Nature Based Orainage Solution for Minmizing the Risk of Flooding in Nekemte City
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Date
2020-12
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Addis Ababa University
Abstract
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 Published and unpublished documents from the municipality of Nekemte and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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Keywords
Urban densification, land-cover, surface runoff, impacted watersheds, retrofitting strategy,, blue- green system