A parallel Python-based tool for meshing watershed rivers at continental scale.

A major challenge in compound flooding simulation is representing small rivers in the model mesh. A parallel Python-based tool is developed to support the construction of unstructured grids (UGs) at continental scales. The tool is driven by Digital Elevation Model (DEM), ensuring accurate representation of geomorphic features in the resulting mesh. Its first component (pyDEM) extends an existing tool to detect river thalwegs from DEMs. The second component (RiverMapper) uses the thalwegs to generate river ‘arcs’, which can be directly ingested into meshing tools (e.g., the Surface-water Modeling System). The novelty lies in the explicit 2D representation of rivers in both along- and cross-channel directions, making it ideal for accurate, efficient, and high-resolution continental-scale research. The tool is employed to create a UG for a 3D creek-to-ocean model encompassing the US East and Gulf Coasts, and it greatly improves the flow exchange between the watershed and the coastal zone.