Water Resource Engineering

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Advancing Bioassessment of Water Quality in Wadeable Rivers and Streams in Ethiopia
(Addis Ababa University, 2024-01) Melaku Getachew; Seid Tiku (Prof.); Geremew Sahilu (PhD); Worku Legesse (PhD); Mary Kelly-Quinn (Prof.)
Numerous international bilateral, plurilateral, and multilateral treaties and conventions were signed between countries to protect human health and environmental pollution. However, most of the signatory countries fail to implement the treaties or conventions (Willis, 2012). For example, though Ethiopia has endorsed or ratified the Basel, Stockholm, and Rotterdam agreements, its legislations and policies for environmentally sound management of hazardous chemicals and wastes are still in infancy and are inefficient in preventing the illegal dumping of waste as well as contamination of water, soil and air resources (Tadesse, 2009). This study reviewed the details of problems of surface water pollution in the metropolitan area of Addis Ababa and the upper Awash River catchment. Urbanisation, population growth, industrialisation without proper waste management facilities, unregulated agricultural practices, uncontrolled liquid and solid wastes, and law enforcement difficulties were the major gaps identified. Furthermore, there are significant gaps limiting efforts to address the magnitude of pesticide pollution in the catchment probably due to the shortage of laboratory facilities and the costs associated with the chemicals and equipment. This study forwarded important conclusions and recommendations to the respective stakeholders. To help the bioassessment of wadeable rivers and streams in Ethiopia, a macroinvertebrate kick sampling protocol has been developed using data from minimally impacted sites and testing it along the pollution gradients. Based on the results, the 2-minute RH kick sampling method is the recommended candidate for the bioassessment of wadeable rivers and streams in the country. Using the developed macroinvertebrate kick sampling protocol in this study, the impacts of the Koka Hydropower dam on benthic macroinvertebrate structure and composition were further investigated. Hydropower has been used for generations to provide reliable, fossil-fuel-free electricity (source of clean energy), water supply for domestic uses and agricultural irrigation, recreational opportunities, several flood-control benefits, as well as a stable system for navigation. However, several disadvantages have also been recognised because of the construction of hydropower dams. It is particularly severe in large dams where there has been extinction of the many fish and other aquatic species, huge losses of forest, the disappearance of birds in floodplains, erosion of deltas, loss of wetland and farmland, and many other irreversible impacts. These impacts can have economic and social (e.g. Community displacement) health implications (consequences). This in turn points towards the need to seek a balance between pros and cons associated with dam construction. Currently, most public and policymakers perceive only the advantages (pros) of the hydropower dam and the impacts mentioned above are largely neglected. To create awareness among stakeholders and to recommend possible solutions to the problem, it was very crucial to conduct the ecological impacts of hydropower dams on the macroinvertebrate communities that include aquatic insects, crustaceans, annelids, mollusks, nematodes, planarians, and other invertebrates as these organisms play a critical role in the transfer of energy from basal resources (bottom layer) (e.g., algae, detritus, and associated microbes) to vertebrate consumers in aquatic food webs, and they serve as the primary food resource for many commercially and economically important fish species. The investigation of the hydropower dam on the structure and composition of macroinvertebrate communities showed that the downstream reach was severely impacted by water pollution compared to the midstream and upstream reaches of the Awash River, however, the results were partly complicated by the nutrient pollution, particularly from the midstream reach. The major factor, amongst others affecting the downstream reach, the water flow change (river velocity) was highlighted as a key variable structuring the macroinvertebrate communities and a variable that can be altered by damming. Similarly, variation partitioning analysis was used to analyze the unique and shared effects of the three sets of predictor variables (environmental, land use, and spatial factors). The findings revealed that the three sets of predictors' shared variation in macroinvertebrate community composition was greater than their contributions. To put it bluntly, anthropogenic activities have a negative global influence on aquatic habitats. As a result, surface water biomonitoring is becoming increasingly crucial in estimating ecosystem deterioration and achieving environmental sustainability. Therefore, the development of methods kick sampling time) based on Ethiopian ecoregions to employ in the bioassessment of surface water quality has been mandatory. This would contribute to the assessment of water quality in wadeable rivers and streams in Ethiopia
Application of a Satellite Based Rainfall-Runoff Estimation: in Upper Omo-Gibe Basin to Simulate the Extreme Flood Event at Omorate
(Addis Ababa University, 2020-02) Samuel, Bekele; Elias, Tedla (PhD)
Satellite-rainfall products are recognized as an essential source of rainfall data, especially in the region where ground based measurements are unavailable. Therefore, the main objective of this study is to Apply a Satellite based Rainfall-Runoff estimation: in Upper Omo-Gibe Basin to simulate the extreme flood event at Omorate and with specific objective of evaluate the capabilities, applicability and limitations of satellite rainfall products such as CMORPH, TRMM 3B42v7 and PERSIANN, and inputs of hydrological models to simulate the Rainfall-Runoff by hydrological model NAM and preparing the Flood Hazard map in the lower water shed using MIKE-11,MIKE-21 and MIKE-FLOOD. These products and inputs were employed to simulate stream flow in the Great Gibe Watershed. The study period 2000-2012 was used for downloading and extracting the selected satellite rainfall estimates with daily-temporal and 0.250 x 0.250 spatial resolution. Sensitivity and uncertainty analysis, calibration and validation of the model were done using MIKE ZERO particularly the Sequential Uncertainty Fitting (SUFI-2) algorism for all rainfall inputs independently. The calibration period was from 2001-2005 leaving one years as a-warm up period and the validation period was from 2006-2012 for satellite rainfall based simulations as well as in situ based simulations. Based on the modeling results of Mike Zero models had showed better performance when calibrated with the in situ rainfall with model performance efficiency of Mean Absolute Error, Maximum Values and Standard Deviation models respectively while, the satellite rainfall estimates (TRMM-3B42v7 and CMORPH) showed relatively good performance when calibrated on the models with Mean Absolute Error (5.21,4.24), Max.Val. (73.74,32.97) and Std. Deva.(7.46,4.24) in the case of Asendabo with relative to the ground based measurements in both satellite based product respectively. But, PERSIANN satellite rainfall estimates showed poor performance for all Mean Absolute Error (3.78), Max. Values (33.06) and Std. Deva. (4.24) before bias corrected. The model output simulation results performance in analyzed of Rainfall-Runoff based up on the coefficient of determination and Nash-Sutcliffe coefficient, during the calibration it is found to be 0.509 and 0.64 respectively and the total water balance error during calibration is 14.75%. And during validation period 0.645 and 0.675 respectively with the total water balance error is 17.5%. Peak and low flows between observed and simulated hydrograph were found matching well. The simulated minimum and maximum runoff for 13 years’ period the maximum annual runoff varies between 1466.3 mm to 7525.4 mm. The simulated runoff was maximum for the month of August (6977.4 m3/s) and minimum for the month of April (5540.6 m3/s). The single flood event of year 100 in the upper part of Gibe confluence flood plain simulated using MIKE FLOOD, which integrated the calibrated and validated 1D MIKE-11 hydrodynamic model with 2D hydrodynamic model MIKE-21 for the flood plain.
Assessment of the Water Distribution Network of Metu Town Water Supply System, Ethiopia
(Addis Ababa University, 2016-11) Bogale, Benyam; Sahilu, Geremew (PhD)
Intermittent water distribution is the key problems of many water authorities in developing countries including Ethiopia. Hence, this research was conducted to carry out the assessment of the water distribution network of Metu town existing water supply system which is located in western Oromia region of Ethiopia. To examine the hydraulic performance of the water distribution network, water CAD modeling was adopted. Accordingly, different reviewed reports, percentage of Non-Revenue for water, and discussions with water service personnel were conducted to analyze water losses and leakage management practice in the town. As per the analyzed results; the current maximum water demand in Metu town is estimated at 4,206.93 m3/day, while small reservoirs capacity and low pump efficiency were observed in the town water distribution networks. According to simulated results; the maximum of 203.68m and 199.49m, and minimum of 5.36m and 2.97m water pressure head were examined in the transmission and distribution main, respectively. Further, the analyzed water losses result in Metu town indicates that about 34.64% of production is Non-Revenue Water. Thereby, apparent losses cover 21.12% of total loss and 13.52 % were physical losses. Accordingly, for the case of Metu town apparent losses are more significant, however physical losses contributed considerable volume of lost. In general, rising in water demand, small capacities of existing infrastructures and large volume of water loss were leads to intermittent water distribution in Metu. Hence, most of residences were not satisfied on the town water service. Therefore, it is significant to rehabilitate and improve the water distribution system capacities and providing more attention to water losses reduction policies and strategies are vital for remedial measures. KEY WORD: water distribution network, hydraulic water CAD modeling, water loss, leakage management, Metu town, Oromia region, Ethiopia.
Assessment of Vulnerability of Alluvial Aquifers of Transition Zone to Contamination: The Case of Danakil Basin, Northeastern Ethiopia
(Addis Ababa University, 2022-06) Kumneger, Mollalegn; Taye, Alemayehun (PhD)
Groundwater is indispensable to humankind, but with the increasing load over this precious resource, it has become necessary to study it in detail with geological as well as hydrogeological aspects to understand the nature of the groundwater resource of a Danakil basin to manage it well and use it sustainably, vulnerability assessment of the resource is conducted to highlight the areas which are more susceptible to contamination. In the present study, an attempt has been made to account for the groundwater vulnerability using an overlay index method, DRASTIC, which is used to prepare a vulnerability map using GIS, of the study area, Danakil basin. The DRASTIC Vulnerability index (DVI) is calculated as the sum of the product of ratings and weights assigned to each of the parameters on a scale of 1 to 10 and 1 to 5 respectively. And a 2D finite element groundwater flow and solute transport model were developed to simulate the spatial and temporal variations of the salinity intrusion in the alluvial aquifer of the Danakil basin taking into account the transition zone between freshwater and saltwater. The available historical records of water table levels were used to calibrate the developed model. Emphasis was devoted to the response of the transition zone to different pumping scenarios in the study area. The vulnerability index ranges from 50-149 and is classified into three classes it reduced approximately 20%, 50% and 30% of the area lies in low, medium, and high vulnerability zones. Results from the solute transport model also indicated that the saltwater intrusion problem has evolved during over-abstraction (pumping). Unlike previous investigations, this study presents the most qualitative assessment of the available groundwater in the alluvial aquifer under different pumping scenarios. In conclusion, Danakil basin alluvial aquifer is vulnerable to geogenic sources of salt intrusion due to over abstraction. Results can be an important input for policymakers in the development of sustainable groundwater protection and abstraction strategies for the region.
Biomarkers of Toxins in Improved Drinking Water and Diarrhea Patients of South Wollo Communities, Northern Ethiopia
(Addis Ababa University, 2022-04) Shibabaw Tadesse; Sirak Robele (PhD.); Adey Feleke (PhD); Jana Jass (Prof.)
The world's most vulnerable communities frequently drink contaminated water, which is linked to a variety of public health issues. Escherichia coli toxins are the most common types of contaminants found in association with disease in E. coli bacteria. They are found in nearly all pathogenic E. coli bacteria either released from the bacteria or E. coli cell or both transmitted via the feco-oral route. The objective was to evaluate the safety of improved water supplies using toxins as a biomarker and correlate with the toxins found in patient stools, and identify gaps between water quality and the global classification of improved water supplies in the South Wollo zone, Ethiopia. This dissertation reports the results of a laboratory-based cross-sectional study conducted in South Wollo, Ethiopia, from January 2019 to June 2020. Two hundred forty-eight samples of household water and patient stool were collected (in a 1:1 match) and toxins were tested using polymerase chain reaction (PCR). The targeted toxins used were (enteroaggregative E. coli heat-stable enterotoxin 1 (EAST1), heat-stable (Sta); shiga-like toxin 1 (Stx1), shiga-like toxin 2 (Stx2), and heat-liable (LT)), which cause diarrhea when people drink contaminated water. A survey questionnaire was used to gather information on the types of water sources, as well as the knowledge and practices of the respondents about household water treatment methods. To analyze the data and examine the relationship between the variables, descriptive statistics, Chi-square (χ2), Fisher’s exact test, logistic regression, and Pearson’s bivariate correlation coefficients were used. In general, 24% of households had positive results from both water and stool samples, 63% [Confidence Interval (CI): 55- 67%] had positive results from water samples only, and 46% [CI: 37- 49%] had positive results from only stool frequently, with 33% in the water and 38% in the stool. Frequently founded contaminants in household water brought from improved water sources were the toxins ESAT1, Stx1, and LT, with Sta the least founded (2%). There were fewer (13%) toxins detected in shallow groundwater sources than in piped water, a statistically significant difference (P=0.031). There was a lower proportion of toxins detected in those who did not know about and used cloth filters than in those who did, and the negative relationship is statistically significant (P=0.017). Approximately one-third of the improved water services sampled, which are considered ‘functional’ by international standards, do not provide potable water due to fecal and toxin contaminants. There was a significant positive correlation (r = 0.412) between toxins in the stool and toxins in the water (P < 0.05). The findings indicate that toxin biomarkers can be used to monitor water safety. Water quality parameters are not currently considered in the classification of basic water services. This suggests that international efforts to address SDG 6 should incorporate water quality and its indicators as a key parameter to better track international progress towards ‘clean water and sanitation’ efforts. More research is needed to determine the sources of pathogenic microbial markers that cause water-related diseases, such as diarrhea, as well as focus areas for water contamination prevention.samples for toxins. Out of the five toxins examined, EAST1 was the one that was found the most
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.
Drinking Water Chlorination Byproducts and Cancer Risks in Addis Ababa, Ethiopia
(Addis Ababa University, 2023-06) Nebiyou Tafesse; Argaw Ambelu (Prof.); Sirak Robel (Assoc. Prof.)
Background: Disinfection byproducts (DBPs) from chlorinated drinking water have been linked to an increased risk of cancer in the bladder, stomach, colon, and rectum. No previous evidence showed the independent trends and prevalence of these cancers in association with DBPs in Ethiopia. Therefore, the study aimed to determine the prevalence and trends of disinfection byproducts related cancers (DBRCs) in Addis Ababa, Ethiopia. Close scrutiny of the published studies showed that this is the first study conducted indicating the association between drinking water source, chlorinated water and colorectal cancer (CRC) in Ethiopia. The present investigation is also the first study in assessing the trihalomethanes level and lifetime cancer risks in the drinking water supply in Addis Ababa, Ethiopia. Methods: A retrospective record review using the Addis Ababa Cancer Registry (AACR) was conducted in Addis Ababa, Ethiopia. The AACR collects data on cancer cases submitted by three public hospitals and twelve private facilities (the only cancer treatment centers) in Addis Ababa, Ethiopia. Spatial data sets were produced and classified into households receiving chlorinated surface water and unchlorinated groundwater. The Cochran-Armitage trend test was used to evaluate whether there was a disinfection byproduct-related cancers (DBRCs) trend among communities receiving chlorinated water. Negative binomial regression was used to analyze the incidence rate. A facility-based matched case control study was conducted in Tikur Anbessa Specialized Hospital (TASH) involving 224 cases and 448 population controls from June 2020 to May 2021. A multivariable conditional logistic regression was used to identify risk factors of CRC. Stratified analysis was used to detect confounding factors and effect modification. A cross-sectional study design was used to collect water samples in the water supply networks of Addis Ababa, Ethiopia. One hundred twenty (120) drinking water samples were collected from 21 sampling points in Addis Ababa, Ethiopia. The three sampling areas were Legedadi, Gefersa and groundwater sources. The United States Environmental Protection Agency (USEPA) protocol and practice for sample collection and handling were followed. The trihalomethanes (THMs) were separated by a DB-5 capillary column and detected by GC-ECD (gas chromatography-electron capture detector). Spectrophotometric and Insitu methods were used for physicochemical parameters. Canonical Correspondence for data analysis of trihalomethanes and environmental variables using CANOCO 4.5. Cancer and non-cancer risks of THMs via inhalation, ingestion and dermal contact routes have also determined. Results: A total of 11,438 cancer cases were registered between 2012 and 2016, and DBRCs accounted for approximately 17%. The majority of the cases were females; 7,706 (67%). The prevalence of DBRCs was found to be higher in communities supplied with chlorinated water. Approximately 56% of colorectal cancer patients and 53% of stomach cancer patients are known to be using chlorinated surface water for drinking regularly. Of 214 colorectal cancer (CRC) cases, 148 (69.2%) used chlorinated water whereas out of 428 controls 161 (37.6%) used chlorinated water. In the final regression model, drinking chlorinated surface water (adjusted matched odds ratio (adjusted mOR) = 2.6;(95% CI: [1.7 ̶ 4.0]), history of swimming (adjusted mOR= 2.4; 95% CI: [1.4 ̶ 4.1]), years at the place of current residence (adjusted mOR=1.5; (95% CI: [1.1 ̶ 2.2]), hot tap water use for showering (adjusted mOR; 3.8= (95% CI: [2.5 ̶ 5.9]) were significantly associated with CRC. The mean concentration of total trihalomethanes in drinking water in Addis Ababa was 76.3 μg/L. The concentration of chloroform in the drinking water supply in Addis Ababa, Ethiopia, ranged between 4.03-79.4μg/L. The results of the average THM concentration followed the order TCM (Trichloromethane) >BDCM(Bromodichloromethane) > DBCM (Dibromochloromethane) > TBM (Tribromomethane). The mean total THMs in the Gefersa and legedadi water supply systems were 77.4μg/L and 69.66μg/L respectively. The lowest THMs concentration was recorded in the groundwater supply system (15.5μg/L). The residual chlorine, phosphates, UV absorbance at 254 nm, and combined chlorine had positive correlations with THMs formation. However, electron conductivity had negative correlation with THMs formation. The cancer risk study discovered that among the examined routes, ingestion causes the greatest risk. The lifetime cancer risk by chloroform contributes the highest (72%) of the total risk, followed by BDCM (14%), DBCM (10%) and bromoform (4%). Conclusions: The prevalence of DBRCs in this study was found to be high. The colon cancer trends increased substantially in Addis Ababa, Ethiopia. Drinking chlorinated water for extended years is a significant risk factor for CRC in Addis Ababa, Ethiopia. In addition, hot tap water use for showering, and swimming have higher level total THMs than groundwater supply. The residual chlorine, UV absorbance, phosphate and hardness as calcium, and electron conductivity were found to be the main predictors determining the abundance and distribution of trihalomethanes. The cancer risk study discovered that among the examined routes, ingestion causes the greatest risk. The monitoring and regulation of the THMs is required on a regular basis to analyses trends and guide the water treatment and distribution system.history are risk factors for CRC. Surface water supply networksAnalysis (CCA) or Redundancy Analysis (RDA) was used
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
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
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.
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.
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.
Groundwater Recharge Estimation: The Case of Hormat-Golina Sub-Basin, Northern Ethiopia
(Addis Ababa University, 2024-01) Seyoum Bezabih; Taye Alemayehu (PhD)
Water is one of the most essential commodities for mankind and the largest available source of fresh water is obtained from groundwater. The Hormat-Golina sub-basin is one of the groundwater-based irrigation areas located in north wollo zone of Amhara region. Due to the erratic nature of rainfall (both time and space) distribution in the area, people often fail to maintain the soil moisture requirement for growing crops. Thus, the need for agricultural development using groundwater resources in the area is growing continuously. However, the ambitious plans for expanding irrigation have not been adequately strengthened through the assessments of groundwater reserves and groundwater recharge estimations. Understanding the spatial variability of groundwater recharge in response to distributed Land-use, soil texture, topography, groundwater level, and hydrometeorological parameters is significant when considering the safety of groundwater resource development. Thus, this study was aimed at estimating the spatial groundwater recharge of Hormat-Golina sub-basin, in northern Ethiopia using a spatially distributed water balance model (WetSpass). Input data for the model were prepared in the form of grid maps using a 30 m grid size and the parameter attribute tables were adjusted to represent the Hormat-Golina sub-basin condition using expert knowledge and scientific literature. The model result shows there was a good agreement between the observed and simulated surface runoff with R2=0.90 and NSE= 0.85. The results of the model indicated that the long-term temporal and spatial average annual rainfall of 828.5 mm was partitioned as 156.4 mm (19%) of surface runoff, 616.7 mm (73%) of evapotranspiration, and 55.4 mm (8%) of recharge. The recharge corresponds to 4.2*105 cubic meters (m3) for the Hormat-Golina sub-basin (with an area of about 698.25 km2) from which 83% of the recharge takes place during the rainy /wet/ summer/ season, while the remaining 17% takes place during the bega (dry) season. The highest recharge was observed in forest land with sandy soil. The analysis of the simulated result showed that WetSpass works well to simulate water balance components of the Hormat-Golina sub-basin and is especially suitable for studying the effects of Land-use changes on the water regime in the basin.
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).
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.
Hydrological processes under changing climate and land use scenarios in the Baro– Akobo River Basin, Ethiopia
(Addis Ababa University, 2023-11-04) Abiy Getachew; Tekalegn Ayele (PhD); Yihun Taddele (PhD) Co-Advisor
Water is an essential component of agricultural productivity and is crucial for food security. It is also a vital component of the environment. Water security is becoming a global issue, but the issue is chronic in most developing countries, including sub-Saharan Africa. Therefore, sustainable water resource management is essential to achieve food and water security in Ethiopia. The Baro– Akobo River basin, which is found in the southwest part of Ethiopia, has witnessed a substantial change in population, climate, and land use during the last four decades. The climate of the region is warming at an alarming rate, and it is expected that this tendency will persist in the coming century. On the other hand, the impacts of climate and land use change on the hydrology of this basin are not well understood. Understanding the impacts of climate and land use change on basin hydrology is critical for developing effective water management practices. Therefore, this study examined the individual and combined impacts of climate and land use changes on the basin hydrology. This study combines a statistical, geospatial, and hydrological model to investigate the hydrologic impacts of climate and land use change. First, seven raw and bias-corrected RCMs (RCA4 (CNRM), RCA4 (ICHEC), RCA4 (MPI), CCLM4 (CNRM), CCLM4 (MPI), REMO (MPI)) and the ensemble mean were evaluated for model skill in reproducing the observed baseline climate for the period 1975–2005 at several weather stations in the basin. A pixel-to-point approach was used to compare RCMs against weather stations. Monthly distribution patterns and several statistical metrics were used for evaluating the performance of RCMs in capturing the historical observed climate of the basin. The Mann-Kendall test and Sen's slope estimate were used to examine the decreasing and increasing trend of the climatic variables, as well as to estimate the magnitudes of the significant decreasing and increasing trends. Furthermore, the ensemble mean and five bias corrected RCMs were used to examine climate and hydrological changes in the baseline and future 2021–2050 (2030s) and 2071-2100 (2080s) periods under the representative concentration pathway (RCP4.5 and RCP8.5) scenarios. On the other hand, the geospatial and synergistic techniques of cellular automata (CA) and artificial neural networks (ANN) were used to develop historical and future land use change scenarios. The maximum likelihood classifier (MLC) in the Earth Resource Data Analysis System (ERDAS) was used to conduct land use change classification for Landsat imagery from 1985, 2002, and 2019. Three land use maps with seven classes were identified, and then a change detection process was conducted. The classified (1985–2002) and (2002–2019) land use maps, along with a transition matrix and spatial drivers, were put into the Module for Land-use Change Evaluation (MOLUSCE) model to predict land use maps for 2019 (current) and 2040 (a business-as-usual scenario) land use scenarios, respectively, using the CA-ANN multilayer perceptron methods (MLP). Besides, this study considered a further increase in altitudinal forest expansion and watershed management practices (conservation) in a land use scenario. Then the best-performing climate model (ensemble mean) under RCP4.5 and RCP8.5 for the 2023–2040 time frame and plausible land use scenarios considering the current, business as usual, and conservation was used as inputs to the calibrated models to examine the individual and combined impacts of climate and land use changes on the hydrology. Three independent climate datasets, including observed, Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS), and Climate Forecast System Reanalysis (CFSR), were used to calibrate and validate the Soil and Water Assessment Tool (SWAT) model for the periods 1990–1998 and 1999–2002, respectively. The Sequential Uncertainty Fitting 2 (SUfI2) method in the SWAT-CUP program was used for model calibration and sensitivity. The Nash–Sutcliffe Efficiency (NSE), Coefficient of Determination (R2), and Percent Bias (PBIAS) as well as two uncertainty measurements (r-factor and p-factor), were used to assess the model's performance. Then the calibrated model using the water balance equation was used to examine the individual and combined impacts of climate and land use change scenarios on the basin hydrology. The climate and land use change impacts on hydrology were analyzed on monthly, seasonal, and annual scales with respect to the baseline period. Statistical tests such as the t-test and Levene test were also used to determine the change in mean and standard deviation between the baseline and different climate and land use scenarios. Besides, the Indicators of Hydrologic Alterations (IHA) method was used to assess the hydrologic changes between the baseline conditions and future climate change scenarios. Results from the global climate models (GCMs) downscaled through the CCLM4, RCA4, and REMO modeling schemes are characterized by several biases, such as shifting the rainy season and under- and overestimation of the observed climate. However, the skill of the models was substantially enhanced after bias correction. All models best capture the annual cycle with less bias. Therefore, it was beneficial to account for such biases using a robust statistical bias correction method before utilizing RCM simulations to generate climatic scenarios and climate impact scenarios. Results from future bias-corrected RCMs show a consistent increase in monthly Tmax and Tmin under RCP4.5 and RCP8.5 in the 2030s and 2080s relative to the baseline climate, while rainfall does not show consistency. The future climate change projections from the ensemble mean show an increase in the R20mm, CDD, R95p, RX1, and RX5 indices, but the R10 indices show a decreasing value under both RCPs. Observed climate and CHIRPS rainfall combined with the CFSR dataset yielded reasonable and comparable streamflow simulation performance in terms of statistical metrics at both Baro and Sore hydrological stations. All climate impact scenarios from the ensemble mean demonstrated a decline in surface runoff and water yield and an increase in evapotranspiration. Except for the extreme flow segment (i.e., 0–3% exceedance probability), the projection for simulation under climate change scenarios shows a decrease in flow. The increase in temperature and the decrease in rainfall is attributed to a relatively higher impact than the combined and land-use change-alone scenarios. This will have an impact on future agricultural production and water availability. Moreover, the projected increase in rainfall extremes, the expansion of agricultural land, and urbanization all lead to increased surface runoff and flooding. Therefore, to implement adaptation and mitigation strategies, the inclusion of predicted climate and land use change in hydrological impact studies is useful.
The Influence of El Niño Induced Drought on The Limnology and Dynamics of Cyanotoxins In A Shallow Tropical Reservoirkoka: Implications for Possible Public Health Threat and Restoration Efforts
(Addis Ababa University, 2020-02) Samson, Tilahun; Demeke, Kifle (PhD)
Studies predict that future climate-change scenarios such as global warming promote the proliferation and dominance of potentially toxic cyanobacteria due to their influence on the limnology of aquatic environments. Lentic systems in the tropics such as Koka Reservoir are largely of riverine origin. They are, therefore, more susceptible to changes in hydrological cycles or rainfall pattern induced by climate change anomalies such as El Niño induced drought and La Niña induced flooding. This study was conducted on Koka Reservoir, which is one of the most severely impacted water bodies by the recurrence of potentially toxic cyanobacteria. Our study period (May 2015-April 2016) coincided with the recent incidence of El Niño induced drought that was reported to be the worst in decades. Physico-chemical and biological parameters were determined using the standard methods. The drought caused a reduction in the flow of Awash River and amount of sediment transported and drying of Modjo River. This expectedly caused a concomitant reduction in the annual nutrient budget of the reservoir received from riverine sources. The consequent low levels of nutrients in the reservoir, which was most pronounced for nitrogen sources, led to the occurrence of Microcystis spp. in unusually low abundance and the emergence and dominance of diazotrophic cyanobacteria, Cylindrospermopsis spp.. The low nitrogen levels (μg L-1) observed in the open water (16.5-135) and near-shore (9.69 -250) sites also suggest that riverine input is probably the major source of nutrients to the reservoir. Total phosphorus (μg L-1), however, exhibited better availability, with its levels varying from 532 (Jul) to 668 (Mar) and 500 (Jul) to 698 (Mar) in the open water and near-shore sites, respectively. The large discrepancy between the model predicted phosphorus concentration (Pλ, 156.6 mg m-3) calculated from the total phosphorus input from allochtonous sources (riverine and atmospheric) and the observed in-lake phosphorus concentration (609 mg m-3), with the former constituting only 25.7 % of the latter, also suggest the supply of phosphorus from autochthonous sources. Frequent horizontal and vertical mixing of the reservoir may have enhanced phosphorus recycling. Horizontal mixing of the reservoir was reflected by the absence of significant differences in limnological parameters. Frequent vertical mixing manifested by turbidity (NTU, 48.39 -2820 and 48.29l-2970), TSS (g L-1), 0.015l-1.672 and 0.029-1.5), Secchi disk transparency (cm,3-17 and 3.05-17.01) between the open water and near-shore sites, respectively, may have promoted the presumed internal phaphorus loading. Despite the low abundance of Microystis spp, the detected intra-cellular concentrations (μg L-1) of the microcystins variants MC-LR (815), MC-YR (466.6) and MC-RR (265.68) by far exceeded the public health safety limit of 1 μg L-1. However, Dolichospermum, the co-occurring diazotrophic cyanobacterium, may have also been responsible for the observed levels of MCs although its confirmation requires further study. The extra-cellular toxins were relatively less concentrated and less frequently detected. However, concentrations (μg L-1) of up to 20 of MC-LR, 6.13 of MC-YR and 1.27 of MC-RR, which also exceeded the permissible limit (μg L-1) set by WHO, were measured. The most potent MC-variant, MC-LR, constituted the greatest proportion (52.6-77.6 %) of total microcystins concentrations in the majority of the samples suggesting the extremely high potential public health risk. The strong positive correlation among the extracellular MCs variants (Spearman Rank Order Correlation, P< 0.05) suggests the possible involvement of a non-specific release mechanism, namely cell lysis, which may have occurred following the collapse of the bloom in May. This study also revealed that all limnological conditions including water residence time (239.5-439.9 days), temperature (22.4 -31.3 oC), and salinity except the limiting level of nitrogen, were within the ranges reported to be optimal for the proliferation of Microcystis and production of microcystins. The strong, positive and significant correlation between Microcystis spp. abundance and nitrogen concentration (Spearman Rank Order Correlation (r= 0.7, P<0.05), and the lack of association with other limnological features suggest that nitrogen was the key environmental factor in the dynamics of Microcystis spp. and microcystins. Absence of correlation between the abundance of diazotrophic cyanobacteria and concentrations of nitrogen (r=-0.173, P>0.05) but the strong and positive correlation with the concentrations of total phosphorus (r=0.718, P<0.05) seem to suggest that phosphorus was the key nutrient influencing this functional group in the reservoir as nitrogen can never be limiting. Considering the long history of sediment deposition and the most likely concurrent nutrient loading since 1960s and the high retention efficiency associated with the prevailing long water residence time, the reservoir may have already accumulated a huge phosphorus reserve in the sediment. Emergence of nitrogen-fixing genera that are capable of satisfying their nitrogen requirement from the inexhaustible atmospheric sources and the presumably huge phosphorus reserve already accumulated in the reservoir implies that reduction in the external input of both nutrients can hardly help in reversing the current situation in Koka Reservoir at least in the near future.
An Integrated Approach to Water Supply Planning: Case of Addis Ababa (Nifas Silk Lafto sub city)
(Addis Ababa University, 2016-10) Eyassu, Amsal; T., Mebrate (PhD)
In planning and designing a water supply planning system, the key emphasis for meeting the growing water demand in Addis Ababa and elsewhere in the world is often focused on the endless desire to search for new resources and development of them. Limited effort is devoted to addressing in the issue in an integrated approach which combines the supply and demand side in a sustainable approach. Integrated water supply planning is a significant issue for sustainable development to maximize economy, secure production and minimize environmental impacts. The identification of sustainable water demand management practices is technically challenging because of lack of educated staff and attitude. Over the past few years, however, some efforts were seen in the developed countries to frame the water supply planning issue in an integrated fashion. However, this approach is not being practiced in developing countries, like Ethiopia, where the water supply problem is critical and the effort seems to repeat the track developed countries have taken without making the most out of the late comer position they maintain. With limited availability of water as a resource, the population pressure, the limited financial resource and other socio economic factors the traditional approach of endless investment is limited in its make to be a sustainable solution to water supply problems. The analytical hierarchy process AHP, which is able to provide solutions for problems involved in determining the priorities of various policies, can also be successfully used to approach water policy and management. With regard to water shortage problem in the sub city of Nifas silk lafto, an AHP structure is constructed for helping decision making with a main objective and sub objectives. Among the various water policies, 22 policies are examined, and a set of six constraints is considered as criteria. A system is formed to support the judgments through a 3 round questionnaire for hierarchy in order to diminish the effect of subjective bias and interview with the manager of the sub city branch office of AAWSA. Computations are processed through AHP using excel. The results provide both qualitative and quantitative information on the policies as well as the priorities from the point of view of water supply planning and development. The AHP model gives not only the relative importance of each factor for each level but also the composite weights in relation to the main objective. Key words: Water demand, Demand management, Analytic hierarchy process, Addis Ababa

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