Identification of the characteristics of the physical vulnerability level of the Kendari Bay coastal landscape to tidal floods using the Quantum Geographic Information System

Kendari City has a coastal stretch that runs into the sea and is feared to be vulnerable to tidal floods. This study aims to identify the tidal flood vulnerability of the coastal landscape of Kendari City, especially in terms of its relationship to the characteristics of the physical aspects of the landscape, distribution mapping, and the extent of tidal flood vulnerability areas in coastal areas. The research method uses spatial descriptive analytics to explain the tidal flood phenomenon in relation to physical aspects of the coastal landscape such as topography, distance from the beach, distance from rivers, and land use aspects. The data collected consists of primary data in the form of observation data on the physical aspects of coastal areas and secondary data in the form of satellite image data and data from related agencies. The analysis technique for describing tidal flood vulnerability uses buffer and overlay analysis, assisted by the QGIS application. The results of the research showed that the level of physical vulnerability to tidal flooding was obtained by three vulnerability classes and their areas: low physical vulnerability at 17,096.82 ha, medium physical vulnerability at 8,169.69 ha, and high physical vulnerability at 1,722.17 ha.


Introduction
The Kendari coast has the potential for tidal flooding, considering the location of the area along the coast and the concentration of population settlements with all their activities.The city of Kendari is the capital of Southeast Sulawesi Province, which is the center of intensive government and economic activities.It is currently undergoing rapid development and has become an attraction for people to come and settle down, thereby triggering a significant increase in population and space utilization [1], [2], [3].The hydrological response to the physical condition of the area and significant land use will trigger the phenomena of erosion, sedimentation, sea level rise, and land subsidence, which can result in areas being inundated and experiencing tidal flooding [4].
So far, there has been no official data on the incidence of tidal floods in Kendari City.However, research by the Research Center for Settlements and Regional Infrastructure in the coastal area of Semarang City shows that there is a sea level rise of 5 mm every year and tidal floods occur, as a response to hydrological aspects of the incessant concentration of population concentration and its activities in IOP Publishing doi:10.1088/1755-1315/1311/1/012067 2 land use, as well as groundwater extraction from layer underneath [5], [6].Tidal floods are a natural phenomenon where the land is intruded by seawater when the sea level rises through rivers, drainage canals, or underground flows [7].The coast of Kendari City, in the form of a coastal landscape at the mouth of Kendari Bay, is vulnerable to tidal flooding in the future, as are other areas along the Kendari coast [8].Several studies show that the location of the area directly adjacent to the sea and has a low elevation makes these areas vulnerable to tidal disasters [9], [10].Other studies show that coastal areas with high potential for land use in several sectors such as fisheries, ports, tourism, and settlements have a vulnerability to causing disasters, one of which is tidal flooding [11], [12].The river network and drainage system can actually accommodate overflowing seawater due to tides, but the shallow river conditions prevent seawater from being accommodated and then inundate the land.Sedimentation processes, waste, and materials, as well as various results of erosion processes originating upstream of the river, will increase the threat of tidal flooding.Likewise, the condition of the drainage embankment, which is poorly maintained and has holes, can accelerate the occurrence of Tidal floods.
The risk of tidal flooding is the result of the interaction between vulnerability and hazard aspects.The risk of tidal floods can be reduced by carrying out various mitigation efforts with an emphasis on the vulnerability aspect, not emphasizing the hazard aspect [13], [14].Aspects of vulnerability can be identified using landscape parameters, which contain data on land subsidence, land use, topography, distance from the coast, and distance from rivers [15].The type of land use can affect the calculation of the level of physical vulnerability to tidal flooding.The determination of land use vulnerability is based on the widest land use inundation in each region [16].The area of land use with different forms of utilization between mangroves, swamps, water catchments, ponds, rice fields, fields, grass, and settlements will have a different effect on the potential for tidal floods to occur.Topography, in the form of land height, is a parameter used to determine the potential for tidal flooding.The height of the land influences finding areas that are threatened with tidal flooding; the lower the height of the land, the higher the potential for tidal flooding.This topography data can be obtained using a digital elevation model (DEM).Meanwhile, the distance from the coast is one of the determining factors in identifying areas that are potentially threatened by tidal flooding.The closer an area is to the coast, the greater the high tide needed to reach land [5].Characteristics of the Physical Vulnerability Level of a landscape to tidal floods can be easily and practically analyzed using the Geographic Information System.Information on the level of physical vulnerability to tidal floods is urgently needed to minimize the impact of victims on areas affected by tidal floods.
The research aims to analyze the physical vulnerability of coastal landscapes and the threat of tidal flooding from several parameters such as topography, land use, distance from the coast, and distance from rivers, as well as produce a map of the distribution of tidal flood-prone areas on coastal landscapes in the Kendari Bay estuary area.

Materials and Methods
The research method used is the case study method, with the object under study being the coastal landscape of Kendari Bay in Kendari City, Southeast Sulawesi Province.The research variables are the physical characteristics of the Kendari Bay coastal landscape, including topographic slope conditions, land use, distance from the beach, and distance from the river.This research will use both primary and secondary data, with the data sources listed in Table 1.
Data analysis techniques use Geographic Information Systems (GIS) in the form of overlay analysis techniques and scoring analysis.1. Overlay analysis is an overlay process that is carried out to combine several maps that contain certain information to produce a tidal flood vulnerability level.The data needed is data on the physical characteristics of the Kendari Bay coastal landscape in the form of land use data, topography (slope), distance from the coast, and distance from the river.2. Scoring analysis is a scoring process that is carried out by giving scores and weights to each parameter that is considered based on its effect on the level of tidal flood vulnerability.The score given to measure the level of vulnerability to tidal floods is 1-5.The greater the score given, the higher the effect (Table 2).From the scores and weights of each parameter that has been collected, then the value of the class interval is determined which aims to distinguish the class of vulnerability level.The formula used is: The study area in this research is Kendari City with a land area of 269.81 km 2 which consists of 11 districts, namely Baruga District has the largest area (49.41 km 2 ) and Kadia District has the smallest area with an area of 6.78 km 2 .Based on Kendari City Regional Regulation No. 5 to 14 of 2005 Kendari City is divided into 65 sub-districts (Table .3).Based on the 2020 population projection results, the population of Kendari City is 345,107 people, consisting of 173,987 men and 171,120 women.

Result and Discussion
The preparation of a tidal flood vulnerability map uses several parameters, namely land use, topography, distance from the coast, and distance from the river.Types of land use have their characteristics for tidal flooding.Therefore, it is necessary to have a variable type of land use.Each type of land use can have a different effect on the calculation of the level of physical vulnerability to tidal flooding.Land use in Kendari City is dominated by mixed gardens, which have an area of 14,281.03ha, and forest which has an area of 6,096.73ha.The settlements in the city of Kendari cover an area of 4,499.77ha.The results of data processing obtained about land use in Kendari City are shown in Table 4. Kendari City has a 69% slope of 0-3%.The slope is a parameter that influences determining areas threatened by tidal flooding.The lower the slope and height of the area, the higher the potential threat of tidal flooding.In searching for topographic data related to slope, we used DEM (Digital Elevation Model) data and then obtained results as shown in Table 5. Distance from the beach is one of the determining factors in knowing areas that are potentially threatened by tidal flooding.The closer an area is to the coast, the greater the high tide needed to reach land.In Kendari City, the distance from the coast is 0-250 meters, covering an area of 1,064.38 ha or around 3.94%.Table 6 shows the distance from the beach in Kendari City, where around 87.37% or an area of 23,618.03ha is at a distance from the beach > 1000 m.Distance from the river can determine the level of vulnerability to tidal floods.Parts of coastal areas near rivers, if high tides occur, will cause seawater to potentially mix with river water and result in backflow in the river body, thereby increasing the potential for tidal floods [5].Kendari City is crossed by several rivers, both rivers that flow throughout the year and those that only flow in the rainy season.These rivers have a range that varies from less than 100 m to > 400 m.Table 7 shows the areas based on distance from the river and the extent of the catchment area in Kendari City, which shows that 19% of the rivers are < 100 meters away with an area of 5,008.22 ha.After obtaining the required data, scoring was carried out with the help of a Geographic Information System (GIS) on the selected variables, namely land use, topography in the form of slopes, distance from the beach, and distance from the river.Scores and weights are obtained from several previous studies with modifications by the author according to the availability of data, then given a score range of 1 to 5 and a weight value of 1 to 10.The weighting is adjusted to the size of the influence of each variable on the occurrence of tidal floods in the study area.
Distance from the beach is given the highest weight, namely 10 because distance from the beach affects the reach of tidal water toward land.Topography in the form of land height and slope also affects the reach of the tide, especially on land with a low elevation and slope class.If there is inundation, it will be a big problem, so it is given a weight of 4. The distance from the river and land use are weighted 3 and 2 because the effect of distance from the river and land use on tidal flooding is not as big as the other variables, but both still have an influence on the occurrence of inundation due to sea tides.After calculating the scoring, an overlay was performed on the selected variables, and a map of the physical vulnerability distribution of tidal floods in Kendari City was obtained (Figure 1). Figure 1 shows the results of the overlay analysis, which is divided into three classifications of vulnerability levels: high level of physical vulnerability, medium level of physical vulnerability, and low level of physical vulnerability.The distribution of vulnerability levels for tidal flood disasters in Kendari City is presented in Table 8.Based on the results of the analysis, the level of physical vulnerability to tidal flooding in Kendari City is as follows: 1.A high level of physical vulnerability, occurs in areas with the following characteristics: land use dominated by Mixed Gardens (Coconut, Cocoa, Cashew, etc.); slopes of 8-15% or the sloping category, distance from the beach ranges from 0-250 meters; and distance from the river ranges from 0-300 meters.This area covers 1,722.17ha (6.38%).2. A moderate level of physical vulnerability occurs in areas with the following characteristics: land use dominated by mixed gardens (coconut, cacao, cashew, etc.), settlements or buildings, and paddy fields, gentle slopes of 8-15%; distance from the beach of around 3000 meters; and distance from the river of > 100 meters.This area covers 8,169.69ha (30.27%).3. A low level of physical vulnerability occurs in areas with the following characteristics: land use dominated by mixed farming (coconut, cacao, cashew, etc.); a slope of 8-15% or a sloping category; a distance from the beach ranging from > 1000 meters; and a distance from the river ranging from > 200 meters.This area covers 17,096.82ha (63.35%).
The results of the analysis show that there are three levels of physical vulnerability to tidal flooding in Kendari City.The tidal flood in Kendari city is due to the location of the area bordering the Kendari Bay coast, with a distance of 0-250 meters and an altitude of < 3 meters above sea level.It is recommended to plant mangroves to mitigate tidal floods in the future.The city of Kendari has mangrove forests, which can withstand the crashing waves but are only concentrated in a few places, and their area continues to decrease.Relevant parties, such as relevant agencies and authorities, need to promote mangrove planting activities in coastal areas accompanied by efforts to maintain them so that the function of mangrove forests is optimal in breaking down and even preventing tidal sea water from easily entering the land.The tidal floods that occur can be detrimental to the surrounding community, especially fishermen who have ponds as well as settlements and buildings in the area.Kendari City's RTRW needs to determine the area for tidal and flood control, which is equipped with a plan to develop coastal embankments along the coast of Kendari Bay, normalize river flows throughout the area, and improve the quality of drainage in Kendari City.In line with this, [7] suggests that local communities affected by tidal flooding can take several control measures in the form of (1) cleaning drainage channels in residential canals and (2) building emergency embankments.
Suggestions for the future of this research need to be followed up by adding several important parameters that determine the level of vulnerability to flooding, including the height of sea level rise and land subsidence, as well as population density, to increase the level of mapping accuracy and increase the level of risk of tidal flood disasters in the Kendari City.

Conclusion
The results of research on the level of physical vulnerability to tidal floods seen from topographic slope, land use, distance from the coast, and distance from the river resulted in three classifications of levels of vulnerability: high level of physical vulnerability, medium level of physical vulnerability, and low level of physical vulnerability.In Kendari City, areas with a low level of physical vulnerability are 17,096.82ha or 63.35%; areas with a medium level of physical vulnerability are 8,169.69ha or 30.27%; and areas with a high level of physical vulnerability are 1,722.17ha or 6.38%.

Figure 1 .
Figure 1.Map of Physical Vulnerability to Tidal Flood in Kendari City (Results of Analysis, 2023)

Table 1 .
Data and Data Sources 3

Table 2 .
[18]e and Weight of Tidal Floods Vulnerability[5],[10],[17],[18] After calculating the value of the interval, determine the class level of vulnerability.Vulnerability level classification is divided into three, namely high physical vulnerability level, moderate physical vulnerability level, and low physical vulnerability level.1311 (2024) 012067

Table 4 .
Land Use in Kendari City

Table 6 .
Distance from beaches in Kendari City

Table 7 .
Distance from the River in Kendari City

Table 8 .
Level of Physical Vulnerability to Tidal Floods in Kendari City