Impact of Built Environment on Hydrological Regimes of Addis Ababa
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Date
2011-09
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Addis Ababa University
Abstract
Urbanization takes place takes place in Ethiopia early 1900‟s. The rate is different from place to place; this is mainly due to social and economic influences. Among the big cities of Africa Addis Ababa is the one with high population low planned urbanization influence. This lack of proper settlement plan of the city influences its hydrological regimes due to influence on main streams of the city
The built environment of Addis Ababa includes Asphalt roads, paved roads, residential areas, commercial and industrial areas and other big infrastructures. The purpose of this study was to show the impact of built environment on hydrological regimes of Addis Ababa through defining hydrological parameters by using SCS (soil conservation Service) method to evaluate surface runoff generated as result of rainfall and it is impact on streams.
The study focused on the city of Addis Ababa without considering the entire Akaki watershed. Three periods of land use maps were considered in the analysis. The land use periods are 1984, 1986 and 2002, the first two maps was obtained from Ethiopian mapping agency and the 2002 one is from Addis Ababa city Administration which developed by City master plan office. The land use maps were digitized using GIS. Based on the three periods the land uses types categorized as Asphalt, Agriculture, Forest, Paved, Built and Park and Cemetery. Using parameter,curve number for each land use types surface runoff was calculated. Accordingly it was found out that since 1984 the runoff potential has changed from 0.28 in 1984to 0.45 in 2002. This is due to the expansion of the city and increasing of built environment, which was expressed by composite Curve Number and Soil Retention. The composite curve number has changed from 84.6 in 1984 to 91.1 in 2002. This change has been also observed when we delineated twelve sub catchments using ARC SWAT and GIS . Based on the analysis we found change of surface runoff was observed. The characteristics of streams which found in the delineated sub catchments also changed .The time of concentration for streams in delineated sub catchments reduced by twenty seven percent in small streams (intermittent). Therefore it is important to consider the impact of land use change in planning and design of urban infrastructure.
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Keywords
Hydrological Regimes, Impact, Addis Ababa, Built Environment