Culvert Scour Assessment
Velvet Creek
Site Information
Site Location:
Coast Range, S Willamette Valley, Siuslaw NF Rd 32
Year Installed:
1981
Lat/Long:
123°48’25.67”W
44°5’55.33”N
Watershed Area (mi2): 1.81
Stream Slope (ft/ft)1:0.013
Channel Type: Pool-riffle
Bankfull Width (ft): 24
Survey Date:
1
March 5 2007
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:
16
Outlet Type:
Mitered
Culvert Length:
93
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.016
Culvert Bed Slope: 0.011
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.67
Alignment Conditions: Mostly inline with natural channel.
Bed Conditions: Material in culvert is gravels and cobbles and appears to be stream-transported and
not placed. It is fairly well sorted by bedform type. Some scour to bedrock (sandstone) is present at
upstream end of culvert.
Pipe Condition: Good condition. Minor rust.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
2-year
Qbf2
5-year
10-year
50-year
100-year
35
140
160
208
256
366
414
2
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull elevations.
A—452
Velvet Creek
Site Evaluations
Points represent survey points
Figure 1—Plan view map.
Velvet Creek
A—453
Culvert Scour Assessment
History
There is no information available for site history.
Site Description
The Velvet Creek culvert is a bottomless arch
pipe that is mitered to the roadfill. A pool through
the inlet of the culvert transitions into a relatively
homogenous riffle. Through the riffle, flow is
concentrated along the right footing, but is also
present along the left footing. There is moderate
footing (stem wall) scour in both cases. There is
also moderate scour down to sandstone bedrock
at the culvert inlet. Bed material through the
culvert was similar to that found along the rest of
the channel.
The upstream representative reach had welldefined riffles composed of gravels and small
cobbles, separated by two moderately deep
pools. Fines were present within the pools and
along the channel margins. The 25-foot-wide
channel sits within a moderately confined valley
with low, but narrow, active flood plain surfaces.
Some vegetation from the banks extends into the
channel adding roughness and providing cover.
Survey Summary
Eleven cross sections and a longitudinal profile
were surveyed along Velvet Creek in March
2007 to characterize the culvert and an upstream
reference reach. No downstream reference
reach was established due to the proximity
of the crossing with the confluence of Indian
Creek. In the culvert, reference sections were
taken at the crest of the pool and through the
riffle. One additional cross section was surveyed
downstream of the culvert to characterize the
outlet as well as the expansion of flow. Another
two cross sections were surveyed upstream to
characterize the inlet as well as the contraction
of flow. Four cross sections were surveyed
to characterize the upstream representative
reach; one at the upstream and downstream
A—454
boundary, one through a pool and one through
a riffle. Additional cross sections were surveyed
for modeling purposes between the upstream
representative reach and the culvert.
Profile Analysis Segment Summary
The profile analysis resulted in a total of nine
profile segments. The culvert consisted of two
profile segments, the upstream one extending
into the inlet transition area. The upstream culvert
segment was compared to one representative
profile segment in the upstream channel. The
downstream culvert segment was compared
to two representative profile segments in
the upstream channel. The upstream and
downstream transition segments were each
compared to two representative segments in the
upstream channel. See figure 1 and tables 1 and 2.
Scour Conditions
Observed conditions
Footing scour – There was no observed scour
undermining footings or threatening structure
integrity. There was, however, concentrated flow
along both walls of the culvert.
Culvert-bed adjustment – The culvert bed
shows some flattening of the profile based
on comparisons of the bed to the slope of the
structure itself (assuming the bed was originally
constructed at the same gradient as the
structure). This flattening appears to be mostly
due to inlet scour within the upstream portion of
the culvert. This inlet scour is primarily associated
with the left bank at the inlet area, where an
18-foot-long by 9-foot-wide area within the pipe is
scoured to the sandstone bedrock. The maximum
footing (stem wall) exposed in this area is about
1.0 foot. In the lower portion of the culvert, the top
of the stem wall is mostly level with the culvert
bed. Material in culvert is gravels and cobbles
and appears to be stream-transported and not
placed.
Velvet Creek
Site Evaluations
Profile characteristics – The profile is generally
uniform through the crossing, with only a slightly
convex shape (figure 2). The slight convexity
makes up the downstream three-quarters of
the culvert bed. Sediment aggradation in this
downstream portion combined with inlet scour
and upstream incision extending approximately
100 feet may be creating the profile shape.
Residual depths – The single culvert residual
depth is similar to the residual depth in the
comparative slope segment (H) (figure 21). This
suggests no significant scour beyond what is
found in the channel outside of the crossing.
Substrate – Culvert bed material distributions do
not differ substantially from the natural channel.
Skewness values are lower in the culvert (table
7), but not by much when compared to the
upstream representative reach downstream cross
section. Sorting values are slightly less in the
culvert than the natural channel but all locations
can be considered poorly or very poorly sorted.
Predicted conditions
Cross-section characteristics – The culvert profile
segments consists of one segment that lies
completely within the pipe (B) and another that
extends upstream of the inlet (C). As a result,
segment C displays cross-section characteristics
that are more similar to the channel outside the
crossing. Therefore, for the discussions of crosssection characteristics the culvert conditions are
considered those represented by segment B.
For all cross-section metrics, the culvert exhibits
conditions that diverge considerably from the
representative channel segments (figures 5
through 9 and 12 through 17). Except for widthto-depth ratio, culvert conditions are generally
similar to channel conditions at the 25 percent
Q2 but begin to diverge at greater flows. For the
downstream transition (A), flow area is similar to
the representative channel, but all other metrics
Velvet Creek
show differences, especially at higher flows.
The upstream transition shows greater accord
with representative channel segments except for
maximum depth. Width-to-depth ratio also has a
much broader range in the upstream transition
segment.
Shear stress – Shear stress in the downstream
culvert segment (B) does not differ significantly
from the representative segments (G and I) at all
flows (figure 19). Culvert segment (C) also shows
good accord with the representative segment (H).
The upstream and downstream transitions also
do not vary substantially from their representative
profile segments outside of the crossing.
Excess shear – The excess-shear analysis
suggests that the culvert has greater potential for
bed mobilization than the representative channel.
This is especially the case if we disregard the
excess-shear value in the downstream reach,
which may represent spurious results because
of backwater effects of the downstream receiving
stream on substrate conditions. Culvert excessshear increases with respect to channel excess
shear as flows increase due to increases in
applied shear stress in the culvert as a result of
greater culvert depths than channel depths at
high flows.
Velocity – Velocity in the downstream culvert
segment (B) is higher than representative channel
segments (G and I) above the 25 percent Q2
(figures 11 and 18). Velocity of culvert segment C
and of the upstream and downstream transition
segments is not substantially different than
corresponding representative segments.
Scour summary
There is some scour at the inlet that is likely
associated with the structure. Assuming the
culvert bed was constructed at the same gradient
as the structure, this scour has flattened the
A—455
Culvert Scour Assessment
channel bed through the crossing. The scoured
inlet area has exposed bedrock that was not
observed in the representative channel reach.
The bedrock may be controlling additional scour
or incision that may otherwise occur at the inlet
and progress upstream. There is concentrated
flow along the culvert walls, along the path of
least roughness. Whereas this does not appear
to be currently causing significant scour of
the footings, over time this could compromise
footing integrity. The similarity of bed-material
distributions between the culvert and the channel
suggests that the channel has reworked the
material that was originally placed in the culvert,
replacing it with sediment transported from
upstream.
AOP Conditions
Cross-section complexity – The sum of squared
height differences in the culvert cross sections
are both within the range of those in the channel
cross sections (table 3).
Profile complexity – Vertical sinuosity in the
culvert and transition segments are within the
range of those in the channel segments (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 more glide habitat
than the representative channel reach (table 6).
Residual depths – The single culvert residual
depth is similar to the residual depth in the
comparative slope segment (H) (figure 21).
The upstream and downstream transitions
have shallower residual depths than their
corresponding channel segments.
A—456
Bed material – Culvert-bed material distributions
do not differ substantially from the natural channel
(table 7). A similar frequency of coarse particles
(cobbles and boulders) suggests that substrate
cover for fish would be similar between the culvert
and the natural channel.
Large woody debris – There was no LWD present
in the culvert (table 8). The representative
channel had low wood quantities. LWD formed
lateral scour pools in portions of the channel
outside the crossing.
AOP summary
Culvert-bed complexity is similar to the natural
channel; however, fish passage may be
limited by a lack of shallow channel-margin
habitat. The culvert also has glide habitat that
is uncharacteristic of the pool-riffle habitat
sequencing in the natural channel. The one
residual depth in the culvert is similar to the
natural channel but residual depths in transition
segments are shallower and may be less ideal for
velocity refuge during fish passage. Because of a
lack of exposed banks during low flows (i.e., time
of survey) terrestrial passage is considered poor.
Design Considerations
The culvert could benefit from stable bank
elements (i.e., large rocks) placed along the
footings to protect footings, concentrate flows
for low-flow passage (away from footings),
and provide accessible banks for passage of
terrestrial organisms. Stable bed elements (large
cobbles and small boulders) near the inlet could
provide scour resistance.
Velvet Creek
Velvet Creek
Relative elevation (ft)
69
B
800
25
97
H
I
XS 1 :
(p o o l ta i l -o u t)
P ebble c ount
A
600
XS 2
0 .01 5
0 .00 5
0 .01 9
0 .01 2
0 .01 9
0 .00 7
0 .00 7
0 .01 4
0 .01 5
400
D
D
A
A
G
I
G
I
G
I
H
B
B
C
U ps trea m T ra n s itio n
E
D is ta n c e a lo n g b e d (fe e t)
XS 7
R epres en ta tiv e
C h a n n el S eg men t
500
(ri ffl e )
XS 6
D
C u lv ert S eg men t
D o w n s trea m T ra n s itio n
Table 1—Segment comparisons
(ri ffl e )
XS 4 :
P ebble c ount
XS 5
C
XS 3 :
B
C u lv e rt
P ebble c ount
S e g m e n t G r a d ie n t
Figure 2—Velvet Creek longitudinal profile.
494
496
81
133
F
64
55
D
E
G
53
C
700
75
A
S e gm en t
L e n g th ( f t)
S egm ent
Relative elevation (feet)
498
500
502
504
506
508
XS 8
21.6%
0.8%
1.6%
23.4%
31.5%
2.2%
34.6%
% D ifferen c e in
G ra d ien t
300
F
200
(ri ffl e )
P ebble c ount
XS 1 0 :
R e p re s e n ta ti ve C h a n n e l
(ri ffl e )
P ebble c ount
XS 9 :
G
100
H
XS 1 1
I
0
Site Evaluations
A—457
n
o
i
t
a
v
e
l
E
)
t
f
(
A—458
0.0688-0.0759
0.0756-0.0759
0.0716-0.0763
0.0725-0.0793
0.0796-0.0810
0.0714-0.0796
0.0700-0.0749
A
B
C
D
G
H
I
SegmentRange of Manning's n values1
1
1
1
1
2
2
2
# of measured XSs
11
3
10
7
6
5
8
# of interpolated XSs
Elevation (ft)
496
498
500
502
504
506
508
510
0
1
2
3
*
4
.
3
100
Figure 3—HEC-RAS profile.
1
*
8
.
3
6
.
5
200
6
*
5
3
.
6
7
.
6
7
*
2
4
1
7
4
.
7
*
5
8
2
4
6
.
7
*
8
2
4
1
8 9
. .
7 7 8
*
6
6
6
6
4
.
8
400
Main Channel Dis tance (ft)
*
5
2
.
7
300
*
1
7
5
8
3
.
7
9
*
1
.
9
*
2
.
9
*
3
.
9
*
4
5
.
.
9
9
500
0
1
*
6
3
.
0
1
*
8
6
.
0
1
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
5
.
4
*
5
2
.
5
*
3
3
3
3
1
.
7
3
0
.
1 1
1 1
600
*
8
5
0
.
1
1
*
6
8
0
.
1
1
700
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
Ground
W S 35 c fs
W S bankfull
W S Q10
W S Q50
W S Q100
L e ge nd
Culvert Scour Assessment
Velvet Creek
Velvet 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
(
0
10
20
10
30
.081
20
Station (ft)
40
RS = 9
Station (ft)
30
50
40
60
.081
50
.075
70
60
80
70
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 35 c fs
WS bankf ull
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)
500
504
508
512
516
520
0
500
-10
504
508
512
516
520
.0845
10
0
20
10
.075
30
20
Station (ft)
40
.0845
RS = 8
Station (ft)
30
RS = 10
50
40
.0714
60
.0845
50
70
60
.075
80
70
L e ge nd
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
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)
500
504
508
.081
0
.07
Elevation (ft)
512
516
520
500
-10
504
508
512
516
520
.075
RS = 11
)
t
f
(
Site Evaluations
A—459
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—460
496
120
130
140
RS = 5
Station (ft)
30
Station (ft)
160
.0716
150
20
170
40
.0817
.075
180
50
190
60
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
B a n k S ta
In e ff
G ro u n d
W S 3 5 c fs
W S b a n kfu ll
200
70
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
496
-40
500
504
508
512
516
496
-10
500
504
508
512
516
-30
0
.
0
7
5
-20
10
Station (ft)
30
40
-10
0
Station (ft)
10
.0759
20
50
.075
RS = 4
Note: n values for first profile.
20
.0735
RS = 6
30
60
40
70
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 35 c fs
WS bankf ull
WS Q10
WS Q50
WS Q100
L e ge nd
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)
500
504
10
.0817
n
o
i
t
a
v
e
l
E
Elevation (ft)
508
512
516
0
.075
.0817
496
-10
500
504
508
512
516
RS = 7
)
t
f
(
Culvert Scour Assessment
Velvet Creek
Velvet 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
(
496
0
10
.075
-30
20
-20
30
0
Station (ft)
40
RS = 1
Station (ft)
.0688
-10
50
10
.0757
60
.075
20
70
30
80
40
B a n k S ta
In e ff
G ro u n d
W S 3 5 c fs
W S b a n kfu ll
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Bank St a
Ground
WS 35 c fs
n
o
i
L e ge nd t
a
WS Q100
v
WS Q50
e
WS Q10 l
E
WS bankf ull
Elevation (ft)
496
500
504
508
512
516
0
10
.075
20
30
40
Station (ft)
.0744
RS = 2
50
60
.075
70
80
L e ge n d
B a n k S ta
In e ff
G ro u n d
W S 3 5 c fs
W S b a n kfu ll
W S Q1 0
W S Q5 0
W S Q1 0 0
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)
500
504
508
512
516
496
-40
500
504
508
512
516
RS = 3
Note: n values for first profile.
)
t
f
(
Site Evaluations
A—461
w
o
l
F
a
e
r
A
q
s
(
)
t
f
A—462
.
P
.
W
l
a
t
o
T
)
t
f
(
0
20
0
A
100
Culvert
B
C
200
10
0
A
100
Culvert
B
Figure 6—Wetted perimeter.
W.P. Total (ft)
20
30
40
50
60
70
C
200
Figure 5—Flow area (total) profile plot.
Flow Area (sq ft)
40
60
80
100
120
140
160
180
D
D
300
F
400
F
400
Main Channel Distance (ft)
300
E
Main Channel Distance (ft)
E
G
G
500
Flow
500
Flow
H
H
600
I
600
I
700
700
W.P. Total 35 cfs
W.P. Total bankfull
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Flow Area 35 cfs
Flow Area bankfull
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Culvert Scour Assessment
Velvet Creek
Velvet Creek
p
o
T
h
t
d
i
W
0
1
2
3
4
5
0
A
100
Culvert
B
Top Width (ft)
A—463
0
A
Figure 8—Top width.
10
20
30
40
50
60
70
100
Culvert
B
Figure 7—Hydraulic radius.
Hydraulic Radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
C
C
200
200
D
D
F
400
300
F
400
Main Channel Distance (ft)
E
Main Channel Distance (ft)
300
E
G
G
500
Flow
500
Flow
H
H
600
I
600
I
700
700
Top Width 35 cfs
Top Width bankfull
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Hydr Radius 35 cfs
Hydr Radius bankfull
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Site Evaluations
r
a
e
h
S
n
a
h
C
q
s
/
b
l
(
1
2
3
4
5
6
7
0
A
100
Culvert
B
A—464
0
0
A
100
Culvert
B
C
C
200
200
Figure 10—Shear stress (channel) profile.
Shear Channel (lb/sq ft)
2
4
6
8
10
Figure 9—Maximum depth.
Maximum Channel Depth (ft)
)
t
f
x
a
M
l
h
C
h
t
p
D
)
t
f
(
D
D
F
400
F
400
Main Channel Distance (ft)
300
E
Main Channel Distance (ft)
300
E
Flow
G
500
Flow
500
G
H
H
I
600
600
I
700
700
Shear Chan 35 cfs
Shear Chan bankfull
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth 35 cfs
Max Chl Dpth bankfull
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Culvert Scour Assessment
Velvet Creek
Velvet Creek
l
e
V
l
n
h
C
)
s
/
t
f
(
Velocity Channel (ft/s)
A—465
0
A
100
Culvert
B
C
200
Figure 11—Velocity (channel) profile plot.
0
2
4
6
8
10
D
300
F
400
Main Channel Distance (ft)
E
G
500
Flow
H
600
I
700
Vel Chnl 35 cfs
Vel Chnl bankfull
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Site Evaluations
80
120
160
H
H
D (US Trans)
25% Q2
D (us trans)
B (culv)
C (culv)
C (Culvert)
B (Culvert)
A (ds trans)
G
G
Figure 12—Flow area (total).
0
I
H
H
D (US Trans)
G
Qbf
D (us trans)
B (culv)
C (culv)
C (Culvert)
B (Culvert)
A (DS Trans)
A (ds trans)
G
I
50%
of the
values
G
H
D (US Trans)
10
I
C (Culvert)
A (DS Trans)
B (Culvert)
A (ds trans)
G
H
H
50
D (us trans)
B (culv)
C (culv)
Minimum value
25th percentile
D (US Trans)
Median (aka 50th percentile)
75th percentile
H
D (us trans)
B (culv)
C (culv)
C (Culvert)
B (Culvert)
A (ds trans)
A (DS Trans)
Maximum value
G
I
A—466
Flow40
Area (ft2)
Flow Area (ft2)
A (DS Trans)
100%
of the
values
G
I
I
Box Plot Explanation
I
H
H
G
D (US Trans)
100
D (us trans)
B (culv)
C (culv)
C (Culvert)
B (Culvert)
A (DS Trans)
A (ds trans)
G
I
Culvert Scour Assessment
Velvet Creek
I
I
G
D (US Trans)
C (Culvert)
H
Hydraulic Radius (ft)
A—467
D (US Trans)
H
25% Q2
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
G
Figure 14—Hydraulic radius.
0
Hydraulic Radius (ft)
1
2
3
4
5
H
Figure 13—Wetted perimeter.
25% Q2
I
I
I
Qbf
G
H
Qbf
D (us trans)
B (culv)
C (culv)
A (ds trans)
H
D (us trans)
B (culv)
C (culv)
A (ds trans)
A (DS Trans)
A (DS Trans)
G
G
D (us trans)
B (Culvert)
B (Culvert)
H
H
B (culv)
C (culv)
C (Culvert)
C (Culvert)
D (US Trans)
D (US Trans)
G
I
I
I
I
A (ds trans)
I
A (ds trans)
10
H
G
H
10
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
H
A (DS Trans)
A (DS Trans)
G
G
G
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
H
0
I
I
I
I
20
A (ds trans)
50
G
H
50
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
H
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
Wetted Perimeter (ft)
A (DS Trans)
A (DS Trans)
G
G
40
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
H
60
I
I
I
I
80
A (ds trans)
100
G
H
100
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
H
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
A (DS Trans)
A (DS Trans)
A (DS Trans)
A (DS Trans)
G
G
B (Culvert)
B (Culvert)
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
H
Velvet Creek
I
I
I
I
Wetted Perimeter (ft)
C (Culvert)
Site Evaluations
D (US Trans)
C (Culvert)
25% Q2
A (ds trans)
G
H
D (us trans)
B (culv)
C (culv)
C (Culvert)
H
H
Figure 16—Maximum depth.
0
I
I
I
B (Culvert)
Max Depth (ft)
2
4
6
D (US Trans)
Figure 15—Top width.
A (ds trans)
A (ds trans)
H
Qbf
D (us trans)
B (culv)
C (culv)
G
D (us trans)
Qbf
G
D (us trans)
C (Culvert)
C (Culvert)
H
H
G
G
25% Q2
I
I
I
A (ds trans)
A (DS Trans)
A (DS Trans)
G
B (culv)
C (culv)
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
I
A (ds trans)
10
H
G
H
10
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
G
A (DS Trans)
A (DS Trans)
G
G
B (culv)
C (culv)
I
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
H
H
I
I
I
G
I
A (ds trans)
50
H
G
H
50
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
0
A (DS Trans)
A (DS Trans)
G
G
15
B (Culvert)
B (Culvert)
D (US Trans)
D (US Trans)
H
H
30
I
I
I
I
45
A (ds trans)
100
H
G
H
100
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
H
D (us trans)
B (culv)
C (culv)
C (Culvert)
C (Culvert)
A (DS Trans)
A (DS Trans)
A (DS Trans)
A (DS Trans)
D (US Trans)
D (US Trans)
Top Width (ft)
Maximum Depth (ft)
B (Culvert)
B (Culvert)
B (Culvert)
G
G
A—468
H
Top Width (ft)
I
I
I
I
60
Culvert Scour Assessment
Velvet Creek
H
G
Velocity (ft/sec)
B (Culvert)
A—469
C (Culvert)
C (Culvert)
25% Q2
A (ds trans)
G
H
D (us trans)
B (culv)
C (culv)
D (US Trans)
Figure 18—Velocity (channel).
0
2
Velocity (ft/sec)
4
6
8
10
G
Figure 17—Width-to-depth ratio.
H
I
A (ds trans)
A (ds trans)
G
H
Qbf
D (us trans)
B (culv)
C (culv)
Qbf
D (us trans)
B (culv)
C (culv)
B (Culvert)
B (Culvert)
D (US Trans)
25% Q2
I
I
D (US Trans)
D (US Trans)
D (us trans)
A (DS Trans)
A (DS Trans)
H
I
I
I
I
G
G
B (culv)
C (culv)
C (Culvert)
C (Culvert)
G
A (ds trans)
10
H
G
H
10
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
B (Culvert)
B (Culvert)
H
H
D (US Trans)
D (US Trans)
A (ds trans)
I
A (DS Trans)
A (DS Trans)
G
G
H
C (Culvert)
C (Culvert)
H
H
G
I
I
I
I
0
A (ds trans)
50
H
G
H
50
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
B (Culvert)
B (Culvert)
10
A (DS Trans)
A (DS Trans)
D (US Trans)
D (US Trans)
Width-to-depth Ratio
C (Culvert)
C (Culvert)
H
H
20
I
I
I
I
30
A (ds trans)
H
G
H
100
D (us trans)
B (culv)
C (culv)
100
A (ds trans)
G
D (us trans)
B (culv)
C (culv)
B (Culvert)
B (Culvert)
G
G
D (US Trans)
D (US Trans)
40
A (DS Trans)
A (DS Trans)
G
G
A (DS Trans)
A (DS Trans)
C (Culvert)
C (Culvert)
H
H
Velvet Creek
I
I
I
I
Width-to-depth Ratio
B (Culvert)
Site Evaluations
A—470
C (Culvert)
B (Culvert)
A (DS Trans)
G
D (US Trans)
H
H
25% Q2
D (us trans)
B (culv)
C (culv)
A (ds trans)
G
I
Excess Shear (Applied/tcrit)
I
200
Discharge (cfs)
D (US Trans)
B (Culvert)
300
Qbf
400
I
G
D (US Trans)
B (Culvert)
H
A (DS Trans)
I
Figure 20—Excess shear stress.
particle size. Values of excess shear greater than 1 indicate bed movement for the D84 particle size.
I
I
DS RR (US pebble count) - tail-out
Culvert (DS pebble count) - riffle
Culvert (US pebble count) - riffle
US RR (DS pebble count) - riffle
US RR (US pebble count) - riffle
10
D (us trans)
B (culv)
C (culv)
C (Culvert)
A (ds trans)
G
H
Excess shear stress is the channel shear divided by the critical shear for bed entrainment of the D84
Excess Shear (Applied / tcrit)
0
0
100
1
2
3
4
5
6
H
H
D (us trans)
G
G
B (culv)
C (culv)
C (Culvert)
A (ds trans)
A (DS Trans)
Figure 19—Shear stress (channel).
Shear Stress (lbs/ft2)
Shear Stress (lbs/ft2)
0
2
4
6
8
G
D (US Trans)
B (Culvert)
H
H
50
D (us trans)
B (culv)
C (culv)
C (Culvert)
A (DS Trans)
A (ds trans)
G
I
D (US Trans)
G
B (Culvert)
H
H
100
D (us trans)
B (culv)
C (culv)
C (Culvert)
A (DS Trans)
A (ds trans)
G
I
Culvert Scour Assessment
Velvet Creek
I
I
Site Evaluations
Table 3. Sum of squared height difference
Reach
XSUnit
Location
type
Culvert
Sum of squared
height difference
Within range of
channel conditions?
US
Riffle
0.01
Yes
DS
Riffle
0.03
Yes
US
Riffle
0.12
DS
Riffle
0.01
Pool/tail-out
0.08
Upstream
Downstream
Table 4. Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS transition
1.001
B
Culvert
1.000
C
Culvert
1.001
D
US transition
1.001
E
US channel
1.002
F
US channel
1.000
G
US channel
1.001
H
US channel
1.001
I
US channel
1.001
Table 5. Depth distribution
Reach
Culvert
XS
25% Q2
Location
Within range of
channel conditions?
US
0
No
DS
0
No
US
2
DS
1
Upstream
Downstream
Velvet Creek
3
A—471
Culvert Scour Assessment
Table 6—Habitat unit composition
P
ercent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
0%
25%
75%
0%
Upstream Channel
30%
0%
70%
0%
1.2

Residual Depth (ft)
1.0

0.8

0.6


0.4
Residual depth (ft)


0.2
Segment F Segment G Segment H
Segment I
Segment H
Segment F
Segment E
Segment D
US Transition
Segment C
US Transition
Segment B
Culvert
Segment A
DS Transition
Culvert
Culvert
Segment E
Segment
A: Segment B: Segment C: Segment
D:
DS Transition
US Transition
Segment G

0.0
Segment I
Figure 21—Residual depths.
Table 7. Bed material sorting and skewness
Reach
XSUnit
Sorting
Location
Type
Culvert
Within range Skewness
of channel
conditions?
Within range
of channel
conditions?
US
Riffle
1.45
No
0.18
No
DS
Riffle
1.54
No
0.17
No
US
Riffle
2.72
0.45
DS
Riffle
1.97
0.20
Pool/tail-out
2.33
0.24
Upstream
Downstream
A—472
Velvet Creek
Site Evaluations
Table 8. Large woody debris counts
Reach
Pieces/Channel Width
Culvert
0
Upstream
0.12
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
View downstream toward culvert inlet.
View upstream toward culvert outlet.
View downstream from roadway.
View upstream from roadway.
Velvet Creek
A—473
Culvert Scour Assessment
Upstream reference reach from upstream end.
Upstream reference reach – upstream pebble
count, riffle.
Upstream reference reach – downstream pebble Upstream view inside culvert.
count, riffle.
Little
Zigzag Creek
A—474
Velvet Creek
Site Evaluations
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 %
17
2
5
1
2
4
6
4
6
16
11
13
9
7
5
1
1
0
0
0
15%
2%
5%
1%
2%
4%
5%
4%
5%
15%
10%
12%
8%
6%
5%
1%
1%
0%
0%
0%
15%
17%
22%
23%
25%
28%
34%
37%
43%
57%
67%
79%
87%
94%
98%
99%
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
18
100%
16
90%
14
80%
70%
12
60%
Frequency
10
50%
8
40%
Frequency
6
30%
4
20%
2
10%
Cumulative Frequency
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
11.3-16
<2
2-4
5.7-8
0%
<2
4-5.7
0
Cumulative Frequency
Cross Section: Upstream Reference Reach – Upstream Pebble Count
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)
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
3
55
159
288
768
Velvet Creek
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
15%
42%
36%
6%
0%
2.72
Skewness Coefficient: 0.45
A—475
Culvert Scour Assessment
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)
<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 %
6
1
6
8
6
7
5
14
13
8
10
14
7
3
1
0
0
0
0
0
6%
1%
6%
7%
6%
6%
5%
13%
12%
7%
9%
13%
6%
3%
1%
0%
0%
0%
0%
0%
6%
6%
12%
19%
25%
31%
36%
49%
61%
68%
77%
90%
96%
99%
100%
100%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
2
Cumulative Frequency
80%
12
Cumulative Frequency
10%
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
11.3-16
16-22.6
5.7-8
8-11.3
2-4
<2
4-5.7
0%
<2
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
Partic le Siz e Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
2
7
34
111
169
309
A—476
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
6%
62%
31%
1%
0%
1.97
Skewness Coefficient: 0.20
Velvet Creek
Site Evaluations
Material
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 C las s (mm)
C ount
Item %
C umulative %
2
0
2
2
8
3
6
11
13
13
18
9
4
0
5
0
0
0
0
7
2%
0%
2%
2%
8%
3%
6%
11%
13%
13%
17%
9%
4%
0%
5%
0%
0%
0%
0%
7%
2%
2%
4%
6%
14%
17%
22%
33%
46%
58%
76%
84%
88%
88%
93%
93%
93%
93%
93%
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
20
100%
18
90%
16
80%
14
70%
12
60%
10
50%
8
Frequency
40%
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
Cross Section: Culvert – Upstream Pebble Count
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
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
7
13
46
105
183
309
Velvet Creek
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
56%
30%
5%
7%
1.45
Skewness Coefficient: 0.18
A—477
Culvert Scour Assessment
Cross Section: Culvert – 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 %
2
2
3
5
5
11
10
8
11
11
12
14
4
1
0
0
0
0
0
0
2%
2%
3%
5%
5%
11%
10%
8%
11%
11%
12%
14%
4%
1%
0%
0%
0%
0%
0%
0%
2%
4%
7%
12%
17%
28%
38%
46%
58%
69%
81%
95%
99%
100%
100%
100%
100%
100%
100%
100%
16
100%
14
90%
70%
Frequency
10
60%
50%
8
40%
Frequency
6
30%
4
20%
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
<2
8-11.3
0%
4-5.7
0
<2
10%
2-4
2
Cumulative Frequency
80%
12
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
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
5
11
36
99
128
218
A—478
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
67%
31%
0%
0%
1.54
Skewness Coefficient: 0.17
Velvet Creek
Site Evaluations
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 %
17
4
3
7
4
11
17
3
11
16
3
3
3
0
0
2
2
0
0
0
16%
4%
3%
7%
4%
10%
16%
3%
10%
15%
3%
3%
3%
0%
0%
2%
2%
0%
0%
0%
16%
20%
23%
29%
33%
43%
59%
62%
73%
88%
91%
93%
96%
96%
96%
98%
100%
100%
100%
100%
18
100%
16
90%
14
80%
70%
Frequency
12
60%
10
50%
8
Frequency
6
40%
30%
4
20%
2
10%
Cumulative Frequency
Bedrock
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
<2
2-4
8-11.3
0%
<2
4-5.7
0
Cumulative Frequency
Cross Section: Downstream of culvert – Only Pebble Count
2-4
4 - 5.7
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
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
1
2
19
59
157
768
Sorting Coefficient:
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
16%
72%
8%
4%
0%
2.33
Skewness Coefficient: 0.24
*This pebble count was not used in the analysis because the downstream reach was not used as a representative reach.
Velvet Creek
A—479