Culvert Scour Assessment
Eames Creek
Site Information
Site Location:
Coast Range, Upper Siuslaw Basin, Wolf Cr Trib, ~0.6hr from Eugene
Year Installed:
Pre-1987
Lat/Long:
123°27’43.0”W
43°55’53.1”N
Watershed Area (mi2):
5.53
Stream Slope (ft/ft)1: 0.0083
Channel Type:
Pool-riffle
Bankfull Width (ft): 31 ft
Survey Date:
March 20, 2007
1
Water surface slope extending up to 20 channel widths up and downstream of crossing.
Culvert Information
Culvert Type:
Bottomless arch
Culvert Material:Annular CMP
Culvert Width:
13 ft
Outlet Type:
Mitered
Culvert Length:
55 ft
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.0003
Culvert Bed Slope: 0.0075
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.42
Alignment Conditions: Culvert moderately off-line with natural channel. Culvert should be at more of
an angle to the road to reduce the bend at culvert inlet.
Bed Conditions: Scoured to sandstone bedrock.
Pipe Condition: Three pieces of large wood at inlet could contribute to capacity and scour issues.
Some undercutting has occurred at right bank footing at downstream end of pipe. The base (spread)
footing is compromised in some areas.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
5-year
10-year
50-year
100-year
78
180
311
486
613
919
1060
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull
elevations.
2
A—130
Eames
Buck Creek
Site Evaluations
Points represent survey points
Figure 1—Plan view map.
Buck
Eames
Creek
Creek
A—131
A—131
Culvert Scour Assessment
History
An Eames Creek culvert was included in the
1987 Western Federal Lands Highway Division
“Oregon Culvert Fish Passage Survey”; but
from the location information and photographs
provided, it was impossible to tell which of two
nearby culverts was analyzed in the study.
Site Description
The Eames Creek culvert is a bottomless
arch with mitered ends that sits on a concrete
foundation. The channel bed is sandstone
bedrock. Three large logs have become lodged
between the left bank upstream of the crossing
and the inlet to the pipe. Additional smaller debris
has been deposited around these pieces. Scour
around the logs is apparent, notably in the form of
a scour pool which extends from the upstream of
the culvert through the inlet around the rootwad
of one of the logs. Downstream of the influence
of the wood, the channel consists of a bedrock
(sandstone) glide. Small amounts of sand were
deposited along the lower velocity margins of the
culvert, but little to no gravels were present.
Log and rock grade control structures beginning
roughly 215 feet upstream of the inlet restricted
the location and length of the upstream
representative reach to that section of channel
immediately upstream of the culvert. The
upstream representative reach consists of deep
long pools with short, well-defined riffle units.
The bed material in the channel is predominately
gravels and cobbles with a significant presence
of sand and fines. Fines line the banks and
cover the bars. A few fallen trees, as a result of
bank erosion along the outside of a bend, have
resulted in a small in-channel wood jam.
upstream representative reach. No downstream
representative reach was established due to
the uncharacteristic reach downstream followed
by the upstream, potential backwater, effects
of another culvert. Two representative cross
sections were taken through the culvert; one
through the scour pool and the other through the
glide. One additional cross section was surveyed
upstream to characterize the inlet as well as the
contraction of flow. Another two cross sections
were surveyed downstream of the culvert to
characterize the outlet and the expansion of flow.
In the upstream representative reach,
representative cross sections were taken through
a riffle and a pool. Two additional sections were
surveyed to characterize the upstream and
downstream ends of the reach.
Profile Analysis Segment Summary
The profile analysis resulted in a total of five
profile segments. There was only one suitable
representative profile segment, located in the
upstream channel. The culvert consisted of
two profile segments, the upper one extending
well upstream through the inlet transition
area. The gradients of the culvert segments
differed from the representative profile segment
by greater than 20 percent but less than 40
percent. Because of the low slope and similar
channel types, the two culvert segments were
believed to be a reasonable comparison with
the representative segment. The downstream
transition segment was also compared to the
upstream representative profile segment. There
was no separate profile segment for the upstream
transition. The upstream culvert segment
represents conditions within the culvert and in the
upstream transition area that is affected by the
culvert.
Survey Summary
Ten cross sections and a longitudinal profile
were surveyed along Eames Creek in March
2007 to characterize the culvert and an
A—132
Eames
Buck Creek
Site Evaluations
Scour Conditions
Predicted conditions
Observed conditions
Cross-section characteristics – The culvert has a
large effect on cross-section flow characteristics
throughout the entire reach. The profile segments
in the natural channel cannot be considered good
reference conditions because they are impacted
by backwater effects from the culvert. Because of
the backwater impacts, flow geometry changes
dramatically from the upstream reach, through the
culvert, and into the downstream reach (figures 5
through 9 and 12 through 17).
Footing scour – The culvert has a 22-inch-wide
spread footing that sites on top of the bedrock
bed. An 18-inch-wide stem wall rises from the
spread footing. The spread footing is scoured and
undermined in a number of locations, including
the upstream end right bank for 6-foot length
(undercut depth 4 inches) and the downstream
end right bank for 3- to 4-foot length (undercut
depth 4 inches). In these cases it appears
the sandstone bedrock has been scoured out
beneath the footing at these locations. The
concrete footings themselves also show minor
signs of scouring.
Culvert bed adjustment – The culvert and
culvert bed are both very near to zero slope. It is
unknown whether streambed material was placed
in the structure during construction.
Profile characteristics – The profile has a uniform
slope through the crossing but drops off at a
steeper gradient beginning 50 feet downstream of
the outlet (figure 2).
Residual depths – The one culvert residual depth
(in segment C) is just below the lower range of
those in the corresponding profile segment (figure
21).
Substrate – The culvert bed consists of
sandstone bedrock with only small occurrences
of sand and fine gravels. The bed downstream of
the culvert is also primarily bedrock with patches
of sand and gravels. Bed material distributions
in the upstream reference reach are very poorly
graded with high sand content.
Buck
Eames
Creek
Creek
Shear stress – Due to backwater effects, the
culvert has a large effect on shear stress in
the upstream and downstream channel, and
these segments cannot be considered suitable
reference conditions. The backwater reduces the
energy slope upstream of the inlet and therefore
reduced shear stress. Shear stress increases
moderately within the culvert and then increases
dramatically downstream of the outlet because of
the sharp increase in energy slope (figure 10).
Excess shear – The excess shear analysis shows
very little excess shear in the upstream channel
because of the low shear stress values that result
from the culvert backwater (figure 20). Excess
shear could not be calculated in the culvert
because of a lack of mobile bed material.
Velocity – Due to backwater effects, the culvert
has a large effect on velocity in the upstream and
downstream channel, and these segments cannot
be considered suitable reference conditions. The
backwater reduces the velocity upstream of the
inlet (figure 11). Velocity increases within the
culvert and then increases dramatically at the
outlet and just downstream as the flow passes
through critical depth.
A—133
A—133
Culvert Scour Assessment
Scour summary
Hydraulic model results indicate that above
the Q2, the entire upstream reference reach is
backwatered by the culvert. The comparable
slope segment in the upstream reach (E) is
therefore not a suitable natural analog for the
culvert reach. This limits the ability to evaluate
culvert conditions in relation to natural channel
conditions.
Severe backwatered conditions are a result of
a combination of a low gradient reach and a
significantly undersized culvert (less than half of
bankfull width). These characteristics along with
the recruitment and stabilization of large logs at
the inlet of the crossing have resulted in scour.
The culvert alignment may also be contributing
to scour; the channel takes a sharp bend just
upstream of the inlet and flow is concentrated
along the left bank at the inlet area. Concrete
footings have been scoured away and undercut
through the scouring of the sandstone bedrock.
Additionally, the base footing has been scoured
along the downstream and upstream right edge
of the pipe. It is unknown whether streambed
material was originally placed in the pipe during
construction; current hydraulic conditions will
not allow material to remain in the pipe. Culvert
hydraulics may also be responsible for the lack
of streambed material in the reach downstream
of the outlet. The sand deposits upstream of the
culvert are a result of backwater influence.
AOP Conditions
Cross-section complexity – The sum of squared
height differences in the culvert cross sections
are either greater than (upstream cross section)
or lower than (downstream cross section) those
found in the natural channel (table 3).
A—134
Profile complexity – Vertical sinuosity in the
culvert is similar to that in the natural channel
(table 4).
Depth distribution – There is less channel margin
habitat in the culvert compared to the channel at
the 25 percent Q2 (table 5).
Habitat units – The culvert has much less habitat
in pools (33 percent compared to 67 percent)
than the upstream channel (table 6).
Residual depths – The one culvert residual depth
(in segment C) is just below the lower range of
those in the corresponding profile segment (figure
21).
Substrate – The culvert bed consists of
sandstone bedrock with only small occurrences
of sand and fine gravels. The bed downstream of
the culvert is also primarily bedrock with patches
of sand and gravels. Bed material distributions
in the upstream reference reach are very poorly
graded with high sand content.
Large woody debris – There were three pieces
of LWD present in the upstream portion of the
culvert (table 8). The wood in the culvert posed a
plugging and scour risk to the culvert. The culvert
was not large enough to transport this size of
material through the pipe without risk of plugging.
The representative channel had high LWD
abundance. LWD formed small steps and scour
pools in the channel outside the crossing and
played a primary role in habitat-unit creation and
complexity. Wood drop structures were present
upstream of the representative channel.
Eames
Buck Creek
Site Evaluations
AOP summary
Although the complexity metrics do not capture
it, site observations indicate that the bedrock
bed of the culvert has much less complexity
than the natural channel upstream of the culvert.
Observations also suggest that complexity in
the culvert is similar to the downstream channel
that is also dominated by bedrock. There is
some LWD at the inlet that would provide habitat
complexity and velocity refuge, but the potential
risk of culvert plugging probably outweighs these
benefits.
The culvert is generally considered a poor design
with respect to fish passage, with very little
shallow channel margin habitat available and
very little velocity refuge such as what is provided
by substrate and pools and wood in the natural
channel (except for some LWD near the inlet).
The super-critical flow near the culvert outlet
(which modeling shows occurs even at 25 percent
Q2) and associated high velocity and shear stress
suggest that fish passage may be impaired
at high flows. At low flows, shallow sheet flow
Buck
Eames
Creek
Creek
over bedrock may present passage limitations.
There are no streambanks to concentrate flows
for passage or to allow for passage of terrestrial
organisms.
Design Considerations
This installation exhibits poor conditions with
respect to scour and AOP. The footings are
being undermined in places, there is no natural
streambed material in the pipe, and AOP
conditions are likely impaired. A larger culvert
with greater capacity would reduce the backwater
effects of the culvert and would prevent the
high shear stress and velocity that occur within
and at the outlet area of the pipe. It may also
allow for bed material to remain within the pipe.
Constructing banks using stable bed elements
(i.e., boulders) within the culvert would protect the
footings from being undermined by scour of the
sandstone bedrock and would allow for passage
of terrestrial organisms. A longer culvert that is
more in line with the original stream channel may
reduce the incidence of inlet scour.
A—135
A—135
A—136
Relative elevation (ft)
111
450
A
350
XS 1
R epres en ta tiv e
C h a n n el S eg men t
E
E
E
C u lv ert S eg men t
C
D
D o w n s trea m T ra n s itio n
B
Table 1—Segment comparisons
B
300
XS 2
0 .0 0 6
0 .0 0 9
0 .0 0 4
0 .0 0 6
0 .0 3 3
XS 6:
Pebble count
(glide)
2.5%
32.0%
39.4%
200
XS 7
D is ta nc e a long bed (feet)
250
XS 5:
Pebble count
(glide)
XS 4
C
C ulvert
% D ifferen c e in
G ra d ien t
XS 3
S e g m e n t G r a d ie n t
Figure 2—Eames Creek longitudinal profile.
90
92
94
400
105
E
54
C
D
53
B
32
A
S egm ent
L e n g th ( f t)
S egm ent
Relative elevation (feet)
96
98
100
102
104
106
108
110
XS 8
D
150
XS 9:
Pebble count
(riffle)
100
E
Representative Channel
50
XS 10:
Pebble count
(riffle)
0
XS 11
Culvert Scour Assessment
Eames
Buck Creek
n
o
i
t
a
v
e
l
E
)
t
f
(
Buck
Eames
Creek
Creek
0.04
0.03 – 0.04
0.0294 – 0.04
0.04
B
C
D
E
SegmentRange of Manning’s n values1
2
3
4
1
# of measured XSs
12
13
4
6
# of interpolated XSs
1
0
2
5
.
2
50
5
6
100
5
.
6 7
*
5 6 7
. . .
8 8 8
200
Main Channel Dis tance (ft)
8
150
*
4
.
8
9
4
.
9
250
*
7
.
9
0
1
1
.
0
1
3
.
0
1
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
3
Figure 3—HEC-RAS profile.
Elevation (ft)
100
105
110
5
.
0
1
300
Obtained using equation from Jarrett (1984): n = 0.39S0.38R-0.16, where S=stream slope; R=hydraulic radius. Jarrett’s equation
only applied within the following ranges: S = 0.002 to 0.08, R = 0.5 ft to 7 ft. For cross sections outside these ranges, n was
computed either from adjacent sections that fell within the ranges, using the guidance of Arcement and Schneider (1987), or from
the HEC-RAS recommendations for culvert modeling.
Table 2—Summary of segments used for comparisons
6
.
0
1
*
8
.
0
1
1
1
350
Ground
W S 78 c fs
W S Qbf
W S Q10
W S Q50
W S Q100
L e ge nd
Site Evaluations
A—137
A—137
n
o
i
t
a
v
e
l
E
)
t
f
(
A—138
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
-20
0
0
20
40
80
.08
100
98
-20
20
Station (ft)
40
.04
60
80
100
B a n k S ta
L e ve e
G ro u n d
W S 7 8 c fs
W S Qb f
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
20
.08
40
60
80
-40
98
100
102
104
106
108
110
98
100
102
-20
0
40
Station (ft)
20
.04
RS = 8
Station (ft)
60
.08
80
100
120
100
WS Q10
106
0
WS Q50
Bank St a
Gr ound
WS 78 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 78 c fs
WS Qbf
WS Q100
108
104
L e ge nd
.08
110
.04
112
.08
RS = 10
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section.
The stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows
represent points identified in the field as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and
topographic analyses are shown below.
Elevation (ft)
100
102
104
.08
RS = 9
Station (ft)
Bank St a
Ground
WS 78 c fs
n
o
i
t
a
v
e
l
E
Elevation (ft)
106
108
110
112
98
100
102
WS Qbf
WS Q10
106
104
WS Q50
108
60
WS Q100
110
.08
L e ge nd
.04
112
.08
RS = 11
)
t
f
(
Culvert Scour Assessment
Eames
Buck Creek
)
t
f
(
Buck
Eames
Creek
Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
40
60
80
100
120
WS Q50
WS Q100
L e ge nd
96
-40
Station (ft)
Bank St a
Ground
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
Elevation (ft)
20
96
-40
98
100
102
104
106
108
110
-20
.05
96
-40 -30 -20 -10
98
30
40
0
. .03 .
0
0
1
1
3
3
40
Station (ft)
20
.05
RS = 4
Station (ft)
50
60
70
80
90 100
60
80
WS Qbf
102
100
WS Q10
100
B a n k S ta
In e ff
G ro u n d
W S 7 8 c fs
W S Qb f
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS 78 c fs
WS Q50
10
L e ge nd
WS Q100
104
0
.03
106
108
110
RS = 6
Note: n values for first profile.
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section.
The stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows
represent points identified in the field as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and
topographic analyses are shown below. (continued)
Elevation (ft)
98
100
WS 78 c fs
WS Qbf
20
100
102
0
80
B a n k S ta
In e ff
G ro u n d
W S 7 8 c fs
W S Qb f
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
WS Q10
-20
60
Station (ft)
40
RS = 5
Note: n values for first profile.
.03
20
.08
RS = 7
104
106
0
.04
Elevation (ft)
108
110
-20
98
100
102
104
106
108
110
.08
)
t
f
(
Site Evaluations
A—139
A—139
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
A—140
96
-20
60
Station (ft)
40
80
100
120
WS Qbf
Bank St a
Ground
WS 78 c fs
Elevation (ft)
96
-20
98
100
102
104
106
108
110
0
.08
20
.04
60
Station (ft)
40
RS = 2
.08
80
100
120
B a n k S ta
In e ff
G ro u n d
W S 7 8 c fs
W S Qb f
W S Q5 0
W S Q1 0 0
W S Q1 0
L e ge n d
Figure 4—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section.
The stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows
represent points identified in the field as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and
topographic analyses are shown below. (continued)
Elevation (ft)
98
100
102
WS Q10
104
100
WS Q50
.08
80
WS Q100
20
RS = 1
60
B a n k S ta
In e ff
G ro u n d
W S Qb f
106
.04
40
Station (ft)
20
.08
L e ge nd
.08
0
.04
108
0
-20
.08
n
o
i
L e ge n d
t
W S Q1 0 0
a
W S Q5 0v
e
W S Q1 0
l
W S 7 8 c fs
E
110
96
-40
98
100
102
104
106
108
110
RS = 3
)
t
f
(
Culvert Scour Assessment
Eames
Buck Creek
w
o
l
F
a
e
r
A
q
s
(
)
t
f
Buck
Eames
Creek
Creek
.
P
.
W
0
100
200
300
400
50
100
200
250
E
300
350
0
50
0
20
Figure 6—Wetted perimeter.
W.P. total (ft)
40
60
80
100
200
Main Channel Distance (ft)
150
Flow
250
300
350
W.P. Total Q100
Legend
W.P. Total 78 cfs
W.P. Total Qbf
W.P. Total Q10
Culvert
D
100
C
Flow Area 78 cfs
Flow Area Qbf
W.P. Total Q50
B
Main Channel Distance (ft)
150
Flow Area Q100
Legend
120
140
160
Figure 5—Flow area (total) profile plot.
Flow area (sq ft)
l
a
t
o
T
)
t
f
(
0
Flow
E
Flow Area Q10
Culvert
D
500
C
Flow Area Q50
B
600
700
800
Site Evaluations
A—141
A—141
A—142
p
o
T
h
t
d
i
W
0
1
2
3
4
5
6
7
8
0
B
50
0
50
0
20
Figure 8—Top width.
Top width (ft)
40
60
80
100
200
Main Channel Distance (ft)
150
Flow
D
250
250
E
300
300
350
350
Top Width Q100
Legend
Hydr Radius 78 cfs
Hydr Radius Qbf
Hydr Radius Q50
Hydr Radius Q10
Hydr Radius Q100
Legend
Top Width 78 cfs
Top Width Qbf
Top Width Q10
Culvert
200
Main Channel Distance (ft)
150
Flow
E
100
C
100
Culvert
D
Top Width Q50
B
C
120
140
160
Figure 7—Hydraulic radius.
Hydraulic radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
Culvert Scour Assessment
Eames
Buck Creek
r
a
e
h
S
n
a
h
C
0
2
4
6
8
10
12
0
Flow
B
50
Buck
Eames
Creek
Creek
0
0
B
50
C
C
100
Culvert
100
Culvert
Figure 10—Shear stress (channel) profile.
Shear channel (lb/sq ft)
2
4
6
8
10
12
14
Figure 9—Maximum depth.
Maximum channel depth ((ft)
q
s
/
b
l
(
)
t
f
x
a
M
l
h
C
h
t
p
D
)
t
f
(
200
200
Main Channel Distance (ft)
150
Flow
D
Main Channel Distance (ft)
150
D
250
250
E
E
300
300
350
350
Shear Chan 78 cfs
Shear Chan Qbf
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth 78 cfs
Max Chl Dpth Qbf
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Site Evaluations
A—143
A—143
A—144
l
e
V
l
n
h
C
)
s
/
t
f
(
0
B
50
C
100
Culvert
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
0
5
10
15
20
200
Main Channel Distance (ft)
150
Flow
D
250
E
300
350
Vel Chnl 78 cfs
Vel Chnl Qbf
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Culvert Scour Assessment
Eames
Buck Creek
300
400
500
600
700
800
25% Q2
E
E
C (culv) D (culv)
C (culv)
B (ds
trans)
D (culv)
Figure 12—Flow area (total).
0
100
200
B (ds
trans)
C (culv)
Qbf
C (culv) D (culv)
100%
of the
values
E
B (ds
trans)
50%
of the
values
C (culv)
B (ds trans)
E
D (culv)
10
E
B (ds
trans)
Minimum value
25th percentile
50
E
E
C (culv) D (culv)
C (culv)
Median (aka 50th percentile)
75th percentile
Maximum value
E
C (culv) D (culv)
D (culv)
Box Plot Explanation
D (culv)
B (ds trans)
Buck
Eames
Creek
Creek
Flow Area (ft2)
Flow area (ft2)
B (ds trans)
B (ds
trans)
E
D (culv)
C (culv)
100
C (culv) D (culv)
E
Site Evaluations
A—145
A—145
B (ds trans)
B (ds trans)
C (culv)
B (ds
trans)
C (culv) D (culv)
25% Q2
C (culv)
Figure 14—Hydraulic radius.
0
E
B (ds
trans)
B (ds trans)
B (ds trans)
B (ds trans)
Hydraulic Radius (ft)
2
4
6
8
Qbf
C (culv) D (culv)
C (culv)
D (culv)
D (culv)
Figure 13—Wetted perimeter.
D (culv)
D (culv)
E
E
C (culv)
Qbf
E
E
E
C (culv) D (culv)
E
B (ds
trans)
B (ds
trans)
10
C (culv) D (culv)
10
E
C (culv) D (culv)
C (culv)
C (culv)
C (culv) D (culv)
B (ds
trans)
B (ds trans)
B (ds trans)
25% Q2
E
D (culv)
D (culv)
B (ds
trans)
E
E
E
0
B (ds
trans)
B (ds
trans)
50
C (culv) D (culv)
50
E
E
C (culv) D (culv)
C (culv)
C (culv)
40
D (culv)
D (culv)
80
B (ds trans)
B (ds trans)
E
E
120
B (ds
trans)
B (ds
trans)
B (ds trans)
B (ds trans)
Wetted Perimeter (ft)
Hydraulic radius (ft)
B (ds trans)
D (culv)
100
C (culv) D (culv)
100
E
E
E
C (culv) D (culv)
C (culv)
C (culv)
A—146
D (culv)
Wetted perimeter (ft)
E
160
Culvert Scour Assessment
Eames
Buck Creek
Maximum depth (ft)
B (ds
trans)
E
25% Q2
E
E
C (culv) D (culv)
Figure 16—Maximum depth.
0
D (culv)
D (culv)
B (ds trans)
3
Maximum
Depth (ft)
6
9
12
B (ds
trans)
Qbf
C (culv) D (culv)
C (culv)
C (culv)
C (culv)
Figure 15—Top width.
D (culv)
D (culv)
C (culv)
Qbf
E
E
E
C (culv) D (culv)
E
B (ds
trans)
B (ds
trans)
10
C (culv) D (culv)
10
C (culv) D (culv)
C (culv)
C (culv)
C (culv) D (culv)
B (ds
trans)
B (ds trans)
B (ds trans)
25% Q2
E
D (culv)
D (culv)
B (ds
trans)
B (ds trans)
B (ds trans)
E
E
E
E
0
B (ds
trans)
B (ds
trans)
50
C (culv) D (culv)
50
C (culv) D (culv)
C (culv)
C (culv)
40
D (culv)
D (culv)
Top Width (ft)
B (ds trans)
B (ds trans)
E
E
E
E
80
B (ds
trans)
B (ds
trans)
B (ds trans)
B (ds trans)
120
100
C (culv) D (culv)
100
E
E
E
C (culv) D (culv)
C (culv)
C (culv)
160
D (culv)
D (culv)
Buck
Eames
Creek
Creek
E
Top width (ft)
B (ds trans)
Site Evaluations
A—147
A—147
B (ds trans)
C (culv)
B (ds
trans)
25% Q2
C (culv) D (culv)
C (culv)
Figure 18—Velocity (channel).
0
5
Velocity (ft/sec)
10
15
20
D (culv)
E
Figure 17—Width-to-depth ratio.
C (culv)
B (ds
trans)
Qbf
Qbf
C (culv) D (culv)
C (culv)
C (culv) D (culv)
D (culv)
D (culv)
E
E
E
E
E
C (culv) D (culv)
E
B (ds
trans)
B (ds
trans)
10
C (culv) D (culv)
10
C (culv) D (culv)
C (culv)
C (culv)
D (culv)
25% Q2
B (ds
trans)
B (ds trans)
B (ds trans)
E
D (culv)
D (culv)
B (ds
trans)
B (ds trans)
B (ds trans)
E
E
E
E
0
B (ds
trans)
B (ds
trans)
50
C (culv) D (culv)
50
C (culv) D (culv)
C (culv)
C (culv)
20
D (culv)
D (culv)
30
B (ds trans)
B (ds trans)
E
E
E
E
40
B (ds
trans)
B (ds
trans)
B (ds trans)
B (ds trans)
Width-to-depth
Ratio
10
Velocity (ft/sec)
B (ds trans)
C (culv)
C (culv)
A—148
E
100
C (culv) D (culv)
100
C (culv) D (culv)
D (culv)
D (culv)
Width-to-depth ratio
E
50
E
E
Culvert Scour Assessment
Eames
Buck Creek
4
6
8
D (culv)
25% Q2
C (culv) D (culv)
C (culv)
B (ds
trans)
E
E
Excess shear (applied/tcrit)
0
200
400
600
Dis charge (cfs )
B (ds trans)
800
B (ds
trans)
C (culv)
1000
Qbf
1200
C (culv) D (culv)
E
10
B (ds trans)
US Channel (DS pebble count) - riffle
Figure 20—Excess shear stress.
E
E
C (culv) D (culv)
C (culv)
US Channel (US pebble count) - riffle
B (ds
trans)
D (culv)
E
D (culv)
Excess shear stress is the channel shear divided by the critical shear for bed
entrainment of the D84 particle size. Values of excess shear greater than 1
indicate bed movement for the D84 particle size.
0
0.1 Shear (Applied / tcrit)
Excess
0.2
0.3
0.4
0.5
0.6
0.7
Figure 19—Shear stress (channel).
0
2
Shear Stress (lbs/ft2)
Shear stress (lbs/ft2)
B (ds trans)
Buck
Eames
Creek
Creek
10
12
14
B (ds
trans)
E
D (culv)
C (culv)
50
C (culv) D (culv)
E
B (ds
trans)
E
D (culv)
C (culv)
100
C (culv) D (culv)
E
Site Evaluations
A—149
A—149
B (ds trans)
B (ds trans)
Culvert Scour Assessment
Table 3—Sum of squared height difference
Reach
XS LocationUnit type
Sum of squared
height difference Within range of
channel conditions?
Culvert
US
Riffle
0.02
No
DS
Riffle
0.003
No
Upstream
US
Glide
0.01
DS
Glide
0.01
Table 4—Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS channel
1.001
B
DS transition
1.000
C
Culvert
1.001
D
Culvert + US transition
1.000
E
US channel
1.001
Table 5—Depth distribution
Reach
XS Location
25% Q2
Culvert
Within range of
channel conditions?
US
1
No
DS
1
No
US
16
DS
3
Upstream
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
23%
77%
0%
0%
Upstream Channel
67%
0%
33%
0%
A—150
Eames
Buck Creek
Site Evaluations
1.2

0.8
0.6



0.4
Residual depth (ft)
0.2
Figure 21—Residual depths.
Segment
B:
DS Transition
Culvert
Segment C:
Culvert
Segment D:
Segment E
Segment A
Segment C:
Culvert
Segment A
0.0
Segment C:
Culvert


Segment B:
DS transition
Residual Depth (ft)
1.0
Segment E
Table 7—Bed material sorting and skewness
Reach
XSUnit Type Sorting
Location
Culvert
US
Riffle
NA
DS
Riffle
Upstream
US
Glide
2.46
0.30
DS
Glide
2.31
0.32
2.02
0.69
Downstream
NA
Within range Skewness
of channel
conditions?
No
NA
No
NA
Within range
of channel
conditions?
No
No
Table 8—Large woody debris
Reach Pieces/Channel
Width
Culvert
1.69
Upstream
3.45
Terminology:US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
Buck
Eames
Creek
Creek
A—151
A—151
Culvert Scour Assessment
View downstream through culvert.
View upstream through culvert.
View of culvert inlet.
View of damaged footing along right side of culvert.
View downstream from road.
View upstream from road.
A—152
Eames
Buck Creek
Site Evaluations
Downstream pebble count in upstream reference reach.
Buck
Eames
Creek
Creek
View upstream at upstream pebble count in upstream reference reach.
A—153
A—153
Culvert Scour Assessment
Cross section: Upstream Reference Reach – Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize R ange (mm)
C ount
Item %
C umulative %
15
4
1
6
8
6
3
9
7
5
11
9
12
3
1
0
0
0
0
0
15%
4%
1%
6%
8%
6%
3%
9%
7%
5%
11%
9%
12%
3%
1%
0%
0%
0%
0%
0%
15%
19%
20%
26%
34%
40%
43%
52%
59%
64%
75%
84%
96%
99%
100%
100%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
> 4096
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
2
Cumulative Frequency
10%
>4096
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
90-128
128-180
64-90
45-64
32-45
22.6-32
11.3-16
16-22.6
5.7-8
8-11.3
<2
4-5.7
<2
0%
2-4
0
2-4
4 - 5.7
5.7 - 8
> 4096
32 -45
45-64
64- 90
8 - 11.3
90 - 128
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
P a r tic le S iz e C a te g o r y ( m m )
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
3
31
122
171
290
A—154
Cumulative Frequency
80%
12
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
15%
49%
35%
1%
0%
2.46
Skewness Coefficient: 0.30
Eames
Buck Creek
Site Evaluations
Cross section: Upstream Reference Reach – Downstream Pebble Count
Material
S ize C las s (mm)
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
C ount
Item %
C umulative %
15
0
0
6
2
7
6
7
5
13
8
11
8
2
1
3
0
0
0
0
16%
0%
0%
6%
2%
7%
6%
7%
5%
14%
9%
12%
9%
2%
1%
3%
0%
0%
0%
0%
16%
16%
16%
22%
24%
32%
38%
46%
51%
65%
73%
85%
94%
96%
97%
100%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
6
Frequency
30%
4
20%
2
Cumulative Frequency
80%
12
Cumulative Frequency
10%
>4096
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
11.3-16
5.7-8
<2
4-5.7
<2
0%
2-4
0
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.3
16- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
P a r tic le S iz e C a te g o r y ( m m )
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
5
40
125
217
450
Buck
Eames
Creek
Creek
Sorting Coefficient:
Material
P ercent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
16%
49%
31%
4%
0%
2.31
Skewness Coefficient: 0.32
A—155
A—155
Culvert Scour Assessment
Cross section: Culvert – Upstream Pebble Count
The culvert reach consists of a glide over bedrock. All of the mobile material was sand at the location of
the upstream pebble count.
A—156
Eames
Buck Creek
Site Evaluations
Cross section: Culvert – Downstream Pebble Count
The culvert reach consists of a glide over bedrock. There was only bedrock at the location of the
downstream pebble count.
Buck
Eames
Creek
Creek
A—157
A—157
Culvert Scour Assessment
Cross section: Downstream Reference Reach – only Pebble Count
This reach consists of some mobile material over bedrock.
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
49
231
370
370
370
A—158
These sizes are based
on percentages of mobile
particles only.
Eames
Buck Creek