HEC-RAS is a computer program that models the hydraulics of water flow through natural rivers and other channels. The program is 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 program was developed by the US Department of Defense, 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.

1. By Karan Tyagi

2.  Stands for Hydrologic Engineering Centre
(Based in California, USA)
 RAS stands for River Analysis System.

3.  HEC-RAS is a computer program that models the
hydraulics of water flow through
natural rivers and other channels. The program is
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 program
was developed by the US Department of Defense,
Army Corps of Engineers in order to manage the
rivers, harbors, and other public works under
their jurisdiction; It was developed in 1995 and
has found wide acceptance in hydrologic
community since.

4.  The Hydrologic Engineering Center[1] (HEC)
in Davis, California developed the River
Analysis System (RAS) to help 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.

5.  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.

6.  For unsteady flow, HEC-RAS solves the full,
dynamic, 1-Dimensional Saint Venant
Equation using an implicit, finite difference
method.
 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.

7.  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: design and analysis
of bridge and culvert and channel
modification studies. It can also be used for
dam breach analysis.

8.  Necessary for planning,
flood risk reduction,
design, environmental
impact assessment and
mitigation, restoration
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9.  Velocity
 Depth
 Shear
 Width
 Area
 etc
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10.  1D River Hydraulics
 Graphical User Interface
 Steady & Unsteady Flow
 Bridges, Culverts, Dams,
weirs, levees, gates, etc…
 Data storage/management
 Graphics, Tabular Output
& Reporting
 GeoRas – ArcGIS
 More coming………
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12.  Geometry
◦ Cross Section
◦ Spacing
◦ Structures
◦ Manning’s n
 Flows
◦ Calibration Data
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13. 9/8/2013

14.  Graphical
 Tabular
 Profile
 Section
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15. 9/8/2013

16. From NRCS workshop by Reep, 2004
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17. From NRCS workshop by Reep, 2004
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18.  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 support 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.

19.  Aquaterra
 Aquaterra is a professional software for canals
and river engineering works design. Seamless
integration in CAD environment makes it really
easy to learn and use. Engineers use Aquaterra to
create detailed designs as well as for conceptual
studies and designs. HEC-RAS interface is
intended for communication between CAD
environment and HEC-RAS. This module prepare
the HEC-RAS geometric input file based on cross
sections, Manning coefficient data and transfer
the resulting water levels back to Aquaterra.

20.  ArcView
 HEC-RAS can also be used in the GIS program,
ArcView (With 3-D analyst and spatial analyst
extensions). ArcView can read-in AutoCAD
drawings for backgrounds and can create a DTM.
In a similar way to river CAD, GEO-RAS can be
used to create cross sections and other
geometrical data for use in HEC-RAS and can be
used to export water surface data from HEC-RAS
back into ArcView to create flood maps with
depths and extents of flooding.

21.  AutoCAD
 HEC-RAS can be used along with AutoCAD. A
digital terrain model (DTM) can be
constructed in AutoCAD and sections can be
cut from the DTM and imported into HEC-
RAS.

22.  RiverCAD
 RiverCAD by BOSS International Inc. supports
the latest version of HEC-RAS and HEC-2[ and
is a standalone AutoCAD compatible
application.
 (needed: impartial review of this commercial
product)

23.  WMS (Watershed Modeling System) provides
pre and post-processing tools for use with
HEC-RAS. The development of WMS was
funded primarily by The United States Army
Corps of Engineers. It is a commercial
software.

24.  Public Domain/Free/Widely used
 Supported by Corps of Engineers
 Continuing Improvement
◦ 2-D capabilities being developed
◦ Expected by end of 2012
 Graphical Abilities
 Good Documentation
 Training Available
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