Culvert Scour Assessment
Upper Eightmile Creek
Site Information
Site Location:
Mt Hood NF, Forest Road 4430 150 spur. Middle culvert in upper Eightmile Campground area
Year Installed:
2000
Lat/Long:
121°27’21.9”W
45°24’24.7”N
Watershed Area (mi2):
4.1
Stream Slope (ft/ft)1:0.0422
Channel Type:
Step-pool
Bankfull Width (ft): 20.5
Survey Date:
April 26, 2007
1
Water surface slope extending up to 20 channel widths up and downstream of crossing.
Culvert Information
Culvert Type:
Open-bottom arch
Culvert Material:Annular CMP
Culvert Width:
12 ft
Outlet Type:
Mitered
Culvert Length:
42 ft
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.047
Culvert Bed Slope: 0.031
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.59
Alignment Conditions: In-line with natural channel.
Bed Conditions: Gravel to large cobble riffle in culvert – plane-bed. Coarse material. Angular material
in culvert. Some may be recruited from riprap at culvert inlet.
Pipe Condition: Good condition.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
5-year
10-year
43
50
171
237
285
50-year 100-year
406
460
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull
elevations.
2
A—190
Upper Eightmile Creek
Site Evaluations
UPPER EIGHTMILE CREEK
Points represent survey points
Figure 1. Plan view map.
Upper Eightmile Creek
A—191
Culvert Scour Assessment
History
There is no information available for site history.
Site Description
The Upper Eightmile culvert is a bottomless
arch culvert that is mitered to the slope of the
road fill. The culvert width is only 59 percent
of the bankfull width of the stream. Inside the
culvert is a plane-bed channel that is well-graded
with coarse, angular material. At the outlet, the
channel drops off into a pool dammed by an
artificial structure roughly 50 feet downstream of
the culvert. This structure appears to be made
up of material that is too small to remain in place
during large flows.
The upstream representative reach contains a
low active flood plain (3- to 4-channel widths) with
large cedar trees along both banks. A series of
wood jams account for most of the drop in grade
through the reach. Backwater pools and riffles are
interspersed between the jams. Wood provides
for much of the stability in the reach. Fines have
accumulated in the backwater pools. At the
downstream boundary of the upstream reach,
the channel drops through a steep riffle before
flattening out again as it enters the culvert.
Survey Summary
Ten cross sections and a longitudinal profile were
surveyed along Upper Eightmile Creek in April
2007 to characterize the culvert and an upstream
reference reach. Downstream of the culvert,
regularly spaced engineered stream structures
affected the channel prohibiting the establishment
of a downstream representative reach.
Only one reference section was taken halfway
through the culvert due to the uniformity of the
bed. Two additional cross sections were 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.
A—192
In the upstream reach, representative cross
sections were taken through a pool and a
riffle. An additional two sections were taken to
characterize the upstream and downstream ends
of the reach.
Profile Analysis Segment Summary
The profile analysis resulted in a total of eight
profile segments. The culvert consisted of one
profile segment. This segment extends just above
the inlet. The culvert segment was comparable
to two representative profile segments in the
upstream channel. The downstream transition
segment was comparable to the same two
representative segments. There was no suitable
comparison segment for the upstream transition
segment. See figure 2 and table 1.
Scour Conditions
Observed conditions
Footing scour – There was no observed scour
undermining footings or threatening structure
integrity. At time of survey, flow extended across
entire bed of culvert.
Culvert bed adjustment – The culvert bed
slope has adjusted to a flatter slope since
construction (assuming the culvert bed was
originally constructed at the same gradient as the
structure). Angular cobbles and small boulders
are present in the culvert bed. These were either
placed there or have been recruited from the
riprap banks at the inlet and outlet. Fines and
small gravels have aggraded inside the culvert.
Profile characteristics – The profile at the
crossing has a concave shape that reflects the
reduction in slope that begins at the culvert inlet
and extends downstream of the outlet. Slope is
partly controlled by a constructed step of large
cobbles downstream of the outlet; a feature that
would likely wash out at high winter flows. There
is evidence of incision upstream (steep eroding
Upper Eightmile Creek
Site Evaluations
banks) that suggests that the new culvert may
have been installed below the profile of the
original stream. This may have occurred to avoid
raising the road prism.
Residual depths – The single culvert residual
depth is just below the lower end of the range of
the corresponding profile segments (E and G).
The single downstream transition residual depth
is only a tenth of a foot greater than the greatest
residual depth in the corresponding profile
segments (E and G) but is below the deepest
residual depth in the natural channel (figure 21).
Substrate – Bed-material distributions in the
natural channel have a greater proportion of fine
material (sand and small gravels) than the culvert
and are more poorly sorted than the culvert.
Inside the culvert is a very plane-bed channel
with coarse angular material.
Predicted conditions
Cross-section characteristics – The culvert has a
dramatic effect on cross-section characteristics at
nearly all flows, but particularly at flows exceeding
bankfull (figures 5 through 9 and 12 through 17).
For top width (figure 15), the culvert segment
shows some widths exceeding the width of the
corresponding profile segment at high flows (Q50
and Q100). This is because the culvert segment
extends upstream of the culvert inlet and the
model shows the culvert inlet backwatering flow
at these high flows. Relationships are similar
between the downstream transition segment and
the natural channel, except for maximum depth,
which is within the range of the natural channel.
Shear stress – Most of the shear-stress values
in the culvert are similar to corresponding
profile segment G, except for at high flows (Q2
and above) where the maximum shear in the
culvert is greater than the maximum shear in the
natural channel (figure 19). Shear stress in the
downstream transition segment is greater than
the natural channel at the Q10 and greater.
Upper Eightmile Creek
Excess shear – The culvert excess shear is about
half that of the excess shear in the upstream
channel (figure 20). This is mainly due to
differences in the D50s of these cross sections.
The greater D50 in the culvert results in a higher
critical shear stress due to the accounting for
less particle protrusion of the D84, which is similar
between the sections.
Velocity – Velocities in the culvert and the
downstream transition segments are greater than
the corresponding channel segments above the
Qbf (figure 18).
Scour summary
There was no significant scour that was observed
in the culvert but cross-section characteristics
indicate severe changes to flow characteristics
and inadequate culvert capacity that may cause
the culvert to flow under outlet control conditions
at high flood flows, which the culvert has not yet
experienced. Although most shear-stress values
in the culvert were within the range of channel
conditions, the maximum shear at high flows was
greater than in the natural channel. The location
of the maximum shear estimated by the model
(see figure 10) is just downstream of the cross
section where excess shear was calculated and
therefore the excess shear analysis may not
accurately reflect the future potential for scour in
the culvert.
There is evidence of incision upstream that
suggests that the new culvert was installed below
the profile of the original stream. This may have
occurred to avoid raising the road prism.
AOP Conditions
Cross-section complexity – The sum of squared
height difference in the culvert cross section is
greater than that found in the natural channel
(table 3).
A—193
Culvert Scour Assessment
Profile complexity – Vertical sinuosity in
the culvert is slightly less than that found in
corresponding slope segments (table 4). Vertical
sinuosity in the downstream transition is the same
as that found in corresponding slope segments.
Depth distribution – There is significantly less
channel margin habitat in the culvert compared to
the channel at the 25 percent Q2 (table 5).
Habitat units – The culvert is 100-percent riffle,
whereas the natural channel has 24-percent pool
habitat (table 6).
Residual depths – The single culvert residual
depth is just below the lower end of the range of
the corresponding profile segments (E and G).
The single downstream transition residual depth
is only a tenth of a foot greater than the greatest
residual depth in the corresponding profile
segments (E and G) but is below the deepest
residual depth in the natural channel (figure 21).
Bed material – Bed-material distributions in the
natural channel have a greater proportion of fine
material (sand and small gravels) than the culvert
and are more poorly sorted than the culvert.
Inside the culvert is a very plane-bed channel
with coarse angular material.
Large woody debris – There was no LWD present
in the culvert (table 8). The representative
channel had very high LWD abundance. LWD
formed steps and scour pools in the channel
outside the crossing and played a primary role in
habitat unit creation and complexity. Features in
the culvert did not mimic the role of wood in the
natural channel.
AOP summary
The flow in the culvert was wall-to-wall at the
time of the survey, suggesting a lack of flow
concentration that may impede passage during
A—194
low flow periods. The depth distribution analysis
suggests that at higher flows (25 percent
Q2) shallow channel margin habitat may be
unavailable to assist fish passage. There are
no channel banks to allow passage of terrestrial
organisms.
Design Considerations
The culvert placed at this site is undersized
to effectively convey flows without significant
impacts to flow geometry and culvert scour. No
significant scour was observed during the survey
but the site is a relatively recent installation and
has likely not yet experienced flows greater than
a 5- or 10-year event. The limited capacity may
create outlet control conditions at high flows,
with the flow passing through critical depth
within the pipe, which may result in future scour
of the culvert bed. The culvert was calculated
as being only 59 percent of the bankfull width
of the stream. A wider culvert at this site would
improve conveyance and reduce scour risk. The
installation may also have benefited from being at
a higher elevation along the profile, thus reducing
what appears to be channel incision in the
channel upstream of the inlet. The pipe may have
been installed low because of limitations imposed
by the height of the road surface.
The plane-bed channel and wall-to-wall flow
in the culvert may impede fish passage at low
flows due to a lack of flow concentration (i.e.,
too shallow flow) and at higher flows due to a
lack of shallow channel-margin habitat or large
roughness elements (e.g., boulders) that can
provide velocity refuge. A wider culvert and the
construction of channel banks within the culvert
would help to concentrate flows for low flow
passage, create bars that would provide shallow
habitat for passage at higher flows, and would
provide low flow passage along the banks for
terrestrial organisms.
Upper Eightmile Creek
Upper Eightmile Creek
Relative elevation (feet)
H
350
57
A
XS 2
250
C ulvert
0 .00 7
0 .10 2
0 .03 5
0 .03 7
0 .05 7
0 .09 6
0 .03 1
0 .03 2
XS 3:
Pebble count
(riffle)
B
S e g m e n t G r a d ie n t
A
A
E
G
E
G
B
B
D o w n s trea m T ra n s itio n
R epres en ta tiv e
C h a n n el S eg men t
C u lv ert S eg men t
Table 1—Segment comparisons
XS 4
14.5%
9.6%
16.6%
11.8%
C
D
XS 6
D is ta nc e a long bed (feet)
200
XS 5
% D ifferen c e in
G ra d ien t
Figure 2­—Upper Eightmile Creek longitudinal profile.
96
98
300
15
E
11
42
22
D
F
G
30
C
XS 1
48
B
Relative elevation (feet)
100
102
104
106
108
110
32
A
S egm ent
L e n g th ( f t)
S egm ent
150
E
XS 7:
Pebble count
(pool)
F
G
100
Representative Channel
XS 8
50
XS 9:
Pebble count
(riffle)
H
XS 10
0
Site Evaluations
A—195
n
o
i
t
a
v
e
l
E
)
t
f
(
A—196
0.0875 – 0.0909
0.0845 – 0.1578
0.0951 – 0.1224
0.0947 – 0.1003
A
B
E
G
1
1
3
2
# of measured XSs
5
2
5
3
# of interpolated XSs
96
98
0
7
.
1 2
5
.
2
*
5
7
.
2
5
2
.
3
50
5
.
3
4
*
5
.
4
5
*
2
.
5
*
4
.
5
100
6
.
5
6
*
5
.
6
7
1
.
7
2 3
. .
7 7
150
Main Channel Dis tance (ft)
*
8
.
5
*
6
6
6
6
4
.
7
*
3
3
3
3
6
.
7
8
.
7
8
5
.
8
200
*
5
7
.
8
9
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
3
Figure 3—HEC-RAS profile.
Elevation (ft)
100
102
104
106
108
110
112
*
5
2
.
9
*
5
.
9
1Obtained 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 section s 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.
SegmentRange of
Manning’s n values1
Table 2—Summary of segments used for comparisons
*
5
7
.
9
0
1
250
Ground
W S Qbf
W S Q2
W S Q10
W S Q50
W S Q100
L e ge nd
Culvert Scour Assessment
Upper Eightmile Creek
Upper Eightmile Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
)
t
f
(
-20
0
.0947
20
20
60
Station (ft)
40
RS = 8
Station (ft)
.0947
40
60
80
.0927
.0947
80
100
100
120
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
104
106
108
110
112
0
0
114
108
110
112
114
116
20
.0951
20
.0932
40
40
Station (ft)
60
.0951
RS = 7
Station (ft)
60
.0932
RS = 9
80
80
.0951
.0932
100
100
B a n k S ta
L e ve e
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
120
120
L e ge n d
W S Q1 0 0
Figure 4—Cross-section plots. Only measured cross section s 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)
108
110
112
0
.0927
n
o
i
t
a
v
e
l
E
Elevation (ft)
114
116
108
110
112
114
116
.0927
RS = 10
)
t
f
(
Site Evaluations
A—197
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—198
-40
-20
.0897
0
-20
Station (ft)
20
.
0
8
9
7
RS = 4
Station (ft)
0
20
.1498
40
40
.0897
.1498
60
60
80
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
Elevation (ft)
98
-40
100
102
104
106
108
100
102
104
106
108
110
-20
-20
0
.1578
RS = 5
40
0
.072
Station (ft)
20
40
RS = 3
Note: n values for first profile.
Station (ft)
20
.1578
60
.1578
60
80
80
L e ge n d
Bank St a
Ground
WS Qbf
WS Q2
WS Q10
WS Q50
WS Q100
L e ge nd
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
Figure 4—Cross-section plots. Only measured cross section s 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)
100
102
-40
RS = 6
Elevation (ft)
104
106
108
104
-60
106
108
110
112
114
.1498
)
t
f
(
Culvert Scour Assessment
Upper Eightmile Creek
Upper Eightmile Creek
n
o
i
t
a
v
e
l
E
)
t
f
(
98
0
20
.0909
40
Station (ft)
60
.0909
RS = 2
80
100
120
B a n k S ta
In e ff
G ro u n d
n
o
L e ge n d
i
W S Q1 0 0t
a
W S Q5 0
v
W S Q1 0
e
W S Q2 l
W S Qb fE
Elevation (ft)
98
100
102
104
106
0
20
.0888
40
60
Station (ft)
.0888
RS = 1
80
.0888
100
L e ge n d
120
B a n k S ta
In e ff
G ro u n d
W S Qb f
W S Q2
W S Q1 0
W S Q5 0
W S Q1 0 0
Figure 4—Cross-section plots. Only measured cross section s 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)
100
102
104
106
108
.0909
)
t
f
(
Site Evaluations
A—199
A—200
.
P
.
W
l
a
t
o
T
0
20
40
60
80
100
120
140
160
180
0
A
50
Culvert
B
0
A
50
Culvert
B
Figure 6—Wetted perimeter.
W.P. total (ft)
0
20
40
60
80
100
Figure 5—Flow area (total) profile plot.
Flow area (sq ft)
)
t
f
(
w
o
l
F
a
e
r
A
q
s
(
)
t
f
100
C
100
C
150
E F
G
150
E F
G
Main Channel Distance (ft)
D
Main Channel Distance (ft)
D
200
200
H
H
250
Flow
250
Flow
300
300
W.P. Total Qbf
W.P. Total Q2
W.P. Total Q10
W.P. Total Q100
W.P. Total Q50
Legend
Flow Area Qbf
Flow Area Q2
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Culvert Scour Assessment
Upper Eightmile Creek
Upper Eightmile Creek
p
o
T
h
t
d
i
W
0
1
2
3
4
5
6
0
A
50
Culvert
0
0
A
Figure 8—Top width.
Top width (ft)
20
40
60
80
100
120
B
B
50
Culvert
Figure 7—Hydraulic radius.
Hydraulic radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
100
C
100
C
150
E F
150
E F
G
G
Main Channel Distance (ft)
D
Main Channel Distance (ft)
D
200
200
H
H
250
Flow
250
Flow
300
300
Top Width Qbf
Top Width Q2
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Hydr Radius Qbf
Hydr Radius Q2
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Site Evaluations
A—201
r
a
e
h
S
n
a
h
C
1
2
3
4
5
6
7
0
A
50
Culvert
A—202
0
0
A
50
Culvert
B
B
Figure 10—Shear stress (channel) profile.
Shear channel (lbs/sq ft)
2
4
6
8
10
12
14
16
18
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
(
100
C
100
C
150
E F
150
E F
Main Channel Distance (ft)
D
Main Channel Distance (ft)
D
G
G
200
200
H
H
250
Flow
250
Flow
300
300
Shear Chan Qbf
Shear Chan Q2
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth Qbf
Max Chl Dpth Q2
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Culvert Scour Assessment
Upper Eightmile Creek
)
s
/
t
f
(
Upper Eightmile Creek
l
e
V
l
n
h
C
0
0
A
50
B
Culvert
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
2
4
6
8
10
12
100
C
150
E F
G
Main Channel Distance (ft)
D
200
H
250
Flow
300
Vel Chnl Qbf
Vel Chnl Q2
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Site Evaluations
A—203
A—204
Flow area (sq ft)
A (ds
trans)
B
(culv)
Qbf
E
Figure 12—Flow area (total).
0
40
Flow Area (ft2)
80
120
160
200
G
A (ds
trans)
B
(culv)
Q2
E
G
A (ds
trans)
100%
of the
values
B
(culv)
50%
of the
values
10
E
G
A (ds
trans)
B
(culv)
50
Minimum value
25th percentile
E
G
Median (aka 50th percentile)
75th percentile
Maximum value
Box Plot Explanation
A (ds
trans)
B
(culv)
100
E
G
Culvert Scour Assessment
Upper Eightmile Creek
Upper Eightmile Creek
Wetted perimeter (ft)
A (ds
trans)
B
(culv)
Qbf
E
Hydraulic radius (ft)
Qbf
A (ds B (culv)
trans)
E
Figure 14—Hydraulic radius.
0
Hydraulic Radius (ft)
2
4
6
Figure 13—Wetted perimeter.
0
Wetted
20 Perimeter (ft)
40
60
80
100
G
G
B
(culv)
E
Q2
Q2
A (ds B (culv)
trans)
A (ds
trans)
E
G
G
A (ds
trans)
A (ds
trans)
10
10
B (culv)
B
(culv)
E
E
G
G
A (ds
trans)
A (ds
trans)
50
50
B (culv)
B
(culv)
E
E
G
G
B
(culv)
100
100
A (ds B (culv)
trans)
A (ds
trans)
E
E
G
G
Site Evaluations
A—205
A—206
Top width (ft)
A (ds
trans)
B
(culv)
Maximum depth (ft)
Qbf
A (ds B (culv)
trans)
E
Figure 16—Maximum depth.
0
2
Maximum
Depth (ft)
4
6
8
E
Qbf
Figure 15—Top width.
0
20
Top40
Width (ft)
60
80
100
120
G
G
B
(culv)
E
Q2
Q2
A (ds B (culv)
trans)
A (ds
trans)
E
G
G
A (ds
trans)
A (ds
trans)
10
10
B (culv)
B
(culv)
E
E
G
G
A (ds
trans)
A (ds
trans)
50
50
B (culv)
B
(culv)
E
E
G
G
B
(culv)
100
100
A (ds B (culv)
trans)
A (ds
trans)
E
E
G
G
Culvert Scour Assessment
Upper Eightmile Creek
Upper Eightmile Creek
Width-to-depth ratio
A (ds
trans)
B
(culv)
Qbf
E
G
Velocity (ft/sec)
A (ds
trans)
B
(culv)
Qbf
E
G
Figure 18—Velocity (channel).
0
Velocity (ft/sec)
3
6
9
12
Figure 17—Width-to-depth ratio.
0
Width-to-depth
Ratio
20
40
60
80
100
A (ds
trans)
A (ds
trans)
B
(culv)
Q2
Q2
B
(culv)
E
E
G
G
A (ds
trans)
A (ds
trans)
B
(culv)
10
10
B
(culv)
E
E
G
G
A (ds
trans)
A (ds
trans)
B
(culv)
B
(culv)
50
50
E
E
G
G
A (ds
trans)
A (ds
trans)
B
(culv)
100
100
B
(culv)
E
E
G
G
Site Evaluations
A—207
A—208
Shear stress (lbs/sq ft)
A (ds
trans)
B
(culv)
Qbf
E
G
A (ds
trans)
Excess Shear (Applied / tcrit)
0
100
E
300
Q2
Dis charge (cfs )
200
B
(culv)
G
400
A (ds
trans)
B
(culv)
500
10
E
A (ds
trans)
B
(culv)
50
E
Culvert - riffle
US Channel (US pebble count) - riffle
G
G
Figure 20—Excess shear stress.
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.
Excess shear (applied/tcrit)
0
4
8
12
16
Figure 19—Shear stress (channel).
0
4
Shear Stress (lbs/ft2)
8
12
16
A (ds
trans)
B
(culv)
100
E
G
Culvert Scour Assessment
Upper Eightmile Creek
Site Evaluations
Table 3—Sum of squared height difference
Reach
XSUnit
Location
type
Sum of squared
height difference
Within range of
channel conditions?
Riffle
0.03
No
US
Riffle
0.002
DS
Pool
0.02
Culvert
Upstream
Table 4—Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS transition
1.002
B
Culvert
1.001
C
US transition
1.007
D
US channel
1.002
E
US channel
1.002
F
US channel
1.024
G
US channel
1.002
H
US channel
1.001
Table 5—Depth distribution
Reach
XS
25% Q2
Location
Culvert
0
Upstream
US
39
DS
23
Within range of
channel conditions?
No
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
0%
0%
100%
0%
Upstream Channel
24%
0%
74%
2%
Upper Eightmile Creek
A—209
Culvert Scour Assessment
0.5
0.4
Residual Depth (ft)
0.4
0.3
0.3
0.2
0.2
Residual depth (ft)
0.1
Segment H
Segment G
Segment F
Segment E
Segment D
Segment C
US Transition
Segment B
Culvert
0.0
Segment A
DS Transition
0.1
US
DS
Culvert
Transition
Transition
B:
C: Segment DSegment ESegment FSegment GSegment H
Segment A: Segment Segment
Figure 21—Residual depths.
Table 7—Bed material sorting and skewness
Reach
XSUnit
Sorting
Location Type
Culvert
Upstream
Within range Skewness
of channel
conditions?
Riffle
1.27
No
0.23
US
Riffle
2.82
-0.15
DS
Pool
1.57
0.19
Within range
of channel
conditions?
No
Table 8—Large woody debris
Reach
Culvert
Upstream
Pieces/Channel
Width
0
6.4
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
A—210
Upper Eightmile Creek
Site Evaluations
View upstream through culvert.
View downstream of culvert inlet.
Upstream reference reach – upstream pebble count, riffle. Upstream reference reach – downstream pebble
count, pool.
View upstream from inlet. Moderate incision can
be seen in upstream channel. View downstream from outlet. Rock step created
for grade control.
Upper Eightmile Creek
A—211
Culvert Scour Assessment
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 C las s (mm)
C ount
Item %
C umulative %
39
4
2
6
3
6
7
1
5
2
5
5
11
3
0
0
0
0
0
0
39%
4%
2%
6%
3%
6%
7%
1%
5%
2%
5%
5%
11%
3%
0%
0%
0%
0%
0%
0%
39%
43%
45%
52%
55%
61%
68%
69%
74%
76%
81%
86%
97%
100%
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
Bedrock
45
100%
40
90%
35
80%
70%
Frequency
30
60%
25
50%
20
Frequency
15
40%
30%
Bedrock
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
Cumulative Frequency
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
1
8
120
151
200
A—212
16-22.6
<2
8-11.3
0%
11.3-16
0
5.7-8
10%
4-5.7
5
<2
20%
2-4
10
Cumulative Frequency
Cross section : Upstream Reference Reach – Upstream Pebble Count
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
39%
36%
24%
0%
0%
Sorting Coefficient:
2.82
Skewness Coefficient: -0.15
Upper Eightmile Creek
Site Evaluations
Cross section : Upstream Reference Reach – Downstream 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 C las s (mm)
C ount
Item %
C umulative %
15
9
6
13
15
11
14
8
5
2
3
0
0
0
0
0
0
0
0
0
15%
9%
6%
13%
15%
11%
14%
8%
5%
2%
3%
0%
0%
0%
0%
0%
0%
0%
0%
0%
15%
24%
30%
43%
57%
68%
82%
90%
95%
97%
100%
100%
100%
100%
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
Bedrock
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
Bedrock
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
Cumulative Frequency
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
3
10
25
40
90
Upper Eightmile Creek
11.3-16
<2
5.7-8
0%
4-5.7
0
<2
10%
2-4
2
Cumulative Frequency
80%
12
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
15%
82%
3%
0%
0%
Sorting Coefficient:
1.57
Skewness Coefficient: 0.19
A—213
Culvert Scour Assessment
Cross section : Culvert – Only Pebble Count; Middle of Culvert
Frequency
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)
<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
C ount
Item %
C umulative %
0
2
1
3
1
2
4
9
10
17
17
14
12
4
2
0
0
0
0
0
0%
2%
1%
3%
1%
2%
4%
9%
10%
17%
17%
14%
12%
4%
2%
0%
0%
0%
0%
0%
0%
2%
3%
6%
7%
9%
13%
22%
33%
50%
67%
82%
94%
98%
100%
100%
100%
100%
100%
100%
18
100%
16
90%
14
80%
70%
12
60%
10
50%
8
40%
Frequency
6
30%
4
20%
2
10%
Cumulative Frequency
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
11.3-16
5.7-8
8-11.3
<2
4-5.7
<2
0%
2-4
0
Cumulative Frequency
Material
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
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
8
26
65
130
191.5
300
A—214
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
50%
48%
2%
0%
Sorting Coefficient:
1.27
Skewness Coefficient: 0.23
Upper Eightmile Creek