Abstract

Southwestern Bangladesh has been seriously affected by perennial waterlogging over the last few decades. It is primarily due to excessive riverbed siltation outside the polders after the construction of embankments along both sides of the tidal rivers. These embankments de-linked the huge natural floodplains and restricted a gradual process of natural deposition inside the polders. An introduction of the tidal basin concept by temporary de-poldering (embankment cut) at some designated locations has substantially solved the issues. The current chapter looks at the historical practice of flood/sediment management, the evolution of embankments and their de-poldering, inclusion of Tidal River Management (TRM) in long term flood/sediment management, and discusses a technical aspect of flood/sediment dynamics across the tidal river system. The process of restoring beneficial tidal flooding by cutting embankment at certain locations, commonly known as TRM, is not a novel method. The TRM has started from age-old practice and proves technically one of the effective methods of sustainable flood/sediment management in the tide-dominated river system. It is an example of building with nature, where little human interventions are needed, and a resilient measure for waterlogging, drainage-congestion, and river-siltation.

Highlights

  • Before the lowlands were enclosed by earthen embankments, that keep the main tidal channels outside the polder, the tidal river would inundate vast tract of lowland two times in a day

  • Tidal River Management (TRM) evolved into an environmentally accepted flood/sediment management practice based on indigenous knowledge and it contributes to land heightening, flood resistance, and food security

  • The landless farmers and poor fishermen are the main sufferers of TRM implementation

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Summary

Introduction

For millennia the Bengal delta has been home to dynamic interplay of sediment, water, and land. They used low earthen embankments during eight dry months of the year (commonly known as “ostomasi bundh” in local Bengali language) for prevention of tidal intrusion and protection of agricultural lands. Polders were constructed to protect land and livelihood from floods, salinity intrusion and to facilitate increased agricultural production. Due to the heavy siltation at the rivers’ mouth, their distributaries virtually gets no water from upstream in dry Temporary De-Poldering for a Long Term Flood/Sediment Management in the Southwestern.

Emergence of de-poldering
Shifting of Tidal River Management
Toward sustainable solution
Findings
Conclusion
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