EP061-0029
Sediment Infilling of Tidal Channels and Repurposing Potential of Dredge Spoils for Reducing Flood Risk in the Poldered Landscape of Bangladesh
Wednesday, 16 December 2020
Poster
Leslie Anne Valentine, Louisiana State University, Baton Rouge, LA, United States, Carol Wilson, Louisiana State University, Geology & Geophysics, Baton Rouge, LA, United States; Coastal Studies Institute, Baton Rouge, LA, United States and Kimberly G Rogers, East Carolina University, Department of Coastal Studies, Greenville, NC, United States
Abstract:
Many distributary channels in the Ganges-Brahmaputra-Meghna (GBM) tidal delta in Southwest Bangladesh have morphed into terminal, headless channels in recent decades as a result of embankment, or “polder”, construction that converted active tidal channels into dead-end segments. Since polder construction began in the 1960s, terminal tidal channels proximal to the polders have been infilling and many channels must be regularly dredged to maintain navigability. Dredge spoils are typically placed alongside channel margins, forming an artificial levee outside of the polder walls. However, dredge spoil material could instead be used to alleviate flood risk by increasing plinth elevation beneath houses, elevating land surfaces within polders, and/or repairing polders that have been breached during cyclones. We quantify the volume of sediment that is infilling tidal channels in southwest Bangladesh and suggest alternative uses for dredge spoils that could reduce flood risk in this vulnerable delta of 15 million people.
Project sites are located along channels proximal to and within Polder 34/2, near the coastal towns of Khulna, Rampal, and Dacope. Aerial imagery from 1984 to 2020 was used to measure change in channel width and estimate the volume of sediment that infilled a 20-km stretch of the channels before and after dredging. We found the average channel width decreased by 39%, 72%, and 87% for Khulna, Rampal, and Dacope channels, respectively, resulting in cumulative deposition of 26.1 x 106 m3 of sediment. Dredging at all three locations between years 2016-2020 removed a total of 1.3 x 106 m3 of sediment. We estimate that this volume of sediment could sufficiently raise nearly 10,000 houses above base flood elevation or contribute to the repair of ~15 km of embankments.
Across SW Bangladesh, approximately 462 x 106 m3 of new land has emerged as a result of channel infilling since polder construction began. If these channels are dredged to 10% of their original width such as the channels in our three study sites, the resulting dredge spoil could elevate an additional ~270,000 houses or repair ~500 km of embankments.
