Comparative Assessment of Low Impact Development Controls on Flood Mitigation (The Case of Wollo Sefer to Gotera Route, Addis Ababa)
No Thumbnail Available
Date
2021-11
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Urbanization alters hydrological cycle and increases runoff by changing permeable surfaces into impermeable ones. In Addis Ababa, which is found in Awash catchment; rapid urbanization and development is altering permeable surfaces into impermeable ones; including impermeable roof surfaces. This phenomenon lowers the capacity of the land to infiltrate and store stormwater, and contributes in increased runoff volume and rate; causing flood damage as a result; which is not adequately managed by the current conventional drainage systems of the city. The study area which is the route from Wollo sefer to Gotera is one of the areas found in the city affected by flood due to immense urbanization. By decreasing runoff volume and increasing storage and infiltration, Low Impact Development (LID) practices are capable of minimizing and even avoiding flood risk if integrated with the existing drainage system. The objectives of the study are, evaluating the performance of the existing drainage system of the study area, apply four hypothetical LID controls (bio-retention cells, rain barrels, green roofs, and permeable pavements) to see the difference, comparing the LID controls on the basis of avoiding flood with a minimum area of application, and selecting the feasible one using storm water management modeling (SWMM) tool. The study revealed that the area has eleven subcatchments and flooding problem exists in it; because the drainage system is not found to adequately prevent this issue solely. Calibration of the model resulted in R2 = 0.9714, and RMSE = 4.867; which proved a good agreement between the model and the actual values. Trials and errors testified that the minimum area on which LID controls can be applied to avoid flood risk was 58320m² (36%) of the area of the third subcatchment. If the aforementioned LID controls except green roofs were applied on such an area, flood problems would be avoided. Since, building areas were found to cover 60% of the third subcatchment, rain barrels were chosen as the feasible LID controls that can be installed on the least area possible to avoid flooding problems.
Description
Keywords
Urbanization, Flood risk, Low Impact Development Controls, SWMM, Feasibility