20180179 Ver 1_Addendum_20210623

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20180179
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Erin Davis
Initial Review Completed Date 06/23/2021
Mitigation Project Submittal - 6/23/2021
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Cara Conder
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20180179
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Project Name: Grassy Creek Tributaries
County: Surry
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GrassyCreekTribs_Addendum.pdf 6.39MB
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Cara Conder

Addendum to the Final Mitigation Plan
Grassy Creek Tributaries Mitigation Project
Surry County, North Carolina
Private Commercial Mitigation Bank for
Stream Compensatory Mitigation Credits
Upper Yadkin River Basin (CU 03040101)
(Warm Water Thermal Regime)
USACE Action ID Number: SAW-2017-02528
Prepared for:
U.S. Army Corps of Engineers, Wilmington District
69 Darlington Avenue
Wilmington, North Carolina 28403-1343
Prepared by:
4 WATER & LAND SOLUTIONS
7721 SIX FORKS ROAD, SUITE 130, RALEIGH, NC D615
(919)614-5�11 woterlondSolWions.com
SIX FORKS ROAD, 130, NC 27615
614 - 5111 I waterlandsolutions.com
June 2021

Addendum - Grassy Creek Tributaries Mitigation Project
Table of Contents
1 Introduction 3
1.1 Background 3
1.1 Site Construction Winter/Spring 2020 3
2 Revised Mitigation Credits 4
3 Mitigation Work Plan Addendum 4
3.1.1 Stream Repair Design Reach Revisions 4
Tables
Table 1. Mitigation Plan Stream Mitigation Credits (SMCs) 3
Table 2. Revised Stream Mitigation Credits (SMCs) 4
Figures
Figure 1 Repair Plan Figure
Figure 2 Revised Mitigation Features
Appendices
Appendix A Design Plan Repair Sheets
Page 2

Addendum - Grassy Creek Tributaries Mitigation Project
1 Introduction
1.1 Background
Water & Land Solutions, LLC (WLS) is submitting this mitigation plan addendum for the Grassy Creek
Tributaries Mitigation Project ("Project") under the WLS Yadkin 01 Umbrella Mitigation Bank ("Bank").
The Project involved the restoration, enhancement, and permanent protection of eight stream reaches
(R1, R2, R3, R4, R5, R6, R6a and R7), totaling approximately 6,154 linear feet of streams. Table 1
summarizes the stream mitigation credits (SMCs) from the final mitigation plan approved on January 27,
2020.
Table 1. Mitigation Plan Stream Mitigation Credits (SMCs)
Project Reach
Designation
Type of Mitigation
Existing Proposed Stream
Stream Stream Length Ratio Mitigation
Length (LF) (LF) Credits (SMCs)
R1
R2
R3
R4
R5
R6
R6a
R7
Stream Restoration (PI)
Stream Restoration (PI)
2,343
651
2,323
476
1:1
1:1
2,243*
426*
Stream Restoration (PI) 1,229
1,198
1:1 1,178*
Stream Enhancement II 1,127 1,122 5:1 225
Stream Restoration (PI/PII) 329 329 1:1 329
Stream Restoration (PI/PII)
Stream Restoration (PI/PII)
Stream Restoration (PI/PII)
242
54
376
247
54
405
1:1
1:1
1:1
247
54
355*
Totals
6,351 6,154 5,057
Note: *SMCs account for deducting crossings/easement breaks. No mitigation credits were calculated outside the
conservation easement boundaries.
1.1 Site Construction Winter/Spring 2020
The site was initially constructed during winter/spring 2020 and there were no major deviations from the
final mitigation plan and construction plans. The site earthwork construction was completed on April 28th,
2020 and the vegetation planting was completed on April 30th, 2020. Baseline or MVO monitoring device
installation and data collection was conducted the week of May 4th, 2020. This included seven permanent
vegetation plots, 12 permanent cross -sections, three flow gauges (R1, R5, and R6), and one crest gauge.
During the month of May 2020, the site experienced two separate 2-year storm events resulting in over
bank flows and floodplain erosion prior to permanent groundcover establishment. The Surry County
Airport Weather Station (KMWK), which is about 15 miles north of the site, reported a total of 9 inches of
rain for the month of May which is +1.5 inches greater than the monthly average. On May 20, 2020 there
was a storm event with 2.74 inches of rain and on May 21, 2020 there was an additional 1.32 inches of
rain. Tropical Storm Bertha made landfall on May 27, 2020 and resulted in 2.61 inches of rain in
approximately four hours. On May 27, 2020 the gage height at the USGS Ararat River Station (02113850)
in Ararat, NC was approximately 2.0 feet and on May 28th the gage was above 9.0 feet. The average gage
height for this station in 2020 was 1.626 feet.
Water & Land Solutions Page 3

Addendum - Grassy Creek Tributaries Mitigation Project
These rain events caused enough damage to portions of the site preventing the as -built survey completion
in 2020. WLS developed a repair plan for the Project, which was implemented in October 2020 and
completed by April 2021.
2 Revised Mitigation Credits
The mitigation credits have been revised based on repair design changes and are from the as -built survey
for Reaches R2 and R3 (Table 2). All the other reaches did not have any channel repair work done and are
based on the mitigation plan lengths.
Table 2. Revised Stream Mitigation Credits (SMCs)
Project Reach
Designation
Type of Mitigation
Existing Proposed Stream
Stream Stream Length Ratio Mitigation
Length (LF) (LF) Credits (SMCs)
R1
R2
R3
R4
R5
R6
R6a
R7
Stream Restoration (PI)
Stream Restoration (PI)
2,343
651
2,323
430
1:1
1:1
2,2431
3771,2
Stream Restoration (PI) 1,229
Stream Enhancement II 1,127
Stream Restoration (PI/PII) 329
1,202
1,122
329
1:1 1,1801,2
5:1 225
1:1 329
Stream Restoration (PI/PII) 242
247 1:1 247
Stream Restoration (PI/PII) 54
54
1:1
54
Stream Restoration (PI/PII)
376
405
1:1
3551
Totals
6,351
6,112 5,010
Note 1: *SMCs account for deducting crossings/easement breaks. No mitigation credits were calculated outside
the conservation easement boundaries.
Note 2: SMCs on R2 and R3 are the as -built survey lengths and were the reaches that were repaired/redesigned.
3 Mitigation Work Plan Addendum
The mitigation work plan addendum involved the restoration, enhancement and permanent protection
of approximately 6,112 linear feet of stream channel. In April 2020 the site was completely planted (8
acres). Following the repair completion (April 2021) 3.43 acres were re -planted. The repair design
approach is described in the following subsections.
3.1.1 Stream Repair Design Reach Revisions
R1: Damage along this reach mainly involved floodplain erosion. The majority of this erosion occurred
downstream of the powerline culvert. There was also one structure failure towards the downstream end
of this reach. In addition, both BMPs experienced hillslope erosion.
The repair of this reach involved grading the floodplain at a 5% slope from the channel top of bank back
to start of the terrace slope. A failed geolift at station 29+25 and 30+50 was also repaired.
The BMP within the powerline easement had the slopes graded at a 3:1 slope. In addition, two small
swales were constructed to direct flow from adjacent farm fields into this BMP. These swales were lined
with matting. Once the swales met the 3:1 slope of the BMP, the remainder of the swale was constructed
Page 4

Addendum - Grassy Creek Tributaries Mitigation Project
as a boulder step pool, as well as lined with a mix of Class B and Class II rip rap to act as a steep cascade
into the BMP. The BMP weir was also be reinforced with Class II stone and boulders.
The larger BMP towards the lower end of the reach was stabilized by regrading and matting eroded side
slopes. A small swale was constructed to direct flow into the BMP from the adjacent farm field into the
BMP. This swale was lined with Class II stone. Both the stone at the inlet and weir of this BMP were
supplemented with additional Class II Stone.
R2: Approximately 281 LF of this reach was impacted with a heavy sediment load from streams within
Pilot Mountain State Park.
The repair approach for this reach was to realign the channel from its start at the park boundary and tie
this new alignment into the newly constructed channel at approximate station 43+64. The channel was
designed more as a Cb-channel with low meander geometry and more step structures to dissipate
energy. The entire floodplain along this reach was undercut by approximately one -foot to remove
unsuitable material from the floodplain. Cohesive soil was then placed back in the floodplain. The channel
and floodplain were regraded along this reach to constrict flood flows slightly and increase shear stress.
This will allow the heavy sediment load coming out of the park to be routed more competently through
this reach. Along with this realignment several point bars were regraded at a 6:1 slope.
Based on the new realignment Reach 2 stream length decreased by approximately 46 feet.
R3: Damage along R3 involved erosion of outside meander bends and slight channel adjustment in two
meanders. Along with these channel changes, areas of floodplain subsidence occurred both within and
outside the conservation easement. Flood flows also eroded many areas of the floodplain.
Repair along this reach included many areas of point bar grading at 6:1 slope and reinforcing failing outside
meander bends with vegetated geolifts. Two meander bends were slightly realigned to soften channel
planform. The first meander bend was realigned starting at station 48+90 and ties back into the ford
crossing at approximate existing channel station 51+30. The second realignment starts at station 56+86
and ties back into the existing channel at approximate station 57+75
Based on the realignments in this reach the stream length increased by approximately 4 feet.
R4, R5, R6, R6a, R7: There were no design changes to these reaches.
Water & Land Solutions Page 5

Figures

Channel realigned
per repair plan
1,000
Feet
Legend
—Stream Repair (Restoration)
II Conservation Easement
[ Pilot Mountain State Park Property
Water Quality Feature
Stream Mitigation Type
Enhancement II
Restoration
Channel realigned
per repair plan
Channel realigned
per repair plan
/WATER & LAND -
SOLUTIONS
Grassy Creek Tributaries
Mitigation Project
Repair Plan
Map
NAD 1983 2011 State Plane
North Carolina FIPS 3200 FT US
FIGURE
1

L_ Pilot Mountain State Park Property
Water Quality Feature
Stream Mitigation Type
Enhancement II
Samoa E o o GeoE-y-, [gyp eog . phi . , MEV
DD USDA,Igt§g§o Z E O cDQ IMQ ad nt1'x�- 1211E2, NAP CUa u G
4WATER &LAND"
SOLUTIONS
Grassy Creek Tributaries
Mitigation Project
Proposed Mitigation
Features Map
NAD 1983 2011 State Plane
North Carolina FIPS 3200 FT US
FIGURE
2

Appendix A

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