Bed-Bank Relationship and Flood Characterisation …
205
5 Conclusion
For flood characterisation, sediment budgeting, spatio-temporal changes in the
pattern of aggradation play crucial role. Reach scale study of river bed and the
river bank relationship can give important clues to assess the trend of flood vulnerability. During 1915–1975, the principal site of aggradation was concentrated mostly
in the upstream part of the Brahmaputra valley which is evident from the reach scale
sandbar/channel area ratios computed for the length of 230 km. However, during
1975–2015, the site of aggradation has shifted further downstream in and around
Majuli. A comparative study of width indices for different times (1915, 1975 and
2015) with the present depth index (2017 imagery) helps to understand the stream
power variability of the river flow and its consequences on the bank erosion and
bed incision. Raising embankments help to incubate flood vulnerability; five-stage
increments in river bed thickness show clearly the spread of vulnerability along both
the right and left bank of the Brahmaputra River. The areal extent of multi-stage
flood inundation was generated in case of flood triggering due to single or multiple
dam failures or embankment breaching. For flood head increases from +0.5 m to +
1.5 m, more of north bank areas are vulnerable; however, for +2.5 m increase in the
flood water head, vulnerability of both the banks reaches uniformity.
Acknowledgements First two authors acknowledge the help extended by Dibrugarh University
for providing financial and administrative support to conduct field visits.
References
1. Schumm SA (1981) Evolution and response of the fluvial system: sedimentologic implications.
Soc Econ Paleontol Mineral Spec Publ 31:19–29
2. Robert, A.: River processes—an introduction to fluvial dynamics. Arnold, a member of the
Hodder Headline Group, GB (2003)
3. Coleman JM (1969) Brahmaputra River channel processes and sedimentation. Sediment Geol
3:129–239
4. Hovius N (1998) Controls on sediment supply by larger rivers. In: Shanley KW, McCabe PJ
(eds.) Relative role of eustasy, climate, and tectonism in continental rocks. Soc Sediment Geol
SEPM Spec Publ 59:3–16 (1998)
5. Goswami DC (1985) Brahmaputra River, Assam, India: Physiography, basin denundation and
channel aggradation. Water Resour Res 21:959–978
6. Latrubesse E (2008) Patterns of anabranching channels: the ultimate end-member adjustment
of mega rivers. Geomorphology 101:130–145
7. Bracciali L, Najman Y, Parrish RR, Akhter SH, Millar I (2015) The Brahmaputra tale of
tectonics and erosion: early Miocene river capture in the Eastern Himalaya. Earth Planet Sci
Lett 415:25–37
8. Brookfield ME (1998) The evolution of the great river systems of southern Asia during the
Cenozoic India-Asia collision: rivers draining southwards. Geomorphology 22:285–312
205
5 Conclusion
For flood characterisation, sediment budgeting, spatio-temporal changes in the
pattern of aggradation play crucial role. Reach scale study of river bed and the
river bank relationship can give important clues to assess the trend of flood vulnerability. During 1915–1975, the principal site of aggradation was concentrated mostly
in the upstream part of the Brahmaputra valley which is evident from the reach scale
sandbar/channel area ratios computed for the length of 230 km. However, during
1975–2015, the site of aggradation has shifted further downstream in and around
Majuli. A comparative study of width indices for different times (1915, 1975 and
2015) with the present depth index (2017 imagery) helps to understand the stream
power variability of the river flow and its consequences on the bank erosion and
bed incision. Raising embankments help to incubate flood vulnerability; five-stage
increments in river bed thickness show clearly the spread of vulnerability along both
the right and left bank of the Brahmaputra River. The areal extent of multi-stage
flood inundation was generated in case of flood triggering due to single or multiple
dam failures or embankment breaching. For flood head increases from +0.5 m to +
1.5 m, more of north bank areas are vulnerable; however, for +2.5 m increase in the
flood water head, vulnerability of both the banks reaches uniformity.
Acknowledgements First two authors acknowledge the help extended by Dibrugarh University
for providing financial and administrative support to conduct field visits.
References
1. Schumm SA (1981) Evolution and response of the fluvial system: sedimentologic implications.
Soc Econ Paleontol Mineral Spec Publ 31:19–29
2. Robert, A.: River processes—an introduction to fluvial dynamics. Arnold, a member of the
Hodder Headline Group, GB (2003)
3. Coleman JM (1969) Brahmaputra River channel processes and sedimentation. Sediment Geol
3:129–239
4. Hovius N (1998) Controls on sediment supply by larger rivers. In: Shanley KW, McCabe PJ
(eds.) Relative role of eustasy, climate, and tectonism in continental rocks. Soc Sediment Geol
SEPM Spec Publ 59:3–16 (1998)
5. Goswami DC (1985) Brahmaputra River, Assam, India: Physiography, basin denundation and
channel aggradation. Water Resour Res 21:959–978
6. Latrubesse E (2008) Patterns of anabranching channels: the ultimate end-member adjustment
of mega rivers. Geomorphology 101:130–145
7. Bracciali L, Najman Y, Parrish RR, Akhter SH, Millar I (2015) The Brahmaputra tale of
tectonics and erosion: early Miocene river capture in the Eastern Himalaya. Earth Planet Sci
Lett 415:25–37
8. Brookfield ME (1998) The evolution of the great river systems of southern Asia during the
Cenozoic India-Asia collision: rivers draining southwards. Geomorphology 22:285–312