15.5 Results and Discussion
Simulation and modelling for flood estimation is
a rapidly developing field in hydrology
(Boughton and Droop 2003). The results are a
good way of providing relevant information on
how the flood is going to behave at the location
where people live and how the flood will affect
them (Shaviraachin 2005). Flood simulation
model gives a clear picture about the extent of
flood water in respect of water levels of the river.
This model has been prepared on the basis of
flood frequency curve and rating curve of the
rivers.
15.5.1 Flood Frequency Analysis
To identify discharge for the 50 and 100 years
return period, flood frequency curve of the Haora
River has been prepared where flood recurrence
and associated discharge have been plotted on
log–log graph along the abscissa and ordinate,
respectively (Fig. 15.2). Then, the frequency
curve has been extrapolated graphically along the
upper trend, so as to include 50 and 100 year
flood event. From the graph, it can be predicted
that in every 10, 50 and 100 years the River
Haora would have a flood discharge of 290, 400
and 470 cumec or more, respectively. Again, by
extrapolating the rating curve along the upper
trend, the water levels associated with each of
these discharge of different return periods have
been determined (Fig. 15.3 and Table 15.1).
The Lohar Nala is an ungauged river and
therefore, no hydrological data is available. On
the basis of field observation and interaction with
the local people it was noted that, during last
100 years, highest inundation depth was
observed as 2.5–3 m above the river bank (where
the contour height is 0–2 m) with 9 m water
level a.m.s.l. It indicates that the chances of
occurrence of this much inundation depth or
more are expected within the next 100 years
period. In the Lohar flood plain the recent inundation depth is 1.5–2.5 m from the river bank
with 8 m water level of the river from the mean
sea level. Thus, the flood simulation model of the
Lohar Nala has been prepared on the basis of 8
and 9 m water level for 50 years and 100 years
return period, respectively. After that, those layers of simulation have been overlaid on West
Tripura District and flood simulation model of
West Tripura District for 50 and 100 years return
periods has been prepared (Fig. 15.4).
15.5.2 Outcome of the Flood
Simulation Model
This model gives the clear picture about the
extent of flood water and also the flood affected
areas in the West Tripura District, which may
occur in the next 50 and 100 years. Government
may take necessary steps to reduce its effects on
the flood plain dwellers on the basis of this
model. The model indicates that about 180 and
300 km
2 areas, situated at 1–26 m contour
height, will be affected in the 50 and 100 years
return period, respectively (Table 15.2).
From this model it is found that, if the water
level of the Haora River and the Lohar Nala
increase up to 11 and 8 m, respectively, in
50 years return period, then inundation depth
will also increase up to 4 m in different affected
mouzas of this district (Fig. 15.5). On the other
hand, in 100 years return period, the inundation
depth will increase up to 5 m when the water
level will reach up to 12 m in case of the Haora
River and 9 m in case of the Lohar Nala
(Fig. 15.6 and Table 15.3). During the flood of
50 years return period about six mouzas, namely
Pratapgarh, Bridhyanagar, Khayerpur, Jogendranagar along the Haora River and Kalkalia,
Bamutia along the Lohar Nala, will be highly
vulnerable to flood hazard due to high inundation
depth of 2.5–4 m, and large number of affected
population (Table 15.3) leads to the high risk of
flood.
But, in the flood of 100 years return period
about 11 mouzas, namely Pratapgarh, Bridhyanagar, Khayerpur, Jogendranagar, Agartala
(capital city of the state), Ramnagar, Uttar
Champamura, Mekhlipara along the Haora River
204
M. Bhowmik and N. Das (Pan)
Simulation and modelling for flood estimation is
a rapidly developing field in hydrology
(Boughton and Droop 2003). The results are a
good way of providing relevant information on
how the flood is going to behave at the location
where people live and how the flood will affect
them (Shaviraachin 2005). Flood simulation
model gives a clear picture about the extent of
flood water in respect of water levels of the river.
This model has been prepared on the basis of
flood frequency curve and rating curve of the
rivers.
15.5.1 Flood Frequency Analysis
To identify discharge for the 50 and 100 years
return period, flood frequency curve of the Haora
River has been prepared where flood recurrence
and associated discharge have been plotted on
log–log graph along the abscissa and ordinate,
respectively (Fig. 15.2). Then, the frequency
curve has been extrapolated graphically along the
upper trend, so as to include 50 and 100 year
flood event. From the graph, it can be predicted
that in every 10, 50 and 100 years the River
Haora would have a flood discharge of 290, 400
and 470 cumec or more, respectively. Again, by
extrapolating the rating curve along the upper
trend, the water levels associated with each of
these discharge of different return periods have
been determined (Fig. 15.3 and Table 15.1).
The Lohar Nala is an ungauged river and
therefore, no hydrological data is available. On
the basis of field observation and interaction with
the local people it was noted that, during last
100 years, highest inundation depth was
observed as 2.5–3 m above the river bank (where
the contour height is 0–2 m) with 9 m water
level a.m.s.l. It indicates that the chances of
occurrence of this much inundation depth or
more are expected within the next 100 years
period. In the Lohar flood plain the recent inundation depth is 1.5–2.5 m from the river bank
with 8 m water level of the river from the mean
sea level. Thus, the flood simulation model of the
Lohar Nala has been prepared on the basis of 8
and 9 m water level for 50 years and 100 years
return period, respectively. After that, those layers of simulation have been overlaid on West
Tripura District and flood simulation model of
West Tripura District for 50 and 100 years return
periods has been prepared (Fig. 15.4).
15.5.2 Outcome of the Flood
Simulation Model
This model gives the clear picture about the
extent of flood water and also the flood affected
areas in the West Tripura District, which may
occur in the next 50 and 100 years. Government
may take necessary steps to reduce its effects on
the flood plain dwellers on the basis of this
model. The model indicates that about 180 and
300 km
2 areas, situated at 1–26 m contour
height, will be affected in the 50 and 100 years
return period, respectively (Table 15.2).
From this model it is found that, if the water
level of the Haora River and the Lohar Nala
increase up to 11 and 8 m, respectively, in
50 years return period, then inundation depth
will also increase up to 4 m in different affected
mouzas of this district (Fig. 15.5). On the other
hand, in 100 years return period, the inundation
depth will increase up to 5 m when the water
level will reach up to 12 m in case of the Haora
River and 9 m in case of the Lohar Nala
(Fig. 15.6 and Table 15.3). During the flood of
50 years return period about six mouzas, namely
Pratapgarh, Bridhyanagar, Khayerpur, Jogendranagar along the Haora River and Kalkalia,
Bamutia along the Lohar Nala, will be highly
vulnerable to flood hazard due to high inundation
depth of 2.5–4 m, and large number of affected
population (Table 15.3) leads to the high risk of
flood.
But, in the flood of 100 years return period
about 11 mouzas, namely Pratapgarh, Bridhyanagar, Khayerpur, Jogendranagar, Agartala
(capital city of the state), Ramnagar, Uttar
Champamura, Mekhlipara along the Haora River
204
M. Bhowmik and N. Das (Pan)