Abstract:
Drainage is one of the most important factors to be considered in the world to road design,
construction and maintenance projects. Commonly, Inadequate drainage structure problems
become one of the most common sources of problems from the residents and runoff water,
flooding problems and this problem becoming worse in every year in Ethiopia. Poor existing
drains and their improper operation of drainage mainly cause damage and problems to the road
users and vehicles. Due to the development of infrastructures in the town, the surface runoff
water greatly increased in Ambo town thus, damaging the drainage structure and road surface.
The main objective of this research is, to investigate the major cause of the failure of drainage
structures and to estimate the quantity of runoff for existing drainage structures. In order to
attain the objective of the study, the researcher focused to collect Structural plan map of Ambo
town, existing drainage structure plan, and rainfall data from Ambo town municipal office and
Ethiopian metrological agency and also the dimensions of the side drainages were measured by
the researcher on the field by using tap meter. The methods of data to be processed was by
QSWAT for peak flow (Qp)to compare with the capacity of existing drainage structures of the
areas if Qc>Qp is safe and Leveling instruments was determine the design slope and measured
slope of the existing drainage structure at the area of case study.
According to the out puts of slope from the leveling instrument of surveying data’s, the slopes of
existing drainage and asphalt cross fall was a problem to drain the water from the road and
drainage structures properly. And peak flows from QSWAT was determined the capacity of the
existing drainage structure of trapezoidal and rectangular shapes. From these existing drainage
types of study area, the rectangular type was drain safely from the structure than trapezoidal
shape.
The concerned authorities are strongly recommended to control and monitor the structural failure
of drainage and Environmental problems by maintain and re-constructing the failure parts,
developing the skill of QSWAT and QGIS software and by providing a specific budget annually to
increase the service life and was the major recommended counter-measure
