The majority of areas in the 23 special wards of Tokyo utilize a combined sewer system. However, due to the inherent structure of this system, it exacerbates various issues, including urban flooding and water pollution. Furthermore, the historical development of sewer and river infrastructure during the process of urbanization often came at the expense of local waterfront environments. This study focuses on the fact that major sewer pipes are laid along former riverbeds, and seeks to reassess water management at the watershed scale by recovering infiltration capacity, utilizing rainwater storage, and reorganizing above-ground spaces such as roadways, primarily through the integration of green spaces. In doing so, the aim was to fundamentally improve the core water-related issues in urban areas while proposing solutions that would enrich the local environment and cultural landscape.