SWOT Satellite Altimetry Reveals Extreme Flood Wave After the Kakhovka Dam Collapse

The collapse of the Kakhovka Dam on 6 June 2023 produced a flood wave, causing widespread ecological damage and inundating numerous settlements along the lower Dnipro River in southern Ukraine. This catastrophic event was captured during the calibration phase of the Surface Water and Ocean Topography (SWOT) satellite, which enables daily two-dimensional water surface elevation measurements, allowing us to document the dam-break flood wave through frequent spaceborne observations. We show that SWOT captures the rapid downstream propagation of the flood wave, with water levels rising by 11.0 m (95% CI [10.6,11.2]), followed by progressive attenuation and stabilisation. Beyond longitudinal propagation, SWOT data further reveal extensive floodplain inundation with steep transverse slopes reaching 218.7 cm/km (95% CI [159.9, 175.9]). Additionally, the wave extends more than 160 km into the Inhulets River, one of Dnipro’s tributaries, generating upstream-directed flow with water surface elevations of 7.8 m (95% CI [7.7, 7.8]) and exhibiting negative slopes of –16.4 cm/km (95% CI [-15.8, -17.4]). These observations underscore the unique capability of wide-swath altimetry missions to resolve the dynamics of extreme flood waves with high spatial and temporal detail, thereby improving prospects for global disaster monitoring.