Abstract:
This study focused mainly on river training and water utilization option in
Derek Wuha Catchment of North Wolo zone of Amhara National Regional
State. In the study, a GIS based semi-distributed watershed model (HEC
HMS), HEC-GeoHMS and arcHYDRO softwares were used to establish
rainfall-runoff transformations of the ungauged basin while HEC-RAS was
utilized for flood depth estimation and bank stability analysis input parameter
generation in the catchments.
From the hydrological analysis the peak discharge of the catchments was
found to be 103 . 7m
3
/sec with 850.9x10
3
m
3
volume of water yield for 100
year return period of 24 hour rainfall at about 31.14km
2
areas of the
catchments.
For the discharge of 103.7m
3
/sec which is obtained from hydrology model,
the corresponding flow depth was generated using HEC-RAS and about
326m of the left river channel [at nursery site starting at 2872m from bridge]
is incapable of safely passing the discharge without over topping .
Furthermore, the bridge near the outlet of the catchment was simulated with
different flood magnitudes and it was observed that the capacity of the
bridge could not safely pass a 25 year return period discharge.
The river bed and bank material was tested in soil laboratory at Kombolcha
Soil and construction materials testing laboratory to determine various
engineering properties of the soils and it was found that 31.6% of the bed
material is voids at the subsurface dam proposed site. Based on this water
holding capacity of the river bed materials, if subsurface barrier or dam is
constructed across the river with a depth of 8m, a water requirement of the
local residents can be fulfilled at least for 6months of the year without any
recharge.
The river bank just downstream of bridge location was analyzed using Bank
Stability and Toe Erosion Model with the protection work incorporated and it
responds to conditionally stable safety factor.
