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Fig. 6. Area captured by the River Khowai in Reach 4 and 5 during the study period 1975-2014.

Figure 6 Area captured by the River Khowai in Reach 4 and 5 during the study period 1975-2014.

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The Khowai River, one of the major rivers of Tripura, is also known as the most disastrous river for its extreme nature, espe- cially during rainy season. The river, after entering into the plain from the higher gradient of Atharamura hill range, spreads its enormous discharge and takes meandering course in the down- stream. The Khowai River is characterized by its exceedingly large flow during rainy season, continuous changes in channel morphol- ogy, rapid bed aggradation and bank line change. The lateral migra- tion of bank line causes failure of huge fertile land every year. The hills of Tripura are made up of semi-consolidated sedimentary rocks. Due to high precipitation (>2200 mm), steep slope, soft soil cover in the hills and alluvial formation in the valleys, there is high velocity and discharge of water laden with high silt discharge. All these factors result into meandering of the river and cause severe erosion in the concave bends (Deb et al., 2012). LULC in less time and low cost effective manner with better accu- racy (Kachhwala, 1985; Rogan and Chen, 2004; Sylla et al., 2012; Boori et al., 2015; Rawat and Kumar, 2015; Hazarika et al., 2015; Jayanth et al., 2016). Several studies have been carried out by many researchers using remote sensing data with GIS technique for multi temporal change analysis of LULC (Ahmed, 2012; Kotoky et al., 2012; Rawat et al., 2013; Yuan et al., 2005; Sun et al., 2009; Jensen, 2005; Lu et al., 2004; Murthy and Rao, 1997). Bank erosion is a natural hazard and this dynamic nature of river changes the LULC of its surrounding basin, which becomes natural phenomena in recent times.
The Khowai River, one of the major rivers of Tripura, is also known as the most disastrous river for its extreme nature, espe- cially during rainy season. The river, after entering into the plain from the higher gradient of Atharamura hill range, spreads its enormous discharge and takes meandering course in the down- stream. The Khowai River is characterized by its exceedingly large flow during rainy season, continuous changes in channel morphol- ogy, rapid bed aggradation and bank line change. The lateral migra- tion of bank line causes failure of huge fertile land every year. The hills of Tripura are made up of semi-consolidated sedimentary rocks. Due to high precipitation (>2200 mm), steep slope, soft soil cover in the hills and alluvial formation in the valleys, there is high velocity and discharge of water laden with high silt discharge. All these factors result into meandering of the river and cause severe erosion in the concave bends (Deb et al., 2012). LULC in less time and low cost effective manner with better accu- racy (Kachhwala, 1985; Rogan and Chen, 2004; Sylla et al., 2012; Boori et al., 2015; Rawat and Kumar, 2015; Hazarika et al., 2015; Jayanth et al., 2016). Several studies have been carried out by many researchers using remote sensing data with GIS technique for multi temporal change analysis of LULC (Ahmed, 2012; Kotoky et al., 2012; Rawat et al., 2013; Yuan et al., 2005; Sun et al., 2009; Jensen, 2005; Lu et al., 2004; Murthy and Rao, 1997). Bank erosion is a natural hazard and this dynamic nature of river changes the LULC of its surrounding basin, which becomes natural phenomena in recent times.
Table 2
Table 2
Description of the Land use/cover classification in the study. Table 3
Description of the Land use/cover classification in the study. Table 3
Detail dataset of the study. *USGS: United states Geological Survey.
Detail dataset of the study. *USGS: United states Geological Survey.
This work adopts three regularly use sophisticated software Geomatica 2012 for channel migration, ARCGIS 10.1 for LULC anal- ysis and ERDAS 9.1 for radiometric correction of the image. The datasets are imported in Geomatica 2012, geo-referenced using
This work adopts three regularly use sophisticated software Geomatica 2012 for channel migration, ARCGIS 10.1 for LULC anal- ysis and ERDAS 9.1 for radiometric correction of the image. The datasets are imported in Geomatica 2012, geo-referenced using
Source: Calculated by the authors from the 1975 Topo. sheet and 2014 LANDSAT imagery. Migration of Khowai River during 1975-2014. Table 4
Source: Calculated by the authors from the 1975 Topo. sheet and 2014 LANDSAT imagery. Migration of Khowai River during 1975-2014. Table 4
Source: Calculated by the authors from the 1975 topo. sheet and 2014 LANDSA’ imagery. Variation of active channel width during 1975 and 2014. Table 5
Source: Calculated by the authors from the 1975 topo. sheet and 2014 LANDSA’ imagery. Variation of active channel width during 1975 and 2014. Table 5
Riverbank failure processes and erosion are complex events caused by the interplay of several factors including river discharge, Lateral channel erosion is one of the significant characteristics of the alluvial river which is mainly observed in the middle course and lead to the widening of the channel. So, in order to know the erosion process (vertical or lateral) and morphological characteris- tics of the bank, determination of the channel width was carried out from two maps of different years. The bank erosion frequency Fig. 3. Variation in radius of curvature of the Khowai River during 1975 and 2014.
Riverbank failure processes and erosion are complex events caused by the interplay of several factors including river discharge, Lateral channel erosion is one of the significant characteristics of the alluvial river which is mainly observed in the middle course and lead to the widening of the channel. So, in order to know the erosion process (vertical or lateral) and morphological characteris- tics of the bank, determination of the channel width was carried out from two maps of different years. The bank erosion frequency Fig. 3. Variation in radius of curvature of the Khowai River during 1975 and 2014.
Fig. 4. Status of the area captured by the River Khowai in Reach 1 during the study period 1975-2014. J. Debnath et al./Egypt. J. Remote Sensing Space Sci. xxx (2017) xxx-xxx
Fig. 4. Status of the area captured by the River Khowai in Reach 1 during the study period 1975-2014. J. Debnath et al./Egypt. J. Remote Sensing Space Sci. xxx (2017) xxx-xxx
Fig. 5. Area captured by the River Khowai in Reach 2 and 3 during the study period 1975-2014. leads to the high percentage of erosion. River erodes one side of the bank and the eroded particles are deposited in the opposite bank, it is the natural character of the river. In the meandering river, due to the presence of loose bank material, lateral erosion predominant and consequently the river erodes deposits and migrates for a long distance. In that period of migration, some unchanged/unaltered portions remain which cannot be eroded due to the existence of flow, bank lithology, stratigraphy and inclination, channel geome- try, as well as anthropogenic activities (e.g. navigation). However, bank erosion primarily depends upon the soil type and river dis- charge rate (Youdeowei, 1997). Erosivity depends on the nature and amount of flow and discharge and velocity together play important role to bank collapse (Majumdar and Das (Pan), 2014). So, in the hilly river, discharge associated with high steep gradient
Fig. 5. Area captured by the River Khowai in Reach 2 and 3 during the study period 1975-2014. leads to the high percentage of erosion. River erodes one side of the bank and the eroded particles are deposited in the opposite bank, it is the natural character of the river. In the meandering river, due to the presence of loose bank material, lateral erosion predominant and consequently the river erodes deposits and migrates for a long distance. In that period of migration, some unchanged/unaltered portions remain which cannot be eroded due to the existence of flow, bank lithology, stratigraphy and inclination, channel geome- try, as well as anthropogenic activities (e.g. navigation). However, bank erosion primarily depends upon the soil type and river dis- charge rate (Youdeowei, 1997). Erosivity depends on the nature and amount of flow and discharge and velocity together play important role to bank collapse (Majumdar and Das (Pan), 2014). So, in the hilly river, discharge associated with high steep gradient
Classification of accuracy of the Supervised Classification and Kappa Co-efficient for 1975. Table 6
Classification of accuracy of the Supervised Classification and Kappa Co-efficient for 1975. Table 6
Fig. 7. Reach-wise area captured by the river during 1975-2014 timeframe. B = erosion, C = deposition, D = unchanged, E = historical migrated aree J. Debnath et al./ Egypt. J. Remote Sensing Space Sci. xxx (2017) xxx-xxx
Fig. 7. Reach-wise area captured by the river during 1975-2014 timeframe. B = erosion, C = deposition, D = unchanged, E = historical migrated aree J. Debnath et al./ Egypt. J. Remote Sensing Space Sci. xxx (2017) xxx-xxx
Fig. 8. Variation in sinuosity index of the Khowai River (1975-2014).
Fig. 8. Variation in sinuosity index of the Khowai River (1975-2014).
Classification of accuracy of the Supervised Classification and Kappa Co-efficient for 2014.
Classification of accuracy of the Supervised Classification and Kappa Co-efficient for 2014.
Land use/Land cover classes of the study area in 1975 and 2014.
Land use/Land cover classes of the study area in 1975 and 2014.
Fig. 9. Land use/Land cover map of the study area for 1975 and 2014.
Fig. 9. Land use/Land cover map of the study area for 1975 and 2014.
Fig. 10. ‘From-to’ change map of the Study area 1975-2014. (A) Cultivated land to other land use/land cover category (B) Open forest to other land use/land cover category (C) Water body to other land use/land cover category.
Fig. 10. ‘From-to’ change map of the Study area 1975-2014. (A) Cultivated land to other land use/land cover category (B) Open forest to other land use/land cover category (C) Water body to other land use/land cover category.
Converted area (km?) under land use/land cover change from 1975 to 2014. Table 9 dynamic nature of the river has changed the land use type of its flood plain area significantly, which falls under historical migrated area. In the overall context in 1975 about 11.22%, 37.37%, 40.69%, 1.68%, 5.63%, and 1.06% area were covered by dense forest, open forest, cultivated land, settlement, water body and barren land respectively, whereas in 2014 these areas were changed into 18.66%, 34.23%, 38.84%, 4.10%, 0.65% and 3.30% respectively (Table 8).
Converted area (km?) under land use/land cover change from 1975 to 2014. Table 9 dynamic nature of the river has changed the land use type of its flood plain area significantly, which falls under historical migrated area. In the overall context in 1975 about 11.22%, 37.37%, 40.69%, 1.68%, 5.63%, and 1.06% area were covered by dense forest, open forest, cultivated land, settlement, water body and barren land respectively, whereas in 2014 these areas were changed into 18.66%, 34.23%, 38.84%, 4.10%, 0.65% and 3.30% respectively (Table 8).
Fig. 11. Adjustment of the area of different land use/land cover in the flood plain of the study area. As it is clear that the area under settlement has been increased by 2.55%, besides this, the bank erosion also intends to capture the nearby settlements located along the Khowai River. The classifica- tion map (Fig. 9) shows that cultivated land area is dominant land use type of the study area but in this time period from 1975 to The adjustment of land use in the flood plain area of the River Khowai is distinctively a highlighting fact. Settlement and culti- vated land have been eroded away and converted into depositional land which was again used for both cultivation and settlement pur- poses. But some portions remain as barren land due to the pres- ence of high percentage of sand, which cannot be used either for cultivation or for settlement. In the study area the river has mostly eroded the cultivated land which is more than 2 km?, whereas it becomes less than 2 km? when deposition took place in the oppo- site bank. Another most identical affected land use type is settled area, which has been eroded for more than 1.5 km? area, whereas
Fig. 11. Adjustment of the area of different land use/land cover in the flood plain of the study area. As it is clear that the area under settlement has been increased by 2.55%, besides this, the bank erosion also intends to capture the nearby settlements located along the Khowai River. The classifica- tion map (Fig. 9) shows that cultivated land area is dominant land use type of the study area but in this time period from 1975 to The adjustment of land use in the flood plain area of the River Khowai is distinctively a highlighting fact. Settlement and culti- vated land have been eroded away and converted into depositional land which was again used for both cultivation and settlement pur- poses. But some portions remain as barren land due to the pres- ence of high percentage of sand, which cannot be used either for cultivation or for settlement. In the study area the river has mostly eroded the cultivated land which is more than 2 km?, whereas it becomes less than 2 km? when deposition took place in the oppo- site bank. Another most identical affected land use type is settled area, which has been eroded for more than 1.5 km? area, whereas
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