Boase Hydrologic Sciences and Water Resources Engineering Seminar Series

About this event

Speaker: Naman Kishan Rastogi, Ph.D Candidate. Joaquin Sainz Hermosillo M.S

Title: A Bayesian Reconstruction for Continuous River Water Surface Elevation from Sparse SWOT Satellite

Data

Snow Dynamics, Soil Freezing, and Groundwater Recharge in a Boreal Aquifer Under Historical and

Future Climate Conditions

Abstract: Continuous river water surface elevation (WSE) records are essential for flood forecasting and water management, yet in-situ gauges remain sparse worldwide. The Surface Water and Ocean Topography (SWOT) mission delivers global WSE at ~200 m node resolution, but its ~11-day revisit limits operational use. We develop Bayesian Reconstruction and Continuous River Elevation (BRACE), a hierarchical Bayesian framework that reconstructs continuous WSE posteriors at each SWOT node from covariate relationships with gauge stage. We apply BRACE to 569 nodes across 11 reaches of the Willamette River, Oregon (WRB), selecting the best of five covariate configurations per node by DIC, and to ~3,400 nodes across 62 reaches of the Brahmaputra River Basin (BRB), where each reach between the Dibrugarh and Bahadurabad gauges uses its two bracketing gauges. K-fold cross-validation (ten-fold WRB, five-fold BRB) yields full posteriors from withheld folds. Fitting skill: R=0.994, NSE=0.987, RMSE=0.225 m (WRB); R=0.980, NSE=0.959, RMSE=0.340 m (BRB). Cross-validated skill: R=0.977, NSE=0.954, RMSE=0.227 m (WRB); R=0.977, NSE=0.955, RMSE=0.361 m (BRB). Independent validation uses 27 pressure transducers (WRB, R>0.97) and the Tezpur gauge (BRB). For the BRB, posteriors regenerate a daily WSE record back to 2010, 13 years before SWOT, valuable for flood early warning in data-scarce basins. BRACE bridges satellite altimetry and the continuous WSE records needed for operational flood forecasting.

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Seasonal freeze–thaw processes strongly influence groundwater recharge in cold regions by controlling the storage and movement of water between the land surface and the subsurface. This study investigates the physical interactions among snow accumulation, soil thermal dynamics, ice formation, and groundwater recharge using the coupled surface–subsurface model Amanzi-ATS for a soil column in the Karhinkangas aquifer in central Finland. Model simulations were evaluated against observations of snow depth and near-surface soil temperature for four winters (2011–2015). The simulations reproduced the observed seasonal evolution of snow accumulation and soil temperature and were used to investigate the physical mechanisms controlling winter recharge. Results demonstrate that the timing of persistent snow accumulation relative to the soil temperature strongly influences soil freezing and thawing. Snow insulation reduces heat exchange between the atmosphere and the soil, but its effectiveness depends not only on snow depth and persistence, but also on soil temperature when the snowpack becomes established. Frozen soil limits groundwater recharge during much of the winter, whereas thawed conditions promote infiltration. The highest recharge rates were generally associated with rain-on-snow events, during which rainfall and snowmelt combined to provide abundant liquid water for infiltration into thawed soils. These findings improve the understanding of the coupled hydrologic and thermal processes controlling winter groundwater recharge and provide a physical framework for evaluating future climate-driven changes in cold-region groundwater systems.

Bio: Naman is a PhD student in Civil Engineering at the University of Colorado Boulder. He received his B.Tech. (Civil Engineering) from G. B. Pant University, India, and M.Tech. (Water Resources Engineering) from Indian Institute of Science, Bangalore, India. His current research focuses on developing a river flood risk framework using Bayesian hierarchical models for daily ensemble river stage forecasts and hydraulic models for inundation. He also uses Bayesian causal networks to understand the large scale climate drivers of floods to enable risk assessment. He is a recipient of the Awtar and Teji Singh Fellowship for the academic year 2023–2024 from the CU College of Engineering and Applied Science, and the CIRES Graduate Student Research Award (GSRA) for 2026 to 2027.

Bio: Joaquin Sainz Hermosillo is a master’s student in Civil Engineering at the University of Colorado Boulder, working under the guidance of Dr. Roseanna Neupauer. His research focuses on using numerical modeling to investigate the interactions between snow dynamics, soil freezing and thawing, and groundwater recharge under historical and future climate conditions. He earned his bachelor’s degree in environmental engineering from Universidad Jesuita de Guadalajara (ITESO) in Mexico. Outside of his research, Joaquin enjoys hiking, running, snowboarding, and playing music with friends.