Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502 Vol. 1(10), 72-81, October (2012) Res.J.Recent Sci. Morphological Change Study of Ghoramara Island, Eastern India Using Multi Temporal Satellite Data Jana Adarsa, Sheena Shamina and Biswas Arkoprovo Department of Geology and Geophysics, Indian Institute of Technology, Kharagpur-721302, West Bengal, INDIA Available online at: www.isca.in Received 29 th August 2012, revised 4th September 2012, accepted 10 th September 2012 Abstract Ghoramara island is situated at 18.36 nautical miles away from Haldia dock in Hooghly estuary, Eastern India. It is a rhombic shaped island covering an area of around 4.8 km² with a total shoreline length of 8.5 kms. This sparingly populated sensitive ecosystem is rapidly changing its morphology due to extensive coastal erosion on the northwestern coast and marginal accretion on the southeastern side. The degradation of the system due to natural and anthropogenic causes leads to the total areal reduction of the island. There is a major loss of agricultural land and fisheries. The two islands Lohachara and Supribhanga lying to the southwest of Ghoramara have already been submerged. The vulnerability and stability of the island is the major fear of the inhabitants. In the present study, multi-resolution and multi-temporal satellite images of Landsat have been utilized to understand the erosion accretion pattern of the island over past four decades (1972-2010). The rate of change in shoreline positions have been estimated using statistical linear regression, end-point rate and net shoreline movement method and cross-validated with regression coefficient (R²) method. Land use land cover map has been prepared for all these years to understand how the erosion-accretion affected the island. It has been shown that the island is constantly shrinking over time and lost almost 50% of its area. Keywords : Hooghly estuary, Ghoramara Island, shoreline change rate, regression coefficient (R²), land use land cover. Introduction The study area Ghoramara Island is located 18.36 nautical miles southeast of Haldia dock. This island is extended between The coastal zone refers to a broad geographical area where the 21°53'56"N to 21°55'37"N latitude and 88°06'59"E to terrestrial and marine factors are mixed to produce 88°08'35"E longitude (figure 1). The island covers an area of 1 dynamic/sensitive ecosystems . The shoreline, interface 4.8km². The major villages on this island include Khasimara, 2,3 between land and sea , is very dynamic feature of the coastal Hathkola, Baghpara, Raipara, Mandirtala, Chunpuri Lakshmi zone. It undergoes frequent changes, short term and long term, Narayanpur and Khasimara Char. Out of these the Kashimara caused by hydrodynamic changes (river cycles, sea level rise), Char, Lakshmi Narayanpur and Kashimara have already been geomorphological changes (e.g. barrier island formation, spit lost. The major occupation of the people is agriculture and development) and other factors (sudden and rapid seismic and fishing. Main plant cover includes coconut, bamboos and 4,5 storm events) . The rate of shoreline changes is one of the casuarinas. The area experiences a tropical warm and humid common measurements used by coastal scientists, engineers and climate. Rain occurs due to southwest monsoon from May to land planners to indicate the dynamics and the hazards of the September, and the northeast monsoon from November to 6-12 coast . December. Maximum rainfall and comparatively lower temperatures are encountered with the onset of the monsoon The Hooghly estuary is a funnel shaped coastal plain estuary period from June to September while the highest temperatures and is one of the largest estuary of the river Ganges. The and minimum rainfall occur during pre-monsoon season from morphometric setting of the estuary is the product of continuous February to May with little or no rainfall. Minimum temperature fluvial sedimentation by a series of para-deltaic lobe occurs from November to January. As the Hooghly estuary progradation systems developed on the western shelf margin experience semidiurnal tide with flood tide of short duration, 3 areas and eastern basinal troughs of the Bengal basin tectonic to 4 hours, and the ebb tide remains for 8 to 9 hours, so the frame, over the entire Holocene period. The quaternary island also experience the stronger flood tides for shorter sediments are underlain by the tertiary sediments indicating an duration. It is 6.5 m above mean sea level 14 . The rise in the sea accumulation in a subsiding tectonic trough 13 . Looking at the level is caused by natural as well as anthropogenic activities like geological setting, the estuary itself occupies the Eocene hinge global warming. In the region, local sea level rise have been zone. Sagar is the largest island of the Sundarban, positioned at estimated as 2.6 mm per year 15,16 . The population of the island the mouth of the Hooghly estuary and divides it into two till 2001 is 5000 17 but due to the submergence of the inhabited channels, the western channel is retained as Hooghly and Lohachara Island under water because of rising sea levels, the eastern is named as Muriganga. Ghoramara and Sagar were people from Ghoramara Island are relocated to other nearby joined and formed a single island till 1903, when Ghoramara got islands like Sagar. The inhabitants are forced to leave the island separated from Sagar and stabilized as a separate island. International Science Congress Association 72 Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502 Vol. 1(10), 72-81, October (2012) Res. J. Recent Sci. due to degradation of the natural habitat. The term Material and Methods environmental refugees have been used for the inhabitants of this island 18 . The area is under severe threat of erosion. Where it Data Sources: Multi-resolution satellite data over the study has already lost around 50% of its area in last four decades and area, such as landsat MSS, TM and ETM+ of different dates the two islands, Lohachara and Supribhanga, are already have been acquired, as the same resolution data is not available drowned under water. Thus the stability of the island is in over the chosen period (1972-2010). The archived Landsat question. Rapid and vast erosion is going on around the island. images are freely available to the users so these are used. The orthorectified Landsat data was downloaded from USGS global Remote sensing techniques integrated with the geographical visualization viewer. The area is covered by Survey of India 19, 20 information system (GIS) has been used for many studies . (SOI) Toposheet No. 79C/1 at 1:50, 000 scales. The integrated method has been used in the shoreline changes studies due to repetitive and synoptic coverage, high resolution, Landsat data is typically used for coastal zones because of the multi-spectral data base and its cost effectiveness. Multi- multi-spectral and multi-temporal capabilities of the data. temporal satellite images of Landsat have been used to However, only multi-temporal data has been utilized that allow understand erosion-accretion processes over past 38 years and to us to keep track of the various changes in characteristics of the demarcate the shoreline position during different periods. In the coastal zone. The details regarding satellites and their present study, an investigation has been carried out in acquisition dates are listed in table 1. Ghoramara Island to delineate the shoreline and land use land cover changes. Figure-1 Location map of Ghoramara Island Table-1 Characteristics of satellite data used with acquisition dates Satellite/sensor Date of acquisition No. of bands Spatial resolution (m) Path/Row Landsat -5, TM February 6,2010 7 30 139/45 Landsat -5, ETM+ November 17,2000 8 30 139/45 Landsat-4, TM January 19,1989 7 30 139/45 Landsat-3, MSS February 9,1979 4 79 149/45 Landsat-1, MSS December 12,1972 4 79 149/45 International Science Congress Association 73 Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502 Vol. 1(10), 72-81, October (2012) Res. J. Recent Sci. Shoreline Mapping: Shoreline is the line distinguishing land position. Each method used to calculate shoreline change rates from water body. The precise definition of the shoreline is given is based on measured differences between shoreline positions by 21 as the line contacting between the mean high water line and through time. The procedure involves the selection of a base the shore. Various methods of the shoreline extraction from the line in the general direction if a shoreline, establishing transects satellite imageries have been developed. Shoreline can be perpendicular to the base line and then finally calculating the identified and delineated from a single band image by using the distance between the shorelines along various transects. Several processed NIR bands of Landsat MSS, and TM, as the statistical methods are used to calculate the shoreline change reflectance of water is nearly zero in reflective infrared band, rates with the most commonly used been are end-point rate and reflectance of majority of land cover is greater than water. (EPR), linear-regression (LR) and net shoreline movement The processing of the NIR bands included ‘Histogram/gray (NSM) 23 . The end point rate calculations are done by dividing level thresholding’ 22 . Band 5 is best for distinguishing land from the distance of shoreline movement by the time gap between the Water because it exhibits a strong contrast between the two oldest and youngest shoreline in the data set 24 . The major where water shows high absorption in the middle infra-red advantage of this method is ease of computation and energy and vegetation strongly reflect the middle infra-red calculations can be done on minimum two shorelines only.