Browsing by Author "Assefa, Alazar"

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    Design With Terrain and Gravels: Nature-Based Drainage Solutions for Sustainable Stormwater Management of Urban Areas
    (2019-11) Assefa, Alazar; Bergen, Marina
    Rapid urban growth and global climatic variability result in frequent flooding in urban areas and pose unprecedented stress on the existing drainage infrastructures. In developed nations, a shift in urban stormwater management from relying exclusively on gray, pipe-based drainage infrastructures towards green, nature-based approaches referred to as Sustainable .Drainage Systems (SuDS), among others, is currently taking place. In cities of developing countries, the existing gray infrastructures are not well developed, prompting an opportunity of performing a technical leapfrogging towards SuDS. Through vigilant adoption of this increasingly-practiced nature-based drainage solution, municipalities can provide better drainage and flood control and create a fertile ground for more co-benefits to local residents in terms of livelihood and livability. This Ph.D. thesis identifies options to improve the drainage challenge of settlements developed over higher slope terrains and low lying plains of urban areas in developing countries with the high rate of urban growth and drainage infrastructure deficit, through terrain modifications and introduction of gravel-based drainage design solutions as a nature based drainage option to control flooding and provide co-benefits. The study is presented in three parts based on two empirical studies from case sites, both developed in the south-western fringe of Addis Ababa, Ethiopia, and one desktop study building upon one of the empirical studies. The case studies present the design of novel drainage and stormwater harvesting solutions constructed by using locally available materials and terrain modifications. The first design is for drainage of cobblestone streets in hilly areas. The design is referred to as Infiltration Bumper with Tree Planter (IBTP) and targets flood prevention, groundwater recharges and city greening simultaneously. The second design is for the management of stormwater in low lying residential areas. The design is referred to as Elevated Retention and Detention Basin (ERDB), and targets waterlogging prevention, stormwater harvesting, and green area improvements. The first solution (IBTP) is developed and tested to control stormwater runoff generated from the local cobblestone streets within the designated case study catchments for a 2-year storm event corresponding to 40 mm over 2 hours. The second solution (ERDB) is developed and tested to control 100% stormwater runoff generated from the Jemo condominium (the multistory residential neighborhood in Addis Ababa) within the designated case study catchments for the same storm event. The desktop-study resulted in a GIS-based planning tool for upscaling of the IBTP to a city-wide solution.
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    Water Sensitive Urban Design for Invironmnetal Quality Improvement of Rivers in Addis Ababa: the Case of Finicha River
    (Addis Ababauniversity, 2015-06) Tesfaye Mahlet; Assefa, Alazar
    Nearly all urban areas developed on riverbanks. For centuries, people have settled along rivers for the purpose of irrigation, transportation, water supply, etc. Rivers are also important source of food for people settled close to their banks. Intensive usages of rivers by human beings for the aforementioned purposes have resulted in the loss of aquatic fauna and flora. This is true for Ethiopia as well. Specially, in Addis Ababa, rivers and riversides are neglected places where solid and liquid wastes are dumped. Additionally, it is also a place for legal and illegal settlers. For this reason, the riparian areas along the city’s rivers were shrinking in size, and there are no greenways along the city’s Rivers. Therefore, the main objective of this study is to develop design strategies by testing on a specific site. In order to achieve the objective, cross-sectional study method is selected. This method is chosen because it examines one specific site, while several outcomes are expected at the same time. In addition, study area was selected based on location, land use, exposure to flood and river pollution using purposive sampling techniques. During the study, it is found that the factors for shrinking of the riparian zones of case area are population growth; settlements along the riverbanks; waste dumping site; lack of awareness and coordination as well as inadequate manpower. Furthermore, the factors that increase flood damage and river pollution of the study area are absence of Stormwater Management Practices (SMPs); due to lack of coordination among different concerned Institutions such as AAEPA, MUDC, CBGB,OAAOSZIDP as well as disposal of solid and liquid wastes around the river. There are no greenways along the river. For these reasons, Finicha River is not suitable for the community of the study area. Therefore, the concerned bodies should take appropriate action as soon as possible. There should be coordination among the concerned sectors. In addition, SMPs should be incorporated into built environments such as buildings, road, parking areas and open spaces. Site-specific design solutions should be provided with a view to having urban river spaces that are accessible, attractive and environmentally sound