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Avulsion cycles and their stratigraphic signature on an experimental backwater-controlled delta

Ganti, Vamsi and Chadwick, Austin J. and Hassenruck-Gudipati, Hima J. and Lamb, Michael P. (2016) Avulsion cycles and their stratigraphic signature on an experimental backwater-controlled delta. Journal of Geophysical Research. Earth Surface, 121 (9). pp. 1651-1675. ISSN 2169-9003. http://resolver.caltech.edu/CaltechAUTHORS:20160818-100157512

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Abstract

River deltas grow in large part through repeated cycles of lobe construction and channel avulsion. Understanding avulsion cycles is important for coastal restoration and ecology, land management, and flood hazard mitigation. Emerging theories suggest that river avulsions on lowland deltas are controlled by backwater hydrodynamics; however, our knowledge of backwater-controlled avulsion cycles is limited. Here we present results from an experimental delta that evolved under persistent backwater hydrodynamics achieved through variable flood discharges, shallow bed slopes, and subcritical flows. The experimental avulsion cycles consisted of an initial phase of avulsion setup, an avulsion trigger, selection of a new flow path, and abandonment of the parent channel. Avulsions were triggered during the largest floods (78% of avulsions) after the channel was filled by a fraction (0.3 ± 0.13) of its characteristic flow depth at the avulsion site, which occurred in the upstream part of the backwater zone. The new flow path following avulsion was consistently one of the shortest paths to the shoreline, and channel abandonment occurred through temporal decline in water flow and sediment delivery to the parent channel. Experimental synthetic stratigraphy indicates that bed thicknesses were maximum at the avulsion sites, consistent with our morphologic measurements of avulsion setup and the idea that there is a record of avulsion locations and thresholds in sedimentary rocks. Finally, we discuss the implications of our findings within the context of sustainable management of deltas, their stratigraphic record, and predicting avulsions on deltas.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/2016JF003915DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2016JF003915/abstractPublisherArticle
ORCID:
AuthorORCID
Lamb, Michael P.0000-0002-5701-0504
Additional Information:© 2016 American Geophysical Union. Issue online: 15 October 2016; Version of record online: 23 September 2016; Accepted manuscript online: 17 August 2016; Manuscript Accepted: 15 August 2016; Manuscript Revised: 8 August 2016; Manuscript Received: 11 April 2016. We thank Brian Fuller for assistance in conducting the experiments and Kirby Sikes for assistance in analysis of the dye videos. Critical and constructive reviews by David Hoyal and two anonymous reviewers on an earlier draft improved the presentation of this work. M.P.L. acknowledges support from National Science Foundation (grants OCE-1233685 and 1427177), the California Institute Technology Terrestrial Hazards Observations and Reporting Center (THOR) program made possible by Foster and Coco Stanback, and the Royal Academy of Engineering Distinguished Visiting Professor Fellowship from the Imperial College London. V.G. acknowledges further support from NCED2 Synthesis Postdoctoral Fellowship, and the Imperial College London Junior Research Fellowship. Data used in this manuscript are available upon request from V.G. (v.ganti@imperial.ac.uk) and A.J.C. (achadwick@caltech.edu).
Funders:
Funding AgencyGrant Number
NSFOCE-1233685
NSFOCE-1427177
Caltech Terrestrial Hazards Observations and Reporting center (THOR)UNSPECIFIED
Foster and Coco Stanback Postdoctoral FellowshipUNSPECIFIED
Imperial College LondonUNSPECIFIED
NCED2UNSPECIFIED
Subject Keywords:Avulsions; backwater; flood variability; sedimentary record
Record Number:CaltechAUTHORS:20160818-100157512
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160818-100157512
Official Citation:Ganti, V., A. J. Chadwick, H. J. Hassenruck-Gudipati, and M. P. Lamb (2016), Avulsion cycles and their stratigraphic signature on an experimental backwater-controlled delta, J. Geophys. Res. Earth Surf., 121, 1651–1675, doi:10.1002/2016JF003915
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69751
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:18 Aug 2016 18:59
Last Modified:03 Mar 2017 19:15

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