RISK ANALYSIS AND ECONOMIC FEASIBILITY EVALUATION OF FLOOD MITIGATION IN THE SIAK RIVER BASIN

Abstract

The Siak River Basin is experiencing rapid socio-economic growth while facing significant flood hazards, creating the need for a comprehensive and integrated assessment. This study evaluates flood risk based on BNPB guidelines by analyzing hazard, vulnerability, and capacity conditions. Hazard levels are examined through two-dimensional hydraulic modelling in HEC-RAS to identify the spatial extent and depth of inundation. Vulnerability is assessed across social, physical, economic, and environmental dimensions, while capacity is measured using the regional resilience index and community preparedness index. The study also incorporates an economic feasibility evaluation of several mitigation alternatives using Benefit–Cost Analysis (BCA). Benefits include improved transportation accessibility, protection of household assets and income, and the sustained functioning of agricultural, fisheries, plantation sectors, and public facilities. Costs consist of both structural and non-structural flood control measures. The results indicate that most areas in the Siak River Basin fall within the medium-risk category, highlighting the need for continued mitigation efforts. Pekanbaru City has the largest share of high-risk zones, whereas Siak and Kampar Regencies are predominantly classified as medium risk. Among the evaluated alternatives, Alternative 4 is identified as the most effective, reducing the inundation area from 9,465.74 hectares under existing conditions to 3,177.00 hectares. This option also provides the highest total benefits, reaching IDR 490,657,826,002, and is the only alternative with a BCR value ≥ 1, indicating economic feasibility. In conclusion, integrating flood risk analysis with economic evaluation supports more informed and strategic decision-making for flood management in the Siak River Basin.