Abstract:
A hydrodynamic coupled 1-D and 2-D flow
model has been developed in a rural terrain of northern India
where an industrial plant has been proposed. The source of
flooding in the area includes breach in canal in addition to
local site rainfall for which flood simulation has been carried
out. The design value of the local site rainfall is computed
based on PMP value obtained from IMD and frequency
analysis of daily rainfall of 6 raingauges in the area. The flow
in canal and breach section has been simulated in 1-D flow
model, MIKE 11 while the flow in floodplain and local site
rainfall has been simulated in 2-D model, MIKE 21 and both
are combined through MIKE FLOOD. Three cases of flood
simulation has been carried out representing the floodplain
by three different DEMs namely; DEM1, DEM2 and DEM3
of grid size of 180 m, 180 m and 10 m respectively. In DEM1,
the floodplain is represented by 180 m grid size using the
topographical information available in Survey of India (SOI)
toposheet at 1: 50,000 scale. The detailed topographical maps
(with CI <=1 m)/ surveys are available for selected areas only,
mainly for the project sites. For the study area the
topographical survey has been carried out at 2m CI and DEM at 10 m regular grid (DEM3) has been generated from it. The
DEM2 is generated by resampling the DEM3 at 180 m grid
size to save computational time and computing resources.
Hence, three cases of floodplain representation have been
developed and the flood inundation depth and flood level due
to rainfall estimates of 100 yr return period have been
computed. The results are analyzed to study the effect of
DEM grid size over the flood parameter. It is found that the
inundation depth is increased while the flood level is
decreased for finer DEM. This is due to better representations
of ponds/ terrain irregularities in finer DEM. The presence of
depressions in the area produces more flooding depth while it
also provides larger storage causing the overall decrease in
flood level. The impact of DEM grid size on computing
resources has also been analysed.
