• Steady and unsteady flow modeling
• Mixed flow regime analysis, allowing analysis of both subcritical and supercritical flow regimes in a single computer run
• Bridge and culvert analysis and design, including FHWA culvert routines for elliptical, arch, and semi-circular culverts
• Multiple bridge and culvert openings of different types and sizes at a roadway crossing
• Bridge scour computations following FHWA Publication HEC-18
• Bridge design editor and graphical cross section editor
• FEMA Floodplain and floodway encroachment modeling
• Multiple profile computations
• Lateral flow, split flow, overbank dendritic networks
• Sediment Transport/Movable Bed Modeling
• Sediment Impact Analysis Methods (SIAM)
• Water Quality Capabilities (Temperature Modeling)
• Tidal boundary conditions
• Reservoir and spillway analysis
• Levee overtopping
• User Defined Rules for Controlling Gate Operations
• Pumping of flooded areas
• Modeling Pressurized Pipe Flow
• Geometric model schematic can be placed over background maps and incorporate clickable scanned images of structures
• Inline weirs and gated spillways analysis, including both radial and sluice type gates and Ogee, broad and sharp crested weirs
• Tributary/diversion flow network capabilities, allowing for fully looped river system analysis in which reaches can be subdivided and combined
• Quasi 2-D velocity distributions
• X-Y-Z (pseudo 3-D) graphics of the river system

Ease of Use

The user interacts with HEC-RAS through a graphical user interface (GUI). The main focus in the design of the interface was to make it easy to use the software, while still maintaining a high level of efficiency for the user. The interface provides for the following functions:

• File Management
• Data Entry and Editing
• Hydraulic Analyses
• Tabulation and Graphical Displays of Input and Output Data
• Reporting Facilities
• Context Sensitive Help

What´s New

The latest version HEC-RAS includes the following new features:

• 
  Sediment Transport/Movable Bed Modeling
• Sediment Impact Analysis Methods (SIAM)
• Water Quality Capabilities:

• Temperature modeling
• Transport and fate of a limited set of constituents

• User-Defined Rules for Controlling Gate Operations
• Modeling Pressurized Pipe Flow
• Pump Station Override Rules
• Hager’s Lateral Weir equation
• New Channel Design/Modification Tools
• Geo-Referencing Tools
• New Gate Types
• New Functionality for Lateral Weirs
• Additional Graphical Outputs
• Shortcut Keys for Graphics
• Revised User Manual and Help System

Steady Flow Water Surface Profiles

This component of the modeling system is intended for calculating water surface profiles for steady gradually varied flow. The system can handle a full network of channels, a dendritic system, or a single river reach. The steady flow component is capable of modeling subcritical, supercritical, and mixed flow regimes water surface profiles.

The basic computational procedure is based on the solution of the one-dimensional energy equation. Energy losses are evaluated by friction (Manning’s equation) and contraction/expansion (coefficient multiplied by the change in velocity head). The momentum equation may be used in situations where the water surface profile is rapidly varied. These situations include mixed flow regime calculations (i.e. hydraulic jumps), hydraulics of bridges, and evaluating profiles at river confluences (stream junctions).

The effects of various obstructions such as bridges, culverts, weirs, and structures in the flood plain may be considered in the computations. The steady flow system is designed for application in flood plain management and flood insurance studies to evaluate floodway encroachments. Also, capabilities are available for assessing the change in water surface profiles due to channel improvements, and levees.

Special features of the steady flow component include: multiple plan analyses; multiple profile computations; multiple bridge and/or culvert opening analyses; and split flow optimization.

Unsteady Flow Simulation

This component of the HEC-RAS modeling system is capable of simulating one-dimensional unsteady flow through a full network of open channels. The HEC-RAS unsteady flow equation solver can perform mixed flow regime computations (i.e., subcritical, supercritical, hydraulic jumps, and draw downs).

The hydraulic calculations for cross-sections, bridges, culverts, and other hydraulic structures that were developed for the steady flow component are also incorporated into the unsteady flow module.

Special features of the unsteady flow component include:

• Dam break analysis
• Levee breaching and overtopping
• Pumping stations
• Navigation dam operations
• Pressurized pipe systems

This component of the modeling system is intended for the simulation of one-dimensional sediment transport/movable boundary calculations resulting from scour and deposition over moderate time periods (typically years, although applications to single flood events are possible).

The sediment transport potential is computed by grain size fraction, thereby allowing the simulation of hydraulic sorting and armoring. Major features include the ability to model a full network of streams, channel dredging, various levee and encroachment alternatives, and the use of several different equations for the computation of sediment transport.

The model is designed to simulate long-term trends of scour and deposition in a stream channel that might result from modifying the frequency and duration of the water discharge and stage, or modifying the channel geometry. This system can be used to evaluate deposition in reservoirs, design channel contractions required to maintain navigation depths, predict the influence of dredging on the rate of deposition, estimate maximum possible scour during large flood events, and evaluate sedimentation in fixed channels.

Water Quality Analysis

This component of HEC-RAS is intended to allow the user to perform riverine water quality analyses. An advection-dispersion module is included, adding the capability to model water temperature. This new module uses the QUICKEST-ULTIMATE explicit numerical scheme to solve the one-dimensional advection-dispersion equation using a control volume approach with a fully implemented heat energy budget. Transport and fate of a limited set of water quality constituents is also provided. The currently supported water quality constituents include:

• Temperature
• Dissolved Nitrogen (NO3-N, NO2-N, NH4-N, and Org-N)
• Dissolved Phosphorus (PO4-P and Org-P)
• Algae
• Dissolved Oxygen (DO)
• Carbonaceous Biological Oxygen Demand (CBOD)

Water Quality Analysis

This component of HEC-RAS is intended to allow the user to perform riverine water quality analyses. An advection-dispersion module is included, adding the capability to model water temperature. This new module uses the QUICKEST-ULTIMATE explicit numerical scheme to solve the one-dimensional advection-dispersion equation using a control volume approach with a fully implemented heat energy budget. Transport and fate of a limited set of water quality constituents is also provided. The currently supported water quality constituents include:

• Temperature
• Dissolved Nitrogen (NO3-N, NO2-N, NH4-N, and Org-N)
• Dissolved Phosphorus (PO4-P and Org-P)
• Algae
• Dissolved Oxygen (DO)
• Carbonaceous Biological Oxygen Demand (CBOD)

Data Storage and Management

Data Storage is accomplished through the use of “flat” files (ASCII and binary), as well as the HEC-DSS. User input data are stored in flow files under separate categories of project, plan, geometry, steady flow, unsteady flow, and sediment data. Output data is predominantly stored in separate binary files. Data can be transferred between HEC-RAS and other programs by utilizing the HEC-DSS.

Data management is accomplished through the user interface. The modeler is requested to enter a single filename for the project being developed. Once the project filename is entered, all other files are automatically created and named by the interface as needed. The interface provides for renaming and deletion of files on a project-by-project basis.

Graphics and Reporting

Graphics include X-Y plots of the river system schematic, cross-sections, profiles, rating curves, hydrographs, and many other hydraulic variables. A three-dimensional plot of multiple cross-sections is also provided. Tabular output is available. Users can select from pre-defined tables or develop their own customized tables. All graphical and tabular output can be displayed on the screen, sent directly to a printer (or plotter), or passed through the Windows Clipboard to other software, such as a word-processor or spreadsheet.

HEC-RAS includes reporting facilities that allow for printed output of input data as well as output data. Reports can be customized as to the amount and type of information desired.

HEC-RAS Extensive Help

Wherever you are in BOSS HEC-RAS, extensive context-sensitive help is available to assist you through any difficulty. The professional documentation includes discussions on the theoretical basis of the model, data requirements, optional capabilities, bridge and culvert hydraulics, floodway computations, as well as a complete description on how to use the software.

Built-in Model Checker

Included with HEC-RAS is a built-in model checker. The HEC-RAS model checker will check over the specified input data. If it encounters an error with the input data, it will explain what is wrong and how you can correct it. The HEC-RAS model checker can be thought of as an expert modeler, pointing out any input data errors contained in the model.