Site Evaluations
Tire Creek
Site Information
Site Location:
Willamette NF, Forest Rd 5826 MP 2.63
Year Installed:
1996
Lat/Long:
122°32’3.95”W
43°48’44.85”N
Watershed Area (mi2): 3.9
Stream Slope (ft/ft)1: 0.0523
Channel Type: Step-pool
Bankfull Width (ft): 22
Survey Date:
1
March 23 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:
17 ft
Outlet Type:
Mitered
Culvert Length:
62 ft
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.094
Culvert Bed Slope: 0.033
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.77
Alignment Conditions: Appears in good alignment with downstream channel but may be placed too
close to confluence of upstream tributaries, which is creating scour at inlet.
Bed Conditions: Large cobble/boulder steps in culvert. At current flow, large boulders are functioning
as channel banks inside the culvert.
Pipe Condition: Potential risk of footing scour near inlet. Pipe in good condition.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
5-year
10-year
50-year
100-year
48
140
193
308
388
566
644
2
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull elevations.
Tire
LittleCreek
Zigzag Creek
A—423
Culvert Scour Assessment
Points represent survey points
Figure 1. Plan view map
A—424
Tire Creek
Little Zigzag
Creek
Site Evaluations
History
There is no information available for site history.
Site Description
The Tire-Creek culvert is a bottomless arch
mitered to conform to the roadfill. The entrance to
the culvert sits at the junction of two steep steppool streams of relatively equal size. The angle at
which they join is roughly 45 degrees off the main
channel and culvert. The channel through the
culvert consists of a scour pool that transitions to
a series of steps. The scour pool at the inlet has
resulted in exposure of the stem walls and spread
footing in places. Downstream of the scour pool
the channel flows along half of the pipe width (left
side) while the other half remains dry due to the
large deposition of material along the right side.
The downstream representative reach consisted
of a high gradient step-pool channel with a low
but narrow active flood-plain surface. Steep riffles
and steps are interspersed by pools. There were
a few downed trees that spanned the channel.
Survey Summary
Fourteen cross-sections and a longitudinal profile
were surveyed along Tire Creek in March 2007
to characterize the culvert and a downstream
representative reach. Representative cross
sections in the culvert were taken through a step
and between steps. One additional cross section
was surveyed downstream of the culvert to
characterize the outlet as well as the expansion
of flow. In order to capture the inlet, the junction
of the two channels, and the contraction of flow,
seven cross sections were taken upstream of the
culvert. Profiles were taken up both channels to
obtain slopes. Four cross sections were surveyed
to characterize the downstream reach; one at the
upstream end, one at the downstream end, one
through a riffle, and one between steps.
Tire
LittleCreek
Zigzag Creek
Profile Analysis Segment Summary
The profile analysis resulted in a total of five
profile segments. The culvert consisted of two
profile segments. The downstream segment in
the culvert was compared to two representative
profile segments in the upstream channel,
although gradients between culvert and
representative segments varied by 37 percent
for each comparison. There was no suitable
comparison segment for the downstream
transition segment. The upstream transition
segment was unique in its position at the
confluence of the two forks; this transition
therefore had no comparable representative
channel segment. See figure 2, table 1, and table
2.
Scour Conditions
Observed conditions
Footing scour – There was evidence of inlet scour
along the right bank where the footing is scoured
to the depth of the base footing. Observed scour
does not appear to be undermining footings or
threatening structure integrity.
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. This flattening appears to be
mostly due to aggradation within the downstream
portion of culvert, with some inlet scour within
the upstream portion of the culvert. However,
compared to most culverts which exhibit bed
flattening, the downstream portion of the culvert is
relatively steep, while the upstream relatively flat.
Profile characteristics – The profile has a convex
shape through the crossing (figure 2) which is a
result of the reorganization of material as some
of the material was scoured out from the inlet
and the channel upstream of the crossing and
deposited downstream.
A—425
Culvert Scour Assessment
Residual depths – Culvert-residual depths in
segment D ranged from 0.19 feet to 0.80 feet.
These values were greater than the single value
found in the downstream representative channel
segment A (0.06 feet), but well within the range
of those found in downstream representative
channel segment B (0.08 feet to 0.87 feet) (figure
21). This suggests no significant scour beyond
what is found in the channel outside of the
crossing.
Substrate – Bed material distributions are similar
in the culvert compared to the channel. Culvert
substrate is slightly coarser than channel pebble
counts, reflecting a higher percentage of bouldersized particles which may be a result of rock
placement during construction. Alternatively,
the coarse material may be sourced from the
upstream tributaries and deposited within the
culvert as the gradient and transport capacity is
reduced. Pebble counts are provided at the end
of this summary.
Predicted conditions
Cross-section characteristics – Cross-sectional
flow area in the culvert is similar to the
downstream channel for lower flows but begins to
diverge by the Q10 (figure 5 and figure 12). Flow
area in the culvert is lower than that found in the
downstream representative channel segment
A above the Qbf but similar to that found in the
downstream representative channel segment
B for all flows. Above the 25 percent Q2, the
wetted perimeter in the culvert is less than in
the downstream channel (figure 13). At the 25
percent Q2, the hydraulic radius in the culvert
is similar to that of both downstream channel
segments (figure 14). For flows at or above the
Qbf, the hydraulic radius in the channel is greater
than in the downstream channel. In contrast,
the top width in the culvert is less than the
downstream channel at and above the Qbf (figure
15). For all flows, the maximum depth is greater
in the culvert than it is in both of the downstream
A—426
channel segments (figure 16). While width-todepth ratio in the culvert is within the range of the
downstream channel segment A at the 25 percent
Q2, it becomes less than both channel segments
at and above the Qbf (figure 17).
Shear stress – Shear stress in the culvert is
similar to the downstream channel for lower flows
but begins to diverge by the Q10 (figure 10 and
figure 19). Above the Q10 both representative
channel segments A and B have greater shearstress values than does the culvert. It is also
above the Q10 that the shear stress in the culvert
remains relatively similar with a slight decline in
magnitude with increasing flows. This is most
likely a result of the backwater created through
the culvert. However, these results may not be
real and may be a function of model limitations.
Excess shear – The excess-shear analysis
shows that the downstream channel has greater
potential for bed mobility than does the culvert,
especially at higher flows (figure 20). This
corresponds with lower shear in the culvert at
higher flows due to outlet-control conditions in the
culvert.
Velocity – Velocity in the culvert is similar to the
downstream representative channel segments for
all flows (figure 11 and figure 18). Additionally, the
range in velocity values for a given flow through
the culvert is relatively similar to the range of
values in the downstream representative channel
segments.
Scour summary
Assuming that the culvert and the culvert bed
were originally constructed on the same grade,
significant bed adjustment has occurred. The
entrance to the culvert sits at the junction of
two steep step-pool streams of relatively equal
size. The angle at which they join is roughly
45 degrees off the main channel and culvert.
Placement of the culvert close to this confluence
Tire Creek
Little Zigzag
Creek
Site Evaluations
has likely altered upstream conditions. Flow
contraction at the inlet has resulted in scouring
of the banks, resulting in the upward retreat
of the channel junction. In order to match this,
the channels have steepened their profiles,
further increasing stream energy and scour
upstream as well as around the culvert inlet.
The transition in profile at the inlet to the culvert
has resulted in scour at the upstream end of the
culvert. Reorganization of material has resulted
in downstream deposition. The exposure of the
footings at the inlet and not at the outlet is likely a
result of this adjustment.
Generally a flattening of the bed results in a
concave bed profile. However, the profile through
the Tire Creek crossing is convex with a relatively
flat segment through the inlet which transitions
to a steep riffle as the channel goes towards the
outlet. This might be a falling limb signature from
a recent flood.
Conditions indicate a low-to-medium risk for
future scour within the culvert. There is likely to
be a continued upstream supply of material as
the channel immediately upstream of the inlet
continues to widen in response to the culvert
installation, potentially resulting in further footing
exposure. Continued aggradation in the culvert
is possible, especially at high flows where outlet
control conditions reduce the energy slope in the
pipe.
AOP Conditions
Cross-section complexity – The sum of squared
height differences in the culvert cross sections
are greater than those measured in the channel
cross sections (table 3). These results may be a
function of the steep sides of the culvert and may
not be representative of the channel bed.
Profile complexity – Vertical sinuosity in the
culvert segments is greater than the range of
those in the channel segments (table 4).
Tire
LittleCreek
Zigzag Creek
Depth distribution – There is more channel
margin habitat in the culvert compared to the
channel at the 25 percent Q2 (table 5). This can
be attributed to a bar along the right channel
which was dry during the time of the survey. At
the 25 percent Q2, this bar is covered by 0.30 feet
or less providing significant shallow water areas
through the culvert.
Habitat units – The habitat-unit composition is
similar between the culvert and the downstream
channel (table 6). More pool habitat and less
riffle habitat exists within the culvert than does in
the downstream channel. While the percentage
of step habitat is not very high within either the
culvert or the downstream channel, there are
numerous short steps in the downstream channel
that do not exist in the culvert. The result of more
numerous short steps, are longer pools in the
downstream channel. There is one step at the
outlet of the culvert.
Residual depths – Culvert-residual depths are
within the range of channel conditions (figure 21).
Bed material – Bed-material distributions are
similar in the culvert compared to the channel
(see pebble count data provided at end of this
site summary). There are slightly less gravels
in the culvert but a similar percentage of sand
compared with the downstream channel. The size
and frequency of the large particles in the culvert
are slightly greater than the downstream channel.
This may reflect the gradient transition and large
source material coming in from the two tributaries.
Culvert bed material sorting values represent the
range of values found at the Tire Creek site. The
upstream culvert cross section, with the lowest
gradient of the segments used in the comparison,
has the highest sorting value which indicates that
it has “very poor” sorting with a relatively wide
distribution including both small gravels and sand
and large cobbles and boulders. The downstream
cross section in the culvert has the lowest sorting
A—427
Culvert Scour Assessment
value and is more similar to the downstream
channel within the range found in the stream
channel (table 7).
Large woody debris – There was no LWD present
in the culvert (table 8). The representative
channel had moderate to 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
Measurements and observations suggest that
the Tire Creek culvert has similar, if not better,
conditions to the natural channel with respect
to AOP. The two measurements of channel
complexity (cross section and profile) indicate
that the culvert has greater complexity than does
the downstream representative channel. These
results must be analyzed with caution, as the
vertical walls of the culvert have been shown to
artificially increase the cross-section complexity.
However, material has aggraded along the right
channel within the culvert creating an exposed
bar during low flows. This aggraded surface
creates good bank habitat, which indeed adds
to channel complexity, flow concentration for fish
passage, and dry streambanks for passage of
terrestrial organisms.
A potential fish passage issue may exist at higher
flows. The high percentage of pool habitat evident
in the habitat unit composition is in the form of
small, short pools, created and maintained by
A—428
the large rock either placed or transported into
the culvert from the steep creeks upstream. This
could result in more turbulent conditions in the
short pools during high flows, with less resting
habitat compared to the channel where pools are
longer.
Bed-material composition is similar between the
culvert and the channel segments, with only slight
differences that can be explained by the gradient
transition through the reach. These similar bed
compositions suggest that AOP is not impaired by
the characteristics of the culvert bed material.
Design Considerations
The Tire Creek culvert was placed very close to
the junction of the two tributaries, likely resulting
in the observed scour, upstream channel
incision, and the upward retreat of the junction
location. Placing the culvert further downstream
may have lessened these impacts. At high
flows, the modeling indicates the potential for
outlet-control conditions in the culvert. This
condition reduces the energy slope and may
cause material to aggrade within the culvert
and further limit hydraulic capacity. The culvert
may be undersized to adequately convey these
high flows. Use of a larger culvert would reduce
the risk of significant bed adjustments. Other
than these considerations, this is considered
a good installation with respect to scour and
AOP. There are stable bed elements within the
culvert that maintain grade and create habitat
complexity. Exposed banks during low flows help
to concentrate flows for passage and also allow
for passage of terrestrial organisms.
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag Creek
Relative elevation (ft)
250
XS 1
A
200
XS 2:
Pebble count
(riffle)
Table 1—Segment comparisons
150
B
A
B
XS 4
D
D
D is ta nc e a long bed (feet)
XS 3:
Pebble count
(riffle/tail-out)
26
E
100
0 .0 0 3
0 .0 6 1
0 .0 0 9
0 .0 3 9
0 .0 9 7
XS 5
C
36.7%
37.0%
% D iffe re n c e in
G ra d ie n t
S e g m e n t G r a d ie n t
C u lv e rt S e g m e n t
Representative Channel
17
43
C
109
B
D
37
A
R e p re s e n ta tiv e
C hannel S egment
Figure 2—Tire Creek longitudinal profile.
80
85
90 elevation (feet)
Relative
95
100
105
110
S egm ent
L e n g th ( f t)
S egm ent
50
XS 6:
Pebble count
(riffle)
D
XS 7:
Pebble count
(riffle)
E
0
XS 8
Confuence of
two forks
C ulvert
Site Evaluations
A—429
n
o
i
t
a
v
e
l
E
)
t
f
(
A—430
0.1128 – 0.1202
0.1069 – 0.12
0.0989 – 0.116
A
B
D
SegmentRange of Manning's n values1
1
2
2
# of measured XSs
8
12
4
# of interpolated XSs
1
80
0
*
5
2
.
1
*
5
.
1
*
5
7
.
1
2
2
.
2
50
*
5
3
.
2
5
.
2
6 7
. .
2 2
5
7
.
2
8
5
.
.
2 3
3
100
4
*
3
.
4
5
150
5
7
.
5
9
.
5
6
Main Channel Dis tance (ft)
5
.
4
*
5
7
.
4
3 5 7
. . .
6 6 6 7
5
2
.
7
200
5
.
7
2
1
3
1
250
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
1
.
2
Figure 3—HEC-RAS profile.
Elevation (ft)
85
90
95
100
105
110
4
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
Ground
W S 48 c fs
W S Qbf
W S Q10
W S Q50
W S Q100
L e ge nd
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
)
t
f
(
Tire
LittleCreek
Zigzag Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
96
-10
0
10
.1233
10
Station (ft)
20
.1233
RS = 12
Station (ft)
20
.1455
30
30
40
40
50
50
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 48 c fs
WS Qbf
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)
100
-10
102
104
106
108
110
112
98
-10
100
102
104
106
108
110
0
0
.1446
.
1
5
1
1
10
10
20
Station (ft)
20
.1446
RS = 11
Station (ft)
.1511
RS = 13
30
.
1
4
4
6
30
.1511
40
40
50
50
L e ge nd
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 48 c fs
WS Qbf
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. *Sections 14-12 represent the left tributary and sections 11-9 represent the right tributary.
Elevation (ft)
98
100
102
.1233
0
.1455
Elevation (ft)
104
106
108
100
-10
102
104
106
108
110
112
.
1
4
5
5
RS = 14
)
t
f
(
Site Evaluations
A—431
Elevation (ft)
A—432
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
)
t
f
(
96
0
10
20
10
Station (ft)
30
.1289
RS = 8
Station (ft)
20
.1425
40
30
.
1
4
2
5
50
.1289
40
50
60
B a n k S ta
In e ff
G ro u n d
W S 4 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 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
-20
96
98
100
102
104
106
96
-10
98
100
102
104
106
108
-10
0
Station (ft)
20
.1312
30
0
Station (ft)
10
.1151
20
RS = 7
Note: n values for first profile.
10
.1312
RS = 9
.1312
30
40
40
50
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 48 c fs
WS Qbf
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. *Sections 14-12 represent the left tributary and sections 11-9 represent the right tributary (continued).
Elevation (ft)
98
100
102
.1289
0
.1425
n
o
i
t
a
v
e
l
E
Elevation (ft)
104
106
98
-10
100
102
104
106
108
110
RS = 10
)
t
f
(
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag 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
(
92
0
10
20
.1156
0
Station (ft)
30
RS = 4
Station (ft)
10
40
.1156
20
50
30
60
40
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
92
94
96
98
100
102
92
94
96
98
0
0
100
102
10
10
.1166
.108
20
20
RS = 3
Station (ft)
30
Station (ft)
30
.1166
.108
RS = 5
40
.1166
40
50
.108
50
60
B a n k S ta
In e ff
G ro u n d
W S 4 8 c fs
W S Qb f
W S Q1 0
W S Q5 0
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
60
L e ge n d
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. *Sections 14-12 represent the left tributary and sections 11-9 represent the right tributary (continued).
Elevation (ft)
94
96
.1156
-10
Bank St a
Ground
WS 48 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
Elevation (ft)
98
100
102
-20
94
96
98
100
102
104
.1095
RS = 6
Note: n values for first profile.
)
t
f
(
Site Evaluations
A—433
n
o
i
t
a
v
e
l
E
)
t
f
(
A—434
88
0
10
20
Station (ft)
30
.1202
40
50
.1202
60
Bank St a
Ground
WS 48 c fs
n
o
L e ge nd i
t
WS Q100
a
WS Q50 v
e
WS Q10
l
WS Qbf E
Elevation (ft)
84
86
88
90
92
94
96
10
.1128
20
40
Station (ft)
30
.1128
RS = 1
50
.1128
60
L e ge nd
Bank St a
Ground
WS 48 c fs
WS Qbf
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. *Sections 14-12 represent the left tributary and sections 11-9 represent the right tributary (continued).
Elevation (ft)
90
92
94
96
98
100
.1202
RS = 2
)
t
f
(
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag Creek
.
P
.
W
l
a
t
o
T
0
20
40
60
80
100
120
140
160
180
0
A
50
B
10
0
A
50
Figure 6—Wetted perimeter.
W.P. total (ft)
20
30
40
50
B
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
100
150
150
200
D
E
Culvert
Main Channel Distance (ft)
C
200
D
E
Culvert
Main Channel Distance (ft)
C
250
Flow
250
Flow
300
300
W.P. Total 48 cfs
W.P. Total Qbf
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Flow Area 48 cfs
Flow Area Qbf
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Site Evaluations
A—435
A—436
p
o
T
h
t
d
i
W
0
1
2
3
4
5
6
0
A
50
5
10
0
A
Figure 8—Top width.
Top width (ft)
15
20
25
30
35
40
45
50
50
Figure 7—Hydraulic radius.
Hydrauliic radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
B
B
100
100
150
150
200
D
E
Culvert
Main Channel Distance (ft)
C
200
D
E
Culvert
Main Channel Distance (ft)
C
250
Flow
250
Flow
300
300
Top Width 48 cfs
Top Width Qbf
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Hydr Radius 48 cfs
Hydr Radius Qbf
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
r
a
e
h
S
n
a
h
C
q
s
/
b
l
(
0
1
2
3
4
5
6
7
8
9
0
50
Tire
LittleCreek
Zigzag Creek
Shear channel (lb/sq ft)
A—437
0
50
Figure 10—Shear stress (channel) profile.
0
5
10
15
20
25
30
Figure 9—Maximum depth.
Maximum channel depth (ft)
)
t
f
x
a
M
l
h
C
h
t
p
D
)
t
f
(
100
100
Main Channel Distance (ft)
150
Main Channel Distance (ft)
150
200
200
250
250
300
300
Shear Chan 48 cfs
Shear Chan Qbf
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth 48 cfs
Max Chl Dpth Qbf
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Site Evaluations
A—438
l
e
V
l
n
h
C
)
s
/
t
f
(
0
0
A
50
B
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
2
4
6
8
10
12
100
150
200
D
E
Culvert
Main Channel Distance (ft)
C
250
Flow
300
Vel Chnl 48 cfs
Vel Chnl Qbf
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag Creek
Flow area (ft2)
A
25%Q2
B
D (culv)
Figure 12—Flow area (total).
0
Flow Area (ft2)
40
80
120
160
A
Qbf
B
D (culv)
100%
of the
values
A
50%
of the
values
10
B
D (culv)
A
Minimum value
25th percentile
50
B
D (culv)
Median (aka 50th percentile)
75th percentile
Maximum value
Box Plot Explanation
A
100
B
D (culv)
Site Evaluations
A—439
A—440
Wetted perimeter (ft)
A
25%Q2
B
D (culv)
Hydraulic radius (ft)
A
25%Q2
B
D (culv)
Figure 14—Hydraulic radius.
0
1
Hydraulic
Radius (ft)
2
3
4
Figure 13—Wetted perimeter.
0
Wetted Perimeter (ft)
10
20
30
40
50
A
A
Qbf
B
Qbf
B
D (culv)
D (culv)
A
A
10
B
10
B
D (culv)
D (culv)
A
A
50
B
50
B
D (culv)
D (culv)
A
A
100
B
100
B
D (culv)
D (culv)
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag Creek
Top width (ft)
A
25%Q2
B
Maximum depth (ft)
A—441
A
25%Q2
B
D (culv)
D (culv)
Figure 16—Maximum depth.
0
Maximum Depth (ft)
2
4
6
8
10
Figure 15—Top width.
0
10
20
Top Width (ft)
30
40
50
A
A
Qbf
B
Qbf
B
D (culv)
D (culv)
A
A
10
B
10
B
D (culv)
D (culv)
A
A
50
B
50
B
D (culv)
D (culv)
A
A
100
B
100
B
D (culv)
D (culv)
Site Evaluations
A—442
Width-to-depth ratio
A
25%Q2
B
D (culv)
Velocity (ft/sec)
A
25%Q2
B
D (culv)
Figure 18—Velocity (channel).
0
Velocity (ft/sec)
3
6
9
12
Figure 17—Width-to-depth ratio.
0
10
Width-to-depth
Ratio
20
30
40
A
A
Qbf
B
Qbf
B
D (culv)
D (culv)
A
A
10
B
10
B
D (culv)
D (culv)
A
A
50
B
50
B
D (culv)
D (culv)
A
A
100
B
100
B
D (culv)
D (culv)
Culvert Scour Assessment
Tire Creek
Little Zigzag
Creek
Tire
LittleCreek
Zigzag Creek
Shear stress (lbs/ft2)
A
25%Q2
B
D (culv)
Excess shear (Applied/tcrit)
0
100
200
300
400
Dis charge (cfs )
500
A
600
700
Qbf
B
A
10
B
DS Channel (DS pebble count) - riffle
DS Channel (US pebble count) - riffle/tail-out
Culvert (DS pebble count) - riffle
Culvert (US pebble count) - riffle
D (culv)
D (culv)
A
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.
0
1 Shear (Applied / tcrit)
Excess
2
3
4
5
6
Figure 19—Shear stress (channel).
0
Shear Stress (lbs/ft2)
5
10
15
20
25
50
B
D (culv)
A
100
B
D (culv)
Site Evaluations
A—443
Culvert Scour Assessment
Table 3—Sum of squared height difference
Reach
XSUnit
Location
type
Culvert
Sum of squared
height difference
Within range of
channel conditions?
US
Riffle
0.07
No
DS
Riffle
0.06
No
US
Riffle/tail-out
0.02
DS
Riffle
0.02
Downstream
Table 4—Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS channel
1.007
B
DS channel
1.005
C
DS transition
1.005
D
Culvert
1.013
E
Culvert
1.008
Table 5—Depth distribution
Reach
XS Location
25% Q2
Within range of channel conditions?
Culvert
US
4
No
DS
11
No
US
3
DS
3
Downstream
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
65%
0%
32%
3%
Downstream Channel
51%
0%
41%
8%
A—444
Tire Creek
Little Zigzag
Creek
Site Evaluations
1.2

Residual Depth (ft)
1.0

0.8
0.6

0.4
Residual depth (ft)




0.2
0.0






Segment A
Segmen B
Figure 21—Residual depths. Segment A
Segment C
DS Transition
Segment B
Segment D
Culvert
Segment
C:
DS Transition
Segment E
Culvert.
Culvert
Segment D:
Culvert
Segment E:
Table 7—Bed material sorting and skewness
Reach
XSUnit
Sorting Within range Skewness Within range
Location
Type
of channel
of channel
conditions?
conditions?
Culvert
US
Riffle
2.01
No
0.30
No
DS
Riffle
1.29
No
0.00
No
US
Riffle/tail-out
1.36
0.32
DS
Riffle
1.84
0.32
Downstream
Table 8—Large woody debris
Reach
Pieces/Channel Width
Culvert
0
Downstream
1.72
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
Tire
LittleCreek
Zigzag Creek
A—445
Culvert Scour Assessment
View upstream towards culvert outlet.
View downstream towards culvert inlet.
Downstream reference reach.
Downstream reference reach – downstream pebble count, riffle.
Downstream reference reach – upstream pebble count, pool.
View upstream from roadway –
confluence of tributaries.
A—446
Tire Creek
Little Zigzag
Creek
Site Evaluations
Culvert – downstream pebble count, riffle/step.
Tire
LittleCreek
Zigzag Creek
Culvert – upstream pebble count, riffle.
A—447
Culvert Scour Assessment
Cross Section: Culvert – 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 C las s (mm)
C ount
Item %
C umulative %
2
5
0
1
1
0
3
2
1
3
7
11
14
8
15
9
9
0
0
0
2%
5%
0%
1%
1%
0%
3%
2%
1%
3%
8%
12%
15%
9%
16%
10%
10%
0%
0%
0%
2%
8%
8%
9%
10%
10%
13%
15%
16%
20%
27%
40%
55%
64%
80%
90%
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
100%
16
90%
14
Frequency
12
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
2
Cumulative Frequency
80%
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
3
44
160
430
700
900
A—448
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
18%
44%
36%
0%
Sorting Coefficient:
2.01
Skewness Coefficient: 0.30
Tire Creek
Little Zigzag
Creek
Site Evaluations
Cross Section: Culvert – 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 %
0
1
0
1
1
0
1
2
8
7
15
14
15
8
13
8
7
0
0
0
0%
1%
0%
1%
1%
0%
1%
2%
8%
7%
15%
14%
15%
8%
13%
8%
7%
0%
0%
0%
0%
1%
1%
2%
3%
3%
4%
6%
14%
21%
36%
50%
64%
72%
85%
93%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
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
11.3-16
16-22.6
5.7-8
<2
8-11.3
0%
2-4
0
4-5.7
10%
<2
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
30
60
140
360
570
830
Tire
LittleCreek
Zigzag Creek
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
21%
51%
28%
0%
Sorting Coefficient:
1.29
Skewness Coefficient: 0.00
A—449
Culvert Scour Assessment
Cross Section: Downstream 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 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 %
1
2
0
0
1
4
2
6
4
8
15
12
23
13
4
4
2
0
0
0
1%
2%
0%
0%
1%
4%
2%
6%
4%
8%
15%
12%
23%
13%
4%
4%
2%
0%
0%
0%
1%
3%
3%
3%
4%
8%
10%
16%
20%
28%
43%
54%
77%
90%
94%
98%
100%
100%
100%
100%
25
100%
90%
20
70%
15
Frequency
60%
50%
10
Frequency
40%
30%
5
20%
Cumulative Frequency
80%
Cumulative Frequency
10%
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
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
Partic le Siz e Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
15
35
120
210
400
600
A—450
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
1%
27%
62%
10%
0%
Sorting Coefficient:
1.36
Skewness Coefficient: 0.32
Tire Creek
Little Zigzag
Creek
Site Evaluations
Cross Section: Downstream 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 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 %
3
1
0
2
2
5
3
2
4
11
10
6
17
11
8
10
4
0
0
0
3%
1%
0%
2%
2%
5%
3%
2%
4%
11%
10%
6%
17%
11%
8%
10%
4%
0%
0%
0%
3%
4%
4%
6%
8%
13%
16%
18%
22%
33%
43%
49%
67%
78%
86%
96%
100%
100%
100%
100%
18
16
90%
14
80%
70%
Frequency
12
60%
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
5.7-8
<2
4-5.7
<2
0%
2-4
0
Cumulative Frequency
100%
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
24.04
130
336.4
472
700
Tire
LittleCreek
Zigzag Creek
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
3%
30%
44%
22%
0%
Sorting Coefficient:
1.84
Skewness Coefficient: 0.32
A—451