Culvert Scour Assessment
Hehe Creek
Site Information
Site Location:
Willamette NF, Forest Road 1831
Year Installed:
Circa 1986
Lat/Long:
122°24’21.63”W
Watershed Area (mi2): 1.86
44°1’58.62”N
Stream Slope (ft/ft)1: 0.0474
Channel Type:
Step-pool
Bankfull Width (ft): 19.5
1
Survey Date: April 4, 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: Hybrid projecting/mitered
Culvert Length:
60 ft
Inlet Type:
Hybrid projecting/mitered
Pipe Slope (structure slope): 0.045
Culvert Bed Slope: 0.041
(First hydraulic control upstream of inlet to first hydraulic control downstream of outlet.)
Culvert width as a percentage of bankfull width: 0.87
Alignment Conditions: Online with natural channel.
Bed Conditions: Large cobbles/boulders forming steps in culvert.
Pipe Condition: Good condition. Little-to-no rust.
Hydrology
Discharge (cfs) for indicated recurrence interval
25% 2-yr
Qbf2
2-year
5-year
10-year
50-year
100-year
45
160
178
258
310
424
471
2
Bankfull flow estimated by matching modeled water surface elevations to field-identified bankfull elevations.
A—268
Hehe Creek
Site Evaluations
Points represent survey points
Figure 1­—Plan view map.
Hehe Creek
A—269
Culvert Scour Assessment
History
There is no information available for site history.
Site Description
The Hehe Creek culvert is a bottomless arch that
is mitered to conform to the slope of the road fill.
There has been some scour to bedrock at the
inlet and just upstream, and the original material
placed inside the culvert has most likely been
repositioned. Nevertheless, at the flow during
the survey, the channel in the culvert appeared
in good condition. Material above the wetted
channel formed intermittent banks and served
to concentrate flow in places, making for good
passage conditions for aquatic and terrestrial
organisms.
Exposed footings (stem walls) run along the
length of the culvert. A rootwad had been
deposited just inside the downstream end
of the culvert while large boulders located
along the footing have resulted in zones of
deposition. Riprap lines both banks upstream and
downstream of the culvert.
After a large rock step upstream of the inlet to the
culvert, the channel transitions to a flatter gradient
through the culvert. Large, angular bed material
creates a riffle interspersed by backwatered
pools during low flows. Grade through the culvert
is controlled by the downstream aggradation of
material, evident by the drop in channel elevation
at the outlet.
The upstream reach consists of a moderate
gradient step-pool channel with an extremely
small low active flood plain surface. Sitting in a
fairly confined and narrow valley, the channel is
frequently against the valley walls. Steep riffles
generally made up of large angular boulders are
interspersed by pools. Large wood had fallen
across the channel in some locations providing
structure and geomorphic complexity.
A—270
The downstream reach was very similar to the
upstream one, except for a large number of
alders that had fallen across the channel, most of
which were spanning the channel. Some of these
were potentially a result of roadside clearing.
Survey Summary
Seventeen cross sections and a longitudinal
profile were surveyed along Hehe Creek in April
2007 to characterize the culvert, an upstream
reference reach, and a downstream reference
reach. Reference sections in the culvert were
taken through a pool and riffle. Two additional
cross sections were surveyed upstream to
characterize the inlet as well as the contraction of
flow. Another two cross sections were surveyed
downstream of the culvert to characterize the
outlet and the expansion of flow.
Four cross sections were surveyed to
characterize the upstream reach; one each at
the upstream and downstream end, one through
a riffle, and one through a pool. Four cross
sections were also surveyed to characterize the
downstream representative reach; one each at
the upstream and downstream end, one through
a riffle, and one through a pool.
Profile Analysis
Segment summary
The profile analysis resulted in a total of 10
profile segments. The culvert consisted of three
profile segments. The downstream segment in
the culvert was comparable to two representative
profile segments. The upstream two segments
in the culvert were comparable to representative
profile segments in the downstream channel. The
upstream transition segment was comparable
to two representative profile segments. The
downstream transition segment was also
comparable to two representative profile
segments. See figure 2 and table 1.
Hehe Creek
Scour Conditions
Observed conditions
Footing scour – There was no observed scour
undermining footings or threatening structure
integrity.
Culvert-bed adjustment – The bed has undergone
no obvious significant adjustment. There is
material throughout the culvert. It is assumed that
some of the largest material was placed during
construction.
Profile characteristics – The profile has a mostly
uniform gradient through the crossing with a slight
concavity that is focused near and upstream of
the inlet. This area is comprised of bedrock and
may represent an area that has experienced
some scour and associated incision.
Residual depths – Culvert residual depths are
within, similar to, or greater than the residual
depths in corresponding profile segments (figure
21). The downstream and upstream transition
segments (C and G) are mostly within the range
of those found in corresponding profile segments
(A and H).
Substrate – Bed material distributions in the
natural channel are very poorly sorted, with a
broad range of size classes well represented.
The culvert cross-sections are less poorly sorted.
The upstream cross section in the culvert, located
in a pool unit, has a very negative skewness,
reflecting the predominance of finer material. The
pool cross sections in the natural channel also
exhibit either low or negative skewness values.
The abundance of fine and coarse material in the
culvert is relatively similar to what is found in the
natural channel.
Predicted conditions
Cross-section characteristics – The culvert has
an effect on cross-section flow geometry (figures
5-7 and 12-19). The effect is most apparent for
the width-related metrics top width and wetted
Hehe Creek
Site Evaluations
perimeter. The culvert begins to reduce these
values at the Qbf and above. Hydraulic radius and
maximum depth appear to be less affected. The
downstream transition (C) is mostly within the
range of the corresponding profile segments (A
and H). The upstream transition (G) has greater
widths but similar depths when compared to the
corresponding profile segments (A and H).
Shear stress – Shear stresses in the culvert
and in the transition segments do not differ
significantly from the ranges of values in
corresponding profile segments (figure 19).
Excess shear – The culvert excess shear is within
the range of excess shear in the natural channel
(figure 20).
Velocity – Velocity in the culvert and in the
transition segments do not differ significantly from
the ranges of values in corresponding profile
segments (figure 18)
Scour summary
There was no scour observed in the culvert. The
presence of bedrock upstream of the inlet and the
slight concavity of the profile in this area suggest
that some inlet scour may have occurred and
resulted in minor channel incision. In general, this
is considered a good installation with respect to
scour. Stable bed elements in the culvert mimic
those in the natural channel.
AOP Conditions
Cross-section complexity – The sum of squared
height differences in the culvert cross sections
are both lower than those in the channel cross
sections (table 3).
Profile complexity – The most downstream profile
segment in the culvert has less vertical sinuosity
than the corresponding profile segment in the
channel; the other two culvert segments have
greater vertical sinuosity than their corresponding
channel segments (table 4).
A—271
Culvert Scour Assessment
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 slightly less pool habitat
in the culvert but the habitat unit distributions are
relatively similar (table 6).
Residual depths – Culvert residual depths are
within, similar to, or greater than the residual
depths in corresponding profile segments (figure
21). The downstream and upstream transition
segments (C and G) are mostly within the range
of those found in corresponding profile segments
(A and H).
Substrate – Bed material distributions in the
natural channel are very poorly sorted, with a
broad range of size classes well represented.
The culvert cross sections are less poorly sorted.
The upstream cross section in the culvert, located
in a pool unit, has a very negative skewness,
reflecting the predominance of finer material. The
pool cross sections in the natural channel also
exhibit either low or negative skewness values.
The abundance of fine and coarse material in the
culvert is relatively similar to what is found in the
natural channel.
Large woody debris – There was a low amount of
LWD present in the culvert (table 8). The natural
channel had high LWD abundance. Some of this
wood was suspended above the low flow channel
but was within the bankfull channel. LWD formed
steps and scour pools in the channel outside the
crossing and played a primary role in habitat unit
creation and complexity.
A—272
AOP summary
This is considered a good installation with respect
to AOP. The unit types and pattern of bedforms
in the culvert are similar to that found in the
natural channel. There is potentially less shallow
channel margin habitat available at certain flows
but residual depths, profile complexity, and the
frequency of coarse material indicate adequate
complexity to provide velocity refuge for fish
passage. At the time of the survey, there were
semi-continuous banks through the culvert. At
lower flows these banks are likely continuous and
would provide for good terrestrial passage but
at the flow during the survey and greater, they
become at least partially inundated and are less
suitable for terrestrial passage.
Design Considerations
The Hehe Creek culvert is a good design with
respect to scour and AOP. The culvert size
appears adequate to convey high flows without
creating significant scour risk. Some scour and
associated incision may have occurred near and
upstream of the inlet but it is unknown whether
this adjustment was related to the current culvert
or a previous installation. The presence of
bedrock helps to limit scour in this area. Culvert
design at this site is made easier by the lack of a
significant valley transition through this area.
The one design consideration for this site relates
to bank construction in the culvert. There are
discontinuous banks in the culvert that likely
provide for terrestrial organism passage at low
flow periods. Construction of continuous banks
would provide for terrestrial passage at a broader
range of flows and may also increase the amount
of shallow channel margin habitat available for
fish passage at flows near the 25 percent Q2.
Hehe Creek
Hehe Creek
Relative elevation (ft)
XS 1
500
XS 2:
Pebble count
(pool)
H
A
A
H
C
C
R epres en ta tiv e
C h a n n el S eg men t
A
H
B
A
G
G
D o w n s trea m T ra n s itio n
C u lv ert S eg men t
D
D
E
F
U ps trea m T ra n s itio n
Table 1—Segment comparisons
400
XS 4
XS 5
C
XS 7:
Pebble count
(riffle)
XS 6
D
17.4%
9.9%
17.0%
10.3%
% D ifferen c e in
G ra d ien t
11.6%
15.8%
0.6%
16.7%
B
0 .0 5 8
0 .0 1 4
0 .0 6 3
0 .0 5 3
0 .0 5 3
0 .0 5 7
0 .0 2 0
XS 3:
Pebble count
(riffle)
Figure 2—Hehe Creek longitudinal profile.
80
85
A
Representative Channel
30
25
I
J
101
H
0 .0 3 9
26
73
29
E
F
20
D
G
0 .0 2 0
29
C
Relative elevation (feet)
90
95
100
105
110
115
27
B
0 .0 4 7
67
A
S e g m e n t G r a d ie n t
S e g m e n t L e n g t h ( f t)
S egm en t
300
XS 8:
Pebble count
(pool)
XS 9
F
XS 10
XS 11
D is ta nc e a long bed (feet)
E
C ulvert
XS 12
G
200
H
XS 13
XS 14
100
Representative Channel
XS 15:
Pebble count
(riffle)
XS 16:
Pebble count
(pool)
I
J
XS 17
0
Site Evaluations
A—273
n
o
i
t
a
v
e
l
E
)
t
f
(
A—274
0.1028 – 0.1151
0.1074 – 0.1107
0.1077 – 0.1137
0.1093 – 0.1137
0.1048 – 0.1118
0.1061 – 0.1143
0.1143 – 0.119
0.107 – 0.1258
A
B
C
D
E
F
G
H
SegmentRange of Manning's n values1
3
2
3
1
1
2
1
2
# of measured XSs
12
8
3
5
3
4
4
7
# of interpolated XSs
Elevation (ft)
85
90
95
100
105
110
115
0
5
.
1
*
8
.
2
*
5
3
.
4 4
5 6
5
7
.
6
7
2
.
7
5
.
1
1
8
.
1
1
*
1
.
2
1
*
2
.
2
1
3
.
2
1
Main Channel Dis tance (ft)
5 5
.
. 0
7 8 1
200
*
5
2
.
1
1
*
5
2 5
5 6 7
. . .
2 2 2
1 1 1
300
*
5
.
3 3 4
1 1 1
*
4
.
4
1
*
7
.
4
1
5
1
3
.
5
1
5
.
5
1
*
2
.
6
1
400
*
4
.
6
1
*
5
6 6
. .
6 6
1 1
Stations with decimal values are interpolated cross sections placed along the surveyed profile.
*
6
.
2
*
5
2 5
. .
3 3 3
100
Figure 3—HEC-RAS profile.
1
*
5
7
.
6
1
*
9
.
6
1
500
Ground
W S 45
W S Qbf
W S Q10
W S Q50
W S Q100
L e ge nd
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
Culvert Scour Assessment
Hehe Creek
Hehe 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
(
.1258
20
0
.
1
1
7
7
30
Station (ft)
RS = 15
Station (ft)
.1258
10
.1177
40
20
.
1
1
7
7
50
.1258
30
60
40
Elevation (ft)
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
n
o
i
t
a
v
e
l
E
n
o
i
t
a
v
e
l
E
)
t
f
(
Elevation (ft)
Elevation (ft)
10
0
111
110
109
108
107
106
105
104
103
102
101
-10
.1099
0
114
113
112
111
110
109
108
107
106
105
104
.1137
Station (ft)
.1137
20
30
RS = 14
Station (ft)
10
20
.1099
RS = 16
30
.1137
40
.1099
40
50
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 45
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.
114
113
112
111
110
109
108
107
106
105
104
10
116
115
114
113
112
111
110
109
108
107
106
-10
RS = 17
)
t
f
(
Site Evaluations
A—275
n
o
i
t
a
v
e
l
E
)
t
f
(
A—276
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
0
105
104
103
102
101
100
99
98
97
96
95
-10
.
1
0
7
.1158
10
10
20
Station (ft)
20
.1158
RS = 11
Station (ft)
.107
.
1
0
7
.
1
1
5
8
30
30
40
40
Elevation (ft)
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 45
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)
Elevation (ft)
104
103
102
101
100
99
98
97
96
95
94
106
105
104
103
102
101
100
99
98
97
96
0
0
.119
10
.1093
10
Station (ft)
20
.1093
RS = 10
Station (ft)
20
.119
RS = 12
30
30
.1093
.119
40
40
L e ge nd
B a n k S ta
In e ff
G ro u n d
WS 45
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 45
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. (continued)
0
108
107
106
105
104
103
102
101
100
99
98
-10
RS = 13
)
t
f
(
Culvert Scour Assessment
Hehe Creek
)
t
f
(
Hehe Creek
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
n
o
i
t
a
v
e
l
E
0
104
103
102
101
100
99
98
97
96
95
94
-10
Station (ft)
50
.111
10
Station (ft)
.1048
20
RS = 7
Note: n values for first profile.
40
.111
30
60
40
70
Elevation (ft)
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
B a n k S ta
In e ff
G ro u n d
n
o
i
W S Q1 0 0
t
W S Q5 0a
v
W S Q1 0
e
W S Qb f l
WS 45 E
L e ge n d
n
o
i
t
a
v
e
l
E
)
t
f
(
103
102
101
100
99
98
97
96
95
94
93
-10
104
103
102
101
100
99
98
97
96
95
94
-10
Elevation (ft)
Elevation (ft)
0
0
.
0
7
10
Station (ft)
.1137
10
20
RS = 6
Station (ft)
.1061
20
.07
RS = 8
Note: n values for first profile.
30
30
40
L e ge nd
40
B a n k S ta
In e ff
G ro u n d
WS 45
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 45
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.. (continued)
30
.111
104
103
102
101
100
99
98
97
96
95
94
20
RS = 9
)
t
f
(
Site Evaluations
A—277
n
o
i
t
a
v
e
l
E
)
t
f
(
A—278
Elevation (ft)
n
o
i
t
a
v
e
l
E
)
t
f
(
0
10
.1123
0
.1095
20
.1123
RS = 3
20
30
Station (ft)
Station (ft)
10
.1095
40
.1123
30
.1095
Elevation (ft)
50
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
40
B a n k S ta
In e ff
G ro u n d
WS 45
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
(
n
o
i
t
a
v
e
l
E
Elevation (ft)
Elevation (ft)
97
96
95
94
93
92
91
90
89
88
87
101
100
99
98
97
96
95
94
93
92
91
0
0
.1028
10
10
.1074
20
.1028
20
Station (ft)
RS = 2
Station (ft)
30
30
.1074
RS = 4
.1028
40
40
.1074
50
50
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Bank St a
Ground
WS 45
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)
99
98
97
96
95
94
93
92
91
90
89
102
101
100
99
98
97
96
95
94
93
92
-10
RS = 5
)
t
f
(
Culvert Scour Assessment
Hehe Creek
w
o
l
F
a
e
r
A
q
s
(
95
94
93
92
91
90
89
88
87
86
85
-10
0
.1083
10
Station (ft)
20
.1083
RS = 1
30
.1083
40
Bank St a
Ground
WS 45
WS Qbf
WS Q10
WS Q50
WS Q100
L e ge nd
Hehe Creek
0
0
A
100
B
C
Figure 5—Flow area (total) profile plot.
Flow area (sq ft)
20
40
60
80
100
120
E
F
G
Flow
300
Main Channel Distance (ft)
200
Culvert
D
H
400
I
J
500
Flow Area 45
Flow Area Qbf
Flow Area Q10
Flow Area Q50
Flow Area 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)
)
t
f
n
o
i
t
a
v
e
l
E
)
t
f
(
Site Evaluations
A—279
r
d
y
H
s
u
i
d
a
R
.
P
.
W
10
15
20
25
30
35
40
45
0
A
0.5
0
A
Figure 7—Hydraulic radius.
Hydraulic radius (ft)
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Figure 6—Wetted perimeter.
W.P. total (ft)
)
t
f
(
A—280
l
a
t
o
T
)
t
f
(
100
B
100
B
C
C
E
E
G
F
G
Flow
Flow
300
300
Main Channel Distance (ft)
200
Culvert
D
F
Main Channel Distance (ft)
200
Culvert
D
H
H
400
400
I
I
J
J
500
Legend
Hydr Radius 45
Hydr Radius Qbf
Hydr Radius Q10
Hydr Radius Q50
Hydr Radius Q100
500
W.P. Total 45
W.P. Total Qbf
W.P. Total Q10
W.P. Total Q50
W.P. Total Q100
Legend
Culvert Scour Assessment
Hehe Creek
x
a
M
l
h
C
h
t
p
D
p
o
T
10
15
20
25
30
35
40
45
0
A
0
A
Figure 9—Maximum depth.
Maximum channel depth (ft)
0
1
2
3
4
5
6
7
Figure 8—Top width.
Top width (ft)
)
t
f
(
Hehe Creek
h
t
d
i
W
)
t
f
(
100
B
100
B
C
C
E
E
G
F
G
Flow
300
300
Main Channel Distance (ft)
200
Culvert
D
F
Main Channel Distance (ft)
200
Culvert
D
Flow
H
H
400
400
I
I
J
J
500
Legend
Max Chl Dpth 45
Max Chl Dpth Qbf
Max Chl Dpth Q10
Max Chl Dpth Q50
Max Chl Dpth Q100
500
Top Width 45
Top Width Qbf
Top Width Q10
Top Width Q50
Top Width Q100
Legend
Site Evaluations
A—281
r
a
e
h
S
n
a
h
C
q
s
/
b
l
(
l
e
V
0
5
0
A
100
B
C
0
0
A
100
B
C
Figure 11—Velocity (channel) profile plot.
Velocity channel (ft/s)
2
4
6
8
10
E
E
Culvert
D
F
G
G
Main Channel Distance (ft)
200
F
Flow
Flow
300
300
Main Channel Distance (ft)
200
Culvert
D
Figure 10—Shear stress (channel) profile.
Shear channel (lbs/sq ft))
l
n
h
C
)
s
/
t
f
(
A—282
10
15
20
25
30
H
H
400
400
I
I
J
J
500
500
Vel Chnl 45
Vel Chnl Qbf
Vel Chnl Q10
Vel Chnl Q50
Vel Chnl Q100
Legend
Shear Chan 45
Shear Chan Qbf
Shear Chan Q10
Shear Chan Q50
Shear Chan Q100
Legend
Culvert Scour Assessment
Hehe Creek
60
90
120
A
B
D (Culv)
E (Culv)
C (DS Trans)
25% Q2
C (ds trans)
A
B
B
A
G (US Trans)
G (us trans)
H
H
F (culv)
D (culv)
E (culv)
F (Culv)
B
Figure 12­—Flow area (total).
0
100%
of the
values
H
G (US Trans)
F (Culv)
D (Culv)
Qbf
A
B
B
A
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
C (DS Trans)
C (ds trans)
H
50%
of the
values
F (Culv)
D (Culv)
10
C (ds trans)
C (DS Trans)
A
B
B
A
G (US Trans)
G (us trans)
H
Minimum value
25th percentile
G (US Trans)
E (Culv)
C (DS Trans)
50
C (ds trans)
A
B
B
A
G (us trans)
H
H
F (culv)
D (culv)
E (culv)
D (Culv)
Median (aka 50th percentile)
75th percentile
Maximum value
H
F (culv)
D (culv)
E (culv)
E (Culv)
Box Plot Explanation
F (Culv)
Hehe Creek
Flow30
Area (ft2)
Flow area (ft2)
A
H
G (US Trans)
E (Culv)
F (Culv)
D (Culv)
C (DS Trans)
100
C (ds trans)
G (us trans)
F (culv)
D (culv)
E (culv)
H
Site Evaluations
A—283
D (Culv)
F (Culv)
E (Culv)
25% Q2
B
A
A
B
25% Q2
C (ds trans)
A
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
Figure 14—Hydraulic radius.
0
B
Hydraulic Radius (ft)
1
2
3
4
F (Culv)
Figure 13—Wetted perimeter.
Hydraulic radius (ft)
C (DS Trans)
B
G (us trans)
H
C (ds trans)
C (DS Trans)
D (Culv)
H
F (culv)
D (culv)
E (culv)
G (US Trans)
G (US Trans)
A
A
B
Qbf
C (ds trans)
Qbf
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
B
B
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
H
C (DS Trans)
C (DS Trans)
D (Culv)
D (Culv)
H
H
B
A
A
G (US Trans)
G (US Trans)
A
B
F (Culv)
10
C (ds trans)
10
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
B
B
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
E (Culv)
B
C (DS Trans)
E (Culv)
F (Culv)
0
C (DS Trans)
D (Culv)
H
H
9 Perimeter (ft)
Wetted
G (US Trans)
G (US Trans)
A
A
50
C (ds trans)
50
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
E (Culv)
18
G (US Trans)
G (US Trans)
B
B
D (Culv)
D (Culv)
H
H
27
C (DS Trans)
C (DS Trans)
F (Culv)
F (Culv)
A
A
B
B
100
C (ds trans)
G (US Trans)
100
C (ds trans)
G (us trans)
F (culv)
D (culv)
E (culv)
H
G (us trans)
H
H
F (culv)
D (culv)
E (culv)
E (Culv)
E (Culv)
B
B
D (Culv)
D (Culv)
36
C (DS Trans)
C (DS Trans)
F (Culv)
F (Culv)
A—284
G (US Trans)
Wetted perimeter (ft)
H
45
Culvert Scour Assessment
Hehe Creek
A
2
4
6
B
25% Q2
A
B
25% Q2
C (ds trans)
H
A
A
G (us trans)
H
B
B
G (us trans)
F (culv)
D (culv)
E (culv)
Figure 16—Maximum depth.
0
A
F (Culv)
F (Culv)
C (ds trans)
C (DS Trans)
Maximum Depth (ft)
Maximum depth (ft)
B
E (Culv)
E (Culv)
Figure 15—Top width.
8
G (US Trans)
G (US Trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
H
H
Qbf
C (ds trans)
Qbf
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
A
A
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
B
G (US Trans)
G (US Trans)
A
C (DS Trans)
C (DS Trans)
H
H
B
B
10
C (ds trans)
10
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
A
A
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
0
C (DS Trans)
C (DS Trans)
H
H
9
G (US Trans)
G (US Trans)
B
B
50
C (ds trans)
50
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
18
C (DS Trans)
C (DS Trans)
A
A
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
Top Width (ft)
H
27
B
B
100
100
C (ds trans)
G (us trans)
F (culv)
D (culv)
E (culv)
H
G (us trans)
H
H
F (culv)
D (culv)
E (culv)
C (ds trans)
C (DS Trans)
C (DS Trans)
36
G (US Trans)
G (US Trans)
E (Culv)
E (Culv)
H
A
A
D (Culv)
D (Culv)
B
B
F (Culv)
F (Culv)
45
G (US Trans)
G (US Trans)
Hehe Creek
H
Top width (ft)
C (DS Trans)
Site Evaluations
A—285
F (Culv)
D (Culv)
E (Culv)
C (DS Trans)
25% Q2
C (ds trans)
Velocity (ft/sec)
B
A
A
B
D (Culv)
C (DS Trans)
25% Q2
C (ds trans)
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
Figure 18—Velocity (channel).
0
A
2
B
Velocity (ft/sec)
4
6
8
10
F (Culv)
H
G (us trans)
F (culv)
D (culv)
E (culv)
G (US Trans)
G (US Trans)
Figure 17—Width-to-depth ratio.
B
H
H
B
B
Qbf
C (ds trans)
Qbf
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
A
A
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
A
C (DS Trans)
C (DS Trans)
H
H
0
G (US Trans)
G (US Trans)
B
B
10
C (ds trans)
10
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
E (Culv)
E (Culv)
A
A
D (Culv)
D (Culv)
B
B
F (Culv)
F (Culv)
6
G (US Trans)
G (US Trans)
Width-to-depth Ratio
C (DS Trans)
C (DS Trans)
H
H
B
B
50
C (ds trans)
50
A
H
A
G (us trans)
F (culv)
D (culv)
E (culv)
C (ds trans)
H
G (us trans)
F (culv)
D (culv)
E (culv)
D (Culv)
D (Culv)
12
C (DS Trans)
C (DS Trans)
A
A
E (Culv)
E (Culv)
B
B
F (Culv)
F (Culv)
18
G (US Trans)
G (US Trans)
24
B
B
G (US Trans)
100
100
C (ds trans)
G (us trans)
F (culv)
D (culv)
E (culv)
H
G (us trans)
H
H
F (culv)
D (culv)
E (culv)
C (ds trans)
C (DS Trans)
C (DS Trans)
H
H
E (Culv)
E (Culv)
A
A
D (Culv)
D (Culv)
B
B
F (Culv)
F (Culv)
A—286
G (US Trans)
Width-to-depth ratio
H
30
Culvert Scour Assessment
Hehe Creek
4
8
12
16
A
B
G (US Trans)
E (Culv)
F (Culv)
D (Culv)
25% Q2
C (ds trans)
A
100
A
200
300
Dis c ha rge (c fs )
B
H
G (US Trans)
F (Culv)
D (Culv)
E (Culv)
C (DS Trans)
400
Qbf
C (ds trans)
A
500
Figure 20—Excess shear stress.
G (US Trans)
D (Culv)
C (DS Trans)
10
C (ds trans)
A
DS Channel (US pebble count) - riffle
Culvert (DS pebble count) - riffle
H
22
A
B
B
A
G (us trans)
F (culv)
D (culv)
E (culv)
F (Culv)
US Channel (DS pebble count) - riffle
B
B
G (us trans)
F (culv)
D (culv)
E (culv)
H
E (Culv)
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
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
Excess
0 Shear (Applied / tcrit)
A
B
G (us trans)
F (culv)
D (culv)
E (culv)
H
H
Figure 19—Shear stress (channel).
0
B
Shear Stress (lbs/ft2)
Shear Stress (lbs/ft2)
C (DS Trans)
Hehe Creek
H
20
H
G (US Trans)
F (Culv)
D (Culv)
E (Culv)
C (DS Trans)
50
C (ds trans)
A
B
B
A
G (us trans)
F (culv)
D (culv)
E (culv)
H
G (US Trans)
H
E (Culv)
F (Culv)
D (Culv)
C (DS Trans)
100
C (ds trans)
G (us trans)
F (culv)
D (culv)
E (culv)
H
Site Evaluations
A—287
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
Pool
0.10
No
DS
Riffle
0.03
No
US
Pool
0.04
DS
Riffle
0.09
Downstream
US
Riffle
0.04
DS
Pool
0.08
Upstream
Table 4—Vertical sinuosity
Segment
LocationVertical Sinuosity (ft/ft)
A
DS channel
1.004
B
DS channel
1.001
C
DS transition
1.007
D
Culvert
1.002
E
Culvert
1.003
F
Culvert
1.015
G
US transition
1.006
H
US channel
1.013
I
US channel
1.003
J
US channel
1.017
Table 5—Depth distribution
Reach
XS Location
25% Q2
Culvert
Within range of
channel conditions?
US
0
No
DS
0
No
US
2
DS
1
US
1
DS
2
Upstream
Downstream
A—288
Hehe Creek
Site Evaluations
Table 6—Habitat unit composition
Percent of surface area
Reach
Pool Glide
Riffle
Step
Culvert
24%
0%
76%
0%
Upstream Channel
38%
0%
50%
1%
Downstream Channel
29%
0%
64%
7%
1.4

0.8








Culvert
Culvert
Culvert
Segment H Segment I
TransitionSegment D: Segment E: Segment F:
Transition
Segment C: DS
Segment G: US
Segment A Segment B
Figure 21—Residual depths.


Segment E
Culvert
Segment B
Segment A
0.0
Segment F
Culvert


Segment D
Culvert
0.2

Segment J
Residual
depth (ft)
0.4
Segment H


Segment G
US Transition
0.6
Segment I
1.0



Segment C
DS Transition
Residual Depth (ft)
1.2
Segment J
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
Pool
2.01
No
-0.25
No
DS
Riffle
1.90
No
0.24
Yes
US
Pool
2.35
-0.07
DS
Riffle
2.77
0.34
US
Riffle
2.08
0.39
DS
Pool
2.44
0.02
Upstream
Downstream
Hehe Creek
A—289
Culvert Scour Assessment
Table 8—Large woody debris
Reach
Pieces/Channel Width
Culvert
0.33
Upstream
3.17
Downstream
3.84
Terminology:
US = Upstream
DS = Downstream
RR = Reference reach
XS = Cross-section
View upstream of culvert outlet.
View downstream from roadway.
A—290
View downstream towards culvert inlet.
View upstream from roadway.
Hehe Creek
Site Evaluations
Downstream reference reach – pebble count in
pool marked with flagging. Downstream reference reach – upstream pebble
count (riffle).
Upstream reference reach – downstream
Upstream reference reach – pebble count in pool
pebble count, riffle. above log step.
View upstream within culvert.
Hehe Creek
View downstream within culvert.
A—291
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
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
4
5
5
4
6
13
9
4
4
4
3
5
11
8
9
4
2
0
0
0
4%
5%
5%
4%
6%
13%
9%
4%
4%
4%
3%
5%
11%
8%
9%
4%
2%
0%
0%
0%
4%
9%
14%
18%
24%
37%
46%
50%
54%
58%
61%
66%
77%
85%
94%
98%
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%
14
80%
Frequency
10
70%
60%
8
50%
6
Frequency
40%
30%
4
20%
2
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
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
3
7
33
250
371
580
A—292
Cumulative Frequency
90%
12
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
4%
54%
27%
15%
0%
Sorting Coefficient:
2.35
Skewness Coefficient: -0.07
Hehe Creek
Site Evaluations
Cross-Section: Upstream Reference Reach – Downstream Pebble Count
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize C las s (mm)
C ount
Item %
C umulative %
7
3
4
4
1
5
5
4
3
7
8
7
7
9
7
2
9
0
0
3
7%
3%
4%
4%
1%
5%
5%
4%
3%
7%
8%
7%
7%
9%
7%
2%
9%
0%
0%
3%
7%
11%
15%
19%
20%
25%
31%
35%
38%
45%
54%
61%
68%
78%
85%
87%
97%
97%
97%
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
9
90%
8
80%
7
70%
6
60%
5
50%
4
Frequency
40%
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
<2
16-22.6
0%
11.3-16
10%
0
5.7-8
1
8-11.3
20%
4-5.7
30%
2
<2
3
Cumulative Frequency
100%
2-4
Frequency
10
2-4
4 - 5.7
5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
Particle Size Category (mm)
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
1
6
75
274
585
730
Hehe Creek
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
7%
38%
33%
19%
3%
Sorting Coefficient:
2.77
Skewness Coefficient: 0.34
A—293
Culvert Scour Assessment
Material
sand
very fine gravel
fine gravel
fine gravel
medium gravel
medium gravel
coarse gravel
coarse gravel
very coarse gravel
very coarse gravel
small cobble
medium cobble
large cobble
very large cobble
small boulder
small boulder
medium boulder
large boulder
very large boulder
bedrock
S ize R ange (mm)
C ount
Item %
C umulative %
5
4
2
10
9
17
11
5
8
9
5
3
4
7
7
0
0
0
0
4
5%
4%
2%
9%
8%
15%
10%
5%
7%
8%
5%
3%
4%
6%
6%
0%
0%
0%
0%
4%
5%
8%
10%
19%
27%
43%
53%
57%
65%
73%
77%
80%
84%
90%
96%
96%
96%
96%
96%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
> 4096
18
100%
16
90%
80%
14
70%
Frequency
12
60%
10
50%
8
40%
Frequency
6
30%
Cumulative Frequency
Bedrock
2048-4096
1024-2048
362-512
512-1024
256-362
180-256
128-180
64-90
90-128
45-64
32-45
22.6-32
16-22.6
11.3-16
5.7-8
<2
8-11.3
0%
4-5.7
10%
0
<2
20%
2
2-4
4
Cumulative Frequency
Cross-Section: Culvert – Upstream Pebble Count
2-4
4 - 5.7
5.7 - 8
> 4096
32 -45
45-64
64- 90
8 - 11.3
90 - 128
11.316
- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
3
8
20
134
268
360
A—294
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
5%
68%
17%
6%
4%
Sorting Coefficient:
2.01
Skewness Coefficient: -0.25
Hehe 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)
C ount
Item %
C umulative %
2
3
1
3
2
4
3
9
9
6
9
11
11
10
11
5
1
0
0
0
2%
3%
1%
3%
2%
4%
3%
9%
9%
6%
9%
11%
11%
10%
11%
5%
1%
0%
0%
0%
2%
5%
6%
9%
11%
15%
18%
27%
36%
42%
51%
62%
73%
83%
94%
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
Bedrock
12
100%
90%
10
70%
Frequency
8
60%
6
50%
40%
Frequency
4
30%
20%
2
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
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
5
20
90
260
422
520
Hehe Creek
5.7-8
<2
4-5.7
<2
0%
2-4
0
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
2%
40%
41%
17%
0%
Sorting Coefficient:
1.90
Skewness Coefficient: 0.24
A—295
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)
C ount
Item %
C umulative %
3
5
2
1
1
3
6
2
4
4
8
10
10
15
9
11
2
0
0
0
3%
5%
2%
1%
1%
3%
6%
2%
4%
4%
8%
10%
10%
16%
9%
11%
2%
0%
0%
0%
3%
8%
10%
11%
13%
16%
22%
24%
28%
32%
41%
51%
61%
77%
86%
98%
100%
100%
100%
100%
<2
2-4
4 - 5.7
5.7 - 8
8 - 11.3
11.3 - 16
16 - 22.6
22.6 - 32
32 - 45
45 - 64
64 - 90
90 - 128
128 - 180
180 - 256
256 - 362
362 - 512
512 - 1024
1024 - 2048
2048 - 4096
Bedrock
16
100%
14
90%
Frequency
70%
10
60%
8
50%
40%
Frequency
6
30%
4
20%
Bedrock
2048-4096
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
Cumulative Frequency
2-4
4 - 5.7 - 8
32 -45
45-64
64- 90
8 - 11.3
90 - 128
Bedrock
11.316- 16
-22.6
22.6- 32
128180
- 180
256
- 256
362
- 362
- 512
Particle Size Category (mm)
512 - 1024
1024
2048
- 2048
- 4096
Particle Size Category (mm)
S ize C las s
S ize perc ent finer
than (mm)
D5
D16
D50
D84
D95
D100
3
20
120
330
403
550
A—296
5.7-8
<2
8-11.3
0%
2-4
0
4-5.7
10%
<2
2
Cumulative Frequency
80%
12
Material
P erc ent C ompos ition
Sand
Gravel
Cobble
Boulder
Bedrock
3%
29%
45%
23%
0%
Sorting Coefficient:
2.08
Skewness Coefficient: 0.39
Hehe Creek