Compound flooding (CF) poses significant risks to human and natural systems. The urgent need for an improved predictive understanding of CF and its impact on sediment dynamics and riverine saltwater intrusion at global scales under a future climate is well recognized. However, several scientific and computational shortcomings in the current version of the Department of Energy's Energy Exascale Earth Model (E3SM) limit its applicability to study CF and its impacts. This presentation provides a high-level overview of the river dynamical core (RDycore) for E3SM, funded through the Scientific Discovery Through Advanced Computing program. RDycore will include efficient and scalable solvers for DOE's exascale-class supercomputers and will be rigorously verified and validated for the study of CF and its impacts on sediment dynamics and riverine saltwater intrusion in a changing climate.