Quantification of the flood discharge following the 2023 Kakhovka Dam breach using satellite remote sensing

Fourteen months post the Ukrainian-Russian war outbreak, the Kakhovka Dam collapsed, leading to weeks of catastrophic flooding. Yet, scant details exist regarding the reservoir draining process. By using a new technique for processing gravimetric satellite orbital observations, this study succeeded in recovering continuous changes in reservoir mass with a temporal resolution of 2–5 days. By integrating these variations with satellite imagery and altimetry data into a hydrodynamic model, we derived the effective width and length of the breach and the subsequent 30-day evolution of the reservoir discharge. Our model reveals that the initial volumetric flow rate is  (5.7±0.8)×10⁴ m³/s, approximately 28 times the average flow of the Dnipro River. After 30 days, the water level in the reservoir had dropped by 12.6±1.1 m and its water volume was almost completely depleted by  20.4±1.4 km³. In addition, this event provides a rare opportunity to examine the discharge coefficient—a key modelling parameter—of giant reservoirs, which we find to be 0.8–1.0, significantly larger than the ~0.6 value previously measured in the laboratory, indicating that this parameter may be related to the reservoir scale. This study demonstrates a paradigm of utilizing multiple remote sensing techniques to address observational challenges posed by extreme hydrological events.