Performance Assessment of Stormwater Drainage System in Alamata Town
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Date
2018
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
Urbanization of an area invariably leads to increase in overall imperviousness of the area. When
land becomes impervious,stormwater will stagnate on the surface thereby affecting the
infrastructure, transportation and causing inconvenience to general populace. Stormwater drainage
problem is one of the major challenges facing many countries in Ethiopia in general and Alamata
town also faced the problem. This study has investigated the overall challenges of the stormwater
drainage system in Alamata town.Rapid expansion of built environment, poor urban drainage
managements and location of Alamata town being at the foothills of mount Gra-Kahsu are the
major problems in the study area. The objective of this study is to evaluate the current stormwater
drainage systems and associated problems. This research involves collection of both primary and
the secondary data and the collected raw data was edited, coded, classified, and tabulated in order
to make it ready for analysis. Furthermore, spatial analyses was conducted using Arc GIS, Bentley
Flow master, Google Earth pro, and Auto CAD software’s as analytical tools. The land use land
cover image was processed for the years 2008 and 2018 by using Arc GIS.10.4.1 and Google earth
pro then for each land use/land cover, annual stormwater runoff volume was calculated and digital
change detection were evaluated. The results indicate that Annual runoff volume of Built -up area
in the study area has increased from 162129.6m
in 2018 which accounts
for 13.35% of the total Annual runoff volume. The Vegetation has decreased from 15616.8m
3
in 2008 to 183772.8 m
3
in
2008 to 4568.4m
3
in 2018 which accounts for 70.75%. The Bare Land area has increased from
8286.3m
3
3
in 2018 which accounts for 153.08%. The existing depth and
width of the stormwater drainage channel were measured for all sub catchments of the town and
used to determine the existing drainage capacity using Bentley Flow master. The hydrological
analysis was computed by the SCS method and rational method. The computed discharge values,
which were determined by both SCS method and rational method, were compared by dividing the
watershed area according to their area of application. The existing condition drainage channel
depths of sub-catchments 6,7 and 8 Increase by 68.40%, 160.20% and 121.07%; and the widths
by 55.44%, 116.83% and 100.98%, and the Design discharge was also 9.29m
in 2008 to 20970.9m
3
/s and
9.13m
3
3
/s, 16.47m
3
/s respectively.
Description
Keywords
Urbanization, Stormwater, Grakahsu Mountain, Bentley Flow master, SCS curve number