Tidal river management in the south west Ganges-Brahmaputra delta in Bangladesh: Moving towards a transdisciplinary approach?

Since the 1960s, ~5000 km2 of tidal deltaplain in southwest Bangladesh has been embanked and converted to densely inhabited, agricultural islands (i.e., polders). This landscape is juxtaposed to the adjacent Sundarbans, a pristine mangrove forest, both well connected by a dense network of tidal channels that effectively convey water and sediment throughout the region. The extensive embanking in poldered areas, however, has greatly reduced the tidal prism (i.e., volume of water) transported through local channels. We reveal that >600 km of these major waterways have infilled in recent decades, converting to land through enhanced sedimentation and the direct blocking of waterways by embankments and sluice gates. Nearly all of the observed closures (~98%) have occurred along the embanked polder systems, with no comparable changes occurring in channels of the Sundarbans (

/pdf/widespread-infilling-of-tidal-channels-and-navigable-4jf1mpcnmm.pdf

Widespread Infilling of Tidal Channels and Navigable Waterways in the Human-Modified Tidal Deltaplain of Southwest Bangladesh

The article analyzes Tidal River Management in Bangladesh from a social learning perspective. Four cases were investigated using participatory assessment. Knowledge acquisition through transformations in the Tidal River Management process was explored as an intended learning outcome. The study finds that social learning occurred more prominently at the individual stakeholder level and less at the collective level. For Tidal River Management to be responsive and sustainable, especially in times of increased uncertainty and climate vulnerability, more attention needs to be paid to coordination and facilitation of multi-level learning that includes all stakeholders.

Social learning for adaptive delta management: Tidal River Management in the Bangladesh Delta

Modern social-ecological systems are often partly engineered to enhance the robustness (or reduce the variance) of human welfare to environmental fluctuations over a foreseeable time horizon. Recent studies show, however, that subtle trade-offs are usually inherent in such efforts of enhancing short-term robustness. Managing variance on short time scales is likely to be associated with the buildup of hidden fragilities on longer time scales. Using a flood-prone social-ecological system (SES) of coastal Bangladesh as an example, this paper investigates some of the ways in which such robustness-fragility trade-offs can manifest. This SES has been extensively modified in the last few decades through the construction of large-scale flood protection structures (polders) and the introduction of commercial shrimp farming to enhance the robustness of food production to hydrological variability. Our case study analysis of the long-term changes in the SES shows that, although the modifications helped with stability in short time scales, the resulting changes also induced unforeseen problems such as infrastructure maintenance issues, land degradation and sinking, and exposure to market volatility. With this paper therefore we contribute to better understanding of the notion of robustness-fragility trade-offs by illustrating an exemplary case of the phenomenon in the engineered coastal environment context.

/pdf/robust-yet-fragile-nature-of-partly-engineered-social-20l6g6djgk.pdf

Robust-yet-fragile nature of partly engineered social-ecological systems: a case study of coastal Bangladesh

. The landscape of southwest Bangladesh, a region constructed primarily by
fluvial processes associated with the Ganges River and Brahmaputra River, is now
maintained almost exclusively by tidal processes as the fluvial system has
migrated east and eliminated the most direct fluvial input. In natural areas such
as the Sundarbans National Forest, year-round inundation during spring high
tides delivers sufficient sediment that enables vertical accretion to keep
pace with relative sea-level rise. However, recent human modification of the
landscape in the form of embankment construction has terminated this pathway
of sediment delivery for much of the region, resulting in a startling
elevation imbalance, with inhabited areas often sitting >1  m
below mean high water. Restoring this landscape, or preventing land loss in
the natural system, requires an understanding of how rates of water and
sediment flux vary across timescales ranging from hours to months. In this
study, we combine time series observations of water level, salinity, and
suspended sediment concentration with ship-based measurements of large
tidal-channel hydrodynamics and sediment transport. To capture the greatest
possible range of variability, cross-channel transects designed to encompass
a 12.4 h tidal cycle were performed in both dry and wet seasons during
spring and neap tides. Regional suspended sediment concentration begins to increase in August,
coincident with a decrease in local salinity, indicating the arrival of the
sediment-laden, freshwater plume of the combined Ganges–Brahmaputra–Meghna
rivers. We observe profound seasonality in sediment transport, despite
comparatively modest seasonal variability in the magnitude of water
discharge. These observations emphasize the importance of seasonal sediment
delivery from the main-stem rivers to this remote tidal region. On tidal
timescales, spring tides transport an order of magnitude more sediment than
neap tides in both the wet and dry seasons. In aggregate, sediment transport
is flood oriented, likely as a result of tidal pumping. Finally, we note that
rates of sediment and water discharge in the tidal channels are of the same
scale as the annually averaged values for the Ganges and Brahmaputra rivers.
These observations provide context for examining the relative importance of
fluvial and tidal processes in what has been defined as a quintessentially
tidally influenced delta in the classification scheme of Galloway (1975).
These data also inform critical questions regarding the timing and magnitude
of sediment delivery to the region, which are especially important in
predicting and preparing for responses of the natural system to ongoing
environmental change.

/pdf/observations-and-scaling-of-tidal-mass-transport-across-the-34ge2ptdoj.pdf

Observations and scaling of tidal mass transport across the lower Ganges–Brahmaputra delta plain: implications for delta management and sustainability

The south west coastal zone of Bangladesh have been affected by rampant water logging due to vulnerable climate, silted rivers and stumpy terrain; and introduction of IWRM and TRM at some places of the zone has substantially safeguarded the circumstance. This study aims to assess the benefits achieved due to implementation of IWRM in parts of Khulna and Jessore districts, and investigate some technical aspects evolving TRM. Analyses have been carried out using satellite images, RS and GIS technology, Digital Elevation Model (DEM) and field investigations. A mathematical formulation has been made to assess rate of tidal sedimentation due to TRM and selection strategies of tidal basins. The study comes up with evidences of considerable advancements in regional livelihood i.e. flood resistance, cultivated lands, cultivable area, cropping intensities and food security due to IWRM. Moreover, the technical facts established on TRM would help planners to have vivid perception regarding the process.

/pdf/integrated-water-resources-management-iwrm-impacts-in-south-2q28bak9gc.pdf

Rahman Md. Atiqur

Papers

Integrated Water Resources Management (IWRM) Impacts in South West Coastal Zone of Bangladesh and Fact-Finding on Tidal River Management (TRM)