Investigation on polderization induced water logging and feasible adaptation measures in Dumuria upazila under Khulna district

Abstract

The South West region of Bangladesh is home to millions of people for its’ enormous potentiality with water resources and mangrove forest offers great income and employment opportunity. This coastal region is ever dynamic and highly sensitive to different kinds of natural disasters like cyclones, tidal flood, river siltation, salinity intrusion, water logging etc. due to natural and anthropogenic reasons. Water logging is one of the dominant environmental problems that squeezing the socio-economic development in the South-west region. Around 60% area was covered by polder in the year 1990 and water logging has gradually increased since then. During 1960, as a flood-protection approach, Coastal Embankment Project (CEP) was initiated by Water and Power Development Authority (WAPDA) to increase food production. Construction of polders and significant reduction of up-stream flow especially in dry season (November to April) accelerate sedimentation only in the river bed. This process ultimately raised the riverbeds in comparison to adjacent beels or wetlands. Because of elevation differences between inside and outside of the polder, rainwater could not drain out easily into the river or canal resulting prolong water logging in number of places in the region. Satkhira, Khulna and Jessore districts of Southwest region are the most vulnerable water logged area. In this study, Dumuria Upazila, Khulna of the south western region was selected as the study area to detect water logging in a chronological pattern within a specified time period and to find out the reason behind evolving this problem. To carry out this detection, Landsat images since 1973 to 2016 were used to delineate the historical changes of water logged areas. The Modified Normalized Water Index (MNDWI) algorithm was applied to all the images to categorize the land-water interface and calculated the extent of the waterlogged area in ERDAS IMAGINE 2014.Afterward, the map was prepared using Arc GIS 10.1 to see the changes over the specified time span. Ground truthing for the calibration of remote sensing data was done through field visit on several unions of the region. The results revealed that around 2% of the landmass of the Southwest region was waterlogged in 1973, which increased significantly to around 34% in 2016. Lack of proper maintenance of polders and sluice gates, embankment failure, and sedimentation have principally accelerated the negative impacts on existing rivers and environment leading to the water logging phenomenon. In response to vulnerable water logging condition, the people of south-west region are trying to develop various community-based adaptation strategies to maintain their day to day life. Integrated farming, Pond Sand Filter, Rain water harvesting, Plinth rising, Tidal river management, re-excavation of rivers and canals are quite numbers of short term and long term adaptation strategies and approaches that are being practiced within the different zone of the southwest region with the financial and technical support of governmental and non-governmental organizations. Feasibility of such community-level adaptation practices can properly be inspected and piloted befitting to the water logged area of the Dumuria Upazila.