HEC-RAS is a computer program that models the hydraulics of water flow through natural rivers and other channels. Prior to the recent 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. The program was developed by the United States Army Corps of Engineers 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 developed the River Analysis System (RAS) to aid hydraulic engineers in channel flow analysis and floodplain determination. It includes numerous data entry capabilities, hydraulic analysis components, data storage and management capabilities, and graphing and reporting capabilities.

3D view


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.[1]


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.


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.


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[2]. This HEC-RAS 1.0 solves the same numerical equation of the 1968 HEC-2.

Version Release Date
HEC-RAS 1.0 1995
HEC-RAS 2.0 April, 1997
HEC-RAS 2.2 October, 1998
HEC-RAS 3.0 April, 2003
HEC-RAS 3.1.1 May, 2003
HEC-RAS 3.1.2 June, 2004
HEC-RAS 3.1.3 May, 2005
HEC-RAS 4.0 (Beta) November, 2006
HEC-RAS 4.0.0 March, 2008
HEC-RAS 4.1 January, 2010
HEC-RAS 5.0 February, 2016
HEC-RAS 5.0.1 April, 2016
HEC-RAS 5.0.3 September, 2016
HEC-RAS 5.0.4 May, 2018
HEC-RAS 5.0.5 June, 2018
HEC-RAS 5.0.7 March, 2019[1]

WMS (Watershed Modeling System)

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:

  • Use feature objects (centerline, cross section lines) and a TIN to develop the geometry of a HEC-RAS model.
  • Edit, merge, and create cross sections in a database for use with HEC-RAS and other hydraulic models.
  • Delineate flood plains from water surface elevation data. Water surface elevations can be computed by HEC-RAS, defined interactively, or imported from a file.
  • Link 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


  1. ^ a b https://www.hec.usace.army.mil/software/hec-ras/documentation/HEC-RAS_5.0.7_Release_Notes.pdf
  2. ^ "Science Engineering & Sustainability: HEC-RAS evolution". Science Engineering & Sustainability. Retrieved 2019-03-24.

External links


Aquaveo is an environmental and water resources 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.

Environmental 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 required for cultural and spiritual needs assumes significance. Through implementation of environmental flows, water managers strive to achieve a flow regime, or pattern, that provides for human uses and maintains the essential processes required to support healthy river ecosystems. Environmental flows do not necessarily require restoring the natural, pristine flow patterns that would occur absent human development, use, and diversion but, instead, are intended to produce a broader set of values and benefits from rivers than from management focused strictly on water supply, energy, recreation, or flood control.

Rivers are parts of integrated systems that include floodplains and riparian corridors. Collectively these systems provide a large suite of benefits. However, the world's rivers are increasingly being altered through the construction of dams, diversions, and levees. More than half of the world's large rivers are dammed, a figure that continues to increase. Almost 1,000 dams are planned or under construction in South America and 50 new dams are planned on China's Yangtze River alone. Dams and other river structures change the downstream flow patterns and consequently affect water quality, temperature, sediment movement and deposition, fish and wildlife, and the livelihoods of people who depend on healthy river ecosystems. Environmental flows seek to maintain these river functions while at the same time providing for traditional offstream benefits.


A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health.

Flooding may occur as an overflow of water from water bodies, such as a river, lake, or ocean, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals.

Floods can also occur in rivers when the flow rate exceeds the capacity of the river channel, particularly at bends or meanders in the waterway. Floods often cause damage to homes and businesses if they are in the natural flood plains of rivers. While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is usually flat and fertile and because rivers provide easy travel and access to commerce and industry.

Some floods develop slowly, while others such as flash floods can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighborhood or community, or very large, affecting entire river basins.

Flood Modeller Pro

Flood Modeller Pro is a computer program that simulates the flow of water through river channels and across floodplains using a range of one- and two-dimensional hydraulic solvers, developed by Jacobs. The software incorporates a user interface for building, running and viewing the results of models, including a GIS map interface. Flood Modeller Pro has a free counterpart (Flood Modeller Free), and is a part of the Flood Modeller Suite range of software products and web applications.

Flood Modeller Pro was unveiled 19 November 2014 at Jacobs' International Flood Management Conference in London.Flood Modeller Pro is Jacobs' next generation flood modelling software and is the successor to ISIS, which was in development for almost 40 years.

Giant current ripples

Giant current ripples are active channel topographic forms up to 20 m high, which develop within near-talweg areas of the main outflow valleys created by glacial lake outburst floods. Giant current ripple marks are morphologic and genetic macroanalogues of small current ripples formed in sandy stream sediments.

The giant current ripple marks are important depositional forms in diluvial plain and mountain scablands.

Hydraulic engineering

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 movement of the fluids. This area of civil engineering is intimately related to the design of bridges, dams, channels, canals, and levees, and to both sanitary and environmental engineering.

Hydraulic engineering is the application of the principles of fluid mechanics to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water. Before beginning a hydraulic engineering project, one must figure out how much water is involved. The hydraulic engineer is concerned with the transport of sediment by the river, the interaction of the water with its alluvial boundary, and the occurrence of scour and deposition. "The hydraulic engineer actually develops conceptual designs for the various features which interact with water such as spillways and outlet works for dams, culverts for highways, canals and related structures for irrigation projects, and cooling-water facilities for thermal power plants."

Hydraulic head

Hydraulic head or piezometric head is a specific measurement of liquid pressure above a vertical datum.It is usually measured as a liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer. In an aquifer, it can be calculated from the depth to water in a piezometric well (a specialized water well), and given information of the piezometer's elevation and screen depth. Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum. The hydraulic head can be used to determine a hydraulic gradient between two or more points.

Hydraulic jumps in rectangular channels

Hydraulic jump in a rectangular channel, also known as classical jump, is a natural phenomenon that occurs whenever flow changes from supercritical to subcritical flow. In this transition, the water surface rises abruptly, surface rollers are formed, intense mixing occurs, air is entrained, and often a large amount of energy is dissipated. In other words, a hydraulic jump happens when a higher velocity, v1, supercritical flow upstream is met by a subcritical downstream flow with a decreased velocity, v2, and sufficient depth. Numeric models created using the standard step method or HEC-RAS are used to track supercritical and subcritical flows to determine where in a specific reach a hydraulic jump will form.

There are common hydraulic jumps that occur in everyday situations such as during the use of a household sink. There are also man-made hydraulic jumps created by devices like weirs or sluice gates. In general, a hydraulic jump may be used to dissipate energy, to mix chemicals, or to act as an aeration device.To produce equations describing the jump, since there is an unknown energy loss, there is a need to apply conservation of momentum. To develop this equation, a general situation in which there may or may not be an energy loss between upstream and downstream, and there may or may not be some obstacle on which there is a drag force Pf is considered. however, for a simple or classic hydraulic jump the force per unit width(Pf) equals 0. From there the momentum equation, and the conjugate depths equation can be derived.

Madidi National Park

Madidi (Spanish pronunciation: [maˈðiði]) is a national park in the upper Amazon river basin in Bolivia. Established in 1995, it has an area of 18,958 square kilometres, and, along with the nearby protected (though not necessarily contiguous) areas Manuripi-Heath, Apolobamba, and (across the border in Peru) the Manu Biosphere Reserve, Madidi is part of one of the largest protected areas in the world.Ranging from the glacier-covered peaks of the high Andes Mountains to the tropical rainforests of the Tuichi River, Madidi and its neighbors are recognized as one of the planet's most biologically diverse regions. In particular, Madidi protects parts of the Bolivian Yungas and Bolivian montane dry forests ecoregions.The Madidi National Park can be reached from Rurrenabaque if you cross the Beni River with the small passenger ferry over to San Buenaventura.

The local people who have migrated here from the Andean highlands speak the Quechua language. The cultures who find their origin here are the Tacana, the Mosete, the Tsimane, and the Ese Ejja, all of which have their own language which pertains to one language group.Some ecolodges are found in and around the Madidi National Park. The oldest and best known is Chalalan Ecolodge in Chalalán on the Tuichi River, a successful community-based enterprise that generates significant economic benefits to indigenous communities (Malky et al., 2007).

National Flood Insurance Program

The National Flood Insurance Program (NFIP) is a program created by the Congress of the United States in 1968 through the National Flood Insurance Act of 1968 (P.L. 90-448). U.S. Congress has the twofold purposes of the NFIP to share the risk of flood losses through flood insurance and to reduce flood damages by restricting floodplain development. The program enables property owners in participating communities to purchase insurance protection, administered by the government, against losses from flooding, and requires flood insurance for all loans or lines of credit that are secured by existing buildings, manufactured homes, or buildings under construction, that are located in a community that participates in the NFIP. U.S. Congress limits the availability of National Flood Insurance to communities that adopt adequate land use and control measures with effective enforcement provisions to reduce flood damages by restricting development in areas exposed to flooding.

This NFIP is designed to provide an insurance alternative to disaster assistance to meet the escalating costs of repairing damage to buildings and their contents caused by floods. As of August 2017, the program insured about 5 million homes (down from about 5.5 million homes in April 2010), the majority of which are in Texas and Florida. The cost of the insurance program was fully covered by its premiums until the end of 2004, but has had to steadily borrow funds since (primarily due to Hurricane Katrina and Hurricane Sandy), accumulating $25 billion of debt by August 2017.

Nexus Tools Platform

The Nexus Tools Platform or NTP is a web-based inventory platform that allows an interactive comparison of environmental models in a statistical way. Developed by the UNU Institute for Integrated Management of Material Fluxes and of Resources (UNU-FLORES), the platform helps a user to analyze existing modelling tools related to environmental resource management and associated nexus perspectives, such as a Water-Energy-Food Nexus. As a result, the user can select the most appropriate tools to fit the research needs.

Shallow water equations

The shallow water equations 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). The shallow water equations in unidirectional form are also called Saint-Venant equations, after Adhémar Jean Claude Barré de Saint-Venant (see the related section below).

The equations are derived from depth-integrating the Navier–Stokes equations, in the case where the horizontal length scale is much greater than the vertical length scale. Under this condition, conservation of mass implies that the vertical velocity scale of the fluid is small compared to the horizontal velocity scale. It can be shown from the momentum equation that vertical pressure gradients are nearly hydrostatic, and that horizontal pressure gradients are due to the displacement of the pressure surface, implying that the horizontal velocity field is constant throughout the depth of the fluid. Vertically integrating allows the vertical velocity to be removed from the equations. The shallow water equations are thus derived.

While a vertical velocity term is not present in the shallow water equations, note that this velocity is not necessarily zero. This is an important distinction because, for example, the vertical velocity cannot be zero when the floor changes depth, and thus if it were zero only flat floors would be usable with the shallow water equations. Once a solution (i.e. the horizontal velocities and free surface displacement) has been found, the vertical velocity can be recovered via the continuity equation.

Situations in fluid dynamics where the horizontal length scale is much greater than the vertical length scale are common, so the shallow water equations are widely applicable. They are used with Coriolis forces in atmospheric and oceanic modeling, as a simplification of the primitive equations of atmospheric flow.

Shallow water equation models have only one vertical level, so they cannot directly encompass any factor that varies with height. However, in cases where the mean state is sufficiently simple, the vertical variations can be separated from the horizontal and several sets of shallow water equations can describe the state.

Sherry Chen (hydrologist)

Sherry Chen (Chinese: 陈霞芬) was a hydrologist working in the National Weather Service (NWS) office in Wilmington, Ohio. She was accused of spying and arrested in October 2014. In March 2015, federal prosecutors dropped all charges against her without explanation before the trial began. Even with the case dropped, Sherry was fired from her job in March 2016 for many of the same reasons that she was originally prosecuted for. In October 2016, Sherry filed a case of wrongful employment termination to the Merit Systems Protection Board (MSPB). In April 2018, MSPB issued a decision stating that Sherry was "a victim of gross injustice" and ordered the Department Of Commerce (NWS is an agency under DOC) to give her job back with back pay. In June 2018, DOC filed an appeal of the MSPB decision. Unfortunately, MSPB has lacked a quorum to process appeals and its backlog has grown to 1,600 cases by the end of October 2018. In January 2019, with her case in an indefinite limbo, Sherry's legal team filed a civil lawsuit against the U.S. government for the malicious prosecution and false arrest in the United States District Court for the Southern District of Ohio. The case is now pending.

Standard step method

The standard step method (STM) is a computational technique utilized to estimate one-dimensional surface water profiles in open channels with gradually varied flow under steady state conditions. It uses a combination of the energy, momentum, and continuity equations to determine water depth with a given a friction slope , channel slope , channel geometry, and also a given flow rate. In practice, this technique is widely used through the computer program HEC-RAS, developed by the US Army Corps of Engineers Hydrologic Engineering Center (HEC).

United States Army Corps of Engineers

The United States Army Corps of Engineers (USACE) is a U.S. federal agency under the Department of Defense and a major Army command made up of some 37,000 civilian and military personnel, making it one of the world's largest public engineering, design, and construction management agencies. Although generally associated with dams, canals and flood protection in the United States, USACE is involved in a wide range of public works throughout the world. The Corps of Engineers provides outdoor recreation opportunities to the public, and provides 24% of U.S. hydropower capacity.

The corps' mission is to "Deliver vital public and military engineering services; partnering in peace and war to strengthen our Nation's security, energize the economy and reduce risks from disasters."Their most visible missions include:

Planning, designing, building, and operating locks and dams. Other civil engineering projects include flood control, beach nourishment, and dredging for waterway navigation.

Design and construction of flood protection systems through various federal mandates.

Design and construction management of military facilities for the Army, Air Force, Army Reserve and Air Force Reserve and other Defense and Federal agencies.

Environmental regulation and ecosystem restoration.

WMS (hydrology software)

WMS (Watershed Modeling System) is a watershed computer simulation and modeling software application from Aquaveo. It was originally created in the early 1990s at the Engineering Computer Graphics Laboratory at Brigham Young University.

The software supports a number of hydraulic and hydrologic models that can be used to create drainage basin simulations.

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