Assessment of coastal vulnerability index (CVI) and its application along the Labuhan Maringgai coast, east Lampung Indonesia

The Coastal Vulnerability Index (CVI) is one of the simplest and commonly used methods to assess coastal vulnerability. In this way, it is a common tool contributing to the decision-making process in long-term coastal planning and management. This study aims to assess the level of coastal vulnerability according to coastal typology of Labuhan Maringgai Coast section. The variable formulation of CVI is divided into hydrodynamic factors (mean significant wave heights, mean tide range, and mean sea level rise) and morpho dynamics factors, i.e. geomorphology, coastal slope, and average width of emerged beach. The morpho dynamics data were obtained through observation, direct measurements in the field by systematic sampling, extraction from aerial photographs and digital surface model (DSM). The results of modelling and predictions by several agencies are derived to obtain the hydrodynamics data. The coast of Labuhan Maringgai was divided into 12 transects and the coastal vulnerability index were classified into three categories such as low, moderate, and high. The results of CVI method showed that the most vulnerable transect is located at Desa Bandar Negeri characterized by mud flats and damaged mangroves.


Introduction
The coastal region is a very complex and dynamic area because it is a meeting place between land and ocean.This condition causes coastal areas to have a high degree of susceptibility to environmental change.This makes coastal environment potentially highly vulnerable and environmentally unstable in settlement areas along the coastal, tourist, and fishing sectors so that they cannot be exploited properly and sustainably over a long period of time.The vulnerability of coastal areas is a description of conditions that are easily influenced by natural factors and human activity factors [1].Labuhan Maringggai district located in Lampung East district is a coastal area that has the potential of coastal areas to be developed from the mining, catch fishing, and tourism sectors.The potential exploitation can be sustainable if supported by the balance and sustainability of coastal regions by identifying the level of vulnerability in coastal areas by mapping the area vulnerability using the Coastal Vulnerability Index (CVI) method.This research aims to identify the physical parameters of vulnerabilities that are located along the coastal areas of Labuhan Maringgai with a variety of data and processing will be subsequently included in the scoring system of the CVI method.Variables used as calculation weights include coastal geomorphology, coastal inclination, waves, change of coastline, and sea level rise.The results of all data processing with variablessuch variables will be categorized according to the range of values on the method of CVI.The result of this study is a map of coastal vulnerability level that can be used as a material for the consideration of the local government to develop dam preserving coastal regions.

Material and methods
This section provides details on the CVI formulation describing the variables used, the ranking score and the mathematical formulation applied to construct the synthetic index.This section also describes the sensitivity analysis carried out for the preparation of this work, and the application and result of CVI formulations present for the case study area.
The area has been divided into 11 transects which were the area considered to Bandar Negeri Village, Karya Makmur Village, Karya Tani Village, Margasari Village, Muara Gading Mas Village, dan Sriminosari Village (Figure 1).

Data Sources
The data collection was carried out along the coastline of Labuhan Maringgai district, the eastern district of Lampung which comprises 6 villages that are located along coastal areas with a coastal line length of ±26 km by purposive sampling method with 12 station.

Geomorphology
The geomorphological observations of the coast were conducted directly at the 12 points of the research station visually to determine the geomorfological conditions of the shore.Coastal geomorphology relates to the sighting of coastal areas [2].At 12 points of stations reached using GPS Hand Garmin 64s.The Geomorphological observation aims to know the characteristics of the coastal area of each village.

Mean Significant Wave Height
Significant high-wave data came from 1 January 2011 -31 December 2020 wind data obtained from the official website of the European Centre for Medium Range-Weather Forecast (ECMWF) or the site https://www.ecmwf.int/, the location of the wind data collection at the coordinates 5°28'48.00"S,105°46'12.00"Elocated on land.The wind data was used for Hindcasting Wave with the SPM 1984 (Shore Protection Manual) method aimed at obtaining significant high wave values.

Tide Range
Recession data is obtained from the MIKE21 prediction with the time used from January 1, 2005, to June 30, 2022, the location of the recession prediction at the coordinates of 5°21'42.62"S,105°49'11.06"Ewith a time interval of 1 hour.The Mike 21 prediction data is verified against field recession measurement data from February 7, 2022, to February 21, 2022, to determine the accuracy of the data obtained from the forecast of MIKE21.

Coastal Slope
Collecting coastal slope data using DEMNAS secondary data obtained from the official INA-Geoportal website or https://tanahair.indonesia.go.id/.Elevator data used in Labuhan Maringgai district, East Lampung district.The elevation data is grouped using a reclassify tool, then a buffer is carried out at the point of the research station (land) to create a new point (sea) with varying distances, so that the reduction between the elevation on land and at sea obtains a difference in elevation at the station point.The obtained coastal angle is interpolated to find out the area of the spread of the value of the coastal tilt, to obtain the angle of coastal inclination using the equation below [3].

Shoreline
Data on coastline changes are derived from Landsat Image 8 data for 2011 and 2021 on Labuhan Maringgai district obtained from the official United States Geological Survey (USGS) website or https://earthexplorer.usgs.gov/,Landsat image data 8 is used to obtain values of the rate of coastal changes at each point of the research station.Image data processing is performed there are several stages such as performing image pre-processing aimed at fixing image data to do the extraction.The threshold approach is the way to separate land and ocean in the image, the band ratio approach is a way to cover the weaknesses resulting from the thresold.The stages were performed using ENVI 5.3 software, then an image overlay was performed to determine the speed of coastline change at the research site using the DSAS method.(Digital Shoreline Analysis System).

Sea Level Rise
Data on sea level rise using secondary data obtained from from National Oceanic and Atmospheric Administration, NOAA (https:// www.star.nesdis.noaa.gov/ socd/ lsa/ SeaLe velRi se/).
Geomorphological landforms represent erosion resistance, and erosion rates are considered markers of susceptibility to coastal processes.Wave energy is connected to erosion capacity, and relief and vertical land motions are seen as indications of flooding danger.Variables are classified on a scale of 1 to 5 (low risk to high risk), with the range divided into five equal parts (Table 1).Apart from the geospatial comparison of various risk classes, the distributions of vulnerability classes are analyzed using statistical analysis (skewness and mean).The cell distribution around moderate vulnerability classes (mean) and their peaks or extreme vulnerability categories are examined in this context.Barrier beaches, sand beaches, salt marsh, mud flats, deltas, mangroves, coral reefs.Mean Significant Wave Height 0 -2.9 m 3.0 -4.9 m 5.0 -5.9 m 6.0 -6.9 m > 6.9 m Mean Tide Range < 1.0 m 1.0 -1.9 m 2.0 -4.0 m 4.1 -6.0 m > 6.0 m Coastal Slope > 10 0 6 0 -9.9 0 4 0 -5.9 0 2 0 -3.9 0 < 2 0 Shoreline Erosion/Accretion (m/yr) > +0.1 0.0 -0.1 --0.5 -0.6 --1.0 > -1.0 Sea Level Rise < -1.0 -1.0 -0.9 1.0 -2.0 2.1 -4.0 > 4.0 The Coastal Vulnerability Index (CVI) of each cell is determined by combining several risk parameters to produce an indicator.The calculation of the index vulnerability score value is based on the originality of the concept of calculating the index of vulnerability value in the CVI method, i.e. is the root of the multiplication of each variable weight value divided by the number of variables as follows [5].
where CVI = value (score) Coastal Vulnerability Index, a, b, c, d, e and f are sequential variable weights; geomorphology, coastline change, coastal bottom tilt, significant wave height, rise range cycle, and sea level change.The determination of the category of the CVI method is classified into 3 category index such as low, moderate, and high.

Geomorphology
Geomorphological observations were conducted directly at 12 research stations located in 6 villages in Labuhan Maringgai district of East Lampung.The results of the observations show that at Labuhan Maringgai district has a type of sandy and muddy beach as well as has a beach building at some point of the station and mangrove that grows at certain points of the Station and at some points it is used as a beach resort and tourist area by the surrounding community.The average of the conditions of the coastal area on Labuhan Maringgai which is beaches with sandy and mud that can be classified vulnerability is very high with the value obtained ranging from 4 -5.

Mean Significant Wave Height
Significant high-wave data generated by wind came from the ECMWF in 2011 until 2020 obtained from the 1984 SPM method.In the coastal waters of Labuhan Maringgai district produced a significant wave height of 0.32 m -0.49m and a wave period of 3.07 s -3.74 s, so that the significant high value of the wave produced was 0.5 m and the significant wavelength resulted was 3.7 s.This elevation data is gathered and utilized to determine the Formzhal number.The mixed tidal type tends to be single daily, with one high tide and one low tide in one day, although there are occasionally two high tides and two low tides with varying heights and periods.The greatest tidal value (HHWL), 1.22 m, was attained, with the lowest ebb value (LLWL), 0.30 m, giving a tidal rise value of 0.92 meters.

Coastal Slope
Dem data processing for coastal angle was carried out at 12 research stations located at 6 villages in Labuhan Maringgai district of Lampung East.Results of data analysis by means of interpolation showed that at Labuhan maringgai has a coastal tilt angle ranging from 0.92o -5,05o, the percentage of coastal inclination at 12 states of the research range from 2.05% -11.21%.

Shoreline
The average rate of coastline change in Labuhan Maringgai district in 2017 -2021 was obtained with the highest accretion at the point of research station 9 of 239.80 m/year and highest abrasion at research station 4 point of -3.67 m/ year.Labuhan Maringgai has a variety of vulnerability classification values, namely highly vulnerable, moderate and non-sensitive with values 1, 3, 4 and 5.

Sea Level Rise
Secondary data analysis from National Oceanic and Atmospheric Administration, NOAA (https:// www.star.nesdis.noaa.gov/ socd/ lsa/ SeaLe velRi se/) shows that Indonesia's waters have an average trend of sea level rise of 6.8 mm/year.

Coastal Vulnerability Index
Based on the calculation of the Coastal Vulnerability Index of each parameter, the coastal vulnerability class of every parameter (i.e.A = geomorphology, B = mean significant wave height, C = tide range, D = coastal slope, E = shoreline, and F = sea level rise) are obtained, as shown in

Conclusions
The CVI results obtained at 12 research stations located in 6 villages, covering 6 physical parameters, range from 4.5 to 12.9, categorizing Labuhan Maringgai District as a moderate and vulnerable area.Table 1 shows that the vulnerable category includes 4 research stations, while the moderate category comprises 8 research stations.Villages classified as vulnerable are Karya Tani and Bandar Negeri, while those in the moderate category include Karya Makmur, Muara Gading Mas, Sri Minosari, and Marga Sari.The vulnerability in Labuhan Maringgai District is attributed to the high classification values of vulnerability in each physical parameter, such as coastal geomorphology, coastal slope, changes in coastline, and trends in sea level rise, excluding parameters like significant wave height 1298 (2024) 012025 IOP Publishing doi:10.1088/1755-1315/1298/1/012025 2
Range MIKE21 prediction data was used to generate tide data over 18.6 years, which was then confirmed using field data.The findings of the field verification of tidal measurement data attained an accuracy of 84.97% with a Mean Realative Error value of 15.03%.

Figure 2 .
Figure 2. Verification of predicted and field tidal data results.