http://ir.bdu.edu.et/handle/123456789/10237 2001-01-13T05:51:51Z http://ir.bdu.edu.et/handle/123456789/10729 Human impact on Hydro-geomorphology of Gumara River upper Blue Nile basin, Ethiopia Abate, Mengiste PHD The physical, biological and societal systems are interrelated each other. The societal system over the other systems have brought complex changes. The increasing population density that leads to human-induced land use change, alter fluxes of water and sediment and in turn produces complex landscape changes in physical structure, hydraulics and hydro-geomorphology of river systems. The landscape of upper Blue Nile Basin has been changed due to anthropogenic effects and climate change. Few studies in the upper Blue Nile basin have detailed the response of the rivers to these effects. However, in the international literature this topic has been well addressed and can be applied to Ethiopia in order to understand the past, the present channel dynamics and predicting future channel changes. The objective of this study was to investigate and analyze the response of rivers in Ethiopia to sedimentation, erosion and change of flow regime. We choose the Tana sub-basin because previous data was available. Specifically, this study quantifies the hydro-geomorphology of the 38 km of Gumara River starting from the confluence with Kizin River to Lake Tana using historical images, historical river cross sections, hydrologic, hydraulic, and geotechnical data. In addition, field observations and information obtained from the local people and existing structures were used as data sources. The results show that the changes to Gumara River channel morphology in the alluvial plain is largely controlled by the interplay between discharge regime and sediment loads, which are influenced by human factors and the lake levels. Old maps show that before 1957 when shifting cultivation was practiced the Gumara delta did not expand indicating that the sediment concentrations in the Gumara were small. After 1957 the iv lower reach of Gumara near its mouth underwent major morphological change and delta expanded on average by 5 ha/yr and increase in height by 3 cm/yr. After 1957 the Gumara River although the planform changes are very slow, the bed has aggregated greatly with in-channel deposition (3 m in 46 years). When the ratio of curvature radius to channel width is 3.5, the Gumara River at its bends is experiencing a maximum bank retreat of 1.95 m/yr and the nearby land is lost on average by 0.075 ha/km/yr. The raise of the river bed level amplifies the flashy nature of the river, and results in more frequent high floods and sediment concentrations. This will further increase the river bed level and in turn reduces the flood carrying capacity of the channel. This dissertation shows that human factors are the major driver for the increasing sediment loads in the changes that occur in Gumara River. Thus, restoration of rivers in the Fogera Plain to decrease flooding should include effective catchment-based management practices to offset the negative aspects of the increasing population density in the uplands. 2020-03-19T00:00:00Z http://ir.bdu.edu.et/handle/123456789/10716 ASSESSMENT OF SURFACE WATER RESOURCE AND IRRIGABLE LAND POTENTIAL IN AMHARA REGION, ETHIOPIA: A CASE STUDY OF JABITEHNAN WOREDA Nigusie, Getenet For strategic planning and decision making on irrigation-related development projects, systematic assessment of irrigable land and the availability of water resources is imperative. This study was initiated with the objective of assessing the surface water resource and irrigable land potential in Amhara region West Gojjam zone, Jabitehnan Woreda using SWAT model and MCDE respectively. For water resource assessment on ungauged catchment using SWAT model, Lah River’s observed flow data were used for sensitivity analysis, model calibration and validation. The result of model performance analysis demonstrated a good agreement between the average monthly simulated and measured values: Nash-Sutcliffe model efficiencies (NSE) of 0.74 for calibration and 0.62 for validation periods. Moreover, the coefficients of determination (R2), 0.83 and 0.82, were obtained during the same period. The calibrated parameter on the gauged catchment was in turn used to estimate runoff yield of the ungauged catchment. The simulated mean monthly and average annual water yields of the Geray and Debolah Watersheds were found to be 0.98m3/s and 0.92m3/s and 11.73m3/s and 11.1m3/s, respectively. To identify potential irrigable land, irrigation suitability factors such as soil type, slope, land cover/use, and river proximity were taken into account. The surface irrigation land suitability analysis indicate that 90.75% of soil , 95.6 % of land cover/use and 95.15 % slope in the study area are in the range of highly suitable to marginal suitable for surface irrigation system. The weighted overlay analysis of these factors gave potential irrigable land among river catchments as Birr and Tikur wuha (7,831.09ha), Gunagun and Leza (17,658.08ha), Lah, Geray, Arara, Debolah, Guysa and Silala (20,105.98ha). Three crops such as onion, cabbage and tomato were selected to grow on the identified irrigable areas, and their gross irrigation demand was calculated by using nearby climatic stations. By comparing gross irrigation demand of irrigable land with available flow in rivers, the actual surface irrigation potential of the study area was obtained as 4,499.7ha. In conclusion, the SWAT model can be used to analyze ungauged watershed runoff yield in areas that have similar hydrometeorological characteristics as those of the Lah Watershed in the region and water should be stored in rainy seasons to irrigate all the irrigable land potential. 2020-03-19T00:00:00Z http://ir.bdu.edu.et/handle/123456789/10715 A CASE STUDY OF ALEWUHA SMALL SCALE IRRIGATION SCHEME, NORTH WOLLO Moges, Getachew This study was initiated to assess and evaluate the performance of Alewuha irrigation scheme using internal performance indices such as conveyance efficiency, application efficiency, deep percolation fraction, water delivery performance, maintenance indicators, and assessment of institutional and support services so as to recommend appropriate measures to improve the scheme management and performance. To realize these objectives, structured household survey questionnaires, interviews, group discussions, field observations and literature were used. For household survey questionnaires a total of 94 sampled households were randomly selected from head, middle and tail-end command area beneficiary farmers. Collecting primary and secondary data of the irrigation scheme has been carried out by the study. Primary data collection included canal water flow measurements using current meter, moisture contents determination of the soils, measurement of depth of water applied to the fields using parshall flume. The required amount of water giving by using cropwat software was 520.96 l/s but the actual volume of water delivered to the main canal was 349 l/s. The secondary data collection has been carried out in collaboration with DAs and government officials. Average conveyance efficiencies were 71.67 % and 59.46% of main and secondary canals of the scheme respectively. The average application efficiency was 49.99. The water delivery performance was about 66.99 %. The effectiveness of infrastructure computed as the ratio of number of functional to total number of structures is approximately 24.62 %, indicating the fact that nonfunctional and the average sustainability of irrigation scheme was about 47.78 %. So, the sustainability of the irrigation scheme is low. The overall results of the Alewuha irrigation scheme performance with respect to the indicators perform as relatively poor (34.01%). 2020-03-19T00:00:00Z http://ir.bdu.edu.et/handle/123456789/10714 Investigating the Morphological Changes in the Lower Reach of Megech River, Lake Tana Basin, Ethiopia Asmare, Getachew River morphology describes the shapes of the river channels and how they change over time. This study examine the morphology or channel adjustment along a 44.43-km stretch of the Lower Reach of Megech River in North Gonder of Amhara Region which drains towards Lake Tana and then to the Blue Nile, Ethiopia. The objectives of this study were to identify and examine the plan-form changes and to investigate the impacts and causes of the plan-form changes of the lower reach of Megech River for the last 30 years. Satellite images of the year 1984, 1995, 2000, 2006, 2009 and 2014 were used to extract the past and the recent channel plan for information. Typical channel cross sections at Megech Bridge were used for the comparison of vertical adjustment. Besides the above data, field observation and key informant interview were made. For data preparation and analysis, Image analysis software (ERDAS 2014), Arc GIS and Terrain analysis tools were used. Lower reach of Megech River has undergone major plan form changes past 30 years. At a distance about 19.3 km from the Lake, the river abounded the old channel course and shifted from west to east and developed new channel which directly drains to Lake Tana. The maximum shift was 4.64 km occurred in the left bank for the period 1995 to 2006 in reach 1, whereas the minimum shift of about 67.8 m was measured for the right bank for 1984 to 2000 and 20.9 m for the period from 2006 to 2009 in reach 7.The stretches showing the highest mobility are located to the left (east ward) in the downstream of the river reach (reach 1 to reach 4). The sinuosity of Megech River shows an overall increase of 8.2% for the 30 year study period. The general trend shows that Sinuosity of river Megech increases from 1984 to present. The Megech River registered an overall net gain of 74.2 % in channel area over 30 years. Generally, the plan form alteration of Megech River at different reach is due to natural and artificial influences. Therefore, responsible bodies should target to minimize the negative aspects of any interventions in the catchment and in the channel by designing appropriate watershed management and river restoration works. 2020-03-19T00:00:00Z