Integrated Urban Drainage System; the Case of Ayat to Megenagna Light Rail Transit Route
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Date
2015-09
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Addis Ababa University
Abstract
Addis Ababa is one of the fastest growing cities in Africa and urbanization is known to increase the amount of runoff generated from the urban catchment. Due to urbanization and lack of proper design and management, the cities transport infrastructure has experienced frequent flooding. The application of Integrated Sustainable Urban Drainage System (SUDS) is a recent trend in developed countries (like the UK) for flood mitigation with added benefit of amenity and water quality. The aim of this study was to assess SUDS applicability in solving the existing drainage problem and minimizing the flood risk associated to transport infrastructure.
In this study Ayat to Megenagna section of the Addis Ababa Light Railway Transit (LRT) line was chosen as a study area. Areas along the route with drainage problems have been identified and catchment was delineated. IDF curves were developed and rational method was used to estimate the existing runoff. Rooftop rainwater harvesting and rain gardens were proposed to solve the drainage problem. A tool that uses daily rainfall records of 30 years is developed in Microsoft Excel to quantify the amount of runoff reduction that can be achieved by using SUDS. The tool calculates the percentage of runoff that can be intercepted using a given storage capacity of rainwater harvesting system for a given daily non potable water demand. The tool is developed in such a way that allows modelling of different demand and storage size scenario.
The result is presented in terms of a typical 90 square meters’ parcel found in the study area of which 89% is covered with roof area and 11% with rain garden. For daily non potable water demand of 257 liters it is found that the optimum storage tank capacity is 1500 liters. Using a tank of 1500 liters’ storage capacity, the percent reduction in runoff that can be achieved is found to be 51% of runoff generated from rainfall of 2cm or less depth. This shows that considerable runoff reduction can be achieved using rainwater harvesting and rainwater gardening. These study shows that integrated sustainable drainage systems can be used to protect transport infrastructure along Ayat to Megenagna route and the author recommends further detailed study and implementation.
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Keywords
Integrated Sustainable Drainage System, Source Control, Runoff Reduction Tool, Rainwater Harvesting, Light Railway, Addis Ababa