In response to the increasing frequency of water-related disasters attributable to climate change, a river-water flow index that integrates synthetic aperture radar (SAR) and multispectral data has been developed in this study. The basic maps of river environment are generated every five years through national censuses based on surveys of river environments and vegetation distributions. However, these maps may not accurately reflect short-term environmental changes, such as vegetation growth over a five-year period. Hence, we focused on satellite imaging that facilitates periodic observations. SAR, an active sensor, effectively captures the densities of objects and materials on the ground. Although the integrated-data-based index may differ according to seasonal variations and coverages, our preliminary findings from the Kuji River case study suggest its potential as an effective evaluation index for river water flowability.