SWOT Captures Hydrologic Waves Traveling Down Rivers

Abstract High discharge events propagate down rivers as flow waves. River wave movements are described theoretically by routing equations or tracked using in‐situ gauge measurements of stage over time at a given location. However, the sparse distribution of gauges makes it challenging to show how stage evolves with along‐river distance as waves propagate downstream. Here we use novel measurements of water surface elevation from the Surface Water and Ocean Topography satellite to detect and analyze flow wave paths, presenting examples of the first direct observations of continuous downstream changes in river height at a given time within a flow wave. By removing long‐scale river elevation profiles, we develop “spatial hydrographs” as analogs to in‐situ time series and demonstrate their value for analyzing wave characteristics, including measuring length, estimating celerity, and partitioning event flow from baseflow. Our methods could be applied globally to study flow waves and their properties.