The purpose of this study was to find solutions for local government dam river management and water supply for maintenance flow. For this purpose, based on data collected and organized on items to be included in the system related to the environment around Unmun Dam and Dongchang Stream, a comparative review of the policy status of other local governments and environmental facilities was conducted, and case analysis was conducted focusing on domestic and international cases. The local government's maintenance flow management plan for water supply in dam river management is, first, to manage the river flow in a stable manner throughout the year in order to perform the smooth function of the river, and second, to pump water to maintain the basic flow rate of the river. A reverse pumping method that sends water from downstream to upstream, and third, artificial supply of soil through flooding or flushing discharge to improve the environment of the river downstream of the dam were proposed. As a result, we tracked changes in the natural ecological environment of Dongchang Stream after the construction of Unmun Dam and proposed dam operation plans and flood control policies to derive implications such as ecological environment restoration, flood prevention measures in downstream areas, and local economy revitalization measures.