Rapid urbanisation and population growth have brought significant transformations in the built and natural environment in Southeast Asian cities. In this process, rivers are crucial components in alleviating the negative impacts of urban development, primarily in relationship with flood prevention, recreational space provision, and agricultural production. Previous research has provided ample knowledge about river management’s ecological and economic impacts; however, limited attention has been given to the impacts of channelisation on rural degradation and non-conforming land-use expansion. This longitudinal research employs quantitative analysis of the spatial-temporal dynamics of the landscape transformations associated with river management, using a case study in Yuen Long, Hong Kong. The results showed intensified degradation in the agricultural landscape with an intense increase in non-conforming land use following channelisation, revealing that the hydrological alterations play a pivotal role in rural degradation. Finally, this research underscored the significance of incorporating river management into urban planning at the catchment level for future rural and periurban development.