DETECTING RECENT COASTLINE CHANGES AROUND THE URIR CHAR ISLAND AT THE EASTERN PART OF MEGHNA ESTUARY USING PALSAR IMAGES

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1 DETECTING RECENT COASTLINE CHANGES AROUND THE URIR CHAR ISLAND AT THE EASTERN PART OF MEGHNA ESTUARY USING PALSAR IMAGES Yusuke Taguchi 1*, Mohammad Asad Hussain 12,Yoshimitsu Tajima 1, Mohammed Abed Hossain 2, Sohel Rana 3, A.K. M. Saiful Islam 2 and Md. Ahsan Habib 3 1 Coastal Engineering Lab, University of Tokyo, Hongo, Bunkyo-ku, Tokyo , Japan 2 Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh 3 GIS Unit, Local Government Engineering Department, Agargaon, Dhaka, Bangladesh of presenting author: yutagu@coastal.t.u-tokyo.ac.jp ABSTRACT The present study focuses on the seasonal as well as longer term change of coastline around Urir- Char island located at the eastern part of the Meghna Estuary in Bangladesh based on satellite images from PALSAR. A total of twenty one imagesfrom January 2007 to April 2011 were analyzed.from the analyses, it was found that the areal extent of the island gets larger during the monsoon compared to the post monsoon and winter. It wasalso found that the island is expanding at a very high rate of about 3.4 km 2 per year. Field observations revealed some erosion prone areas at the southern coast of Noakhali mainland which was also well captured by the image analysis. Keywords: Meghna estuary, urir-char, coastline change, PALSAR image 1. INTRODUCTION Meghna Estuary is located in the south of Bangladesh and is one of the most dynamically deforming estuaries on the earth. The Ganges, the Brahnmaputra, and the Meghnajoin together and find their way to the Bay of Bengal through Meghna Estuary. These rivers have enormous catchment area and, consequently, huge amount of sediment is carried and flowed into Meghna Estuary, especially during the monsoon due to heavy rainfall. It results in high accretion rate in this area. Moreover, coastline is being eroded by strong waves from the Bay of Bengal. These strong accretion-erosion processes have significant influence on the shape of coastlines of Meghna Estuary. The process of land accretion is dominant in the region of the Meghna Estuary. About one fifth of the original supply of 1,100 million tons is retained in the Meghna Estuary and forms the material for land accretion in the central part of the coastal zone (Koenet al., 2011). This area is also subject to natural disasters, e.g. floods, cyclones and storm surges. Comparison of satellite images in 1990 and 2010 shows that the eastern part of the Meghna Estuary has changed drastically (see Figure 1). Coastline of south Noakhali has moved southward, and the morphology of Hatiya has changed at the same time. Urir-Char, located between Noakhali and Sandwip, appears to be one of the most changing areas. Bathymetric surveys, carried out in 2000 and 2001, showed the largest net accretion in the area between Noakhali and Sandwip and 451

2 the south of Sandwip (Koenet al., 2011). As can be seen from the satellite image in 1990, Urir- Char was divided into some parts by estuarine channels. However, these parts were connected to form a single island. Figure 1: Map of eastern part of Meghna estuary around urir-char in 1990 (left) and 2010 (right) Since its emergence, Urir-Char has been growing and shifting its location from the south to the north. The net increase of the area of the island has not been found uninterrupted. The rate of increase was around 4.7 km 2 /yr during and later, during the rate was decreased to 0.6 km 2 /yr. From 1996, the rate of enlargement of Urir-Char has been increased again to2.85 km 2 /yr and from 2001 the prevailing rate of increase is found 2.45 km 2 /yr. If the present enlargement of Urir-Char continues in the near future, its area would be more than 125km 2 within the next 10 years (Koenet al., 2011). The total area of Urir-Char exceeded100km 2 by the year 2007 and at present population of the island is about 20,000. Land-formation processes still continue and the shape of the island is changing drastically. Apart from the annual change in land formation processes, there also are seasonal phenomena, e.g. hydrological and meteorological forcing factors, which may influence the erosion-accretion process. The present study focuses on the recent erosion-accretion process of Urir-Char Island and identifies the seasonal trend between January 2007 and April 2011 using PALSAR(The Phased Array L-band Synthetic Aperture Radar) images. 2. METHODOLOGY Application of satellite images is one of the most efficient measures to identify the coastlines and to estimate the area of Urir-Char. Large areas can be considered at a time from a single image with 452

3 relatively low cost in contrast to the ground base tedious and expansive survey. In this study, use of high-resolution image is an important factor because it can help to distinguish the border between land and sea precisely. To find seasonal and yearly trend, comparing as many satellite images as possible is also essential. For this purpose, PALSAR images are suitable because it has not only a high-resolution mode but also its images are more frequently taken than other satellites of this kind. Its maximum ground resolution of PALSAR is 7m, and twenty-one images are available during the period PALSAR is equipped with ALOS (The Advanced Land Observing Satellite), which was developed in Japan. (a) (b) Figure 2: Example of coast line extraction from PALSAR image on the (a) March 7, 2009 and (b) July23, 2009 Primarily the coastlines have been identified by drawing lines over the satellite image considering that the land areas are brighter compared to sea (Figure 2). If the coastline is ambiguous and it is difficult to distinguish the border between land and sea, envelope curves have been used which crosses the mouths of the small creek, as can be seen from Figure 2(b). These creeks look as white lines on PALSAR images. Coastline has been drawn as such that it passes through the tips of the white lines. Later, five reference points have been identified whose exact latitude and longitude are already known and which are easy to identify on all images. Then images are converted into the same coordinate system such as way that they overlap each reference points. Finally, all the coastlines have been extracted and compared to identify the seasonal and annual trends (see Figure 3). 3. RESULTS FROM IMAGE ANALYSES 3.1Results of Extracted Coastlines During 2009 a fairly stable coastline is seen at the south of Urir-Charin Figure 3 (a), however, this line is shifted towards the north from 2007 to 2011 as shown in Figure 3(b). According to Koenet al.(2011)during the last two and a half decades, bank erosion has been continuing at the southern part of Urir-Char, resulting in a northward shifting. Hence, the present result agrees well with that 453

4 statement. The remaining coastlines of the island have been seemed to change both seasonally and annually. In some parts of the island, the shifting of coastlines is substantial even on a seasonal scale. Accretion is dominant in the north-west, south-west and north-eastern parts in terms of annual change, and new land emerged along the coastline. The outer periphery of Urir-Char, except for the south, extends outward every year. (a) (b) Figure 3: (A) Seasonal change in 2009 and (b) Annual change from 2007 through Results of Estimated Land Areas Figure 4 shows the change in land area of Urir-Char, calculatedfrom the extracted coastlines, during Figure 4: Area change of Urir-Char and regression line 454

5 From the figure, it appears that during the monsoon, the area of Urir-Char is at its peak. After this period, the area reduces and then increases again before the monsoon. An attempt has been made to establish a statistical prediction model of deposition for Urir-Char are using linear regression equation. The result of regression analysis is as follows; Y=0.0094X (1) In equation (1), X means the days from January 1, 2007, and Y means the areas (km 2 ). According to this equation, the area of Urir-Char increases by 9400m 2 per day, and 3.43km 2 per year on an average. This gain in area can be regarded as long-term trends of the study area. The periodic change is shown by subtracting the regression equation from the original data in order to consider the dominant dynamics. Figure 5: Seasonal change for four years (difference from regression line) In terms of seasonal change, there is a consistent trend every year (see Figure 5). It has found that deposition is apredominant trend beforeand during the monsoon.however, erosion is found dominant than deposition after the monsoon and during the dry season. 3.3 Field Survey Field visit was conducted at the coast of Noakhali and Urir-Char in order to observe the morphological condition of coastlines during December Figure 6 shows the locations where photographs were taken during the survey, which have been shown later. 455

6 Figure 6: Locations of photographs taken during the field visit. Figure 7: Left: the southern coast of Urir-Char (a) and Right: trace of recent erosion (b) Figure 7 shows the southern coast of Urir-Char where trace of recent erosionhas been observed. The coastline in this area has steep cliffs.such observation is analogous to the results of PALSAR image analyses, suggested that the process of erosion is dominant at the southern coast of Urir- Char. 456

7 Figure 8: Left: Mudflat in northern part of Urir-Char and Right: coast on the opposite side at Noakhali mainland As seen from the left panel of Figure 8, large-scale mudflat was observed at the north of Urir-Char. This area goes below the water duringthe high tide. Therefore, tidal level at the time when the satellite image has been taken influences the land area. Not only this location but also most of the areas at the periphery of Urir-Char, except for the south coast, are covered with mudflats and shallow sea. These areas are expected to become as stable land in the near future.the right panel of the same figure shows steep cliffs and traces of recent erosion at the southern coast of Noakhali Mainland. It appears that coastlines at Noakhali Mainland are shiftingto the northward in response to the northward shift of Urir-Char. 4. DISCUSSION One of the limitations of the present study is that it does not directly consider for the effects of tidal water level on the change of coastline of Urir-Char. As the Urir-Char area is very shallow, tidal fluctuations may considerably change its shorelines. In general, the water levels in the Meghna Estuary are influenced by tides, river discharges (seasonal effects) and cyclonic events (cyclone surge). According to Koen (2011), the mean water level shows a marked seasonal variation along the Bangladesh coast. The mean water level during the monsoon can be higher than that of during the dry season because of the direction of wind and the amount of river discharge. Wind field over the Bay of Bengal area is characterized by a south-westerly monsoon of 4-5 m/s, which predominates from June to September and a north-easterly monsoon of m/s predominating from December to February (Jakobsenet al., 2002). Numerical experiments with a multilevel model have shown that the SW monsoon wind holds up a huge amount of flood water inside Bangladesh (Aliet al., 1995). The discharge varies from 8,000 m 3 /s during the dry season to 120,000 m 3 /s during the wet season. This strong south-westerly wind and high river discharge can increase the water level around Urir-Char during the monsoon.therefore, even if the images during the monson are taken during lowtide (which may show large areas of Urir-Char), the mean water level at that time will be highcompared to that during the dry season which may be large enough to negate the tidal influence. The flow and the movement of sediments can account for the seasonal trend of the morphological change. The residual flow around Urir-Char is generated mainly by the tide. Counter-clockwise net circulation is observed around Urir-Char and Sandwip, regardless of seasons and the variation of the inflow from the river (Hussain etal.,2009). This circulation is expected to influence the 457

8 accretion-erosion process around the area. Sediments entering the Hatia channel are trapped into the anticlockwise circulation before being settled or transported out of the estuary (Ali et al., 2007).When sediment flux from rivers is high, the process of accretion should be dominant. As during the monsoon the supply of material is high, a part of materials accumulate within the estuary (Sokolewiczand Louters, 2007). On the other hand, when the supply is low, the circular residual flow can erode Urir-Char and retain the material, which is finally taken away from this area. According to Ali et al.(2007) during the monsoon season, sediment load flowing out of the estuary is distributed through the major channels almost in proportion to discharge.moreover, during the dry season, although the upstream sediment concentration is significantly low, the net sediment transport (relative to the flow magnitude) has been found to be similar to that of the monsoon. It indicates the higher potential of erosion within the outer estuary during the dry season when the sediment supply from the river is low. 5. CONCLUSIONS Seasonal and annual change of coastline around Urir-Char island was studied. Satellite images from PALSAR were employed for capturing frequent change of the shoreline. From the analyses it was found that the total land area of the island tends to expand more during the monsoon season and the yearly rate of the expansion was about 3.43 km 2 per year from 2007 to On the other hand, field observation revealed severe erosion areas at the southern coast of Noakhali Mainland. More observation data are required to clarify the driving forces of such observed seasonal morphology changes around the Meghna estuary. ACKNOWLEDGEMENTS This research has been carried out under a collaborative research project, Space Application for Environment (SAFE), one of international activities under the Asia-Pacific Regional Space Agency Forum (APRSAF). The subject of this specific project is "Investigation of sedimentation process and stability of the area around the cross-dams in the Meghna Estuary", and is financially and technically supported by JAXA. REFERENCES Ali, A. (1995). A numerical investigation into the back water effect on flood water in the Meghna river in Bangladesh due to the south-west monsoon wind. Estuarine, Coastal and Shelf Science, 41, Ali, A., Mynett, A.E. and Azam, M.H. (2007). Sediment Dynamics in the Meghna Estuary, Bangladesh: A Model Study, Journal of Waterway, Port, Coastal, and Ocean Engineering, ASCE, 133, Jakobsen, F., Azam, M. H. and Kabir, M. M. (2002). Residual flow in the Meghna Estuary on the coastline of Bangladesh, Estuarine, Coastal and Shelf Science, 55, Hussain, M. A., Hossain, M. A. and Haque, A. (2009), Seasonal Variation of Residual Currents in the Meghna Estuary of Bangladesh, Proceedings of Coastal Dynamics 2009,6-11 September, Tokyo, Japan, World Scientific, Paper ID 30, Koen de Wilde (2011). Moving Coastlines: Emergence and Use of Land in the Ganges- Brahmaputra-Meghna Estuary. University Press Limited, Dhaka. Sokolewicz, M. and Louters, T. (2007). Hydro-Morphological Processes in the Meghna Estuary, Bangladesh, Pre conference volume of the 1 st International Conference on Water & Flood Management, March 14-16, 2007, Dhaka, Bangladesh. 458

9 CRISIS AND POLICY FOR THE ENVIRONMENTAL REFUGEES IN GHORAMARA ISLAND (INDIA) Rituparna Hajra 1*, Anirban Mukhopadhyay 2, Hamidul Huq 3, Md. Munsur Rahman 4 and Tuhin Ghosh 5 1 School of Oceanographic Studies, Jadavpur University, Kolkata, India, ritu.hazra@rediffmail.com 2 School of Oceanographic Studies, Jadavpur University, Kolkata, India, anirban_iirs@yahoo.com 3 Institute of Livelihood Studies, Bangladesh, hhuqils@gmail.com 4 Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka, Bangladesh, mmrahman@iwfm.buet.ac.bd 5 School of Oceanographic Studies, Jadavpur University, Kolkata, India, tuhin_ghosh@yahoo.com ABSTRACT Environmental Refugees are those people who can no longer maintain a secure livelihood in their own land due to environmental problems, with minor optimism to return. They include the people who are displaced as a result of loss or degradation in ecosystem services, due to the disruption in physical and/or social system. The impacts of sea level rise in combination with complex hydrodynamic condition causing severe coastal erosion in Ghoramara Island (21 53'56"N to 21 55'37"N latitude and 88 06'59"E to 88 08'35"E longitude), within the Indian Sundarban. Within the Hugli River (lower course of River Ganga) estuary, three islands namely Lohachahara, Suparibhanga and Bedford completely vanished and Ghoramara Island eroded significantly which resulted in a considerable population of environmental refugees. Time series analysis using multi-temporal satellite imageries of 1975 and 2010 shows that four villages are already under water, resulted into an increased rate of migration from this island. The poorer people were compelled to move adjacent mainland (Kakdwip/Namkhana) or comparatively stable island (Sagar Island), with little or without any token compensation from the Government. This environmentally refused people expect the formulation of any universal policy, from which they will be compensated by cash or land, in near future. Keywords: Island, crisis, migration, policy 1. INTRODUCTION A widespread view that is gaining ground is that environment related migration could evolve into a global crisis by displacing a large number of people from their origin and forcing them to flee. Environmental Refugee is a new phenomenon in the global arena (Myers, 2002). The concept of environmental refugees was first introduced by Lester Brown of the World Watch Institute in the 1970s (Black 2001). The concept became popular after the studies by El-Hinnawi (1985) and Jacobson (1988) on forced migration of people due to environmental degradation and natural disasters. El-Hinnawi defined environmental refugee as a group of people who have had to leave their habitat either temporarily or permanently because of environmental hazards of disruption in their life supporting ecosystems (El-Hinnawi, 1985). Jacobson (1988) notes that, environmental refugees have become the single largest class of displaced persons in the world. Homer-Dixon 459