Site Evaluations
Cool Creek
Site Information
Site Location:
Mt. Hood NF. 2.5 miles off US 26 on Still Ck Rd (FR 2612)
Year Installed:
1984
Lat/Long:
121°53’11.02”W
45°17’53.01”N
Watershed Area (mi2): 1.7
Stream Slope (ft/ft)1: 0.0519
Channel Type:
Step-pool
Bankfull Width (ft): 19.5
Survey Date:
4-6-2007
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:
13 ft
Outlet Type:
Projecting
Culvert Length:
48
Inlet Type:
Projecting
Pipe Slope (structure slope): 0.022
Culvert Bed Slope: 0.015
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.66
Alignment Conditions: Culvert placement perpendicular to road likely differs from original steam
channel alignment. Outlet possibly oriented further south than original alignment. Lateral scour pool at
inlet may be associated with alignment. Energy is directed at left wall of pipe at inlet.
Bed Conditions: Cobbles to small boulders in pipe. Similar to natural channel.
Pipe Condition: Good condition. Only minor rust in places.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
21
70
83
5-year 10-year 50-year 100-year
134
172
262
302
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull
elevations.
2
Cool Creek
A—35
Culvert Scour Assessment
Points represent survey points
Figure 1—Plan view map.
A—36
Cool Creek
Site Evaluations
History
The exact installation date is unknown, but
the culvert was included in the 1987 Western
Federal Lands Highway Division (WFLHD)
“Oregon Culvert Fish Passage Survey.” The field
survey for the WFLHD study was conducted on
10/19/1987. Special features that were noted
included the observation that the footings were 4
feet below the streambed and “manmade pools
were built at outlet with log and rock barriers.”
With respect to fish passage, Oregon Department
of Fish and Wildlife (ODFW) staff described the
culvert as a “very good open bottom arch,” but
they note that the “manmade pools at outlet may
require periodic maintenance.” WFLHD staff rated
overall culvert condition as “poor,” culvert capacity
as “fair,” condition of foundation as “fair,” and with
“negligible” outlet scour. The culvert hydraulics
were considered “compatible” with the natural
stream hydraulics. In their comments they note
that “despite the poor installation procedures,
the Cool Creek culvert is a good fish passage
design.”
The following are photos from the WFLHD study:
Culvert inlet.
Cool Creek
Typical stream channel.
It is unknown whether the log-drop structure 15
to 20 feet downstream of the outlet was placed
during construction or was placed in response to
scour of the culvert bed at some point following
construction. The drop structure was present at
the time of these 1987 photos.
Site Description
The Cool Creek culvert is a short bottomless
arch that projects from the roadfill. At the inlet
to the culvert the steep channel, predominately
comprised of step-pool channel units, abruptly
flattens. A deep pool has formed up against
the left wall, creating a depositional bar along
the right bank. The downstream half of the
culvert consists of a relatively plane bed glide.
Downstream of the culvert outlet, and extending
to the confluence of Still Creek, there are a series
of constructed log-drop structures that are serving
as the hydraulic controls for this reach. Artificial
log-drop structures are also present upstream of
the culvert.
The presence of artificial log drops upstream
of the culvert required that the upstream
representative reach be located a couple hundred
yards upstream of the inlet. The upstream
reach consisted of a moderate gradient steppool channel with active flood-plain terraces
intermittent along both sides. Large material
A—37
Culvert Scour Assessment
through the reach provided the framework for the
step/cascade units that made up the majority of
the reach. A plunge pool adjacent to a log jam
was the only pool within the reach and served as
a reference cross section.
downstream transition area was comparable
to a representative segment in the upstream
channel. There was no comparable segment for
the upstream transition segment (H). See figure 2
and table 1.
Survey Summary
Scour Conditions
Thirteen cross sections and a longitudinal profile
were surveyed along Cool Creek in April 2007
to characterize the culvert and an upstream
reference reach. No downstream reference
reach was established due to the presence of
artificial log drops. In the culvert, representative
cross sections were taken through the pool
and the glide. Three additional cross sections
were surveyed downstream of the culvert to
characterize the outlet as well as the expansion of
flow. Two additional cross sections were surveyed
upstream to characterize the inlet as well as the
contraction of flow.
Observed conditions
Due to the complexity of the channel between the
upstream representative reach and the culvert,
two separate hydraulic models were run to
evaluate the hydraulics through these reaches.
While a longitudinal profile was surveyed, cross
sections did not capture grade breaks and
hydraulic controls between reaches.
Four cross sections were surveyed to
characterize the upstream representative reach;
one at the upstream and downstream boundary,
one along the top of a step and one through a
pool.
Profile Analysis Segment Summary
The profile analysis resulted in 13 profile
segments. The culvert consisted of one profile
segment that extended into the culvert outlet
transition area. The culvert segment was
comparable to one representative segment
in the upstream channel. A segment in the
A—38
Footing scour—There was minor scour along the
left bank footing at the inlet. Footings were not
scoured to the base or undermined in any way
that threatens 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 (assuming the culvert bed was
constructed at the same gradient as the culvert
structure). This flattening appears to be a
combination of scour at the inlet and aggradation
towards the outlet. A scour pool has formed
along the left edge of the culvert, leaving a
raised surface along the upper right channel
within the culvert. Material has deposited through
the downstream half of the culvert filling in the
channel to resemble a glide. Backwatering and
grade control has been provided by the presence
of log-drop structures downstream of the culvert.
Profile characteristics—The profile has a concave
shape through the crossing (figure 2). This shape
reflects scour at the inlet region, combined with
aggradation in the downstream portion of the
culvert and in the channel downstream of the
culvert. A significant transition in the channel
gradient occurs at the inlet to the culvert as
the channel flows through a series of log-drop
structures. It is this transition, along with the
contraction of flow through the culvert that has
created the scour along the left edge of the
culvert.
The low crown elevation of the culvert and
the deep level of embedment suggest that the
Cool Creek
Site Evaluations
installation of the Cool Creek crossing may have
been placed too low in relation to the original
channel profile, which may have occurred in order
to avoid raising the road bed. Deep embedment
during construction and/or deposition (partially
related to the downstream drop structure) is
contributing to reduced capacity during flood
flows.
Residual depths —The residual depth of the
single pool within the culvert (segment G) is
greater (0.94) than the upstream channel (0.360.82) (figure 21). Additionally, the downstream
transition segment (F) has greater residual depths
(0.43-0.54) than does the upstream channel
(0.15-0.23). This suggests that the culvert has
experienced additional scour beyond what is
found in the channel outside of the crossing. No
units of measure.
Substrate—Substrate in the upstream channel is
coarser than that found in the culvert, with more
frequent large particles and less frequent smaller
particle sizes (including sand and small gravels).
A greater frequency of smaller particles in the
culvert may be due to the gradient transition in
the culvert and the reduced capacity at higher
flows. Backwatering and reduced sediment
transport capacity (i.e., low shear stress) allows
for the deposition of smaller particles. All values
are poorly sorted and positively skewed, which is
typical for mountain streams (table 7). Although
culvert sorting and skewness values fall outside
the range of the natural channel, values do not
diverge substantially. Pebble counts are provided
at the end of the site summary.
Predicted conditions
Cross-section characteristics—Cross-sectional
flow area, wetted perimeter, top width and the
width-to-depth ratio are considerably reduced
by the culvert (figure 12, figure 15, figure 17)
reflecting the reduced capacity of the culvert.
Hydraulic radius and maximum depth in the
Cool Creek
culvert (segment G) are similar to the upstream
channel (segment L) for flows up to the Qbf and
then become greater within the culvert above
the Qbf (figure 14, figure 16). Flow area, top
width, and maximum depth are similar for the
downstream transition segment (F) as they are
for the upstream channel (M) for the range of
flows (figure 12, figure 15, figure 16). The wetted
perimeter and hydraulic radius of the downstream
transition (segment F) are similar to the upstream
channel (segment M) up to the Q10, above which
the wetted perimeter is less in the downstream
transition than in the upstream channel, while
the hydraulic radius is greater (figure 13, figure
14). The downstream transition segment (F) has
a greater width-to-depth ratio as the upstream
channel segment (M) for flows up to the Qbf,
above which the transition segment’s width-todepth ratio is less than the upstream channel’s
(figure 17).
Shear stress—The shear stress within the culvert
(segment G) is similar to that of the upstream
channel (segment L) for all flows modeled (figure
10, figure 19). Similarly, the shear stress of the
downstream transition segment (F) is similar to
the upstream channel segment (M) for all flows
modeled. However, the range of shear-stress
values found in the transition segment is great
and the median value is greater than the median
value of the upstream channel.
Excess shear—The excess shear analysis shows
that the culvert and upstream channel have
similar excess shear values for the 25-percent
Q2 and the Qbf, but diverge above the Qbf (figure
20). It is above the Qbf that the potential for bed
mobilization in the upstream channel increases
at a greater rate than in the culvert. This
corresponds with lower shear in the culvert at
higher flows.
Velocity—Velocity in the upstream culvert
segment (G) is higher than the downstream
representative segment (L) for all flows modeled
(figure 11, figure 18). These higher culvert
velocities correspond to the flow contraction
A—39
Culvert Scour Assessment
(reduction in flow area) caused by the culvert.
Velocity at the downstream transition (F) is similar
to the upstream representative segment (M) at all
flows.
Scour summary
The Cool Creek culvert showed signs of bed
adjustment including inlet scour and downstream
aggradation. Scour at the inlet is likely related to
inlet-control conditions (limited capacity) during
floods. The downstream aggradation is likely
caused by the grade control log-drop structures
located downstream of the crossing that lower
the local slope. The abrupt transition in gradient
from the upstream log-drop structures to the
culvert may be a function of the placement of
the crossing. Continued aggradation in the
downstream portion of the culvert could further
reduce the capacity of the culvert.
AOP Conditions
Cross-section complexity—The sum of squared
height differences in the culvert cross sections
are not within the range of those in the channel
cross sections (table 3). The upstream culvert
cross section, taken through a pool has a higher
value than the upstream channel. The inlet scour
has created a deep pool along the left channel,
leaving a higher bar surface along the right
channel creating complexity in the channel. In
contrast, the downstream culvert section, taken
through the glide is relatively flat and featureless
and represents the aggraded portion of the
culvert which is backwatered by the downstream
log-drop grade control structures.
A—40
Profile complexity—Vertical sinuosity in the
culvert is similar to that found in the upstream
channel (segment L) (table 4). However, the
vertical sinuosity of the downstream transition
(segment F) is much higher than the upstream
channel (segment M), a result of the grade
control log structures.
Depth distribution—There is more channel margin
habitat in the culvert compared to the channel at
25-percent Q2 (table 5).
Habitat units—The habitat-unit composition in
the culvert is very different than the upstream
channel (table 6). Whereas the culvert is made up
of one long scour pool followed by a long glide,
the upstream channel is composed of steep riffles
interspersed by short pools, a step, and a plunge
pool.
Residual depths—The residual depth of the
plunge pool in the culvert (0.95) is greater than
that found in the upstream channel (0.36-0.82)
(figure 21). Similarly, residual depths in the
downstream transition (0.43-0.54) are greater
than those in the upstream channel (0.15-0.23).
Bed material—The bed material in the upstream
channel is coarser than that found in the culvert.
The distributions of the two pool units are fairly
similar, with a slightly greater number of coarser
particles and a noticeable lack of sand and very
fine gravels in the upstream channel. The step
has no rocks less than 11.3 millimeters and the
glide has no rocks greater than 362 millimeters.
The larger material in the natural channel may
provide for velocity refuge for fish that exceeds
what is available in the culvert.
Cool Creek
Site Evaluations
Large woody debris—There was no LWD present
in the culvert (table 8). The representative
channel had 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. The culvert, which has a low rise, is
unlikely to be able to transport or retain LWD
without considerable scour risk. Constructed
wood-drop structures were present in the channel
upstream and downstream of the crossing.
AOP summary
Some metrics, such as cross-section complexity
and shallow-water habitat availability at
25-percent Q2 are greater in the culvert than the
natural channel. However, cross-section shape
(e.g., width-to-depth ratio and wetted perimeter)
changes sharply at the crossing, with potential
impacts on availability of channel margin habitat
as flows increase. The habitat unit composition
is very different in the culvert with only one long
Cool Creek
pool unit whose residual depth is greater than
that found in the upstream channel. The greater
residual depth may create good holding cover in
the culvert; however, large substrate elements
that are also important for velocity refuge are
scarcer in the culvert.
Design Considerations
This culvert is deeply embedded and may
have capacity limitations, especially if material
continues to aggrade inside the structure.
Because of the low height (rise) of the structure,
woody debris may become easily impinged at the
inlet or inside the culvert, further limiting capacity.
Flattening of the gradient through downstream
grade control has possibly kept material from
scouring out over the years but it also could lead
to further aggradation and capacity reduction that
could cause overtopping during a large event.
Increasing the culvert rise could ameliorate these
potential issues, but it would require raising the
road prism because of the low elevation of the
road fill above the pipe. A—41
A—42
Relative Elevation (ft)
800
B
C
Log drop structures
D
700
E
XS 1
F
XS 7
F
M
L
G
D o w n s tre a m T ra n s itio n
R e p re s e n ta tiv e C h a n n e l
S egment
C u lv e rt S e g m e n t
Table 1—Segment comparisons
XS 6
H
XS 5:
Pebble count
(pool)
600
XS 4:
Pebble count
(glide)
XS 2 XS 3
C ulvert
G
Figure 2—Cool Creek longitudinal profile.
480
490
A
500
Relative elevation (feet)
510
520
530
540
I
XS 10
XS 11
400
D is ta nc e a long bed (feet)
J
35%
34%
% D iffe re n c e in
G ra d ie n t
500
XS 8
XS 9
Log drop structures
300
S egm ent
A
B
C
D
E
F
G
H
I
J
K
L
M
K
S egm ent
L ength (ft)
22
17
47
12
36
26
76
22
72
66
245
78
68
200
XS 12
L
S egm ent G ra dient
0.046
0.075
0.022
0.130
0.030
0.060
0.015
0.101
0.054
0.080
0.060
0.023
0.039
100
Representative Channel
XS 13:
Pebble count
(pool)
XS 15
XS 14:
Pebble count
(step)
M
0
Culvert Scour Assessment
Cool Creek
Cool Creek
G
L
M
0.1136—0.1164
0.1095—0.1179
0.058—0.123
0.123—0.1279
2
2
4
2
# of measured XSs
6
9
6
3
# of interpolated XSs
1
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.
F
SegmentRange of Manning’s n values1
Table 2—Summary of segments used for comparisons
Site Evaluations
A—43
)
t
f
(
n
o
i
t
a
v
e
l
E
496
0
1
526
528
530
532
534
536
0
*
5
.
1
.
.
.
.
1
1
2
2
1
*
5
.
2
20
.
.
.
.
2
1
Figure 3—HEC-RAS profile.
Elevation (ft)
498
500
502
504
506
508
510
512
Elevation (ft)
)
t
f
(
A—44
n
o
i
t
a
v
e
l
E
3
4
.
.
.
.
2
1
40
3
.
4
.
.
.
.
2
1
*
5
6
.
4
5
. .
. .
. .
3 3
1 1
60
80
*
3
3
3
8
.
3
1
5
.
5
6
100
*
5
.
6
Main Channel Dis tance (ft)
5
2
.
5
100
1
.
7 7
*
5
2
.
7
b) Culvert Reach
Main Channel Distance (ft)
5
.
3
1
*
6
6
6
6
.
3
1
4
1
*
4
.
7
5
2
.
4
1
*
5
5
.
7
150
5
.
4
1
120
7
.
7
*
5
8
.
7
5
7
.
4
1
8
*
5
4
.
8
5
1
140
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
50
.
.
.
.
2
1
.
.
.
*
3
.
3
1
a) Upstream Channel Reach
9
.
8 9
200
160
Le gen d
Ground
W S 20 c fs
W S Qbf
W S Q10
W S Q50
W S Q100
L e ge nd
G rou nd
WS 20 cfs
WS Q bf
WS Q 10
WS Q 50
WS Q 100
Culvert Scour Assessment
Cool 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
(
Cool Creek
526
0
20
.1095
20
RS = 13
40
Station (ft)
60
60
Station (ft)
.1095
40
80
.1095
80
.1152
100
Bank St a
Ground
WS 20 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
100
B a n k S ta
L e ve e
G ro u n d
W S 2 0 c fs
W S Qb f
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
526
528
530
532
534
536
530
532
534
536
538
0
0
20
20
.1162
.1136
40
60
60
.1162
RS = 12
Station (ft)
Station (ft)
40
.1136
RS = 14
.1136
80
.1162
80
W S Qb f
W S Q1 0
W S Q5 0
Bank St a
Ground
WS 20 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
B a n k S ta
L e ve e
G ro u n d
W S 2 0 c fs
100
100
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.
Elevation (ft)
528
530
0
.1152
n
o
i
t
a
v
e
l
E
Elevation (ft)
532
534
536
532
534
536
538
540
.1152
RS = 15
)
t
f
(
Site Evaluations
A—45
)
t
f
(
A—46
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
502
-20
-10
0
10
20
Station (ft)
30
.
1
3
9
4
RS = 7
Station (ft)
.1394
0
40
20
50
60
40
70
80
60
Bank St a
Ground
WS 20 c fs
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 20 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)
500
-10
502
504
506
508
510
-40
506
508
510
512
514
0
10
-20
20
.075
30
0
Station (ft)
40
.0653
RS = 6
50
20
.137
Station (ft)
.
1
3
7
RS = 8
60
.075
.
1
3
7
70
40
80
60
90
B a n k S ta
In e ff
G ro u n d
W S 2 0 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 20 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. (continued)
Elevation (ft)
504
506
.1394
-20
.137
n
o
i
t
a
v
e
l
E
Elevation (ft)
508
510
512
-40
508
510
512
514
516
.
1
3
7
RS = 9
)
t
f
(
Culvert Scour Assessment
Cool Creek
Cool 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
.1195
10
-20
10
50
20
Station (ft)
40
.1195
RS = 3
Station (ft)
30
0
60
.1195
30
70
40
80
50
60
90
B a n k S ta
In e ff
G ro u n d
W S 2 0 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
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
-20
500
502
504
506
508
500
-40
502
504
506
508
510
-10
-30
0
-20
10
.1264
-10
10
50
30
.1264
40
20
Station (ft)
30
.1264
RS = 2
Station (ft)
20
0
.0656
RS = 4
Note: n values for first profile.
60
40
50
70
60
80
B a n k S ta
In e ff
G ro u n d
W S 2 0 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 20 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. (continued)
Elevation (ft)
500
-10
502
504
-30
Ground
WS 20 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)
506
508
510
-40
500
502
504
506
508
.0629
RS = 5
Note: n values for first profile.
)
t
f
(
Site Evaluations
A—47
Elevation (ft)
A—48
-20
498
500
502
504
506
-10
0
10
.1279
20
40
.1279
Station (ft)
30
.1279
RS = 1
50
60
70
80
B a n k S ta
In e ff
G ro u n d
W S 2 0 c fs
W S Qb f
W S Q1 0
W S Q5 0
W S Q1 0 0
L e ge n d
Figure 4­—Cross-section plots. Only measured cross sections are included. Manning’s n values are included at the top of the cross section. The
stationing (RS) corresponds to the stationing on the HEC-RAS profile. Green arrows define the ineffective flow areas. Black arrows represent
points identified in the field as the bankfull channel boundary. Only those points identified in the field and supported by hydraulic and topographic
analyses are shown below. (continued)
n
o
i
t
a
v
e
l
E
)
t
f
(
Culvert Scour Assessment
Cool Creek
Cool Creek
Flow Area (sq ft)
Flow Area (sq ft)
0
20
40
60
80
100
0
20
40
60
80
100
120
140
0
0
F
20
Figure 5—Flow Area (total) profile plot.
w
o
l
F
a
e
r
A
q
s
(
)
t
f
w
o
l
F
a
e
r
A
q
s
(
)
t
f
L
50
40
G
80
100
Main Channel Distance (ft)
100
H
I
150
Flow
120
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
Culvert
60
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
Flow Area 20 cfs
Flow Area Qbf
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Flow Area 20 cfs
Flow Area Qbf
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Site Evaluations
A—49
A—50
W.P. Total (ft)
W.P. Total (ft)
5
10
15
20
25
30
35
40
10
20
30
40
50
60
70
80
0
0
F
Figure 6—Wetted perimeter.
.
P
.
W
l
a
t
o
T
)
t
f
(
.
P
.
W
l
a
t
o
T
)
t
f
(
20
L
50
40
G
80
100
Main Channel Distance (ft)
100
H
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
Culvert
60
I
150
Flow
120
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
W.P. Total 20 cfs
W.P. Total Qbf
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
W.P. Total 20 cfs
W.P. Total Qbf
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Culvert Scour Assessment
Cool Creek
Cool Creek
r
d
y
H
s
u
i
d
a
R
)
t
f
(
1.6
1.8
2.0
2.2
0
Hydr Radius (ft)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.4
0.6
0.8
1.0
1.2
1.4
Hydr Radius (ft)
0
F
20
Figure 7—Hydraulic Radius.
r
d
y
H
s
u
i
d
a
R
)
t
f
(
L
50
40
G
80
100
120
Main Channel Distance (ft)
100
H
I
Flow
150
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
Culvert
60
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
Hydr Radius 20 cfs
Hydr Radius Qbf
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Hydr Radius 20 cfs
Hydr Radius Qbf
Hydr Radius Q10
Hydr Radius Q100
Hydr Radius Q50
Legend
Site Evaluations
A—51
A—52
Top Width (ft)
5
10
15
20
25
30
35
10
20
30
40
50
60
70
0
0
Figure 8—Top Width.
p
o
T
Top Width (ft)
h
t
d
i
W
)
t
f
(
p
o
T
h
t
d
i
W
)
t
f
(
F
20
L
50
40
G
80
100
Main Channel Distance (ft)
100
H
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
Culvert
60
I
150
Flow
120
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
Top Width 20 cfs
Top Width Qbf
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Top Width 20 cfs
Top Width Qbf
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Culvert Scour Assessment
Cool Creek
Cool Creek
x
a
M
Max Chl Dpth (ft)
l
h
C
h
t
p
D
)
t
f
(
x
a
M
l
h
C
h
t
p
D
)
t
f
(
0
0
0
F
20
Figure 9—Maximum Depth.
Max Chl Dpth (ft)
1
2
3
4
5
6
0
1
2
3
4
5
6
L
50
40
Culvert
G
60
100
120
Main Channel Distance (ft)
100
H
150
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
80
I
Flow
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
Max Chl Dpth 20 cfs
Max Chl Dpth Qbf
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Max Chl Dpth 20 cfs
Max Chl Dpth Qbf
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Site Evaluations
A—53
A—54
r
a
e
h
S
12
14
12
Shear Chan (lb/sq ft)
F
20
L
50
40
Figure 10—Shear stress (channel) profile.
0
2
4
6
8
10
0
0
14
0
2
4
6
8
10
Shear Chan (lb/sq ft)
n
a
h
C
q
s
/
b
l
(
)
t
f
r
a
e
h
S
n
a
h
C
q
s
/
b
l
(
)
t
f
G
80
100
Main Channel Distance (ft)
100
H
I
150
Flow
120
b) Culvert Reach (sections 9-1)
Main Channel Distance (ft)
Culvert
60
M
a) Upstream Reach (sections 15-12)
140
Flow
200
160
Shear Chan 20 cfs
Shear Chan Qbf
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Shear Chan 20 cfs
Shear Chan Qbf
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Culvert Scour Assessment
Cool Creek
Cool Creek
Vel Chnl (ft/s)
Vel Chnl (ft/s)
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
0
0
F
20
L
50
40
Figure 11—Velocity (channel) profile plot.
l
e
V
l
n
h
C
)
s
/
t
f
(
l
e
V
l
n
h
C
)
s
/
t
f
(
G
Main Channel Distance (ft)
80
100
Main Channel Distance (ft)
100
H
b) Culvert Reach (sections 9-1)
Culvert
60
Flow
I
150
Flow
120
M
a) Upstream Reach (sections 15-12)
140
200
160
Vel Chnl 20 cfs
Vel Chnl Qbf
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Vel Chnl 20 cfs
Vel Chnl Qbf
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Site Evaluations
A—55
A—56
80
120
0
F (ds
trans)
40Area (ft2)
Flow
Flow Area (ft2)
L
25%Q2
G
(culv)
Figure 12—Flow Area (total).
50
M
F (ds
trans)
G
(culv)
Qbf
L
100%
of the values
M
F (ds
trans)
50%
of the values
G
(culv)
10
L
M
F (ds
trans)
M inim um value
th
G
(culv)
25 th percentile
Median (aka 50
75 th percentile
Maxim um value
Box Plot Explanation
50
L
percentile)
M
F (ds
trans)
G
(culv)
100
L
M
Culvert Scour Assessment
Cool Creek
Cool Creek
Wetted Perimeter (ft)
F (ds
trans)
L
25%Q2
G
(culv)
F (ds
trans)
L
25%Q2
G
(culv)
Figure 14—Hydraulic Radius.
Hydraulic Radius (ft)
0
1
Hydraulic Radius (ft)
2
3
4
Figure 13—Wetted Perimeter.
0
20 Perimeter (ft)
Wetted
40
60
80
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
Qbf
Qbf
L
L
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
10
10
L
L
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
50
50
L
L
M
M
F (ds
trans)
F (ds
trans)
100
100
G
(culv)
G
(culv)
L
L
M
M
Site Evaluations
A—57
A—58
Top Width (ft)
F (ds
trans)
F (ds
trans)
L
25%Q2
G
(culv)
Figure 16—Maximum Depth.
Maximum Depth (ft)
0
Maximum Depth (ft)
2
4
6
L
25%Q2
G
(culv)
Figure 15—Top Width.
0
Top Width (ft)
20
40
60
80
M
M
F (ds
trans)
F (ds
trans)
Qbf
Qbf
G
(culv)
G
(culv)
L
L
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
10
10
L
L
M
M
F (ds
trans)
F (ds
trans)
50
50
G
(culv)
G
(culv)
L
L
M
M
F (ds
trans)
F (ds
trans)
100
100
G
(culv)
G
(culv)
L
L
M
M
Culvert Scour Assessment
Cool Creek
Cool Creek
Width-to-depth Ratio
F (ds
trans)
L
25%Q2
G
(culv)
M
Velocity (ft/sec)
F (ds
trans)
L
25%Q2
G
(culv)
Figure 18—Velocity (channel).
0
Velocity (ft/sec)
2
4
6
8
M
Figure 17—Width-to-depth Ratio.
0
10
Width-to-depth Ratio
20
30
40
F (ds
trans)
F (ds
trans)
G
(culv)
Qbf
Qbf
G
(culv)
L
L
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
10
10
L
L
M
M
F (ds
trans)
F (ds
trans)
G
(culv)
G
(culv)
50
50
L
L
M
M
F (ds
trans)
F (ds
trans)
100
100
G
(culv)
G
(culv)
L
L
M
M
Site Evaluations
A—59
A—60
Shear Stress (lbs/ft2)
F (ds
trans)
L
25%Q2
G
(culv)
M
Excess Shear (Applied/tcrit)
150
200
Dis charge (cfs )
F (ds
trans)
G
(culv)
250
Qbf
L
300
M
350
F (ds
trans)
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
0
50
100
0.5
1
1.5
2
2.5
3
Figure 19—Shear Stress (channel).
0
4
Shear Stress (lbs/ft2)
8
12
16
10
L
M
F (ds
trans)
Culvert (DS pebble count) - glide
US Channel (US pebble count) - step
G
(culv)
G
(culv)
50
L
M
F (ds
trans)
G
(culv)
100
L
M
Culvert Scour Assessment
Cool Creek
Site Evaluations
Table 3—Sum of squared height difference
Reach
XS LocationUnit type
Culvert
Sum of squared
height difference
Within range of
channel conditions?
US
Pool
0.10
No
DS
Glide
0.03
No
US
Step
0.09
DS
Pool
0.07
Upstream
Table 4—Vertical sinuosity
Segment
A
DS Channel
1.040
B
DS Channel
1.046
C
DS Channel
1.049
D
DS Channel
1.001
E
DS Channel
1.018
F
DS transition
1.018
G
Culvert
1.002
H
US transition
1.006
I
US Channel
1.015
J
US Channel
1.015
K
US Channel
1.007
L
US Channel
1.003
M
US Channel
1.002
Cool Creek
LocationVertical Sinuosity (ft/ft)
A—61
Culvert Scour Assessment
Table 5—Depth distribution
Reach
XS Location
25% Q2
Culvert
Within range of
channel conditions?
US
2
No
DS
0
No
US
4
DS
4
Upstream
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
32%
44%
0%
0%
Upstream Channel
15%
0%
76%
7%
3.5

2.5
2.0


1.5





Segment M


Segment L
Segment I
Segment H:
US Transition
Segment G:
Culvert

Segment F:
DS Transition
Segment B
Segment A

Segment E

0.0


Segment K

Segment D
0.5




Segment J
Residual
depth (ft)
1.0
Segment C
Residual depth (ft)
3.0
Culvert
SegmentISegment Segment
J
Segment L
Segment A
Segment B
Segment C
Segment D
Segment E
K
Segment M
Segment G:
Segment
F:
Segment
H:
DS Transition
US Transition
Figure 21—Residual depths.
A—62
Cool Creek
Site Evaluations
Table 7—Bed material sorting and skewness
Reach
XS LocationUnit Type
Sorting
Within range
of channel conditions?
Skewness
Within range
of channel
conditions?
Culvert
US
Pool
1.34
No
0.16
No
DS
Glide
1.70
No
0.15
No
Upstream
US
Step
1.45
0.23
DS
Pool
1.64
0.26
Table 8—Large woody debris
Reach
Pieces/Channel Width
Culvert
0
Upstream
2.6
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
Cool Creek
A—63
Culvert Scour Assessment
View upstream through culvert.
View downstream through culvert.
Culvert—downstream pebble count, glide.
Culvert—upstream pebble count, pool.
Upstream reference reach—upstream pebble count, riffle. Upstream reference reach—downstream pebble count, pool.
A—64
Cool Creek
Site Evaluations
View upstream from culvert.
Cool Creek
View downstream from culvert (log step in center).
A—65
Culvert Scour Assessment
Cross section: Upstream Reference Reach—Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
sm all 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
0
0
0
0
4
0
6
7
8
18
4
18
15
7
9
3
0
0
0
0%
0%
0%
0%
0%
4%
0%
6%
7%
8%
18%
4%
18%
15%
7%
9%
3%
0%
0%
0%
0%
0%
0%
0%
0%
4%
4%
10%
17%
25%
43%
47%
66%
81%
88%
97%
100%
100%
100%
100%
20
100%
18
Frequency
14
60%
12
10
40%
8
Frequency
20%
6
4
Cumulative Frequency
80%
16
Cumulative Frequency
0%
2
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
2-4
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
1024
2048
2048
- 4096
Particle Size Category (mm)
Partic le Siz e Category (mm)
S ize C las s
S ize percent finer
than (mm)
D5
D16
D50
D84
D95
D100
25
41
130
293
450
650
A—66
5.7-8
<2
4-5.7
<2
-20%
2-4
0
Sorting Coefficient:
Material
P ercent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
25%
56%
19%
0%
1.45
Skewness Coefficient:0.23
Cool Creek
Site Evaluations
Cross section: Upstream Reference Reach—Downstream Pebble Count
Material
S ize C las s (mm)
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
C ount
Item %
C umulative %
0
0
3
3
2
5
5
4
5
13
15
9
16
10
4
6
0
0
0
0
0%
0%
3%
3%
2%
5%
5%
4%
5%
13%
15%
9%
16%
10%
4%
6%
0%
0%
0%
0%
0%
0%
3%
6%
8%
13%
18%
22%
27%
40%
55%
64%
80%
90%
94%
100%
100%
100%
100%
100%
18
100%
16
80%
Cumulative Frequency
Frequency
14
12
60%
10
40%
8
Frequency
6
20%
4
2
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
-20%
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
1024
2048
2048
- 4096
Particle Size Category (mm)
Partic le Siz e Category (mm)
S ize C las s
S ize percent finer
than (mm)
D5
D16
D50
D84
D95
D100
8
22
80
220
410
490
Cool Creek
Cumulative Frequency
0%
Sorting Coefficient:
Material
P ercent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
40%
50%
10%
0%
1.64
Skewness Coefficient:0.26
A—67
Culvert Scour Assessment
Cross section: Culvert—Upstream Pebble Count
Ma terial
C ount
Item %
C umula tive %
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
S ize R ange (mm)
1
3
2
4
0
5
2
1%
3%
2%
4%
0%
5%
2%
1%
4%
6%
10%
10%
15%
18%
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
10
10
9
15
12
9
11
2
10%
10%
9%
15%
12%
9%
11%
2%
28%
38%
47%
63%
75%
85%
96%
98%
small boulder
medium boulder
large boulder
very large boulder
bedrock
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
> 4096
2
0
0
0
0
2%
0%
0%
0%
0%
100%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
6
Frequency
30%
4
20%
2
10%
Cumulative Frequency
>4096
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
11.3-16
5.7-8
<2
4-5.7
<2
0%
2-4
0
Cumulative Frequency
80%
12
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
5
19
70
D84
D95
D100
176
242
490
A—68
Sorting Coefficient:
Materia l
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
1%
46%
48%
4%
0%
1.34
Skewness Coefficient:0.16
Cool Creek
Site Evaluations
Cross section: Culvert –Downstream Pebble Count
Material
S ize C la s s (mm)
C ount
Item %
C um ulative %
0
0%
0%
very fine gravel 2 - 4
fine gravel 4 - 5.7
3
1
3%
1%
3%
4%
fine gravel 5.7 - 8
medium gravel 8 - 11.3
2
3
2%
3%
6%
9%
medium gravel 11.3 - 16
coarse gravel 16 - 22.6
coarse gravel 22.6 - 32
5
4
5
5%
4%
5%
14%
18%
23%
17
16
17%
16%
39%
55%
small cobble 64 - 90
medium cobble 90 - 128
17
8
17%
8%
72%
79%
large cobble 128 - 180
very large cobble 180 - 256
15
4
15%
4%
94%
98%
small boulder 256 - 362
small boulder 362 - 512
2
0
2%
0%
100%
100%
0
0
0
0%
0%
0%
100%
100%
100%
0
0%
100%
sand <2
very coarse gravel 32 - 45
very coarse gravel 45 - 64
medium boulder 512 - 1024
large boulder 1024 - 2048
very large boulder 2048 - 4096
bedrock Bedrock
18
16
90%
14
80%
70%
Frequency
12
60%
10
50%
8
Frequency
6
40%
30%
4
20%
2
10%
>4096
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
11.3-16
5.7-8
4-5.7
<2
<2
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
180
- 180
256
- 256
362
- 362
- 512
Particle Size Category128
(mm)
512 - 1024
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
6
20
60
140
190
300
Cool Creek
Cumulative Frequency
0%
2-4
0
Cumulative Frequency
100%
Sorting Coefficient:
Material
1.70
P erc ent C ompos ition
Sand
Gravel
0%
55%
Cobble
Boulder
Bedrock
43%
2%
0%
Skewness Coefficient:0.15
A—69