Delineation of sensitive coastal zone of northern Ramanathapuram coast, Tamilnad

Gurugnnm Blsurmnin , Sreechitr Suresh , Sntonu Goswmi ,Birvi Swminthn , Glitson Frncis Pereir

a Centre for Applied Geology, The Gandhigram Rural Institute - Deemed to Be University, Dindigul, Tamil Nadu, India

b National Remote Sensing Centre, India

Keywords:End point rate Linear regression rate Geographic information system Beach profile Ramanathapuram

ABSTRACT This research aims to assess the sensitive coastal zones by analyzing the shoreline changes such as accretion and erosion in the eastern coastal part of Ramanathapuram District,Tamil Nadu,India.The study focused on Mandapam, Pirappanvalsai, Enmanamcondam, Nagachi, Terbogi, Athyuthu, Chitrakkottai,Pathengal,Attangarai,Alagankulam,and Devipattinam villages.Some of these areas are distinguished as highly sensitive ecological zone. The erosion of an area leads to irreplaceable disturbances to nature.Hence,erosion and accretion studies are top priorities when studying the coastal area.In addition to GIS technology, which has been widely used in the past 20 years, the End Point Rate (EPR) and Linear Regression Rate(LRR)analyses were conducted to better understand the shoreline changes.The stability of the coastal region was analyzed by observing the slope variations of the beach during the profile survey. In the study, we analyzed that the Quaternary deposits of sand are the dominant geological feature of the study area. Coral reefs and salt pans are highly distributed along the coastal stretch. The coast of Mandapam village has been detected as a highly sensitive region, with an average erosion rate of-3.1 m/yr and an average accretion rate of 1.22 m/yr,resulting in high erosion and low accretion.The coast is a steep coast with an average slope angle of 0.24°. This study provides insight into sustainable coastal zone management.

1. Introduction

Coastal regions are considered vital resources to the world's national and global economies.Due to various events,these regions are under rising strain, resulting in land and assets demand [1]. Like other coastal nations, India also has many coastal areas with fragile habitats, which tend to decline because of human activity [2]. The coastal region is susceptible to environmental changes, particularly during storm and ocean level ascent issues. The characteristics of coasts include the factors such as waves, tides, wind forces, sediments, and early deposition, as discussed by Refs. [3-7]. A study done by Kodzo and Addo[8]shows that 70%of the coast in the world has dangerous hazards, most likely to generate coastal erosion in coastal areas.Often,the coastal area is tremendously vulnerable and is mostly unveiled to the environmental elements such as rivers,estuaries, wave actions, and anthropogenic activities that cause the coastal geomorphology reform [9].A study was done by Shum[10]and Vousdoukas [11], which shows that the coastal environment is too tender to get easily affected by its surrounding disturbances.Day by day,the coastal area is developing due to anthropogenic activities,resulting in a serious issue in managing the coastal environment[12,13].The coastal region also influences the economic aspect,and further, it will affect human well-being [14]. Coastal regions are considered the main sources of economic and global development.It also showcases sociocultural importance on a global scale. These regions are always exposed to natural hazards[15].

A recent study by Gary[16]indicates how the human activities of developing the coastal neighbourhood and sea-level rise correlate.These findings support the work done by Cooper and Pilkey [17],which claims that an increase in sea level impacts the coastal zone in various ways, such as elevation, tidal forces, coastal erosion, and flooding.The hydrodynamics of the tides shows some changes in the sediment movement [18,19] circulation and influx processes. Croft and Ian [20,21] conveyed that the beach profile is a widely used technique for understanding the beach changes,and it can be done quickly,revealing the coastal evolution.Numerous study techniques can be utilized to study beach profile changes,whether short-term or long-term. Mapping the shoreline or the coastal mapping is inevitably essential for marine researchers [22]. Nowadays, the DSASDigital Shoreline analysis tool is considered one of the major tools for shoreline change analysis[23].This analysis enables us to do the research using satellite data.The DSAS computes the changes insights for a timeline series of shorelines.The baseline required for the study was built to fill in as the initial stage for all transects cast by the DSAS application[24].Therefore,it is more economical and can be used as a cross-reference in the study. In this work, shoreline changes were analyzed in spatial and temporal aspects for the Ramanathapuram area using remote sensing and GIS techniques[25].The beach profile provides field evidence of the digitally acquired results[21].Physical parameters like wind data and temperature variations are studied to better understand the shoreline changes[26,27].

The structure and characteristics of coastal dynamics elements are critical for logical data and effective coast management.Remarkably,no broad consideration has been given,and there is scarcely any data on the geomorphology of Ramanathapuram[3-5,28,29].

2. Study area

The area chosen for this study is a part of the eastern coast of Ramanathapuram district in Tamil Nadu, India. The survey begins from Pathanendal village (9°30′35.63′′N, 78°54′33.21′′E) in the north till Mandapam village(9°16′48.63′′N, 79°07′11.69′′E) in the south of the district, as shown in (Fig.1). Mainly the study area is bounded by Palk Bay on its eastern side and the Gulf of Mannar in the southwest part of the district. It comprises 49.85 km length along the Pak Bay shoreline. The study area falls under Survey of India toposheet numbers 58K/74 &76, 58O/3 & 4.

Quaternary fluvial and marine sediments cover a large portion of the Ramanathapuram district. Fluvial deposits of sand, silt, and clay occur along channels of the Vaigai, Gundar, Manimuthar, and Pamban rivers, with varying levels of grain size [30]. The area is listed in a moderate zone of cyclone region and a high zone of drought by the National Disaster Management Authority (NDMA),Government of India. During the study period, a westsouthwestward wind developed a cyclone called Gaja was hit in the year 2018.The district's average annual rainfall is 827 mm,with the highest concentration in Pamban and along the shore and decreasing inland [31]. The average temperature in the area is around 28°C;the maximum temperature shoots up to 31.3°C and the minimum temperature is about 21°C.According to the study by Natesan[32],the distribution of beach ridges and the accumulation of sediments from the neighboring rivers along the coastline demonstrates that the shoreline has a path toward the ocean.

3. Materials and method

3.1. Data and processing

Fig.1. Study area.

The imageries of Landsat were used for the study to interpret the shoreline changes [8,33,34]. For this paper, the study was carried out for 20 years. Data was collected from the Earth Explorer - USGS and the Survey of India websites. Landsat (TM,ETM+ and OLA) (Table 1) data for 2000, 2005, 2010, 2015, and 2020 were geo-referenced in ArcGIS software with UTM projection WGS 1984. Resampling has been performed utilizing the cubic interpolation strategy to diminish the spatial distortion.By swiping one image over the other, the accuracy of the geocorrection was tested and confirmed by field inspection. Ground control points (GCPs) from the field were used to correct the satellite data, which included the important pit points along the Vaigai Riverbank and the main road leading to the Pamban bridge from Pathanendal village to Mandapam village. GCPs were collected uniformly from the major build-up and geomorphic features. The wind data used for the study to understand the shoreline changes were acquired from the POWER NASA Data Access viewer website https://power.larc.nasa.gov/data-accessviewer/. The wind speed and wind direction data from 2000 to 2020 were used for the study. These data were analyzed and converted to graphs for further interpretation.

The DSAS tool created by the United States Geological Survey(USGS)[35]was used as a major element to interpret the shoreline changes over two decades from 2000 to 2020. The erosion and accretion of the research area were determined using a DSASbased shoreline change assessment in ArcGIS software [36-38].This tool was used to draw the parallel transect line perpendicular to the shoreline. Then the shoreline was cautiously digitized and converted to shapefile for further change analysis studies[28,39].A quantitative analysis report of Linear Regression Rate(LRR)was prepared over each transect using the DSAS technique for the respective years. The analytical report of LRR was classified into five categories [40], High Erosion, Low Erosion, Stable, High Accretion and Low Accretion [41]. The study by Mullick, Islam, and Tanim[42],shows that LRR had more area-wise uncertainty than End Point Rate (EPR). Fitting least-squares regression lines to all the shoreline locations demonstrate temporal changes for a certain transect.The linear regression rate is the slope of the line,and the purpose of the regression line is to minimize the number of squared residuals [43].

Table 1 Data used in the study.

In DSAS,EPR was employed for statistical analysis[44].Changes in positions between the oldest and the most recent estimations were used to calculate the EPR[45].The accuracy was obtained by including more numbers of satellite data in the study of the respective years. The EPR's main advantage is that only two shoreline dates are required[28].It is utilized to forecast advanced shoreline positions [29]. The negative value of EPR and LRR indicates that the shoreline is moving landward, whereas the positive value indicates that the shoreline is moving seaward [46].Here,five years of shoreline data were studied to get more accurate data [36], showing the changes from 2000 to 2005, 2005-2010,2010-2015,and 2015-2020.

E.P.R=Distance(in meters)/Time between

the oldest and the most recent shoreline

3.2. Beach profile

The method followed to conduct the beach profile along the Ramanathapuram eastern coast is a simple, effective, efficient method less complicated than the Emery method[47].This beach profiling strategy compares well with standard geological methods,producing precise quantitative data at a lesser cost,with greater portability and usability. The experiment was done by erecting two poles or scales with a 3-m gap between the poles.Then the measurement of elevation was recorded in the seaward direction. As a result, we obtain a table with the distance and elevation of the beach. The data analysis is quite simple, making this technique more suitable for most educational and other applications. Unlike Emery's rod method, this profiling approach does not require a visible horizon or a correction for the Earth's curvature. It has the advantage of being speedier due to the changeable distance between the graduated poles [13,48-50].After measuring the degree of slope using the graph plotted for distance-elevation with the raw data collected from the field,we get the profile of the beach.

3.3. Physical parameter

The physical parameters such as the wind and temperature help us understand the ongoing climate changes in the coastal region.Wind data collected from NASA's POWER Data Access Viewer website include the wind speed and direction,enabling us to create a Ross diagram. This study used the average wind speed and direction for the last 20 years. The wind is a key parameter for the sediment movements along the coastal zone. Hence, this makes it an important parameter for the beach profile study. The average temperature for the study period from 2000 to 2020 was collected from the same website to support the climatic changes experienced in the study area [25,51].

4. Result

4.1. Rate of shoreline change

The LRR and EPR have been calculated from the DSAS, which helped derive the shoreline changes of each village in the study area. As shown in Fig. 2, short-term analysis was done using EPR data arrived by a comparative result of the newest and the oldest shoreline data. This method is suitable for quick analysis as it requires less time to complete the task.The long-term analysis using LRR data is also considered accurate as it involves all the data,even those with slight accuracy or trend variation [52].

Mandapam's coastal length is 12.4 km;this narrow region is on the eastern tip of the Rameswaram mainland. The roadway and railway line connecting Rameswaram Island pass through this narrow region. This area's shoreline is coming under stable, high erosion, and low erosion categories. These regions are intermittently distributed as stable regions (-0.99 to 0.99 m/yr) ranging cumulatively from 8.2 km. The coastal region undergoing high erosion ranging from -4.3 to -2.01 m/yr is intermittently distributed for a cumulative value of 1.8 km. Low erosion ranging from 1.92 to -1.01 m/yr is intermittently distributed for a cumulative value of 1.8 km stretch of the coastal region.

Pirappanvalsai's coastal length is 3.9 km; this region is coming under a stable zone. Enmanamkondan's coastal length is 1.2 km,which also has a stable shoreline,and its rate of shoreline change is negligible or nil. There were no accretional or erosional changes noticed on this coast. Nagachi's coastal length is 2.7 km; its shoreline is stable.There were no accretional or erosional changes noticed on this coast.

Attangarai's coastal length is 1.8 km, and its shoreline is stable,ranging from -0.91 to 0.0 m/yr intermittently distributed for a cumulative value of 1.7 km. Low erosion ranging from -1.40 to -1.1 m/yr intermittently distributed for a cumulative value of 0.81 km. There were no other significant changes noted on this coast.

The coastal length of Alagankulam is 5.3 km; the shoreline is stable, ranging from -0.99 to 0.8 m/yr intermittently distributed for a cumulative value of 4.6 km. Low erosion ranging from -1.63 to-1.02 m/yr is intermittently distributed for a cumulative value of 0.73 km. This shore has no high accretion, high erosion, or low accretion zone.

Fig. 2. Shoreline change distribution map.

The shoreline length of Terbhogi is 1.9 km, a stable region ranging from -0.88 to 0.0 m/yr intermittently distributed for a cumulative value of 1.8 km. This shore has not been affected by strong accretion or erosion. The coastal length of Athyuthu is 1.7 km. The shoreline is stable, ranging from -0.41 to 0.0 m/yr intermittently distributed for a cumulative value of 1.7 km. There were no accretional or erosional changes noticed on this coast.Chitrakkotai's coastal length is 4.5 km; the whole shoreline is stable,ranging from-0.57 to 0.04 m/yr.Devipattinam's coastal length is 4.6 km; a stable region ranging from -0.94 to 0.22 m/yr is intermittently distributed for a cumulative value of 4.2 km. Low erosion ranging from -1.68 to -1.03 m/yr, is intermittently distributed for a cumulative value of 0.35 km.This shoreline has no other changes.

The coastal length of Pathanendal village is 2.8 km;in the stable regions,the shoreline changes range from-0.18 to 1 m/yr(Table 2).

The study reveals that 7% of the study area comes under the“High Erosion” category, 43% is under the “Low Erosion” category,40%of the area is under the“Stable Zone”,and the rest falls under the “Low Accretion” zone. The “High Accretion” category is negligible or nil (Fig. 3).

4.2. Slope distribution

A beach profiling survey was carried out on March 2020 to analyze the slope angle of coastal locations. The raw data were collected from each village. Based on the altitude measurements obtained from the beach profile survey,a graph was plotted,and its slope was calculated for the study(Fig.4).The average slope angle of Pathanendal village was 7.5°from the readings of 2 locations.The average slope angle of Devipattinam village was 0.64°from the readings of 15 locations. The average slope angle of Chitrakkottai village was 0.80°from the readings of 11 locations. The average slope angle of Athyuthu village was 0.58°from readings of 11 locations.The average slope angle of Terbhogi village was 0.33°from the readings of 11 locations. The average slope angle of Alagankulam village was 1.53°from the readings of 8 locations.The average slope angle of Attangarai village was 0.15°from the readings of 8 locations. The average slope angle of Nagachi village was -0.41°from the readings of 8 locations. The average slope angle of Enmanmkondam village was 1.65°from the readings of 7 locations.The average slope angle of Pirappanvalsai village was -0.63°from the readings of 8 locations. The average slope angle of Mandapam village was measured; this region showed a steep coast and its obtained value was 0.24°from the readings of 9 locations(Table 3).

4.3. Impact of physical parameters

Fig. 3. Shoreline change classification of the study area.

The impact of physical parameters, including wind, temperature, waves action, and pressure, affect the coastal dynamics. The wave action, and constant wind action leads to the erosion and deposition of the sediments along the coastal zone. The wind develops the wind waves along the shoreline, leading to stronger erosion [26,51]. This study analyzed the monthly data of wind direction, wind speed, and temperature for 20 years from 2000 to 2020. Wind direction (expressed with reference to wind speed in percentage)observed along the study area was towards WSW 1.0%,SW 2.5%, SSW 2.4%, S 2.0%, SSE 1.0%, SE 1.2%, E 1.0%, ENE 0.2%, NE 0.2%and NNE 0.1%,showed in rose diagram(Fig.5).The wind speed was between 19.19 m/s to 15.17 m/s (Fig. 6). The Average yearly change in temperature in the study area from 2000 to 2020 was 28.01-28.69°C (Fig. 7). The temperature in northern Ramanathapuram shows a steady increase mainly due to the urbanization along the beaches [32,37].

4.4. Discussion

This coastal zone has a unique feature that is dynamically,morphologically and geographically important [32,53]. The coastline of the beach is a vulnerable feature which geographically separates the sea and land[24].Due to climate change and sea-level variation, beaches around the globe are facing erosion. Nowadays,the population around the beachside is increasing due to urbanization. It leads to the change in shoreline distributed towards the seaside making the beaches more dangerous[43].Hence,the study of shoreline changes is necessary and important. This study from 2000 to 2020 reveals that the changes are noticed on the eastern coast of Ramanathapuram. These changes are due to erosion and accretion of sediment.

From the calculations and graphs, it is clear that the northern portion of Mandapam village seashore has a very high amount of erosion. Remote sensing and GIS technique is used to analyze erosion and accretion. Geospatial technology of its multidatedatabase helps to understand the shoreline changes. It also provides data support throughout the study and accuracy [29]. Field investigations using the traditional beach profile method confirm the digitally acquired results [21]. According to [25], the shoreline changes are triggered due to the sediment movements, which depend on factors including wind action, tides, wave actions, and climate changes. The erosion and accretion in the study area are analyzed using the EPR and LRR methodology.The EPR technique is used for the short-term graphical analysis. It is an advanced method used in shoreline change analysis developed using DSAS extension.It helps us categorize the area into Erosional,Stable and Accretional zones. The beach profile is carried out to better understand shoreline changes; it provides information regarding the slope degree and evidence for erosion and accretion in the field[21].The Beach profile method used here is better than Emery's Rod method due to its portability, speedier results, simple calculation and earth's curvature correction [13,48-50].

Table 2 Shoreline accretion and erosion situation (Unit:m/yr).

Fig. 4. Slope measurement of villages.

Table 3 Slope measurement of the study area.

Table 3 (continued)

Fig. 5. Rose diagram of wind direction for the period of 2000-2020.

Fig. 6. Wind speed (m/s) for the period of 2000-2020.

Fig. 7. Average temperature (°C) from 2000 to 2020.

The majority of the study area is categorized as stable to low erosion zone,High Accretion zone is present in a negligible amount,the rest of the portion falls under Low Accretion zone,and a minor portion comes under High Erosion zone. The slope value obtained suggests that most of the study area is covered with a steep to gentle coast.The value obtained from the slope investigation using the field results and the remote sensing and GIS method suggests that this sensitive region has erosion of approximately one m/year towards the landward side. If this amount of erosion is carried for the next 20-40 years, we might see the seashore eroding faster than expected. The wind direction and wind speed for 20 years indicate that major wind actions are happening in the southwest direction. It triggers the erosion seen in the southern tip of Mandapam village on the northern Ramanathapuram coastline. The wind and wind-induced wave activity will influence a constant change on the coast. The increase in temperature over the past 20 years, from 2000 to 2020 about 0.67°C is mainly due to human activities such as urbanization.If the temperature is not maintained or slightly increased from the present condition, then the living organism, including humans of the coastal zone, might lead to an unbearable atmosphere affecting their health.

This study can be further extended in the future. It could be a potential topic for discussion on further erosion along the coastal zone due to wave action,slope,wind,and sediment transport.The studies show that most of the study area is stable.However,in some sensitive narrow regions, the rate of erosion is slightly increasing over the last 20 years,revealing that this activity can be continued and may lead to depletion of shoreline in the future.

5. Conclusion

The shoreline change affects the marine habitat,including marine organisms, plants, and corals. Conservation and protection of shorelines are essential for the safe habitat of marine life and those who depend on them.The study result shows the rate of erosion and accretion of the northern Ramanathapuram.The shoreline transition has been categorized into five groups depending on the DSAS results:High Erosion,Low Erosion,Stable,Low Accretion,andHigh Accretion.The changes in the shoreline have been calculated using EPR and LRR techniques from the year 2000-2020.The DSAS add-in extension in ArcGISisvery handyfor shorelineanalysis and continuousevaluation of the shoreline changes.The highest rate of erosionwas noted on the coast of Mandapam village. Wind direction, wind speed, and temperature variations along the study area have been analyzed as physical parameters for the 20 years from 2000 to 2020. It showed that wind influences sediment transport leading to erosion and accretion, and the temperature change leads to climatic variations.These physical parameters provide a shred of strong evidence for the shoreline changes. Through this study, we could understand the present shoreline condition and its potential changes in the future.

In Pathanendal village, the slope obtained from the elevation-distance graph was very high, indicating a raised coast.The slope obtained from the elevation-distance graph was very low in Mandapam village. Therefore, the study indicates that the area on the eastern coast of northern Ramanathapuram is stable;however,the highly active erosion might lead to future depletion of the shoreline if this trend continues(Fig.8).The data can be used to conserve similar erosion in other areas.

Fig. 8. Eroded region of Mandapam village.

Author contribution

Gurugnanam Balasubramanian:writing the original draft,formal analysis, and framing methodology. Sreechitra Suresh:writing the original draft,editing,data collection and investigation.Santonu Goswami: investigation. Bairavi Swaminathan:data curation and data processing. Glitson Francis Pereira: data processing,editing, and writing the original draft.

Conflict of interest

The authors declare that there is no conflicts of interest.

Acknowledgement

The authors are thankful to the Indian Space Research Organization (ISRO) - Respond Program and National Remote Sensing Centre (NRSC). They are also thankful to The Gandhigram Rural Institute (DTBU), Center for Applied Geology (Deemed to be University)for providing facilities to carry out this work.