Flood Inundation Modeling Using the Surface Water Ocean Topography Mission

Flood risk mapping requires detailed river bathymetry, yet these data are unavailable for most rivers. We propose a new algorithm to estimate river bathymetry from multitemporal observations of water height by the Surface Water and Ocean Topography (SWOT) mission. The robustness of bathymetry estimates were evaluated against detailed in situ data on a narrow river (40–70 m width) that is often below SWOT's mission specification. Typical SWOT errors, not always flagged by the SWOT processing algorithm, could severely impact bathymetry estimates. However, a simple “Tulip” shaped misfit function could largely mitigate for these and was especially important along narrow sections of the river. SWOT River Single Pass node (∼200 m reaches) height errors against in situ gauge levels with stringent quality filtering were 0.16 m, approaching the mission accuracy requirements for much larger 1 km² waterbodies. Derived channel bed elevations were physically plausible (∼1 m error) when estimated at a spatial resolution below half the river backwater length. A flood model built from SWOT-derived bathymetry had commensurate accuracy to a model based on high-resolution sonar bathymetry. For flooding in 2000, the model had a Critical Success Index of 0.88 against airborne SAR and absolute differences from gauged levels ranging from 0.14 to 0.31 m across the event.