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Backwater controls of avulsion location on deltas
Author(s) -
Chatanantavet Phairot,
Lamb Michael P.,
Nittrouer Jeffrey A.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2011gl050197
Subject(s) - geology , beach morphodynamics , overbank , river mouth , delta , hydrology (agriculture) , fluvial , river delta , submarine pipeline , channel (broadcasting) , plume , geomorphology , deposition (geology) , structural basin , oceanography , sediment transport , sediment , geotechnical engineering , geography , electrical engineering , aerospace engineering , meteorology , engineering
River delta complexes are built in part through repeated river‐channel avulsions, which often occur about a persistent spatial node creating delta lobes that form a fan‐like morphology. Predicting the location of avulsions is poorly understood, but it is essential for wetland restoration, hazard mitigation, reservoir characterization, and delta morphodynamics. Following previous work, we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length, i.e., the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin. To explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges. Results show that avulsion is less likely in the downstream portion of the backwater zone because, during high‐flow events, the water surface is drawn down near the river mouth to match that of the offshore plume, resulting in river‐bed scour and a reduced likelihood of overbank flow. Furthermore, during low‐discharge events, flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel‐fill timescale there. Both mechanisms favor preferential avulsion in the upstream part of the backwater zone. These dynamics are fundamentally due to variable river discharges and a coupled offshore river plume, with implications for predicting delta response to climate and sea level change, and fluvio‐deltaic stratigraphy.