Analysis of determining the location of potential flood evacuation shelter in Butuh District, Purworejo Regency

Map of flood events in Purworejo Regency, on January 16 2019 there were 7 flood-affected subdistricts, namely Butuh District, Bayan District, Banyuurip District, Pituruh District, Purwodadi District, Grabag District, and Ngombol District. Butuh District is the area most affected by flooding in Purworejo Regency. There are 9 villages out of 41 villages in Butuh District that are not affected. The flooding in Butuh District was caused by the overflow of several rivers, such as tributaries of the Wawar River, Gebang Besar River, and Kedunggupit River. This study aims to determine the distribution of flood vulnerability and potential shelter flood disaster evacuation in Butuh District, Purworejo Regency. The water level is estimated to reach 1 meter and makes all access closed. According to the Commander of Kodim 0708 Purworejo, there were still some residents who did not want to be taken to a safe location and with a good approach, the residents were eventually evacuated. Losses caused by floods in Butuh District were only damage to household appliances and there were no casualties. Another problem caused by the flooding in Butuh District is itching of the skin. There must be efforts to prevent floods in the Butuh District so that they do not happen again and cause the same losses. Flood disaster mitigation is an action that must be taken. Interpolation IDW (Inverse Distance Weight) and scoring to get flood hazard results and digitization to get evacuation routes. The research results show that the area is prone to flooding. Interviews showed that the southern region experienced the worst flooding because the further south you go, the lower the slope and several villages in the southern region are affected by the discharge of water into rivers from other areas. Meanwhile, secondary data shows that the northeast to south and northwest regions of Butuh District experienced the worst flooding due to high rainfall and a soil profile that was saturated with water so that several areas that had flat and sloping slopes were affected by flooding. Interviews and potential secondary evacuation shelters obtained 18 evacuation shelters and 37 evacuation shelters.


Introduction
Floods are river flow discharges that are much larger than usual due to continuous rain upstream or in a certain place, causing the existing river flow to be unable to accommodate it, so the water overflows and inundates the surrounding area [1].This disaster is a natural disaster that has the greatest frequency and also causes great losses, even the frequency of floods from year to year is increasing (Nugroho, 2008).The increasing frequency of flood events from year to year has several factors, such as natural and non natural factors.These natural factors are caused by high rainfall, low topographical conditions, down to basins, low soil infiltration capacity which causes the soil to no longer be able to absorb water, and surface water runoff (runoff) which overflows and the volume exceeds the irrigation capacity of the drainage system or river flow system [2].Non natural factors are caused by human behavior in the form of changes in land use and the use of river banks for settlements and industry (Nugroho, 2008).These natural and non natural factors are interrelated where humans have increasing needs from year to year and from year to year humans also need land to fulfill these needs, as well as human behavior that has bad habits such as throwing garbage into rivers.Increasing needs and meeting needs causes the existing land to decrease.This reduction in land causes the water catchment area to decrease as well.Lack of water catchment areas coupled with natural conditions makes it possible for floods to occur in an area, both rural and urban, and even a country also has the opportunity to experience this disaster.Natural process phenomena on lowland areas is flood as an effect of the overtooping stream water over natural levees and inundate the area of surrounding the river.Most of lowland (such as Butuh sub-district) surround the rivers is used by man for settlements, agriculture land, high way, and other activities to support their life intensively [3].The impact of urban heat island (UHI) is also the cause of flood disasters.Nowadays, urban heat island (UHI) occurs in big cities worldwide, this is because urban heat island (UHI) of the impact of global climate change.The urban heat island (UHI) phenomenon is indicated by the difference in temperature between the urban and rural area [4].An increase in the urban heat island (UHI) causes an increase in aerosol concentrations and this condition triggers an increase in extreme rainfall which has an impact on flood intensity [5].
According to the National Disaster Management Agency [6], in 2019 there were 784 flood disasters in Indonesia and occupied the number two position out of eight rankings consisting of tornado, forest and land fires (karhutla), landslides, droughts, earthquakes, tidal waves and abrasion, and volcanic eruptions which can be seen in figure 1. Law Number 24 of 2007 concerning disaster management has explained that natural disasters can result in human casualties, environmental damage, loss of property and impacts psychological [7].Data from the National Disaster Management Agency for 2019 stated that 589 people died and were missing, 3,422 people were injured, 6,100,000 people were displaced and affected, 73,726 houses were damaged, 2,024 facilities were damaged, and 725 offices and bridges were damaged due to natural disasters [6].Settlement is the most important area in the activity of disaster mitigation.The biggest detriment caused by disaster is generally placed at the settlement or residential area.Thereby, the identification of settlement characteristics is required to be able to recognize the disaster risk [8].The flood event map in Purworejo Regency explains that there are 7 subdistricts affected by flooding, namely Butuh District, Bayan District, Banyuurip District, Pituruh District, Purwodadi District, Grabag District, and Ngombol District which can be seen in Figure 2. Quoted from PurworejoNews [9].Butuh District is the area worst affected by flooding in Purworejo Regency.There are 9 villages out of 41 villages in Butuh District that are not affected.The flooding in Butuh District was caused by the overflow of several rivers, such as tributaries of the Wawar River, Gebang Besar River, and Kedunggupit River.The water level is estimated to reach 1 meter and makes all access closed.According to the Commander of Kodim 0708 Purworejo, there were still some residents who did not want to be taken to a safe location and with a good approach, the residents were eventually evacuated.Losses caused by floods in Butuh District were only damage to household appliances and there were no casualties.Another problem caused by the flooding in Butuh District is itching of the skin.There must be efforts to prevent floods in Butuh District so that they do not happen again and cause the same losses.Flood disaster mitigation is an action that must be taken.Research on flooding has been carried out by Kurnia Darmawan, Hani'ah, Andri Suprayogi [10] with the results of research in the form of flood-prone areas and the extent of coverage of the level of flood vulnerability, Mayahati [11] with research results in the form of area; distribution, and dominant factors causing flood disasters, and Abror [12] with research results in the form of potential shelter evacuation; traveling time accessbility modeling by method cost distance and flood evacuation routes.Therefore, this research will obtain flood hazard maps and determine potential maps shelter flood evacuation based on flood vulnerability map.The purpose of this study is to analyze the distribution of flood vulnerability and analyze the potential shelter flood disaster evacuation in Butuh District, Purworejo Regency.

Methods
Butuh District is one of the sub-districts in Purworejo Regency, Central Java Province and this subdistrict has 41 villages with an area of 46.08 km 2 .Butuh District has the following territorial boundaries, to the north it borders Pituruh District and Kemiri District, to the west it borders Kebumen Regency, to the east it borders Kutoarjo District, and to the south it borders Grabag District which can be seen in Figure 3.  Conduct field survei and censuses to see directly and observe the condition of public facilities and goverment offices and then conduct interviews with residents and village officals.

Interpolation of IDW (Inverse Distance Weight)
Interpolation of IDW (Inverse Distance Weight) is a process used to find out the area or areas affected by flooding from the results of interviews processed using the Microsoft Excel application and ArcGIS.Result of IDW interpolation can tell the extent and level of flood vulnerability interview data.

Scoring
Scoring is giving a value to each parameter that will be used to get the total value.The parameters used to get the total value are as follows: 2.2.1.Slope.The slope of the slope is the appearance of the earth's surface that has different heights.The difference in the height of the slope determines whether an area experiences flooding or not.Classification and slope scores can be seen in Table 3. 2.2.3.Land.Soil is a rock that becomes small particles caused by several factors.Land classification uses the highest and lowest two categories.The order from highest to lowest in the category of land classification, namely order, suborder, great group, subgroup, family and serie and in this study used the soil order.Land classification and scores can be seen in table 5.

Overlay
Overlay processed using the application ArcGIS where combine some attribute from several maps to produce a combined map (Guntara, I, 2013) [15].Before doing overlay, the map to be processed must have a score according to the classification parameters used.Results overlay this is used to get the area and level of flood vulnerability.

Flood Vulnerability Classification
The flood hazard classification class is obtained from the total number of parameters used and has a score.The total number of parameters is obtained from the results of overlay in ArcGIS and used to get the highest score and the lowest score total and divided by the desired number of classes [16].The classification of flood hazard uses the following formula: Potential determination shelter evacuation has several criteria for main points shelter evacuation, such as travel time, capacity, number or availability of toilets (cactus washing baths) and kitchens.In addition, the determination of potential shelter evacuation also has several provisions, namely, the location of the evacuation site must be in a flood-free area, the number of toilet washing facilities must be sufficient for the number of evacuates, the higher the height of the evacuation building, the better it is used as an evacuation site, the building is sufficient to accommodate the number of evacuees and accessibility.From the gathering point to the evacuation building point must have good, efficient and short distance access (Harsini, 2014) [17].According to Amalia, et al, [10] there are several criteria shelter, as follows: 1. Room (2 -3 m 2 ) per person 2. Warehouse (1 x 3 m 2 ) 3. Bathroom or WC (1 bathroom or WC for 20 people) 4. Tub or reservoir (each shelter has a water supply with a capacity of 1 m 3 ) 5. Electricity and generators (Generators are available in public kitchens with a minimum output of 3,000 KvA).

Flood Vulnerability Analysis
The method used to analyze flood vulnerability is a quantitative and qualitative method.This quantitative method provides scores and total calculation results for each parameter used.The parameters used are soil, rainfall, and slope.This qualitative method uses interview data from residents or village officials which is processed using Microsoft Excel andinterpolasi IDW (Inverse Distance Weight).Scoring results and interpolasi IDW (Inverse Distance Weight) then do the classification of flood vulnerability.The purpose of this method is to obtain the level, extent and distribution of flood vulnerability.

Potential Location Analysis Shelter Evacuate
This analysis is to find out the distance and travel time from the gathering point to the point shelter the intended evacuation by means of digitization.The travel time is obtained from the formula, as follows: Traveling Time = Distance Speed (2) This method uses a qualitative method in the form of data on public facilities and government offices and a quantitative method in the form of travel time.This analysis uses several criteria for the main points of evacuation shelters, such as travel time, capacity, number or availability of toilets and kitchens.Some of these criteria are scored by all criteria and to find out the candidates shelter evacuation is feasible or not feasible to be shelter evacuation.

Results and Discussion
The determination of flood vulnerability in this study is assisted by using a field work box map to collect respondents, the number of respondents, and makes it easier for respondents to explain areas that are affected or not affected.The determination of work boxes is made along the river and must contain administrative boundaries, rivers, roads, and images in the subdistrict.It is necessary to clarify respondents in providing information which can be seen in Figure 5.This study took a maximum of five respondents per box and randomized them with the same distance.not close to get information about the height of the flood and which areas are affected and which are not affected.Respondents who were interviewed in each box were residents or village officials.Flood data obtained from interviews with residents or village officials in this study regarding the 2019 flood incident.The number of respondents taken was 79 respondents representing each working box which can be seen in table 4 and figure 5.This interview aims to provide accurate information about flooding because residents or village officials witnessed and experienced flooding directly.Resident respondents who were interviewed in this study were natives and migrants who lived in Butuh District before 2019.Information provided given by respondent numbers 71, 72, 74, 75, 76, and 77 explained that the flood did not reach the settlements and only the rice fields.Information about flood height in this study uses height from ankle to head.The average height of adult Indonesians is 166.26 cm for men and 154.36 cm for women [18].Estimated flood height based on height makes it easier to determine flood heights in the field without using tools (meters).The average height of the flood in the Butuh District between the ankles and calves of adult men and between the calves and knees of adult women is around 26 cm.The lowest flood height reached the ankles of adult men and women, about 10 cm and the highest reached the ears of adult men, about 150 cm.The duration of the receding of floods in the Butuh District is about 2 days at the fastest and 10 days at the most.
The evacuation route in this study is used to determine the travel time from the gathering point to the candidates shelter so get the travel time score.The determination of the evacuation route is done by digitizing to make it easier to make evacuation routes.Candidate shelter the aim of this research is shelter which has a capacity that can meet all residents affected by flooding.There are many interview and secondary evacuation routes in this studyshort routes compared to long routes which can be seen in Figures 6 to 10   10,12,13,14,16,17,18,19,20,22,23, 24, and 28 According to Abror [12], the closer the evacuation distance is, the more potential the shelter has to be used as an evacuation shelter and also considers the capacity according to the number of evacuation blocks.Potential evacuation shelters interviewed obtained 18 evacuation shelters consisting of 7 village offices, 7 elementary schools (SD), 1 junior high school (SMP), 1 teacher training high school (SMK), and 1 church, and 1 mosque.Meanwhile, the potential for secondary evacuation shelters is 37 evacuation shelters consisting of 1 district office, 10 village offices, 15 elementary schools (SD), 3 junior high schools, 6 mosques and 2 churches.All prospective shelters and potential shelters are located in areas that are safe from flooding which can be seen in figure 11.The typology of resident living in disaster prone areas is important as inputs for policy-makers, especially regarding the relocation of people from disaster-prone areas to be effective [20].

Conclusions
The results of the flood vulnerability interview data in the Butuh District provide information that the further south the slope is, the lower the slopeseveral villages in the south are affected by the discharge of water into rivers originating from other areas.Meanwhile, the results of secondary flood vulnerability data in Butuh District provide information that rainfall is high and has a water saturated soil profile so that several areas that have flat slopes and gentle slopes are affected by flooding.A saturated soil profile results in the soil being unable to accommodate water into the soil pores and is supported by high rainfall.The interview data's flood hazard affected 14 villages and the secondary data's flood hazard affected 26 villages.The area affected by the flooding from the interview data was 935.44 ha and 3,782.98ha were not affected, while the area affected by secondary data was 3,650.74ha and 4,833.21ha were not affected.
Potential evacuation shelters Interview obtained 18 evacuation shelters consisting of 7 village offices, 7 elementary schools (SD), 1 junior high school (SMP), 1 teacher training high school (SMK), and 1 church, and 1 mosque.Meanwhile, the potential for secondary evacuation shelters is 37 evacuation shelters consisting of 1 district office, 10 village offices, 15 elementary schools (SD), 3 junior high schools, 6 mosques and 2 churches.

Figure 3 .4
Figure 3. Map of research locations

8 Figure 5 .
Figure 5. (a) Map of the field work box (b) Map of the distribution of flood respondents .

Table 1 .
Tools used in research

Table 2 .
Data used in research Data DEMto obtain data and map slope slopes http://tides.big.go.id/

Table 3 .
Classification of slope slope Rainfall is the main factor causing flooding.High rainfall resulted in the river being unable to hold water and creating puddles.Classification and rainfall scores can be seen in table4.

Table 5 .
Soil type classification Determination of evacuation routes is done by means of digitization.Evacuation route digitization is carried out from the gathering point of each settlement per village to the nearest or intended shelter to get the distance and travel time results.

Table 6 .
Criteria for the main points of evacuation shelters