SCS method and a soil water balance simulation using WatBal model, was then carried out in order to determine the runoff from un-gauged catchments and the results from the two models were compared. Results indicated that the soil water balance simulation model gave better correlation with the observed than the SCS method. Therefore, runoff estimation from un-gauged catchments was carried out using the soil water balance simulation techniques. Lake water balance simulation was finally carried out using continuity equation within simulation time span of 1998 to 2003 considering the variables, i.e. inflow estimation form the contributing catchments, the improved evaporation estimation; the rainfall data obtained incorporating TRMM images and water lost in the flood plains due to evaporation. Simulation results were compared with the Lake Tana Storage computed using the recorded Lake water surface elevation. The six year average results indicated that out of the total of 7,688 MCM estimated runoff from the catchments 3.59% is lost in the flood plains due to evaporation. Similarly, out of the 10,574 MCM inflow to the lake (net runoff plus rainfall over lake area) 5,110 MCM is lost through evaporation from the lake surface, 5,012 MCM is outflow from the lake to the head of main Abbay river. Average reduction in reservoir storage was computed to be 330 MCM. Therefore, the remaining 1414 MCM is assumed to be seepage loss and other unaccounted losses from the system
Flood Generated from Tana Lake Basin
(Addis Ababa University, 2008) Tamiru, Mossie; Seleshi, Yelma(PhD)
The computation of runoff usually consists of applying a stage- discharge relation to daily gage heights to determine mean daily discharges. However, for this particular study a hydrologic model, HEC-HMS is applied to compute the hourly base runoff generated from Lake Tana basin. The basin was sub divided in to eleven sub basins with a total area of 15046.32 square kilometers including the area of the lake. The Basin has many streams of which the seven have daily gauged data. The gauged data from six streams are used for parameter estimation for the ungauged sub catchments. Since the study focuses on the computation of flood particularly peak flood, these daily discharge data are hourly distributed using the formula QT = M*T ½.Where T is time in hours and M is a coefficient of which value is determined from known discharges and respective time or return period. The Probable Maximum Flood (PMF) entering Lake Tana from the sub basins would be determined based on the convolution of the Unit Hydrograph (UH) with the Probable Maximum Precipitation (PMP) using the storm frequency meteorological model built in HEC-HMS. The Bahir Dar 24 hours maximum annual rain fall depth values were the basis for the evaluation of 24 hours PMF values for the return period 25-years, 50-years, 100- years.The direct runoff contributed by each sub-basin is computed for return period of 10-, 25-, 50- and 100-years.Finally the calculated direct runoffs are combined to know the magnitude of peak runoff coming into Tana Lake. Flood generated from Lake Tana basin is determined in such a way that adding the rivers base flow to the direct runoff and summing the floods from sub basins assuming all sub basins are active at a time. The highest combined incoming flood from all sub catchments to the Lake are 4,053 m3/sec ,4,241 m3/sec,5,040.0 m3/sec and 25372 m3/sec. While the corresponding total inflow are 235,474 m3,250,687m3,235,474.2 m3,292,258 m3,643611m3 for v the respective return periods. The water surface elevation at the time of this highest incoming flood ranges from 1787.9 m a.m.s.l for 10 – years return period to 1789 m a.m.s.l for 100 –years return period. The probable maximum flood (PMF) computed using the model is 56,526m3/s(or 9,522,011 m3) and the corresponding lake water surface elevation is 1789.3m, too. This shows that the Lake level is raised by more than two meters. Hence, low laying area of Bahirdar and Fogera and Dembia flood plain will be affected.
A Study of Flexural and Compressive Strengths of Jute Fibre-Reinforced Concrete
(Addis Ababa University, 2010-03) Bantie, Enyew; Adamu, Asnake(PhD)
The problems associated with low efficiency in tensile strength of structural elements, brittle mode of failure, rapid crack propagation and increased overload are common in the concrete construction industry. Whereas ordinary steel reinforced concrete is the most popular mechanism developed so far to alleviate such problems, it is rather becoming expensive in production costs, transportation of pre-cast members, maintenance costs and the supply of much amount of steel. These impediments have driven the development of contemporary concrete technologies such as high strength concrete and fibre reinforced concrete in which all the advancements entail an investigation into the constitutive materials. This thesis is part of such works dealing with the experimental assessment of flexural and compressive strengths of JFRC with different jute fibre contents. To achieve this objective a series of compression and two point bending tests were conducted. The results of the compression test indicated that the presence of jute fibre tends to reduce the compressive strength of concrete at higher fibre content. Despite the minimal reduction in the compressive strength at higher jute fibre content, there is an improvement of ductility after cracking of concrete. Similarly, the bending test results indicated that the modulus of rupture of concrete increases by 50% at 0.50% jute fibre content. Moreover, jute fibre significantly improves the toughness behavior of concrete. There is as much as 28%, 82% and 105% increment in5I, 10I, and 20I respectively at 1.00% jute fibre. In spite of the limited scope of the thesis work and the shortcomings associated with jute fibre, the thesis work results elite a hope that JFRC can be used in areas where small tensile reinforcement is expected and also in the construction of temporary structures. The least cost of jute fibre, its being renewable resources, the reduced weight of the JFRC composite and the reduction in consumption of other constitutes of the concrete matrix would indicate its economic advantage. While an assessment of flexural and compression strengths of JFRC have been shown and described in detail in this thesis, various additional changes and modifications may be made to study other properties of JFRC.
Water Use and Operation Analysis of Water Resource Systems in Omo Gibe River Basin
(Addis Ababa University, 2011-05) Asefa, Daniel; Hailu, Dereje (PhD)
In this study, HEC-ResSim (Hydrologic Engineering Center-Reservoir System Simulation) model was used to simulate water use and operation of existing, ongoing and planned hydraulic infrastructures, and irrigation schemes in Omo Gibe river basin. For these purpose five different water resource scenarios were simulated viz. Scenario-T, Scenario-A, Scenario-B, Scenario-C and Scenario-D. Scenario-T was first set up to simulate gauged flow routing without taking into account effects of development and a good agreement was observed between simulated and measured flow at Karadus station. The Nash-Sutcliffe efficiency criterion obtained for the catchment was 0.782. Following this, the model was configured to simulate the recent and proposed development interventions on water resource. Scenario-A result showed that an average annual energy of 780GWh/year and 1911GWh/year are produced by Gibe I and Gibe II respectively when they are operated in tandem. Equivalent storage distribution was also examined among reservoirs in the entire simulation period. The current study, HEC-ResSim simulation in scenario B, has discovered that long term effects of operation of Gibe III power plant would increase the dry season outflow and decrease in flood season outflow from the Omo- Gibe river system. An average increase of 130% in mean monthly inflows from November to June and decrease of 25% in mean monthly inflows from July to October was observed at Karadus. But the mean annual outflow from the basin at Karadus will be decrease by 1.14%. Simulation of Gibe III power plant produced an average annual energy of 6,488GWh/year and power of 758.94MW.The firm energy and power that can be guaranteed 90% of the time are 5885GWh/year, 625.0MW respectively. The average energy obtained is close with the study made by EEPCO. The firm energy obtained is also similar and greater than the energy obtained during reservoir operation studied by EEPCO. Due to upstream regulation i.e. intervention the proposed power plants, Gojeb and Hallele Warabesa stage I and II, in the upstream Omo-Gibe basin under scenario D can increases firm energy production of Gibe III power plant to 6023GWh (2.75%) per year with same reliability and the average annual energy can also increase to 7587 GWh per year (by 15.66%). Moreover, during scenario D simulation annually about 1.87BCM volume of water will be diverted into irrigation site under full irrigation development (142,000ha) and the annual volume of water from Omo-Gibe river system below the proposed irrigation sits will decrease by 14.15%. Keywords: Firm Energy, HEC-ResSIM, Reservoir Operation, Simulation scenario, Karadus, and Reservoir Network IV Dedication This work is dedicated solely to my mother Abeba Yemataw,
Water Supply Coverage and Water Loss in Distribution System with Modeling (The Case Study of Addis Ababa)
(Addis Ababa University, 2011-11) Kabeto, Shimeles; Sileshi, Yilma (PhD)
Leakage in water distribution pipes is a major problem faced by the water industry. Water utilities often employ traditional audit methods to estimate water lost as leakage. As a result demand for additional water sources and infrastructure is growing. More ever, nearly 37% of the total water production is loss at different level of distribution system before reaching to the consumer. The focus of this study is to evaluate the city’s distribution coverage of the water supply and evaluating the total water loss. The water supply coverage at the city level and the total water loss both at the city level and at the sub system level, the collected data was assembled in EPANET and controls were added to best represent the functioning of the water system. Water production that is only for the city and the water consumption as aggregated from individual customer meter reading was to evaluate the total water loss at the city level. Select the pilot area in around Gottera the selection of the area from the branch based on the following criteria. Hydraulically easily desecrate area, 24hr water availability, Customer not more than 1000, and more leakage complain. The sub-system that has isolated networks and production and consumption data were used to evaluate and compare the spatial distribution of water loss. There are several reasons for the high level of water loss in Addis Ababa., and some advisory solutions were briefly proposed for the major effect of the water loss like age of pipe networks, poor maintenance of networks, water scheduling, customer side leakage and illegal connection. The reduction of NRW (Non Revenue Water) by Water Balance Method shows the difference between predicted and actual water losses in water distribution network, The results also shows that after leakage reduction control works took place, the volume of water loss in water distribution network has reduce about 39% of the total production supply to the sub-system. The distribution system model was then used to evaluate three alternative scenarios to improve system performance. The objective of the first and second scenario was to increase the flow rate at taps of low supply; the third scenario aimed at adding taps to parts of the sub-system without easy access to running water. The first scenario consisted in opening valves to connect subsystems: it increased the flow rate at taps of large supply more so than at taps of low supply. This scenario was not recommended because it would quickly drain parts of the water supply.
Prediction of Sediment Inflow to Gefersa Reservoir (Using Swat Model) and Assessing Sediment Redution Methods
(Addis Ababa University, 2012-03) G/meskel, Fasil; Sileshi, Yilma (PhD)
Sediment transport is a worldwide environmental problem that degrades soil productivity, water quality, causes sedimentation to the reservoirs and increases the probability of floods. Gefersa reservoir, one of the surface water supply sources of Addis Ababa city for the last 70 years, face this problem. The reservoir supplies an average of 30,000m3 of treated water per day to the city. Based on the 1979 and 1998 bathymetric surveys, with the assumption of linear yearly siltation rate there is 22,252 m3/year of sediment inflow to the reservoir. In terms of soil loss from the catchment area, this constitutes a loss of 575 tons/km2/year contributed by the catchment area. In this study, Soil and Water Assessment Tool (SWAT) was used to calibrate and validate a hydrologic component and sediment yield of Gefersa watershed. Back-calculation process was carried out to estimate the natural inflow to the Gefersa reservoir. Sensitivity analysis, model calibration and validation were also performed to assess the model performance. Nine highly sensitive parameters were identified of which curve number (CN2) was the most sensitive one. The coefficient of determination (R 2 ), Nash-Sutcliffe (E NS ) and the percent difference for a quantity (D) was used to evaluate model performance during calibration and validation. Results found were satisfactory and plausible for ungauged station i.e. R 2 = 0.78. E NS = 0.77 and D=-15.3 for calibration and R 2 = 0.72, E NS = 0.70 and D=-20.7 for validation period. Sediment were calibrated and validated on annual basis using D i.e.-1.37 for calibration and -6.9 for validation. Four scenarios are developed to observe the impact of land use changes. Based on this, change of 53% and 16% forest to agriculture resulted in 74.5% and 52.89% increase in sediment load. And change of 35% and 18% rangeland to agriculture land increase 40.47% and 29.51% increase in sediment load .Based on results of modeling, sediment reduction methods in the catchment as well as recovering storage capacity are proposed. Of the available reservoir sediment management approach, watershed management is the best method to reduce the yield of sediment and its entry into the reservoir. Periodic sluicing of sediments through operation of bottom outlet gates would also help to ease the problem. Key words: - Gefersa, Sediment, SWAT Watershed, Bathymetric survey
Effect of Topography in Satellite Rainfall Estimation Errors: Observational Evidence across Contrasting Elevation in the Blue Nile Basin
(Addis Ababa University, 2013-05) Gebrehiwot, Niguse; Mekonnen, Gebremichael (PhD); Menberu, Meles (PhD)
In this study, the effect of topography on spatial and temporal variability of rainfall on local (25 km by 25 km grid) scale was analyzed across two contrasting elevation locations. We deployed 10 in high elevation grid (average elevation 2097m) and 9 tipping rain gauges in low elevation grid (average elevation= 695 m). Based on high quality data from the dense rain gauges, we evaluated the spatio-temporal properties of rainfall and evaluated the errors in widely used high resolution satellite rainfall estimates. Three satellite rainfall estimates; TMPA 3B42RT, TMPA 3B42V7 and CMORPH were evaluated using statistical and categorical verification measures. Our results showed that there is significantly large spatio-temporal variability of rainfall at local scale. Diurnal cycle also indicated that, low elevation receives more rainfall at early morning and the high elevation gets more rainfall between the afternoon and mid-night. Compared to the high elevation grid, low elevation grid receives less seasonal accumulation which is less frequent but intense rainfall. High elevation area has more rain events (varying 91 to 105) than low elevation (range; 66 to 7 5) using 6hour minimum inter-event time. In high elevation maximum event rain rate is 67mm/hour but low elevation is l 22mm/hour. Our results also demonstrated clear difference between the two grid cells not only in terms of rainfall magnitude and property but also on the accuracy of satellite rainfall estimates which could be attributed to topography. 3B42RT, 3B42V7 and CMORPH overestimated total 3hour mean rainfall in low elevation (with bias 1.2, I.land 1.5 and ME 0.2, 0.1 and 0.5 respectively). All underestimated in high elevation by 0.9, 0.8 and 0.7, and ME 0.2, -0.2 and -0.5 for 3B42RT, 3B42V7 and CMORPH respectively. The categorical statistics indicated that CMORPH performed better in its probability of detection (POD), but it is influenced by non rainy clouds. All products highly affected by miss rainy events on high elevation area and by more false alarms at low elevation area. From our results 3B42V7 is best in the low elevation and 3B42RT performed better in the high elevation area.
The Effect of Topography on Rainy season Rainfall Variability over Blue Nile River Basin
(Addis Ababa University, 2013-05) Habte, Shambel; Gebremicheal, Mekonnen (PhD)
The effect of topography on rainfall variability in the East Africa highlands is less studied rainfall processes. 37 rain gauges and 5 complete weather sensors along four transects in the complex terrain region of the Blue Nile River Basin were deployed. The transects span along elevation ranges from about 677 m in lowland areas around the border between Sudan and Ethiopia to 4000 m in the central Ethiopia mountains. High quality summer monsoon rainfall data from the newly deployed rain gauges along each transects was used for this study. Based on the high temporal scale data obtained from the sensors, we presented the effect of topography on the spatial and temporal variability of rainfall across transects, and rain event properties using statistical techniques. Over the Blue Nile basin, the maximum % of hourly rainfall occurrence with a range of 18% to 24% at south west of choke mountain and western edge of the basin namely, Mendi, Nejo, Gimbi and the minimum % of hourly rainfall occurrences is 10.78% at south east of choke mountain .There is high spatial variability of total rainfall depth during the study period over the Blue Nile River Basin which is varied from 471.17mm south east of the choke mountain to 1569.97mm north west of choke mountain near Tana sub bain water divide. There was observed two rain reach zones over the basin, one is at south west of the basin and the other on south west of Choke Mountain. The terrain elevation greater than 2500 m along transects have the capacity to block the moist air movement over the basin. There is high variability of rainfall at relatively high elevation stations compared to low elevations at various temporal scales (15 min, 30 min, 1 hr, 3 hr and daily). Generally low total rainfall depth and frequency is observed from late morning to early after noon (10:00 to 14:00 LST) on each LST and high total rainfall depth and frequency from 4:00 to 7:00 after midnight and 15:00 LST to 19:00 LST during the afternoon while stations at Zanbit, chagni, Anjeni, Kuchit the low total rainfall depth and frequency for each hour during the day is from mid night to late morning and high total rainfall depth and frequency is only during afternoon which are located at the foot and mid elevation of mountain Unlike other station over the basin. The rain event properties, rain event depth, rain event duration, mean event intensity increase as elevation increase while Inter event time decrease as elevation increase. These results on the rainfall variability, effect of topography on rainfall rate and space time variability have significant importance for the understanding of rainfall processes, and its distribution, for evaluation of accuracy of satellite based rainfall estimates, for designing of ways of merging satellite rainfall estimates and ground based observations given sparsely distributed rain gauges. Keywords: Topography, Transect, rainfall variability, rain event properties, rainy season, Blue Nile River Basin
Error in High–Resolution Satellite Rainfall Products in Streamflow Prediction in Birr Watershed, Ethiopia
(Addis Ababa University, 2013-05) Solomon, Nebiyu; Gebremicheal, Mekonnen (PhD)
The main objective of this study is to evaluate the performance of high – resolution satellite rainfall products (TMPA 3B42RT, 3B42V6, and 3B42V7) under sparse ground based data and complex topography medium sized watershed (Birr at 952.8 km2 ) in Blue Nile River basin Ethiopia through semi – distributed hydrological model HBV – light for daily streamflow simulation. First, the model is calibrated for the watershed to average rainfall input from rain gauge for the period of 2003 – 2008. Then the calibrated parameter values are used for daily streamflow simulations using rainfall input from each satellite products; comparison of the magnitude of rainfall and simulations to the observed streamflow at the outlet of each watershed forms the basis for the conclusions of this study. The comparison results of rainfall magnitudes revealed that both new version 7 TMPA 3B42RT and 3B42V7 rainfall estimates gave reasonably accurate result compared to rain gauge rainfall estimates. This result reveals that, in this region, 3B42RT accurately estimated the total average rainfall with negligible bias, but underestimated the seasonal rainfall with % bias less than - 11 %; while very small overestimation of average seasonal and total rainfall observed in 3B42V7 rainfall estimates with % bias less than 6%. However; version 6 TMPA 3V42V6 rainfall estimates consistently underestimated both the total and seasonal rainfall with % bias greater than – 40%, which probably suggests that rainfall estimates based on TMPA 3B42V6 can’t be a replacement of rain gauge measurements in this region. The result of this study revealed the applicability of satellite rainfall products as an input in hydrological model to simulate streamflow. Simulation from all rainfall inputs captured the trend of observed hydrograph with slight underestimation of large flood events. Simulation based on the new version 7 of TMPA 3B42RT and 3B42V7 gave reasonably accurate streamflow simulation for large flood events compared to others. On the other hand, the 3B42V6 simulation shows poor performance which underestimates consistently the daily streamflow. Dense rainfall network for rainfall measurement and stage – discharge rating curves should be given priority to improve the comparison results. Key words: Satellite rainfall products, HBV – light model, Birr watershed.
Runoff Estimation and Water Management for Holetta River, Awash Subbasin, Ethiopia
(Addis Ababa University, 2013-06) Mahtsente, Tibebe; Assefa, Melesse (PhD); Dereje, Hailu (PhD); Birhanu, Zemadim (PhD)
The hydrology of Holetta River and its seasonal variability is not fully studied. In addition to this, due to scarcity of the available surface water and increase in water demand for irrigation, the major users of the river are facing a challenge to allocate the available water. Therefore, the aim of this research was to investigate the water availability of Holetta River and to study the water management in the catchment using Geographical Information Systems (GIS) tool, statistical methods, and hydrological model. The rainfall runoff process of the catchment was modeled by Soil and Water Assessment Tool (SWAT). According to SWAT classification, the watershed was divided in to 6 subbasins and 33 hydrological response units (HRUs). The only gauged subbasin in the catchment was subbasin one that is found in the upper part of the area. Therefore, sensitivity analysis, calibration, and validation of the model was performed at subbasin one and then the calibrated model was used to estimate runoff at the ungauged part of the catchment. The performance of SWAT model was evaluated by using statistical (coefficient of determination [R2], Nash-Sutcliffe Efficiency Coefficient [NSE] and Index of Volumetric Fit [IVF]) and graphical methods. The result showed that R2, NSE, and IVF were 0.85, 0.84 and 102.8 respectively for monthly calibration and 0.73, 0.67 and 108.9 respectively for monthly validation. These indicated that SWAT model performed well for simulation of the hydrology of the watershed. After modeling the rainfall runoff relation and studying the availability of water at the Holetta River, the water demand of the area was assessed. The survey form was used to identify information, which includes the number of Holetta River consumers, major crops grown by irrigation and the total area coverage. CropWat model was used to calculate the irrigation water requirement for major crops. Based on the result of CropWat model and survey analysis, the irrigation water demand for the three major users of Holetta River was calculated. The total water demand of all three major users was 0.313, 0.583, 1.004, 0.873 and 0.341 MCM from January to May respectively. The available river flow from January to May was taken from the result of SWAT simulation at subbasins 2,3,4 and 5. The average flow was 0.749, 0.419, 0.829, 0.623 and 0.471 MCM from January to May respectively. From the five months, the demand and the supply showed a gap during February, March and April. This indicated that there is shortage of supply during these months with 0.59 MCM. Therefore, in order to solve this problem alternative source of water supply should be studied and integrated water management system should be implemented.
Remote Sensing Based Estimation of Evapo-Transpiration Using Selected Algorithms; The Case of Wonji Shoa Sugar Cane Estate
(Addis Ababa University, 2013-06) Mulugeta, Genanu; Tena, Alamirew (Ph.D); Gabriel, Senay (Ph.D)
The goal of every grower is to practice irrigation management to fulfill water needs profitably, safely, and in an environmentally responsible way. For this, accurate knowledge of the amount of evapotranspiration (ET) is critical. The focus of this study was to estimate and compare the actual evapotranspiration (ETa) of the Wonji Shoa Sugarcane Estate using different remote sensing algorithms. The daily ETa of the sugarcane was estimated and thematically mapped pixel-by-pixel using Surface Energy Balance Algorithm for Land (SEBAL), Simplified Surface Energy Balance (SSEB) and Operational Simplified Surface Energy Balance (SSEBop) algorithms on Landsat7 ETM+ and MODIS images acquired on four days in 2002. The algorithms were based on image processing which uses spatially distributed spectral satellite data (visible, near infrared and thermal infrared) and ground meteorological data to derive the surface energy balance components. The results obtained revealed that the ranges of the daily ETa estimated on January 25, February 26, September 06 and October 08, 2002 using SEBAL were 0.0 - 6.85, 0.0 – 9.36, 0.0 – 3.61, 0.0 – 6.83 mm/day; using SSEB 0.0 - 6.78, 0.0 – 7.81, 0.0 – 3.65, 0.0 – 6.46 mm/day, and SSEBop were 0.05 - 8.25, 0.0 – 8.82, 0.2 – 4.0, 0.0 – 7.40 mm/day, respectively. The Root Mean Square Error (RMSE) values between SSEB and SEBAL, SSEBop and SEBAL, and SSEB and SSEBop were 0.548, 0.548, and 0.99 for January 25, 2002; 0.739, 0.753, and 0.994 for February 26, 2002;0.847, 0.846, and 0.999 for September 06, 2002; 0.573, 0.573, and 1.00 for October 08, 2002, respectively. The standard deviation of ETa over the sugarcane estate showed high spatio-temporal variability perhaps due to soil moisture variability and surface cover. Dry periods exhibit greater variability compared to wetter periods. Generally during the dry season, ET is limited to the well watered sugarcane fields and water storage areas only. During the peak rainy season, ETa was high throughout the entire sugarcane estate. All the three algorithm results showed that generally well watered sugarcane fields in the mid-season growing stage of the crop and water storage areas had higher ETa values compared with the other dry agricultural fields confirming that they consumptively use more water. The evaporation fraction (ETrF) results also followed the same pattern as the daily ETa over the sugarcane estate. Comparison of ETa obtained from the MODIS Product (MOD16) with those obtained from the Landsat based algorithms resulted in a very poor correlation. The total crop and irrigation water requirement and effective rainfall estimated using the Cropwat model were 2468.8, 2061.6 and 423.8 mm/yr for January 2001 planted and 2281.9, 1851.0 and 437.8 mm/yr for March 2001planted sugarcanes, respectively. The mean annual ETa estimated for the whole estate were 107 Mm3, 140 Mm3, 178 Mm3 and 80 Mm3 using SEBAL, SSEB, SSEBop and MOD16, respectively. Though the algorithms need to be validated through field observation, either of these algorithms tested in this study have potential to be used for effective irrigation water management.
Understanding Runoff Generation Processes and Rainfall Runoff Modeling in Meja Watershed
(Addis Ababa University, 2013-06) Solomon, Berhane; Birhanu, Zemadim (PhD); Dereje, Hailu (PhD); Assefa, Melesse (PhD)
Understanding the basic relationships between rainfall, runoff, soil moisture and ground water level are vital for an effective and sustainable water resources planning and management activities. But so far there are no hydrological studies in Meja watershed that aims to understand the watershed characteristics and runoff generation processes. This study was conducted to understand runoff generation processes and model rainfall runoff relationship in Meja watershed having a drainage area of 96.6 km2.The watershed is one of the three research sites of International Water Management Institute (IWMI) developed in early 2010 in the upper Blue Nile Basin Ethiopia. In the study, primary data of soil moisture, shallow ground water level, rainfall and runoff were collected from the hydrological monitoring network in the watershed. Two nested sub- watersheds namely Galessa and Kolu were defined in the watershed for detail analysis of hydrologic variables. Galessa has drainage area of 1.6 km2 and Kolu has a drainage area of 2.5 km2. Hydrological models like HBV and RRL SMAR were configured to understand the relationship between rainfall and runoff in the watershed. Relationships between rainfall, soil moisture, shallow ground water level and runoff were developed to understand runoff generation processes in the watershed. Analysis of rainfall data indicated weak daily correlation (r2<0.35) of areal rainfall between Galessa, Serity and Kolu and similar annual total and average rainfall of the three sites of Meja watershed. However monthly correlation of areal rainfall between the three sites was better than daily correlation (r2>0.8). According to one year and three months data, there is no strong daily rainfall and runoff relationship (r2<0.5) in Meja and Kolu which is nested sub - watershed; this may be due to abstractions such as irrigation and human interventions in the watershed. Ground water level and runoff has strong relationship (r2>0.65) in monthly basis of Kolu nested sub watershed but there is moderate relationship of rainfall and ground water level. There is spatial variability of soil moisture content in Meja watershed, this variation occurs due to heterogeneity of the soil, which means the places are different in soil texture and also the variation is due to vegetation cover and change of slope. There is strong linear relationship of rainfall and monthly averaged volumetric soil moisture in most soil moisture layers of Meja and its nested sub-watersheds. The general relationship between runoff and monthly averaged soil moisture at different layers in Meja watershed and Kolu is strong. Analysis of rainfall runoff models indicated that relationships of rainfall with observed and simulated runoff was similar.HBV model performs better than RRL SMAR model in Meja and Kolu. RRL SMAR model couldn’t capture low flow in Meja and Kolu. This inaccurate result of SMAR model in Kolu sub-watershed may be due to inability of the model to simulate runoff in very small catchments like Kolu.
Hydrogeological and Hydrological Characterizations and Classification using Remote Sensing Datasets and Models
(Addis Ababa University, 2013-06) Guta, Wakbulcho; Awange, Joseph L. (Prof.); Mekonnen, Gebremichael (PhD)
Ethiopian water resource is facing a range of challenges in water management caused by several natural and man-made impacts, namely over exploitation, deforestation, land degradation and climate variability. Understanding the spatio-temporal characteristics of water storages is therefore crucial for the country, since the welfare of the society depends on the availability of water. The prime objective of this study is to apply remotely sensed and model data to Ethiopia in order to i) analyze the inter-annual, intra-annual and seasonal variabilities of Total Water Storage (TWS), ii) understand the relationship between TWS variations, rainfall and soil moisture anomaly, and iii) study the relationship between the characteristics of aquifers’ and TWS anomalies. The data used in this study includes; monthly gravity field data from the Gravity Recovery And Climate Experiment (GRACE) mission to assess the variation in TWS; monthly rainfall data from the Tropical Rainfall Measuring Mission (TRMM) to assess the response of water storages to the incoming water mass and the effect of rainfall on TWS, and the hydrological model data of Global Land Data Assimilation System (GLDAS) to obtain soil moisture. Our investigation covers a period of 8 years from 2003 to 2011. The results of the study shows that the western part and the north-eastern lowland of the country lost water at a rate of not less than 0.108 cm/year, whereas all the other regions gained water mass at a rate of more than 0.60 cm/year. The impact of rainfall seasonality was also seen on TWS changes, with losing seasons being summer and autumn, and gaining seasons being spring and winter for majority of the regions. From the TWS duration curve (TDC), the percentage time of water mass loss in all regions is also observed as 55% of the study period. Applying the statistical method of Principle Component Analysis (PCA) on TWS, soil moisture, and rainfall variations shows the dominant annual water variability in the western, north-western, northern and central regions, and the dominant seasonal variability in the western, north western and the eastern regions. A correlation analysis between TWS and rainfall indicate a minimum time lag of zero and maximum of six months, whereas no lag has been seen between soil moisture anomaly and TWS. A significant increase in TWS deficit has also been seen in the central highlands of the country over the period of three years (2003 to 2006) with Total Storage Deficit Index (TSDI) ranging from nearly zero in 2003 to -500 % in western region and -800 % in the central and northern regions of the country in 2006. A classification of the country based on TWS Duration Curve shows that TWS variation is high in the western and low in the north eastern parts. The delay response and correlation coefficient between rainfall and TWS is also related to recharge mechanism and revealed that most regions of the country receive indirect recharge. The hydrological characterizations and classification has been carried out as Part-II, separately from the hydrogeologic characterization section only for watersheds in one selected basin which is located in region 2. The Part-II finding shows the possibility of characterizing and classifying watersheds in a data limited regions through the help of remote sensing instruments and models. Here, the characterization and classification has been made using the catchment climate, catchment function and catchment structure descriptors. The detailed findings of this section have been described in a separate “Abstract” provided at the beginning of Part-II.
Evaluation of Drainage system in Kebena stream catchment, Addis Ababa
(Addis Ababa University, 2013-08) Tafete, Eskedar; Ayalew, Semu(PhD)
This study has investigated the overall challenges of the urban drainage system in three sample Woredas (Woreda 6, 7 and 8) in Kebena Stream Catchment of Addis Ababa. These Woredas were selected because of the fact that they are the most flood prone areas and representative to address the objectives of this study. Rapid expansion of built environment and poor urban drainage managements are the major problems in the study area. The objective of this research is to evaluate the existing storm water drainage system of Addis Ababa by selecting sample representative sample area. An exploratory and descriptive type of research methods were used to describe and explore the existing condition of the general urban drainage system and the natural water ways with the help of Ms-excel, AutoCAD and ArcGIS, HEC-GEOHMS, Google earth, Flow Master and the results have been presented with known statistical tools. The result of this study shows that the major cause of flooding in the drained part of Addis Ababa is a changing flood regime due to mainly the expansion of built environment. Sample design flood calculation based on the guideline for three sample Wereda’s shows, in Woreda 6, of all the drains 17.74% of the drainages are capable of conveying safely the runoff in to the water ways. In woreda 7 out of the total drains only 29.75% of the drains have the capacity to convey the run off in to the stream. And also in woreda 8 out of the total drains only 16.5 % have the required capacity. Apart from significant flood regime change, field visits and survey reveals that there is inadequate integration between road and urban storm water drainage lines, luck of sustainable urban storm management, extraordinary challenge of damping solid and liquid waste water in the drainage system. Before, the urban drainage becomes a permanent socio-economic nuisance and brings irreversible damage to the city, this study strongly recommends immediate implementation of Best Management Practice (BMP) that is supported by strong institutional setup, policy framework, and the public at large.
Prediction of Soil Water Characteristic Curve Based on Gsd and Pi for Red Clay and Expansive Soils Found In Addis Ababa
(Addis Ababa University, 2013-08) smail, Nuru I; Seged, Hadush (PhD)
Many researchers have done researches on unsaturated soil mechanics worldwide to bring the unsaturated soil mechanics in to practices. Among those researches some of them focused on simplifying the complex and expensive testing mechanism by developing models which can be used to predict the unsaturated soil parameters from basic soil prosperities such as Grain Size Distribution (GSD) and Plasticity Index (PI) along with the saturated shear strength parameters. Soil water characteristic curve (SWCC) was proved to have good relationship with the unsaturated soil parameters. In this study an attempt was made to check whether those developed models would work for expansive and red clay soils found in Addis Ababa. Using the model developed by Fredlund and Xing (1994) along with the correlation equation given by Perera et.al (2005), family of SWCC for soils found in Addis Ababa has been plotted. It was observed that the family of SWCC plotted was out of the widely referenced family of curves developed by Zapata et.al (2000) to some extent. Even though the family of curves seems to be out of the range provided by Zapata et.al (2000), the model gave good prediction for the unsaturated shear strength parameter Φb. The percentage error between the measured values of unsaturated shear strength parameter Φb in previous researches of Habtom (2010) and Getaneh (2010) with predicted unsaturated shear strength parameter Φb in this study was compared. For red clay samples the percentage error lie in the range 2.07 to 6.37% for suction ranges of 36.67 to 52.9 kPa and at lower suctions of 16.75 and 21.5 kPa the percentage error ranges from 11.42 to 25.39% . For expansive soil samples for suction of 23.1 and 32.9 kPa, the percentage error is in the range from 3.86 to 6.13%. For suction values of 14.5 and 52 kPa the range of error is about 9.45 to 13.40% and for suctions of 38.8 and 48.6 kPa the error lies between 18.94 and 38.84%.
Ensuring Functional Sustainability of Water and Sanitation Developments in Rural Areas (Southern Ethiopia)
(Addis Ababa University, 2014-04) Israel, Fiseha; Sahilu, Geremew (PhD)
Ensuring functional sustainability of water and sanitation developments throughout the design period is vitally necessary. It helps to identify the main causes of non functionality and indicate the troubleshooting for non functionality per scheme system components at the stage of design, construction and service period. To identify the major causes of non functionality the research has employed both primary and secondary data sources. Secondary data was collected from respective governmental and non-governmental organization at federal, state and woreda level. Primary data, on the other hand, was obtained using questionnaire, Focus group Discussion (FGD) and observation. Data from the secondary and primary sources enabled the researcher to scan and investigate more than 95 % of water and sanitation schemes in Chencha woreda rural areas. The common rural water and sanitation technologies include hand dug well, shallow well, spring with gravity distribution, spring at spot and simple pit latrine. All have been studied and evaluated for their cause of non functionality. The research found that 87 % of non functionality occurred before its estimated design period, which is within ten years. But the average non functionality occurrence of the schemes is between six years up to seven years. The most common non functionality causes are poor design, below the standard construction and poor institutional set ups of water and sanitation infrastructures. It includes: spring capping failure, management and financial problems, construction materials problems, source yield decreasing, poor quality of water, pumping system failure, poor quantity of water and pipe line failures. Water and sanitary schemes are functionally sustainable, only when social, financial, technical, institutional and environmental factors are integrated with every project life stages. The stages are needs assessment, conceptual design, design and action planning, implementation, and operation and maintenance. To get rid of non functionality every system component design and construction activity should be in accordance with the applicable design and construction methods. All respective governmental, nongovernmental and community stakeholders should carry out responsibility for functionality and sustainability of water and sanitation schemes. It is impossible to meet the functionality of water and sanitation schemes developments, without the integration of all respective bodies in all project life stages through feasibility study, designing, construction and service periods
Hydraulic Network Modeling of the Existing Water Distribution System of Addis Ababa City (Legedadi sub system as a case study)
(Addis Ababa University, 2015-03) Tessema, Dureti; Taffese, Mebrate (PhD)
The primary goal of this study is to review the hydraulic performance of the existing distribution system of the city, Addis Ababa, Legedadi subsystem which is aimed to help the city understand its distribution system needs and assist them in long-term planning of water assets. The scope of the study is to evaluate the performance of the existing drinking water distribution system using hydraulic simulation software in integration with GIS, and recommends the possible remedies to improve the efficiency of the existing system. The hydraulic simulation software used for this study is Water CAD V8i distributed by Bentley Systems. Bentley Water CAD V8i was selected due to ease of model building and operation and its greater programming capabilities as compared to EPAnet. Hydraulic modeling of the system is performed by considering the system as a continuous supply system, and the evaluation process adopted the Extended Period Simulation method. The system has been checked for different scenarios and alternatives to deepen our investigation. Considering, the model is calibrated at specific locations and the results with field measurements show reasonable difference, so that we use some fine tuning using Hazen Williams C –value to align with the field data. As a matter of fact, I have proved that, there is hydraulic inefficiency in the existing water system to serve the city (Legedadi sub system) and to cope with the future demand. The outputs show that the network is exposed to relatively high and low values of pressure and velocity, which have negative effects on the performance of the network as well as in the water quality of the system. Besides, failure is forecasted in considering the age of pipes for reinstallation and maintenance. As a result, Pipes with ages more than 30 years are replaced and over and under sized pipes have been re-sized. Consequently, the Hazen Williams C-value has been totally improved and it enhances the system performance. The evaluation study of the water hammer in the Addis Ababa distribution system, which has been implemented to investigate the effects of this phenomena shows that the water hammer values increase by increasing the velocity of water in pipes, and the values of shock pressures were within the limits of the shock pressures in water pipes systems. In the study, the major hydraulic parameters, the variations, and the relations between them and other factors, which control the performance of the water supply networks are considered and discussed in detail during analysis. To this end, the network is assessed and possible corrections are given for Optimum water supply network even using Darwin Optimum Pipe Network Designer tool so as to at least the system meet the required design criterion as a constraints. Moreover, the Legedadi subsystem has been categorized for 14 optimum Pressure zones with their corresponding Reservoirs (Pumping stations).
Rainwater harvesting for Addis Ababa city; a Case of Jemo Condominium site
(Addis Ababa University, 2015-05) Kebede, Ashebir; Sahilu, Geremew(PhD)
The main objective of this thesis is to assess the potential of rain water harvesting practice to solve problems of both increasing water demand and storm water in Addis Ababa city. The research is carried out based on case-study of Jemo condominium site, from November 2014 to May 2015 that is found in the south western part of Addis Ababa city. The site has about 337 residential blocks with an average roof area of 286m2 and 50 communal blocks with an average roof area of 216m2 roof area and serves for about 9,800 households in which they serve for about 42,140 population. A descriptive quantitative study was carried out in order to achieve the objectives of the study. A monthly rainfall data, catchment characteristics, roof material, population data, water consumption and water demand data were collected from primary and secondary sources. People's attitude and practice towards rainwater was also assessed. The collected data was analyzed using different tools including samsamwater RWH model, Google earth, rainwater harvester, AutoCAD, MS Excel spread sheets and etc. Calibration and validation of the finding was carried out using appropriate instruments. Based on the findings the total annual rainfall in an average year is 1219mm. A 6 months of water consumption data of Jemo I collected from AAWSA Mekanisa branch shows that only 30% of the demand is supplied to residents by the municipality at private water pipes. The average annual RWH potential at Jemo I condominium site is not enough to fulfill the total water demand at this site. However, it might still be worthwhile to construct a rainwater harvesting system. With a storage reservoir of 113400 litres (113.4 m3) for a single building a rainwater harvesting system could provide about 36% of non-potable demand and RWH can reduce water demand problems by 36% for only non-potable demands and 10% for all domestic demands based on the current AAWSA standard. The total cumulative runoff generation from this site throughout the year is 723,450m3 and the amount of water that RWH system only from roof tops can harvest could be 90,290.2m3. With this estimation RWH from roof tops at Jemo condominium site can reduce runoff by 12%. This contributes for sustainable storm water management and best management practices. Therefore RWH has many benefits once it is applied for any building for sustainable alternative water supply and sustainable storm water management. The big problem here will be the size of storage tank should be big enough since the rainfall is concentrated for limited months which will not be cost effective but related to other interventions RWH is more cost effective and sustainable than other options. Key words: Rainwater, Harvesting, water demand, Stormwater, Alternative source, Non potable, Jemo, Domestic, Urbanization, Condominium, Addis Ababa, Ethiopia

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