Investigation on the causes of highway drainage system problem in addis ketema sub city of addis ababa

Abstract

Proper drainage system is required in developing urban areas. In Addis Ababa, drainage problem become an issue during rainy season. This study deals with investigation of urban drainage problem of Addis Ababa and a possible mitigation measure to overcome the problem. Despite there are many places in the addis ketema sub city facing urban drainage problem by considering major road and economical value selecting criteria; are selected for this study. Data collection methods were carried out using both primary and secondary data sources, which was accomplished with the help of topographic map and design data. The method used to investigate management problem direct field data collection and site visit the construction problem is analyzed using field survey as well as comparison of design with what is implemented in the ground. And evaluated by redesigning of the system using the computation sheet used in (FHWA) urban drainage design manual and (AACRA) urban drainage design manual. Design of urban drainage system evaluated in this research includes inlet spacing, pipe sizing and The Values of inlet spacing and pipe sizing obtained by redesigning was compared with what was implemented in the ground. Finally the collected data were after analyzed presented using Microsoft-excel, AutoCAD, tables, graphs and percentages. The result of this study shown that the problem was caused by sedimentation and insufficient drainage operation, over spaced inlet spacing and minimum pipe size was used. The investigation also shown; the curb inlets were over spaced and constructed with very small opening, the operation system of the drainage was in sufficient, negligence of siltation and debris control analysis in pipe size design, lack of Morphometry of hydrology consideration on design and Insufficient drainage operation maintenance and management Large inlet spacing was a cause over spread of storm water in the pavement of the road. This can be minimized by providing extra inlets especially on the sag point. The hydraulic capacity of existing pipe size was not sufficient to accommodate the flow with debris and silt sediment. Because of negligence of siltation and debris control analysis in pipe size design. Lack of consideration Morphometry of hydrology on design this leads to failure of drainage structures due to inadequate pipe size of drainage structures. Inadequate drainage operational management was also a cause of inlet not to work properly which aggravate the problem in the study area, so scheduled follow up and maintenance activity should be done Another measure to be taken was the upgrading of wetland; this will help stop the frequent back-flows which cause flooding and increase infiltration