Relative elevation data was extracted from the map of residual topography over 25-40 km swaths extending from the Rio Bermejo channel centerline. We quantified the superelevation and incision of the Rio Bermejo relative to the surrounding topography by making a residual elevation map (sensu Cohen et al. (2015, doi:10.1130/2015.1212(16); McGlue et al. (2016, doi:10.2110/jsr.2016.82)). We created a series of 1 km wide swaths set perpendicular to the Rio Bermejo flow direction and extracted the minimum elevation of the active Rio Bermejo channel within each swath using the TanDEM-X DEM. Variability in DEM values for water surfaces created ~2-4 m noise in elevation values of the active channel which we smoothed by fitting a 4th order polynomial to the extracted active channel elevations to estimate the downstream change in elevation. We subtracted the polynomial fit from the DEM to yield a DEM that was de-trended from the Rio Bermejo channel slope, with values representing the local relief between the active channel and the surrounding terrain.

Relative elevation is the elevation of the flood basin surface relative to the river channel. Positive values represent channel incision, negative values represent channel superelevation.