HEC-RAS

HEC-RAS
Name	HEC-RAS
Developer	United States Army Corps of Engineers
Released	1995
Latest release	(varies)
Operating system	Microsoft Windows
License	Public domain
Website	(see developer)

HEC-RAS HEC-RAS is a hydraulic modeling software package developed for one-dimensional and two-dimensional river flow analysis. It is used by practitioners for floodplain mapping, channel design, reservoir operations, and infrastructure assessment in regulatory, academic, and engineering settings. The program interfaces with geospatial datasets and is often applied alongside remote sensing and hydrologic models in major projects worldwide.

Overview

HEC-RAS combines steady, unsteady, and two-dimensional hydraulic simulation capabilities for open-channel and mixed-flow systems, serving as a tool in flood risk assessment, river restoration, and urban drainage planning. It integrates with geospatial platforms and is commonly paired with watershed models, mapping tools, and design standards. The software supports modeling of bridges, culverts, levees, and braided river networks, enabling users to evaluate conveyance, stage-frequency relationships, and sediment transport for regulatory submittals and engineering studies.

History and Development

Development began within the United States Army Corps of Engineers to replace earlier hydraulic codes and to standardize river analysis across Corps districts. Early releases in the 1990s followed work on channel hydraulics techniques derived from legacy programs and manuals produced by the Corps and influenced by practices in Federal Emergency Management Agency flood mapping and National Oceanic and Atmospheric Administration hydrology guidance. Subsequent versions incorporated numerical methods from academic research at institutions such as University of California, Berkeley, Colorado State University, and Massachusetts Institute of Technology, while engaging with standards from ASCE committees and collaborations with state departments of transportation like California Department of Water Resources and Texas Department of Transportation.

Capabilities and Features

HEC-RAS provides modules for steady flow analysis, unsteady flow routing, sediment transport modeling, and two-dimensional flow simulation using finite volume schemes. It handles boundary conditions, lateral inflows, and hydraulic structures including bridges and culverts with form loss and contraction effects referenced to standards used by American Association of State Highway and Transportation Officials and the Federal Highway Administration. The software outputs stage-discharge curves, water surface profiles, velocity fields, shear stress distributions, and sediment grading changes, supporting permit applications to regulators such as the Environmental Protection Agency and state environmental agencies.

Technical Components and Models

The core numerical engine solves the Saint-Venant equations for one-dimensional unsteady flow and extends to two-dimensional shallow water equations using implicit and explicit solvers. Sediment transport modules implement empirical and semi-empirical relations developed in the literature at University of Iowa, University of Illinois Urbana–Champaign, and Texas A&M University; options include transport formulas aligned with research from NIH? (note: see developer docs for specifics). Hydraulic structure models parameterize energy losses using coefficients referenced in manuals from USACE and guidance from FEMA flood studies. Computational meshes and geometric representations are commonly created from elevation datasets produced by United States Geological Survey and photogrammetry by firms such as Esri partners and surveyed by agencies like National Geodetic Survey.

Applications and Case Studies

HEC-RAS has been applied in urban flood studies for metropolitan areas such as New York City, Houston, and New Orleans, in watershed planning for basins like the Mississippi River and Colorado River, and in restoration projects on rivers including the Sacramento River, Mekong River, and Thames River. It supports bridge scour analysis for interstate highway projects involving agencies such as Federal Highway Administration and port infrastructure managed by authorities like Port of Los Angeles. Case studies in academic journals from University of Washington, University of Oxford, and Imperial College London illustrate use in combined 1D/2D modeling for floodplain mapping informing flood insurance rate maps overseen by FEMA and regional planners such as Metropolitan Transportation Authority in complex urban contexts.

Validation, Limitations, and Uncertainty

Validation exercises compare model outputs against observed hydrographs, stage records from gauging stations maintained by USGS, and lidar-based flood extents evaluated by agencies like NOAA and research groups at Purdue University and University of Colorado Boulder. Limitations arise from assumptions of hydrostatic pressure distribution, grid resolution constraints, parameter uncertainty in roughness coefficients (often estimated via field surveys from firms like Jacobs Engineering), and simplified structure representations. Uncertainty quantification methods employ sensitivity analysis, ensemble approaches, and calibration techniques developed in hydrology literature from ETH Zurich and Delft University of Technology to bound predictive error for engineering design and risk assessment.

User Interface, Data Input, and Output Formats

The graphical user interface supports geometric editors, plan and profile visualization, and integration with terrain viewers that read data formats from USGS DEMs, Esri shapefiles, and Open Geospatial Consortium standards. Input data workflows typically involve preprocessing in GIS platforms such as ArcGIS, QGIS, or hydrologic models like HEC-HMS and SWAT to produce hydrograph boundary conditions. Outputs include tabular reports, cross-section plots, ASCII time series, GIS-compatible rasters for inundation mapping, and animations used by practitioners at municipal utilities, consulting firms like AECOM, and academic researchers for dissemination and regulatory submissions to agencies including EPA and state environmental departments.

Category:Hydraulic modeling software