This Special Problem entitled "Physical Vulnerability Assessment of the Coastal Environment of Bunaken Island, North Sulawesi" prepared and submitted by Bernaliza B. Espina is a graduate student at the Environment and Natural Resource Management Department under the Faculty of Management and Development Studies (FMDS), University from the Philippines Open University. She completed her bachelor's degree in Chemical Engineering from the University of the Philippines - Diliman.
Consuelo Habito for providing insightful advice and guidance to improve the content and presentation of the methodology and results of this study.
Background of the Study
Assessment of the physical vulnerability of Bunaken Island, North Sulawesi 2. based on the principles of vulnerability and resilience aim to achieve two objectives:. This study is focused on assessing the physical vulnerability of Bunaken Island, which is one of the most popular tourist destinations in Indonesia.
Significance of the Study
The results from this study will provide insight into the physical factors that contribute to the island's vulnerability and the vulnerability profile of the different zones on the island.
Objectives of the Study
Conceptual Framework
Physical Vulnerability Assessment of Bunaken Island, North Sulawesi 6/2007) states that the island's permanent residents rely on marine resources to sustain their livelihoods and sustain their communities. Average PCVI values for each physical parameter and different sites are calculated and tabulated. Most parts of the island still have good vegetation with an average distance from vegetation of 324 m.
The CVI results suggest that dune width and coastal slope are the main factors affecting the island's physical vulnerability. Comparison of PCVI scores of individual parameters and sites provided insights into the vulnerability profile of the island.
Review of Related Literature
Profile of Bunaken Island
- Biophysical and socio-economic setting
- Biodiversity
- Tourism
The western and central parts of the island are slightly elevated at 71 meters above mean sea level (msl) with a flat plateau at about 50 meters above mean sea level (msl) (UNESCO, 2005). For each location, square cells were drawn with each side measuring 500 meters or 0.5 kilometers. The individual scores for all six parameters were then summed to determine a total Physical Coastal Vulnerability Index (PCVI) value for each of the sites.
The results of the PCVI analysis are presented in this study in tables and graphical presentations. The coastal measurements for each of the first six variables were derived for each of the locations based on the methodology described in Chapter 3. The summary of CVI, PCVI values and findings for each of the locations is shown in Tables 7-13 .
However, most sites are physically vulnerable and exposed due to the lack of dune forms. Relatively good PCVI scores of 14 and 11 were obtained for Pangalisang and Alung Banoa G indicating that these parts of the island have low and very low physical vulnerability respectively. The physical vulnerability assessment of Bunaken Island was carried out by integrating survey and spatial analysis using Google Earth map images and findings in the coral composition study presented by Nafil Rabbani Attamimi and Ratna Saraswati (2019).
Application of Coastal Vulnerability Index
Methodology
Development of Vulnerability Matrix
This study adopted the physical parameters and matrix proposed by Kantamaneni et al. 2018) which considers seven (7) different parameters as presented in Table 1, except for rock outcrop, which is replaced by coral cover status to capture the unique feature of the island as a marine park.
Plotting of Representative Coastal Cells
Modified from Assessing Coastal Vulnerability: Development of a Combined Physical and Economic Index by Kantamaneni et al., 2018, Ocean and Coastal Management, 158, p.166.
Survey and determination of individual CVI ratings
- Coastal cell with transect lines for Core Zones
- Coastal cell with transect lines for General Use Zones
- Coastal cell with transect lines for Tourism Zones
Beach width Measured from the back beach to the mean low water (MLW) mark. Slope is calculated by dividing the elevation gain between the front and back transects by the distance between the same points. In the event that there are built structures (paths, roads and residential and commercial buildings), the width of the structures is subtracted from the surface of the vegetation.
Distance between the back beach where structures are to be built (paths, roads and residential and commercial establishments). If vegetation is present, the width of the vegetation is subtracted from the length of the structures. Sea defenses Derived from the percentage of coastline covered by sea defenses, such as rock revetments, solid walls, timber, natural material and bedrock.
Adapted from Assessing Coastal Vulnerability: Developing a Combined Physical and Economic Index by Kantamaneni et al., 2018, Ocean and Coastal Management, 158, p.167. Study site locations with overlay of coastal cells and transect lines used to derive measurements for each of the physical parameters.
Analysis and interpretation of CVI values
As can be observed from Figure 5, most of the coastline has good vegetation cover, but with random structures built close to the transect lines of the island. The comparison of average PCVI scores per management area presented in Table 17 shows that General Use and Tourism areas received scores of 16.68 and 16.33, respectively. CVI scores differ for each of the parameters with beach width having the lowest mean CVI of 1.02 and dune width having the highest mean of 3.58.
Bunaken Village received a CVI rating of 4 for this parameter, suggesting high physical vulnerability, while the rest of the zones were all rated as 2 or moderate vulnerability. The physical vulnerability of the island due to distance from vegetation behind the back beach and coral reef condition still falls under low vulnerability, but may run the risk of sliding to moderate if proper control measures and interventions are not implemented. The use of CVI values was useful in determining the overall vulnerability of the island, as well as determining the relative vulnerability of each of the management zones and eight (8) sites on the island.
However, as it is a protected site with diverse marine life, a low or very low rating would be ideal and would help ensure the island's resilience. Analysis of the PCVI scores in this study proved useful in determining the relative vulnerability of the different management zones and specific localities. This will provide a more holistic view of the vulnerability in each of the sections and can also capture the impact of different economic activities allowed in each of the locations.
Results and Discussion
Analysis of the CVI and PCVI Scores of each of the Sites
The results in Table 5 and Table 6 showed that all sites except Alung Banoa C have a beach width higher than the ideal 150 m. The average width of the beach is 283 m with measurements between the minimum values of 149 m recorded for Alung Banoa C and the maximum value of 496 measured for Raymonds. Most sites showed short dune landforms with all measured widths less than the safe value of 150 m and with an average of only 22 m.
Liang Inti C has an almost non-existent dune because it is bordered by vegetation and structures. Alung Banoa G has a short dune width of 56 m, but is the highest measured compared to other locations. Bunaken Village and Liang Inti have the least gradient at 2.8%, while Alung Banoa G has the steepest gradient at 12.5%.
The least vegetation distance is recorded for Bunaken Village, while Raymonds and Alung Banoa G have vegetation beyond 500 m. The values are fairly spread with minimum value at 0 m at Raymonds and maximum value recorded at 500 m for Liang Inti C. The average sea defense is 52% with lowest value recorded at 6% for Raymonds while the highest value is 85% for Pangalisan .
Summary and Comparison of CVI and PCVI Scores of the Different
As shown in Table 16, the highest PCVI score is recorded for Alung Banoa C, followed by Raymonds with cumulative points of 21 and 20. Liang Inti C, Bunaken Village and Lekuan Liang have equal PCVI scores of 19, which also makes it highly vulnerable makes.
Comparison of CVI Scores of Different Management Zones
However, core areas which are areas designated to protect high biodiversity areas received the highest PCVI score of 20 suggesting high physical vulnerability. These results reinforce the need to ensure effective monitoring and intervention to protect these sites.
Analysis of CVI Scores Based on Different Physical Parameters
The CVI scores for distance from built structures behind the back beach are quite varied with three (3) sites rated 4 or high vulnerability, two (2) sites rated 3 or moderate vulnerability and the other two (2) have ratings of 2 or low vulnerability. The spread of CVI results for built structures is most likely due to the zoning policies where land use and activities are restricted in some areas. There are four (4) zones that are slightly vulnerable, three (3) zones that are moderately vulnerable and one (1) zone - Raymonds that is highly vulnerable.
The average CVI score for coral reef status is 2.31, indicating generally low physical vulnerability associated with this parameter. The individual ratings are quite spread out, with three locations – Alung Banoa C, Liang Inti and Lekuan Liang rated as highly vulnerable, while two (2) areas and three (3) areas have medium and low vulnerability ratings respectively. The next contributing factor is the distance of the built structures behind the back beach, which has an average rating close to moderate.
The island has a generally good beach width which reduces exposure and provides protection to the coastlines.
Overall Vulnerability Profile of the Island Physical Parameters
Long beach width and the presence of natural sea defenses in the form of rocks, diverse corals and seagrass habitats provide a layer of protection and enhance the island's resilience. The assessment suggests that the island has an average rating of moderate vulnerability, which can be considered a reasonable score. Alung Banoa G had the lowest PCVI score and were the least vulnerable places on the island.
In general, the island is vulnerable due to its limited dunes and gentle slope. On the other hand, a long beach and the presence of natural marine defenses such as healthy corals and seagrass habitat along the shallow water protect the island. Strict implementation of effective conservation and development policies and ongoing monitoring will play a key role in protecting vulnerable management areas and maintaining or even improving the island's resilience.
This study can be further improved by improving the geospatial analysis methodology using more advanced satellite mapping analysis tools. This will also help develop a more comprehensive coastal management strategy to protect the island. Moreover, this study can also be replicated and extended to other nearby islands in Bunaken National Park.
Summary and Conclusion
Recommendations
