Coastal zones are extremely important. The ecosystems in the coastal zone are important for biological and economic productivity, storm protection and erosion control. The adjoining zone along the coastline contains some of the most productive and valuable habitats of the biosphere. A general estimates points that about 60% of world's population - about 3 billion people lives in within 60 kilometers of the coast. This number is increasing rapidly due to a combination of population growth, migration and urbanization. Two thirds of cities with population over 2.5 million are situated near estuaries. Coastal zone supports many different types of livelihood that are sometimes at odds with each other. Fishing, tourism, manufacturing, farming, and other industries are all very important to the coastal areas, but without proper planning, damaging conflicts can emerge that can destroy the very resources that support these economic activities. This specific division deals with different studies related with coastal zone. Some of the important projects already implemented or are being implemented at this Institute are mentioned below:
Land Use Mapping of Coastal Regulation Zone (CRZ) of West Bengal :
Realising the importance of Coast and especially the coastal wetlands, Ministry of Environment & Forests, Government of India enacted CRZ notification, 1991. According to the notification, the coastal stretches of seas, bays, estuaries, creeks, rivers and back waters which are influenced by the tidal action (in the landward side) up to 500 m from the High Tidal Line (HTL) and the land between the HTL and LTL (Low Tide Line) as Coastal Regulation Zone and imposes, with effect from the date of this notification, the restrictions on the setting up and expansion of industries, operation or processes etc. in the said Coastal Regulation Zone (CRZ).
In view of this, it was necessary to have the knowledge about the existing landuse / wetland conditions of the zone with special reference to built-up land, sand mining, construction activities etc. Landuse maps within the CRZ of West Bengal was thus prepared on 1:25,000 scale based on SPOT HRV MLA data of 1989 and supplemented by IRS 1B LISS II data of 1991 remote sensing data using visual interpretation techniques taking Survey of India (SOI) topographical maps as base maps. A nationally accepted classification system was followed during the mapping period. Extensive ground truth survey was done before finalisation of the individual maps.
All along the coast, in the intertidal region and even beyond the reach of the daily tidal waves, exist a continuous line of marshes and swamps, sometimes even covered with algae and other aquatic vegetation. Partly terrestrial and partly aquatic, our “coastal wetlands” support both terrestrial as well as aquatic flora and fauna and by far the most productive eco-system having biological productivity far greater than found on dry land. Many birds, alligators and turtles spend their life time commuting between wetlands and adjacent bodies of water while land animals that normally occupy dry land visit the wetlands to feed. The larvae of shrimp, crab and other marine crustaceans find shelter in the marsh from larger predators. Blue fish, flounder, oysters and clams spend all or part of their lives feeding on other species supported by the marsh. Wetlands also act as cleansing mechanisms for ground and surface waters. These important ecosystems were constantly under pressure since people at large and the policy makers in particular were not aware of their importance. Examples of such coastal wetlands are different types of tidal flats, barrier islands, mangrove forests, coral reefs etc. CRZ Notification, 1991 was promulgated to save these wetlands.
The Coastal Regulation Zone (CRZ) notification of 19th February, 1991 is the direct outcome of Environmental Protection Act, 1986. Notification under section 3(1) and 3(2)(v) of Environmental Protection Act, 1986 rule 5(3)(d) of the Environment (Protection) Rules, 1986 states the specific portion of coastal stretches as Coastal Regulation Zone and also mentioned about the Regulating Activities in the Coastal Regulation Zone.
For the purpose of this notification, the High Tide Line (HTL) will be defined as the line up to which the highest water line reaches during the spring tide. The High Tide Line shall be demarcated uniformly in all parts of the country by the demarcating authority or authorities so authorised by the Central Government in accordance with the general guide lines issued in this regard.
The distance from the High Tide Line shall apply to the both sides in the case of rivers, creeks and backwaters, and may be modified on a case by case basis for reasons to be recorded while preparing the Coastal Zone Management Plan (CZMP) and, however, this distance shall not be less than 100 meters (amended to 50 meters by notification dated 18.8.1994 but restored to 100 meters by Supreme Court order dated 18.4.1996) or the width of the creek, river, or backwater whichever is less. [As inserted by notification dated 21.05.2002] :
The distance up to which development along rivers, creeks and backwaters is to be regulated shall be governed by the distance up to which the tidal effects of sea is experienced which shall be determined based on salinity concentration of 5 parts per thousand (ppt). For the purpose of this notification, the salinity measurement shall be made during the driest period of the year and the distance up to which tidal effects are experienced shall be clearly identified and demarcated accordingly in the Coastal Zone Management Plans.
As already mentioned, CRZ maps of West Bengal was prepared by this Institute in collaboration with Space Applications Centre, ISRO, Ahmedabad. The project was sponsored by Ministry of Environment & Forests, Government of India. Altogether, 81 CRZ maps of West Bengal coast were prepared demarcating all the land use / land cover units following the guidelines of Ministry of Environment & Forests, Government of India. The project was completed during 1997-98.
As a mark of recognition of this work, Ministry of Environment & Forests, Government of India later on declared this Institute as an authorised agency for delineating High Tide Line(HTL) and consequently fixing up the CRZ boundary in any part of Indian Coast.
The objective of the work was to prepare Coastal Wetland/Landform maps on 1:50,000 scale using IRS LISS II data and to prepare shoreline changes maps on 1:50,000 over the years starting from 1980 to 1993 using IRS LISS II and Landsat MSS/TM data through visual interpretation. The project was sponsored by Department of Space, Government of India and was implemented in collaboration with Space Applications Centre, ISRO, Ahmedabad.
The shoreline change maps were prepared using the available Survey of India topographic sheets (which are mostly surveyed during 1967-68 and published during 1971-72 for West Bengal coast) as base maps. The project was completed during 1997-98. Subsequently, a detail digital database of all these maps have been prepared and have been kept in ARC Info format for regular analysis and monitoring of coastal zone of West Bengal.
Updation of Coastal Zone Maps of West Bengal :
Land use maps within the CRZ of West Bengal were prepared on 1:25,000 scale based on SPOT HRV MLA data of 1989 and IRS LISS II data of the year 1991. However, later on, it was found that out of this total coastal stretches, some of the areas are relatively more dynamic and within a span of only ten years have undergone major changes due to natural as well as anthropogenic reasons. This project envisaged to carry out mapping of those selected region in more detail and prepare updated maps on 1:25,000 scale using mainly IRS-1C LISS III data and also PAN data. The work was carried out using merged product. The project was sponsored by Department of Environment, Government of West Bengal. The land use pattern and the delineation of HTL within these stretches were updated through this exercise. This project was completed during 2002-03.
Application of Remote Sensing for Coastal Habitat Studies in parts of West Bengal :
This project was implemented as a part of the Integrated Coastal and Marine Area Management Project (ICMAM Project) of the Department of Ocean Development, Government of India. Efforts were made to develop methodologies for zoning major communities of mangroves using satellite data coupled with sufficient ground truth information. The project was carried out in collaboration with Space Applications Centre, ISRO, Ahmedabad and was funded by the World Bank through Department of Ocean Development, Government of India.
Development activities, population pressure coupled with natural causes has contributed heavily towards the degradation of the mangrove ecosystem. Therefore, need has arose to collect information on mangroves (a vital coastal habitat) for preparation of their sustainable management plan. Information regarding different mangrove community zonation is a valuable input for phyto-diversity assessment, for assessing the environmental condition of the habitat and for the preparation of management plans for conservation. It is also important to assess the economic value of mangrove resources as different mangrove species have different importance.
IRS –1C/1D LISS III data of the period 1998-2000 was used for the study. Multi-temporal data was mainly used to establish and verify the accuracy of the methodology. As this was an attempt to establish the methodology, only selected part of Sundarbans namely, Lothian Island and the Dhanchi Island and the mangrove assemblage at the mouth of Subarnarekha estuary were taken up for this specific study. In spite of its immense scenic beauty, one of the major problems with Sundarbans is its inaccessibility . The study areas were also selected keeping in mind accessibility for making ground truth survey, different geomorphic settings and its influence on community distribution.
Methodology for zoning the dominant communities of mangroves using satellite data has been established which includes data selection, classification system, combination of image processing steps to extract maximum information from IRS LISS III and PAN data on different communities, interpretation key, ground data collection and accuracy estimations. Classification system has been evolved which takes care of the influence of the substrate, tides and geomorphology on the distribution of different mangrove communities. Mangroves have been mapped up to genus level. This kind of information is generated for the first time using satellite data. The analysis was supported with extensive ground truth data.
Mangrove zonation maps have an accuracy of 83% at 90% confidence level. The study demonstrated the usefulness of extracting information on major mangrove communities using IRS LISS III data.
The Lothian Island
The study shows that the mangrove zones on the Lothian Island (total area 38 square kilometres) are characteristically based on the land geomorphology with the low lying northern region harbouring Avicennia community (major zone) and the southern island (ground level is high) harbouring Phoenix as the major community along with sparsely distributed Avicennia. The central region which has the mangrove vegetation distributed in a near-circular shape distinctly separates out from the northern and the southern region. The land is elevated and mostly has marsh vegetation, sparse Avicennia and saline blanks.
Study of spectral behaviours from multi-temporal IRS 1D LISS III data helps in identification and delineation of spatial distribution of major mangroves communities of Lothian Island. Analysis of consecutive years from 1998 to 2000 were made. Initial analysis of IRS 1D LISS III data of February, 1998 data identified seven different assemblages of mangroves at Dhanchi Island. The same experiment was repeated using IRS 1D LISS III data of February, 1999 which yielded the similar pattern of distribution of mangrove assemblages at Lothian Island . Spectral behaviour of major mangrove communities helped in this differentiation. Similar experiment using IRS 1D LISS III data of March, 2000 confirmed the distribution of major mangrove communities of Lothian Island.
The northern low-lying region
Fringe mangrove community makes up a very narrow belt comprising Avicennia (mostly) A.marina, Ceriops, Sonneratia, Xylocarpus and Exocoecaria etc. Fringe mangroves have not been mapped everywhere.
The most seaward community on the northern region of the island is homogenous and pure Aveicennia alba. It is distributed linearly and makes a wider first belt in the northwest and narrower belt in northeast. Due to its homogenous distribution, this was the only community wherein the classification has gone up to species level helping in differentiating A. alba and A. marina.
Avicennia marina is the most dominant community in the Lothian Island covering almost 26% of the mangrove area. It makes up the second belt and covers a significant portion of the northern region. Other mangroves that are also present in this zone are A. alba, A. officinalis, Aegiceras, Ceriops, Bruguiera, Excoecaria, Acanthus, Derris, etc.
Aegialitis community makes up the third and most inward belt. It is an association of Aegialitis, Exocoecaria, A.marina, Ceriops assemblage with Aegialitis being the most dominant community in this association. Other species present are Aegiceras, Acanthus, Derris, Dulbergia, within this zone. Heights of the Aegialitis trees are about 3-4 meters.
Grass comprising mainly Porteresia species makes up the most seaward zone in the east of the northern region. It grows on intertidal mudflats and makes a very narrow and linear zone.
The Central elevated region
The central elevated region has maximum portions occupied by sparsely distributed Avicennia. Avicennia of sparse density is located in the areas where mangrove communities are under tremendous stress as implied by the stunted growth of the species here. The maximum height of the trees here is about 1 meter. Avicennia, Suaeda, Sesuvium and Acanthus are also associated with Avicennia. Marsh comprising Suaeda, Sesuvium, Salicornia brachiata, Acanthus and Avicennia (stunted growth) is the second most major zone in the elevated central portion of the island. Saline blanks fringe the outer portions of the island.
The Southern region
With a slightly higher ground level, the southern region harbours following mangrove communities.
Phoenix community is the largest community in this region occupying almost the entire south-eastern region. It is significantly absent in the northern and the central region. Exocoecaria, Heritiera fomes and Aegiceras are also found along with Phoenix. Heritiera fomes and Exocoecaria are comparatively taller trees and Ceriops, Aegiceras along with Phoenix are shrub like.
Heritiera fomes is also present in the southern seaward side, however, as it occupies very small areas as a pure community, it could not be delineated separately.
The south western region has fringe mangroves as the most seaward zone. The fringe mangroves comprise Avicennia alba, Aegialitis and Avicennia marina as linear patches. The inward zone in the west has sparsely distributed Avicennia, Marsh vegetation and A. marina.
Lothian Island is a wild life sanctuary and hence the mangrove forests here are protected. Dense mangroves occupy 67% of the area. However, during ground truth surveys, it was observed that the mangrove habitat of the island is undergoing degradation due to purely natural causes. Overall, the mangrove habitat of Lothian comprises more of pure communities like Avicennia marina and A. alba making up 34% of the island. There are also dominant communities like Phoenix and Aegialitis, which make up significant portion of the island. Heritiera fomes is also present albeit in small numbers, showing that here too the influence of freshwater is almost negligible. The Lothian mangroves are distributed based on geomorphology of the island. The low-lying northern region has Avicennia as a major community, the higher ground in the south leads to the habitation of Phoenix and the elevated central region has more of marsh vegetation and sparse and stunted Avicennia along with Saline blanks as a result of increase in salinity due to increase in elevation probably because of deposition.
The Dhanchi Island
The Dhanchi Island is located east to the Lothian Island and is in the confluence of the Thakuran River (in the east), the Jagdal Ganga in the west and the Bay of Bengal in the south. There are two prominent creeks (one creek originates from the east and the other originates from the west). The eastern creek in earlier times (based on the SOI topographical map of 1960) touched the western creek. Today, the creek travels up to the north central region only. The western creek has more or less maintained its own status.
Study of spectral behaviour of different mangroves communities help in identification as well as determining their spatial distribution in Dhanchi Island. Analysis of consecutive years from 1998 to 2000 were made. Initial analysis of IRS 1D LISS III data of February, 1998 identified five different assemblages of mangroves at Dhanchi Island. The same experiment was repeated using IRS 1D LISS III data of February, 1999 which yielded the similar pattern of distribution of mangrove assemblages. Spectral behaviour of major mangrove communities helped in identification as well as determining their spatial distribution at Dhanchi Island. Similar experiment using IRS 1D LISS III data of March, 2000 confirmed the distribution of major mangrove communities in Dhanchi Island.
Three distinct physiographic zones are observed from satellite data. Zone 1 is the area above the eastern creek (Binidar creek). Zone 2 makes up the area between the two creeks and Zone 3 is the area south to the western creek. Apart from these two major creeks, there are two more creeks originating from the east.
Till 1990, aquaculture ponds occupied north-eastern part of Zone 1. After abandoning of the aquaculture ponds, Forest department carried out extensive plantation of heterogeneous mangrove communities comprising Excoecaria, Avicennia, Bruguiera etc. Ceriops-Aegialitis-Excoecaria (dominant association) community, Avicennia dense community. Phoenix and Grass make up this zone (based on satellite data). Overall the eastern portion of this zone has communities high in density and the western portion has degraded mangroves and mangroves with low density.
Seaward fringing mangroves
Avicennia makes the most seaward zone in the north, northwest and west. The eastern region of this zone has Avicennia, Ceriops-Aegialitis-Excoecaria, Phoenix and grass community fringing the coast.
Apart from making up the fringe mangroves in the north, Avicennia (A. marina and A. alba) community makes up small patches in the northwest also. Small and scattered patches are also present in the central portion along the creek. This community is associated with Sonneratia followed by few trees of Aegialitis, Ceriops, Bruguiera, Xylocarpus and Suaeda.
Ceriops-Aegialitis-Excoecaria community is the major community, which is found all over the Dhanchi Island. It is well distributed in this zone with slightly heavier distribution on the eastern side. A marked decrease has been noted from 1998-2000 with the distribution being limited to the eastern region during the year 2000. A. marina, Aegiceras, Acanthus and Suaeda are also observed along with this community (ground observations).
Phoenix dominating (60%) the assemblage, which also comprises Excoecaria and Aegialitis makes up the zone on the landward side (or where the region is elevated) on the northern portion as well as south-eastern portions of Zone-I. Also present along with Phoenix community are A. marina, A. alba, Dalbergia, Derris and Acanthus (ground observations).
Small-scattered patches are observed in this zone. Some saline patches in the central portion have been replaced by marsh vegetation in the year 2000.
Zone II lying between the two creeks has dense Phoenix community as the major zone occupying the eastern and the southern portions. The central and the western region has more of degraded mangroves, grass community, sparsely distributed Avicennia. Phoenix is the major mangrove zone here, distributed in a deep U-shaped from the east of the island and extends up to the west. It is wider on the eastern side and is the second belt after the narrow seaward fringing Ceriops-Aegialitis-Excoecaria community in the east. Fringing Seaward belt is made up of Ceriops-Aegialitis-Excoecaria community. It also makes up a major zone in the central portion after the Phoenix zone on the landward side.
Marsh vegetation occupies the elevated and landward portion adjoining saline blanks in the west. A large patch of saline blank is mapped on the north-western side at the end of the eastern creek. Grass patches have also been mapped along with marsh and saline patches in this central zone.
Zone III (area south to the western creek) is a zone comprising of sparser density. Dense mangroves are found in few places. Ceriops-Aegialitis-Excoecaria association makes up the most seaward zone in this region. It is also the dominant association in this region. Homogenous dense patches of this association are significantly mapped in the west and southern tip of the island. The south-eastern edge comprises mixed mangroves as fringing community. Avicennia community inhabits the zone after the Ceriops-Aegialitis-Excoecaria community on the landward side. The height of A. marina is 1 meter only, whereas in other areas, it grows up to 6 meters height.
Grass is distributed in the central belt along with Avicennia and Ceriops-Aegialitis-Excoecaria. Marsh vegetation comprising Suaeda, Sesuvium, Salicornia brachiata, Ipomoea biloba, Acanthus etc., also inhabits this belt along with grass (Porteresia, Alleuropus etc.).
Apart from these mangroves, which were mapped using satellite data, other mangroves such as Rhizophora, Xylocarpus , Bruguiera and Sonneratia are also present in small numbers.
There is a marginal decrease in Dense Mangrove coverage of Dhanchi from December 1998 to March, 2000. Degradation is more prominent towards the end of the creeks (on landward side) which are elevated areas and therefore under the anthropogenic influence and also the influence of tidal water is less here. By highly degraded, it is meant that the area is a saline blank now with no mangrove cover on it. The dominant community is Ceriops-Aegialitis-Excoecaria (three species dominance, followed closely by homogenous community of Phoenix and Avicennia. Although not so wide spread, but in certain pockets, especially on the western side of the island, erosion is prominent leading to the degradation of mangrove forest. In some small pockets, even clearing of mangroves have been observed during ground truth survey. Most significant however is the absence of Heritiera fomes (Sundari tree) on Dhanchi Island. This community does not even occur as isolated or small patches on this island (It was not encountered at all during ground surveys).
A part of this study, especially the detailed methodology, was presented in the International Symposium organised jointly by ISPRS and ISRS in December, 2002.
Mangroves of Subarnarekha Estuary
Subarnarekha delta in Orissa and partly in West Bengal is situated in a meso-tidal zone, as part of Balasore-Contai coastal plain. It is the western most estuary of the West Bengal coast. A wide patch of mangrove habitat occupies the eastward intertidal medflats covering an area of nearly 3.76 square kilometres. Earlier it occupied an area of 10.38 square kilometres (SOI topographical map of 1968-69). Three broad zones of major mangrove assemblages have been identified in this region.
The seaward fringing community comprises Excoecaria-Avicennia association. This association is also the major zone of this mangrove habitat and surrounds the central patch of Avicennia dominated assemblage. It is the largest mangrove assemblage in this region occupying 24% of the total vegetative cover of this region. Mostly it has dense canopy coverage. Occurrence of Ceriops, Aegialitis, Derris, Dalbergia and Acanthus are also noted in this group. Avicennia dominated community occupies central portion of the patch, the tallest plant noted in this region. Acanthus illicifolius occupies the landward side of this patch and occurs as small shrubs. Extremely scattered growth of Ceriops and Avicennia is also noted in this zone.
Coastal Zone Management for Selected Areas of West Bengal :
The project was sponsored by Department of Space, Government of India. The increased dependence on the coastal zone for various industrial, commercial and recreational activities are causing concerns as these are the major threats in sustaining the biological richness of coastal areas. Whereas long-term management and sustainable development of coastal resources is urgently required, most coastal areas of India face increasingly severe problems of rapidly growing human populations, deteriorating environmental quality, loss of critical habitats, loss of biodiversity, and increased risk from natural hazards. The overall objective of the Coastal Zone Management (CZM) is to provide for sustainable use of natural resources, maintenance of high levels of biodiversity and real conservation of critical habitats. It provides the opportunity to allow policy orientation and development of management strategies to address the issue of resource use conflicts and to control the impacts of human intervention on the environment. The objectives of the project were (I) Creation of database in Geographical Information System (GIS), based on existing information, for selected study area; (ii) Integration of Remote Sensing (RS) based inputs with environmental parameters collected on ground as well as secondary data; (iii) Formulation of management strategies, based on the integrated database including outputs of impact assessment studies (iv) Assignment of different management zones, based on the ecological sensitivity and the importance of the habitat. The detail database created out of this project helped in preparation of management plan of the coastal region of West Bengal.
Preparation of Integrated Coastal Zone Management Plan for identified Coastal Stretches of West Bengal :
The project was sponsored by National Coastal Zone Management Authority (NCZMA), Ministry of Environment & Forests, Government of India. Government of India has declared the coastal stretches of seas, bays, estuaries creeks and backwaters which are influenced by tidal action up to 500 meters (in the land ward side) from High Tide Line (HTL) and the land between the Low Tide Line (LTL) and HTL as Coastal Regulation Zone (CRZ) and imposed certain restrictions on setting up and expansion of industries, operations and processes, etc. in CRZ. In view of this, it is necessary to have knowledge about the present landuse / wetland conditions of the zone with special reference to built-up land, sand mining, construction activities etc. Landuse maps within the CRZ of West Bengal were previously prepared by this Institute on 1:25,000 scale based on SPOT /IRS LISS II remote sensing data of the year 1989 using visual interpretation techniques. More than 15 years have passed from then. There should be a stocktaking after such a long period. Hence, the objectives of this project are (i) redefinition of the redundant CRZ in the above stretches of the coastal West Bengal, based on the declination of the new HTL's, (ii) production of new sets of maps of present day landuse pattern and (iii) formulation of an integrated management plan for these stretches. This project yielded certain extremely important results. The outcome of the projects were subsequently utilised for regular monitoring of the West Bengal coast.