Assessing the changes of the landmass surrounded by the Indian coast

This study explores the changes in the landmass bounded by the coast of India during 1975-2005 by using on-screen visual interpretation technique (with 100m resolution and 1:50,000 scale) from NASA Landsat Imagery in three different time periods viz. 1975, 1990, and 2005. The result indicated an overall expansion of 130 sq. km area of the landmass that surrounded by the Indian coast during 1975-2005 (74 sq. km during 1975-1990 and 56 sq. km during 1991-2005). These estimations are based on the preliminary analysis and may be estimated more accurately by reducing the scale and using further higher resolution images.


Introduction
It is well recognized that the landmass and coastal region are changing in many places around the world (Kunte and Wagle, 2005;Webb and Kench, 2010;Australia Network News, 2010;BBC News, 2010;Nayak et al., 2013;Nayak and Mandal, 2019a). Kunte and Wagle (2005) documented an increase of 30-35 km towards the sea along eastern coast of India since the Holocene period. Jayappa et al. (2003) surveyed eight beaches in Dakshina Kannada and Udupi districts of India to understand morphological changes in the coast due to erosion and sediment deposition. Their study indicated that the shoreline has protruded by about 225 m on up-drift side and retreated by 165 m on down-drift side between December 1993 and July 1995. Mergner and Scheer (1974) reported a significant rise in corals along the coast of India. An expansion in the low lying Pacific Islands is also highlighted in Webb and Kench (2010), which were mostly due to the atoll reef platforms, dynamic landform.
Australia Network News (2010) and BBC News (2010) reported that 80% of the Pacific islands mostly either unchanged or expanded and some expanded by 20-30 %. 2 Soil erosion plays major role for sediment formation and run off plays major role for transportation of sediments (Narayanna and Babu, 1983;Manjunatha and Shankar, 1992;Thanh et al., 2004;Kunte and Wagle, 2005;Mettier et al., 2008;Li et al., 2011). Thus if sediment deposits along the coastline for years and years, it results expansion of the coastal landmass. In a study, Narayanna and Babu (1983) highlighted that India has lost ~29% of its total eroded soil into the sea and the rivers plays the major rule for the discharge of sediments into the sea. Chandramohan et al. (2001) documented an annual discharge of nearly 1.2 × 10 12 kilograms of sediments into the coast of India. Manjunatha and Shankar (1992) reported sedimentation rates at 0.72 and 0.56 mm/yr in 2 cores along continental shelf of western India. All these studies indicated an expansion in Indian coastal landmass.
However, the changes in Indian landmass is so far not well documented in previous researches. In a recent study, Nayak and Mandal (2019a) 1975-1990 and 1991-2005. Section 2 presents the study area, data and methods are presented. Section 3 presents the results and discussions of this study. The conclusions drawn from the study are given in the last section.

Methodology and Data used
This study focused on the Indian landmass that lies on the Indian Plate and bounded by the Arabian The geometrically rectified bands were combined together by the process of layer stacking and mosaicking using ERDAS Imagine to find the whole study region as a single image for each year 3 viz. 1975, 1990, and 2005 image resolution and the scale are kept as 100 meter and 1:50,000 respectively for each year. Finally, the total area of the whole study region (Figure 1) for each year were estimated separately.

Results and Discussions
The entire area of the landmass bounded by the coast of India coast for the years 1975, 1990, and 2005 are shown in the Figure 2. The figure 2a, 2b, and 2c show the area of the study region for the year 1975, 1990, and 2005 respectively. The total areas of the study region in 1975, 1990, and 2005 are calculated and given in Table 1. It shows that the total areas of the landmass of the study region in 1975, 1990, and 2005    Although the sediment depositions along the Indian coast on satellite images were identified (as shown in Figure 3), but the quantitative estimation of sediment was not considered in the present study. Only the whole area of the landmass that bounded by the coast of India is estimated in this study from the Landsat datasets. The previous researches and our snapshots confirmed that the sediment deposits along the Indian coast for the years and years and causes expansion.  , 1983). Manjunatha and Shankar (1992) also documented the sedimentation rates at 0.72 and 0.56 mm/yr in 2 cores along the continental shelf of western India. All these lead to expansion in landmass. Many precious studies including the Indian coastal regions highlighted about the land use and land cover changes during this period (e.g., Nayak and Mandal, 2012, 2019b, 2019cNayak et al., 2021). Our overall estimations are based on the preliminary analysis with very low resolution and high scale parameters. Thus these estimations may be associated with some errors because of the resolution and scale selected in this study. However, these results can be more accurately reproduced by reducing the scale and using further higher resolution images. Thus it is suggested to further investigate on the same issue with very high resolution datasets and extent the analysis to recent years.

Concussions
The inference that can be drawn from the results and discussions presented in the previous sections are as follows: 7 The landmass that bounded by the Indian coast is expanding and it is assessed as 130 sq km during . This estimation is based on screen visual interpretation technique from the NASA Landsat imageries. The results indicate that the total landmass is expanded by 74 sq. km in first fifteen years and it is further expanded by 56 sq. km in next fifteen years. The overall analysis indicates that such expansion could be because of sediment deposition along the Indian coast during this period which mostly caused by the soil erosion and transforming them from the inland into the sea by rivers.