Time and tide: examining the potential for sediment delivery to a heavily modified tidal delta plain

Richard P Hale, Vanderbilt University, Nashville, TN, United States, Steven Lee Goodbred Jr, Vanderbilt University, Earth and Environmental Science, Nashville, TN, United States, Rachel Louise Bain, Vanderbilt University, Dept. of Earth and Environmental Sciences, Nashville, TN, United States and Carol Wilson, Louisiana State University, Baton Rouge, LA, United States
Abstract:
In SW Bangladesh, man-made barriers (“polders”) built since the 1960s to protect agricultural resources from seasonal flooding have drastically altered delta-plain dynamics. With the link between tidal channels and the delta plain destroyed and no pathway for the delivery of new sediment, compaction, tectonic subsidence, and global sea-level rise have resulted in a scenario where much of the land surface behind the barriers sits ~1.5 m below mean sea level. In the adjacent the Sundarbans National Forest (SNF), the lack of polders has allowed for sediment deposition during spring high tides, and sedimentation rates on the delta plain have kept pace with local sea level rise.

Recent research has demonstrated the potential for rapid sedimentation in the inhabited areas following polder damage or destruction (Auerbach et al., 2015). These authors observed ~40 cm/yr accumulation rates inside the poldered area following bank failures associated with a typhoon, and no obvious seasonality associated with the deposits. Preliminary research from within SNF, however, suggests that the accumulation rates are slightly faster during then monsoon (1.0-2.0 cm/yr) than the dry season (0.2-1.4 cm/yr). In this study, we address seasonal differences through a comparison of tidal elevations and suspended sediment concentrations (SSC) across tidal ranges and seasons, in both the SNF, and the tidal channels adjacent to the poldered region (PR). Water velocity appears to be the primary control on SSC, and there is no obvious seasonal variability in maximum observed SSC (PR: 0.1-0.8 g/l; SNF: 0.01-0.35 g/l). Peak tidal elevations remain unchanged across seasons, however the time of delta plain inundation time increases during the monsoon, which might control seasonal accumulation rates. Understanding more about this seasonal variability will be critical for future engineering and policy decisions surrounding how to best mitigate and manage land loss in the PR going forward.

Back to: Response of Coastal Sedimentary Systems to Anthropogenic Alterations and Climate Change I