Browsing by Author "Assefa, Alazar (PhD)"

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    Application of Curb Extension for Sustainable Storm Water Management of Local Streets in Water Logging Lands:The Case of Residential Areas in Addis Ababa:
    (Addis Ababa University, 2021-02) Beyene, Tsega; Assefa, Alazar (PhD)
    The application of sustainable stormwater management system in waterlogging areas of urbanized catchments is the most effective method that helps to control surface stormwater runoff caused by recurrent and extreme rain events. Applying a bio-retention system for flood reduction through infiltration and evapotranspiration processes will help to create an attractive urban street with better environmental performance. Since cities are becoming more impervious, the stormwater runoff increases and will affects the downstream land and water bodies by flooding. In Addis Ababa, applying a sustainable stormwater management system is a timely act due to the ongoing rapid urbanization and increment in impervious surfaces that result in stormwater runoff that causes flooding and surface water pollution. In this regard, innovative and flat terrain considerate design responses are needed in low-lying plains with difficulties to apply conventional pipe-based drainage systems. The design intervention will reduce the waterlogging effect occur due to extreme rain events. The objective of the research is to apply curb-extensions as a bio-retention system for sustainable stormwater management of waterlogging local streets in the low-lying residential areas of Addis Ababa. Specifically, the study identified areas affected by peak stormwater flow that creates a waterlogging problem over local streets of the case study area. A sustainable design solution is proposed by considering the infiltration, retention, and evapotranspiration capacity of curb-extensions. The study identified flooding and waterlogging areas in the city, at the river catchment, and in the study, site using hydrological and spatial data. Using ArcGIS-based hydrologic analyst tools, blue spots located along the flow direction of the streams identified as depressions usually experienced an overflow of stormwater and waterlogging. To minimize the risk of waterlogging, a sustainable design solution as a curb extension system designed by estimating the water balance from the actual water holding capacity of natural depression (blue-spot) and the stormwater runoff generated from the catchment area that naturally drained into the specific blue-spot. The curb-extension system was designed as a bio-retention and streetscape element by modifying the native soil, gravel fill, water intake plants on the top of the system for infiltration and retention purpose. In this regard, the designed curb extension will substantially manage the highest intensity of precipitation (40 mm/hr) of 10 years of rain event from IDF curve of Addis Ababa. The design reduces the volume of stormwater runoff from 22.895 m3 to 8.477 m3, which is 62 % of runoff. The study concludes that if the municipality of Addis Ababa develops a curb extension system over the local streets of the entire neighborhoods affected by waterlogging, the flooding problem will be reduced substantially with more greening & environmental benefits. The system will also contribute to the reduction of downstream flooding by minimizing stormwater runoff flowing into the Akaki river system. As a multifunctional drainage design facility, the system has the potential to create a green street that helps to improve the standard of living and boost the environmental quality of the area. Finally, the study recommended further study on the upscaling of proposed curb-extension by developing more empirical and experimental settings as a pilot project. The pilot projects will help the city to consider the curb-extension system for the greening, drainage design, and urban planning practices. Moreover, the tests and demonstration works will justify its competency for improving the livability and livelihood of the local people within urban settings that were frequently affected by waterlogging.
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    Local Development Plan for Inner City Areas, Particular Emphasis Based on Evaluation of Basic Urban Design Parameters the Case of Meskel Square Entrance Pocket Area, Addis Ababa
    (Addis Ababauniversity, 2013-06) Fissha, Dawit; Assefa, Alazar (PhD)
    Addis Ababa is the capital as well as the political and cultural center of Ethiopia. But the slum areas in the inner city are found to be the prominent problems that hide the international image of the city. Hence, extensive redevelopment activities are under way to transform the city in to a more livable city in Africa. However, Addis Ababa faces huge challenges in redeveloping slum areas. Thus, this paper tried to assess physical aspects of the redevelopment practices of Kaza-INCHIS/ECA/Economic Commission for Africa/ area and analyze the proposed Local Development plan of Meskel square entrance pocket area. This paper, therefore, applied snowballing random sampling method to select respondents for this paper. The paper further utilized purposive sampling to select officials in different hierarchies’ and area of expertise. Both primary and secondary data are collected with the help of interviews, structured questionnaires, site reconnaissance and observation. The collected data were analyzed, interpreted and presented with the help of various software packages: MS-excel, GIS, AutoCAD, ArchiCAD, Artlantis Studio, Adobe Photoshop, Adobe Illustrator and computer programs. The results were presented in text, tables, pictures, charts, graphs and maps. Accordingly, the research concluded that the redevelopment practice in Addis Ababa has problems with respect to physical issues of urban design concepts, absence of visual satisfaction or aesthetics, comfort, efficiency, identity and sustainability, poor proportional integration of different land uses, road hierarchy, poor consideration of urban public spaces as a breathing open space and poor landscaping among others. Hence, the recommendations, the design concepts and spatial proposals presented in this thesis paper will pave the way for physically Livable, Vibrant and Sustainable design and implementation of redevelopment interventions in the city. Key word: Urban, Redevelopment, Local Development Plan, Urban Design
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    Nature Based Orainage Solution for Minmizing the Risk of Flooding in Nekemte City
    (Addis Ababa University, 2020-12) Feyisa, Nuywalif; Assefa, Alazar (PhD)
    In Ethiopia, the recent urban expansion and increment of impervious surfaces in high rainfall areas resulted in flooding and associated environmental problems. Nekemte city is one of the urban centers in the country facing the challenges associated with a high level of imperviousness and flooding. This study mainly focused on estimating the level of impervious surfaces and introducing nature-based drainage design solutions for sustainable stormwater management of the city by targeting water-resilient strategies for the future of Nekemte. Spatial data collected and processed by using ArcGIS for mapping & quantification of impervious surfaces eventually for calculating stormwater runoff generated from the most impacted watershed. None spatial data collected to understand the perception of local people about the situation of flooding using questionnaires, structured interviews, observation & focus group discussions. Published and unpublished documents from the municipality of Nekemte and planning institutes utilized for verification of both spatial and non-spatial data. The collected primary data analyzed statistically under SPSS version 20. The principal result of this research showed that factors enabling flooding problems are the sum of factors associated with impervious surface increments, intensive recurrent rainfall in the area, densification of settlements in the higher slopes, and inadequate drainage facilities for stormwater management. Based on this factor, the watershed that covers the area around Bake Jama and nearby neighborhoods estimated to be 201.06ha watershed area identified as the most impacted with 95.77ha of impervious surface coverage. The problem associated with imperviousness in this particular watershed can be reduced by retrofitting through the application of nature-based drainage solutions using the available open spaces and public realms. The study also developed watershed level strategies applicable in different parts of the city with similar flooding problems. Finally, the study recommended further assessment of the socio-economic aspect of flooding in the area to link the nature-based drainage solutions with more co-benefits for the local people affected by flooding. In this regard, the designed nature-based solutions as a blue green system have the potential for creating more jobs and income for the local people through water harvesting and urban farming schemes
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    Nature-based Design for Stream Rehabilitation Affected by Imperviousness in Addis Ababa: The Case of Kaba River
    (Addis Ababa University, 2020-10) Abebe, Mengistu; Assefa, Alazar (PhD)
    Urbanization of watersheds substantially changes the health of a stream by increasing impervious surfaces that deliver pollutants directly to waterways. The major environmental problem that Addis Ababa facing is the increasing impervious surface. Although improving the riparian zone has been attempted to restore urban stream health in Addis Ababa, that does not significantly improve it, since it is not equivalent to the scale of degradation of streams based on recent studies. The main objective of the study is to introduce an appropriate type of watershed-level nature-based design measures for the rehabilitation of urban streams affected by the higher level of imperviousness in Addis Ababa. Stream restoration can be achieved in this case by a cross-sectional study of the specific case watershed to address the issue of urban streams and river system rehabilitation at the watershed level by introducing appropriate nature-based design solutions and by upscaling the solution from the case site into the entire city river system. The study site is selected based on the density by comparing the built-up of upper catchments. The study estimates the existing level of effective impervious area for ‘Kaba’ river watershed and stream health improvement solution. The total impervious cover of the city and effective impervious cover of the study area are 52 and 27.8 percent respectively. The current condition of the stream will not support its intended hydro-ecological functions. Different design scenarios are proposed in the watershed to reduce the effective impervious areas to a level at which measurable improvement in the ecological indicators. Finally, the study concludes that the proportion of the effective impervious areas is a good predictor of the ecological condition of streams and it should be reduced to a level of recommended proportion to maintain stream health.