The mapping of the vulnerability coastal area in Pangandaran District by the coastal vulnerability index (CVI) approach

The phenomenon of sea level rise (SLR) in Pangandaran Regency threatens the continuity of human activities such as tourism, fisheries and trade that gives value to coastal regions. The southern coast of Java directly faces the Indian Ocean and sea levels are expected to rise by 2 – 4 mm/year, leaving the Pangandaran Regency relatively vulnerable to SLR. Coastal vulnerability can be mapped using the Coastal Vulnerability Index method to determine levels of vulnerability based on six parameters which are geomorphology, elevation, tidal range, significant wave height (SWH), shoreline change and rate of SLR. The results show that the geomorphology of Pangandaran Regency is considered to be very vulnerable (Score 5) due to the number of sandy beaches present. Elevation is dominated by the vulnerable category (Score 4). Tidal range of the coastal region is considered moderately vulnerable (Score 3). SWH of the coastal region is very vulnerable (Score 5). Shoreline change is considered to be moderately vulnerable (Score 3) with overall erosion in the region. Rate of SLR is considered to be very vulnerable (Score 5). The coastal region Pangandaran Regency is leaning towards being vulnerable against sea level rise.


Introduction
Activities in coastal communities such as tourism, fisheries and trade, are important for coastal areas because it provides economic value to the region.Phenomena sea level rise is a looming threat for the sustainability of coastal communities because of the potential damage it can cause to infrastructures and contribute towards loss of land.Pangandaran Regency has a high vulnerability to seawater intrusion and is projected to experience sea level rise of 2-4 mm/year [1].These results show a similarity to the IPCC [2] projections, which found the earth experience will experience an overall sea level rise of 4.9 mm/year, a significant increase from the 3.1 mm/year found in the 1993-2003 observations.In the period of 1995-2014, the entire southern waters of Java Island experienced an average sea level rise of 1.4 mm/year [3] and Wuriatmo et al. [4] found evidence of sea level rise on the range of 0.38 -1.04 mm/year throughout the 2000-2010 period in Pangandaran Regency.According to Dasanto [1], Pangandaran Regency will lose 42.1 ha of land by 2050 and 106.4 ha by 2100 which includes settlements and nonsettlements.These issues are why we need to map the vulnerabilities of coastal areas that the steps taken to improve the situation will be more more focused and effective [5].
The Coastal Vulnerability Index (CVI) method by Gornitz [6] and Pendleton et al. [7] is a commonly used method for assessing coastal vulnerability to sea level rise.Studies on the application of CVI have been carried out throughout Indonesia such as, on the coast of Riau by Sandhyavitri et al. [8] which uses four vulnerability classes, namely low, medium, high, very high where the result of the study is to determine the level of priority of coastal management and construction of breakwater structures.Studies of vulnerability using this method has also been carried out in Papua by Loinenak et al. [9] who used five vulnerability classes, of which are very low, low, medium, high, very high and six geological and physical parameters to map vulnerability in Doreri Bay, Manokwari Regency.The results of the study found that 20.9% of Doreri Bay is classified as Vulnerable.The CVI method is a method that is easily adaptable to the needs and conditions of the region.Such as Koroglu et al. [10] which tested the variability of the results of the Gornitz [6], Shaw et al. [11], Thieler [12], and Lopez et al. [13] to find a realistic approach to be applied on the coast of Barcelona.
This research is important for Pangandaran because there are not many studies regarding CVI in Pangandaran Regency.Existing research such as Dhiauddin et al. [14] only discusses the west coast of Pangandaran District.There is also research by Prayogi et al. [15] which uses three classes of vulnerability and does not discuss Cimerak and Cijulang Regencies.This research is expected to provide a broader picture regarding the condition of vulnerability on the coast of Pangandaran Regency.

Processing procedure
The polygon was created as long as 2 km of the coast and 1 km each seaward and landward to form observation segments PG1-42.These segments are later integrated with GIS data to create visualizations of each studied variable.Firstly, geomorphologic data was acquired through Landsat satellite imagery, DEM data and land use maps.Elevation data was extracted from DEM data.Tidal range data was IOP Publishing doi:10.1088/1755-1315/1260/1/0120513 acquired by finding the average monthly tidal range over the study period.Significant wave height data and sea level rise was extracted from hydro-oceanography modelling courtesy of Marine Copernicus.Shoreline changes were seen by comparing two satellite imagery of which has been corrected, to determine the annual rate of shoreline change in the region.
The results of these variables will produce scores based on the CVI matrix [6; 7] (Table 1).Where they will be given scores of 1 to 5 based on their vulnerability.These scores are then calculated using a quadratic formula which is as follows: Where These CVI values are then further classified into 5 classes, namely not vulnerable, less vulnerable, moderate, vulnerable and very vulnerable.

Result and discussion
The physical character of Pangandaran coast can be identified through geomorphology, elevation, tides, significant wave height, shoreline changes, sea level rise which can be seen in Figure 2.

Geomorphology
The coastal geomorphology of Pangandaran Regency generally consists of sandy beaches with various geomorphological features such as high cliffs, medium cliffs, low cliffs, barrier beaches and estuaries are scattered along the coast.The results show that 64.2% of Pangandaran Regency coastal zones, namely zones of stations PG1-12, PG17, PG19-23, PG25-28, PG34-37, and PG42 are classified as very vulnerable (score 5).This is due to the abundance sandy beaches such as Batu Hiu beach and Pangandaran beach which are relatively vulnerable to submersion and erosion.A total of 7.1%, namely PG16, 18, and 24 are estuary areas classified as vulnerable (score 4).Zones PG39 and 40 which are beaches with low cliffs is classified as moderate (score 3).Zones PG13-15 and PG41 are areas with cliffs being classified as less vulnerable (score 2).Zone PG29-33 is the Pangandaran nature reserve area and the PG38 zone are surrounded by high cliffs resulting in a not vulnerable (score 1) classification (Figure 2).

Tidal range
The overall coastal tidal range is in the moderate category (score 3).The lowest tidal range value of 1.58m was found in PG28 and the highest of 2.21m was found in PG42 (Figure 2).These values have similarities with the findings of Basith [16] who found tidal range results of 2.12 m.

Significant wave height
Significant wave height on the coast indicates very high vulnerability (score 5) with a wave height range of 1.63-1.77m.The lowest value was found in PG29 and the highest was found in PG1.On average, significant wave height in Pangandaran Regency is 1.67 m (Figure 2).Fitrian et al. [17] found that significant wave height at the Batu Karas beach tourist zone (PG16) has an annual average of 1.6 m.

Shoreline change
Shoreline changes such as abrasion and accretion are observed in different areas.One station (PG17) is classified in the very vulnerable category (score 5) with a rate of change as high as -2.63 m/year.This is due to the Bojong Salawe estuary area having lots of alluvial plains in its coast and is densely populated to add.Stations PG14 -16, PG35 dan PG38-39 is vulnerable (score 4) caused by relatively high vulnerability of sandy beaches to coastal physical processes like erosion.Zones of moderate vulnerability (score 3) such as stations PG3-13, PG18-19, PG23, PG26-27, PG31-34, PG36-38 and PG41 are relatively less vulnerable to and erosion due to the existence of cliff areas.Certain areas experience accretion, such as PG1-2, PG20-22, PG24-25, PG28-30, and PG42 which are caused by the accumulation of sedimentation from rivers (Figure 2).

Sea level rise
Sea level rise is classified to be very vulnerable, with the whole Pangandaran Regency showing very high vulnerability towards sea level rise.The lowest rate of rise, 5.97 mm/year is found in PG3, and the highest rate of rise, 6.27 mm/year is found in PG42 (Figure 2).

Coastal vulnerability
Classification based on the range of index values for the "not vulnerable" category is in the range 8.66 -14.83, "less vulnerable" in the range 14.83 -21.01, "moderate" in the range 21.02 -27.18, "vulnerable" in the range 27.19 -33.35, "very vulnerable" at index value 33.35 -39.53.The graph (Figure 3) represents a percentage of total coastal zones in regards to their vulnerability (Figure 3).It shows the coast is dominated by the vulnerable class, amounting to 42.86% with a total of 18 stations and found mostly in Cimerak (PG3-12).The vulnerable category generally has the geomorphology of sandy beach.The very vulnerable category was only found in 1 station, located in the Bojong Salawe estuary, covering 2.38% of coastal land cover.The moderately vulnerable category was found in 10 stations covering 23.81% land cover.The less vulnerable category found in 6 stations contributing to 14.29% of land cover.The not vulnerable category was found at 7 stations with 16.67% of total coastal land cover.The map with vulnerability classes towards sea level rise (Figure 4) shows that the lowest CVI value, 8.66, was found in PG29 and 30 on the west side of the Pananjung Tombolo whereas the highest CVI value, 39.53 is found in PG17 on Bojong Salawe estuary.The vulnerability map shows that vulnerable locations tend to be found at low elevation areas such as sandy beaches.This is similar [18] findings where two variables have a relatively bigger impact on vulnerability, namely coastal slope and geomorphology.The vulnerability map shows that areas of relatively higher vulnerability have low elevation and is densely populated, in contrast to areas with relatively lower vulnerability are areas where cliffs are found, as these are more resilient against sea level rise and erosion [19].Overall, the vulnerability of the Pangandaran Regency coastal region has varying vulnerability, with a tendency to be vulnerable towards sea level rise.It is for this reason; further study is needed to defend against sea level rise.Dhiauddin et al. [14] shows that the steps taken can include the implementation of green belts in coastal area, focused observation of the area, and building sea-side structures that protect the coast.

Conclusion
The rate of sea level rise in the Pangandaran Regency coasts is considered to be very vulnerable, on the range of 5.97 -6.27 mm/yr.Vulnerability of the coast is varied, with the categories of not vulnerable, less vulnerable, moderate, vulnerable and very vulnerable.As much as 16.67% of the coastal area in classified as not vulnerable.The less vulnerable class covers 14.29% of the coast.As much as 23.81% of the coastal area is of moderate vulnerability.The vulnerable class covers 42.86% of the coast.Lastly, 2.83% of the coastal area is classified as very vulnerable.This shows that the Pangandaran Regency coastal region is leaning towards vulnerable against sea level rise.Further study can be done with more variables such as land subsidence and focuses on areas with high vulnerability such as in PG17 station.
: a = geomorphologic vulnerability score b = shoreline change vulnerability score c = elevation vulnerability score d = sea level rise vulnerability score e = tidal range vulnerability score f = significant wave height vulnerability score

Figure 3 .
Figure 3. Percentage of coastal land cover.