Hydrologic and Hydraulic Adequacy Assessment of Drainage Structures in Bila Town
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Date
2019-03
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Addis Ababa University
Abstract
The objective of the study is to assess adequacy of Drainage structures of Bila town. The study
employed both primary and secondary data collection. The primary data collection were observation
(field visit), and photographs that show the existing drainage structure conditions and information that
were gathered from the residents about the drainage structures during the rainy season. The secondary
data sources were master plan of the town, rainfall data, and demography of the area, socio economy
of the town, land use land cover information and climatic condition.
Daily rainfall data is obtained from nearby Nedjo rain gage station. Consistency of the rainfall was
checked With Double mass curve analysis using rain gage stations Gimbi, Dengero, Deddessa, Ayira
and Dembidollo and fitting distribution frequency is checked using log Pearson type III method.
The catchment is divided in to 5 small sub catchments, 13 conduits, with 13 junction nodes and 5
outfall. Tape meter and GPS is used to obtain dimension width, depth and elevation of each drainage
structures. Sub catchment Imperviousness is obtained using land use land cover data and percentage
of imperviousness for different land surface.
Hydrologic analysis and hydraulic analysis was carried out by EPA SWMM 5 in which used to
simulate response of catchment to rainfall events in which runoff, water depth profile, node surcharge,
outfall loading, node flooding ,link flow and conduit surcharge are obtained. Runoff is also obtained
from rational formula for comparison purpose. Parameters needed for rational method are taken from
ERA manual. And selected extreme daily event was disaggregated into hourly events using reduction
formula. At point culvert found is where outfall loading obtained therefore maximum discharge and
peak discharge is used to analysis culverts using HY-8 culvert analysis tool.
The results from the model show that there are nodes flooded, storm water network system has been
not well planned and has not sufficient carrying capacity to satisfy the simulated rainfall event.
Then storage facilities Detention pond was proposed for reduction of flooding effect at downstream
where coffee plant is affected
Finally appropriate recommendation is given in order to have a standardized and harmonized urban
drainage systems
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Keywords
Drainage Structures, Hydrologic, Hydraulic Adequacy