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'''HEC-RAS''' (short for Hydrologic Engineering Center River Analysis Software) is a [[Simulation software|simulation software]] used to model the [[Physics:Hydraulics|hydraulics]] of water flow through natural [[Earth:River|river]]s 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.<ref name="HEC-2 to RAS">{{cite web |last1=Dewberry & Davis, LLC |title=HEC-RAS Procedures for HEC-2 Modelers |url=https://www.fema.gov/sites/default/files/documents/fema_floodplain-modeling-manual_hec-ras-procedures-hec-2-modelers_4-2002.pdf |website=www.FEMA.gov |publisher=Federal Emergency Management Agency |access-date=23 January 2026 |ref=1}}</ref> HEC-RAS version 1.0 was released in July 1995, with the capability to model steady flow in one dimension;<ref name="RAS Review">{{cite journal |last1=More |first1=D. D. |last2=Gavit |first2=B. K. |last3=Nandgude |first3=S. B. |title=Hydrologic Engineering Centers-River Analysis System (HEC-RAS) - A Review |journal=Journal of Agricultural Research and Technology |date=2024 |volume=49 |issue=1 |pages=139–150 |doi=10.56228/JART.2024.49120 |url=https://www.jart.co.in/uploads/168/15441_pdf.pdf}}</ref> 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.)<ref name="Tech Ref">{{cite book |last1=Brunner |first1=Gary W. |title=HEC-RAS, River Analysis System Hydraulic Reference Manual |date=2024 |publisher=United States Army Corp of Engineers |location=Davis, CA |pages=520 |url=https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_Hydraulic_Reference_Manual_v6.6.pdf |access-date=23 January 2026}}</ref> The program is free to download from HEC, though there is no support provided for non-USACE users.<ref name="RAS Review"></ref>
'''HEC-RAS''' (short for Hydrologic Engineering Center River Analysis Software) is a [[Simulation software|simulation software]] used to model the [[Physics:Hydraulics|hydraulics]] of water flow through natural [[Earth:River|river]]s 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.<ref name="HEC-2 to RAS">{{cite web |last1=Dewberry & Davis, LLC |title=HEC-RAS Procedures for HEC-2 Modelers |url=https://www.fema.gov/sites/default/files/documents/fema_floodplain-modeling-manual_hec-ras-procedures-hec-2-modelers_4-2002.pdf |website=www.FEMA.gov |publisher=Federal Emergency Management Agency |access-date=23 January 2026 |ref=1}}</ref> HEC-RAS version 1.0 was released in July 1995, with the capability to model steady flow in one dimension;<ref name="RAS Review">{{cite journal |last1=More |first1=D. D. |last2=Gavit |first2=B. K. |last3=Nandgude |first3=S. B. |title=Hydrologic Engineering Centers-River Analysis System (HEC-RAS) - A Review |journal=Journal of Agricultural Research and Technology |date=2024 |volume=49 |issue=1 |pages=139–150 |doi=10.56228/JART.2024.49120 |url=https://www.jart.co.in/uploads/168/15441_pdf.pdf}}</ref> 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.)<ref name="Tech Ref">{{cite book |last1=Brunner |first1=Gary W. |title=HEC-RAS, River Analysis System Hydraulic Reference Manual |date=2024 |publisher=United States Army Corp of Engineers |location=Davis, CA |pages=520 |url=https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_Hydraulic_Reference_Manual_v6.6.pdf |access-date=23 January 2026}}</ref> The program is free to download from HEC, though there is no support provided for non-USACE users.<ref name="RAS Review"></ref>


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<ref name="HEC-2 to RAS" /><ref name="FEMA Software">{{cite web |title=Software for Flood Mapping |url=https://www.fema.gov/flood-maps/software |website=www.FEMA.gov |publisher=FEMA |access-date=23 January 2026}}</ref>. It is also used by hydraulic modelers for various applications worldwide,<ref name="RAS Review" /><ref name="Review of RAS Uses">{{cite journal |last1=Zaina |first1=Norsaliha Najwa |last2=Abu Talib |first2=Siti Hidayah |title=Review paper on applications of the HEC-RAS model for flooding, agriculture, and water quality simulation |journal=Water Practice and Technology |date=2024 |volume=19 |issue=7 |pages=2883–2900 |doi=10.2166/wpt.2024.173 |bibcode=2024WatPT..19.2883Z |url=https://iwaponline.com/wpt/article/19/7/2883/103280/Review-paper-on-applications-of-the-HEC-RAS-model |access-date=23 January 2026}} </ref>both in academia<ref name="Yang et al. (2023)">{{cite journal |last1=Yang |first1=Yiye |last2=Lu |first2=Zhong |last3=Ouyang |first3=Choajun |last4=Xie |first4=Hu |last5=Zhang |first5=Qin |title=Glacial Lake Outburst Flood Monitoring and Modeling through Integrating Multiple Remote Sensing Methods and HEC-RAS |journal=Remote Sensing |date=2023 |volume=15 |issue=22 |page=5327 |doi=10.3390/rs15225327 |doi-access=free |bibcode=2023RemS...15.5327Y }}</ref> and industry.<ref name="NC Sewer RAS">{{cite journal |last1=Bush |first1=Samual T. |last2=Dresback |first2=Kendra M. |last3=Szpilka |first3=Christine M. |last4=Kolar |first4=Randall L. |title=Use of 1D Unsteady HEC-RAS in a Coupled System for Compound Flood Modeling: North Carolina Case Study |journal=Journal of Marine Science and Engineering |date=2022 |volume=10 |issue=3 |page=306 |doi=10.3390/jmse10030306 |doi-access=free |bibcode=2022JMSE...10..306B }}</ref>
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<ref name="HEC-2 to RAS" /><ref name="FEMA Software">{{cite web |title=Software for Flood Mapping |url=https://www.fema.gov/flood-maps/software |website=www.FEMA.gov |publisher=FEMA |access-date=23 January 2026}}</ref>. It is also used by hydraulic modelers for various applications worldwide,<ref name="RAS Review" /><ref name="Review of RAS Uses">{{cite journal |last1=Zaina |first1=Norsaliha Najwa |last2=Abu Talib |first2=Siti Hidayah |title=Review paper on applications of the HEC-RAS model for flooding, agriculture, and water quality simulation |journal=Water Practice and Technology |date=2024 |volume=19 |issue=7 |pages=2883–2900 |doi=10.2166/wpt.2024.173 |bibcode=2024WatPT..19.2883Z |url=https://iwaponline.com/wpt/article/19/7/2883/103280/Review-paper-on-applications-of-the-HEC-RAS-model |access-date=23 January 2026|doi-access=free }} </ref> both in academia<ref name="Yang et al. (2023)">{{cite journal |last1=Yang |first1=Yiye |last2=Lu |first2=Zhong |last3=Ouyang |first3=Choajun |last4=Xie |first4=Hu |last5=Zhang |first5=Qin |title=Glacial Lake Outburst Flood Monitoring and Modeling through Integrating Multiple Remote Sensing Methods and HEC-RAS |journal=Remote Sensing |date=2023 |volume=15 |issue=22 |page=5327 |doi=10.3390/rs15225327 |doi-access=free |bibcode=2023RemS...15.5327Y }}</ref> and industry.<ref name="NC Sewer RAS">{{cite journal |last1=Bush |first1=Samual T. |last2=Dresback |first2=Kendra M. |last3=Szpilka |first3=Christine M. |last4=Kolar |first4=Randall L. |title=Use of 1D Unsteady HEC-RAS in a Coupled System for Compound Flood Modeling: North Carolina Case Study |journal=Journal of Marine Science and Engineering |date=2022 |volume=10 |issue=3 |page=306 |doi=10.3390/jmse10030306 |doi-access=free |bibcode=2022JMSE...10..306B |hdl=11244/335849 |hdl-access=free }}</ref>


== Program History ==
== Program history ==
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.<ref name="HEC-2 (1991)">{{cite book |last1=CEIWR-HEC |title=HEC-2 Water Surface Profiles User's Manual |date=1991 |publisher=United States Army Corp of Engineers |location=Davis, CA |page=1 |url=https://www.hec.usace.army.mil/publications/ComputerProgramDocumentation/HEC-2_UsersManual_(CPD-2a).pdf |access-date=23 January 2026}}</ref>
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.<ref name="HEC-2 (1991)">{{cite book |last1=CEIWR-HEC |title=HEC-2 Water Surface Profiles User's Manual |date=1991 |publisher=United States Army Corp of Engineers |location=Davis, CA |page=1 |url=https://www.hec.usace.army.mil/publications/ComputerProgramDocumentation/HEC-2_UsersManual_(CPD-2a).pdf |access-date=23 January 2026}}</ref>


The first version of HEC-RAS was released in July of 1995.<ref name="Tech Ref" /> Though one-dimensional HEC-RAS solves the same  equations as HEC-2, the computational routines and numerical methods are completely different.<ref name="Tech Ref" />
The first version of HEC-RAS was released in July of 1995.<ref name="Tech Ref" /> Though one-dimensional HEC-RAS solves the same  equations as HEC-2, the computational routines and numerical methods are completely different.<ref name="Tech Ref" />


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.<ref name="6.0 Release Notes">{{cite web |last1=HEC |title=HEC-RAS Release Notes 6.0 |url=https://www.hec.usace.army.mil/confluence/rasdocs/rasrn/6.0/new-features |website=HEC-RAS |publisher=United State Army Corp |access-date=23 January 2026}}</ref>
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.<ref name="6.0 Release Notes">{{cite web |last1=HEC |title=HEC-RAS Release Notes 6.0 |url=https://www.hec.usace.army.mil/confluence/rasdocs/rasrn/6.0/new-features |website=HEC-RAS |publisher=United States Army Corps of Engineers |access-date=23 January 2026}}</ref>


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|user interface]], new meshing methods, and an explicit solver.<ref name="Future of RAS">{{cite web |last1=Kennedy |first1=Alexander |title=Future of HEC-RAS |url=https://www.hec.usace.army.mil/confluence/hecnews/fall-2024/future-of-hec-ras |website=HEC Newsletter |publisher=United States Army Corp |access-date=23 January 2026}}</ref> The transition between an alpha version of HEC-RAS 2025 and an industry-ready version is expected to last several years.<ref name="Alpha Timeline">{{cite web |last1=HEC |title=RAS 2025 |url=https://www.hec.usace.army.mil/software/hec-ras/2025/ |website=HEC-RAS 2025 |publisher=United State Army Corp |access-date=23 January 2026}}</ref>
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|user interface]], new meshing methods, and an explicit solver.<ref name="Future of RAS">{{cite web |last1=Kennedy |first1=Alexander |title=Future of HEC-RAS |url=https://www.hec.usace.army.mil/confluence/hecnews/fall-2024/future-of-hec-ras |website=HEC Newsletter |publisher=United States Army Corp |access-date=23 January 2026}}</ref> The transition between an alpha version of HEC-RAS 2025 and an industry-ready version is expected to last several years.<ref name="Alpha Timeline">{{cite web |last1=HEC |title=RAS 2025 |url=https://www.hec.usace.army.mil/software/hec-ras/2025/ |website=HEC-RAS 2025 |publisher=United States Army Corps of Engineers |access-date=23 January 2026}}</ref>


== Functionality ==
== Capabilities ==
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.
As of the HEC-RAS 6.6 release, HEC-RAS seeks to support four major capabilities: 1D steady flow modeling; 1D or 2D unsteady flow modeling; sediment transport modeling; and 1D water-quality modeling.<ref name="Tech Ref" /> The major HEC-RAS features are discussed in more detail below.
[[File:1DRAS flood control channel.jpg|alt=Water is contained in the channel as seen in the cross-sections of the HEC-RAS model.|thumb|270x270px|A 1D HEC-RAS model of a flood control channel, with auto-generated cross-sections. ]]


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.
=== 1D Modeling ===
When modeling in 1D HEC-RAS, users define a river line along the [[Earth:Thalweg|thalweg]] of the primary watercourse and specify cross-sections across the channel, either by use of terrain data (such as LiDAR) or with exact elevations. Additional information, including peak discharge, Manning’s n of the channel, and specification of boundary conditions, is necessary for the model to run. <ref name="User's Manual">{{cite book |last1=Brunner |first1=Gary W. |url=https://www.hec.usace.army.mil/confluence/rasdocs/rasum/latest |title=HEC-RAS User's Manual |date=2024 |publisher=HEC |location=Davis, CA |access-date=23 January 2026}}</ref> HEC-RAS solves the [[Physics:One-dimensional Saint-Venant equations|one-dimensional Saint-Venant equations]], a simplification of the [[Navier-Stokes equations]],<ref name="Tech Ref" /> resulting in cross-sectionally averaged results. Various capabilities in the software allow for the modeling of bridges, culverts, levees, obstructions, ice impacts, and debris build-up.<ref name="User's Manual" />


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.
Though many industry users and regulatory interests are moving towards 2D analysis as standard,<ref name="FHWA Bridge">{{cite book |last1=Robinson |first1=Dusty |url=https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hif19061.pdf |title=Two-Dimensional Hydraulic Modeling for Highways in the River Environment |last2=Zundel |first2=Alan |last3=Kramer |first3=Casey |last4=Nelson |first4=Royd |last5=deRosset |first5=Will |last6=Hunt |first6=John |last7=Hogan |first7=Scott |last8=Lai |first8=Yong |date=2019 |publisher=Federal Highway Administration |location=Austin Texas |access-date=23 January 2026}}</ref> some applications still favor 1D analysis. These scenarios include very large river systems, or rivers with many structures (e.g., bridges and culverts), where flow is contained and primarily in a single direction. In these cases, a two dimensional model may take an unrealistic amount of time to run compared to the much less computationally complex one dimensional model.<ref name="2D User's Manual">{{cite book |last1=Brunner. |first1=Gary W. |url=https://www.hec.usace.army.mil/confluence/rasdocs/r2dum/latest |title=HEC-RAS 2D User's Manual |date=2024 |publisher=HEC |location=Davis, CA |access-date=23 January 2026}}</ref>


Version 5.0.7 as of March 2019 supports Windows 7, 8, 8.1, and 10 64-bit only.<ref name="Release 5.0.7">{{Cite web| title=HEC-RAS - River Analysis System | url=https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_5.0.7_Release_Notes.pdf | archive-url=https://web.archive.org/web/20200710214013/https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_5.0.7_Release_Notes.pdf | archive-date=2020-07-10}}</ref>  Version 6.0 and newer support 64-bit Windows 7-11,<ref>{{Cite web |title=HEC-RAS Release Notes |url=https://www.hec.usace.army.mil/confluence/rasdocs/rasrn/6.5 |access-date=2024-03-16 |website=www.hec.usace.army.mil}}</ref> and version 6.1 is available for Linux.<ref>[https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_610_Linux_Build_Release_Notes.pdf HEC-RAS 6.1 Linux Release Notes]</ref>
=== 2D Modeling ===
When modeling in 2D HEC-RAS, users define a mesh across their terrain data. Though the mesh is nominally rectangular, refinement tools such as breaklines allow the mesh to be composed of various nesting polygons of up to eight faces.<ref name="Tech Ref" /> Boundary conditions are used to allow flow to enter and leave the model. Inflow boundary conditions can utilize hydrographs or stage data, amongst other methods, while outflow boundary condition options include rating curve, normal depth, stage hydrograph, and flow hydrograph. <ref name="2D User's Manual" />
[[File:2D RAS.jpg|alt=A 2D HEC-RAS model of a river and floodplain, showing flood depth and the bridge.|thumb|356x356px|A 2D HEC-RAS model, with a flow hydrograph as an upstream boundary condition, models flow through a river floodplain before contracting at a bridge and the embankment. ]]
2D HEC-RAS solve can various forms of the depth-averaged Saint-Venant Equations, and allows the user to choose which equation set to utilize for modeling. The Diffusion Wave equation set drops the unsteady, advection, turbulence and Coriolis terms of the Saint-Venant equations, and increase computational efficiency for simple models.<ref name="Tech Ref" /> However, in certain situations (including modeling structures, highly dynamic flows, or superelevation), the more robust Shallow Water Equations (SWE) are recommended, though this tends to increase computation times. <ref name="2D User's Manual" /> When using SWE, the user can also chose to model turbulence, using either a conservative or non-conservative formulation.<ref name="2D User's Manual" />


== Applications ==
The 2D solver uses an implicit finite volume solution algorithm, and as of the 6.6 release, does not support GPU computing.<ref name="2D User's Manual" />
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 ==
Though 2D models are generally more accurate than 1D, especially for modeling complex floodplains and unconfined flow, they also are reliant on the assumption that flow varies significantly more horizontally than it does vertically.<ref name="FHWA Bridge" /> In situations that violate this assumption, such as vertical drops, complex structure hydraulics, or river bends, 2D models such as HEC-RAS may fail to accurately model fluid flow.<ref name="CFD in WR">{{cite journal |last1=Hajimirzaie |first1=Seyed |last2=Constantinescu |first2=George |last3=Liu |first3=Xiaofeng |last4=Stoesser |first4=Thorsten |last5=Zamani |first5=Kaveh |date=December 2022 |title=Computational Fluid Dynamics (CFD) Applications in Water-Resources Engineering |url=https://www.researchgate.net/publication/367591179_Computational_Fluid_Dynamics_CFD_Applications_in_Water-Resources_Engineering |journal=Journal of Irrigation and Drainage Engineering |volume=148 |issue=12 |access-date=26 March 2026}}</ref> In order to model these scenarios, [[Computational fluid dynamics|CFD]] solvers such as [[Software:OpenFOAM|OpenFOAM]] or [[Company:Flow Science, Inc.|Flow-3D Hydro]], amongst [[Physics:List of computational fluid dynamics software|others]] may be more appropriate choices.
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 [[Social:Public domain|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 ==
=== Distributed Modeling ===
Users may find numerical instability problems during unsteady analyses, especially in steep and/or highly dynamic rivers and streams.<ref>{{Cite web |title=Model Stability |url=https://www.hec.usace.army.mil/confluence/rasdocs/rasum/6.0/performing-a-1d-unsteady-flow-analysis/model-accuracy-stability-and-sensitivity/model-stability |access-date=2024-03-16 |website=www.hec.usace.army.mil}}</ref> 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 method|finite difference]] numerical solution schemes.
Since HEC-RAS 6.0, the software has had the capability to distributively hydraulic model utilizing the Rain-on-Grid feature. Utilizing provided rainfall data and an infiltration layer along with the terrain data, the software will simulate rainfall, losses, and runoff over the entire model area, rather than relying on inflows dictated at a boundary condition. Three loss methods are currently supported: [[Earth:Runoff curve number|NRCS Curve Number]], [[Earth:Infiltration (hydrology)#Green and Ampt|Green & Ampt]], and Deficit and Constant.<ref name="Tech Ref" />


== Version history ==
While distributed modeling has many advantages, including providing a better understanding of highly complex flow paths, longer runtimes and limitations of available loss methods in HEC-RAS are drawbacks.<ref name="ROG Guidance">{{cite web |last1=Hydrologic Engineering Center |last2=Juniata College |title=Watershed Scale Rain-on-Mesh Modeling in HEC-RAS |url=https://www.hec.usace.army.mil/confluence/rasdocs/hgt/files/latest/290456384/290456405/1/1742410606032/Watershed+Scale+Rain-on-Mesh+Modeling+in+HEC-RAS.pdf |access-date=26 March 2026 |publisher=United States Army Corps of Engineers}}</ref> Additionally, high resolution terrain data (typically better than 10 meter) is essential when developing a distributed hydraulic model.<ref name="ROG Guidance" />
The first version of HEC-RAS was released in 1995.<ref>{{Cite web|url=https://sciengsustainability.blogspot.com/2016/08/some-months-ago-new-version-of-hec-ras.html|title=Science Engineering & Sustainability: HEC-RAS evolution|website=Science Engineering & Sustainability|access-date=2019-03-24}}</ref> 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 [[Earth:Sediment|sediment]] transfer modeling capabilities.  
=== Sediment Transport Modeling ===
HEC-RAS is capable of modeling sediment either in 1D or, since 6.0, in 2D. Options are also available for modeling Non-Newtonian fluids, such as debris flows. The 1D sediment approach is based on HEC 6 and HEC 6T, which were developed by Tony Thomas for USACE.<ref name="1D Sed Users">{{cite web |last1=Hydraulic Engineering Center |title=1D Sediment Transport User's Manual |url=https://www.hec.usace.army.mil/confluence/rasdocs/rassed1d/1d-sediment-transport-user-s-manual |access-date=26 March 2026 |publisher=United States Army Corp of Enginners}}</ref> Sediment continuity is modeled using the [[Exner equation]], which HEC-RAS solves by computing a sediment transport capacity. Based on a comparison of capacity to sediment supply, a volume of sediment is either eroded or deposited.<ref name="1D Sed Tech">{{cite web |last1=Hydraulic Engineering Center |title=1D Sediment Transport Technical Reference Manual |url=https://www.hec.usace.army.mil/confluence/rasdocs/rassed1d/1d-sediment-transport-technical-reference-manual |publisher=United States Army Corp of Engineers}}</ref> Sediment data is entered as gradations, which the model then converts into volumes. Based on the results of the sediment transport model, the bed can either aggrade or degrade.


== GeoHECRAS ==
In 1D, the quasi-unsteady flow function simulates a hydrograph using a series of steady flow calculations, and is typically used to model sediment in an existing 1D model. As of 5.0, sediment transport is supported in 1D unsteady flow modeling.<ref name="1D Sed Users" /> Nine sediment transport functions are included in 1D, utilized to model sediment transport potential. Theses include Ackers and White, England and Hansen, Laursen-Copeland, Meyer-Peter and Müller (MPM), Toffaleti, MPM-Toffaleti, Yang, and Wilcock and Crowe. <ref name="1D Sed Tech" /> Selection of a sediment transport function depends on the bed material of the modeled reach.
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 [[Earth:River|river]] engineering studies.


Features related to HEC-RAS include:
In 2D, the sediment transport model is added to an existing 2D hydraulics model. The complex nature of sediment transport requires the use of the shallow water equation se. The conservative turbulence model was specifically developed for sediment transport applications. <ref name="2D Sed Ref">{{cite web |last1=Sanchez |first1=Alejandro |title=HEC-RAS 2D Sediment User Manual |url=https://www.hec.usace.army.mil/confluence/rasdocs/h2sd/ras2dsed/latest/introduction/report-documentation-page |access-date=26 March 2026 |publisher=United States Army Corp of Engineers}}</ref> In addition to the sediment transport functions available in 1D, 2D also supports Soulsby-van Rijn, Van Rijn, and Wu et al., and does not support MPM-Toffaleti.<ref name="2D Sed Tech">{{cite web |last1=Hydraulic Engineering Center |title=HEC-RAS 2D Sediment Technical Reference Manual |url=https://www.hec.usace.army.mil/confluence/rasdocs/d2sd/ras2dsedtr/latest/introduction |access-date=26 March 2026 |publisher=United States Army Corps of Engineers}}</ref>
* [[Undo]] and redo HEC-RAS editing
* [[Multiple document interface]] (MDI) of HEC-RAS projects
* Use of [[Software:AutoCAD|AutoCAD]] and [[Software:MicroStation|MicroStation]] CAD drawings and terrain surfaces
* Use of GIS databases
* Automated cross section generation
* Automated production of floodplain maps
* Design and analysis of roadway crossings ([[Engineering:Bridge|bridge]] and [[Engineering:Culvert|culvert]])
* Adaptive 2D [[Mesh generation|mesh generation]]


== WMS ==
== Applications & Users ==
{{main|Software:WMS (hydrology software)}}
HEC-RAS is widely used in both academic and industry applications, as well as by USACE for official applications.<ref>{{Cite web |title=HEC-RAS |url=https://www.hec.usace.army.mil/confluence/cweyr/latest/hec-ras-308222644.html |access-date=2026-03-26 |website=www.hec.usace.army.mil}}</ref> HEC-RAS is approved by FEMA for use in floodplain mapping in the United States, and is widely used in modern floodplain studies.<ref>{{Cite web |last=Federal Emergency Management Agency |title=Software for Flood Mapping |url=https://www.fema.gov/flood-maps/software |access-date= |website=FEMA}}</ref> Outside of [[Engineering:Hydraulic engineering|hydraulic engineering]] applications such as modeling culverts, bridges, levees, and floodplains, HEC-RAS has been utilized to model lava flows,<ref>{{Cite journal |last=Prawira |first=Akbar Bagus |last2=Hidayah |first2=Entin |last3=Wiyono |first3=Retno Utami Agung |date=2024-03-22 |title=Mapping the Lava Flood Hazard Using the Flood Discharge Approach and 2D Hydrodynamic Modeling at the Rejali River, Mount Semeru |url=https://jurnal.ugm.ac.id/v3/JCEF/article/view/8463 |journal=Journal of the Civil Engineering Forum |pages=139–150 |doi=10.22146/jcef.8463 |issn=2549-5925}}</ref> dam breaches,<ref>{{Cite journal |last=Phyo |first=Aung Pyae |last2=Yabar |first2=Helmut |last3=Richards |first3=Delmaria |date=2023-12-01 |title=Managing dam breach and flood inundation by HEC-RAS modeling and GIS mapping for disaster risk management |url=https://www.sciencedirect.com/science/article/pii/S2666016423001925 |journal=Case Studies in Chemical and Environmental Engineering |volume=8 |article-number=100487 |doi=10.1016/j.cscee.2023.100487 |issn=2666-0164}}</ref> debris flows,<ref>{{Cite journal |last=Pramesthi |first=Zelandi Yura |last2=Harlan |first2=Dhemi |last3=Irianto |first3=Eko Winar |date=2024 |editor-last=Setiyo |editor-first=M. |editor2-last=Rozaki |editor2-first=Z. |editor3-last=Setiawan |editor3-first=A. |editor4-last=Yuliastuti |editor4-first=F. |editor5-last=Pambuko |editor5-first=Z.B. |editor6-last=Edhita Praja |editor6-first=C.B. |editor7-last=Soraya Dewi |editor7-first=V. |editor8-last=Muliawanti |editor8-first=L. |title=Modeling of 2D Hec-Ras Simulation on Debris Flow Analysis on Morphological Changes of the Omu River, Sigi Regency, Central Sulawesi |url=https://www.e3s-conferences.org/10.1051/e3sconf/202450003041 |journal=E3S Web of Conferences |volume=500 |pages=03041 |doi=10.1051/e3sconf/202450003041 |issn=2267-1242}}</ref> [[Earth:Glacial lake outburst flood|glacial lake outburst floods]],<ref name="Yang et al. (2023)" /> and coupled with water quality tools to model pollutants two-dimensionally.<ref>{{Cite journal |last=Shabani |first=Afshin |last2=Woznicki |first2=Sean A. |last3=Mehaffey |first3=Megan |last4=Butcher |first4=Jonathan |last5=Wool |first5=Tim A. |last6=Whung |first6=Pai‐Yei |date=December 2021 |title=A coupled hydrodynamic ( HEC‐RAS 2D ) and water quality model ( WASP ) for simulating flood‐induced soil, sediment, and contaminant transport |url=https://onlinelibrary.wiley.com/doi/10.1111/jfr3.12747 |journal=Journal of Flood Risk Management |language=en |volume=14 |issue=4 |doi=10.1111/jfr3.12747 |issn=1753-318X |pmc=8811800 |pmid=35126656}}</ref>
[[Software: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:
Extension softwares developed for use by civil engineers, such as GeoHEC-RAS and WMS, provide additional visualization and data processing capabilities to HEC-RAS users.


* Using feature objects (centerline, cross section lines) and a TIN to develop the geometry of a HEC-RAS model.
HEC-RAS is free to download from USACE, and is supported on Windows 10/11 64-bit operating systems, as well as Linux systems.<ref>{{Cite web |last=Hydraulic Engineering Center |date=2026 |title=HEC-RAS Downloads |url=https://www.hec.usace.army.mil/software/hec-ras/download.aspx |access-date=2026-03-25}}</ref>
* 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==
==See also==
*Hydraulic engineering
*HEC-HMS
*HEC-HMS


Latest revision as of 05:00, 11 April 2026

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

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]

Capabilities

As of the HEC-RAS 6.6 release, HEC-RAS seeks to support four major capabilities: 1D steady flow modeling; 1D or 2D unsteady flow modeling; sediment transport modeling; and 1D water-quality modeling.[3] The major HEC-RAS features are discussed in more detail below.

Water is contained in the channel as seen in the cross-sections of the HEC-RAS model.
A 1D HEC-RAS model of a flood control channel, with auto-generated cross-sections.

1D Modeling

When modeling in 1D HEC-RAS, users define a river line along the thalweg of the primary watercourse and specify cross-sections across the channel, either by use of terrain data (such as LiDAR) or with exact elevations. Additional information, including peak discharge, Manning’s n of the channel, and specification of boundary conditions, is necessary for the model to run. [12] HEC-RAS solves the one-dimensional Saint-Venant equations, a simplification of the Navier-Stokes equations,[3] resulting in cross-sectionally averaged results. Various capabilities in the software allow for the modeling of bridges, culverts, levees, obstructions, ice impacts, and debris build-up.[12]

Though many industry users and regulatory interests are moving towards 2D analysis as standard,[13] some applications still favor 1D analysis. These scenarios include very large river systems, or rivers with many structures (e.g., bridges and culverts), where flow is contained and primarily in a single direction. In these cases, a two dimensional model may take an unrealistic amount of time to run compared to the much less computationally complex one dimensional model.[14]

2D Modeling

When modeling in 2D HEC-RAS, users define a mesh across their terrain data. Though the mesh is nominally rectangular, refinement tools such as breaklines allow the mesh to be composed of various nesting polygons of up to eight faces.[3] Boundary conditions are used to allow flow to enter and leave the model. Inflow boundary conditions can utilize hydrographs or stage data, amongst other methods, while outflow boundary condition options include rating curve, normal depth, stage hydrograph, and flow hydrograph. [14]

A 2D HEC-RAS model of a river and floodplain, showing flood depth and the bridge.
A 2D HEC-RAS model, with a flow hydrograph as an upstream boundary condition, models flow through a river floodplain before contracting at a bridge and the embankment.

2D HEC-RAS solve can various forms of the depth-averaged Saint-Venant Equations, and allows the user to choose which equation set to utilize for modeling. The Diffusion Wave equation set drops the unsteady, advection, turbulence and Coriolis terms of the Saint-Venant equations, and increase computational efficiency for simple models.[3] However, in certain situations (including modeling structures, highly dynamic flows, or superelevation), the more robust Shallow Water Equations (SWE) are recommended, though this tends to increase computation times. [14] When using SWE, the user can also chose to model turbulence, using either a conservative or non-conservative formulation.[14]

The 2D solver uses an implicit finite volume solution algorithm, and as of the 6.6 release, does not support GPU computing.[14]

Though 2D models are generally more accurate than 1D, especially for modeling complex floodplains and unconfined flow, they also are reliant on the assumption that flow varies significantly more horizontally than it does vertically.[13] In situations that violate this assumption, such as vertical drops, complex structure hydraulics, or river bends, 2D models such as HEC-RAS may fail to accurately model fluid flow.[15] In order to model these scenarios, CFD solvers such as OpenFOAM or Flow-3D Hydro, amongst others may be more appropriate choices.

Distributed Modeling

Since HEC-RAS 6.0, the software has had the capability to distributively hydraulic model utilizing the Rain-on-Grid feature. Utilizing provided rainfall data and an infiltration layer along with the terrain data, the software will simulate rainfall, losses, and runoff over the entire model area, rather than relying on inflows dictated at a boundary condition. Three loss methods are currently supported: NRCS Curve Number, Green & Ampt, and Deficit and Constant.[3]

While distributed modeling has many advantages, including providing a better understanding of highly complex flow paths, longer runtimes and limitations of available loss methods in HEC-RAS are drawbacks.[16] Additionally, high resolution terrain data (typically better than 10 meter) is essential when developing a distributed hydraulic model.[16]

Sediment Transport Modeling

HEC-RAS is capable of modeling sediment either in 1D or, since 6.0, in 2D. Options are also available for modeling Non-Newtonian fluids, such as debris flows. The 1D sediment approach is based on HEC 6 and HEC 6T, which were developed by Tony Thomas for USACE.[17] Sediment continuity is modeled using the Exner equation, which HEC-RAS solves by computing a sediment transport capacity. Based on a comparison of capacity to sediment supply, a volume of sediment is either eroded or deposited.[18] Sediment data is entered as gradations, which the model then converts into volumes. Based on the results of the sediment transport model, the bed can either aggrade or degrade.

In 1D, the quasi-unsteady flow function simulates a hydrograph using a series of steady flow calculations, and is typically used to model sediment in an existing 1D model. As of 5.0, sediment transport is supported in 1D unsteady flow modeling.[17] Nine sediment transport functions are included in 1D, utilized to model sediment transport potential. Theses include Ackers and White, England and Hansen, Laursen-Copeland, Meyer-Peter and Müller (MPM), Toffaleti, MPM-Toffaleti, Yang, and Wilcock and Crowe. [18] Selection of a sediment transport function depends on the bed material of the modeled reach.

In 2D, the sediment transport model is added to an existing 2D hydraulics model. The complex nature of sediment transport requires the use of the shallow water equation se. The conservative turbulence model was specifically developed for sediment transport applications. [19] In addition to the sediment transport functions available in 1D, 2D also supports Soulsby-van Rijn, Van Rijn, and Wu et al., and does not support MPM-Toffaleti.[20]

Applications & Users

HEC-RAS is widely used in both academic and industry applications, as well as by USACE for official applications.[21] HEC-RAS is approved by FEMA for use in floodplain mapping in the United States, and is widely used in modern floodplain studies.[22] Outside of hydraulic engineering applications such as modeling culverts, bridges, levees, and floodplains, HEC-RAS has been utilized to model lava flows,[23] dam breaches,[24] debris flows,[25] glacial lake outburst floods,[6] and coupled with water quality tools to model pollutants two-dimensionally.[26]

Extension softwares developed for use by civil engineers, such as GeoHEC-RAS and WMS, provide additional visualization and data processing capabilities to HEC-RAS users.

HEC-RAS is free to download from USACE, and is supported on Windows 10/11 64-bit operating systems, as well as Linux systems.[27]

See also

  • HEC-HMS

References

  1. ↑ 1.0 1.1 Dewberry & Davis, LLC. "HEC-RAS Procedures for HEC-2 Modelers". Federal Emergency Management Agency. https://www.fema.gov/sites/default/files/documents/fema_floodplain-modeling-manual_hec-ras-procedures-hec-2-modelers_4-2002.pdf. 
  2. ↑ 2.0 2.1 2.2 More, D. D.; Gavit, B. K.; Nandgude, S. B. (2024). "Hydrologic Engineering Centers-River Analysis System (HEC-RAS) - A Review". Journal of Agricultural Research and Technology 49 (1): 139–150. doi:10.56228/JART.2024.49120. https://www.jart.co.in/uploads/168/15441_pdf.pdf. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Brunner, Gary W. (2024). HEC-RAS, River Analysis System Hydraulic Reference Manual. Davis, CA: United States Army Corp of Engineers. pp. 520. https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_Hydraulic_Reference_Manual_v6.6.pdf. Retrieved 23 January 2026. 
  4. ↑ "Software for Flood Mapping". FEMA. https://www.fema.gov/flood-maps/software. 
  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. doi:10.2166/wpt.2024.173. Bibcode: 2024WatPT..19.2883Z. https://iwaponline.com/wpt/article/19/7/2883/103280/Review-paper-on-applications-of-the-HEC-RAS-model. Retrieved 23 January 2026. 
  6. ↑ 6.0 6.1 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. doi:10.3390/rs15225327. Bibcode: 2023RemS...15.5327Y. 
  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. doi:10.3390/jmse10030306. Bibcode: 2022JMSE...10..306B. 
  8. ↑ CEIWR-HEC (1991). HEC-2 Water Surface Profiles User's Manual. Davis, CA: United States Army Corp of Engineers. p. 1. https://www.hec.usace.army.mil/publications/ComputerProgramDocumentation/HEC-2_UsersManual_(CPD-2a).pdf. Retrieved 23 January 2026. 
  9. ↑ HEC. "HEC-RAS Release Notes 6.0". United States Army Corps of Engineers. https://www.hec.usace.army.mil/confluence/rasdocs/rasrn/6.0/new-features. 
  10. ↑ Kennedy, Alexander. "Future of HEC-RAS". United States Army Corp. https://www.hec.usace.army.mil/confluence/hecnews/fall-2024/future-of-hec-ras. 
  11. ↑ HEC. "RAS 2025". United States Army Corps of Engineers. https://www.hec.usace.army.mil/software/hec-ras/2025/. 
  12. ↑ 12.0 12.1 Brunner, Gary W. (2024). HEC-RAS User's Manual. Davis, CA: HEC. https://www.hec.usace.army.mil/confluence/rasdocs/rasum/latest. Retrieved 23 January 2026. 
  13. ↑ 13.0 13.1 Robinson, Dusty; Zundel, Alan; Kramer, Casey; Nelson, Royd; deRosset, Will; Hunt, John; Hogan, Scott; Lai, Yong (2019). Two-Dimensional Hydraulic Modeling for Highways in the River Environment. Austin Texas: Federal Highway Administration. https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hif19061.pdf. Retrieved 23 January 2026. 
  14. ↑ 14.0 14.1 14.2 14.3 14.4 Brunner., Gary W. (2024). HEC-RAS 2D User's Manual. Davis, CA: HEC. https://www.hec.usace.army.mil/confluence/rasdocs/r2dum/latest. Retrieved 23 January 2026. 
  15. ↑ Hajimirzaie, Seyed; Constantinescu, George; Liu, Xiaofeng; Stoesser, Thorsten; Zamani, Kaveh (December 2022). "Computational Fluid Dynamics (CFD) Applications in Water-Resources Engineering". Journal of Irrigation and Drainage Engineering 148 (12). https://www.researchgate.net/publication/367591179_Computational_Fluid_Dynamics_CFD_Applications_in_Water-Resources_Engineering. Retrieved 26 March 2026. 
  16. ↑ 16.0 16.1 Hydrologic Engineering Center; Juniata College. "Watershed Scale Rain-on-Mesh Modeling in HEC-RAS". United States Army Corps of Engineers. https://www.hec.usace.army.mil/confluence/rasdocs/hgt/files/latest/290456384/290456405/1/1742410606032/Watershed+Scale+Rain-on-Mesh+Modeling+in+HEC-RAS.pdf. 
  17. ↑ 17.0 17.1 Hydraulic Engineering Center. "1D Sediment Transport User's Manual". United States Army Corp of Enginners. https://www.hec.usace.army.mil/confluence/rasdocs/rassed1d/1d-sediment-transport-user-s-manual. 
  18. ↑ 18.0 18.1 Hydraulic Engineering Center. "1D Sediment Transport Technical Reference Manual". United States Army Corp of Engineers. https://www.hec.usace.army.mil/confluence/rasdocs/rassed1d/1d-sediment-transport-technical-reference-manual. 
  19. ↑ Sanchez, Alejandro. "HEC-RAS 2D Sediment User Manual". United States Army Corp of Engineers. https://www.hec.usace.army.mil/confluence/rasdocs/h2sd/ras2dsed/latest/introduction/report-documentation-page. 
  20. ↑ Hydraulic Engineering Center. "HEC-RAS 2D Sediment Technical Reference Manual". United States Army Corps of Engineers. https://www.hec.usace.army.mil/confluence/rasdocs/d2sd/ras2dsedtr/latest/introduction. 
  21. ↑ "HEC-RAS". https://www.hec.usace.army.mil/confluence/cweyr/latest/hec-ras-308222644.html. 
  22. ↑ Federal Emergency Management Agency. "Software for Flood Mapping". https://www.fema.gov/flood-maps/software. 
  23. ↑ Prawira, Akbar Bagus; Hidayah, Entin; Wiyono, Retno Utami Agung (2024-03-22). "Mapping the Lava Flood Hazard Using the Flood Discharge Approach and 2D Hydrodynamic Modeling at the Rejali River, Mount Semeru". Journal of the Civil Engineering Forum: 139–150. doi:10.22146/jcef.8463. ISSN 2549-5925. https://jurnal.ugm.ac.id/v3/JCEF/article/view/8463. 
  24. ↑ Phyo, Aung Pyae; Yabar, Helmut; Richards, Delmaria (2023-12-01). "Managing dam breach and flood inundation by HEC-RAS modeling and GIS mapping for disaster risk management". Case Studies in Chemical and Environmental Engineering 8. doi:10.1016/j.cscee.2023.100487. ISSN 2666-0164. https://www.sciencedirect.com/science/article/pii/S2666016423001925. 
  25. ↑ Pramesthi, Zelandi Yura; Harlan, Dhemi; Irianto, Eko Winar (2024). Setiyo, M.; Rozaki, Z.; Setiawan, A. et al.. eds. "Modeling of 2D Hec-Ras Simulation on Debris Flow Analysis on Morphological Changes of the Omu River, Sigi Regency, Central Sulawesi". E3S Web of Conferences 500: 03041. doi:10.1051/e3sconf/202450003041. ISSN 2267-1242. https://www.e3s-conferences.org/10.1051/e3sconf/202450003041. 
  26. ↑ Shabani, Afshin; Woznicki, Sean A.; Mehaffey, Megan; Butcher, Jonathan; Wool, Tim A.; Whung, Pai‐Yei (December 2021). "A coupled hydrodynamic ( HEC‐RAS 2D ) and water quality model ( WASP ) for simulating flood‐induced soil, sediment, and contaminant transport" (in en). Journal of Flood Risk Management 14 (4). doi:10.1111/jfr3.12747. ISSN 1753-318X. PMID 35126656. PMC 8811800. https://onlinelibrary.wiley.com/doi/10.1111/jfr3.12747. 
  27. ↑ Hydraulic Engineering Center (2026). "HEC-RAS Downloads". https://www.hec.usace.army.mil/software/hec-ras/download.aspx. 



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