Wetlands along the Dhansiri River channel, Assam The rivers of the NE region of India manifest frequent changes in morphometric behaviour with resultant changes in associated fluviosedimentological attributes. It is therefore felt that the characterization and quantification of different types of swamp along the stretch of the river Dhansiri within a specific geomorphic setup may throw an insight into their origin and development. The study area is included between 93030/ E to 940 0/ E longitudes and 260 00/ N to 260 45/N latitudes and covers a total length of about 185km (Fig.1). The total length of the channel has been divided into sectors by 30km each so that a detailed evaluation could be made to have a clear idea about its characteristics and geomorphologic evolution. The configuration of the bils within each reach has been investigated to evaluate their significance (Deka and Goswami, 1992: Sharma and Goswami, 1993). Five different types of swamp are identified and characterised (Figure 2) as i) compact(C), ii) linear(L), iii) irregular(I), (iv) discrete(D) and (v) ox-bow(O) and the respective populations of each were counted. The areas of the different bils were measured and the generated data used for the present study. A number of field checks have also been conducted to understand the characteristics and comparative evaluation of the data resource as evident from toposheets and imageries.  Figur 1 : Location map of the study area. Brinson et al. (1994) classified wetlands into four broad geomorphic groups: riverine, depressional, fringe (coastal) and extensive peat lands and known as Brinson's Hydrogeomorphic Classification (HGM). Wetlands are also classified according to the source of water (precipitation, overland flow and ground water) and hydrodynamics (the strength and direction of flow). In the present study the wetlands or swampy lands are classified following Deka and Goswami (1992) and Sharma and Goswami (1993) in relation to localised basinal characteristics, flow behaviour, soil type, and geomorphologic attributes.  Figure 2: Different types of wetlands (Swamps) Methodology: The present approach employs Survey of India (SOI) toposheets (1914 and 1975) and Indian Remote Sensing (IRS) satellite imagery (1990, 1995 and 2000) to investigate spatial changes over available period of time. Such information is considered valuable in providing information for a period of 87years, which is often beyond the scope of empirical observation. The Survey of India toposheets of 1975 (Scale 1:50,000) were scanned, georeferenced, mosaiced and used to prepare the base map. The Survey of India toposheets from 1910-1914 (Scale 1:63,360) were scanned, registered and resampled. The IRS black and white (B/W) imageries on band four (wave length 0.77 to 0.86µm, with spatial resolution 36.25m, Linear Imaging and Self Scanning II) at 1:50,000 scale were also scanned, registered and resampled to keep the uniformity in data set. The satellite imageries and SOI toposheets from 1910-1914 were registered to the base map using a set of Ground Control Points (GCPs) in ERDAS IMAGINE 8.5 software. Thematic maps of different periods were prepared on 1:50.000 scale and were integrated using Arc view GIS. The meanders were then characterized, quantified and natures of movements were measured to generate database for the present exploratory study. Results and discussion: The different types of wetlands are not uniformly distributed through out the Dhansiri River basin. The number of wetlands and their corresponding areas for five different period of study are projected through Figures 3 & 4. The pre 1914 period as evidenced from the Survey of India (SOI) toposheets exhibited dominant association of linear  Figure 3: Development of Swamps in different periods variety of swamps (26.67%) and represented mainly by the paleochannels of the earlier river. The association of different varieties of swamps can be represented as L(26.67%) >C(24%)>O(22.67%)>D(20.0%)>I(6,67%). Out of six sectors the Sector 1 represents highest development of wetlands with equal proportion (36.36%) of compact and linear varieties. However, on closer observation in terms of areas covered by the wetlands, in all sectors other than Sector 4 within the studied stretch abundant presence of oxbow type swamps was clearly observed. The abundance of oxbow type swamps has been clearly  Figure 3: Spatial distribution of Swamps in different periods |