20061909 Ver 2_More Info Received_20070823

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June 11, 2007
Subject: June 9, 2007 SAV Analysis Ashbee Harbor Club
Skyco, Dare County, NC ~ , ~, ~--~ +~;
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To: State and Federal Permit Agencies ~ ~ ~~
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From: Brian Rubino, P.G., Quibte 8 Associates, P.C. r~~~~ri - ~'jl ~~~ ~uf~.'-'~ ~,;
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Purpose:
The purpose of this document is for Quibte & Associates, P.C. (Quibte) to provide state
and federal regulatory agencies with a review of submerged aquatic vegetation (SAV) in
proximity to the proposed Ashbee Harbor project to accompany the CAMA Major
Application Package that is currently under review. The subject property lies adjacent to
the Croatan Sound, and the proposed project involves connecting two existing navigable
canals to a proposed upland basin system. The existing canals are referred to as Canal
A and Canal B (Canal A has historically been referred to as Howards Creek and Canal B
is an unnamed tributary). There are 46 boat slips and 46 homesites proposed in
association with this project. The CAMA Major Application Package was accepted as
complete by NCDCM on June 18, 2007 and is currenty under inter-agency review.
The July 9, 2007 SAV analysis at Ashbee Harbor Club was conducted to examine the
substrate of the waters within Canal A and Canal B and waters at the mouth of the
canals in the Croatan Sound. The objective was to investigate for the presence of SAV,
and to document the conditions that may relate to SAV habitat.
The SAV survey was conducted in July, which is typically near peak growing season for
SAV in this region and setting (prior to the dominant humcane/tropicalstoan season).
1

State and Federal Rules:
The State of North Carolina protects areas that are dominated by submerged aquatic
vegetation (SAV), which are called "SAV beds". According to the North Carolina
Administrative Code (NCAC), SAV beds are described as "habitats in public trust and
estuarine waters vegetated with one or more species of submergent vegetation. These
vegetation beds occur in both subtidal and intertidal zones, and may occur in isolated
patches or in extensive areas. In either case, the bed is defined by the presence of
above-ground leaves or below-ground rhizomes and propagules° (NCAC 07H
.0208(a)(6)). SAV is further referenced in Chapter 4 of the 2004 North Carolina Coastal
Habitat Protection Plan (NCCHPP).
On the Federal level, areas of SAV are considered to be "Essential Fish Habitat". As
defined in the Magnuson-Stevens Fishery Conservation and Management Ad
(MSFCMA), EFH is considered "those waters and substrate necessary to fish for
spawning, breeding, feeding, or growth to maturity".
Conditions on May 31, 2007:
Air Temperature: 30.5°C
Wind: ~15-20 mph SSW
Station 1 (Canal A terminus)
Water Temerature: 28.9°C
Water Visibility (secchi reading): 3.0 ft
pH: 6.70 (2 it below surface)
Dissolved Oxygen: 4.7 mg/L
Turbidity: N/A
Conductivity: 12.1 mS/cm
Salinity: 6.9 ppt
Station 2 (Canal A mouth)
Water Temerature: 29.6°C
Water Visibility (secchi reading): 2.5 ft
pH: 7.5
Dissolved Oxygen: 7.76 mg/L
Turbidity: 7 NTU
Conductivity: 12.8 mS/cm
Salinity: 7.3 ppt
2

Station 3 (Canai B terminus)
Water Temerature: 30.13°C
Water Visibility (secchi reading): 3.0 ft
pH: 6.57
Dissolved Oxygen: 6.32 mg/L
Turbidity: 12 NTU
Conductivity: 13.9 mS/cm
Salinity: 7.3 ppt
Station 4 (Canal B mouth)
Water Temerature: 29.4°C
Water Visibility (secchi reading): 2.75 ft
pH: 7.57
Dissolved Oxygen: 6.71 mg/L
turbidity: 5 NTU
Conductivity: 13.0 mSlcm
Salinity: 1.9 ppt
Methodology:
The method of analyzing the substrate at the subject property for this survey involved
visual inspections performed by diving with a snorkel and mask by two environmental
scientists from Quible. A small boat was used for transportation to the site and to hold
sampling equipment, water quality meters, aerial photography, GPS, etc.
Water depths were measured using a 10 foot graduated measuring rod (depths rounded
to the nearest 0.25 feet) and compared to surveyed water depths from 2006 (based on
nwl) that are depicted on the attached map. Water depths taken on July 9, 2007 were
found to correspond with the previous measurements, however, wind conditions on July
9th has caused higher than normal water levels that appeared to be approximately 0.75 ft
above normal.
The investigations began from the terminus of each canal and visual observations of
bottom conditions were made, working out toward the sound. The boat was moved and
tied to the bank of the canals as the investigation progressed, so to have sampling
equipment readily available, and to make field notes during the investigation.
in an area where SAV was encountered, the extent was mapped by GPS and aerial
photography. In order to evaluate coverage and distribution of SAV in the area where it
3

was identified, coverage estimates were made based on percent cover standards'. In
addition, species composition was recorded and samples were taken to key species in
the laboratory with SAV manuals.
Findings:
Canals A and B
The bottom conditions along the canals consisted of soft, loose organic bottom and peat
with partially decomposed wood and plant material. The existing channels within the
canals were clearly identifiable, and, according to the property owners, these are historic
channels that have been maintained. Near vertical walls were identified on each side of
the channels. Visibility was sufficient to clearly see the substrate when closely
observed. Based on secchi disc readings, the visibility was 2.5 to 3.0 ft. Most areas
along the canals were devoid of any live SAV, but there were some minor occurrences
of ripped-up SAV lying on the bottom2. There was one location where SAV was
detected as presented on Exhibit A. The SAV area was found in Canal A, near the
mouth of the canal. All living SAV was ident~ed as Rttppia maritime (widgeon grass).
The SAV growth extent was limited to a gently sloping shelf on either side of the
navigable channel. No SAV was found in the cut where boats are proposed to
operate/navigate. This shelf was found to have a veneer of fine sand that was underlain
by peat. The eastern side of the shelf had a greater abundance of SAV and there was a
narrow band of SAV that was found to have a cover of approximately 60-70 percent with
growth heights of 414 inches. This band of SAV was found in approximately -2 to -2.25
ft of water. In slightly more shallow water, there was sparse SAV with up to 20 percent
cover with growth heights of 2 to 6 inches. Cores were pertormed in these areas and
rhizomes were detected in the more dense SAV zone. Outside of this zone of SAV,
there were minimal rhizome systems detected.
' A resource on hand during the investigation was percent cover standards (photographs) that were taken
from http://seagrasswatch.org/home.html
z Small amounts of ripped-up SAV was detected in several locations. The rippefl-up plant matter is not
living and was transported to its current location in the water column from unidentified sources. This
matetaal was found to be decomposing inmost instances and was discolored. This was found to have a flat
ribbon-like leave and was either Zostera marina (Eelgrass) or Vallisneria americans (Wild celery). Both of
these species have a similar appearance and without a live plant, the species could not positively be
identified.
4

Croatan Sound
As depicted on the Exhibit A, the evaluation extended into the sound to naturally
occurring water depths of about -5 ft. During the evaluation, wave heights were up to 2
ft with white caps. The substrate material was peat and sand. In some areas, there was
a thin sand layer over peat. This was a very high energy area. There was no live SAV
detected, however there were some minor amounts of ripped-up SAV found.
Interpretations:
Most of the areas evaluated had no SAV on July 9, 2007. The reasons for this include,
but may not be limited to water depth, water visibility, substrate material and energy
regime. The water depth in the canals was found to be at least - 5 ft in the channel
where boats will navigate and in many places ~ was deeper. The bottom was comprised
of loose organic material and peat that is not normally conducive to SAV growth.
At the mouth of the canals, into Croatan Sound, energy levels were found to be
extremey high. Since the prevailing wind direction is from the southwest throughout the
majority of the growing season, is it not likely that this area that is exposed to several
miles of fetch, will support signficant SAV growth.
The location that did have SAV is a fairly stable shelf that has a thin blanket of sand.
While this SAV area receives some wave energy, the majority of the wave energy
dissipates on the outer edge of this shelf, allowing a more protected zone.
Discussion:
There is a clearly identifiable channel of navigable waters in the Croatan Sound into
Canals A and B that was found to be void of SAV. The project as proposed does not
include any boat traffic in areas of SAV. And, there is no proposed dredging outside of
the confines of the existing channels in Canals A and B extending into Croatan Sound
(this existing channels will be involved with routine maintenance dredging for safe
navigation). However, channel markers should be posted at the mouth of the canals,
especially Canal A, to clearly demarcate the navigable channel in order to protect the
limited SAV resource that was detected on July 9, 2007.
5

Wdh submission of this document, Quible requests any documentation from the
resource/permitting agencies that relates to historic SAV presence in this area. Please
feel free to contact Brian Rubino if you have any questions regarding this SAV survey.
You can reach me at [phone] at Quible ~ Associates, P.C.
Respectfully Submitted,
Quible 8 Associates, P.C.
Brian Rubino, P.G.
6

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ENSR k~COM
Prepared tor:
Skyco Development, LLC
Roanoke Nsland, North Carolina
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Hydrodynamic Modeling Evaluation of
the Proposed Skyco Development
Project
Manteo, North Carolina
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ENSR Corporation
August 2007
Document No.: 12121-001.2

ENSR
Prepared for:
Skyco Development, LLC
Roanoke Island, North Carolina
Hydrodynamic Modeling Evaluation of
the Proposed Skyco Development
Project
Manteo, North Carolina
Prepared By
Reviewed By "'
ENSR Corporation
August 2007
Document No.: 12121-001.2
a~y~s~ zoos

ENSR
Contents
1.0 Introduction .............................................................................................................................................1-1
1.1 Modeling Objectives ........................................................................................................................1-1
1.2 Conceptual Approach ............................................................:.........................................................1-1
2.0 .Hydrodynamic Model Development .....................................................................................................2-1
2.1 Model Input Parameters ..................................................................................................................2-1
2.1.1 Skyco Development Bathymetry ....................................................................................... 2-2
2.1.2 Pirates Cove Bathymetry ................................................................................................... 2-2
2.1.3 Tidal Boundary Conditions ................................................................................................2-2
2.1.4 Wind Speed and Direction .................................................................................................2-2
2.1.5 Eddy Viscosity ....................................................................................................................2-2
2.2 Water Quality ...................................................................................................,...............................2-3
3.0 Hydrodynamic Modeling Results .........................................................................................................3-1
3.1 Skyco Development Site ................................................................................................................. 3-1
3.2 Pirates Cove Site ............................................................................................................................. 3-2
4.0 Summary and Conclusions .....................................................:.............................................................4-1
5.0 References ..............................................................................................................................................5-1
August 2007

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List of Tables
ENSR
Table 1 Monthly and Seasonal Summary of Wind Speed and Direction of Cape Hatteras (NOAA,1995)
List of Figures
Figure 1 Existing/Proposed Channels
Figure 2 Skyco Bathymetric Data Points
Figure 3 Pirates Cove Channels and Bathymetric Data
Figure 4 Average Tidal Water Level Used in Modeling
Figure 5 Skyco Canal A and B Predicted 1-Day Concentrations
Figure 6 Skyco Canal A and B Predicted 4 -Day Concentrations
Figure 7 Skyco Canal A and B Predicted 7 -Day Concentrations
Figure 8 Skyco Canal A and B Predicted 10 -Day Concentrations
Figure 9 Skyco Canal A Predicted 1-Day Concentrations
Figure 10 Skyco Canal A Predicted 4 -Day Concentrations
Figure 11 Skyco Canal A Predic#ed 7 -Day Concentrations
Figure 12 Skyco Canal A Predicted 10 -Day Concentrations
Figure 13 Pirates Cove Predicted 7-Day Concentrations
Figure 14 Pirates Cove Predicted 2-Week Concentrations
Figure 15 Pirates Cove Predicted 3-Week Concentrations
Figure 16 Pirates Cove Predicted 1 Month Concentrations
iv
August 2007

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1.0 Introduction
Skyco Development, LLC proposes to construct a residential development at a coastal site (the Site) in the
village of Skyco on the west side of Roanoke Island, North Carolina. The proposed project includes
development of 50 residential units and creation of a new canal around the residential area that will connect to
Croatan Sound via two existing canals. The locations of the proposed new canal (to be constructed in existing
upland areas) and the existing canals are shown in Figure 1. The canal system is proposed to be
interconnected to provide a navigable waterway between the newly constructed residential development and
Croatan Sound. An additional goal of the canal system design is to provide enhanced flushing of the system
to maintain acceptable water quality throughout the canals and the waterway along the residences.
1.1 Modeling Objectives
The primary objective of this modeling investigation was to develop atwo-dimensional hydrodynamic model
that could be used to evaluate the effectiveness of the canal system in providing flushing and dilution within
the canals to maintain water quality. Additional hydrodynamic modeling was performed at an existing site with
' a comparable canal system (and thus similar hydrodynamics) to provide a comparative tool for the evaluation
of the proposed project at the Skyco Site. This second site was selected based on proximity to the Skyco Site,
similarity of canal systems, and availability of exis#ing data demonstrating good water quality.
' I A roach
1.2 Conceptua pp
' The objectives of this hydrodynamic modeling investigation were met by evaluating site information, proposed
canal system configuration, and local and regional hydrologic, hydrodynamic, and climatic data. These data
were used to develop the mathematical model of the Site's hydrodynamics. Evaluation of water quality was
' estimated qualitatively with the hydrodynamic model through the simulation of a conservative tracer. The
tracer, as applied in the model, was used as a proxy to evaluate the circulation and flushing dynamics of the
canal system for the proposed conditions and bathymetry.
A second site was simulated with the same hydrodynamic model to serve as a tool for comparing the results of
the proposed Skyco Site with an existing residential development and canal system. The Pirates Cove si#e in
' Manteo, North Carolina was used for this second model. The Pirates Cove site was assumed to be an
acceptable comparable site given the proximity to the Skyco site and thus similar hydrodynamic, climatic, and
' tidal forcings; long canals with both straight and winding configurations; and acceptable water quality
conditions.

1-1 August 2007

' EN R
S
' mi Model Develo ment
2.0 Hydrodyna c p
' The two-dimensional hydrodynamic and water quality. modeling system, TABS, developed by the United
States Army Engineers Waterways Experiment Station in Vicksburg, Mississippi, was selected and applied to
the proposed Skyco and Pirates Cove sites. The TABS modeling system is afree-surface, depth-averaged,
finite element program capable of performing steady state and transient solutions. The TABS system contains
two components, a hydrodynamic component, RMA-2 (USAGE, 2005), and a water quality component, RMA-4
(USAGE, 2003). In addition to simulating the hydrodynamics of the proposed Skyco Development on the west
side of Roanoke Island, the models were used to simulate the hydrodynamics of the existing Pirates Cove
development on the east side of the island. The Pirates Cove simulations were used to qualitatively ascertain
' the level of confidence implied by the model of the proposed Site.
The TABS modeling system was deemed to be the appropriate modeling tool for this application since it
provides simulation of:
• Complex hydrodynamics of the Skyco Development channels,
• Highly dynamic flow field, and
• Nature and extent of flushing and circulation using a conservative tracer.
The hydrodynamic component, RMA-2, computed water surface elevations and flow velocities at nodal points
in a finite element mesh representing the water body. The water quality component, RMA-4, simulated the
transport of constituents on the mesh and velocity field generated by RMA-2. Because available data
indicated the potential of significant difference in wind speed and direction during the warmer and cooler
months of the year (presumably because of the relative differences between land and ocean water
temperatures), model simulations were also performed for conditions representative of seasonal wind patterns
' to evaluate the effects of these differences on the overall model results.
2.1 Model Input Parameters
The hydrodynamic investigation was conducted using bathymetric data for both the proposed Skyco
' Development site and the existing Pirates Cove site, and tidal and wind data obtained for Roanoke Island.
Hydrodynamic and water quality simulations were developed fora 28-day period to correspond to a complete
lunar tidal cycle in order to capture the long term effects of tidal exchange on canal flushing. The wind speeds
and directions applied to the hydrodynamic model were representative of summertime conditions. During this
' period, water quality concerns would reasonably be expec#ed to have the grea#est potential impact on water
quality conditions in the canals due to increased loading rates, potential for stratification, and the dominant
wind direction blowing up into the canals.

' 2-~ August 2007

ENSR
2.1.1 Skyco Development Bathymetry
Bathymetric information used for this investigation included both direct measurements of channel bathymetry
as well as design bathymetric information for the proposed channels (Figure 2). The outline of the existing
channels for the proposed Skyco Development was derived from aerial photographs of the area and the
design information was used to describe the outlines of the proposed channels. Bottom elevations in the
central parts of the existing channels are approximately -7.0 feet based on normal water level (NWL)
conditions. Channel depths shallowed to approximately -3.0 feet to -4.O feet (NWL) near the edges of the
channels. The existing channels generally become shallower from their mouths in Croatan Sound inland to
the proposed development. The proposed channels were assumed to be -5.0 feet (NWL) throughout, based
on development plans. The measured and proposed channel bathymetry for the proposed development was
contoured to describe the channel geometry in the RMA-2 model.
2.1.2 Pirates Cove Bathymetry
Recently collected bathymetric measurements for the Pirates Cove canal system indicated little variability,
generally showing a consistent bottom elevation of approximately -6.0 feet (NWL) (Figure 3). Based on this
overall consistency, the bathymetry for the Pirates Cove system was simplified and a bottom elevation of -6.0
feet was applied to describe the channel geometry in the RMA-2 model of Pirates Cove.
2.1.3 Tidal Boundary Conditions
Tidal information for the hydrodynamic models was derived from predicted water levels for a site in the vicinity
of the Skyco project site at the Oregon Inlet Marina, NC (National Oceanic and Atmospheric Administration
(NOAA) Station ID: ORIN7-8652587). A representative average 28-day tidal cycle was generated using
predicted tide calculations for this NOAA site from mid-May 2005 through mid-May 2006 (Figure 4).
Using the NOAA-derived predicted tide calculations, the tidal range for the Site is approximately 0.4 feet during
the spring tide portion of the tidal cycle. Tidal range during the neap tide portion of the tidal cycle is less than
0.2 feet. ThE:,e data correlate well with local estimates of tidal range in Croatan Sound.
' 2.1.4 Wind S eed and Direction
p
Wind information for both the Skyco Development and Pirates Cove models was obtained from NOAA
historical climatological data (NOAA, 1995) for a nearby site at Cape Hatteras, NC. The average wintertime
and summertime wind speeds and directions were incorporated in#o the RMA-2 model in an effort to increase
the accuracy of the model predictions of water movement during different periods of the year when wind
patterns were significantly different (Table 1).
' 2.1.5 Ed:iq ~ iscosity
.The eddy viscosity term in the RMA-2 hydrodynamic model accounts for small and large scale mixing. The
eddy viscosity for both the Skyco Development and Pirates Cove models was fixed at the mid-range of values
recommended in the RMA-2 model documentation for a slow moving river system. This assumption was
considered justifiable based on the conceptual understanding of the flow dynamics through the existing and
' 2-2 August 2007

' ENSR
proposed canal systems and the corresponding relationships of eddy viscosity as modeled in the RMA-2
computer model
' 2.2 Water Quali
The primary input parameters to the RMA-4 water quality model are the concentration of the conservative
tracer and the diffusion coefficient. The initial concentration of conservative tracer in both the Skyco
Development model and the Pirates Cove models was fixed at 100 parts per million {ppm) everywhere and the
-tidal boundary concentrations were fixed at zero. By using an arbitrary concentration of 100 ppm,
concentrations throughout the simulation may be most simply interpreted as representing a direct percentage
of the initial concentration remaining in the canal systems without making any corrections or data
transformations. Thus, the model results are most directly translated for visualization and overall evaluation.
Since the constituent being modeled was assumed to be conservative, no decay is simulated and therefore
the only decrease in the predicted concentration of the conservative tracer occurs as a result of transport out
of the model through the tidal boundary outlet.
The diffusion coefficient was fixed at the mid-range of values recommended in the RMA-2 model
documentation for a slow moving river system. Consistent with the assumption applied for the eddy viscosity
model parameter, this assumption was considered justifiable based on the conceptual understanding of the
system and the diffusion relationships as modeled in the RMA-2 computer model

2-3 Auyusc zoos

ENSR
~ 3.0 Hydrodynamic Modeling Results
The RMA-2 hydrodynamic model and the RMA-4 water quality model were used to simulate water depths,
velocities, and conservative tracer concentrations in both the proposed Skyco Development and existing
' Pirates Cove systems. Two different canal configurations were evaluated:
1. Canal A and Canal B connected to the proposed canal, with a 700-foot shortening of the western
extent of the proposed canal
2. Canal A, only, connected to the proposed canal, with a 700-foot shortening of the western extent of
the proposed canal
The Skyco Development model was used to predict the degree of flushing for the proposed system and the
Pirates Cove model was used as a qualitative comparative tool to evaluate the results of the Skyco
Development model. Simulations for each system were run to depict the 28-day lunar tidal cycle. Model
results were calculated on an hourly basis throughout the time period. Model results for the proposed Skyco
Development project are presented in Figures 5 though 8 at 7 days, 2 weeks, 3 weeks, and 4 weeks,
respectively. Model results for the existing Pirates Cove are presented in Figures 9 though 12 at similar
intervals. Note that the concentration units shown in the legend for each of these figures represent percentage
of exchange, or flushing, based on a unit concentration of a simulated conservative constituent.
' 3.1 Sk co Development Site
Y
Average summertime wind conditions were used to simulate the effect of the wind forcing component on tidal
exchange and residence time in the canal system. These conditions were assumed to be representative of
practical worst case conditions since the predominant wind direction in this scenario is into the canal system.
This orientation creates conditions that would allow for a consistent "piling up" of water along the existing
canals and toward the proposed canal (see Table 1). Tidal forcings in the model varied between
approximately 0.2 and 0.4 feet across the ebb and neap tide cycles, respectively; using the annually averaged
tidal data as described above in Section 2.1.3.
The bathymetry, wind conditions, and tidally varying water elevation boundary were identical for each modeled
' configuration. For each configuration, the modeling results for the dilution of the theoretical constituent,
described above, were compared with one another to illustrate the direct effect of canal layout and design on
the flushing characteristics within the canal system.
The results of the Skyco Development simulations indicate a moderate rate of exchange of water between the
existing canals and proposal canal as well as between the existing canals and Croatan Sound. The model
results indicate a slightly lower rate of exchange from the proposed canal with the existing canals. The
attenuation in water exchange rates in the proposed canal is attributed to the increased distance from Croatan
Sound and thus the direct tidal forcings that drive the physical mechanism for exchange.
The average tidal prism in a tidally driven system is equivalent to the difference between the average high tide
water volume and the average low tide water volume. This value, expressed as a percentage of the average
high tide volume, gives an indication of the average level of tidal exchange that takes place. The predicted
average tidal prism in the proposed Skyco Development for the Canal A and Canal B configuration is 51,100
' ft3, which is 4.0 percent of the predicted maximum volume in the system during high #ide. With two #idal cycles
3-1 August 2007

ENSR
per day, approximately 8 percent of the water in the system is exchanged with water from the harbor on a daily
basis under summertime average wind conditions. The predicted average tidal prism for the Canal A, only,
configuration, is 44,700 ft3, which is 4.1 percent of the predicted maximum volume in the system during high
tide.
The model predictions for the Canal A and Canal B configuration of the proposed Skyco Development indicate
that after 24 hours the tidal exchange of water with the canal system would reduce the initial concentration of
the tracer to 93 percent at the northeastern extent of the proposed canal (Figure 5). By the end of 4 days of
' simulation the maximum concentration was reduced to 41 percent of the initial concentration (Figure 6); by 7
days to 17 percent (Figure 7); and by 10 days to a maximum of only 7 percent (Figure 8). Flushing generally
occurs most rapidly through Canal A and more slowly through Canal B. These flushing dynamics are
attributed to the channel's orientation, which is directly along the axis of the summertime wind vector.
However, by the end of two weeks the mixing and exchange offered by the existing channels is sufficient to
substantially reduce initial concentrations throughout the system. These results indicate that the residence
time for the proposed canal, under the modeled conditions, is approximately two weeks, as the water flushes
through the canals and exchanges with the water in Croatan Sound.
The model predictions for the Canal A, only, configuration of the proposed Skyco Development indicate that
after 24 hours the tidal exchange of water with the canal system would reduce the initial concentration of the
tracer to 99.5 percent at the northeastern extent of the proposed canal (Figure 9). By the end of 4 days of
' simulation the maximum concentration was reduced to 87 percent of the initial concentration (Figure 10); by 7
days to 67 percent (Figure 11); and by 10 days to a maximum of only 51 percent (Figure 12). These results
indicate that the residence time for the proposed canal, under the modeled conditions, is greater than four
' weeks, as the water flushes through the canals and exchanges with the water in Croatan Sound. At the end of
four weeks, the maximum .predicted concentration in the northeastern extent of the proposed canal is 10
~ percent of the initial concentration.
While only the results for summertime wind conditions are presented, simulations were also run without any
wind and with wintertime wind conditions. Summertime winds are predominantly from the southwest and
wintertime winds are predominantly from the northeast. The most significant difference between the
simulations is that the extent of dilution per tidal cycle is slightly less during summertime conditions as wind
blows toward the end of the channels, diminishing the mixing of water at the tidal boundary with water in the
interior of the channel.
3.2 Pirates Cove Site
Average wintertime wind conditions were used to simulate the effect of the wind forcing component on tidal
exchange and residence time for the Pirates Cove model. These conditions were assumed to be
representative of practical worst case conditions since the predominant wind direction in this scenario is into
the canal system. By using these wind conditions, the Pirates Cove model may be more directly compared
with the Skyco summertime wind condition. The ::~i.^.d forcing in each of the two models is toward the
orientation of the canals and thus each model simulates the potential effect of "piling up" of water along the
canals. Tidal forcings for the Pirates Cove model were the same as those used for the Skyco model, varying
between approximately 0.2 and 0.4 feet across the ebb and neap tide cycles, respectively, using the annually
averaged tidal data as described above in Section 2.1.3.

3-2 A~9~51200~

ENSR
The results from the Pirates Cove model simulations indicate that water flushes through the canals and
exchanges with water from the harbor at similar and even slightly higher rates as those calculated for the
proposed Skyco development. The predicted average tidal prism in the existing Pirates Cove development
canal system is 204,000 ft3, which is 3.4 percent of the predicted maximum volume in the system during high
tide. This indicates that, on average, 3.4 percent of the water in the system is exchange with water from the
' harbor during each tide cycle, or roughly 7% exchange per day.
Model predictions of the Pirates Cove indicated that after 7 days the tidal exchange of water with the canal
' system would reduce the initial concentration of the tracer by 80 to 90 percent in Canal A (Figure 13). These
maximum concentrations in this channel are predicted to decrease to 50 to 60 percent after two weeks (Figure
14); to 35 to 50 percent after three weeks (Figure 15); and to 25 to 35 percent after four weeks (Figure 16).
Dilution along Canal B was simulated to be complete by the end of four weeks, indicating complete exchange
between the canal and the open water; thus the residence time for this canal is less than four weeks. Flushing
through Canal C, as depicted in the model results, was lower, with up to 45% of the initial water remaining in
the canal after four weeks (Figure 16). The decreased flushing rate in this segment of the system is attributed
to the small tidal forcing from the open water and the orientation of this canal in the interior of the development.
While only the results for wintertime wind conditions are illustrated, simulations were also run without any wind
and with summertime wind conditions; summertime winds are from the southwest and wintertime winds are
from the northeast. The primary difference between the three simulations is that dilutions are slightly greater
' during summertime conditions as wind blows away from the end of the channels, effectively acting in favor of
the mixing of water at the tidal boundary with water in the interior of the model domain. Model resul#s indicated
that this mixing effect was insignificant, overall, between the winter and summer wind simulations.
3-3 August 2007

ENSR
4.0 Summary and Conclusions
. The RMA-2 model predicted tidal prism for the proposed Skyco Development configurations indicates that
there is tidal mixing and dilution in the canal system during each tidal cycle. For the Canal A and Canal B
' configuration, the predicted rate of exchange is sufficient to dilute the system to less than 2% of the original
water at the end of two weeks based on summertime average wind conditions. These model results are
indicative or likely practical worst case conditions, with low tidal forcing (0.2 to 0.4 foot tidal range) and wind
' forcing in the direction of the canal system, creating a "pile up" of water that further inhibits tidal exchange
through the canal system. The model results indicate similar conditions for the existing Pirates Cove
development, in which the average model-predicted tidal prism provides an average tidal exchange of 3.4
percent during each tidal cycle for wind conditions blowing predominantly into the canal system. Under these
model conditions and assumptions, the Pirates Cove model results indicated an average water exchange of 7
percent daily.
The Skyco model results indicate that the residence time of water for the proposed project is less than four
weeks, as dilution will occur throughout the average lunar tidal cycle. This continual exchange is predicted to
occur, even during summertime wind conditions when mixing conditions are lowest as a result of canal
orientation and wind forcings along the canals and in from Croatan Sound. Model simulations with wind
forcings in the opposite direction, in which the wind would predominantly blow along the canals outward toward
Croatan Sound, exhibited shorter residence times than for summer conditions.
A second hydrodynamic model was created to evaluate flushing dynamics in the Pirates Cove canal system.
The Pirates Cove system has a comparatively similar canal system. The two systems also experience similar
wind forcing effects, albeit in opposite seasons than the proposed Skyco site, due to the locations on the
opposite sides of Roanoke Island and opposing orientations. The existing Pirates Cove development has not
experienced historic water quality problems. Therefore, it was assumed for this investigation that similar
model results for flushing and hydrodynamics of the two sites would indicate that similar dilution, flushing, and
water quality at the proposed Skyco site.
The model results for the two sites indicate similar extents of flushing rates and residence times. Modeled tidal
exchange rates are similar for the two sites. Given these results, and the similarity in external hydrodynamic,
tidal, and wind forcings at the two sites and the similarly complex canal geometries, it is reasonable to assume
that water quality conditions would be similar for the two sites. Therefore, the proposed canal system
configuration at Skyco development site should provide adequate flushing and dilution potential to maintain
water quality in the overall canal system at the site. The three existing canals have sufficient physical
connectivity across the length of the proposed canal to provide pathways for dilution and mixing to occur in the
proposed canal.
4-1 August zoos

1
1
1
1
1
1

1
1
1
1
5.0 References
ENSR
NOAA, 1995. Climatic Average and Extremes for U.S. Cities. June 1995. Historical Climatology Series 6-3.
Editors: R.G. Quayle, R.S. Cram, and M.G. Burgin. U.S. Department of Commerce. NOAA, National Climatic
Data Center, Asheville, NC.
USACE, 2005. RMA2 WES Version 4.5. US Army, Engineer Research and Development Center, Waterways
Experiment Station, Coastal and Hydraulics Laboratory. 277 pages.
USACE, 2003. RMA4 WES Version 4.5. US Army, Engineer Research and Development Center, Waterways
Experiment Station, Coastal and Hydraulics. Laboratory. 173 pages.
5-1
August 2007

1

1
Tables

1
1
1
ENSR ' `rt6~~~~~~".
August 2007
1

Table 1.
' Monthly and Seasonal Summary of Wind Speed and Direction of Cape Hatteras (NOAA,
1995)

1
1
Month Wind S eed m h Wind Direction
Janua 12 NNE
Februa 12.2 NNE
March 11.9 SW
April 11.7 SW
Ma 10.8 SW
June 10.6 SSW
Jul 10 SW
Au ust 9.6 SW
Se tember 10.5 NE
October 11.2 NNE
November 11 NNE
December 11.5 NNE
Annual Avera a 11.1 NNE
Summertime Mar-Au 10.8 SW
Wintertime (Sept-Feb) 11.4 NNE
1

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Au tst 200 Job No. 12121-001 www.ensr.aecom.com
August 2007

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Hydrodynamic Modeling Roanoke Island, NC
Au ust 2007 Job No. 12121-001 www•ensr.aecom.com
August 2007

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Hydrodynamic Modeling Roanoke Island, NC
www.ensr.aecom.com
Au ust 2007 Job No. 12121-001
August 2007

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August 2007

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August 2007 Job No. 12121.001 www,ensr.aecom.com
August 2007

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Hydrodynamic Modeling
August 2007 Job No. 12121-001 WWW.ensr.aeCOm.com
August 2007

ENSR
Skyco Canal A and B
Skyco Development, LLC Predicted 10-Day Figure s
Concentrations
Skyco Development Skyco Development
Hydrodynamic Modeling
August 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
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- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
august 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
Skyco Canal A Predicted
r Skyco Development, LLC 4-Day Concentrations Figure 10
Pirates Cove Development
- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
August 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
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~ Skyco Development, LLC 7-Day Concentrations Figure 11
Pirates Cove Development
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Hydrodynamic Modeling
August 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
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Skyco Canal A Predicted
Skyco Development, LLC 10-Day Concentrations Figure 12
Pirates Cove Development
6-- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
August 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
Concentration (mgl/L)
95.0
85.0
75.0
65.0
55.0
45.0
35.0
25.0
15.0
- 5.0
Pirates Cove Predicted
Skyco Development, LLC 7-Day Concentrations Figure 13
Pirates Cove Development
-- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
august 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007

ENSR
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Concentration
95.0
85.0
75.0
65.0
55.0
Pirates Cove Predicted
Skyco Development, LLC 2-Week Concentrations Figure 14
Pirates Cove Development
-- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
AUg~st 2007 Job No. 12121-001 www,ensr.aecom.com
August 2007

ENSR
Concentration (mg/L)
95.0
85.0
75.0
65.0
55.0
Pirates Cove Predicted
Skyco Development, LLC 3-Week Concentrations Figure 15
Pirates Cove Development
- Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
August 2007 Job No. 12121-001 vvww.ensr.aecom.com
August 2007

ENSR
S
(mg/L)
Pirates Cove Predicted
Skyco Development, LLC 1 Month Concentrations Figure 16
Pirates Cove Development
Skyco Development Roanoke Island, NC
Hydrodynamic Modeling
August 2007 Job No. 12121-001 www.ensr.aecom.com
August 2007