Importing HEC-2 Data Into HECRAS
What you need to know…
L-1621/Klipsch98
1
What you should know first…

Not all HEC-2 options have a parallel in
HEC-RAS
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Computation of Manning’s n values from high
watermarks.
Archiving (AC)
Free format (FR)
These options are ignored by the importer, so data sets which
contain them can still be imported.
Some HEC-2 options are available, but are not
imported

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L-1621/Klipsch98
Split flow
Vertical variation of Manning’s n values
Storage outflow for HEC-HMS
2

All imported data should be reviewed carefully for
accuracy and completeness, especially...
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Special bridges (SB) and culverts (SC)
Normal bridges (X2, BT)
Encroachments and floodway determination (X3, ET)
Ineffective flow areas (X3)
Channel improvements and modifications (CI)
How the HEC-2 cross sections are Identified…
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L-1621/Klipsch98
By river mile or station?
By an arbitrary numbering scheme?
Are the section ID numbers increasing from downstream to
upstream?
Are there duplicate section ID numbers?
3
The Import Process – Step 1

Create a new project …
L-1621/Klipsch98
4

Give your new project a title and a unique file
name …

Confirm your title and file name…
L-1621/Klipsch98
5
The Import Process – Step 2

After a new project has been opened, select
Import HEC-2 data… from the File menu.
L-1621/Klipsch98
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
Select the HEC-2 file to be imported…

Tell HEC-RAS how to identify the cross sections
as they are imported…
L-1621/Klipsch98
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
Use the Geometry and Steady Flow Editors to
review the imported data*.
– The note below will appear whenever an HEC-2 data
set that contains bridge or culvert data is imported.
This is a reminder that bridges and culverts are not
handled in the same way in HEC-RAS as they are in
HEC-2. You will need to check that the data has been
interpreted correctly.
L-1621/Klipsch98
8
Computational Differences
between HEC2 & HEC-RAS
Cross Section Conveyance Calculations
 Critical Depth Calculations
 Bridge Hydraulics

L-1621/Klipsch98
9
• Cross Section Conveyance Calculations
– HEC-RAS Method: subdivisions at n-value
break points.
n1
A1 P1
n2
A2 P2
n3
Ach Pch
Klob = K1 + K2
n4
A3 P3
Krob = K3
Kch
L-1621/Klipsch98
10
– HEC-2 Method: subdivisions at every ground
point.
n1
A2P2
n3
n2
A3 P3
A4 P4
Ach Pch
n4
A5 P5
A6 P6
A7 P7
A1 P1
A8 P8
Krob = K5 + K6 + K7 + K8
Klob = K1 + K2 + K3 + K4
Kch
L-1621/Klipsch98
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– To choose the conveyance subdivision method to use,
select Steady Flow Analysis… from the Simulate
menu:
L-1621/Klipsch98
12
– Select Conveyance Calculations… from the Options
menu of the Steady Flow Analysis editor
– And select your method…
L-1621/Klipsch98
13
• Critical Depth Calculations
HEC-RAS
– Parabolic Method
– Secant Method
Used if parabolic
method…
 Does not converge.
 Finds a value at the
top of a levee or at an
ineffective flow
elevation.
L-1621/Klipsch98
HEC-2
– Parabolic Method
Uses first local
minimum it finds.
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– To choose, first select Critical Depth Computation
Method… from the Options menu of the Steady
Flow Analysis editor:
– Then select the method:
L-1621/Klipsch98
15
• Bridge Hydraulics
HEC-RAS
– 4 Low Flow Methods
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Energy
Momentum
Yarnell
WSPRO
– 2 Independent High
Flow Methods
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L-1621/Klipsch98
Energy
Pressure &/or Weir
HEC-2
– 2 Low Flow Methods
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Normal (Energy)
Special (Yarnell)
– 2 High Flow Methods
dependent upon
Low Flow Method
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
Energy
Pressure & Weir
16
• HEC-2’s Special Bridge Method – Low Flow
HEC-RAS
– All methods (including
Yarnell’s) use actual
bridge geometry to
determine flow area
– Each pier is defined
and located
individually
– Bridge opening is
determined by
geometry.
L-1621/Klipsch98
HEC-2
– Trapezoidal
approximation of bridge
opening used to
determine flow area
– Single equivalent width
pier centered within
trapezoid
– Net flow area input for
pressure flow.
17
• HEC-2’s Special Bridge Method – Pressure Flow
HEC-RAS
– Fully submerged or
upstream-only
submerged.
– Bridge opening
based on geometry.
– Weir profile is the
union of the cross
section and bridge
deck.
L-1621/Klipsch98
HEC-2
– Fully submerged
condition assumed
– Net flow area input for
pressure flow.
– Weir profile is defined
by BT or X2 data – not
cross section.
18
• HEC-2’s Normal Bridge Method
HEC-RAS
– Piers are defined
separate from the
deck or ground.
– The deck data must
have a spatial
relationship to the
cross section(s) but
need not match
ground points.
L-1621/Klipsch98
HEC-2
– Piers were defined as
part of the cross section
data or deck data.
– Each BT data point was
required to match a
cross section GR point.
19
• Culvert Hydraulics
HEC-RAS
HEC-2
– Wide variety of shapes
available:
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Box
Pipe
Arch
– Pipe
– Low & High Profile
– ConSpan

– 2 Shapes available:
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Box
Pipe
– Multiple barrels of only
one shape and size can be
used at a single crossing.
Ellipse
– Vertical
– horizontal
– Multiple culverts of
different shapes and sizes
can be placed at a single
crossing.
L-1621/Klipsch98
20
• Floodway Determination
HEC-RAS
– Methods 1-3
– Method 4

0.01 ft. accuracy
– Method 5

Optimizes for Water
Surface or Energy or
Both.
– Floodway
determination is
independent of
blocked obstructions.
L-1621/Klipsch98
HEC-2
– Methods 1-3
– Method 4

Parabolic Interpolation
– Method 5

Optimizes for a change
in Water Surface
– Method 6

Optimizes for a change
in Energy
– X3 encroachments
override ET floodway
determination.
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What can HEC-RAS do that
HEC-2 cannot?
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Mixed Flow
Multiple Openings
Momentum computation at bridges and junctions
Complex dendritic streams and looped networks
Blocked Ineffective Areas
Normal Ineffective Areas at any station
Blocked Obstructions
Levees
Inline and Lateral weirs and gated spillways
Geometric cross section interpolation
L-1621/Klipsch98
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