Temporary De-Poldering for a Long Term Flood/Sediment Management in the Southwestern Bangladesh

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.

Coastal Water: Wisdom, Destruction, Conflicts and Contestation. A Case of Southwest Coastal Region of Bangladesh

The coastal zone of Bangladesh is full of opportunities and vulnerabilities. Water is the central source of these opportunities and vulnerabilities. Seawater, river water, canal water, floodplain water, wetlands water, pond water is the dominant source of livelihoods of coastal people. The propel of the coastal economy is dependent on this water. But salinity alone creates vulnerability of the economy and people dependent on this water. Tidal surge, storm surge, drainage congestion, waterlogging, saline water aquaculture are the driving forces of water crises. Water crises are the unsolved issues ever despite large scale interventions. A shortage of freshwater suffers coastal people ever in regards to crop production, drinking water, health, aquaculture, and so on. Uncertainties driven by cyclones, river erosion, outsiders’ interventions-led consequences are the big challenges of the coastal zone in managing water. Coastal people are challenging, resilient, adaptive, and strong in contestations in managing water resources for their livelihoods. They exploit the opportunities using their ability of reconstruction.

Effect of Increasing Elevation of Lowland Coastal Saline Soils of Sundarbans (India) on Soil Salinity and Its Seasonal Variation

The delta region of the river Ganges spreads over India (West Bengal) and Bangladesh is popularly known as Sundarbans. Crop productivity of the region is very poor. Agricultural lands of the region are mostly saline and low-lying with drainage congestion due to presence of brackish groundwater table at shallow depth and flat topography. In recent years, improvement in productivity of these lands was witnessed by farmers when the elevation of lowlands was increased through land shaping. In the present study changes in the salinity status of soil were due to raise of land elevation through land shaping was investigated for two years and 3 seasons (winter, summer and late summer). It was found that there was a considerable decrease in soil salinity due to increase in elevation of lowlands through land shaping. The salinity of original lowlands was about 200% higher than the raised lands or uplands made through land shaping. Salinity of rhizosphere soil decreased with depth and there was a strong seasonal variation of soil salinity. At all soil depths soil salinity increased as the dry season progressed from winter to late summer through summer and soil salinity was highest in the surface (0-10 cm). The depth to groundwater table and the groundwater salinity also showed strong seasonal variation and were maximum in late summer season. The drainage condition of soil improved with increasing in land elevation.

Sediment management in tidal river: A case study of East Beel Khuksia, Bangladesh

The widespread construction of coastal embankments limited the natural deposition on the floodplain and accelerated the silt deposition in river channels. It resulted in drainage congestion and large-scale waterlogging problem. The temporary de-poldering is one of the effective methods to solve this issue. During high tide, muddy water enters the selected tidal basin depositing a major portion of sediment and at low tide, relatively clearer water erodes the riverbed. This paper presents a twodimensional numerical model to simulate the mechanism of sediment transport and deposition during the process of controlled flooding. The model was applied to three different scenarios of the embankment cuts in East beel Khuksia, Bangladesh. The study recommends operating single embankment cut at a time if the tidal equilibrium is fulfilled by the opening size of that embankment cut. The developed model can be used to assess the land heightening in sediment-starved tidal basins and ultimately plan the rotation of tidal basins for sustainable sediment management.

A Study on Moyna Basin Water-Logged Areas (India) Using Remote Sensing and GIS Methods and Their Contemporary Economic Significance

The prime objective of this paper is to identify and map the water-logged areas within Moyna basin, India, and to explore their contemporary economic significances. The Landsat 5 TM, ASTER data, and topographical sheets have been taken into consideration with field observations. Maps on relief, slope, canal density, embankments, a supervised classification of the study area and then NDVI, NDWI, and modified NDWI or NDMI have been prepared here. At Moyna, the piezometric surface ranges from five to ten metres below the ground level. The percentage of clay particles is high throughout the surface soil. The total rainfall is nearly 1400 mm and most of it happened during the monsoon period. Two well-marked depressions are observed there within the basin and the nearly central one is wide and is clearly identified from the relief map also. Problem of drainage congestion there accelerates the onset of water-logged situation. In general, water-logged areas are not suitable for humans. People once were worried about the water-logged environment due to underwater scenario of low-lying agricultural fields for a certain period, but today local people are taking this environmental condition as an opportunity for fishing activity and thus they are becoming economically benefitted as well.

Quality of urban environment: a case of citizen’s perception in Satkhira Municipality, Bangladesh.

In this study, an attempt has been made to identify the major problems of urban environment in Satkhira Municipality. The perceptual data were collected through field survey based on structural questionnaire. It designed 100 selected respondents and framed 32 environmental variables including 3 points satisfaction index. It was observed from the study that drainage congestion is the major urban environmental problem of Satkhira Municipality and it creates a variety of physical environmental problems such as water logging, increasd soil and water salinity level, water and soil pollution etc. of the area. Because of the absence of certain urban facilities such as employment opportunity, recreational level, shortage of electricity supply (illegal connection, improper meter reading, system loss and load shedding etc.) inadequate local security, city dwellers are found to be dissatisfied. These lead to the generation of various social disorders including hijacking, vandalism and phonongraph, etc. However, there are ample scopes to develop a sustainable (eco-friendly) city keeping these considerations in mind. DOI: http://dx.doi.org/10.3329/cujbs.v6i1-2.17082 The Chittagong Univ. J. B. Sci.,Vol. 6(1&2):65-76, 2011