Technical Study of the Concept of Permanent Housing Relocation around the Palu Koro Fault after the 28 September 2018 Disaster

The earthquake that struck Central Sulawesi on September 28, 2018, had a significant impact on Palu City, Donggala Regency, and Sigi Regency. The impact included a tsunami along the coast of Palu Bay and liquefaction in several areas, leading to extensive damage to infrastructure. As part of the post-disaster recovery efforts, permanent shelters (HUNTAP) are being constructed for the survivors. The purpose of this research is to perform a technical assessment of residential relocation based on risk factors that could lead to future disasters. The method involves descriptive analysis, including the following stages: (1) Reviewing literature from various journals, regulations, technical provisions, and related databases, and (2) identifying variables and criteria that could lead to disasters in areas designated for permanent residential relocation. The research results reveal several influential variables, as follows: (1) Potential for flooding, including: (a) high rainfall, (b) susceptibility to air infiltration, (c) risk of flash floods, (d) erosion of river basins, (e) sedimentation, (f) availability of adequate drainage system facilities; (2) risk of landslides is significantly influenced by: (a) shear angle, (b) pore water pressure, (c) slope gradient; (3) liquefaction indicators include (a) Groundwater level less than 10 meters, (b) sandy soil thickness less than 12 meters underground, (c) increased surface earthquake activity, (d) soil density; (4) tsunami risk is associated with several influential variables: (a) Shallow epicenter with a depth of less than 33 km (b) angle and type of fault, with thrust or thrust faults being the most dominant, (c) distance from the epicenter and location in the middle of the sea, (d) characteristics such as beach shape, open beach morphology, low surface slope, and seabed depth; (5) high current voltage is indicated by the distance and type of voltage capacity; and (6) airplane trajectories are influenced by runway distance and flight path.

Introduction

According to the announcement by BNPB (2018), an earthquake disaster with a scale of 7.7 on the SR on September 28, 2018, affected the areas of Palu City, Donggala Regency, and Sigi Regency (PASIGALA). The fault line occurred around 150 km from the center of the earthquake in Lende Village, Sirenja District, Donggala Regency, and ended in Boladangko Village, Kulawi District, Sigi Regency. The earthquake caused a tsunami in the coastal area of Palu Bay and liquefaction in several places, including Ballaroa Housing, Petobo Village, and Jono Oge Village, as well as several local liquefaction in Palu City (BNPB, 2021).

The impact of the disaster caused damage to basic infrastructure, such as office buildings, commercial buildings, residential areas, educational facilities, and places of worship. So, after a disaster, it is necessary to restore the condition of the affected areas in the form of reconstruction and rehabilitation. One of the infrastructures that experienced serious damage was residential houses, which need attention during the current reconstruction, rehabilitation, and relocation period. After the disaster, several houses were damaged, namely (1) Palu City 41,852 units, (2) Kab. Sigi 30,236 Units, and (3) Kab. Donggala 21,378 Units, and (4) Kab. Parigi Moutong 5550 Units (Anonymous, 2021).

In general, the construction of Permanent Residential Houses (HUNTAP) is in the form of clusters, namely in the form of sites built in one complex and consisting of several housing units spread over three regions (Palu City, Sigi Regency, and Donggala Regency). The construction of this HUNTAP was built in the previous location (in situ) is considered a disaster-safe zone, and the relocated HUNTAP was divided into several types of areas, namely (1) large scale in Tondo and Talise Districts and Pombewe Village, (2) satellite area in Palu City two locations, two locations for Sigi Regency, and fifteen locations for Donggala Regency, and (3) for independent relocation of 3050 units spread across several places (Anonymous, 2021).

The relocation of residents’ residences in several places is interesting to study from technical aspects related to disaster vulnerability criteria. The Indonesian National Standard (SNI, 2004) establishes several natural disaster risk criteria for residential locations, such as whirlwinds, landslides, floods, and earthquakes. Likewise, the National Disaster Management Agency (BPBN) has established a disaster hazard map in Indonesia. However, the risk of disasters that can occur in residential areas has not been fully studied in the form of a concept of residential areas that are safe against various types of disasters. For example, some natural disasters in the form of earthquakes will cause tsunamis in areas around the coast and can cause liquefaction. Apart from that, other types of disasters can also occur because residential areas are in the path of airplanes, the influence of high voltage currents, or disasters caused by volcanoes.

For this reason, a technical study is needed regarding the concept of post-disaster housing relocation based on disaster aspects. This research will be carried out on the relocation of permanent residences around the Palu Koro fault line after the 28 September 2018 disaster using several disaster criteria or variables. This research is still ongoing, so the indicators for each disaster risk variable cannot yet be demonstrated.

Literature Review

Some basic definitions based on existing regulations and standards in Indonesia are as follows:

• Settlements are part of a residential area consisting of more than one housing unit that has infrastructure, facilities, public utilities, and other supporting functional activities in urban or rural areas (Anonymous, 2021).
• Housing is a collection of houses as part of settlements, both urban and rural, which are equipped with public infrastructure, facilities, and utilities as a result of efforts to provide livable houses (Anonymous, 2021).
• Disaster-prone is a condition or characteristic of geology, biology, hydrology, climatology, geography, society, culture, politics, economy, and technology in an area within a certain period which reduces the ability to prevent, reduce, achieve readiness and reduce the ability to respond adverse impacts of certain hazards (BNPB, 2017).
• Recovery is a series of activities to restore the condition of the community and environment affected by the disaster by re-functioning institutions, infrastructure, and facilities by carrying out rehabilitation efforts (BNPB, 2017).
• Disaster prevention is a series of activities carried out to reduce or eliminate disaster risk, either through reducing the threat of disaster or the vulnerability of parties threatened by disaster (BNPB, 2017).
• Disaster Risk is the potential loss arising from a disaster in an area and a certain period, which can be in the form of death, injury, illness, life at risk, loss of sense of security, displacement, damage or loss of property, and disruption of community activities (BNPB, 2017).
• Permanent housing (huntap) is a place for disaster victims to live after living in permanent, temporary housing. Huntap is intended for disaster victims who no longer have a place to live and is intended for those whose residences are included in disaster-prone areas where they are no longer permitted to live according to government regulations (Government of Indonesia, 2021).

Residential Environmental Standards

Some of the standard housing environment locations used in Indonesia are as follows:

• The housing location must be by the land use plan stipulated in the local Regional Spatial Planning (RTRW) or other planning documents stipulated in local Regional Regulations, with criteria including (1) meeting security criteria, (2) not being a residential area, protected area (catchment area), (3) not agricultural land, (4) not a production forest area, (5) free from factory waste disposal, (6) not located around the airport area, (7) free from high voltage electricity networks high (Anonymous, 2021).
• Detailed Regency/City Spatial Plan, hereinafter referred to as RDTR, is a detailed plan for regency/city spatial planning completed with regency/city zoning regulations (Anonymous, 2021).
• Zoning regulations are provisions governing space utilization requirements and control provisions and are prepared for each allotment/zoning block whose zoning is determined in a detailed spatial plan (Anonymous, 2021).

Standard Housing Location Factors

The residential environment location standards used in Indonesia are based on the Indonesian National Standard SNI 03-1733-2004 concerning procedures for planning residential environments, which can be seen in Table I.

Table I. Housing Location Standard Factors

Data type (Environmental physical condition)	Description	Output
Topography	Physical condition of soil surface	Building shape and area
		Environmental characteristic
		River flow
		Land contour
		Transportation
		Sanitise system
		Termination
		Spatial pattern
Location	Geographical location of the house environmental about other areas and facilities around the house by the land use plan	Distance to facilities, number of facilities, form of facilities, relationship with the around in environmental
Climate	The direction of the sun	Location facilities
	Long sun exposure	Type of connection between building
	Average temperature	Building form
	Humidity	Building orientation
	Average rainfall	Building layout
	Season	Opening for natural lighting during the day
	Wind velocity	Ventilation
Natural disaster	Whirlwind	Ground surface height
	Earthquake	Structure/construction
	Landslide	Building layout
Vegetation	Type of tree and plants	Green set pattern
	Influence environmental	Other for formation
	Planting period	The type of tree to the planted
	The maximum height that can be reached
Building around the environmental	Type and type of building	Facility form
	Population distribution and density	Number of capacity facility
	Access to facilities outside the residential area
	Service capacity of each type of facility	Distance between facility
	Available facilities	Facility the must be provided

Previous Research Housing Relocation

Research that has been conducted regarding post-disaster housing relocation in several countries, including Indonesia, includes (1) survivor participation, (2) management aspects, (3) design and design aspects, (4) construction workforce capacity, (5) accessibility aspects (6) recommendations to pay attention to disaster risk, namely as follows. (Dikmen, 2007) and (Oliver-Smith, 1991) conducted research in Turkey, which showed the low participation of survivors in selecting locations and ignoring their livelihood background; similar things also happened in India (Joshi & Nishimura, 2016) and Sri Lanka (Sangasumana, 2019) shows something similar.

Several studies also show that management aspects are not implemented effectively, such as organizational management (Bilauet al., 2015) and (Mukherji, 2017). In Indonesia, post-disaster housing reconstruction and relocation efforts following the 2004 Aceh tsunami, the 2006 Yogyakarta earthquake, the 2009 West Java earthquake, and the 2009 West Sumatra earthquake have led to research findings recommending the urgent need for capacity building among construction workers and survivors. This can be done through outreach and training on earthquake-resistant building guidelines, rules, and standards (Pribadiet al., 2014).

Meanwhile, the housing relocation planning aspect shows that accessibility planning is the main thing as a basic need, such as planning a good transportation network system between regions (Tanet al., 2022; Chenet al., 2021; Sridarranet al., 2016) physical infrastructure is planned optimally for the needs of survivors and residents living around the relocation location (Di Gregorio & Soares, 2017) recommends planning various types of post-disaster recovery, such as psychosocial, social capital, and livelihoods, as well as settlement governance. Furthermore, research by (Wijegunarathnaet al., 2018) states that planning must pay attention to provisions for changes that can be made by survivors, such as the layout of the house, number of rooms, and lighting systems, as well as air circulation.

Furthermore, research conducted in the Philippines regarding the relocation of settlements after the Typhoon Haiyan disaster shows the need to consider aspects of disaster risk in the relocation determination stage as a future risk reduction stage (Bodineet al., 2022)

Methodology

The stages of research regarding the technical review of the concept of post-disaster housing relocation are as follows:

1. In the initial stage, a literature review was carried out from various journals, technical regulations and provisions, books, and databases related to post-disaster permanent housing. At this stage, the variables and factors used to develop the concept of safe and reliable post-disaster housing relocation are identified.
2. The next stage is to determine indicators for several disaster risk variables and develop a hierarchy based on the results of literature reviews and expert opinions from several expertise groups.
3. Then, the next stage is to create an illustration to show the hierarchical relationship between variables and criteria.

Analysis and Discussion

According to existing regulations in Indonesia, the relocation of settlements is determined based on the physical conditions of the environment, taking into account several factors such as (1) vegetation, (2) topography, (3) surrounding buildings, (4) location, (5) climate, and (6) disaster risk.

A technical review of the post-disaster permanent housing relocation concept involves identifying variables from various sources, including regulations and the Indonesian National Standard (SNI). The natural disaster factors mentioned in these sources include (1) floods, (2) landslides, (3) earthquakes, and (4) tornadoes. In addition, based on the literature review and expert opinions, several additional variables were identified, including (1) tsunami, (2) liquefaction, (3) unstable soil, (4) high voltage current, and (5) aircraft trajectory. This led to the identification of nine recommended variables for planning and determining the relocation of permanent residential areas after a disaster (Fig. 1).

Fig. 1. Recommended concept of post-disaster residential areas.

Based on an analysis of various literary sources and studies of residential areas that are safe from disasters or resistant to disaster threats, the information is summarized in Table II.

Table II. Disaster Risk Variables and Indicators

Earthquake	Flood	Landslide	Liquefaction	Tsunami	High current voltage	Airplane trajectory
Located around the fault channel	High rainfall area	Heavy condition of the soil contents	Positioned in a zone susceptible to earthquakes	Tsunami disaster hazard index map	Direct Current (DC) voltage air duct (250 kV–500 kV). Minimum Distance: 12.5 m	Radius 4 km from the runway, maximum height 45 m
Featured on the earthquake hazard index map	Are within the catchment area	Ground shear angle	Liquefaction disaster hazard index map	Located along the coast	Extra high voltage air ducts (275 kV–500 kV) Minimum Distance 12.5 m	Radius 8 km from the runway, maximum height 90 m
Areas affected by earthquake	The area is susceptible to flooding	Water content/Pore pressure	Located at the shallow groundwater table	Located around the coastline		Radius 12 km from the runway, maximum height 110 m
	The watershed is highly vulnerable to erosion and sedimentation, posing a significant threat to the local ecosystem	Steep surface slope	The soil condition is at low soil consolidation	Located in the lowlands	High Voltage Air Lines (35 kV–230 kV) Minimum Distance: 12.5 m	Radius 15 km from the runway, maximum height 130 m
	Availability of drainage facilities	The elevation of the surface in the area	Area conditions with fine soil particles			Radius 15 km from the runway, maximum height 150 m

Conclusion

The research results indicate the factors and variables that influence the risk of potential disasters in permanent residential relocation. Assessing earthquake risk involves (a) evaluating proximity to fault lines, (b) disaster-prone areas, and (c) previous earthquake-affected areas.

1. Please remain vigilant for signs of potential flooding, such as (a) heavy rainfall, (b) vulnerable catchment areas, (c) flash flood risk, river basin erosion, (d) sedimentation, and (e) the availability of proper drainage systems.
2. The risk of landslides is significantly affected by (a) the shear angle, (b) pore water pressure, and (c) steep slope.
3. Please consider the following crucial liquefaction indicators: (a) Groundwater level less than 10 m deep, (b) Sandy soil thickness of less than 12 m below ground, (c) Increased surface earthquake activity, (d) Soil density.
4. Please be aware of the following signs indicating a significant tsunami: (a) a shallow earthquake epicenter, less than 33 km deep, and a magnitude greater than 6.0 on the Richter scale; (b) the angle and type of fault, with thrust or down faults being the most dominant, (c) distance from the epicenter and location in the middle of the sea are also important considerations, and (d) Characteristics such as beach shape, open beach morphology, low surface slopes, and seabed depth should also be taken into account.
5. High current voltage is indicated by distance and type of voltage capacity.
6. Airplane trajectory is influenced by runway distance and flight path.