Site Evaluations
Simpson Creek
Site Information
Site Location:
Willamette NF, Forest Rd 21 MP 21.1
Year Installed:
1995
Lat/Long:
122°23’48.74”W
43°29’48.24”N
Watershed Area (mi2):11.3
Stream Slope (ft/ft)1: 0.0516
Channel Type: Step-pool
Bankfull Width (ft): 25
Survey Date:
1
March 22, 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:
22
Outlet Type:
Mitered
Culvert Length:
114
Inlet Type:
Mitered
Pipe Slope (structure slope): 0.083
Culvert Bed Slope: 0.044
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.89
Alignment Conditions: Online with natural channel.
Bedform Conditions: Coarse material forming many continuous steps in culvert.
Pipe Condition: Good condition. Little to no rust or open joints. No footing scour.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
2-year
Qbf2
5-year
10-year
50-year
100-year
65
258
330
407
511
751
858
2
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull elevations.
Simpson Creek
A—391
Culvert Scour Assessment
Points represent survey points
Figure 1—Plan view map.
A—392
Simpson Creek
Site Evaluations
History
The Simpson Creek culvert was installed in
1995. The previously installed culvert had a
14-foot diameter, a 3- to 4-foot perch and a
sediment wedge was apparent at the culvert
inlet (Kim Johansen, personal communication).
According to the designer (Kim Johansen), class
VII riprap was specified, which would have had
the largest particles 1.6 feet in diameter. Local pit
material was actually placed in the culvert, which
contained a more well-graded but fine-lean mix.
This included up to 24-inch-diameter boulders.
It also included 3.5- to 4.5-foot “fish rest stop
rocks” placed at 16-foot intervals in two rows 11
feet apart centered in the structure and offset by
8 feet from one another. There was 12 inches of
screened aggregate approximately 2-inch to 1/2inch was placed on top of the constructed bed.
The spread footing is 5 feet deep and 5 feet wide.
There was a 7-foot-deep scour pool below the
old culvert. The downstream scour pool was filled
placing a group of 3- to 5-foot-diameter boulders
in the bottom, then pulling tailout material into
the hole to restore a long profile. The channel
exhibited at least two major historic channels
downstream within the delta area downstream of
the culvert. The culvert experienced the February
1996 flood, which was estimated to be a 100-year
flood on Simpson Creek. The flood resulted in
upstream channel incision and deposition in the
culvert.
which is followed by a large drop and a plunge
pool at the inlet. Evidence of channel incision
upstream of the culvert can be observed along
both banks, but is most apparent on the actively
eroding left bank.
The Simpson Creek culvert is a bottomless
arch that is mitered to conform to the roadfill.
The channel through the crossing consists of a
series of steep riffles and steps interspersed by
turbulent plunge pools. Assuming the culvert and
culvert bed were originally installed on the same
grade, there has been bed adjustment within the
pipe consisting of incision in the upstream portion
and/or aggradation in the downstream portion.
The above information was provided by
Kim Johansen.
Downstream of the culvert, the channel remains
relatively flat, opening to a braided reach. An
abandoned channel runs along the right valley
wall. The channel splits at an island below the
culvert. Below the island, gradient picks up and
the reach consists of steep riffles and steps
interspersed with turbulent plunge pools. The
substrate here is finer than in the culvert and
in the channel upstream of the culvert, and is
comprised of large cobbles and small-to-medium
boulders. A more extensive and well-defined flood
plain exists in the downstream reach compared to
the upstream reach. This is largely a depositional
area as the Simpson Creek valley transitions into
the broad valley of the mainstem Middle Fork
Willamette. Small wood pieces have accumulated
along the margins of the stream. A gravel road
runs along the left bank.
Site Description
The upstream channel consists of a high gradient
step-pool channel with a low but narrow active
flood-plain surface. The channel sits in a confined
and narrow valley and at times abuts the valley
walls. Boulder steps are interspersed by turbulent
plunge pools. Downed trees stretched across the
channel while some in-channel wood forms jams
along the edges. The upstream channel flattens
as it enters the culvert. There appears to be some
material that has deposited upstream of the inlet,
Survey Summary
Fifteen cross sections and a longitudinal profile
were surveyed along Simpson Creek in March
2007 to characterize the culvert, the upstream
channel, and the downstream channel. Four
cross sections were measured upstream of the
culvert to characterize the upstream channel.
Four cross sections were measured downstream
of the culvert to characterize the channel
downstream of the crossing. In the culvert,
cross sections were taken through a step and
Simpson Creek
A—393
Culvert Scour Assessment
between steps. Two additional cross sections
were surveyed downstream of the culvert to
characterize the outlet and the expansion of flow.
Another cross section was surveyed upstream
to characterize the inlet and the contraction of
flow. Six pebble counts were taken at crosssection locations. The cross-section locations and
pebble-count locations are depicted on the map
(figure 1)
Profile Analysis Segment Summary
The profile analysis resulted in 10 profile
segments (figure 2). The culvert consisted of
one profile segment (F). The culvert segment
matched the gradient of a representative segment
in the upstream channel (H), which is affected by
channel incision; interpretations of results take
this into account. Another representative segment
in the upstream channel (J) had a gradient
difference of 35 percent, but was included as a
potential comparison segment due to similarities
in bed morphology (closely spaced step-pool
sequences) (table 1).
The inlet transition segment (G) has comparable
gradient to two downstream channel segments (A
and C) and one upstream segment (J). The outlet
transition segment has comparable gradient to
segment H, with the same caveats mentioned
above.
Segment comparisons must consider that
throughout this reach is a geomorphic transition
from the narrow Simpson Creek valley into the
broad Middle Fork Willamette River valley. This
transition is characterized by a downstream
widening of the valley and a concave longitudinal
profile shape. Geomorphic influences, such as
gradient and valley width that change throughout
this reach are taken into consideration when
interpreting comparisons between segments.
A—394
Scour Conditions
Observed conditions
Footing scour – There was no observed scour
undermining footings or threatening structure
integrity.
Culvert-bed adjustment – Assuming that the
culvert structure and culvert bed were originally
constructed at the same gradient, the culvertbed profile has flattened since construction.
This flattening appears to be mostly due to
aggradation within the downstream portion of the
culvert, with potentially some inlet scour within
the upstream portion of the culvert. Approximately
100 cubic yards were estimated to have been
entrained during the 1996 flood, depositing
downstream of the culvert into the mainstem
Middle Fork Willamette River and extending
upstream to aggrade the entire culvert bed and
about 30 feet of upstream channel. Since then,
the upstream extent of deposits has moved
downstream to the midpoint of the culvert. Inlet
contraction during other smaller flood events has
maintained transport of material through the inlet
region (Kim Johansen, personal communication).
Profile characteristics – The profile has a concave
shape through the crossing (figure 2). This
shape reflects channel incision in the upstream
channel and scour at the inlet region, combined
with aggradation in the downstream portion of
the culvert and in the channel downstream of
the culvert. Incision in the upstream channel
potentially resulted from a headcut propagating
upstream from inlet scour. In the absence of the
culvert, natural concavity of the profile would
be expected based on the geomorphic valley
transition through this reach. The adjustments
observed at this site may reflect the tendency
towards this concave profile condition.
Simpson Creek
Residual depths – Culvert residual depths ranged
from 0.11 feet to 1.17 feet and were within the
range of the comparable slope segment J (figure
21). The upstream transition segment was also
within the range of comparable slope segments.
Residual depth in the downstream transition
segment was within a few inches of that found in
the comparable slope segment H. These results
suggest no significant local scouring at the
channel-unit scale beyond what is found in the
channel outside of the crossing.
Substrate – Culvert bed material distributions
are similar to segments in the channel outside of
the crossing. Culvert substrate is slightly coarser
than channel pebble counts, reflecting large rocks
placed in the culvert during construction. Culvert
substrate generally has less material in the fine
size classes. Pebble counts are provided at the
end of this summary.
Predicted conditions
Cross-section characteristics – Cross-section
characteristics appear to be affected by the
culvert (figures 5 through 7 and 12 through 17).
In the absence of the culvert, we might expect a
gradual change in cross-section characteristics
as the reach transitions into the broader valley of
the Middle Fork Willamette. However, for widthto-depth ratio, wetted perimeter, and top width,
the culvert is an anomaly in that trend. With the
exception of flow area, the range of values for
the culvert differs from that of comparable slope
segments for nearly all of the cross-section
metrics.
For all the cross-section metrics, the upstream
transition segment (G) is mostly within the range
of values of the upstream comparable segment
(J). However, downstream segments with
comparable gradient (A and C) differ substantially,
especially at the higher flows. Although these
discrepancies may be partly due to culvert
influences, they are also likely affected by the
natural change in valley width between these
segments.
Simpson Creek
Site Evaluations
The downstream transition segment (E) is
substantially different for nearly all crosssection metrics than segment H. It is difficult
to distinguish the effect of the culvert from the
influence of transitioning valley width and gradient
through this reach. Segment H also has potential
influence from channel incision, which limits its
utility for comparisons.
Shear stress – The culvert (F) has lower shear
stresses than the upstream comparative
segments (H and J) (figures 10 and 19). Lower
shear stress may be attributable to a lower
energy slope in the pipe that is caused by
outlet control conditions related to reduced pipe
capacity from aggradation in the downstream
portion of the pipe. The upstream transition
segment (G) has similar shear to the upstream
comparable segment (J) at the Q10 and below but
less shear above the Q10. Shear is comparable
between G and the downstream segments with
similar gradient (A and C). The downstream
transition segment (E) has lower shear than
comparable segment H.
Excess shear – The excess-shear analysis
suggests that the potential for bed mobilization in
the culvert is within the range of the downstream
channel (figure 20) but is lower than the upstream
channel. Higher channel shear in the upstream
channel and slightly smaller D84 contribute to
higher estimated bed mobility in the upstream
channel when compared to the culvert.
Velocity – The variation of velocity in the culvert
segment is more similar to the upstream channel
than the downstream channel (figures 11 and
18). Culvert velocity is generally similar to the
comparative segments H and J for all modeled
flows. The range of velocity in the upstream
transition segment (G) does not substantially
differ from the comparable slope segments
(A, C, and J). Velocity in the downstream
transition segment (E) is generally lower than the
comparative segment H, especially at the higher
flows.
A—395
Culvert Scour Assessment
Scour summary
The culvert shows no significant bed scour.
However, assuming the culvert and culvert bed
were originally constructed at the same gradient,
there has been bed adjustment. This adjustment
is believed to be primarily related to the February
1996 flood event (approximately a 100-year
flood), which resulted in profile adjustment
through aggradation in the downstream
portion of the pipe (Kim Johansen, personal
communication). Some culvert capacity has been
lost as a result. This is reflected in the model, with
elevated water surface profiles through the culvert
due to outlet control conditions. Despite this slight
capacity reduction, this large culvert is at low risk
of significant backwater or overtopping.
Conditions indicate a low risk for future scour
in the culvert. There is likely to be a continued
upstream supply of material as the channel
continues to widen in response to the 1996
incision. Continued aggradation may occur
downstream of the outlet where the valley widens
and the slope flattens. 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 both within the range of those in the channel
cross sections (table 3).
Profile complexity – Vertical sinuosity in the
culvert segment (F) and in the upstream transition
segment (G) are greater than their comparable
channel segments (table 4). This reflects a higher
frequency of steps through these segments.
Vertical sinuosity in the downstream transition
segment (E) is the same as comparative segment
H.
A—396
Depth distribution – There is less channel margin
habitat in the culvert compared to the channel at
the 25 percent Q2 (table 5).
Habitat units – There is a similar habitat-unit
composition between the culvert and the channel
outside the crossing (table 6). There is slightly
more pool habitat in the culvert and less step
habitat. The number of steps in the culvert is
high but they are shorter steps than the natural
channel with more pool habitat in between. 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 and more pool area is outside the
influence of turbulence created by the upstream
step.
Residual depths – Culvert-residual depths ranged
from 0.11 feet to 1.17 feet and were within the
range of the comparable slope segment J (figure
21). The upstream transition segment was also
within the range of comparable slope segments.
Residual depth in the downstream transition
segment (E) was within a few inches of that found
in the comparable slope segment H.
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. The size and frequency of the large
particles in the culvert are similar to the upstream
channel but greater than the downstream
channel. This partly reflects the gradient transition
through the crossing but also reflects the large
rocks that were placed during construction.
Culvert bed material sorting values are all within
the range found in the stream channel (table 7).
Sorting values indicate “poor” sorting, which is
typical for step-pool systems. The bed material
skewness value in the upstream cross section
Simpson Creek
in the culvert is less than any skewness values
in the channel. The low value indicates a nearly
normal (symmetrical) distribution, which is
due to a lack of material in most of the smaller
size classes (less than 22.6 millimeters). The
distribution among the larger size classes is
similar to that found in the channel cross sections.
Large woody debris – There was no LWD present
in the culvert (table 8). The representative
channel had very high LWD abundance, but most
of the wood was smaller pieces of alder along the
channel margins, with occasional large pieces
creating lateral scour pools. This channel margin
wood would provide velocity refuge for fish at
high flows. This condition was not present in the
culvert.
AOP summary
Measurements and observations suggest that
the Simpson-Creek culvert has similar conditions
to the natural channel with respect to AOP, with
potential passage issues only at higher flows
when turbulence and lack of margin areas in the
culvert may reduce passability.
Cross-section complexity in the culvert is within
the range of that found in the channel. Culvertresidual depths are also similar to the channel;
however, the vertical sinuosity in the culvert
(and in the upstream transition) is greater, which
indicates a different bedform pattern in the
culvert region. This is likely related to the large
material that was placed at frequent intervals
in the culvert during construction, including the
“fish rest stop” rocks. At lower fish passage flows
(i.e., an average spring, summer, or fall flow)
these frequent steps could provide ample velocity
refuge for passage; however, at larger flows the
frequent steps could create turbulence within
the adjoining small pools, potentially limiting
the availability of low energy areas for fish to
Simpson Creek
Site Evaluations
hold during migration. Furthermore, based on
the depth-distribution analysis, suitable channel
margin areas would not be available during these
higher events.
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 and the placement of
boulders during construction. These similar bed
compositions suggest that AOP is not impaired by
the characteristics of the culvert bed material.
Design Considerations
Despite moderate bed adjustments, this design
has functioned well, especially considering
that it experienced an approximate 100-year
flood within 5 months following installation. It is
uncertain the degree to which channel incision
is related to the culvert design as opposed to
naturally occurring incision during the Q100 flood.
In either case, over 10 years later the culvert
appears capable of conveying flood flows without
overtopping, scouring, or significantly altering
channel hydraulics. Hydraulic modeling indicates
that even at the Q100, the total culvert diameter
would only be submerged 50 percent at the inlet
and less than 75 percent at the outlet, which
exceeds standard design criteria.
An increase in channel margin areas (i.e.,
through bank construction within a wider culvert)
could benefit fish passage by creating shallower
flows along channel margins during high fish
passage flows (e.g., 25 percent Q2). Additionally,
lengthening the pool/step sequence in the culvert
so that it better matches the spacing found in the
channel could improve passability by reducing the
inter-step (pool) turbulence.
A—397
A—398
Relative elevation (ft)
122
47
42
26
172
F
G
H
I
J
800
700
(rif fle )
Pe b b le c o u n t
A
3
600
(s te p /rif fle )
Pe b b le c o u n t
B
4
C
0 .0 6 8
0 .0 4 2
0 .0 9 7
0 .0 7 1
0 .0 4 4
0 .0 3 4
0 .0 9 4
0 .0 5 8
0 .0 2 9
6
H
J
J
A
C
H
G
G
G
D o w n s trea m T ra n s itio n
E
U ps trea m T ra n s itio n
400
(p o o l)
17.6%
4.3%
16.5%
24.5%
5.1%
35.0%
9
300
(s te p /rif fle )
Pe b b le c o u n t
% D ifferen c e in
G ra d ien t
8
C ulvert
Pe b b le c o u n t
7
F
D is ta nc e a long bed (feet)
5
F
F
500
E
R epres en ta tiv e C h a n n el
S eg men t
D
Split channel
through this
section
C u lv ert S eg men t
Table 1—Segment comparisons
Figure 2—Simpson Creek longitudinal profile.
80
85
90
1
72
E
2
37
69
C
D
Representative Channel
72
B
0 .0 8 5
G r a d ie n t
22
A
Relative elevation (feet)
95
100
105
110
115
120
125
130
S egm en t
S egm ent
L e n g th ( f t)
S egm ent
G
10
11
H
I
200
12
(s te p )
Pe b b le c o u n t
13
J
100
Representative Channel
14
(p o o l)
Pe b b le c o u n t
15
0
Culvert Scour Assessment
Simpson Creek
Simpson Creek
n
o
i
t
a
v
e
l
E
)
t
f
(
0.1138 – 0.1143
0.115 – 0.1164
0.1147 – 0.127
0.105 – 0.1299
0.0903 – 0.1409
0.1309 – 0.1376
0.117 – 0.131
A
C
E
F
G
H
J
SegmentRange of Manning’s n values1
2
2
3
3
1
1
1
# of measured XSs
12
4
4
16
9
5
4
# of interpolated XSs
Elevation (ft)
80
90
100
110
120
130
0
.
.
.
3
3
3
3
.
1
.
.
.
6
6
6
6
.
1
*
5
2 5
. .
2 2 2
1
.
3 3
*
2
.
3
*
3
.
3
*
5
.
3
100
*
4
.
3
*
6
.
3
*
7
.
3
Figure 3—HEC-RAS profile.
1
*
8
1
.
4
*
5
2
.
4
*
9
3
.
4
200
*
2
3
.
4
*
6
4
.
4
*
3
5
.
4
6
.
4
*
6
6
.
4
*
2
7
.
4
*
8
7
.
4
*
4
8 9
. .
4 4
*
3
3
3
3
5
.
5
8
.
5
5
7
.
6
8
7
.
6
8
.
6
7
4
.
7
5
.
7
8
400
5
2 2
. .
8 8
Main Channel Distance (ft)
300
*
6
6
6
6
2
.
5
5
.
8
*
3
3
3
3
3
.
9
*
6
*
6
5
6
*
2
6
5
1
6
.
.
. 0 0 1 1
9 1 1 1 1
*
5
2
.
1
1
5
.
1 2
1 1
500
*
5
7
3
.
1
1
5
.
2 3
1 1
3
1
.
3
1
5
2
.
3
1
*
5
7
3
.
3
1
*
5
.
3
1
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
8
.
3
*
9
.
3 4
*
5
0
1
.
4
*
5
2
6
.
3
1
5
.
4
1
600
5
7
.
3 4
1 1
7
.
4
1
*
5
8
.
4
1
5
1
1
.
5
1
700
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
L eg en d
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
Site Evaluations
A—399
)
t
f
(
A—400
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
110
112
-40
-20
-20
0
0
20
.1301
Station (ft)
.1301
RS = 13
Station (ft)
20
.
1
3
1
40
40
.1301
60
60
80
80
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
Elevation (ft)
0
20
20
40
.117
80
60
100
80
WS Q50
WS Q100
Legend
110
-20
112
114
116
118
120
122
124
.1309
.1309
Station (ft)
40
60
.1309
RS = 12
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
116
Station (ft)
Bank Sta
118
0
Ground
120
-20
WS Bnkfl
WS 65 cfs
122
WS Q10
-40
.117
RS = 14
124
126
128
130
.117
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)
114
116
118
-40
.131
RS = 15
Elevation (ft)
120
122
124
120
122
124
126
128
130
132
134
.131
)
t
f
(
Culvert Scour Assessment
Simpson Creek
Simpson 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
20
40
RS = 9
60
.128
40
80
60
100
80
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
106
-20
Station (ft)
Bank Sta
Ineff
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
Elevation (ft)
104
-40
106
108
110
112
114
116
118
106
108
110
112
-20
20
0
60
RS = 8
Station (ft)
.115
Station (ft)
20
40
Note: n v alues f or f irs t prof ile.
40
80
100
80
120
60
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
Bank St a
Ground
WS 65 c fs
WS Bnkf l
WS Q10
WS Q50
116
114
L e ge nd
WS Q100
.1409
118
0
RS = 10
.1409
120
.1409
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)
108
110
.128
Station (ft)
20
Ground
0
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
WS 65 cfs
.128
-20
.1326
112
-40
.1326
RS = 11
Elevation (ft)
114
116
118
120
108
110
112
114
116
118
120
122
.1326
)
t
f
(
Site Evaluations
A—401
)
t
f
(
A—402
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
0
.127
0
40
20
40
60
.127
80
98
20
60
80
100
120
Station (ft)
Bank Sta
Ineff
Levee
102
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
.1152
.1152
60
80
100
120
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
90
92
94
96
98
100
102
104
100
102
20
40
Station (ft)
60
RS = 4
Station (ft)
80
100
.1152
120
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
Bank Sta
Ineff
Ground
40
.1124
WS 65 cfs
20
.1124
104
0
RS = 6
106
108
110
112
114
.1124
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)
100
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
104
106
108
.127
RS = 5
Bank St a
Ground
n
o
i
t
a
v
e
l
E
Elevation (ft)
110
112
114
102
-40
104
Station (ft)
WS Bnkf l
108
106
WS Q10
110
WS 65 c fs
WS Q50
-20
L e ge nd
WS Q100
112
114
116
.116
RS = 7
Note: n values for first profile.
)
t
f
(
Culvert Scour Assessment
Simpson Creek
Simpson 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
(
84
0
0
20
.1115
20
40
.1138
60
Station (ft)
40
.1115
RS = 1
Station (ft)
60
RS = 3
.1115
80
80
.1138
100
100
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
Bank Sta
Ground
WS 65 cfs
120
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
n
o
i
t
a
v
e
l
E
Elevation (ft)
86
88
90
92
94
96
98
100
0
.1145
20
40
.1145
Station (ft)
60
RS = 2
80
.1145
100
120
Bank Sta
Ground
WS 65 cfs
WS Bnkfl
WS Q10
WS Q50
WS Q100
Legend
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)
86
88
90
92
94
96
98
88
90
92
94
96
98
100
102
.1138
)
t
f
(
Site Evaluations
A—403
A—404
.
P
.
W
l
a
t
o
T
0
50
100
150
200
250
300
0
A
100
B
C
0
0
A
100
B
Figure 6—Wetted perimeter.
W.P. total (ft)
20
40
60
80
100
120
C
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
200
D
200
D
300
400
Culvert
F
300
400
Culvert
F
Main Channel Distance (ft)
E
Main Channel Distance (ft)
E
G
G
500
H
500
H
Flow
I
Flow
I
600
J
600
J
700
700
W.P. Total 65 cfs
W.P. Total Bnkfl
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Flow Area 65 cfs
Flow Area Bnkfl
Flow Area Q10
Flow Area Q50
Flow Area Q100
Legend
Culvert Scour Assessment
Simpson Creek
Simpson Creek
p
o
T
h
t
d
i
W
0
1
2
3
4
5
0
A
100
B
0
0
A
Figure 8—Top width.
Top width (ft)
20
40
60
80
100
120
100
B
Figure 7—Hydraulic radius.
Hydrauliic radius (ft)
)
t
f
(
r
d
y
H
s
u
i
d
a
R
)
t
f
(
C
C
200
D
200
D
E
300
400
Culvert
F
400
Main Channel Distance (ft)
300
F
Culvert
Main Channel Distance (ft)
E
G
G
H
500
500
H
I
I
Flow
Flow
J
600
600
J
700
700
Top Width 65 cfs
Top Width Bnkfl
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Hydr Radius 65 cfs
Hydr Radius Bnkfl
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
Legend
Site Evaluations
A—405
r
a
e
h
S
n
a
h
C
0
1
2
3
4
5
6
7
8
0
A
100
B
A—406
0
A
100
B
C
C
200
D
200
D
Figure 10—Shear stress (channel) profile.
Shear channel (lb/sq ft)
0
10
20
30
40
Figure 9—Maximum depth.
Maximum channel depth (ft)
q
s
/
b
l
(
)
t
f
x
a
M
l
h
C
h
t
p
D
)
t
f
(
300
Culvert
F
400
300
400
F
Culvert
Main Channel Distance (ft)
E
Main Channel Distance (ft)
E
G
G
500
H
500
H
I
I
600
J
Flow
600
J
Flow
700
700
Shear Chan 65 cfs
Shear Chan Bnkfl
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Max Chl Dpth 65 cfs
Max Chl Dpth Bnkfl
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
Legend
Culvert Scour Assessment
Simpson Creek
Simpson Creek
l
e
V
l
n
h
C
)
s
/
t
f
(
0
0
A
100
B
C
200
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
2
4
6
8
10
12
D
400
Culvert
F
Main Channel Distance (ft)
300
E
G
500
H
I
600
Flow
J
700
Vel Chnl 65 cfs
Vel Chnl Bnkfl
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Site Evaluations
A—407
Flow area (ft2)
A
C
J
J
F (Culv)
E (DS Trans)
25% Q2
E (ds trans)
G (us trans)
H
H
F (culv)
G (US Trans
C
Figure 12—Flow area (total).
0
50
A
Flow Area (ft2)
100
150
200
250
300
A
C
G (US Trans
F (Culv)
F (culv)
J
Qbf
A
50%
of the
values
J
H
E (DS Trans)
E (ds trans)
G (us trans)
H
100%
of the
values
C
A
H
J
10
A
Minimum value
25th percentile
C
F (culv)
H
J
J
H
E (DS Trans)
50
E (ds trans)
G (us trans)
F (Culv)
Median (aka 50th percentile)
J
H
E (ds trans)
G (us trans)
E (DS Trans)
C
75th percentile
F (culv)
F (Culv)
Maximum value
G (US Trans
C
A
A—408
G (US Trans
Box Plot Explanation
A
C
F (culv)
J
J
H
G (US Trans
F (Culv)
E (DS Trans)
100
E (ds trans)
G (us trans)
H
Culvert Scour Assessment
Simpson Creek
C
A
C
A
F (Culv)
E (DS Trans)
25% Q2
C
F (culv)
H
25% Q2
E (ds trans)
G (us trans)
F (Culv)
A
A
C
C
J
E (DS Trans)
H
J
Qbf
E (ds trans)
G (us trans)
F (culv)
Qbf
A
E (ds trans)
G (us trans)
F (culv)
H
A
A
C
C
C
A
A
G (US Trans
Figure 14—Hydraulic radius.
0
C
C
C
J
F (culv)
10
H
J
10
A
E (ds trans)
G (us trans)
F (culv)
H
E (ds trans)
G (us trans)
E (DS Trans)
C
Hydraulic Radius (ft)
1
2
3
4
5
J
E (ds trans)
G (us trans)
F (culv)
A
E (DS Trans)
F (Culv)
H
J
F (Culv)
G (US Trans
J
G (US Trans
H
J
A
H
J
H
E (DS Trans)
F (Culv)
J
A
F (Culv)
G (US Trans
C
G (US Trans
H
G (US Trans
H
Figure 13—Wetted perimeter.
A
A
A
C
C
A
C
C
J
F (culv)
50
H
J
50
A
E (ds trans)
G (us trans)
F (culv)
H
E (ds trans)
G (us trans)
E (DS Trans)
0
E (DS Trans)
F (Culv)
H
J
F (Culv)
G (US Trans
40
G (US Trans
H
J
A
H
J
20 Perimeter (ft)
Wetted
Hydraulic radius (ft)
C
A
A
C
C
60
C
C
H
J
F (culv)
100
H
J
E (ds trans)
G (us trans)
F (culv)
H
J
100
E (ds trans)
G (us trans)
E (DS Trans)
80
E (DS Trans)
F (Culv)
J
A
F (Culv)
G (US Trans
100
G (US Trans
H
Simpson Creek
J
Wetted perimeter (ft)
E (DS Trans)
Site Evaluations
A—409
E (DS Trans)
A
C
F (culv)
H
J
25% Q2
E (ds trans)
G (us trans)
Figure 16—Maximum depth.
0
2
A
C
F (culv)
J
C
E (DS Trans)
H
J
Qbf
E (ds trans)
G (us trans)
F (culv)
Qbf
A
E (ds trans)
G (us trans)
H
C
A
A
C
A
C
A
Max Depth (ft)
4
6
8
A
F (Culv)
G (US Trans
25% Q2
F (Culv)
Figure 15—Top width.
Maximum depth (ft)
C
F (culv)
C
C
C
F (culv)
J
F (culv)
10
H
J
10
A
E (ds trans)
G (us trans)
H
E (ds trans)
G (us trans)
E (DS Trans)
C
E (DS Trans)
G (US Trans
H
E (ds trans)
G (us trans)
A
E (DS Trans)
F (Culv)
H
J
F (Culv)
G (US Trans
J
G (US Trans
H
J
A
H
J
H
E (DS Trans)
F (Culv)
J
A
F (Culv)
G (US Trans
C
G (US Trans
H
A
C
A
A
C
0
C
C
F (culv)
J
F (culv)
50
H
J
50
A
E (ds trans)
G (us trans)
H
E (ds trans)
G (us trans)
E (DS Trans)
20
E (DS Trans)
F (Culv)
H
J
F (Culv)
G (US Trans
40
G (US Trans
H
J
A
H
J
Top Width (ft)
C
A
A
C
60
C
C
F (culv)
H
G (US Trans
J
F (culv)
100
H
J
E (ds trans)
G (us trans)
H
J
100
E (ds trans)
G (us trans)
E (DS Trans)
80
E (DS Trans)
F (Culv)
J
A
F (Culv)
G (US Trans
A—410
H
Top width (ft)
J
100
Culvert Scour Assessment
Simpson Creek
E (DS Trans)
H
G (US Trans
F (Culv)
25% Q2
Velocity (ft/sec)
A—411
A
H
J
25% Q2
E (ds trans)
G (us trans)
F (culv)
F (Culv)
A
C
C
J
H
J
Qbf
E (ds trans)
G (us trans)
F (culv)
Qbf
E (ds trans)
G (us trans)
F (culv)
H
A
A
C
C
C
C
C
C
C
G (US Trans
Figure 18—Velocity (channel).
0
Velocity
3 (ft/sec)
6
9
12
H
Figure 17—Width-to-depth ratio.
E (DS Trans)
J
J
F (Culv)
F (Culv)
E (ds trans)
G (us trans)
C
G (US Trans
G (US Trans
F (culv)
A
A
A
H
H
J
E (DS Trans)
E (DS Trans)
J
J
H
J
H
J
10
E (ds trans)
G (us trans)
F (culv)
10
E (ds trans)
G (us trans)
F (culv)
F (Culv)
F (Culv)
H
G (US Trans
G (US Trans
C
A
A
H
H
A
A
A
C
C
C
C
0
E (DS Trans)
E (DS Trans)
J
J
H
J
H
J
50
E (ds trans)
G (us trans)
F (culv)
50
E (ds trans)
G (us trans)
F (culv)
F (Culv)
F (Culv)
20
G (US Trans
G (US Trans
Width-to-Depth Ratio
A
A
H
H
40
E (DS Trans)
E (DS Trans)
J
J
60
A
A
C
C
C
C
A
A
A
A
H
J
J
H
J
100
E (ds trans)
G (us trans)
F (culv)
100
E (ds trans)
G (us trans)
F (culv)
F (Culv)
F (Culv)
80
G (US Trans
G (US Trans
100
E (DS Trans)
E (DS Trans)
H
H
Simpson Creek
J
Width-to-depth ratio
C
Site Evaluations
A—412
Shear stress (lbs/ft2)
A
C
H
G (US Trans
E (DS Trans)
J
25% Q2
A
200
D is c h ar g e (c fs )
400
C
F (culv)
J
J
H
G (US Trans
F (Culv)
E (DS Trans)
800
Qbf
1000
A
C
F (culv)
J
J
G (US Trans
F (Culv)
E (DS Trans)
10
E (ds trans)
G (us trans)
H
H
C
A
DS channel (DS pebble count - riffle)
DS channel (US pebble count - step/riffle)
Culvert (US pebble count - step/riffle)
US channel (DS pebble count - step)
E (ds trans)
G (us trans)
H
Figure 20—Excess shear stress.
A
A
C
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
Excess Shear (Applied / tcrit)
0
1
2
3
4
5
6
A
A
600
E (ds trans)
G (us trans)
H
J
Figure 19—Shear stress (channel).
C
F (culv)
F (Culv)
Shear Stress (lbs/ft2)
0
10
20
30
40
C
H
G (US Trans
F (Culv)
F (culv)
J
J
E (DS Trans)
50
E (ds trans)
G (us trans)
H
A
C
H
G (US Trans
F (Culv)
F (culv)
J
J
E (DS Trans)
100
E (ds trans)
G (us trans)
H
Culvert Scour Assessment
Simpson Creek
C
A
C
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
Step
0.04
Yes
DS
Pool
0.13
Yes
US
Pool
0.03
DS
Step
0.19
US
Step
0.03
DS
Riffle
0.03
Upstream
Downstream
Table 4—Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS channel
1.007
B
DS channel
1.001
C
DS channel
1.008
D
DS channel
1.003
E
DS Transition
1.005
F
Culvert
1.015
G
US Transition
1.015
H
US channel
1.005
I
US channel
1.024
J
US channel
1.009
Table 5—Depth distribution
Reach
Culvert
XS
25% Q2
Location
Within range of
channel conditions?
US
0
No
DS
0
No
US
5
DS
10
US
5
DS
9
Upstream
Downstream
Simpson Creek
A—413
Culvert Scour Assessment
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
53%
0%
39%
8%
Upstream Channel
47%
0%
30%
23%
Downstream Channel
20%
0%
63%
26%
1.4
1.2




1.0


0.8


Segment G
(US Transition)
Segment F
(Culvert)
Segment E
(DS Transition)
Segment D
Segment C
Segment B
Segment A
0.0








Segment I

0.2
Segment J
Residual
depth (ft)
0.4
Segment H
0.6



(culvert)
Segment ASegment BSegment CSegment D
Segment F
Segment HSegment I Segment J
Segment E
Segment G
(DS transition)
(US transition)
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
Step
1.45
Yes
0.03
No
DS
Pool
1.53
Yes
0.13
Yes
US
Pool
1.95
0.12
DS
Step
1.71
0.14
US
Step
1.46
0.31
DS
Riffle
1.21
0.12
Upstream
Downstream
A—414
Simpson Creek
Site Evaluations
Table 8—Large woody debris
Reach
Pieces/Channel Width
Culvert
0
Upstream
4.13
Downstream
5.12
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross section
View upstream towards outlet.
View downstream towards inlet.
View upstream from roadway.
Upstream reference reach.
Simpson Creek
A—415
Culvert Scour Assessment
Upstream reference reach – upstream pebble count, pool.
Upstream reference reach –
downstream pebble count, step.
Downstream reference reach.
Downstream reference reach –
downstream pebble count (riffle).
Downstream reference reach – View upstream in culvert.
upstream pebble count (riffle/step).
A—416
Simpson Creek
Site Evaluations
Cross Section: Upstream Reference Reach – Upstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize 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 %
2
3
1
3
1
6
5
7
8
9
14
7
7
13
11
7
3
0
0
0
2%
3%
1%
3%
1%
6%
5%
7%
7%
8%
13%
7%
7%
12%
10%
7%
3%
0%
0%
0%
2%
5%
6%
8%
9%
15%
20%
26%
34%
42%
55%
62%
68%
80%
91%
97%
100%
100%
100%
100%
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
Bedrock
2048-4096
512-1024
1024-2048
362-512
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
8-11.3
Cumulative Frequency
2-4
4 - 5.7
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
5.3
19.92
80
300
457
700
Simpson Creek
11.3-16
<2
5.7-8
0%
4-5.7
0
<2
10%
2-4
2
Cumulative Frequency
80%
12
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
40%
38%
20%
0%
Sorting Coefficient:
1.95
Skewness Coefficient: 0.12
A—417
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)
C ount
Item %
C umulative %
0
1
1
2
1
1
5
3
7
6
10
8
15
9
9
6
6
3
0
0
0%
1%
1%
2%
1%
1%
5%
3%
8%
6%
11%
9%
16%
10%
10%
6%
6%
3%
0%
0%
0%
1%
2%
4%
5%
6%
12%
15%
23%
29%
40%
48%
65%
74%
84%
90%
97%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
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
5.7-8
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
13
35
130
365.6
682
1200
A—418
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
29%
45%
26%
0%
Sorting Coefficient:
1.71
Skewness Coefficient: 0.14
Simpson 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 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
0
3
0
0
0
0
6
5
6
16
8
11
7
16
12
8
0
0
0
1%
0%
3%
0%
0%
0%
0%
6%
5%
6%
16%
8%
11%
7%
16%
12%
8%
0%
0%
0%
1%
1%
4%
4%
4%
4%
4%
10%
15%
21%
37%
45%
57%
64%
80%
92%
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
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
Cross Section: Culvert – Upstream Pebble Count
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.3
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
25
50
140
403.2
610
800
Simpson Creek
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
1%
20%
42%
36%
0%
Sorting Coefficient:
1.45
Skewness Coefficient: 0.03
A—419
Culvert Scour Assessment
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
0
0
2
0
1
3
1
12
5
10
11
9
18
8
10
7
0
0
0
0%
0%
0%
2%
0%
1%
3%
1%
12%
5%
10%
11%
9%
19%
8%
10%
7%
0%
0%
0%
0%
0%
0%
2%
2%
3%
6%
7%
20%
25%
35%
46%
56%
74%
82%
93%
100%
100%
100%
100%
20
100%
18
14
60%
Frequency
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
5.7-8
<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
11.316- 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
21.6
40
140
386.4
554
720
A—420
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
0%
25%
49%
26%
0%
Sorting Coefficient:
1.53
Skewness Coefficient: 0.13
Simpson Creek
Cross Section: Downstream Reference R
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 %
1
1
1
0
1
1
5
3
6
2
12
8
17
17
17
7
2
0
0
0
1%
1%
1%
0%
1%
1%
5%
3%
6%
2%
12%
8%
17%
17%
17%
7%
2%
0%
0%
0%
1%
2%
3%
3%
4%
5%
10%
13%
19%
21%
33%
41%
57%
74%
91%
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
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
Cross Section: Downstream Reference Reach – 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
20
40
160
340
470
900
Simpson Creek
Reach – Downstream Pebble Count
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
1%
20%
53%
26%
0%
Sorting Coefficient:
1.46
Skewness Coefficient: 0.31
A—421
Culvert Scour Assessment
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)
C ount
Item %
C umulative %
3
0
0
0
1
1
3
10
6
9
25
8
20
5
6
2
1
0
0
0
3%
0%
0%
0%
1%
1%
3%
10%
6%
9%
25%
8%
20%
5%
6%
2%
1%
0%
0%
0%
3%
3%
3%
3%
4%
5%
8%
18%
24%
33%
58%
66%
86%
91%
97%
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
30
100%
90%
25
70%
20
Frequency
60%
15
50%
40%
Frequency
10
30%
20%
5
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
11.3-16
16-22.6
5.7-8
8-11.3
2-4
<2
4-5.7
0%
<2
0
Cumulative Frequency
80%
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
19.75
30
82.5
171.6
281
600
A—422
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
3%
30%
58%
9%
0%
Sorting Coefficient:
1.21
Skewness Coefficient: 0.12
Simpson Creek