HEC-RAS (Hydrologic Engineering Center's River Analysis System) is a software program developed by the U.S. Army Corps of Engineers. It is used for modeling the flow of water in rivers and streams, helping engineers and planners analyze flood risks, design hydraulic structures, and manage water resources. The software allows users to simulate various scenarios, including steady and unsteady flow conditions. It provides tools for calculating water surface profiles, floodplain mapping, and sediment transport, making it a valuable resource for floodplain management and environmental studies.