Wetlands are the lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Wetlands are among the world's most productive environments. They are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. Realising the importance of Wetlands in regards to supplementing human dietary requirements, and their ecological significance in terms of flood control, water purification, aquatic productivity and microclimate regulation etc the Ministry of Environment and Forest, Government of India, carried out a Nation-wide Wetland Mapping and Inventorying project following a classification system adopted on the national level and utilising the manifold advantages of Remote Sensing technology. Space Applications Centre (SAC), ISRO, Ahmedabad was made the nodal agency for implementation of this project. The present work is a part of that work and was carried out by this institute under this division for the State of West Bengal and Tripura. Maps were prepared on 1:50,000 scale. Altogether, 181 maps were prepared through this exercise.

Wetlands are the lands transitional between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. The Convention on Wetlands of International Importance, especially for Waterfowl Habitat (the Ramasar Convention) defines wetlands as "areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres".

Wetlands are among the world's most productive environments. They are cradles of biological diversity, providing the water and primary productivity upon which countless species of plants and animals depend for survival. They support high concentrations of birds, mammals, reptiles, amphibians, fish and invertebrate species. Of the 20,000 species of fish in the world, more than 40% live in fresh water. Wetlands are also important storehouses of plant genetic material. Rice, for example, which is a common wetland plant, is the staple diet of more than half of humanity.

The interactions of physical, biological and chemical components of a wetland, such as soils, water, plants and animals, enable the wetland to perform many vital functions, for example: water storage; storm protection and flood mitigation; shoreline stabilization and erosion control; groundwater recharge (the movement of water from the wetland down into the underground aquifer); groundwater discharge (the movement of water upward to become surface water in a wetland); water purification through retention of nutrients, sediments, and pollutants; and stabilization of local climate conditions, particularly rainfall and temperature.

Wetlands provide tremendous economic benefits, for example: water supply (quantity and quality); fisheries (over two thirds of the world's fish harvest is linked to the health of coastal and inland wetland areas); agriculture, through the maintenance of water.

In addition, wetlands have special attributes as part of the cultural heritage of humanity: they are related to religious and cosmological beliefs, constitute a source of aesthetic inspiration, provide wildlife sanctuaries, and form the basis of important local traditions.

These functions, values and attributes are the basic cause behind nutrient retention in floodplains; timber production; energy resources, such as peat and plant matter; wildlife resources etc; Transport and recreation and tourism opportunities be maintained if the ecological processes of wetlands are allowed to continue functioning. Unfortunately, and in spite of important progress made in recent decades, wetlands continue to be among the world's most threatened ecosystems, owing mainly to ongoing drainage, conversion, pollution, and over-exploitation of their resources.

Realising the importance of Wetlands in regards to supplementing human dietary requirements, and their ecological significance in terms of flood control, water purification, aquatic productivity and microclimate regulation etc the Ministry of Environment and Forest, Government of India, was keen to embark on a comprehensive work on matters relating to wetlands at the national level. Any systematic approach towards classification and inventorying of these wetlands had not been taken so far. To fill this void, a Nation-wide Wetland Mapping and inventorying project was initiated by the MOEF, following a classification system adopted on the national level and utilising the manifold advantages of Remote Sensing technology. Wetlands of West Bengal were mapped as a part of this project.

In the context of importance of wetlands, the state of West Bengal assumes special significance in view of its unique geographical location, a claim, which is adequately borne out by the presence of three different wetland systems, namely, Himalayan, Flood Plain and Coastal. These wetlands constitute an important source of natural resources for the state, supporting a number of economic activities, such as fisheries, agriculture, navigation, fish-cum-paddy culture, providing means of livelihood to thousands of people. At the same time, West Bengal is one of the most populated states with a population density of 767 per square kilometre (as per 1991 census) against the backdrop of national population density of 267 per square kilometer. With such a population density, there is increasing pressure on the natural resources existing in the state. There is increasing necessity for taking proper initiative for conserving the primary productive sectors like wetlands.

The work was carried out using IRS (Indian Remote Sensing Satellite) 1B LISS II (Linear Imaging and Self Scanning Sensor) multi-temporal, synoptic False Colour Composite (FCC) data. Visual interpretation of both Pre-monsoon and Post-monsoon data of 1992-93 were used for delineation, mapping and classifying wetlands. The definition of wetland employed in this particular work is a modified International Union for the Conservation of Nature (IUCN) definition, as follows: All submerged or water-saturated lands, natural or man-made, inland or coastal, permanent or temporary, static or dynamic, vegetated or non-vegetated, which necessarily have a land-water interface are defined as wetlands.

Detail ground truth survey was carried out in problematic areas as identified through preliminary interpretation. Target was to carry out field checks covering at least 20% of the study area. Site specific data were collected to resolve image interpretation questions. Through this exercise, the image interpretation key has also been further developed. With the help of the updated image interpretation key, final interpretation of the remote sensing data were carried out, incorporating the experience gathered from the field. In certain cases, follow up field trips were also made to resolve the new problems that arose during image interpretation. These specific areas were further interpreted to resolve all the problems. Maps, thus prepared were made ready for cartographic work.

Maps were prepared on 1:50,000 scale. The minimum mapping unit was 3 mm X 3 mm. At this scale it represents an area of 2.25 hectare. This means all wetlands having area more than 2.25 hectare were mapped through this work. Out of 25 different types of possible wetlands, 20 types have been identified and mapped through this work. Altogether, 7056 wetlands (individual area > 0.0225 square kilometer) have been identified through this work. Total area for wetlands in the state is 5043.068 square kilometer. Two broad categories of wetlands namely, inland wetlands and coastal wetlands were made.

During the course of this work, it has been observed that a large number of small water-bodies whose individual area is less than 0.0225 square kilometer (which is the minimum mapping unit in this case) exist, particularly in the rural areas, often with a density of 400 to 500 wetlands per 700 square kilometer (i.e. the approximate area covered by a 15' x 15' interval SOI topographic sheet). These small water bodies need to be inventoried and conserved, particularly, if the total coverage of these wetlands in a cumulative manner is considered and the role that they play in maintaining the ground water regime. From this point of view, an attempt has been made to identify smaller wetlands up to the size of 0.0025 square kilometer which actually occupy an area of 1 mm x 1 mm size on 1:50,000 scale maps. In such a case, the other parameters like relative turbidity, aquatic vegetation, separate pre and post-monsoon boundaries have not been considered. These wetlands have been marked on the map as 2 mm x 2 mm black squares, irrespective of their exact size and shape and their individual areas have not been calculated. A separate database system for these small wetlands has also been created. Altogether 55,607 such wetlands have been identified within the state. Barddhaman shows highest concentration of such wetlands (12,471) followed by Bankura (8,610) and Medinipore (7,660). In case of Calcutta, occurrence of such wetlands are very less, only 10 in number. The presence of such wetlands in hilly area is also considerable. In case of Darjeeling district, about 185 such wetlands are present.

Through this work a computerised database giving details of location, nature, spatial extent, etc. of individual wetlands has already been prepared so that these could be readily accessed by the decision makers. This may be the first step towards the creation of a Wetland Information System (WIS) for the state of West Bengal, which can be further updated and enriched with time. Such a WIS will help policy makers and planners for taking speedy decision and to protect the wetlands from the ever-increasing pressure of reclamation and degradation as a consequence of population explosion. Also, this database will help in selecting the wetlands for protection and management needs. The detail report of this project can be downloaded from here.

Wetland Mapping of Tripura was carried out following the same technique as detailed above. Tripura is one of the seven North-Eastern States of India having an area of 10,477 square kilometers. It accounts for only 0.32% of total land area of India and occupies 22nd position in terms of area among the states and Union territories of India. It is located between 22 degree and 56 minutes and 24 degree and 32 minutes north latitude and between 90 degree and 09 minutes and 92 degree and 20 minutes east latitude. It is bounded on the north, west, south and south-east by Bangladesh whereas in the east it has a common boundary with Assam and Mizoram. Total Population 27,57,205 as per 1991 Census. Total number of districts is only three. Although it is a small state, but from the environmental and ecological point of view, the state is of immense importance. Almost 60% of the State is under forest cover. Tourism is the main Industry here.

Wetlands assumes special importance here. Average annual rainfall is 2100mm. The wetlands help in harvesting this rainwater and helps in agriculture during the lean season. Through the mapping exercise, altogether 411 wetlands of size greater than 2.25 hectare occupying an area of 6327.70 hectare in pre-monsoon season have been identified and mapped here. In addition, 3407 wetlands smaller than 2.25 hectare also exist in the state. The detail report of this project can be downloaded from here.

Studied in Howrah, Burdwan and Nadia District. The objective of this project was to prepare an inventory of surface water and to examine its quality for sustainable use of surface water.

The project was executed by National Remote Sensing Agency in collaboration with this Institute. Major task of this Institute was to collect field information and to correlate with the Remote Sensing data. The project was completed in September, 1995. The standard visual interpretation technique was employed to delineate various categories of wetlands and to evaluate the potential of various image processing approaches mentioned above for detecting these lands.

Wetlands playa major role in global biogeochemical cycling through anaerobic production of trace gases like methane, nitrous oxide, etc. and in maintaining the environmental quality especially in aquatic habitats by removing nutrients, processing chemicals and organic wastes and reducing sediment of water. Wetlands have been defined as the lands that are in transition between terrestrial and aquatic systems where the water table is usually at or near the surface or the land is covered by shallow water. Among the three wetland classification systems of Martin, Anderson and Cowardin developed in US, the Cowardin System grouping ecologically similar habitats defining habitat units for inventory and mapping; and providing uniformity in concepts and terminology throughout the United States is most systematic. In India, the Space Applications Centre, Department of Space, Government of India, has developed a wetland classification system suiting to Indian conditions.

Both air and spaceborne multispectral data along with aerial photographs have been extensively used for inventorying wetlands. By virtue of cloud penetration capability the Synthetic Aperture Radar (SAR) data has been found ideal for mapping wetlands in the coastal and other regions with persistent cloud cover. In this study, the European Remote Sensing Satellite (ERS-l) SAR data over Sundarban delta was used to generate information on wetlands and to study the temporal behaviour of these lands. The approach essentially involves speckle removal from digital SAR data, image registration, merging of SAR and the Indian Remote Sensing (IRS-l) satellite Linear Imaging Self-scanning Sensor (LISS-II) data and generation of the Intensity, Hue and Saturation (IHS) transform.

The standard visual interpretation technique was employed to delineate various categories of wetlands and to evaluate the potential of various image processing approaches mentioned above for detecting these lands.

Amongst various speckle removal filters, namely, median, Kuan, Lee, Frost and Gamme MAP employed, the last filter was found to be quite ideal as it retains the image features while substantially removing the noise (speckles) The IRS transformation helped in better delineation of two categories of mangroves in terms of crown density. Incorporation of SAR data as a channel in the standard FCC print of LISS-II data has not Only improved the overall image contrast but also brought out the upland areas supporting plantations and vegetable crops. In addition, the adverse effect of cloud cover on detectability of various terrain feature was found to be minimum with the incorporation of SAR data into FCC band combination.

The interpretation of Landsat-MSS data of 1973 and of ERS-1 SAR of 1993 for the same season is another noteworthy feature of the study which enabled the authors to study the temporal behaviour of wetlands. In the coastal areas, formation of new islands and expansion of existing islands has been observed. The shrinkage of wetlands abutting Calcutta city due to human encroachment for urbanization and agriculture was also noted.

The detail report of this project can be downloaded from here.

A menu driven Wetland Information System was developed in ArcView GIS software for the State of West Bengal. Input wetland maps were at a scale of 1:50,000 prepared during Nation-wide wetland mapping project using IRS LISS II data of 1992-93. NRIS standards were used for codification. Menu System facilities information retrieval and data input functions both in tabular as well as in spatial form at district or state level based on wetland types are the major components of the Information System. Incidentally, West Bengal is the first state in India which is having such digital information system. It has been termed as WINSYS. The project was sponsored by Ministry of Environment & Forests, Government of India. It was executed in collaboration with Space Applications Centre, ISRO, Ahmedabad (who acted as the nodal agency) and National Atlas & Thematic Mapping Organisation (NATMO), Kolkata. The project was completed in April, 2003.

The detail\ report of this project can be downloaded from here.