GeoHECRAS is described as 'speeds up HEC-RAS model creation using AutoCAD and GIS data sources. Work directly off of Google Maps, viewing and editing the model in 2D and 3D. Automated cross section cutting reduces time in building a model' and is an app. There are nine alternatives to GeoHECRAS for Windows, Linux and Wine. The best alternative is HEC-RAS, which is free. Other great apps like GeoHECRAS are Storm Water Management Model, MIKE 11, GeoHECHMS and ISIS Free.
GeoHECHMS greatly speeds up the creation, analysis, and review of stormwater models. It automates subbasin delineation, curve number (CN) computation using land use and soils maps, and lag time (time of concentration) computation.
SOBEK is a powerful modelling suite for flood forecasting, optimisation of drainage systems, control of irrigation systems, sewer overflow design, river morphology, salt intrusion and surface water quality.
MIKE 21 is the ultimate Swiss army knife of coastal modelling. If you need to simulate physical, chemical or biological processes in coastal or marine areas, MIKE 21 almost certainly has the tool you need.