Management of Coral Reefs in Gulf of Mannar using Remote Sensing and GIS Techniques – with Reference to Coastal Geomorphology and Land Use Land use/Land cover Mapping Geocoded multi-date IRS (1A LISS – II of June 1988 and 1D LISS – III of May 1998) imageries on 1:50,000 scale were visually interpreted based on image characteristics, and various land use / land cover categories were identified and mapped around Gulf of Mannar. The basic information like transport network, tanks, rivers etc are transferred from Survey of India toposheet. After identification and delineation, an accuracy test was made for 150 sample points on SOI toposheet. The study area map at 1:50, 000 scale was divided into grids and intersecting points of each grid within the study area were taken as sample points for validation of classified satellite data in ground truth checking. Over the ground, out of the 150 sample points, 139 points were found to be correctly interpreted giving an accuracy of about 92 per cent. The georeferenced land use maps of 1988 and 1998 were digitized in ARC/INFO and were overlaid using TIC coordinates of the study area. Digitized maps were edited and labeled. Finally a temporal land use/ land cover change map was generated using intercept operation of ARC/INFO. Socio-Economic Studies The fifth approach is by collection of socioeconomic data. The result of this approach is expected to provide information on (i) various economic activities of coastal communities in Gulf of Mannar and (ii) identification of coral reef degradation due to economic activities. Coral reef Mapping IRS LISS-II and IRS LISS-III imageries on 1:50,000 scale were visually interpreted based on image characteristics, various coral reef were identified and mapped categories in Gulf of Mannar. In the present study, the classification system developed by Space Application Center for the national coral reef mapping project (Anjali Bahuguna and Nayak, 1994) has been adopted. After identification and delineation, an accuracy test was made for sample points on Survey of India Topographic sheets (SOI). The study area map on 1:50,000 scale was divided into grids and intersecting points of each grid within the study area were taken as sample points for validation of classified satellite data in ground truth checking. Over the ground, out of the 112 sample points, 95 points were found to be correctly interpreted giving an accuracy of about 84.82 percent. The geo-referenced coral reef maps were digitized, edited, assigned corresponding labels and projected using ARC-INFO. Finally a coral reef map was generated using intercept statistics of coral reef classes in the map. 4. Result and Discussion Coastal Land form The coastal plain between Dhanuskodi and Tuticorin has various geomorphic units with different types of configurations (Figure 2). The geomorphic units, interpreted from remotely sensed data and checked subsequently through fieldwork, have been categorized into four genetic classes – marine, fluvio-marine, fluvial, aeolian and biogenic landforms.  Figure 2 Coastal geomorphology map of Gulf of Mannar derived from IRS LISS-III satellite data Marine Landforms In the coastal zone varies marine landform features such as beaches, spit, beach ridges, swales and backwater zone, mudflat, offshore islands, coral reefs, wave cut platform, sea cliff, sea cave, water logged land and strand lines have been identified. Beach Beaches are extensively developed along the entire coast of Gulf of Mannar except at some places. The shore between Tuticorin to south Sippikulam ( 2.04 km˛) , Vaippar River and Gundar River (2.56 km˛), Gundar River and Palar River,(2.64 km˛), Palar River and Kottakkarai River (2.189 km˛),Kottakkarai River and Marakkayarpattanam (2.18 km˛)southern coastal parts of the Rameswaram Island (2.91 km˛)and the western part of the Rameswaram Island from Pamban to Peikkarumbu are observed as a important beach areas in Gulf of Mannar coast. All along the shore the beach is observed to be gently sloping and marked with altered crusts and troughs that are formed due to wave action. Spit Among the various depositional landform features encountered, the formation of spit is a significant feature of recent age. South of Tuticorin coastal area two spit formations have been observed. It appears to have been built by the sediments brought by long shore current during southwest monsoon. As the Gulf of Mannar is on the lee of the northeast monsoon, there is no long shore drift from the northeast that might be the cause for the inward curving of this spit (Ahmad 1972). The southwestern shore of Rameswaram has a tongue shaped spit. SOI toposheet of the year 1969 does not shown any spit but recent IRS LISS-III imagery (1998) clearly shows the spit. Hence it may be assumed that these spits are recently formed. It can be explained that the Rameswaram spit may have been the result of littoral current from Palk Bay to Gulf of Mannar during northeast monsoon period. Beach ridges Beach ridges are moderately undulating terrain features of marine depositional type, formed during Pleistocene to Recent age, in the plains of Gulf of Mannar coast. In the Gulf of Mannar coast areas between Mandapam and East of Vaippar River are covered by well-developed beach ridges. There are twelve beach ridges observed in the region. Almost all beach ridges in the study area are parallel to each other, and cover an area of 155.49 km˛ and trend from east to west and northeast to southwest direction. On the basis of the nature and dispositions of beach ridges, it can be grouped into (i) Beach ridges south of Vaigai River, (ii) Beach ridges between Kotangudi River and Palar River, (iii) Beach ridges between Palar River and Gundar River system, (iv) Beach ridges between Gundar River and Vaippar River and (v) Beach ridges south of Vaippar River. Swales and backwater zone Swales and backwater zones are seen between coastal plains of Mandapam and Kottakkarai River; they are branched and arranged in series of linear patterns. They are situated almost parallel to the present coastline. Prominent backwater zones have been observed in the coastal plains between Valinockkam and Vaippar River, Mandapam and Southeast of Tiryppullani near Tinaikkulam. These are divided in to two parts by beach ridges. The coastal areas between Mandapam and Tinaikkulam, Valinokkam and Krishnapuram and North of Terku Mukkaiyur and Tukukankulam consist of prominent and wide backwater zones. These three backwater zones are connected by small, linear and narrow swales to the sea by means of few creeks, which supply water from sea to backwater channels during high tide. The basin bed is composed of silt and mud. The adjacent low lying area, as a part of swale zone is used at present for salt production. Mud flat Mud flats are wide expense of deposit of clay, silt, ooze, etc (Davies 1972). The mudflats are observed near Vaippar River mouth, around Valinokkam backwater lagoon, Kallar River mouth and Gundar River mouth. The area covered by mudflat has been estimated to be 14.50 km˛. |