ASSESSMENT OF URBAN DRAINAGE SYSTEMS: THE CASE OF ADAMA CITY,DEMBELA SUB-CITY

Abstract

This study was conducted to investigate the storm water drainage of Dembela Sub-City. Recently, Dembela Sub-City has become one of the flood prone sub-cities of Adama City. Rapid population pressure and poor urban drainage managements are the major driving problems in the area. Moreover, most of drainage structures are not giving the intended purpose since they refilled up with debris and waste materials. So, the main objective of the study is to assess the existing storm water drainage system of Dembela Sub-City.GPS survey, drainage lines dimensions and metrological data(1978-2011) were collected. The catchments contribute flow were delineated and drainage network in the catchment was generated using DEM (20x20). Frequency analysis of rainfall was computed using Gumbel and log Pearson Type III probability distribution functions and the later found to fit the actual data using the goodness of fit test. IDF curve were developed for different return periods. The Storm water drainage and hydraulic structures had been analyzed and evaluated the performance of drainage lines and catchments with the help of AutoCAD and Arc GIS, EPA SWMM, Flow Master and other statistical tools were employed. SWMM 5.1 was implemented to simulate areas of 27 sub-catchments, the water level in the 73 links and 49 nodes, flow in links and flooding at nodes by considering the current land use condition. The results shows that in Dagaga Zone from135DL 59.26%,in Irrecha Zone from 89DL 82.42% and in Melka Adama Zone from 150 DL 61.33% are in sever condition. Most of drainage lines sever and no capacity to carry the runoff stormwater.Hence, recommendations is referring this document use the appropriate proposed drainage network on specific site which measures should be taken to avoid problems of inadequate urban storm water drainage systems, lack of sustainable urban storm management system and integrated waste management systems