Mapping of Tsunami Evacuation Routes and Shelters in Batukaras Village, Pangandaran Regency, Indonesia

Batukaras is a village located on the Southern Coast of Java Island. The village is part of Pangandaran Regency, one of the top tourist destinations in West Java. Every year, the village attracts national and international tourists alike to Batukaras beach, famous as a surfing destination. However, the village has seen records of tsunami as recently as 2006, where a tsunami from a 7.7 magnitude earthquake struck the village and caused the death of hundreds and economic losses valued at millions of rupiahs. A series of activities aimed to increase disaster preparedness in the village has been done ever since. Recently, a team from ITB Research and Community Service Institute (LPPM) has made an effort to identify IOC-UNESCO Tsunami Ready indicators in Batukaras Village. Part of the effort is to identify tsunami evacuation routes in the village. Field observation was done to locate evacuation shelters and signages around the village, and the data is presented in the form of a tsunami evacuation map. Our study resulted in a successful mapping of evacuation routes and shelters in Batukaras Village. Furthermore, the data can be used towards the fulfillment of the IOC-UNESCO Tsunami Ready indicators in Batukaras Village.


Introduction
Batukaras Village is an administrative unit located in Cijulang District, Pangandaran Regency, West Java Indonesia.According to data from Statistics Indonesia, Pangandaran Regency is the most visited tourist destination in West Java.In 2021, the regency attracted 3,604,128 national and international tourists [1].The village is located in an enclosed bay facing the Indian ocean.Tourism is one of the main pillars of the local economy, alongside fishery and agriculture.Due to its unique geographical location, Batukaras beach is popular among surfers compared to other beaches in Pangandaran Regency.Coastal ecotourism such as mangrove tourism is part of the wider efforts conducted by the government of Pangandaran Regency to empower the local economy [2].The agriculture and fishery being prominent industries in Batukaras' economy contributing of up to 26,73% in Gross Domestic Product of Pangandaran [3].
On July 17 th , 2006, a tsunami earthquake of 7.7 magnitude occurred on the south of Java, resulting in a large tsunami striking the southern coast of Java.More than 600 deaths were observed and more than 75,000 people were displaced in the days following the event [4].Batukaras Village was one of the villages affected in the disaster.Relatively few people felt the shake of the earthquake in the coastal areas.At the time there were no tsunami warning systems or evacuation signages in place, when the tsunami occurred there was a lack of public awareness [5].In the end, this event becomes an important reminder of the need for disaster mitigation and preparedness in Batukaras Village community.Since the event, the local government in Pangandaran has enacted the Community-based Settlement Rehabilitation Project (CSRRP), aimed not only for community recovery but also resilience [6].
Tsunami evacuation shelters have emerged as one of the mitigation efforts in the event of a tsunami disaster in several cities of Indonesia [7].Such shelters must consider several factors such as the topography, tsunami evacuation route, and maximum inundation height [8].Recent efforts carried out by local authorities has resulted in the installation of evacuation route signs leading to evacuation shelters placed strategically around the village [9].There are five temporary evacuation shelters and one permanent shelter located in the vicinity of Batukaras beach.The temporary shelters serve as the earliest point of evacuation in the event of a tsunami, increasing survival rate during disaster [10].After the initial inundation of tsunami, subsequent recovery efforts are directed towards the final evacuation shelter.These shelters are located in elevated topography around the beach.
However, there has been no significant previous effort to identify the locations of existing evacuation route signs and evacuation shelters in Batukaras Village.Therefore, as part of an effort to identify IOC-UNESCO Tsunami Ready indicators in Batukaras Village done by ITB Research and Community Service Institute (LPPM) team, mapping of tsunami evacuation routes and public shelters was conducted in July 2022.In this study, identification of routes, signage, and shelters was obtained from field observation and presented in a tsunami evacuation map for Batukaras Village.The work presented provides a new approach in the planning of evacuation routes by using network analysis method, providing a more efficient approach in support of tsunami mitigation efforts compared to one without spatial analysis.

Methodology
In order to conduct mapping of tsunami evacuation routes and shelters in Batukaras, first data collection in the field must be done.A three-day visit to the village was materialized in July 2022 to gather data of existing evacuation shelters in Batukaras Village.The location and condition of each evacuation shelter was recorded using smartphone geotagging applications.Tracking of evacuation signage located in Batukaras village was also conducted during the visit.
A tsunami evacuation simulation by foot was done in order to determine the travel time from designated evacuation starting points to the shelters.The starting points were determined according to one of two criteria: points farthest from the final evacuation point that is within the inundation zone, and/or points that are of high tourist activity in the village.The visit was part of an ongoing effort by ITB Research and Community Service Institute (LPPM) to support Batukaras' attempt to become IOC-UNESCO recognized Tsunami Ready Community.
After the field data acquisition has been conducted, for each evacuation starting point the optimum destination shelter can be determined based on the shortest travel time by means of spatial analysis.An Origin-Destination (OD) matrix is first developed to determine the possible routes from the evacuation starting points to the evacuation shelter.OD matrix is commonly used in the study of transport process [11], in this case the movement of humans in the event of tsunami evacuation.The OD matrix provides all the possibilities of the number of trips between two spatial points [12].The Dijkstra algorithm is used in determining the optimal evacuation route to the evacuation shelter.The algorithm determines the shortest part between two end points based on the number of arcs and its weights [13].Based on the determination of shortest paths from these algorithms, a map showing the evacuation routes is produced and aimed to be implemented as part of disaster mitigation efforts in Batukaras village.

Evacuation Shelters and Signage
After the field visit, five Temporary Evacuation Shelters (TES) and one Final Evacuation Shelter (FES) have been identified in Batukaras village.These temporary shelters are designed as first destination for evacuees as they flee the coastline.After the initial inundation has receded, evacuees are directed to the FES located in Tanjakan Heras.Here, a more permanent evacuation center may be installed that includes lodging, public kitchen, and medical facilities.Figure 1 shows the map of TES and FES around Batukaras Village, with Table 1 details of which can be found in Table 1.All evacuation shelters were found to be in good condition and able to serve as a temporary destination.Furthermore, mapping of evacuation signages was also conducted, shown in Figure 1 as orange signage icons.16 out of 19 evacuation signs were found to be in good condition, the rest was found to be missing.

Evacuation Routes
During the field visit to Batukaras Village, determination of evacuation routes was made based on existing evacuation signages pointing to TES and FES in the village.Five spots around Batukaras Village are identified as evacuation starting points based on one of two criteria: farthest distance from FES or locations of high tourist activity in the village.A list of starting points is shown in Table 2.
Route of evacuation can be found in Figure 1 shown in orange lines on the map overlaid on local road networks.Additionally, evacuation simulation by foot was conducted along the evacuation routes, duration of each route traversed in the simulation can be found in Table 3.Here, only one shelter was shown as the optimum destination for each starting point based on the shortest duration of evacuation simulation and the rough capacity of each tsunami evacuation point.

Network Analysis
Network analysis was carried out using several stages, including digitizing aerial photographs of Batukaras Village, making OD matrixes for each evacuation starting point, analyzing the shortest distance from each evacuation starting point to the nearest temporary evacuation shelter (TES), and implementing the closest route to the nearest TES from each building on the mapped area.The digitization process was carried out using Quantum GIS 3.26 software.Digitization is carried out on several objects, including buildings, roads, evacuation starting points, evacuation signs, and temporary evacuation site points.Aerial photography is sourced from a local survey conducted in the same year.Digitization results can be seen in Figure 2. The Origin-Destination Matrix aims to determine which routes can be taken to get to all evacuation places from all evacuation starting points.The OD Matrix created will be selected based on the closest distance to the evacuation site using a SQL query.From all of the routes determined, the nearest OD matrix will be determined.The OD matrix can be seen in Figure 3a and the nearest OD matrix can be seen in Figure 3b.The results show that for most of the evacuation starting points, the matrix points to the Gunung Tumpeng evacuation shelter as the optimum destination for evacuation, albeit for evacuation starting point E where the Kabuyutan site is selected as the optimum evacuation shelter.
The application of Djikstra algorithm is used to obtain the shortest route that can be taken to get to the evacuation site.The Dijkstra algorithm estimates the shortest route by considering the distance between vertices as weights [14].The shortest route taken from the initial point of evacuation to the evacuation site can be seen in Figure 4a.
In this study, an additional approach is conducted by considering buildings as evacuation starting points in addition to the previously predetermined start points.The same framework is then implemented on each building in the mapped area to obtain the OD matrix closest to the evacuation site and the shortest route to the nearest evacuation site.The OD matrix closest to the evacuation site can be seen in Figure 4b.The shortest evacuation route to the nearest evacuation site can be seen in Figure 5.
The building-based approach to optimum shelter determination shows similar results to the evacuation starting point-based approach presented earlier.Here one can observe that Gunung Tumpeng TES is selected as the optimum destination based on the OD matrix for much of the area in Batukaras village, in particular areas north and central to the village.In the southern part of the village, the Gunung Tumpeng TES is selected as the optimum evacuation site for most of the buildings.One could observe that this scenario would cause overcapacity if implemented in the TES.The algorithm does not take into account the capacity of the shelter, hence the load.However, the routes shown in Figure 5 show a clearer plan compared to Figure 4a.

Conclusion
Based on the data from field observation done during a visit to Batukaras Village, mapping of tsunami evacuation routes and shelters was successfully conducted.Five temporary evacuation shelters and one final evacuation shelter have been located in the village, as well as routes leading to the shelters from five evacuation start points around the village as well as from buildings.However, this study still has several limitations, primarily in the parameters used as the consideration for the network analysis.The capacity of each evacuation shelter has not yet been taken into consideration.Distance from the shore as well as elevation of the topography should also be included in the analysis for future studies.Regardless, it is believed that the resulting evacuation map would be sufficient used for preliminary disaster preparedness efforts in Batukaras, including fulfillment of the IOC-UNESCO Tsunami Ready indicators in Batukaras Village.

6 Figure 3a .
Figure 3a.OD matrix result from start points in Batukaras Village Figure 3b.Shortest OD matrix from start to nearest evacuation shelter

Figure 5 .
Figure 5. Shortest route from buildings to the nearest evacuation shelter

Table 1 .
List of Evacuation Shelters

Table 2 .
Route and duration of evacuation Figure 1.Evacuation Route Map in Batukaras

Table 3 .
List of evacuation start points