
HECRAS is designed to perform one and twodimensional hydraulic calculations for a full network of natural and
constructed channels. The following is a description of the major capabilities of HECRAS.
User Interface
The user interacts with HECRAS 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
 Inundation mapping and animations of water propagation
 Reporting Facilities
 Context Sensitive Help
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Hydraulic Analysis Components
The HECRAS system contains several river analysis components for: (1) steady flow water surface profile
computations; (2) one and twodimensional unsteady flow simulation; (3) movable boundary sediment transport
computations; and (4) water quality analysis. A key element is, that all four components use a common geometric
data representation and common geometric and hydraulic computation routines. In addition to these river analysis components,
the system contains several hydraulic design features that can be invoked once the basic water surface profiles are computed.
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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 onedimensional 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).
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One and TwoDimensional Unsteady Flow Simulation
This component of the HECRAS modeling system is capable of simulating onedimensional; twodimensional; and
combined one/twodimensional unsteady flow through a full network of open channels, floodplains, and alluvial
fans. The unsteady flow component can be used to performed subcritical, supercritical, and mixed flow regime
(subcritical, supercritical, hydraulic jumps, and draw
downs) calculations in the unsteady flow computations module.
The hydraulic calculations for crosssections, bridges, culverts, and other hydraulic structures that were developed for the steady flow component were incorporated into the unsteady flow module.
Special features of the unsteady flow component include: extensive hydraulic structure capabilities Dam break analysis; levee breaching and overtopping; Pumping stations; navigation dam operations; pressurized pipe systems; automated calibration features; User defined rules; and combined one and twodimensional unsteady flow modeling.
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Steady Transport/Movable Boundary Computations
This component of the modeling system is intended for the simulation of onedimensional 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 longterm 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.
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Water Quality Analysis
This component of the modeling system is intended to allow the user to perform riverine water quality analyses. An advectiondispersion module is included with this
version of HEC–RAS, adding the capability to model water temperature. This new module uses the QUICKESTULTIMATE explicit numerical scheme to solve the onedimensional
advectiondispersion 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 now also available in HECRAS. The currently available water quality constituents are: Dissolved Nitrogen (NO3N, NO2N, NH4N, and OrgN); Dissolved
Phosphorus (PO4P and OrgP); Algae; Dissolved Oxygen (DO); and Carbonaceous Biological Oxygen Demand (CBOD).
For details on how to use the water quality capabilities in HECRAS, please review Chapter 19 of the User's Manual.
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Data Storage and Management
Data storage is accomplished through the use
of "flat" files (ASCII and binary), the HECDSS
(Data Storage System), and HDF5 (Hierarchical
Data Format, Version 5). User input data are
stored in flat files under separate categories of
project, plan, geometry, steady flow, unsteady
flow, quasisteady flow, sediment data, and
water quality information. Output data is
predominantly stored in separate binary files
(HEC and HDF5). Data can be transferred
between HECRAS and other programs by
utilizing the HECDSS.
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, moving, and deletion of files
on a projectbyproject basis.
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Graphics and Reporting
Graphics include XY plots of the river system schematic, crosssections, profiles, rating curves, hydrographs,
and inundation mapping. A threedimensional plot of multiple crosssections is also provided. Inundation mapping
is accomplished in the HECRAS Mapper portion of the software. Inundation maps can also be animated, and
contain multiple background layers (terrain, aerial photography, etc…). Tabular output is available. Users can
select from predefined 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 wordprocessor or spreadsheet.
Reporting facilities 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.
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RAS Mapper
HECRAS has the capability to perform inundation mapping of water surface profile results directly from HECRAS.
Using the HECRAS geometry and computed water surface profiles, inundation depth and floodplain boundary
datasets are created through the RAS Mapper. Additional geospatial data can be generated for analysis of
velocity, shear stress, stream power, ice thickness, and floodway encroachment data. In order to use the RAS
Mapper for analysis, you must have a terrain model in the binary raster floatingpoint format (.flt). The resultant
depth grid is stored in the .flt format while the boundary dataset is store in ESRI's Shapefile format for use with
geospatial software.
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