ASSESSMENT OF WATER-LOGGING EXTENT USING RS AND GIS TECHNIQUES AND ITS POSSIBLE REMEDIAL MEASURES AT THE KOPOTAKSHO BASIN AREA, BANGLADESH Shahriar Rahman 1* , Syed Hafizur Rahman 2 and Md. Waji Ullah 3 1* Junior Environmentalist, Center for Environmental and Geographic Information Services (CEGIS), House # 6, Road # 23/C, Gulshan-1, Dhaka-1212, Bangladesh. E-mail: rajpeerless@yahoo.com 2 Associate Professor, Department of Environmental Sciences, Jahangirnagar University, Dhaka- 1342, Bangladesh. 3 Deputy Executive Director, Center for Environmental and Geographic Information Services (CEGIS), House # 6, Road # 23/C, Gulshan-1, Dhaka-1212, Bangladesh. ABSTRACT Since 2000, water-logging had been a regular phenomenon for the hundreds of villages adjacent to the Kopotaksho River in Jessore and Satkhira district of Bangladesh. The analysis of satellite images revealed that over the years water-logging problem had increased, as in 1999, the water- logged area was about 865 hectares; in 2000, 2003, 2006 and 2008 it was about 12867, 12238, 11723 and 19467 hectares respectively. Upstream freshwater flow reduction, unplanned and unauthorized structural interventions and regular encroachment at the upstream and downstream of the Kopotaksho River were the main causes of this unwanted prolonged water-logging. Ecological and social environment has been degrading as the people of the waterlogged area have been experiencing settlement, economic, health and sanitation problem due to four to seven months prolonged water-logging. Alternative Drainage routes and Tidal River Management (TRM) technique were suggested for the long-term possible remedial measures and participatory TRM practice was identified as the best possible long-term remedial option to diminish water-logging problem at the Kopotaksho Basin Area. Water-logging, Sedimentation, Landsat TM, Participatory, TRM 1. INTRODUCTION Water-logging is a form of flooding within the embankments caused by hydro-geophysical factors where water remains stagnant for long time due to increased sedimentation of Riverbeds and reduced height differential between embankment and peak water level [1]. Water- logging has been affecting about millions of people in Bangladesh during the past two decades leading to a large scale damages of crop, employment, livelihoods and national economy [2]. Water-logging is a form of flooding within the embankments caused by hydro-geophysical factors where water remains stagnant for long time due to increased sedimentation of Riverbeds and reduced height differential between embankment and peak water level [3]. Water-logging involves deterioration of drainage condition in coastal Rivers of south-western Bangladesh causing difficulties towards maintaining livelihoods [4]. River Kopotaksho is one of the main arteries of the water resources system located in the south west region of Bangladesh. It is flowing from north to south over the most matured part of the Gangetic delta. Its total length is around 200 kilometer from Tahirpur to its confluence with the Sibsa River. This River drains an area of about 1,067 square kilometer spread over nine upazilas in Jhenidah, Jessore, Satkhira and Khulna district. Numerous existing drainage channels/khals in south-west region drain out water through the Kopotaksho River. About two hundred years ago, the Mathabhanga River supplied fresh water throughout the year to the Kopotaksho River [5]. Since then, the Mathabhanga River had remained a flood spill channel, deteriorating over time. The Farakka barrage in upstream across the Ganges in India aggravated the deterioration of the Mathabhanga River. So, the Kopotaksho River virtually could not be fed from the Mathabhanga River any more, and it is now only drains flood spill from the Ganges through the Mathabhanga River and surface run-off generated from the monsoon precipitation. After being cut-off from the Mathabhanga River, the Kopotaksho had been subjected to tidal domination, associated with increasing sedimentation by tidal pumping process, particularly in the dry season. During the last few decades, the flow of the Kopotaksho River had been declining very rapidly. Tide generated from the bay brings huge sediment towards the inland through the so-called “tidal pumping process”. As a result of successive