RISK-LEVEL ASSESSMENT SYSTEM ON BENGAWAN SOLO’S FLOOD PRONE AREAS USING AHP AND WEB GIS Haris Rahadianto, Arna Fariza, Jauari Akhmad Nur Hasim Electronics Engineering Polytechnic Institute of Surabaya, [email protected], [email protected], [email protected]

ABSTRACT INTRODUCTION Indonesia has the geographical conditions which are particularly vulnerable to disasters, especially floods and climate change. Throughout Indonesia, it is recorded that there are 5,590 main rivers and 600 rivers Indonesia has the geographical conditions that are particularly vulnerable to disasters, especially floods and have the potential to cause flooding among others. One of it is Bengawan Solo River, which is the longest climate change. One of classical problems that always happen in Indonesia is the overflow of the river in the river in . The floods that hit the area have resulted in disruption of public health, disrupted economic rainy season, the river floods are common in tropical Indonesia, especially in areas with a gentle slope. activity, and damaged urban infrastructure. The phenomenon of floods and their negative impacts in the area of the Bengawan Solo river banks, indicating a condition of the area and the public about the lack of Bengawan Solo River is the largest river in Java which is always flooding every year, although the areas along understanding of the characteristics of the hazards, behaviours that lead to degradation of natural the Bengawan Solo River are not densely populated and also have good water absorption rate. If every year resources, and lack of early warning that causes unpreparedness and inability in the face of danger. the floods still occur without a reduction, it will have so many losses due to damaged infrastructure and The purpose of this project is to be able to create an information system that can provide an assessment disrupted economic activities. While the visible reality is the floods has been occuring continously and always of the risk management in the Bengawan Solo's flood prone areas that passed in the province of East claimed fatalities, property, material damage, and business interruption. Java, by building a web-based information system that includes information on threats, vulnerabilities, The phenomenon of floods and their negative impacts in the area of the Bengawan Solo River banks signaling and capacities, summarized in the disaster risks analysis that integrated with Geographic Information a lack of vigilance and readiness in the face of danger. Moreover, indicates a condition of the area and the System to provide mapping areas that have high levels of risk in accordance. Based on the factors that public about the lack of characteristics understanding of the hazards, attitudes or behavior that resulted in a are already said above and calculated by Analytical Hierarchy Process, the result of this project is a map decrease of natural resources the qualities (vulnerability), and lack of information or early warning which with marked regions divided into three levels of risk like High, Medium, and Low. It also by providing the causes unpreparedness, and helplessness or inability in the face of danger. risk-level for the regions help the system to assess how much impact and damage that will be hit the risky area and give the recommendation to government and people how to increase the preparedness so it Disaster risk assessment is an approach to demonstrate the potential negative impacts that may arise from a can reduce the damage from flood. potential disaster struck. Potential negative impacts are calculated based on the degree of vulnerability and Keywords : Flood, Bengawan Solo River, Risk Assessment capacity of the region. The potential negative impact is seen on the potential number of people who are exposed, loss of property, and damage to the environment. This approach cannot be equated with a mathematical formula to show the relationship between threats, vulnerabilities, and capacity building for disaster risk mangement for each region. Based on this approach, disaster risk level is very dependent on the METHODS level of threat the region, the level of vulnerability of areas threatened and endangered regional capacity level. In this study, the assessment of the flood risk level of the Solo River in area will be consisting of 5 regencies, Ngawi, Bojonegoro, Tuban, Lamongan, Gresik. AHP is used as a decision support system in risk-level disaster risk assessment. The output of the AHP in the form of the priority affected area, then classified it using the head / tail to generate the level of disaster risk which consists of three levels: low, medium and high that will be shown in Web GIS.

There are five regencies in East Java included in the flood-prone areas of the Solo River. From all these regencies, there are 36 sub-districts included in the flood-prone areas because the entire district is drained by the Bengawan Solo river that are at risk for flooding.

Fig. 1 is a general overview of the system architecture which will describe the system of the application. Data will be collected and screened before it processed further. The selected data than inputed in the database and calculated using AHP method and divided into 3 level of risk using Head/Tails Break. This information will be displayed in information system website as choropleth map.

The criteria used to measure the flood risk is divided into three, namely in terms of Hazard Analysis, which covers the depth of the river (Water Level), rainfall precipitation, and catastrophic events recorded; Vulnerability Analysis (Physical, Economic, and Social), and Capacity Analysis. As for the alternative is a sub-district located in disaster-prone areas along the river basin with the aim of getting the level of risk ranging from low, medium, and high.

After calculation of each district for all the criteria, then we calculate the risk level for each district by dividing it into 3 levels of risk, low, medium and high. The level of risk is intended to provide a difference impact that will be accepted based on the criteria. In addition, the level of this risk also will facilitate the provision of capacity for disaster-prone areas in accordance with the required sub-districts.

RESULT Based on the results of the calculation of the level of vulnerability to flooding using AHP and classification Head / Tails break, do a risk map visualization as in Figure 3. The level of disaster risk is divided into three levels, namely a high level (red), medium (yellow), and low (green color).

Fig. 1 System Architecture

Fig. 3 Flood Risk Map in Bengawan Solo's Flood Prone Areas

Fig. 2 The Hierarchy of AHP

CONCLUSION In determining the level of disaster risk of 36 sub-districts in the Bengawan Solo river banks using Analytical Hierarchy Process (AHP) and classification Head / Tails breaks, has a 70% accuracy rate. AHP-head/tails break produce a risk map that divide flood-prone areas into three risk-levels, these are low (symbolized in green), medium (symbolized yellow), and red (symbolized in red). Rainfall is the main cause of flooding so that the higher the rainfall, the higher the risk level and capacity is a factor that is able to threats and vulnerabilities so that the level of risk to be low.