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HEC-RAS

From Wikipedia, the free encyclopedia
1D HEC-RAS model, showing river line and cross-sections. Each cross-section is depth-averaged.

HEC-RAS (short for Hydrologic Engineering Center River Analysis Software) is a simulation software used to model the hydraulics of water flow through natural rivers and other open channels. The program was developed by the United States Army Corps of Engineers (USACE) at the Hydrologic Engineering Center (HEC) in Davis, California as a successor to their HEC-2 Water Surface Profiles program.[1] HEC-RAS version 1.0 was released in July 1995, with the capability to model steady flow in one dimension;[2] since then, further releases have increased the modeling capabilities to include quasi-unsteady and unsteady flow, two dimensional modeling, sediment transport and water quality modeling, and distributed hydrologic modeling (Rain-on-Grid.)[3] The program is free to download from HEC, though there is no support provided for non-USACE users.[2]

Though HEC-RAS was initially developed by USACE for use on their own projects, other United States federal agencies have adopted it for use, including FEMA[1][4]. It is also used by hydraulic modelers for various applications worldwide,[2][5]both in academia[6] and industry.[7]

Program history

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In 1964, Bill S. Eichert, working at HEC for USACE, developed a step-backwater program. Eventually released as "Backwater Any Cross Section" in FORTRAN in 1966, this would be the first of many iterations of HEC-2, designed to model flow in open channels in one dimension.[8]

The first version of HEC-RAS was released in July of 1995.[3] Though one-dimensional HEC-RAS solves the same equations as HEC-2, the computational routines and numerical methods are completely different.[3]

HEC-RAS 1.0 - 4.1 focused on improving one-dimensional modeling capabilities. In 2016, HEC released HEC-RAS Version 5.0, which including two-dimensional modeling capabilities. Version 6.0, released in May 2021, including distributed hydraulic modeling (Rain-on-Grid), as well as sediment transport and water quality modeling capabilities.[9]

In the fall of 2024, HEC announced they were in the process of developing the next generation of HEC-RAS, which they compared to the transition from HEC-2 to HEC-RAS. Intended to streamline and update the existing software, HEC-RAS 2025 will feature a new, modern user interface, new meshing methods, and an explicit solver.[10] The transition between an alpha version of HEC-RAS 2025 and an industry-ready version is expected to last several years.[11]

Functionality

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The basic computational procedure of HEC-RAS for steady flow is based on the solution of the one-dimensional energy equation. Energy losses are evaluated by friction and contraction / expansion. The momentum equation may be used in situations where the water surface profile is rapidly varied. These situations include hydraulic jumps, hydraulics of bridges, and evaluating profiles at river confluences.

For unsteady flow, HEC-RAS solves the full, dynamic, 1-D Saint Venant Equation using an implicit, finite difference method. The unsteady flow equation solver was adapted from Dr. Robert L. Barkau's UNET package.

HEC-RAS is equipped to model a network of channels, a dendritic system or a single river reach. Certain simplifications must be made in order to model some complex flow situations using the HEC-RAS one-dimensional approach. It is capable of modeling subcritical, supercritical, and mixed flow regime flow along with the effects of bridges, culverts, weirs, and structures.

Version 5.0.7 as of March 2019 supports Windows 7, 8, 8.1, and 10 64-bit only.[12] Version 6.0 and newer support 64-bit Windows 7-11,[13] and version 6.1 is available for Linux.[14]

Applications

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HEC-RAS is a computer program for modeling water flowing through systems of open channels and computing water surface profiles. HEC-RAS finds particular commercial application in floodplain management and [flood insurance] studies to evaluate floodway encroachments. Some of the additional uses are: bridge and culvert design and analysis, levee studies, and channel modification studies. It can be used for dam breach analysis, though other modeling methods are presently more widely accepted for this purpose.

Advantages

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HEC-RAS has merits, notably its support by the US Army Corps of Engineers, the future enhancements in progress, and its acceptance by many government agencies and private firms. It is in the public domain and peer-reviewed, and available to download free of charge from HEC's web site. Various private companies are registered as official "vendors" and offer consulting services and add-on software. Some also distribute the software in countries that are not permitted to access US Army web sites. However, the direct download from HEC includes extensive documentation, and scientists and engineers versed in hydraulic analysis should have little difficulty utilizing the software.

Disadvantages

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Users may find numerical instability problems during unsteady analyses, especially in steep and/or highly dynamic rivers and streams.[15] It is often possible to use HEC-RAS to overcome instability issues on river problems. Numerical stability concerns are an intrinsic property of finite difference numerical solution schemes.

Version history

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The first version of HEC-RAS was released in 1995.[16] This HEC-RAS 1.0 solves the same numerical equation of the 1968 HEC-2.

Prior to the 2016 update to Version 5.0, the program was one-dimensional, meaning that there is no direct modeling of the hydraulic effect of cross section shape changes, bends, and other two- and three-dimensional aspects of flow. The release of Version 5.0 introduced two-dimensional modeling of flow as well as sediment transfer modeling capabilities.

GeoHECRAS

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GeoHECRAS is a 2D/3D visualization and editing data wrapper to the HEC-RAS software and used for flood control and flood mitigation engineering studies, including production of Federal Emergency Management Agency flood hazard maps and other river engineering studies.

Features related to HEC-RAS include:

WMS

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Main article: WMS (hydrology software)

WMS (watershed modeling system) is a hydrology software that provides pre and post-processing tools for use with HEC-RAS. The development of WMS by Aquaveo was funded primarily by The United States Army Corps of Engineers.

Features related to HEC-RAS include:

  • Using feature objects (centerline, cross section lines) and a TIN to develop the geometry of a HEC-RAS model.
  • Editing, merging, and creating cross sections in a database for use with HEC-RAS and other hydraulic models.
  • Delineating flood plains from water surface elevation data. Water surface elevations can be computed by HEC-RAS, defined interactively, or imported from a file.
  • Linking multiple simulations of HEC-1 to HEC-RAS to determine the uncertainty in modeling parameters on a delineated flood plain. Curve Number and Precipitation can be stochastically varied among HEC-1 parameters and Manning's n value for HEC-RAS.

See also

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References

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  1. ^ a b Dewberry & Davis, LLC. "HEC-RAS Procedures for HEC-2 Modelers" (PDF). www.FEMA.gov. Federal Emergency Management Agency. Retrieved 23 January 2026.
  2. ^ a b c More, D. D.; Gavit, B. K.; Nandgude, S. B. (2024). "Hydrologic Engineering Centers-River Analysis System (HEC-RAS) - A Review" (PDF). Journal of Agricultural Research and Technology. 49 (1): 139–150. doi:10.56228/JART.2024.49120.
  3. ^ a b c Brunner, Gary W. (2024). HEC-RAS, River Analysis System Hydraulic Reference Manual (PDF). Davis, CA: United States Army Corp of Engineers. p. 520. Retrieved 23 January 2026.
  4. ^ "Software for Flood Mapping". www.FEMA.gov. FEMA. Retrieved 23 January 2026.
  5. ^ Zaina, Norsaliha Najwa; Abu Talib, Siti Hidayah (2024). "Review paper on applications of the HEC-RAS model for flooding, agriculture, and water quality simulation". Water Practice and Technology. 19 (7): 2883–2900. Bibcode:2024WatPT..19.2883Z. doi:10.2166/wpt.2024.173. Retrieved 23 January 2026.
  6. ^ Yang, Yiye; Lu, Zhong; Ouyang, Choajun; Xie, Hu; Zhang, Qin (2023). "Glacial Lake Outburst Flood Monitoring and Modeling through Integrating Multiple Remote Sensing Methods and HEC-RAS". Remote Sensing. 15 (22): 5327. Bibcode:2023RemS...15.5327Y. doi:10.3390/rs15225327.
  7. ^ Bush, Samual T.; Dresback, Kendra M.; Szpilka, Christine M.; Kolar, Randall L. (2022). "Use of 1D Unsteady HEC-RAS in a Coupled System for Compound Flood Modeling: North Carolina Case Study". Journal of Marine Science and Engineering. 10 (3): 306. Bibcode:2022JMSE...10..306B. doi:10.3390/jmse10030306. hdl:11244/335849.
  8. ^ CEIWR-HEC (1991). HEC-2 Water Surface Profiles User's Manual (PDF). Davis, CA: United States Army Corp of Engineers. p. 1. Retrieved 23 January 2026.
  9. ^ HEC. "HEC-RAS Release Notes 6.0". HEC-RAS. United States Army Corps of Engineers. Retrieved 23 January 2026.
  10. ^ Kennedy, Alexander. "Future of HEC-RAS". HEC Newsletter. United States Army Corp. Retrieved 23 January 2026.
  11. ^ HEC. "RAS 2025". HEC-RAS 2025. United States Army Corps of Engineers. Retrieved 23 January 2026.
  12. ^ "HEC-RAS - River Analysis System" (PDF). Archived from the original (PDF) on 2020-07-10.
  13. ^ "HEC-RAS Release Notes". www.hec.usace.army.mil. Retrieved 2024-03-16.
  14. ^ HEC-RAS 6.1 Linux Release Notes
  15. ^ "Model Stability". www.hec.usace.army.mil. Retrieved 2024-03-16.
  16. ^ "Science Engineering & Sustainability: HEC-RAS evolution". Science Engineering & Sustainability. Retrieved 2019-03-24.
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