Abstract:
This study focused mainly on application of a GIS based semi-distributed
watershed model (HEC-HMS) for estimation of peak discharges and run off
hydrographs. The Digital Elevation Model (DEM) of the study area was used to
extract the physical characteristics of the watershed using Arc-Hydro and
Geospatial Hydrologic Model Extension HEC-GeoHMS. HEC-HMS Hydrological
Model was used to estimate discharges and Runoff Hydrographs for different
return period at different locations of the water shed. Finally determination of
water surface profiles for different flow scenarios were made using HEC-RAS
and mitigation measures were proposed to alleviate the flood problem in the
study area. The peak discharge generated by the HEC-HMS Model at the
upstream end of Upper Shelle River is 57.7m
3
/s and this value falls to 34.4m
3
/s
when flood is diverted at the upstream of the river. From the HEC-RAS Model
analysis, it is observed that ,when there is no diversion of upstream flood, most
part of the river is overtopped by flood of 100-year return period and when flood
is diverted from upstream junction, 50% of the length of the reach will not be
over topped totally and the depth of the overtopping · flood decreased by 50%
for the rest of the length of the reach when compared with when there is no
diversion of upstream flood. Therefore, diversion of upstream flood or
construction of levees has been proposed as alternative remedial measures inboth cases to protect flooding of upper shelle river.
