20180339 Ver 1_west range 401 response letter 050218_20180502

Headwaters Engineering, PC
9 Elk Mountain Road
Asheville, NC 28804
828.606.0306

May 2, 2018

Mr. Zan Price, PE
NCDEQ – Division of Water Resources
2090 US Highway 70
Swannanoa, NC 28711

Subject: Additional Information
West Range Outfall Stabilization and Stream Restoration
Buncombe County, North Carolina (DWR Project 20180339)

Dear Mr. Price:

This letter responds to your April 23, 2018 request for additional information for the subject project.

Proposed stabilization and restoration of the stormwater outfalls and streams at the West Range site is based on
natural channel design techniques. We made use of reference reaches (including two on relatively undisturbed
unnamed tributaries on the West Range property), regression analyses of rural stream discharge predictions and
professional judgment. Design parameters for UT1, UT5, UT6 and Long Valley Branch are summarized on the
attached tables (Tables 1-6). These tables include notes regarding reference reaches where applicable;
summaries of reference reach geomorphic parameters are included in this response. Channel side slopes are
indicated on the typical section sheets in the plan set. Proposed work on UT2, UT3 and UT4 (each an ephemeral
channel) consists primarily of improving road drainage, re-grading sections of road near crossings, and
controlling rilling from overland flow. As such, geomorphic parameters for these reaches are not reported.

As we discussed during the site visit, we anticipate that the locations, sizes, elevations and types of stabilization
and restoration measures will need to be adjusted somewhat during construction from what is depicted on the
plans. This is largely because the topographic survey provides accurate information regarding channel position
and reach-wide slope, but not each and every grade control feature such as a bedrock seam or a tree root were
captured in this survey. In an effort to optimize the quality of the construction work while minimizing
disturbance, staff from Headwaters Engineering will be on-site during key phases of construction in order to
position in-stream structures and set grading limits to take advantage of such existing features. This may result in
variations in channel dimensions, bank slopes, facet slopes, pool-to-pool spacing, etc.

We trust that this information adequately responds to your request. If you have any additional questions, please
call me at 828.606.0306 or email me at [e-mail].

Sincerely,
Headwaters Engineering, PC

Andrew Bick, PE
Principal

Attachments
DESIGN PARAMETER SUMMARY TABLES 

min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 14 29 28
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 0.9 1.2 1.0
max depth ratio dmax/dbkf 1.3 1.7 1.5
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0360 0.0540
step height over structures feet 0.6 1.5
riffle slope Sriffle feet/ foot 0.0450 0.0900
riffle slope ratio Sriffle/Schannel 1.3 1.7
UT to Austin/UT to Sandy
Branch Ref
riffle length Lrif feet
riffle length ratio Lrif/wbkf
pool-to-pool spacing Lp-p feet 15 55
pool spacing ratio Lp-p/wbkf 1.9 6.9
UT to Austin/UT to Sandy
Branch Ref
radius of curvature Rc feet N/A
radius of curvature ratio Rc/ wbkf N/A
Ref. USGS 2009 Flood
Frequency Equations SIR 2009-
5158; extrapolated 1 to 2 yr
Pattern Features
0.7
11.6
Slope
Riffle Features
Pool Features
5.1
N/A - riffles are incorporated
into slides and steps
Table 1: UT1 Reach 1 (100+00 to 115+00) Design Parameters
Notation Units
Designed Conditions Notes
8.0
B4
0.09
Cross-Section Features
5.5
min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 24.0 37.0 33
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 1.0 1.3 1.2
max depth ratio dmax/dbkf 1.2 1.6 1.5
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0200 0.0234 0.0234
step height over structures feet 0.20 1.10 one step with 2' drop at bedrock
riffle slope Sriffle feet/ foot 0.0212 0.0645
riffle slope ratio Sriffle/Schannel 1.1 2.8 steepest riffles in on-line sections
riffle length Lrif feet 18.0 51.0
riffle length ratio Lrif/wbkf 1.8 5.2
pool-to-pool spacing Lp-p feet 30 70
pool spacing ratio Lp-p/wbkf 3.1 7.1
UT to Austin/UT to Sandy
Branch Ref
radius of curvature Rc feet 20 35
radius of curvature ratio Rc/ wbkf 2.0 3.6
UT to Austin/UT to Sandy
Branch Ref
Ref. USGS 2009 Flood
Frequency Equations SIR 2009-
5158; extrapolated 1 to 2 yr
Table 2: UT1 Reach 2 (115+00 to 129+65) Design Parameters
Notation Units
Designed Conditions Notes
9.8
C4
0.19
Cross-Section Features
8.2
4.1
Pattern Features
0.8
11.8
Slope
Riffle Features
Pool Features
min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 86 121 106
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 1.8 2.1 2.0
max depth ratio dmax/dbkf 1.4 1.4 1.4
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0070 0.0147 0.0147
step height over structures feet N/A
riffle slope Sriffle feet/ foot 0.0084 0.0230
riffle slope ratio Sriffle/Schannel 1.2 1.6 steeper riffles are on bedrock
riffle length Lrif feet 18.0 68.0
some shorter riffles shown in
areas of bedrocck
riffle length ratio Lrif/wbkf 1.1 4.3 N/A
pool-to-pool spacing Lp-p feet 40 100
pool spacing ratio Lp-p/wbkf 2.5 6.3 Boyd Branch Reference
radius of curvature Rc feet 32 66 Some radii dictated by bedrock
radius of curvature ratio Rc/ wbkf 2.0 4.1 Boyd Branch Reference
Ref. USGS 2009 Flood Frequency
Equations SIR 2009-5158;
extrapolated 1 to 2 yr
Pattern Features
1.4
11.6
Slope
Riffle Features
Pool Features
16.0
C/E
1.08
Cross-Section Features
22.0
4.8
Table 3: Long Valley Branch Design Parameters
Notation Units
Designed Conditions Notes
min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 10 22 18
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 0.6 0.8 0.7
max depth ratio dmax/dbkf 1.4 1.4 1.4
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0600 0.0690 0.0690
step height over structures feet 0.50 1.10
riffle slope Sriffle feet/ foot 0.0630 0.1100
riffle slope ratio Sriffle/Schannel 1.1 1.6
riffle length Lrif feet 8.0 20.0
riffle length ratio Lrif/wbkf 1.2 3.1
pool-to-pool spacing Lp-p feet 13 33
pool spacing ratio Lp-p/wbkf 2.0 5.1
UT Austin Branch DS/UT Kelly
Branch/UT Gap Branch
radius of curvature Rc feet N/A
radius of curvature ratio Rc/ wbkf N/A
Ref. USGS 2009 Flood
Frequency Equations SIR 2009-
5158; extrapolated 1 to 2 yr
Pattern Features
0.5
12.7
Slope
Riffle Features
Pool Features
6.5
B
0.06
Cross-Section Features
3.3
5.4
Table 4: UT5 (outfalls 9, 10,11) Design Parameters
Notation Units
Designed Conditions Notes
min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 11 17 17
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 0.7 0.9 0.8
max depth ratio dmax/dbkf 1.4 1.7
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0350 0.0514 0.0514
step height over structures feet 0.70 1.10
riffle slope Sriffle feet/ foot 0.0360 0.1100
riffle slope ratio Sriffle/Schannel 1.0 2.1
UT Austin Branch/UT to Gap Branch
riffle length Lrif feet 10.0 16.0
riffle length ratio Lrif/wbkf 1.5 2.4
pool-to-pool spacing Lp-p feet 13 37
pool spacing ratio Lp-p/wbkf 1.9 5.4
UT Austin Branch/UT to Gap Branch
radius of curvature Rc feet N/A
radius of curvature ratio Rc/ wbkf N/A
Ref. USGS 2009 Flood
Frequency Equations SIR 2009-
5158; extrapolated 1 to 2 yr
Pattern Features
0.5
13.1
Slope
Riffle Features
Pool Features
6.8
B4
0.02
Cross-Section Features
3.5
4.7
Table 5: UT6A (outfalls 12,13) Design Parameters
Notation Units
Designed Conditions Notes
min max design
stream type
drainage area DA sq mi
bankfull design discharge Qbkf cfs 31 40 34
bankfull cross-sectional area Abkf SF
average velocity during bankfull event vbkf fps
width at bankfull wbkf feet
mean depth at bankfull dbkf feet
bankfull width to depth ratio wbkf/dbkf
maximum depth at bankfull dmax feet 1.0 1.3 1.2
max depth ratio dmax/dbkf 1.3 1.7 1.5
bank height ratio BHR 1.0 1.0
channel slope Schannel feet/ foot 0.0239 0.0253 0.0253
step height over structures feet 0.60 0.80
riffle slope Sriffle feet/ foot 0.0360 0.1100
riffle slope ratio Sriffle/Schannel 1.5 4.3
UT Austin Branch/UT to Sandy Branch
Ref
riffle length Lrif feet 15.0 49.0
two shorter riffles are part of step
structures
riffle length ratio Lrif/wbkf 1.5 4.8
pool-to-pool spacing Lp-p feet 20 71
pool spacing ratio Lp-p/wbkf 2.0 7.0
UT Austin Branch/UT to Sandy Branch
Ref
radius of curvature Rc feet 20 40
radius of curvature ratio Rc/ wbkf 2.0 3.9
UT Austin Branch/UT to Sandy Branch
Ref
Ref. USGS 2009 Flood
Frequency Equations SIR 2009-
5158; extrapolated 1 to 2 yr
Pattern Features
0.8
13.1
Slope
Riffle Features
Pool Features
10.2
B/C
0.15
Cross-Section Features
7.9
4.3
Table 6: UT6 (outfalls 9-13) Design Parameters
Notation Units
Designed Conditions Notes
REFERENCE REACH GEOMORPHIC DATA 

min max
stream type
drainage area DA sq mi
design discharge Q cfs
bankfull cross‐sectional 
area Abkf SF 13.8 15.4
average velocity during 
bankfull event vbkf fps 3.2 3.8
width at bankfull wbkf feet 13.5 16.6
maximum depth at 
bankfull dmax feet 1.7 1.9
mean depth at bankfull dbkf feet 0.80 1.10
bankfull width to depth 
ratio wbkf/dbkf 11.8 20.0
depth ratio dmax/dbkf feet 1.7 2.1
bank height ratio BHR
floodprone area width wfpa feet 37.0 41.0
entrenchment ratio ER 2.5 2.8
valley slope Svalley feet/ foot
channel slope Schnl feet/ foot
riffle slope Sriffle feet/ foot 0.015 0.028
riffle slope ratio Sriffle/Schnl 1.7 3.1
pool slope Sp feet/ foot 0.0008 0.0020
pool slope ratio Sp/Schnl 0.1 0.2
pool‐to‐pool spacing Lp‐p feet 260.0 345.0
pool spacing ratio Lp‐p/wbkf 19.3 25.6
pool cross‐sectional area Apool SF
pool area ratio Apool/Abkf 1.3 1.5
maximum pool depth dpool feet 2.6 3.0
pool depth ratio dpool/dbkf 2.4 3.8
pool width at bankfull wpool feet 16.0 20.2
pool width ratio wpool/wbkf
sinuosity K
belt width wblt feet 42.0 100.0
meander width ratio wblt/wbkf 2.8 6.6
linear wavelength 
(formerly meander 
length)
Lm feet 60.0 107.0
linear wavelength ratio 
(formerly meander 
length ratio)
Lm/wbkf 4.0 7.1
meander length feet 66.0 139.0
meander length ratio 4.4 9.2
radius of curvature Rc feet 18.7 91.0
radius of curvature ratio Rc/ wbkf 1.2 6.0
20.1
1.2
Pattern
1.6
Profile
1.0
Slope
0.012
0.009
Cross‐Section
Reference Reach Geomorphic Parameters
Notation Units Boyd Branch
E4
0.90
51
min max
stream type
drainage area DA sq mi
design discharge Q cfs
bankfull cross‐sectional 
area Abkf SF
average velocity during 
bankfull event vbkf fps
width at bankfull wbkf feet
maximum depth at 
bankfull dmax feet
mean depth at bankfull dbkf feet
bankfull width to depth 
ratio wbkf/dbkf
depth ratio dmax/dbkf feet
bank height ratio BHR
floodprone area width wfpa feet
entrenchment ratio ER
valley slope Svalley feet/ foot
channel slope Schnl feet/ foot
riffle slope Sriffle feet/ foot 0.025 0.073
riffle slope ratio Sriffle/Schnl 0.6 1.8
pool slope Sp feet/ foot 0 0.015
pool slope ratio Sp/Schnl 0 0.4
pool‐to‐pool spacing Lp‐p feet 13.9 30.6
pool spacing ratio Lp‐p/wbkf 2.2 4.9
pool cross‐sectional area Apool SF
pool area ratio Apool/Abkf
maximum pool depth dpool feet
pool depth ratio dpool/dbkf
pool width at bankfull wpool feet
pool width ratio wpool/wbkf
2.4
8.8
1.4
9.4
2.1
1.7
26.60
4.30
Slope
0.048
0.04
Profile
1.00
Slightly entrenched 
B4a or A4
0.12
27
4.40
6.2
Cross‐Section
6.20
1.20
0.70
8.80
1.71
Reference Reach Geomorphic Parameters
Notation Units
UT to Austin Branch 
DS
min max
stream type
drainage area DA sq mi
design discharge Q cfs
bankfull cross‐sectional 
area Abkf SF
average velocity during 
bankfull event vbkf fps
width at bankfull wbkf feet
maximum depth at 
bankfull dmax feet
mean depth at bankfull dbkf feet
bankfull width to depth 
ratio wbkf/dbkf
depth ratio dmax/dbkf feet
bank height ratio BHR
floodprone area width wfpa feet
entrenchment ratio ER
valley slope Svalley feet/ foot
channel slope Schnl feet/ foot
riffle slope Sriffle feet/ foot 0.081 0.29
riffle slope ratio Sriffle/Schnl 0.8 2.9
pool slope Sp feet/ foot 0 0.17
pool slope ratio Sp/Schnl 0 1.7
pool‐to‐pool spacing Lp‐p feet 10 17
pool spacing ratio Lp‐p/wbkf 1.5 2.5
pool cross‐sectional area Apool SF
pool area ratio Apool/Abkf
maximum pool depth dpool feet
pool depth ratio dpool/dbkf
pool width at bankfull wpool feet
pool width ratio wpool/wbkf
sinuosity K
d16 mm
d35 mm
d50 mm
d84 mm
d95 mm
d100 mm
170
256
9.4
2.6
1.7
3.2
8.8
Pattern
1
Particle Size Distribution from Reach‐wide Pebble Count
d50 Description
11
1.3
42
59
130
Profile
6.70
0.80
0.50
12.80
1.60
1.00
17.70
2.60
Slope
0.100
0.0986
Cross‐Section
Reference Reach Geomorphic Parameters
Notation Units UT to Austin Branch US
Slightly entrenched B4a 
or A4
0.12
26
3.60
7.3
min max
stream type
drainage area DA sq mi
design discharge Q cfs
bankfull cross‐sectional 
area Abkf SF
average velocity during 
bankfull event vbkf fps
width at bankfull wbkf feet
maximum depth at 
bankfull dmax feet
mean depth at bankfull dbkf feet
bankfull width to depth 
ratio wbkf/dbkf
depth ratio dmax/dbkf feet
bank height ratio BHR
floodprone area width wfpa feet
entrenchment ratio ER
channel slope Schnl feet/ foot
riffle slope Sriffle feet/ foot 0.01 0.14
riffle slope ratio Sriffle/Schnl 0.16 2.06
pool slope Sp feet/ foot 0.00 0.06
pool slope ratio Sp/Schnl 0.06 0.90
pool‐to‐pool spacing Lp‐p feet 18.4 26.8
pool spacing ratio Lp‐p/wbkf 2.99 4.35
pool cross‐sectional area Apool SF
pool area ratio Apool/Abkf
maximum pool depth dpool feet
pool depth ratio dpool/dbkf
pool width at bankfull wpool feet
pool width ratio wpool/wbkf
d16 mm
d35 mm
d50 mm
d84 mm
d95 mm
d100 mm
256
>2048
d50 Description
0.37
8
19.02
102.3
Particle Size Distribution from Reach‐wide Pebble Count
7.10
0.068
Profile
0.99
6.10
2.54
1.55
1.89
Slope
3.8
1.7
10.1
0.6
1.0
3.4
20.9
1
6.2
Slightly entrenched 
B4a or A4
0.04
18.7
Cross‐Section
5.0
Reference Reach Geomorphic Parameters
Notation Units UT to Gap Branch 
min max
stream type
drainage area DA sq mi
design discharge Q cfs
bankfull cross‐sectional 
area Abkf SF
average velocity during 
bankfull event vbkf fps
width at bankfull wbkf feet
maximum depth at 
bankfull dmax feet
mean depth at bankfull dbkf feet
bankfull width to depth 
ratio wbkf/dbkf
depth ratio dmax/dbkf feet
bank height ratio BHR
floodprone area width wfpa feet
entrenchment ratio ER
valley slope Svalley feet/ foot
channel slope Schnl feet/ foot
sinuosity K
belt width wblt feet 18 34
meander width ratio wblt/wbkf 24
linear wavelength 
(formerly meander 
length)
Lm feet 27 94
linear wavelength ratio 
(formerly meander 
length ratio)
Lm/wbkf 312
radius of curvature Rc feet 8 26
radius of curvature ratio Rc/ wbkf 13
5.74
5.9
1.13
0.73
10.90
1.30
2.47
9.10
0.049
0.03 ‐ 0.065
Pattern
1
Slope
1.15
Reference Reach Geomorphic Parameters
Notation Units UT to Kelly Branch
B4/B4a
0.08
23
Cross‐Section
7.91