AquaSWMM
EPA SWMM editor with 2D overland flow, 1D-2D coupling and sewer design
...Imports Civil 3D .stm, LandXML, DXF, shapefiles, GeoJSON and GeoTIFF terrain.
Windows, macOS and Linux. The desktop app has a 30-day free trial (email only, no card). The simulation engine, command-line tools and Python package are open source under GPL-3.0, and StormSewer releases 0.11.0 and earlier remain GPL-3.0.
Written by a practicing water resources PE.