20180765 Ver 2_Stream enhancement memo 030519_20190306

Headwaters Engineering, PC
NCBELS Lic. No. C-4500
MEMORANDUM
TO: David Brown, US Army Corps of Engineers
Kevin Mitchell, NC Division of Water Resources
FROM: Andrew Bick, PE
DATE: March 5, 2019
RE: Stability Assessment and Stream Enhancements
UTs to Fowler Creek
High Hampton Resort, Cashiers, Jackson County, NC
Approximately 880 linear feet (LF) of culvert was removed from an unnamed tributary to Fowler
Creek (referred to in the attached plans as UT1) at the High Hampton Resort golf course, which
is currently undergoing a renovation. The banks of the daylighted channel were sloped and large
stone was placed in the bed and on the banks. A subsequent sediment removal effort was
completed at the request of DWR.
UT2 is located about 1,700 LF east of UTI in the #2 fairway. The Corps and DWR expressed
concern with the height of the drop at the beginning of the UT2 channel at a headwall where two
culverts discharge, specifically with regard to stability and aquatic organism passage.
The purpose of this memo is to document as -built surveys completed by C1earWater
Environmental Consultants (CEC), to summarize our analysis of channel stability based on this
survey and our observations of the site, and to present proposed stream enhancements.
As -Built Survevs
In February 2019, CEC staff completed total station surveys of the daylighted UT 1 channel and
UT2 near the headwall. The surveys were based on a local datum. The UT 1 survey included
points along the top of both banks, the thalweg and water surface, four cross sections and several
ground points. The UT2 survey collected points along the thalweg of the channel and at a
transect immediately downstream of the headwall. The attached plans show the results of the
surveys superimposed on 2015 aerial imagery, which was collected prior to the stream
daylighting.
The plan view of UT 1 indicates a relatively straight alignment through roughly the low point of
the valley between a culvert under a cart path at the upstream end and a sediment trap at the
downstream end. The profile data indicate a slope of approximately 6 percent; the relatively
straight alignment would be expected for a slope in this range. The slope over the downstream
200 LF is noticeably flatter than the upstream 500 LF, apparently in response to the effects of the
sediment trap, which is currently a 3 -foot tall riprap check dam. (In late January 2019,
Headwaters Engineering completed a laser level reference reach survey of UTI downstream of

the sediment trap in order to support a design to remove the trap and create a stable transition to
a bedrock slide immediately downstream of the trap.)
Cross section surveys through the daylighted reach of UTI indicate a relatively narrow and deep
channel, with width -depth ratios of 10 or less. Bank heights range from 2.4 to 3.2 feet and top
widths range from 11 to 20 feet. Cross section plots with dimension parameters are attached. As
shown on the attached photos, the bed and banks contain abundant riprap, generally ranging in
median size from 8 inches to more than 24 inches.
The UT2 survey indicates a drop of 1.8 feet from the invert of the north culvert to the thalweg
and a relatively flat slope of 1.8 percent from this point downstream. The cross-section survey
shows a relatively large channel with 3.4:1 side slopes and a maximum depth of 3.7 feet.
UT 1 Stabili . Analysis
We used the USGS web -based hydrology tool StreamStats to estimate the drainage area above
the subject reach of UTI and found it to be 22 acres. A digitized watershed boundary using the
Jackson County contours indicated a slightly smaller drainage area. Land use in the watershed
includes forest, the golf course and low density residential.
The North Carolina Mountain regional curve predicts a bankfull discharge of about 8 cubic feet
per second (cfs) for a 22 -acre watershed. Previous experience indicates that regional curve
predictions at the extreme low end of the drainage area range such as this are not as reliable as
those in the middle of the range (between 2 and 30 square miles). Analysis of the surveyed riffle
cross sections indicates the discharge corresponding to the low bank stage is on the order of 140
to 200 cfs. The reference cross section survey by Headwaters in the relatively undisturbed
reference reach indicates a bankfull discharge of about 60 cfs.
Based primarily on a comparison to the reference reach cross section, it appears that the
daylighted channel was constructed deeper and wider than would have been designed based on a
natural channel design approach. Analyses of the as -built cross sections indicate shear stresses
in the riffles on the order of 5 to 6 pounds per square foot (psf). With reference to Shield's
equation, the predicted grain size for threshold of motion ranges from 240 to 300 mm, or 9 to 12
inches. Analysis of the reference cross section flowing full at a discharge of about 150 cfs
indicates a shear stress and threshold grain size similar to those of the constructed channel (4.8
psf and 230 mm, respectively).
We are aware of the daylighted channel being subjected to multiple flood events since it was
constructed and there does not appear to be bank erosion or bed scour. In our experience,
constructed streams are typically weakest immediately after construction and become more
resilient with time. The large stone in the channel and on the banks does not appear to have been
mobilized during any of these recent storms, and calculations indicate that even when flowing
full (well above the predicted "bankfull" discharge), the majority of the bed and bank materials
would not be mobilized. The proposed boulder steps at the downstream end of UTI will provide
additional grade control. A visual monitoring program over the next two to three years will
likely provide the data necessary to evaluate long term stream stability.
UT2 Perched Conditions
The concern expressed for UT2 is the high drop from the culverts to the receiving channel. The
proposed boulder step downstream of the headwall will reduce the drop height to about 9 inches,
and the proposed pool between the step and the headwall will help dissipate energy and promote

better aquatic organism habitat. As with UTI, the UT2 channel has been subjected to multiple
large floods and we have not observed stability issues even without the energy dissipation effects
of the proposed pool and step. A visual monitoring program seems appropriate for UT2 as well.
Closure
Based on our review of the data and our calculations, we do not recommend any repairs or
modifications to UTI at this time beyond the sediment trap removal and boulder steps at the
downstream end. For UT2, the proposed boulder step and pool should address energy
dissipation and aquatic organism passage concerns.
If you have any questions. please call me at 828.606.0306.
Attachments:
Stream Enhancement Plans
Cross Section Plots and Shear Stress Calculations
Photos
Zvi
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STREAM ENHANCEMENTS
TRIBUTARIES TO FOWLER CREEK
HIGH HAMPTON RESORT
CASHIERS, NORTH CAROLINA
SHEET INDEX
1. TITLE
2. UT1 AS -BUILT PLAN & PROFILE (DAYLIGHTED REACH)
3. UT1 ENHANCEMENT PLAN & PROFILE
4. UT2 ENHANCEMENT PLAN & PROFILE (PERCHED CULVERTS)
5. DETAILS
VICINITY MAP
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PROJECT SITE
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— 8.0'-1
1.0' - - L 3.0'
RIFFLE
10.5'
1.5' 3.0'
IaeTelI
1 TYPICAL SECTIONS
1 1" = 10'
CONSTRUCTION NOTES:
1. WORK SHALL BE STAGED SUCH THAT NO MORE CREEK
BANK/BED IS DISTURBED THAN CAN BE STABILIZED AT THE
END OF THAT WORK DAY.
2. A PUMP -AROUND SHALL BE USED TO DIVERT FLOW
AROUND THE WORK AREAS ON UT1 AND UT2. SEE DETAIL.
3. FINE SEDIMENT ACCUMULATED BEHIND THE ROCK
CHECK DAM ON UT1 SHALL BE REMOVED AND DISPOSED
OFF-SITE BEFORE REMOVING THE CHECK DAM.
4. STREAM BANKS SHALL BE STABILIZED WITH SEED,
MULCH AND MATTING WITHIN 24 HOURS OF REACHING
FINAL GRADES.
5. LOCATIONS AND ELEVATIONS OF BOULDER STEPS MAY
BE ADJUSTED DURING CONSTRUCTION PER THE DIRECTION
OF THE ENGINEER BASED ON FIELD CONDITIONS.
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ROP. BOULDER STEPS;
RIFFLE TYPICAL ROCK CHECK DAM
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POOL TYPICAL —
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6+00 6+30 6+60 6+90 7+20
PROFILE
BEDROCK SLIDE
SCALES:
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V: 1" = 10'
ELEVATIONS BASED ON
ARBITRARY DATUM OF 100.0'
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UT1
ENHANCEMENTS
PLAN & PROFILE
SHEET 3 OF 5

100
UT2 PROFILE DOWNSTREAM OF NORTH CULVERT
SET TOP OF BOULDER STEP 9"
-BELOW INVERT OF
0+30 0+60 0+90 1+20 1+50
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1+80
SCALES:
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V..1"=10'
ELEVATIONS BASED ON
ARBITRARY DATUM OF 100.0'
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UT2
ENHANCEMENT
PLAN & PROFILE
SHEET 4 OF 5

TOP OF BANK
1' MIN.
REMOVE ALL DEBRIS,
SCARIFY SURFACE, PLACE
TOPSOILAND SEED/MULCH
BEFORE PLACING MATTING
MATTING PLACED FLUSH WITH BANK SURFACE, LAP
OVER DOWN STREAM / DOWN SLOPE SEAMS
12" WOOD STAKE PLACED IN
3' O.C. DIAMOND PATTERN
NON -WOVEN SILT BAG
110101N. FROM STREAM
CLASS B STONE PAD
OR PALLET SILT BAG
MATTING ANCHORED 1'
BELOW STREAM BED
COFFER DAM; CLASS B STONE OR
IT,
ON-SITE COBBLE W/ PLASTIC SHEETING
NOTES:
1. MATTING SHALL BE 780 G/Mz COIR. EROSION CONTROL MATTING
2. SEED BANKS WITH RYE GRAIN AND rl
NATIVE RIPARIAN MIX, AND COVER 5 NTS
WITH WHEAT OR OAT STRAW MULCH
BEFORE INSTALLING MATTING.
V DEEP
SETTLING POOL
FLOW
II ANCHOR NON -WOVEN FILTER
TOE OF BANK (TYP) FABRIC ON UPSTREAM SIDE OF DIVERSION PUMP
TOP OF BANK (TYP) 17 I I BOULDERS AND BACKFILL WITH SIZED FOR 150% OF
ON-SITE COBBLE AND GRAVEL BASE FLOW
VARIES; D/S DAM MAY NOT BE NEEDED
RIFFLE TYPICAL SECTION
6' +/ ANCHOR 4' INTO BANK
ELEV. AT TIE -IN-1—
HEADER
APPROX. 1' HIGHER I FOOTER
THAN INVERT ELEV. /--\\
FLOW �
POOL TYPICAL SECTION
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NOTES:
1. BOULDERS SHALL BE DURABLE STONE,
MIN. 2'X3'X3' AND RELATIVELY FLAT. 2 BOULDER STEP
2. DIMENSIONS AND NUMBER OF
BOULDERS MAY BE ADJUSTED BASED ON 5 NTS
FIELD CONDITIONS.
10"
HDPE SHEETING WITH 6" OF
ON-SITE COBBLE OVERLAY;
USE SAND BAGS AT BASE
AS NECESSARY
DEWATERING PUMP SILT BAG ON PALLET OR
AS NEEDED STONE, SEE DETAIL
ABOVE
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WORK AREA
TOE OF BANK (TYP)
T(1P nF RANK (TYM I I
3'
PROFILE
PROTECT EXIST.
BANK VEGETATION
FOR ADD'L FILTER
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WORK AREA SHALL BE STABILIZED BY
THE END OF EACH WORK DAY.
TOP OF BANK BANK TO BANK
MAX DEPTH
STREAM BOTTOM +
COFFER DAM
3 PUMP -AROUND SCHEMATIC
'\�5j NTS
SECTION
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DETAILS
SHEET 5 OF 5

High Hampton Resort
Cross Section Plots and Shear Stress Calculations

88
87
86
0 85
c�
w 84
83
82
0
5
Bankfull Dimensions
20.2
x -section area (ft.sq.)
11.2
width (ft)
1.8
mean depth (ft)
2.4
max depth (ft)
13.1
wetted parimeter (ft)
1.5
hyd radi (ft)
6.2
width -depth ratio
Bankfull
Flow
10
15
UT to Fowler Creek, riffle
Width (ft)
Flood Dimensions
20 25 30 35
Materials
28.7 W flood prone area (ft)
2.6 entrenchment ratio
2.4 low bank height (ft)
1.0 low bank height ratio
Flow Resistance
--- D50 (mm)
--- D84 (mm)
292 threshold grain size (mm):
Forces & Power
9.9 velocity (ft/s) 0.050 Manning's roughness 6.2 channel slope (%)
199.5 discharge rate (cfs) 0.25 D'Arcy-Weisbach fric. 5.94 shear stress (Ib/sq.ft.)
1.40 Froude number --- resistance factor u/u* 1.75 shear velocity (ft/s)
--- relative roughness 69 unit strm power (Ib/ft/s)

91
90
89
C:
0 88
c�
w 87
86
85
0 5 10
Bankfull Dimensions
16.4
x -section area (ft.sq.)
11.1
width (ft)
1.5
mean depth (ft)
2.4
max depth (ft)
13.0
wetted parimeter (ft)
1.3
hyd radi (ft)
7.6
width -depth ratio
Bankfull
Flow
UT to Fowler Creek, riffle
15 20 25 30 35 40 45
Width (ft)
Flood Dimensions Materials
--- W flood prone area (ft) --- D50 (mm)
--- entrenchment ratio --- D84 (mm)
2.4 low bank height (ft) 240 threshold grain size (mm):
1.0 low bank height ratio
Flow Resistance
Forces & Power
8.7 velocity (ft/s) 0.050 Manning's roughness 6.2 channel slope (%)
141.7 discharge rate (cfs) 0.27 D'Arcy-Weisbach fric. 4.88 shear stress (Ib/sq.ft.)
1.36 Froude number --- resistance factor u/u* 1.59 shear velocity (ft/s)
--- relative roughness 49 unit strm power (Ib/ft/s)

Cross Section UT1, XS3
0 5 10 15 20 25
r111G[iKfDl
Bankfull Dimensions Flood Dimensions
39.9 x -section area (ft.sq.) --- W flood prone area (ft)
19.6 width (ft) --- entrenchment ratio
2.0 mean depth (ft) --- low bank height (ft)
3.2 max depth (ft) --- low bank height ratio
21.8 wetted parimeter (ft)
1.8 hyd radi (ft)
9.7 width -depth ratio
Bankfull Flow
11.1 velocity (ft/s)
441.9 discharge rate (cfs)
1.45 Froude number
Flow Resistance
0.050 Manning's roughness
0.24 D'Arcy-Weisbach fric
--- resistance factor u/u*
--- relative roughness
30 35 40 45
Materials
--- D50 (mm)
--- D84 (mm)
347 threshold grain size (mm):
Forces & Power
6.2 channel slope (%)
7.06 shear stress (Ib/sq.ft.)
1.91 shear velocity (ft/s)
87 unit strm power (Ib/ft/s)
0 5 10 15 20 25
r111G[iKfDl
Bankfull Dimensions Flood Dimensions
39.9 x -section area (ft.sq.) --- W flood prone area (ft)
19.6 width (ft) --- entrenchment ratio
2.0 mean depth (ft) --- low bank height (ft)
3.2 max depth (ft) --- low bank height ratio
21.8 wetted parimeter (ft)
1.8 hyd radi (ft)
9.7 width -depth ratio
Bankfull Flow
11.1 velocity (ft/s)
441.9 discharge rate (cfs)
1.45 Froude number
Flow Resistance
0.050 Manning's roughness
0.24 D'Arcy-Weisbach fric
--- resistance factor u/u*
--- relative roughness
30 35 40 45
Materials
--- D50 (mm)
--- D84 (mm)
347 threshold grain size (mm):
Forces & Power
6.2 channel slope (%)
7.06 shear stress (Ib/sq.ft.)
1.91 shear velocity (ft/s)
87 unit strm power (Ib/ft/s)

Cross Section
UT1,
XS4
UT to Fowler Creek, run
122
121
120
F
119
c
0 118
.6
a> 117
w
116
115
114
0
5 10
15 20 25
30
35 4
Width (ft)
Bankfull
Dimensions
Flood Dimensions
Materials
25.9
x -section area (ft.sq.)
--- W flood prone area (ft)
---
D50 (mm)
14.5
width (ft)
--- entrenchment ratio
---
D84 (mm)
1.8
mean depth (ft)
--- low bank height (ft)
269
threshold grain size (mm):
2.4
max depth (ft)
--- low bank height ratio
18.3
wetted parimeter (ft)
1.4
hyd radi (ft)
8.1
width -depth ratio
Bankfull
Flow
Flow Resistance
Forces &
Power
9.3
velocity (ft/s)
0.050 Manning's roughness
6.2
channel slope (%)
241.9
discharge rate (cfs)
0.26 D'Arcy-Weisbach fric.
5.47
shear stress (Ib/sq.ft.)
1.39
Froude number
--- resistance factor u/u*
1.68
shear velocity (ft/s)
--- relative roughness
65
unit strm power (Ib/ft/s)

UT to Fowler Creek, riffle
102
x -section area (ft.sq.)
101
width (ft)
100
mean depth (ft)
99
max depth (ft)
c 98
0
wetted parimeter (ft)
1.8
97
m
15.4
w 96
95
Bankfull
94
93
0
Bankfull Dimensions
10
54.2
x -section area (ft.sq.)
28.8
width (ft)
1.9
mean depth (ft)
3.7
max depth (ft)
29.8
wetted parimeter (ft)
1.8
hyd radi (ft)
15.4
width -depth ratio
Bankfull
Flow
7.4 velocity (ft/s)
402.5 discharge rate (cfs)
0.97 Froude number
20 30
Width (ft)
Flood Dimensions
--- W flood prone area (ft)
--- entrenchment ratio
--- low bank height (ft)
--- low bank height ratio
Flow Resistance
0.040 Manning's roughness
0.15 D'Arcy-Weisbach fric.
--- resistance factor u/u*
--- relative roughness
40
50
Materials
--- D50 (mm)
--- D84 (mm)
100 threshold grain size (mm):
Forces & Power
1.8 channel slope (%)
2.04 shear stress (Ib/sq.ft.)
1.03 shear velocity (ft/s)
15.7 unit strm power (Ib/ft/s)
0

96.5
96
95.5
95
0 94.5
0 94
w 93.5
93
92.5
92
91.5
0
E
Bankfull Dimensions
14.5
x -section area (ft.sq.)
10.2
width (ft)
1.4
mean depth (ft)
2.1
max depth (ft)
11.7
wetted parimeter (ft)
1.2
hyd radi (ft)
7.2
width -depth ratio
Bankfull Flow
10.7 velocity (ft/s)
154.0 discharge rate (cfs)
1.69 Froude number
UT to Fowler Creek, Riffle
4 6 8 10
Width
Flood Dimensions Materials
49.5 W flood prone area (ft)
4.8 entrenchment ratio
2.1 low bank height (ft)
1.0 low bank height ratio
Flow Resistance
0.040 Manning's roughness
0.17 D'Arcy-Weisbach fric.
--- resistance factor u/u*
--- relative roughness
12 14
--- D50 (mm)
--- D84 (mm)
234 threshold grain size (mm):
Forces & Power
6.2 channel slope (%)
4.77 shear stress (Ib/sq.ft.)
1.57 shear velocity (ft/s)
58 unit strm power (Ib/ft/s)

High Hampton Daylighted Stream (UT1) Cross Sections, 2/25/2019
XS2- Facing Upstream
XS1- Facing Downstream
XS2- Facing Downstream

High Hampton Daylighted Stream Cross Sections, 2/25/2019

High Hampton Daylighted Stream Photo Points, 2/25/2019
PP2- Facing Upstream
}Sl-
PP:- Facing Downstream
PP3- Facing Upstream PP3- Facing Downstream

High Hampton Daylighted Stream Photo Points, 2/25/2019
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14
PP4- Facing Upstream
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PP4- Facing Tributary Upstream
PP4- Facing Downstream
PP5- Facing Upstream PP5- Facing Downstream

High Hampton Perched Culverts (UT2)

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