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Title page for ETD etd-11162012-235327


Type of Document Dissertation
Author Rogers, Kimberly Gay
URN etd-11162012-235327
Title Spatial and temporal sediment distribution from river mouth to remote depocenters in the Ganges-Brahmaputra delta, Bangladesh
Degree PhD
Department Environmental Engineering
Advisory Committee
Advisor Name Title
Steven L. Goodbred, Jr. Committee Chair
David J. Furbish Committee Member
Frank L. Parker Committee Member
James H. Clarke Committee Member
Keywords
  • Coastal Sediment Transport
  • Delta
  • Ganges
  • Submarine Canyon
Date of Defense 2012-11-02
Availability unrestricted
Abstract
The Ganges-Brahmaputra Rivers annually transport >700 x 106 tons of sediment to the world ocean. Sediment delivery to the coast has kept pace with sea level rise since the early Holocene, allowing subaerial and subaqueous growth of the delta. However, dispersal of these sediments beyond the river mouth has been only partially quantified. The goals of this research are to identify dispersal mechanisms and pathways on the understudied inner shelf of the Bay of Bengal, and to determine how river sediments are delivered to offshore and onshore depocenters. This research focuses on the ‘abandoned’ Sundarbans region of the lower delta, and a nearshore submarine canyon head.

The Sundarbans delta plain is disconnected from major distributaries and is susceptible to the meter of sea level rise predicted for the 21st century. However, direct sedimentation measurements reveal high regional accretion rates (1.0 ±0.9 cm yr-1). The high (2-4 m) tidal range and monsoon set up enable sediment transport far inland from the coast. Short-lived radioisotope inventories indicate ~50% of new sediment is sourced from the flood pulse; the remaining half are diluted with reworked older sediments. Net sedimentation accounts for ~10% of annual river discharge; accretion rates are double regional sea level rise rate of 5 mm yr-1.

The Swatch of No Ground is a shallow-headed, aggradational canyon. Sediment transport in the canyon head occurs through progradation of the subaqueous delta onto canyon flanks, sediment bypass via gullies, and erosional mass failures. Although the canyon head is 150 km from the active river mouth, very high sedimentation rates (5-50 cm yr-1) have balanced the loss of mass from failures caused by storms that appear to recur on decadal timescales. Widespread failures around the canyon head associated with the passing of large storm in 2007 resulted in the removal of >2 years of river sediment input. Overall, the results of this research indicate sediment transported west of the river mouth is partitioned each year between the canyon head and the lower delta plain.

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