Assessment of Failure on Drainage Structures along the Ethiopian National Railway line of Sebeta-Mieso(Case Study of Akaki River Crossing Drainage Structure)
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Date
2015-11
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Addis Ababa University
Abstract
A railway drainage system gives vital role for effective, efficient operation of rail track. This
study worked on an assessment of railway drainage system problem along the Addis Ababa-
Mieso railway line, specifically on Akaki rives crossing. It was done to check adequacy of
hydraulic structure provided on Akaki River crossing by undertaking hydrologic and hydraulic
analysis.
Hydrologic modeling of the Akaki catchment area was developed by HEC-GeoHMS program
with the help of Arc-GIS and hydrologic analysis was computed by HEC-HMS program. The
catchment land use, soil type, rainfall data, Akaki river stream flow data, etc were used to
develop hydrological model. SCS unit hydrograph and flood frequency analysis methods were
used to estimate instantaneous peak design discharge for 50 and 100 year return period. Model
input parameters were calibrated and verified with observed flow data of the river at Akaki
gauging station. Design discharge computed in this case for 50/100 year return period was
743.2m3/s and 834.5m3/s respectively at bridge location from catchment area of 894km2, where
these values were used to check adequacy of the bridge.
Hydraulic models were developed to determine water-surface profiles along the stream reaches
for the discharges established in the hydrologic analyses The HEC-RAS step-backwater
hydraulic analysis model was used to determine water-surface profiles for the bridge. Crosssectional
elevation data, hydraulic-structure geometries, roughness coefficients along with peakdischarge
estimated were used as input for the model. Based on available data’s water surface
profile for peak discharge was determined by the program.
Finally adequacy of the bridge was evaluated for both peak discharges. Although the site of the
bridge was fixed based on geometrical alignment of railway, the output of HEC-RAS analysis
confirmed that Akaki Railway Bridge has sufficient size to safely convey both peak design flow
during the design period. Thus, it is Akaki Railway Bridge was hydraulically efficient over its
design period.
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Keywords
Hydrologic models- HEC-HMS, HEC-RAS, Akaki New Railway Bridge, Objective function, Calibration, validation, Simulation