20120658 Ver 1_Restoration Repair Plan_20240524

Homewood, Sue
From: Jennifer Burdette <[e-mail]>
Sent: Friday, May 24, 2024 11:03 AM
To: [e-mail]; Homewood, Sue
Cc: Rebecca Stubbs; James Eason; Ryan Lavinder ([e-mail])
Subject: [External] Duke Unv Campus Dr Stream Restoration (AID SAW-2012-01043/DWR #
20120658)
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Greetings,
The Campus Drive Stream Restoration is the permittee-responsible mitigation plan required by the IP issued on
March 4, 2013 for the Duke University Water Reclamation Pond. Monitoring for this project was suspended for a
time because of COVID constraints. Due to instability observed by monitoring and a site visit with USACE and DWR
representatives in 2022, the team agreed a repair plan would be needed. McAdams has prepared a Repair Plan for
you to review and approve before proceeding with the necessary repairs.
Please feel free to contact Rebecca Stubbs with McAdams directly if you have any questions about the repair
design. As Julia was not part of the team during the 2022 site visit, I am happy to give Julia a tour to familiarize her
with the project.
7r.
0 2024-05-16 CampusDriveStreamRestoration-Remedia[MitP[an.pdf
Thanks,
Jennifer
Jennifer Burdette
Natural Resource Consultants
308 W Millbrook Rd, Ste D #200, Raleigh, NC 27609
burdette(cDnrconsultnc.com — 919.422.3605
JNatuResource
ral
Consultants

�� MCADAMS
CAMPUS DRIVE
STREAM RESTORATION
REMEDIAL ACTION PLAN
Project Owner: Duke University
Designed By: Rebecca Stubbs, PE
Date: May 2024
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TI MCADAMS
PROJECT SUMMARY
DKU23005 > REMEDIAL ACTION PLAN
The Duke University Water Reclamation Pond Stream Restoration project (Stream Restoration project) is on the main
campus of Duke University, in Durham, Durham County, North Carolina (Appendix A, Figure 1). More specifically, the
Conservation Easement (CE) forthe Stream Restoration project is 7.01 acres in size and startsjust south of NC Highway
147, runs parallel to Campus Drive, crosses Campus Drive and ties back into the receiving waters at Oregon Street
(Appendix A, Figures 2.1 and 2.2). The Stream Restoration project is approximately 1.5 miles from the proposed stream
impacts associated with the Duke University water reclamation pond.
The Stream Restoration project is located within the Cape Fear River Basin USGS Hydrologic Unit 03030002 (USGS
1974), local watershed 14-digit basin 03030002060110, and the North Carolina Division of Water Resources (DWR)
sub -basin 03-06-05. The unnamed tributary flows directly into Sandy Creek (DWR stream index number of 16-41-1-
11) approximately 2.5 miles downstream of the project terminus.
The drainage area of the unnamed tributary is approximately 141 acres at the downstream end. Based on a detailed
watershed analysis, approximately 27 percent (39 acres) of the watershed area is impervious. The Stream Restoration
project is located within the Piedmont Physiographic Province of North Carolina. A review of the Ecoregions of North
Carolina and South Carolina (Griffith et al., 2002) shows the geology of the Stream Restoration project is comprised of
quaternary to tertiary red sandy loam to silty clay decomposition residuum, sandstone, conglomerate, mudstone,
shale, coal, dikes, and sills within the Triassic Basin.
As -Built surveying and baseline monitoring of the stream restoration was completed and reported on July 9, 2014.
Monitoring Year 1 also began in 2014. Monitoring has been completed in general accordance with the restoration
plan dated October 2012. After visual assessments in monitoring year 4 (2017) identified bank erosion around log sills,
a comprehensive log sill assessment was completed and reported in the monitoring year 5 report. Invasive species
monitoring and treatment ceased after the spring of monitoring year 4 to be re-evaluated after log sill repairs were
completed. Three areas of mowing within the CE were also noted in monitoring year 4. Repairs were not made, and
monitoring ceased after monitoring year 6 due to pandemic constraints. Monitoring resumed in monitoring year 9
(2022). On November 29, 2022, Sue Homewood and Kelsey Rowland with the NC Division of Water Resources and
April Norton with the US Army Corps of Engineers joined Ryan Lavender, PE with Duke University along with staff from
McAdams and Natural Resource Consultants for visual inspection of the stream restoration project. From that site
walk, a comprehensive repair plan has been developed to improve the stability of the original stream restoration
design. The included construction drawings contain the proposed restoration repair measures.
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TI MCADAMS
PROPOSED REMEDIAL ACTION PLAN
INSTABILITY ASSESSMENT
DKU23005 > REMEDIAL ACTION PLAN
After the site walk in November 2022, McAdams reviewed past monitoring year data to identify potential causes for
instability and understanding trends of the channel adjustments observed. Assessment of monitoring data indicated
significant channel adjustment in the Northern Reach (outlet from culvert under Hwy 147 to inlet Campus Drive
culvert). Some channel adjustment has been observed in the Middle and Southern Reaches throughout the monitoring
period, however, to a much lesser extent than the Northern Reach. It is presumed that channel widening and
deepening has occurred more in the Northern Reach due to:
> Herbaceous vegetation along the banks and floodplain not as abundant as in the Middle and Southern
Reaches. While, maturing trees are present, there is a lack of smaller woody vegetation throughout the area
identified for realignment and remedial grading.
> The Northern Reach generally has a narrower flood prone area than in the other reaches, resulting in more
concentrated flows during larger storm events.
> The original design alignment of the Northern Reach had a high sinuosity coupled with many log sills that did
not adequately re -direct in -stream flows away from outer bends resulting in significant bank scour along the
outer bends and adjustment of the channel alignment and dimension over time.
As a result, mid -channel bars and sediment deposition within the channel are currently observed.
REPAIR PLAN GOALS
Based on the observed and identified instabilities of the Northern Reach of UT Sandy Creek, there is significant
potential for improved geomorphic function and stability. The remedial action plan design was developed to address
these needs by:
> Enhancing channel stability through re -stabilization of degraded areas and establishing a stable channel
dimension, pattern, and profile.
> Reconnecting the stream with its floodplain by grading a bankfull bench and reducing channel dimensions.
> Restoring riparian zones through revegetation and supplemental planting with native trees in disturbed and
adjacent areas.
REPAIR PLAN DESIGN APPROACH
The Northern Reach remedial action plan employed a combination of established design methods with data analysis
informed by seven years of post -construction monitoring. Key considerations during the design process included:
> Reference reach data provided the basis for morphological design parameters and dimensions.
> The North Carolina Piedmont Regional Curve (Harman et al. 1999) was used to determine the design
discharge and size of the channel.
> Natural channel design methods guided the sizing of the bankfull floodplain bench and structure design.
> The proposed removal and reconfiguration of existing structures were informed by existing channel
instability, past monitoring years data, and improving bedform diversity.
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TI MCADAMS
DKU23005 > REMEDIAL ACTION PLAN
More specifically, the Northern Reach remedial action plan is divided into two distinct reaches.
> Reach 1: This area will included channel realignment, existing channel fill, floodplain benching, and grade
control structures.
> Reach 2: This area is downstream and contiguous with Reach 1 but will not include channel realignment.
Proposed work will include remedial grading of the existing channel banks, existing structure removal and
reconfiguration, and bench grading.
Reach 1— Realignment Design
Within the limits of the realignment reach, the previously restored channel exhibits channel incision, bank migration,
and limited floodplain access. Several structures are not functioning and have been flanked. The original design had
a high sinuosity through this section which has increased post -construction due to bank erosion. The level of channel
degradation in this area warrants a realignment and redesign of the stream in lieu of remedial bank grading.
The proposed channel realignment was designed to be a C3 stream type. Reference C/E channels do form high
sinuosity and low radius of curvature ratios however, past experience indicates that lower limits of these ratios are
not suitable for Priority I restoration as was originally proposed. The repair plan channel realignment section was
designed with radius of curvature ratios between 2-3 and a meander width ratio of 2.5. These design parameters will
reduce bank shear stress during high flows and dissipate energy through meander bends.
The design discharge for the realignment section was primarily informed by the Rural Piedmont Regional curve. This
in contrast with the original constructed design which was sized using the NC Urban Piedmont Regional Curve. The
NC Urban Piedmont Regional Curve overestimates bankfull channel dimensions. Since the time of the original
design, the NC Urban Piedmont Regional Curve has fallen out of standard acceptable design methods typically used
by stream restoration engineers. It is a better practice to size the flood prone area to accommodate increased peak
flows due to urbanization and size the primary stream channel based on NC Rural Piedmont Regional Curve data.
The repair plan stream was designed to a width -to -depth ratio of 13.0 and a bankfull area of 5.1 sf. Pool widths are
1.2-1.3 times the width of the riffles to provide space for point bars and riffle pool transition zones. Pool depths
were 2.9 times deeper than the riffles to provide for energy dissipation and bedform diversity. Floodplain benches
are to be a minimum of 6-ft wide but are maximized within the available floodplain. The entrenchment ratio for this
section varies between 3.5-6.0 to provide for expansive floodplain access.
Reach 2 - Remedial Design
Within the Northern Reach remedial section, the right bank's existing floodplain exhibits steeper slopes, reduced
flood prone area, and denser vegetation when compared to the left bank. The proposed bench design integrates
these existing features as the right bench grading conforms to the existing floodplain and terrace limits, minimizing
disturbance in areas with stable banks and dense native vegetation. The left bank floodplain bench design prioritizes
the maximum available area and includes a minimum bench width of 6-ft. The proposed benching will also
reconfigure unstable sections of bank and decrease channel dimensions.
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TI MCADAMS
DKU23005 > REMEDIAL ACTION PLAN
The remedial design includes the installation of constructed riffles and bank toe stabilization to prevent channel
incision and bank migration. Ten existing log sills were identified as underperforming and increasing channel
instability. These structures will be removed and repurposed in other proposed structure locations. Additionally,
three existing log sills and their downstream meander bends will be reconfigured into log-J hooks to reduce
downstream bank stress and provide dissipation. Locations of the proposed constructed riffles, log J-hooks, log sill
removal and existing log sills to remain were designed intentionally to provide an appropriate pool -to -pool spacing
and improve stability throughout the reach.
CONCLUSION
Based on detailed review of monitoring data collected to date coupled with revised design practices of stream
restoration in NC Piedmont urban watersheds, the proposed remedial action plan is intended to restore appropriate
channel dimension, pattern, and profile through incorporation of broader, more accessible flood prone area and
more -effective grade control and bank protection structures.
REFERENCES
Griffith, G.E., J.M. Omernik, J.A. Comstock, M.P. Shafale, W.H. McNab, D.R. Lenat, J.B. Glover, and V.B. Shelburne.
2002. Ecoregions of North Carolina and South Carolina. (2 sided color poster with map, descriptive text, summary
tables, and photographs). U.S. Geological Survey, Reston, VA. Scale 1:1,500,000.
Harman, W.H. et al. 1999. Bankfull Hydraulic Geometry Relationships for North Carolina Streams. AWRA Wildland
Hydrology Symposium Proceedings. Edited By: D.S. Olsen and J.P. Potyondy. AWRA Summer Symposium. Bozeman,
MT.
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�� MCADAMS
APPENDIX A
FIGURES
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APPENDIX 6
REPAIR PLAN CONSTRUCTION DRAWINGS
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