Flood mitigation strategies for settlement area in Kediri District

Corresponding Author: Dinia Putri  Student Department of Environmental Engineering, Faculty of Civil, Planning, and Earth Engineering, Sepuluh Nopember Institute of Technology; Tel. +6281292998473 Email: diniaputri8@gmail.com Abstract. According to the Disaster Risk Index released by BNPB in 2013, Kediri District is one of the administrative areas in East Java with a high flooding disaster index. This flooding was also caused by population and residential increases. Based on BPS data from Kediri Regency, until 2019, there was an increase in the population of 0.5-1%. Until 2019, the population increased by 8%, accompanied by an increase in residential areas by 25%. Act Law Number 24 of 2007 Article 47 states that to reduce disaster risk for people living in disaster-vulnerability areas, so has to identify the vulnerability of flooding area, do an evaluation of the land suitability for residential area, after that have to take some mitigation strategies. Technically, before developing a mitigation strategy, it is necessary to identify areas vulnerable to flooding using the Flood Vulnerability Index method. After that, an evaluation of the land suitability of residential areas vulnerable to flooding is carried out using the Multi Criteria Evaluation method, followed by an analysis of the carrying capacity of the residential environment. The last, for determining the priority of the flood disaster mitigation strategy and the authorized institution using the Simple Multi-Attribute Rating Technique Exploiting Ranks method. The results showed that areas with a high flood vulnerability index were Badas, Kras, and Ringinrejo. The existing residential land is not suitable for settlement and has a low carrying capacity. So there are five criteria obtained along with alternative mitigation strategies suitable for being applied in Kediri District.


INTRODUCTION
According to the IRB (Disaster Risk Index) released by BNPB in 2013, it shows that Kediri Regency is one of the administrative areas in East Java that has a high disaster index, one of which is flooding. DIBI (2016) also stated that flooding is one of the disasters with high intensity, including Kediri Regency. A total of 1 635 294 people live in Kediri Regency. Based on BPS data from Kediri Regency, from 2012 to 2019, there has been an increase in the population of 0.5-1%. From 2007 to 2019 the population increased by 8%, accompanied by an increase in the number of residential areas by 25%. However, from 2007-2019 green areas such as plantations, forests, and agriculture, decreased by 45%, 1%, and 38% from the previous. The population problem is one of the main problems in developing countries, including Indonesia. Uncontrolled population growth will encourage changes in land use, especially for housing and development facilities. That factors can increase the risk of flooding in this area, so we have to take some actions to reduce the risk. Sustainable development that pays attention to land suitability can reduce the risk of flooding (Iswandi, 2016). Other than that, according to Act Law Number 24 of 2007 Article 47, we have to take mitigation actions to reduce disaster risk for people living in disaster-vulnerability areas.
Technically, to determine the distribution of flooding vulnerability areas in Kediri Regency, it is necessary to conduct a vulnerability assessment using the Flood Vulnerability Index (FVI) by considering social, economic, and environmental components (Balica et al., 2012). After that, losses caused by flood disasters can be anticipated by assessing environmental aspects, one of which is by evaluating land suitability, especially in residential areas located in flood-vulnerability areas. Evaluation of land suitability can be done using the Multi Criteria Evaluation (MCE) method (Muta'ali, 2012). This method considers several environmental factors such as rainfall, slope, geological conditions, soil types, flood susceptibility maps, and landslide susceptibility maps.
In addition, the carrying capacity of settlements needs to be calculated to determine the projected future needs of residential land and can be used as a reference for determining strategies in developing residential areas that are in accordance with the conditions of Kediri Regency (Pantow et al., 2018). In addition to the technical and environmental aspects, the aspect that affects the mitigation actions of a region is the institutional aspect. As an official institution, the Regional Apparatus Work Unit (SKPD) must play a role in determining strategies to mitigate flood disasters that are suitable to be applied in Kediri Regency. To determine the right strategy from the institutional aspect, the method that can be used is the Simple Multi Attribute Rating Technique (SMARTER-ROC) (Okfalisa and Gunawan, 2014). Therefore, this study aims to determine areas that are vulnerable to flooding in Kediri Regency, evaluate the suitability of land and the carrying capacity of the residential environment in flood-vulnerability areas in Kediri Regency, and determine suitable mitigation strategies to deal with flood disasters in Kediri Regency.

Location and Time
The research was conducted in Kediri Regency, East Java Province. Astronomically Kediri Regency is located at 7 o 36'12''-8 o 0'32'' S and 111 o 47'05"-112 o 18'20'' E. Based on its geographical position, Kediri Regency is surrounded by five regencies with the northern boundary of Nganjuk Regency and Jombang Regency, the southern boundary of Blitar Regency and Tulungagung Regency, the western boundary of Tulungagung Regency and Nganjuk Regency, while the eastern boundary is Jombang Regency and Malang Regency. The area of Kediri Regency is 1 386.05 km 2 with 26 districts. The topography (the shape of the earth's surface) in the Kediri Regency consists of lowlands and mountains through which the Brantas River flows, which divides from south to north. The air temperature ranges from 23 o C to 31 o C, with an average height of 81 meters above sea level. Rain occurred almost throughout 2019. The highest rainfall occurred in March, with a total of 360 mm, while the rainiest days occurred in January (BPS, 2020). The study began in February 2021 and ended in April 2021.

Collecting Method
The types of data needed in this study are primary and secondary data. Primary data is data obtained directly from the field, while secondary data is obtained through literature and data-providing agencies.

Primary Data
Primary data was obtained from the first questionnaire which was filled out by the people of Kediri Regency. This questionnaire is needed as supporting data for the discussion of technical aspects in determining the FVI index to identify flood-vulnerability areas. The questionnaire uses an attitude rating scale, which means that raw data in the form of numbers will be interpreted in a qualitative sense (Singarimbun et al., 1989). The distribution of the questionnaire is based on the number of samples taken by the proportional random sampling technique. The proportional random sampling technique is a sampling technique where all members have the same opportunity to be sampled according to their proportions according to the number of populations (Sugiyono, 1999). The proportion will be adjusted to the total population or population density in each subdistrict in Kediri Regency. The higher the population or population density, the higher the sample taken in the sub-district. So that the number of samples obtained is representative, the number of samples is determined by the slovin formula (Umar, 2000): (1) Note: n= total sample; N= total population; d= precision/error In accordance with the total population in Kediri Regency of 1 635 400 (BPS, 2020) and a precision of 5%, this requires 400 people, 400 respondents spread over 26 sub-districts with the distribution according to the formula proposed by Sugiyono (2010) as follows: Note: n= total number of samples The second questionnaire is used to determine the priority of flood disaster mitigation strategies from the institutional aspect. Respondents are representatives of the authorities of the Regional Government Work Unit (SKPD) in accordance with the divisions related to the discussion of flood disaster mitigation strategies in Kediri Regency. They are National Disaster Management Authority (BPBD), Environmental Service (DLH), Development Planning Agency at Sub-National Level (BAPPEDA), Residential Office (PERKIM), and Public Works-Human Settlements and Spatial Planning (PUPR).

Secondary Data
Secondary data were obtained from the literature and data provider agencies. Secondary data is needed for data analysis from technical and environmental aspects. The technical aspects are analyzed using the Flood Vulnerability Index (FVI) method, which will produce a flood vulnerability index, while the environmental aspects use the Multi Criteria Evaluation (MCE) method and analysis of the carrying capacity of the residential environment, list of secondary data at Table 1.

Data Analysis Method
The analytical method used in this study is a mathematical approach that is collected from secondary data or primary data. The method used is as follows:

The Weighting of the Flood Vulnerability Questionnaire
The rating scale for the questionnaire used is 1-3, for exposure and susceptibility the weighting conversion is in accordance with Table 2 while for resilience, the weighting conversion is in accordance with Table 3.

Flood Vulnerability Index (FVI)
Flood Vulnerability Index (FVI) is applied to measure flood vulnerability. The FVI method uses three flood vulnerability factors, namely exposure (E), susceptibility (S), and resilience (R). Exposure and susceptibility positively affect flood vulnerability, while resilience negatively affects flood vulnerability. The main components used to assess flood vulnerability are social, economic, and environmental/physical. The three components of the vulnerability index are aligned with the components for displaying indicators (Balica et al., 2012). The FVI formula is as follows: Balica et al., (2012) and Jelmer (2013) stated that the Flood Vulnerability Index (FVI) in each component could be expressed by developing formula (3). The formulas are expressed in equations below:

Multi Criteria Evaluation (MCE)
Land suitability analysis for residential areas is generated from overlaying several thematic maps that become research inputs, including a) slope maps, b) flood vulnerability maps, c) landslide susceptibility maps, d) rainfall maps, e) soil type maps, and f) geological map. Indicators and sub-indicators in the MCE analysis on land suitability analysis for settlements based on USDA (1971) and Muta'ali (2012). The weighting can be seen in Table 4.

Carrying Capacity of Settlements (DDPm)
The carrying capacity of a residential area can be interpreted as the ability of an area to provide residential land to accommodate a certain number of residents to live properly. According to Muta'ali (2015), the carrying capacity of settlements can be calculated using the formula: = / (7) Note: DDPm for the carrying capacity of settlements, LPm for the suitable land area for settlements, JP for the total population, and the coefficient of space requirement/capita (m 2 /capita).
The area of land requirement m 2 /capita refers to the Indonesian National Standard (SNI) Number 03-1733-2004 concerning Procedures for Planning for the Housing Environment, which is 26 m 2 /capita. Furthermore, after obtaining the value of the carrying capacity of the settlement, the optimal population can be calculated as follows: Note: JPo for optimal population, DDPm for the carrying capacity of settlements, and JP for total population.

SMARTER-ROC
SMARTER is one of the decision support techniques in policy analysis. SMARTER is a multi-criteria decision making technique developed by Edwards and Baron in 1994. This technique is a modification of the Simple Multi Attribute Rating Technique (SMART) technique (Okfalisa and Gunawan, 2014). The multicriteria decision-making technique is based on the theory that each alternative from a number of criteria has values and each criterion has a weight that describes how important it will be compared to other criteria. The weighting of Rank-Order Centroid (ROC) on SMARTER is based on the criteria's level of importance or priority using a range from 0 to 1, and respondents give numbers 1-100. SMARTER with ROC weighting is more accurate than Analytical Hierarchy Process (AHP) weighting, based on the sensitivity value to measure the accuracy of a value. The ROC weighting sensitivity value is smaller than the AHP weighting sensitivity value (Kusmiyanti et al., 2017). The formula used is as follows: Note: : The weight of the i-th criteria; Value: values ranging from 0-100 given by expert respondents against certain criteria; Total Value: total value obtained from all respondents; : average criteria weight; i: number of respondents; k: number of criteria; = average alternative value; * : ROC/priority value; : the i-th alternative value of the k-th criterion.

RESULTS AND DISCUSSION
In the Figure 1, the higher the weighting value of the exposure and susceptibility components, the higher the level of flood vulnerability. On the contrary, the higher the weighting of the resilience component, the lower the level of flood vulnerability. The results showed that the social aspect of flood vulnerability in Kediri Regency was the highest among the other two aspects. According to Munyai et al. (2019) and Balica et al. (2012), several social aspects that can impact flood vulnerability are population density (KP), population age (UP), education level ( Nine sub-districts have a high-status social FVI index, one sub-district has a high-status environmental/physical FVI index, and no sub-district has a high economic FVI index. After being average, the highest FVI index in Kediri Regency is in three sub-districts, namely Kras, Ringinrejo, and Badas Districts. The most influential indicators of social FVI are high population density, productive age of the population, and level of technological adaptation. The increase in population increases the opening of residential land, so vegetation areas are reduced, and flooding occurs, especially in areas with poor drainage. The higher the dependency ratio, the higher the level of vulnerability to disasters because the higher the burden that must be borne by the productive age population to finance the lives of people who are not or are not productive. The results of land suitability can found in the Figure 2 analysis by overlaying flood susceptibility maps, landslide susceptibility maps, annual rainfall maps, geological maps, slope maps, and soil type maps show that the total land in Kediri Regency which is very suitable for settlement is 8 344.69 hectare (ha) (19.68), according to 18 694.15 ha (44.08%), according to marginal 10 995.14 ha (25.93%), and not suitable with an area of 4 374.02 ha (10.31%). According to the research conducted, the most influential thing on land suitability is landslide susceptibility with a weight contribution of 27.2%. Areas that have high flood vulnerability, namely the Districts of Badas, Kras, and Ringinrejo, have standing settlements on land with marginal and inappropriate status and low carrying capacity. So these areas should not be suitable for residential development.
What needs to be done is relocation or evaluation for environmental improvement to increase the carrying capacity of the environment. Thus, to overcome the risks that arise, it is necessary to determine criteria and alternative flood mitigation strategies that are appropriate to be applied in Kediri Regency, especially social aspects. The criteria and alternatives are improving infrastructure resilience-improving health service performance in existing disaster scenarios and we can identify, understand, and use current and future risk scenarios by conducting disaster threat studies. For the economic aspect, it is necessary to strengthen financial capacity for disaster resilience-making financial plans and budgets for resilience, including funds for contingency plans, while for the environmental aspect the criteria and mitigation alternatives are the development and design of a disaster-resilient city by making a zoning plan for the use of space and preserving the area. Buffers and ecosystem services by identifying transboundary environmental problems. The implementer of the mitigation strategy activities is the BPBD (Regional Disaster Management Agency) of Kediri Regency assisted by SKPD (Regional Work Units) according to the type of activity. The flood disaster mitigation strategy and the concept of residential development should be prioritized for the Badas, Kras, and Ringinrejo sub-districts.

CONCLUSION
Based on the results of the research, the areas with a high flood susceptibility index are in the Districts of Badas, Kras, and Ringinrejo. The results of the evaluation of residential land in the three areas also stand on land that is not suitable for settlement and has low carrying capacity. So that five criteria are obtained along with alternative mitigation strategies that are suitable to be applied in Kediri Regency, especially in residential areas that are prone to flooding according to social, economic, and environmental aspects.