Draft Mit Plan Comment Memo_NCDMS Casey Creek_SAW-2022-01239

DEPARTMENT OF THE ARMY
WILMINGTON DISTRICT, CORPS OF ENGINEERS
69 DARLINGTON AVENUE
WILMINGTON, NORTH CAROLINA 28403-1343

CESAW-RGM/Tugwell March 28, 2024

MEMORANDUM FOR RECORD

SUBJECT: Action ID. SAW-2022-01239, NCDMS Casey Creek: Comments from 30-day
NCIRT Mitigation Plan Review, Wayne County, NC

1. The comments listed below were received from the NCIRT during the 30-day
comment period in accordance with Section 332.8(d)(7) of the 2008 Mitigation Rule. The
30-day comment deadline was February 1, 2024.

2. Maria Polizzi, NCDWR (NCDWR # 20220664v2):

a. Please include a list of all soil amendments used on site in the As-built and
subsequent monitoring reports if applied. Soil test results are also a welcome
inclusion in the appendix.

b. DWR also recommends incorporating organic matter prior to planting, if possible,
especially in areas with P2 cuts.

c. DWR recommends that the performance standard for flow on intermittent channels
be 60 consecutive days of flow during the growing season.

d. Section 11.0: DWR would like more information about why 50 ft. buffer widths
cannot be provided across the entirety of the site. Although the 2016 guidance
does not require a credit adjustment under 5%, this is not ideal and buffer widths
should 50 ft or wider on all project streams unless there is there is a significant
constraint that prevents this from being possible. DWR also does not consider
wider buffers in other areas to be adequate justification, since these areas are
proposed for buffer/nutrient offset credit.

e. Please include the buffer mitigation plan as an amendment to the draft plan.

f. Please note that these comments are only regarding the Stream and Wetland
portion of this project. Katie Merritt (DWR) will be reviewing the Appendix I-Buffer
Mitigation and Nutrient Offset Plan separately. Additionally, all project components
(stream/wetland and buffer/nutrient) must be constructed simultaneously. The
approval of one plan before the other does not allow for separate construction
timelines.

g. DWR appreciates that the project area is shown on the historical aerials.
h. Please include a figure showing all mitigation credit types on one map
(stream/wetland and buffer/NO). This should be included in the Figures section of
the Appendix.

i. IRT Site Visit Meeting Minutes: The IRT recommended culvert crossings on sand
bed streams; however, the Alfon Branch crossing is proposed as a ford. Why was
a culvert not proposed for this crossing? There is also no specification provided for
this ford.

j. DWR appreciates the diversity of species proposed for the buffer planting zone.

k. Consider installing a crest gauge on Alfton Branch.

l. Section 6.3, Page 20: WEI states that slightly larger design discharges are
proposed, leading to larger channels, which has been successful on past projects.
What is the reasoning for this? What benefits have been found and what risks does
WEI foresee if a smaller channel/discharge was proposed? It seems like higher
discharge would be riskier, especially in a system with only moderate sediment
inputs and a sand bed system with smaller particles.

m. Section 6.5.3, Page 25: This section explains that higher design discharge is
proposed to maintain transport capacity, but aggregation is not currently an issue
and sediment inputs are expected to go down as a result of the project. If
degradation is a current problem, wouldn’t it be preferable to decrease the
discharge? DWR is unsure whether hurricane resiliency is worth an increased
need to armor the channel with larger rock. Won’t activated floodplains also help
to improve hurricane resiliency without direct channel discharge needing to be this
high?

n. Design Sheet 1.1: An “existing drainage” is shown connecting to Casey Creek at
STA 122+00 but is not shown on other maps or figures. What is the condition of
this drainage? Could a BMP of some kind be utilized in this location? Please be
sure to show drainages/ditches like this on the site map.

o. Design Sheet 5.1:

a. Please provide more information about the Native Material Constructed
Riffle. Will all material for this structure type be sourced on site? Is it all
stone material? Sizing is TBD, which makes it difficult to evaluate whether
this structure type is appropriate for the location/ecoregion, especially if
material will not be sourced locally.

b. There are multiple references to a riffle material table, but no table was
found. DWR would like to review the sizing of the riffle material, so please
include that in the final plan or provide a page number if it has been
overlooked somewhere.
p. Design Plans General:

a. There are very few angled log riffles, and a lot of stone-based riffles. Could
more woody structure types be incorporated? From the particle size
analysis, the largest diameter particles in the current system are 28 mm,
and most are much smaller. DWR is concerned that the amount of rock
proposed for this project will make the system less natural from that
perspective. DWR is not opposed to the occasional “immovable larger
stone” in riffles but wants to avoid a significant replacement of native bed
material with larger diameter particles.

b. Some riffles are not labeled on the plans and since the symbology is the
same for all riffles, it is unclear what type of riffles these are.

c. There are several riffles that are quite long (~40 ft.), which feel like they are
functioning more as channel hardening rather than creating bedform
diversity. Is there a reason for these extra long riffles? Would a sequence
of structures be able to provide similar function with greater uplift potential?

d. It would be helpful if more grading details were shown on the plans. This
would provide the IRT with a better understanding of where P2 cuts are
located, as well as their shape and size.

q. Is there a reason why Casey Creek Reach 1 is only a reference for pattern and not
for profile, discharge, etc.? It seems that this feature would be the most relevant
reference since it is directly upstream of the restoration reach.

r. Would it be possible to fully incorporate wetland B in the conservation easement?
This would help prevent any future land uses from degrading the wetland and/or
water quality in this area.

3. Erin Davis, USACE:

a. Page 5, Section 3.1 – Thank you for investigating multiple planning resources to
inform on potential future project vicinity and watershed development.

b. Page 15, Section 3.5 – This section states that easement boundaries provide the
required 50-ft minimum stream buffer. However, Section 11 identifies 4.3% of the
site as having less than the 50-ft standard stream buffer width. Please make sure
section information is consistent. Additionally, Section 3.4 hydrology subsection
asserts that site constraints necessitated the stream restoration to be designed as
Priority 2, which has an affect on the potential functional uplift of the site and should
be discussed in Section 3.5 as a limiting factor for achieving Priority 1 restoration.

c. Page 27, Section 6.6.4 –

a. The IRT site walk meeting minutes dated July 27, 2022, included a
recommendation to coordinate with NC DOT on the perched culvert under
Highway 13 to allow a degree of backwatering which would aid in aquatic
species passage and potentially reduce the amount of Priority 2 restoration.
Please include a brief discussion on coordination with NC DOT.

b. Typically, we ask that Priority 2 restoration be limited to tie-in areas and that
widening of the stream buffer be the first choice considered to reduce the
risk of hydrologic trespass, which is based on Priority 2 restoration having
functional uplift limitations. However, we also have concerns about the long-
term stability of a series of log drop structures as grade control in certain
stream systems. Casey Creek Reach 3 appears to have a middle section
of approximately 250 feet of Priority 1 restoration followed by 100-foot
straight channel log step system. What is the worst-case scenario if the log
step system fails after project closeout? What is the potential likelihood of
structure/system failure? Would the log step system be necessary if the
short section of Priority 1 was adjusted to a continuation of Priority 2?

d. Page 27, Section 6.6.5 – During the IRT site walk, the IRT expressed concerns
about the culvert just downstream of the project terminus. The meeting minutes
note that it may be necessary for Wildlands to obtain a temporary construction
easement to install a stable connection. Has this action been coordinated?

e. Sheets 1.1 – 2.2 – The lack of approximate proposed grading contours and limits
of disturbance lines made this review difficult, especially given the considerable
amount of proposed Priority 2 restoration. This information is required in the Final
Mitigation Plan and since that will be the first opportunity the IRT has to review this
information, it may result in additional questions/comments. Moving forward we
recommend inclusion of rough/approx. grading and limit of disturbance lines in
draft mitigation plans.

f. Sheet 1.5 – What is the rationale for shifting the section of Casey Creek Reach 3
approximately 80 feet to the east? Is this additional linear footage needed to
achieve the downstream section of Priority 1 restoration?

g. Sheet 1.7 – Please callout the roadside ditch top of bank. Is the ditch running
between the mapped wetland area and road fully excluded from the conservation
easement? If not, will a portion of the ditch be filled? Will allowable ditch
maintenance and offset boundary signage be addressed in the easement
agreement and plat?

h. Sheet 5.1 – Chunky riffle is a proposed constructed riffle type included in the design
details. However, all of the project streams have been identified as sand bed
systems. Were boulders and 20-ft long cobble/gravel riffles observed in reference
sand bed streams of similar watershed size and slope? What functions will these
structures be providing? Have chunky riffles been successful in other sand bed
stream restoration projects?

i. Sheet 5.3 – Please provide a detail for the proposed swale with pilot channel,
including dimensions and materials.

j. Figures – Please include a figure showing all mitigation credit types on one map,
including all proposed stream and buffer/nutrient offset assets.

k. Figure 10 –

a. Please shift the upstream flow gauge on Martha Branch further up to the
photo point location.

b. Please shift two fixed veg plots based on the figure markup provided. And
due to concerns regarding vegetation establishment on Priority 2 bench and
slope areas, please change the division of veg plot type to 3 random plots
and 8 fixed plots.

c. Please add a photo point at the start of the BMP on Marth Branch, and shift
photo points upstream and downstream of the culvert crossing (#1) closer
to the structure.

l. While we did not reiterate all concerns noted by DWR, we support their comments
included above.

Sincerely,

Todd Tugwell
Chief, Mitigation Branch

Electronic Copies Furnished:

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