Bruce L Rhoads (University of Illinois Urbana-Champaign, United States); Jida Wang (University of Illinois Urbana-Champaign, United States)

Lateral water-surface superelevation, i.e., the rise in water level along the outer bank, is a common phenomenon in meandering rivers caused by the curvature-induced centrifugal force. Accurate data on water-surface superelevation are critical for modeling the hydrodynamics of meandering rivers, including free surface deformation and prediction of mean velocity near bends. Despite its significance, superelevation has been studied in only a limited number of cases, primarily in laboratory curved channels. Field measurement of superelevation remains challenging due to water surface disturbance and temporal variability associated with changing hydrological conditions. This study aims to evaluate the potential of high-rate data from the Surface Water and Ocean Topography (SWOT) satellite mission to accurately detect superelevation of the water surface in large meandering rivers. The lateral variation in water-surface elevation (WSE) was evaluated for bankfull flows in a series of sharply curved bends at three sites - two on the Mississippi River and one on the Wabash River. A grid-based spatial-averaging model was applied to determine lateral variation in WSE at discrete cross sections from SWOT pixel cloud data. Plots of lateral WSE gradients at cross-sections around the bends show that distinct superelevation is evident on the Mississippi River bends with the pattern of superelevation varying directly with the pattern of bend curvature. Data for the Wabash River, which is only about one-third as wide as the Mississippi reaches, is less conclusive. Mean flow velocities estimated from the WSE gradients are consistent with estimated velocities based on data for nearby gaging stations. Overall, the results suggest that SWOT is capable of accurately detecting superelevation of the water surface in bends of large rivers, providing a promising foundation for global assessments of lateral gradients in WSE in large meandering rivers.