Urban Design

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Browsing Urban Design by Author "Alazar Assefa (PhD)"

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    Low Impact Development (LID) Design Retrofit to Reduce the Impact of Flooding and Diffused Pollutants from Affecting the Urban Lakes, The Case of Hawassa City, Ethiopia
    (Addis Ababa University, 2022-06-01) Yared Dereje; Alazar Assefa (PhD)
    Rapid urbanization has become a prevalent trend in the twenty-first century, putting development pressures on existing urban areas as a result of socio-economic changes, which has an impact on the natural system, particularly the hydro logical system, by increasing flooding and degrading water quality. The recent expansion and densification of Hawassa city contribute greatly to the generation of more pollutants, which are transported to the city's lake through storm water runoff from built-up areas. The objectives of the study is to see how fast urbanization impacts the city's natural environment, particularly the lake ecology, while also addressing sustainable storm water management to safeguard the city's lake using the Low Impact Development (LID) site design approaches. The city's natural and man-made land cover were investigated to determine the source of Lake Hawassa's ecological problem, which was connected to an increase in impermeable surfaces. In this regard, the study used a data set that included a Digital Elevation Model (DEM), a high-resolution satellite image, an existing land use map, precipitation data, and water quality samples. Using spatial analysis tools in QGIS 3.6.3 and a simulation model in SWMM 5.1, the quantity and quality of stormwater runoff impacting the lake environment were evaluated. The imperviousness level of 14 sub-catchments that directly flow into the lake, as well as the pollution load from impacted catchments, have all been investigated to determine which sub-watersheds contribute the most pollutants to the lake. The study revealed that between 2013 and 2018, the imperviousness level in catchments that directly drain to the lake increased from 12.20 % to 20.32 %. That shows an increment of 43.4 % of runoff from impervious covers within five years period. COD, TSS, TN, and TP levels in water samples tested from the degraded catchments' lake intake streams were 2307.5, 510.5, 2.09, and 10.4 mg/l, respectively, which are all above the permitted range. The SWMM model's simulation results also show that surface water quality is substantially degraded and exceeds acceptable limits. The study identified various types of LID design features as well as potential retrofitting open spaces in the study catchments. After incorporating the proposed LID retrofits, simulated results reveal a reduction of 16.0 % and 17.4 % in storm water runoff and peak flows for catchment 10 (C10) and a drop of 66.3 % and 5.0 % for catchment 11 (C11). Regarding to water quality, the COD, TSS, TN, and TP pollutant loads were reduced by 16.5 %, 16.2 %, 16.3 % and 16.3 %, and for C10 and 26.7 %, 13.1 %, 26.6 percent, and 26.2 %, for C11 respectively. Finally, flooding and water quality impairment shows the disruptions in the urban hydro logic cycle resulting from the construction of more impermeable surfaces have contributed to the degradation of Hawassa Lake's water quality. Incorporating effective LID solutions into the city watershed management systems and limiting a significant increase in impervious surfaces in urbanized catchments has the potential to reduce urban flooding, non point source pollution into the lake, and the oncoming environmental crisis. Keywords Imperviousness, Urban Hydrology, Urbanization
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    Potential Solutions for Spatially Disconnected Ginfile Sub Watershed of Woliso Town, Ethiopia
    (Addis Ababa University, 2023-05-01) Demelash Geremew Jebessa; Alazar Assefa (PhD)
    The Woliso town, originally centered around the natural spring 'Filwuha,' features abundant natural resources like the valuable hot spring 'Hora Ayetu,' scenic landscapes, and perennial streams sustaining fertile soil year-round. However, rapid population growth and urban expansion are disrupting the delicate ecological balance. Understanding the spatial organization of surface water in urbanized areas is crucial for sustainable water resource management and mitigating environmental impacts. In the study area, the majority of potential blue spots and wetlands are encroached upon by impermeable surfaces, leading to fragmented hydrological channels and limited connectivity with the broader stream network, exacerbating flood risks during extreme events. The research aims to assess the spatial and temporal connectivity of urban streams, considering the influence of land use changes and raising awareness of surface water management in the Omo Gibe sub-basin region. Employing GIS and remote sensing techniques, the study evaluates watershed characteristics and stream connectivity using morphometry, graph metrics, and spatial analysis. Results indicate that urban expansion has significantly altered surface water bodies and riparian zones, leading to their reduction, disappearance, and pollution. Addressing these challenges requires an integrated, proactive approach to land management and planning at both regional and local scales, emphasizing the importance of incorporating water bodies and riparian areas into sustainable urban design strategies to preserve their social and environmental value. Key words: Graph Metrics, Morphometric, Stream connectivity, Watersheds, Wetlands/blue-spot, Woliso town
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    Space- Syntax as a Tool for Place Making by Restructuring Public Spaces Within Mixed-Residential Areas Of Addis Ababa, the Case Of Meskel Flower District
    (Addis Ababa University, 2022-04-01) Daniel Sileshi Leggese; Alazar Assefa (PhD)
    Placemaking is a process that inspires people to reinvent or reimagine public spaces as the heart of every community. It also strength the connection between peoples and places they share. The main existing problem in the study area is the existence of fewer open spaces when compared to standards. The existing open spaces are not providing the intended services and most of them are leftover spaces without any function and some are even used for emerging slum housing. The general objective of this study is identifying spatial capital of the neighbourhoods and redesign open. In this paper analytical research is used together with qualitative and quantitative data types. Software like GIS, AUTOCAD, and depthmapX are used for data analysis. The main finding from this paper is, the Study area is poorly connected in relation to the required function, the linkage and integration of public spaces with people's primary uses are poor and roads within residential areas have poor connection and are characterized by dead ends. So, the overlayed street integration and open space map was developed in response to creating functional open spaces to achieve the desired mixing of functions and accessibility based on the standards, which provides responses to the problems that were collected and analysed. This study attempts to provide sample design proposals of selected areas or nodes of the overlayed map, with placemaking as the main focus area.