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13.4.5 Flood Mitigation Measures
13.4.5.1 Diversion of Channel
Diversion of channel is another significant aspect by which we can take measures to
reduce the magnitude of floods in this area. It is mainly constructed to divert waters
from the main channel to control the flood. It can be controlled by diverting excess
water to purpose-built canals or floodways, which in turn deflect the water to temporary holding ponds or any other bodies of water where there is a minor risk or
impact to flooding. Here the study area is located at the junction between Ajay and
Bhagirathi rivers. Farakka Barrage can control the flow condition of Bhagirathi
River, and diversion of flow can be done for the Bhagirathi River through Farakka
Barrage during the flood season (Fig. 13.12), which will reduce the flow. In case of
Ajay River, we have not found any suitable area for diversion of flow due to absence
of palaeochannels as this region is agricultural dominated and highly populated
about 1000–1500 person/km
2
(Census of India 2011); it is difficult to divert the river
through this region. So flow diversion of Ajay River will cause inundation or floodlike situation in other areas which will not be a sustainable solution for region.
13.4.5.2 Channel Improvement
The main cause of flood in this region is gradually narrow river channel. So, channel
improvement will be the most important one step to mitigate the flood. We have
found that the Ajay River has decreases about 333.47 sq. metre of its bankfull crosssectional area from Noapara to its mouth. So, it is strongly recommended that if we
have to mitigate the flood condition in this region, we have to improve the channel
capacity. It can be done by deepening, widening and cleaning out of vegetation and
debris from the river bed; these changes in the river channel will help to increase the
water discharge capacity of the river. Channel improvement is supplemented by
natural river bank stabilization by constructing ripraps, planting deep root trees on
both sides of the river. Here the zone of no human encroachment has been demarcated based on the fluvial signature of the river (Fig. 13.13); this will give the space
for natural oscillation of river as well as to improve the bankfull carrying capacity
during peak flow. It is also recommended that if this method is being followed for
rest of the rivers in this region, it will reduce the flood magnitude to a greater extent.
13.4.5.3 Planting of Vegetation
Planting of vegetation can help to reduce rainfall runoff in flood-prone areas because
when plants grow in an area, the roots of plants dig deep into the soil and create
space between soil particles. When it rains in highlands, water that flows downhill
gets drained into the space created by the root system of plants. Due to this, chance
13 Flood Frequency Analysis and Its Management in Selected Part of Bardham…
13.4.5 Flood Mitigation Measures
13.4.5.1 Diversion of Channel
Diversion of channel is another significant aspect by which we can take measures to
reduce the magnitude of floods in this area. It is mainly constructed to divert waters
from the main channel to control the flood. It can be controlled by diverting excess
water to purpose-built canals or floodways, which in turn deflect the water to temporary holding ponds or any other bodies of water where there is a minor risk or
impact to flooding. Here the study area is located at the junction between Ajay and
Bhagirathi rivers. Farakka Barrage can control the flow condition of Bhagirathi
River, and diversion of flow can be done for the Bhagirathi River through Farakka
Barrage during the flood season (Fig. 13.12), which will reduce the flow. In case of
Ajay River, we have not found any suitable area for diversion of flow due to absence
of palaeochannels as this region is agricultural dominated and highly populated
about 1000–1500 person/km
2
(Census of India 2011); it is difficult to divert the river
through this region. So flow diversion of Ajay River will cause inundation or floodlike situation in other areas which will not be a sustainable solution for region.
13.4.5.2 Channel Improvement
The main cause of flood in this region is gradually narrow river channel. So, channel
improvement will be the most important one step to mitigate the flood. We have
found that the Ajay River has decreases about 333.47 sq. metre of its bankfull crosssectional area from Noapara to its mouth. So, it is strongly recommended that if we
have to mitigate the flood condition in this region, we have to improve the channel
capacity. It can be done by deepening, widening and cleaning out of vegetation and
debris from the river bed; these changes in the river channel will help to increase the
water discharge capacity of the river. Channel improvement is supplemented by
natural river bank stabilization by constructing ripraps, planting deep root trees on
both sides of the river. Here the zone of no human encroachment has been demarcated based on the fluvial signature of the river (Fig. 13.13); this will give the space
for natural oscillation of river as well as to improve the bankfull carrying capacity
during peak flow. It is also recommended that if this method is being followed for
rest of the rivers in this region, it will reduce the flood magnitude to a greater extent.
13.4.5.3 Planting of Vegetation
Planting of vegetation can help to reduce rainfall runoff in flood-prone areas because
when plants grow in an area, the roots of plants dig deep into the soil and create
space between soil particles. When it rains in highlands, water that flows downhill
gets drained into the space created by the root system of plants. Due to this, chance
13 Flood Frequency Analysis and Its Management in Selected Part of Bardham…