Assessment Of Failure On Drainage Structures Along The Ethiopian National Railway Line Of Sebeta-mieso

A railway drainage system gives vital role for effective, efficient operation of rail track. Thisrnstudy worked on an assessment of railway drainage system problem along the Addis Ababa-rnMieso railway line, specifically on Akaki rives crossing. It was done to check adequacy ofrnhydraulic structure provided on Akaki River crossing by undertaking hydrologic and hydraulicrnanalysis.rnHydrologic modeling of the Akaki catchment area was developed by HEC-GeoHMS programrnwith the help of Arc-GIS and hydrologic analysis was computed by HEC-HMS program. Therncatchment land use, soil type, rainfall data, Akaki river stream flow data, etc were used torndevelop hydrological model. SCS unit hydrograph and flood frequency analysis methods werernused to estimate instantaneous peak design discharge for 50 and 100 year return period. Modelrninput parameters were calibrated and verified with observed flow data of the river at Akakirngauging station. Design discharge computed in this case for 50/100 year return period wasrn743.2m3/s and 834.5m3/s respectively at bridge location from catchment area of 894km2, wherernthese values were used to check adequacy of the bridge.rnHydraulic models were developed to determine water-surface profiles along the stream reachesrnfor the discharges established in the hydrologic analyses The HEC-RAS step-backwaterrnhydraulic analysis model was used to determine water-surface profiles for the bridge. Crosssectionalrnelevation data, hydraulic-structure geometries, roughness coefficients along with peakdischargernestimated were used as input for the model. Based on available data’s water surfacernprofile for peak discharge was determined by the program.rnFinally adequacy of the bridge was evaluated for both peak discharges. Although the site of thernbridge was fixed based on geometrical alignment of railway, the output of HEC-RAS analysisrnconfirmed that Akaki Railway Bridge has sufficient size to safely convey both peak design flowrnduring the design period. Thus, it is Akaki Railway Bridge was hydraulically efficient over itsrndesign period.

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