HEC-RAS is described as 'is designed to perform one-dimensional hydraulic calculations for a full network of natural and constructed channels. The following is a description of the major capabilities of HEC-RAS'. There are eight alternatives to HEC-RAS for Windows and Linux. The best alternative is GeoHECRAS. It's not free, so if you're looking for a free alternative, you could try Storm Water Management Model or ISIS Free. Other great apps like HEC-RAS are MIKE 11 (Paid), SOBEK Suite (Paid), MIKE Flood (Paid) and Delft3D (Free, Open Source).
GeoHECRAS 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.
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.