Riverine Flood Susceptibility Analysis Through Frequency Ratio Model – A Case Study in the Sepik River Basin, Papua New Guinea

Abstract

Riverine Flooding occurs when the rivers exceed the capacity of their natural channels to accommodate water flow and water overflows the banks, spilling out into adjoining low-lying land. A fishnet analysis generated 206 flood locations based on the historical flood inventory database of the Papua New Guinea Resource Information System (PNGRIS). 144 (70%) flood sample locations were selected randomly for model building. The Frequency Ratio (FR) model was used for flood susceptibility analysis in the Sepik River basin based on eight independent variables, namely, landforms, slope, rainfall, hydrological soil group, land use, distance from the river, soil drainage, and elevation. The developed flood susceptibility database was reclassified into five (5) flood susceptibility zones segmenting on the FR values, namely very low (less than 5.0), low (5.0-7.5), medium (7.5-10.0), high (10.0-12.5) and very high (more than 12.5). The FR model output was validated with the remaining 62 (30%) flood points, where 55 points were marked as correct predictions which shows an accuracy of 88.71%. The assessment report identifies a total population of 125936 residing within the very high-risk zone. The findings provide valuable insights for local authorities and stakeholders in flood risk management and mitigation strategies.