Abstract-This study explored using database environments to develop a tailor-made geospatial web-based system to identify flood risk. This approach can directly target specific needs and has advantages over existing noncommercial systems. We analyzed the river network in the Chubu region, which encompasses nine prefectures in Central Japan, to understand rainfall-water-level relationships. A spatial web-based system was then developed to monitor rainfall and river-water levels in the study area. This database system assesses near-real-time rainfall and water-level data. A map service was configured using OpenLayers, an open-source software package. This proposed system will deliver early-warning flood messages via a scripting mailer system. However, device error could occur, which necessitates human verification before a final decision is made. Self-geolocation helps individual users determine their risk. Improvements in the visualization and recognition of existing data using map-service tools and technology may help reduce tragedies and damage resulting from flooding.Index Terms-Database information systems, map services, web-based systems, warning systems, environmental disaster, floods.