Short name: HEC-RAS
Long name: Hydrologic Engineering Center-River Analysis System
Model type: 1D, 2D, 1D/2D
Usage: HEC-RAS is used for most riverine and reservoir analyses and some coastal applications: Flood risk, damage, hazard, and life loss analysis, Dam and levee breach, Navigation, River Restoration, Reservoir Management, Precipitation, Wind, Sediment transport, Mud and Debris Flow (1D/2D) and Water Quality (1D)
Background: HEC-RAS 1.0 was first released as a 1D, steady-flow model in 1995. Unsteady flow was added in version 3.0. Sediment transport and water quality were added in 4.0. 2D modeling was added in 5.0. Precipitation and non-Newtonian flows were added in 6.0. Pipes were added in 7.0. 7.0 will be the final version. HEC is rewriting HEC-RAS and has released an alpha version of the new software (RAS2025).
Grid Shape: Rectangular, hexagonal, and unstructured native cells. Can import meshes from other sources (e.g. RAS2025) with triangular and Laplacian contoured quadrilaterals to align with channel flow.
Grid Type: Unstructured SubGrid
Model Assumptions:
– 2D Shallow Water Equations (St Vennant)
– 2D Diffusive Wave Equations (DWE)
– 2D Local Inertial Approximation (LIA)
Assumptions:
- Sub-grid bathymetry.
- Vertical fluid motion is negligible.
- Velocity is vertically averaged at each cell face.
- Water surface elevations are computed at face points, faces, and cell centers to produce a sloping water surface over the domain.
- Manning’s roughness can vary across each cell face, resulting in a roughness-elevation relationship for each face.
- Precipitation on a 2D mesh is spatially variable, and accepts a variety of gridded input types.
- Rainfall initial abstraction and other losses can be accounted for with three methods: Deficit and Constant Loss method; the Curve Number method; and Green and Ampt.
- Time step selection should consider cell size and wave speed.
Input Data:
- DEM, topography, hydraulic structures, surface characteristics/roughness
- Mesh with breaklines and refinement regions
- Structure data (bridges, culverts, dams, etc.)
- Gridded rainfall
- Inflow boundary conditions (tide, upstream flows)
- Dambreak parameters
Input Format: HDF, CSV, HEC-2, UNET, DSS
Input Time Interval: Time series data can be input at any time interval (Sediment and water quality data can be input with regular or irregular time steps).
- Input Data – model runtime: Gridded rainfall, Inflow boundary conditions (tide, upstream flows), Dambreak / releases
Optimization or Calibration: 1D has automated calibration tools that modifies n-values based on observed water.
Data Assimilation: Yes
Ensemble: Yes. HEC-RAS can be called from HEC-WAT which can run it with ensemble, stochastic, forecasts. Many users also use HEC-RAS as part of customized ensemble, stochastic, runs using our API.
Uncertainty: Uncertainty is represented in multiple simulations.
Simulation Time Interval: Users can choose time steps between 0.1 seconds and 1 day but adaptive time step capabilities can compute smaller Courant driven time steps when necessary.
Model Output Time-Series: Water Surface Elevation, Depth, Velocity, Flow, Courant (2types) Froude #, Shear Stress, DepthXVelocity, Energy, Pressure, Stream Power, Pipe results (depth, %full, Courant, velocity), Bridge results, >100 Sediment variables, and many more.
Time-Series Format: HDF, DSS
Model Output Statistics: Max, Min, Arrival Time, % wet cells, % time inundated, max iterations per cell, max water surface error per cell
Statistics Format: HDF
Inventory Platform: –
Additional Platform: –
Installation: Self-extracting install package
User Education: BSc (Undergraduate hydraulics and open channel courses)
Degree of Difficulty: 3 (from 1 to 5 depending on application) Can be very easy to get a quick answer (simple 1D bridge hydraulic analysis – 5) or can be used for very difficult model applications (e.g. very large sediment studies – 1)
GIS support: GIS is all fully integrated with RASMapper and has automatic downloads of terrain and parameter data
Data Preparation: HEC-RAS can automatically import time series data from other HEC models with HEC-DSS. We can download and prepare time series data with our companion program HEC-DSSVue. Some model components can import time series data directly from the USGS API.
Model Parameters: flow, n-values, infiltration properties, impermeable %, turbulence properties (Sediment includes: boundary and initial concentration, grain-size distributions, cohesive parameters; Water Quality includes: solar index, constituent boundary conditions, reaction parameters)
Parameter Estimation: Automated import of USGS data (terrains) and USDA soil and land use data
Model Calibration: Calibration regions to adjust spatial parameters for 2D models, automated calibration algorithms for 1D mode. Training materials include information and videos on how to calibrate models.
Model Verification: Same tools used for calibration could be used for a split time-series validation phase.
Model setup interface: Integrated mapping and sophisticated UI make model setup all within the software.
Visualization of model output: Includes RASMapper a customized GIS with Integrated Mapping, Visualization GUIs, Terrain Modification
Hardware Requirements: PC
- Parallelization: Can use multiple CPU Cores
Operating System: MS Windows, LINUX run capabilities
Language of Core Code: Fortran
Open Source: No
Last Update and Version: HEC-RAS 6.6 (full release) HEC-RAS 6.7 Beta 5
Next Update and Version: HEC-RAS 7.0
Active Development Community: Yes
Platform Integration: –
Download URL: https://www.hec.usace.army.mil/software/hec-hms/downloads.aspx
Free to Download and Use: Yes
Language of Software Interface: English
Online Support URL: https://www.hec.usace.army.mil/software/support_policy.aspx
Training Material URL (including example data sets): https://www.hec.usace.army.mil/software/hec-ras/documentation.aspx
• Training courses
• Online training
• Support forums – via internet and CoP
Language of Trainings: English
Guidance Material URL (including case studies and benchmarking of performance/speed): https://www.hec.usace.army.mil/software/hec-hms/documentation.aspx
Language of Guidance: English
References: Bergstrom, S. (1995) The HBV Model. In V.P. Singh (Ed.) Computer models of watershed hydrology, pp. 443-476, Water Resources Publications, Highland Ranch, Colorado, USA.
Owner, Developer:
US Army Corps of Engineers
https://www.hec.usace.army.mil
Mailing Address:
Department of The Army
Corps of Engineers
Institute for Water Resources
Hydrologic Engineering Center
609 Second Street
Davis, CA 95616-4687
HEC Phone: +1 530.756.1104
HEC Fax: +1 530.756.8250