ANNUAL REPORT FOR 2004
Hanging Rock Creek Stream Mitigation Site
Avery County
WBS Element 34402.4.1
TIP No. R-2237WM
Prepared By:
Office of Natural Environment & Roadside Environmental Unit
North Carolina Department of Transportation
March 2005
Summary
The following report summarizes the stream monitoring activities that have occurred during
the Year 2004 at the Hanging Rock Stream Mitigation Site in Avery County. This site was
designed and constructed during 2003 by the North Carolina Department of Transportation
(NCDOT). This report provides the monitoring results for the first formal year of
monitoring (Year 2004). The Year 2004 monitoring period was the first of five scheduled
years for monitoring on Hanging Rock Creek.
Based on the overall conclusions of monitoring along Hanging Rock Creek and its
associated tributary, the Hanging Rock Site has met the required monitoring protocols for
the first formal year of monitoring. Localized areas of active bank scour and erosion exist;
however, immediate stabilization is not warranted at this time.
Based on information obtained from the USGS, the Hanging Rock Creek Site has met the
required hydrologic monitoring protocols of two bankfull events. Biological and vegetative
sampling is being conducted by NCDOT as part of the overall monitoring activity for this
site. Data from biological and vegetative monitoring is not included in this report and will
be submitted separately by NCDOT.
Per the letter from the Ecosystem Enhancement Program (EEP) to NCDOT dated August
25, 2004, the EEP has accepted the transfer of all offsite mitigation projects. The EEP will
be responsible for fulfilling the remaining monitoring requirements and future remediation
for this project.
1.0 INTRODUCTION
1.1 Project Description
The following report summarizes the stream monitoring activities that have occurred during
the Year 2004 at the Hanging Rock Stream Mitigation Site. The site is located adjacent to
NC 184 and SR 1337 (Dobbins Road) in the eastern portion of Avery County (Figure 1). It
is approximately 1 mile south-southeast of Banner Elk and nearly 14 miles southwest of
Boone. The Hanging Rock Site was constructed as one of three projects to provide
mitigation for stream impacts associated with Transportation Improvement Program (TIP)
number R-2237WM in Avery County.
The mitigation project covers approximately 2,500 linear feet of channel length (facing
downstream) of Hanging Rock Creek, and approximately 250 linear feet of channel length
on an unnamed tributary. Design and construction was implemented during 2003 by the
North Carolina Department of Transportation (NCDOT). Stream restoration involved the
installation of rootwads and various rock structures, and sloping the adjacent streambanks to
reduce overall erosion. It also included the installation of native vegetation.
1.2 Purpose
According to the mitigation plan report (NCDOT, 2001), the objectives for this mitigation
site were to improve water quality, riparian quality and stability, and fisheries habitat
associated with Hanging Rock Creek and its unnamed tributary. The following specific
objectives were proposed:
Restore the channel to a natural and stable form,
Improve floodplain and wetland functionality,
Reduce sediment load discharge to the Elk River,
Improve the trout fishery and natural aesthetics of the stream corridor,
Acquire mitigation credits for other unavoidable impacts to streams within the same
HUC (06010103).
Successful stream mitigation is demonstrated by a stable channel that does not aggrade or
degrade over time. It is also demonstrated by reduced erosion rates, the permanent
establishment of native vegetation, and bed features consistent with the design stream type.
Results of stream monitoring conducted in 2004 at the Hanging Rock Site are included in
this report.
Activities in 2004 reflect the first formal year of monitoring following the restoration efforts.
Included in this report are analyses on stability (primarily the longitudinal profile and cross
sections) and site photographs.
1.3 Project History
Fall 2003 Construction Completed.
Spring 2004 NCDOT Planted Live Stakes and Bare Root Trees
October 2004 Stream Channel Monitoring (1 yr.)
Significant rainfall events in September 2004 resulted in Hanging Rock Creek reaching stages
above bankfull. These events caused the erosion of streambanks and undermined rock
structures throughout the restored channel, principally in a section of the main channel
immediately downstream of the Dobbins Road culvert. Action to correct the damage was
completed by the time of monitoring.
2.0 STREAM ASSESSMENT
2.1 Success Criteria
The success criteria, as defined by federal guidelines for stream mitigation, includes the
following main parameters: no less than two bankfull events for the five-year monitoring
period, reference photos, plant survivability analyses, and channel stability analyses (USACE,
2003). Biological data was not required; however, benthic monitoring was conducted as part
of pre-construction sampling.
Natural streams are dynamic systems that are in a constant state of change. Longitudinal
profile and cross section surveys will differ from year to year based on changes in the
watershed. Natural channel stability is achieved by allowing the stream to develop a proper
dimension, pattern, and profile such that, over time, channel features are maintained and the
stream system neither aggrades nor degrades. A stable stream consistently transports its
sediment load, both in size and type, associated with local deposition and scour. Channel
instability occurs when the scouring process leads to degradation, or excessive sediment
deposition results in aggradation (Rosgen, 1996). The following surveys were conducted in
support of the monitoring assessment:
Longitudinal Profile Survey. This survey addressed the overall slope of the reach, as
well as slopes between bed features. The bed features are secondary delineative
criteria describing channel configuration in terms of riffle/pools, rapids, step/pools,
cascades and convergence/divergence features which are inferred from channel plan
form and gradient. The surveys are compared on a yearly basis to note and/or
compare aggradation, degradation, head cuts, and areas of mass wasting. The
longitudinal profile is expected to change from year to year. Significant changes may
require additional monitoring.
Cross Section Surveys. These surveys addressed the following characteristics at
various locations along the reach: entrenchment ratio, width/depth ratio, and
dominant channel materials. The entrenchment ratio is a computed index value used
to describe the degree of vertical containment. The width/depth ratio is an index
value which indicates the shape of the channel cross section. The dominant channel
materials refer to a selected size index value, the D50, representing the most
prevalent of one of six channel material types or size categories, as determined from
a channel material size distribution index.
2.2 Stream Description
2.2.1 Post-Construction Conditions
The mitigation of Hanging Rock Creek and its unnamed tributary involved the construction
of j-hook vanes, single rock vanes, rock cross vanes, rootwad revetments, double wing
deflectors and additional bank sloping. A rock cross vane was installed upstream of the NC
184 culvert to prevent bank erosion and to direct higher velocities into the center of the
channel. A rootwad complex was installed in the apex of several bends with cover logs for
habitat. Cross vanes were installed between glides and riffles. Throughout the entire reach
the inner berm was maintained, enhanced, or created as channel modifications were made.
2.2.2 Monitoring Conditions
Hanging Rock Creek was initially classified as a C4 stream type according to the Rosgen
Classification of Natural Rivers. The unnamed tributary was constructed as an E4. A total
of eight cross sections (seven along Hanging Rock Creek and one along its tributary) were
surveyed. For this report, only cross sections containing riffles were used in the comparison
of channel morphology presented below in Table 1. Data shown in Table 1 includes one
cross section chosen to represent a riffle section and minimum and maximum values for the
riffle cross sections along the reach.
Table 1. Abbreviated Morphological Summary (Hanging Rock Creek Site)
Variable Hanging Rock Creek - Main Channel (Combined Cross Sections #1, 3, 6, and 7)
Proposed 2004 2005 2006 2006
Cross-Section #7 Min - Max
Drainage Area (mi2) 3.0 3.0 3.0
Bankfull Width (ft) 21.5 - 22.3 23.1 23.6 - 40.9
Bankfull Mean
Depth (ft) 1.9 - 1.9 1.5 1.1 - 1.5
Width/Depth Ratio 11.6 - 12.0 15.4 16.0 - 37.4
Bankfull Cross
Sectional Area (ft2) 40.0 - 41.7 34.7 30.3 - 44.7
Maximum Bankfull
Depth (ft) 2.2 - 2.8 2.1 2.1 - 2.9
Width of Floodprone
Area (ft) 300 300 300
Entrenchment Ratio 13.4 - 14.0 >5 7.3 - 12.7
Slope 0.0059 0.0062 0.0062
Particle Sizes (Riffle
Sections)
D16 (mm) 8.4 0.091 - 13.5
D35 (mm) 22.8 0.24 - 22.8
D50 (mm) 29.3 13.3 - 29.3
D84 (mm) 57 35 - 57
D95 (mm) 79 62 - 79
*Drainage Area, Floodprone Width, and Slope are averaged values only. No minimum/maximum values were referenced.
2.3 Results of the Stream Assessment
2.3.1 Site Data
The assessment included the survey of eight cross sections of the two streams and the
longitudinal profile of Hanging Rock Creek and its tributary established by the NCDOT
after construction. The length of the profile along Hanging Rock Creek was approximately
2,500 linear feet. The profile associated with the UT was approximately 255 linear feet. Six
cross sections were established prior to the 2004 monitoring year. An additional cross
section was added to the main channel, and one cross section was added along the UT.
Cross section locations were subsequently based on the stationing of the longitudinal profile
and are presented below. The locations of the cross sections and longitudinal profiles are
shown in Appendix A.
Cross Section #1. Hanging Rock Creek, Station 3+66.6, midpoint of riffle
Cross Section #2. Hanging Rock Creek, Station 4+72.6, midpoint of pool
Cross Section #3. Hanging Rock Creek, Station 4+95.6, midpoint of riffle
Cross Section #4. Hanging Rock Creek, Station 6+26.6, midpoint of pool
Cross Section #5. Hanging Rock Creek, Station 8+89.6, midpoint of pool
Cross Section #6. Hanging Rock Creek, Station 13+38.6, midpoint of riffle
Cross Section #7. Hanging Rock Creek, Station 17+75.6, midpoint of riffle
Cross Section #8. Unnamed Tributary, Station 8+74.74, midpoint of run
Based on comparisons of design cross section data and Year 2004 monitoring data, all eight
cross sections appear stable with little or no active bank erosion. Graphs of the cross
sections are presented in Appendix A. Future survey data will vary depending on actual
location of rod placement and alignment, however, this information should remain similar in
appearance.
An estimate of bank erosion was taken at each cross section using the bank erodibility
hazard index (BEHI) and calculating near-bank shear stress. The BEHI and near-bank shear
stress evaluations indicated a bank erosion potential that ranged from moderate to very high.
The very high scores are likely a result of newly constructed banks overlain with matting and
will probably decrease once vegetation is established. These measurements will be taken
once a year at the same time the monitoring surveys are completed. Permanent bank toe
pins were installed at each cross section to insure the measurements were taken at the same
location every year. Bank erosion data sheets are presented in Appendix B.
Pebble counts were also taken at each cross section as a means to determine the bed material
at each cross section location. However, only pebble counts taken at riffle sections will be
utilized to classify the stream. No existing data was available for Hanging Rock Creek or its
tributary. The pebble counts taken during the Year 2004 monitoring period noted that the
D50 (50 percent of the sampled population is equal to or finer than the representative particle
diameter) for the riffle sections of Hanging Rock Creek was approximately 22.7 mm, which
is indicative of a gravel-bed stream.
A chart depicting the particle size distributions for Hanging Rock Creek for the Year 2004 is
presented below.
Hanging Rock Creek (Main Channel)
Particle Size Distribution (October 2004)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0.1 1 10 100 1000
Particle Size - Millimeter
% Cumula tiv e (Finer T han)
Combined XS1 XS2 XS3 XS4 XS5 XS6 XS7
A longitudinal profile survey was conducted on a predetermined segment of Hanging Rock
Creek. Bank stability was assessed during the cross section and longitudinal profile surveys.
Two areas of active scouring were observed in 2004. Descriptions and evaluations of these
areas are as follows:
Hanging Rock Creek (Main Channel)
Station 7+55.6. Active scouring was noted around the rootwad on the left bank
(facing downstream) in 2004. The scour did not appear to be compromising the
structure. Establishment of vegetation should help to stabilize this area.
Station 16+45.6. Bank undercutting was noted around a rootwad structure
embedded in the left streambank. The structure, however, appeared stable. This
area will be reassessed during the next monitoring period.
2.3.2 Climatic Data
Monitoring requirements state that at least two bankfull events must be documented
through the five-year monitoring period. No U.S. Geological Survey (USGS) surface water
gages exist on Hanging Rock Creek or its tributaries. A review of known USGS surface
water gages identified one gage within 7 miles (11 kilometers) of the mitigation site. The
gage is located 3 miles (5 kilometers) southwest of Sugar Grove, NC just off Watuaga River
Road near Rominger Road.
The Watuaga River gage was utilized for this report since it is the only active gage station in
North Carolina located in the Watuaga River Basin. The Watuaga River Gaging Station has
a drainage area of 92.1 square miles. It is situated in USGS Hydrologic Unit 06010103.
Datum of the gage is 2,607.84 feet above sea level NGVD29. Based on the drainage area
associated with the gage, the correlated bankfull discharge according to the NC Rural
Mountain Regional Curves (USACE, 2003) is between 2,000 and 4,000 cubic feet per second
(cfs). A review of peak flows was conducted for the period between October 2002 and
October 2004. According to the graph, there were four bankfull events occurring during
this period, three of which were in August 2004. Three of these events exceeded 6,000 cfs,
well above the bankfull discharge. The USGS graph depicting these peak flows is presented
below.
3.0 OVERALL CONCLUSIONS
The Hanging Rock Creek Site has met the required monitoring protocols for the first formal
year of monitoring. Localized areas of active bank scour and erosion existed in 2004;
however, these areas should stabilize in upcoming years with the increased establishment of
vegetation. No remedial actions are warranted at this time.
Based on information obtained from the USGS, the Hanging Rock Creek Site has met the
required hydrologic monitoring protocols as it relates to bankfull events. Biological and
vegetative monitoring is being conducted by NCDOT and will be included with this report.
4.0 REFERENCES
North Carolina Department of Transportation (NCDOT), 2001. Mitigation Report for the
Hanging Rock Creek Mitigation Site, Banner Elk, Avery County.
Rosgen, D.L, 1996. Applied River Morphology. Wildland Hydrology, Pagosa Springs,
Colorado.
US Army Corps of Engineers (USACE), 2003. Stream Mitigation Guidelines. Prepared with
cooperation from the US Environmental Protection Agency, NC Wildlife Resources
Commission, and the NC Division of Water Quality.
US Geological Survey (USGS), 2004. Real-time Data for USGS 03453000 Ivy River near
Marshall, NC. http://waterdata.usgs.gov/nc/nwis.
APPENDIX A
CROSS SECTIONS AND THE LONGITUDINAL PROFILE COMPARISON
Cross Section #1
3662.0
3663.0
3664.0
3665.0
3666.0
3667.0
3668.0
3669.0
3670.0
3671.0
3672.0
0 10 20 30 40 50 60 70 80
Station (ft)
Elevation (ft)
October 2004
Flood Prone Area
Bankfull
Cross-Section #1 (Riffle) Abbreviated Morphological Summary
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 37.4
Maximum Bankfull Depth (ft) 2.7
Width of the Floodprone Area (ft) 300
Bankfull Mean Depth (ft) 1.5
Width/Depth Ratio 16.6
Entrenchment Ratio >5
Bankfull Width (ft) 24.9
Cross Section #1 at Station 3+66.6
Cross Section #2
3659.0
3660.0
3661.0
3662.0
3663.0
3664.0
3665.0
3666.0
3667.0
3668.0
0 10 20 30 40 50 60 70 80 90 100
Station (ft)
Elevation (ft)
October 2004
Bankfull
Cross-Section #2 (Pool) Abbreviated Morphological Summary*
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 91.8
Maximum Bankfull Depth (ft) 5.8
Bankfull Mean Depth (ft) 2.7
Bankfull Width (ft) 34
* According to the Rosgen Classification of Natural Rivers floodprone width, entrenchement ratio,
and width depth ratio are not measured in pool, glide, or run features.
Cross Section #2 at Station 4+72.6
Cross Section #3
3660.0
3662.0
3664.0
3666.0
3668.0
3670.0
3672.0
0 10 20 30 40 50 60 70 80 90
Station (ft)
Elevation (ft)
October 2004
Bankfull
Flood Prone Area
Cross-Section #3 (Riffle) Abbreviated Morphological Summary
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 44.7
Maximum Bankfull Depth (ft) 2.9
Width of the Floodprone Area (ft) 300
Bankfull Mean Depth (ft) 1.1
Width/Depth Ratio 36.9
Entrenchment Ratio >5
Bankfull Width (ft) 40.6
Cross Section #3 at Station 4+95.6
Cross Section #4
3659.0
3660.0
3661.0
3662.0
3663.0
3664.0
3665.0
3666.0
0 10 20 30 40 50 60 70 80 90 100
Station (ft)
Elevation (ft)
October 2004
Bankfull
Cross-Section #4 (Pool) Abbreviated Morphological Summary*
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 41.6
Maximum Bankfull Depth (ft) 3.9
Bankfull Mean Depth (ft) 2.0
Bankfull Width (ft) 20.8
* According to the Rosgen Classification of Natural Rivers floodprone width, entrenchement ratio,
and width depth ratio are not measured in pool, glide, or run features.
Cross Section #4 at Station 6+26.6
Cross Section #5
3658.0
3660.0
3662.0
3664.0
3666.0
3668.0
3670.0
0 10 20 30 40 50 60 70 80
Station (ft)
Elevation (ft)
October 2004
Bankfull
Cross-Section #5 (Pool) Abbreviated Morphological Summary*
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 37.0
Maximum Bankfull Depth (ft) 3.8
Bankfull Mean Depth (ft) 2.5
Bankfull Width (ft) 14.8
* According to the Rosgen Classification of Natural Rivers floodprone width, entrenchement ratio,
and width depth ratio are not measured in pool, glide, or run features.
Cross Section #5 at Station 7+89.6
Cross Section #6
3657.0
3658.0
3659.0
3660.0
3661.0
3662.0
3663.0
3664.0
0 10 20 30 40 50 60 70
Station (ft)
Elevation (ft)
October 2004
Bankfull
Flood Prone Area
Cross-Section #6 (Riffle) Abbreviated Morphological Summary
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 30.3
Maximum Bankfull Depth (ft) 2.2
Width of the Floodprone Area (ft) 300
Bankfull Mean Depth (ft) 1.1
Width/Depth Ratio 25.0
Entrenchment Ratio >5
Bankfull Width (ft) 27.5
Cross Section #6 at Station 13+38.6
Cross Section #7
3655.0
3656.0
3657.0
3658.0
3659.0
3660.0
3661.0
3662.0
3663.0
0 10 20 30 40 50 60 70 80 90 100
Station (ft)
Elevation (ft)
October 2004
Bankfull
Flood Prone Area
Cross-Section #7 (Riffle) Abbreviated Morphological Summary
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 34.7
Maximum Bankfull Depth (ft) 2.1
Width of the Floodprone Area (ft) 300
Bankfull Mean Depth (ft) 1.5
Width/Depth Ratio 15.4
Entrenchment Ratio >5
Bankfull Width (ft) 23.1
Cross Section #7 at Station 17+75.6
Cross Section #8 (Tributary)
3658.5
3659.0
3659.5
3660.0
3660.5
3661.0
3661.5
0 5 10 15 20 25 30 35 40 45 50 55
Station (ft)
Elevation (ft)
October 2004
Bankfull
Cross-Section #8 (Run) Abbreviated Morphological Summary*
2004 2005 2006 2007 2008
Bankfull Cross Sectional Area (ft2) 3.6
Maximum Bankfull Depth (ft) 1.1
Bankfull Mean Depth (ft) 0.7
Bankfull Width (ft) 5.1
* According to the Rosgen Classification of Natural Rivers floodprone width, entrenchement ratio,
and width depth ratio are not measured in pool, glide, or run features.
Cross Section #8 at Station 8+74.74 on Tributary
Hanging Rock Creek Main Channel
3645.0
3650.0
3655.0
3660.0
3665.0
3670.0
220 720 1220 1720 2220 2720
Channel Distance (ft)
Elevation (ft)
bed water srf Terrace --- BKF --- x-section
Hanging Rock Creek Tributary
3657.0
3658.0
3659.0
3660.0
3661.0
3662.0
711 761 811 861 911
Channel Distance (ft)
Elevation (ft)
bed water srf Terrace --- BKF --- x-section
APPENDIX B
BANK EROSION DATA SHEETS
APPENDIX C
SITE PHOTOGRAPHS
Photo Points: Hanging Rock Creek
Photo Point #1: Looking
downstream at Cross Section #7
Photo Point #1: Looking upstream at
Cross Section #7
Photo Point #2: Looking
downstream on Tributary at Cross
Section #8
Photo Point #2: Looking
upstream on Tributary at Cross
Section #8
Photo Point #3: Looking
downstream at Cross Section #4
Photo Point #3: Looking
upstream at Cross Section #4
Photo Points: Hanging Rock Creek (continued)
Hanging Rock Creek Photos
Photo Point #4: Looking
downstream at Cross Section #1
Photo Point #4: Looking upstream
at Cross Section #1
Overview of site looking downstream from Dobbins Road
culvert
Overview of site looking upstream from NC Highway 184
culvert
Hanging Rock Creek Photos (continued)
Bank undercutting around rootwads at Station 16+45.6
Scour behind rootwad at Station 7+55.6
Damaged culvert at downstream end of site; NC Highway 184