HEC-RAS is a

computer program A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components. A computer program ...

that models the

hydraulics Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counte ...

water flow Environmental flows describe the quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems and the human livelihoods and well being that depend on these ecosystems. In the Indian context river flows requir ...

through natural

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...

s and other channels. 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 Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

transfer modeling capabilities. The program was developed by the

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

in order to manage the rivers, harbors, and other public works under their jurisdiction; it has found wide acceptance by many others since its public release in 1995. The Hydrologic Engineering Center (HEC) in

Davis, California Davis is the most populous city in Yolo County, California. Located in the Sacramento Valley region of Northern California, the city had a population of 66,850 in 2020, not including the on-campus population of the University of California, Davi ...

, developed the River Analysis System (RAS) to aid

hydraulic engineers Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the mov ...

in channel flow analysis and

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

determination. It includes numerous data entry capabilities, hydraulic analysis components, data storage and management capabilities, and graphing and reporting capabilities.

Functionality

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 The shallow-water equations (SWE) are a set of hyperbolic partial differential equations (or parabolic if viscous shear is considered) that describe the flow below a pressure surface in a fluid (sometimes, but not necessarily, a free surface). T ...

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.https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_5.0.7_Release_Notes.pdf

Usages

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 lood insurancestudies 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

HEC-RAS has merits, notably its support by the

US Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

, the future enhancements in progress, and its acceptance by many government agencies and private firms. It is in the

public domain The public domain (PD) consists of all the creative work to which no exclusive intellectual property rights apply. Those rights may have expired, been forfeited, expressly waived, or may be inapplicable. Because those rights have expired, ...

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

Users may find numerical instability problems during unsteady analyses, especially in steep and/or highly dynamic rivers and streams. It is often possible to use HEC-RAS to overcome instability issues on river problems.

Version history

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

GeoHECRAS

GeoHECRAS is a 2D/3D visualization and editing data wrapper to the HEC-RAS software and used for

flood control Flood control methods are used to reduce or prevent the detrimental effects of flood waters."Flood Control", MSN Encarta, 2008 (see below: Further reading). Flood relief methods are used to reduce the effects of flood waters or high water level ...

and flood mitigation engineering studies, including production of

Federal Emergency Management Agency The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Ex ...

flood hazard maps and other

engineering studies. Features related to HEC-RAS include: * Undo and redo HEC-RAS editing *

Multiple document interface A multiple-document interface (MDI) is a graphical user interface in which multiple windows reside under a single parent window. Such systems often allow child windows to embed other windows inside them as well, creating complex nested hierarchies ...

(MDI) of HEC-RAS projects * Use of

AutoCAD AutoCAD is a commercial computer-aided design (CAD) and drafting software application. Developed and marketed by Autodesk, AutoCAD was first released in December 1982 as a desktop app running on microcomputers with internal graphics controllers. ...

and 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 (

bridge A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

and culvert) * Adaptive 2D

mesh generation Mesh generation is the practice of creating a mesh, a subdivision of a continuous geometric space into discrete geometric and topological cells. Often these cells form a simplicial complex. Usually the cells partition the geometric input domain. ...

WMS

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 Aquaveo is a modeling software company based in Provo, Utah that develops software used to model and simulate groundwater, watershed, and surface water resources. Its main software products include SMS, GMS, WMS, and Arc Hydro Groundwater. Hist ...

was funded primarily by The

United States Army Corps of Engineers , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

. 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.

References

External links

HEC-RAS home page
{{Webarchive, url=https://web.archive.org/web/20190307033408/http://www.hec.usace.army.mil/software/hec-ras , date=2019-03-07 at the US Army Corps of Engineers, Hydrologic Engineering Center
An output video of a flood analysis done with HEC-RAS and visualization in ArcGIS

GeoHECRAS Homepage
at CivilGEO Hydraulic engineering Scientific simulation software Hydrology software