HEC-RAS (Hydrologic Engineering Center’s River Analysis System) is a hydraulic modelling software package developed and maintained by the US Army Corps of Engineers (USACE). It is one of the most widely used river modelling tools worldwide, available free of charge, and is accepted by the Environment Agency for Flood Risk Assessments in England.

HEC-RAS supports multiple analysis modes:

1D steady-state flow: Computes water surface profiles for a series of design flows, suitable for simple channel and bridge analyses
1D unsteady flow: Simulates time-varying flows through channel reaches, capturing flood wave attenuation and timing
2D unsteady flow: Full two-dimensional simulation across a structured or unstructured mesh, suitable for complex floodplain analysis
Linked 1D-2D: Combines detailed 1D channel representation with 2D floodplain modelling
Sediment transport: Models bed erosion and deposition over time
Water quality: Simulates transport and fate of pollutants

In UK practice, HEC-RAS is commonly used for:

River flood modelling for planning applications, particularly smaller watercourse studies
Bridge and culvert capacity assessments
Flood defence appraisals and options studies
Reservoir flood routing

HEC-RAS benefits from a large global user community, extensive documentation, and regular updates. The software’s 2D capabilities have improved significantly in recent versions, though for complex urban pluvial modelling, TUFLOW remains the preferred tool in the UK.

Aegaea’s engineers are experienced with HEC-RAS for 1D and linked 1D-2D flood modelling projects, selecting the most appropriate tool for each study’s requirements and the expectations of the reviewing authority.