Potential Development of Estuarine Islands-1988

POTENTIAL DEVELOPMENT
OF
ESTUARINE ISLANDS
IN
NEW HANOVER COUNTY
-NEW HANOVER COUNTY PLANNING DEPARTMENT
MAY 1988
THE PRPARATION OF THIS DOCL'NENT WAS FI\ANCFD. IN PART,'I'HROI:GH A COASTAL. AREA NIANAGI:-
NIENT AC ! GRA\ T PROVIDED BY THE NORTH CAROLINA COASTAL MANAGE)IENTPROGRA.M, THROUGH
FUNDS FROVIDED BYTHE COASTAL ZONE `1ANAGEMENT ACT OF 1972, AS AN[ENDED,WHICH IS ADMINI-
STERED 3Y THE OITICE OF OCEAN AND COASTAL RESOu RCE NIANAGE.V111NT, NATIONAL OCEANIC AND
AT>IOS?: T-RIC ADNIINISTRATION.

POTENTIAL DEVELOPMENT OF ESTUARINE ISLANDS
IN NEW HANOVER COUNTY
INTRODUCTION
I. THE ISSUES
New Hanover County has numerous islands in its rivers and
sounds. These islands, which are presently undeveloped, may
encounter significat development pressure in the future as
waterfront property becomes more scarce and valuable.
Development of these islands, however, may result in increased
water pollution from runoff and from septic tanks. -Development
of these islands also may impact the aesthetics of the County's
waters, disrupt colonial bird nesting sites, and create
difficulties- for evacuation during hurricanes. Questions have
risen concerning the . potential of developing these islands.
These questions include:
Is the use of these islands for the disposal of materials
dredged from the County's waterways, primarily by the U.S.
Corps of Engineers, compatible with possible development?
Would residents of these islands be adequately protected
from hurricane and other dangers?
This study, - funded by a Coastal Area Management Act Grant,
examines these -questions and makes several recommendations.
II. INVENTORY OF ESTUARINE ISLANDS
A. Definition
Estuarine islands are defined, for purposes of this study,
as those masses of land with an area greater than one acre above
mean high water that are separate from the mainland. Barrier
islands, however, are not included in this study because they
either are already developed and connected to the mainland by
bridge or are under protection by the State as part of the
Estuarine Sanctuary Reserve Program. In -addition, the barrier
islands were examined as part of the study "Hurricane Protection
Plan - A Vulnerability Analysis of Barrier Islands in New Hanover
County", published ir: 1983 by the County Planning Department.
B. Classification
. Estuarine islands, for purposes of this study, can be
classified as occurring either in the AIWW (Atlantic Intracoastal
Water Way) and its associated sounds and creeks, or in. the
County's rivers. The islands can also be classified as being
naturally formed or cf man-made origins.

C. AIW14 Islands
AIW'W islands are composed of dredged spoil islands and, to a
lesser extent, of natural islands.
i. Dredged Spoil Islands
a. Physical Characteristics
AIWW islands are overwhelmingly composed of.spoil islands
created by the U.S. Corps of Engineers for the disposal of
dredged materials during -the construction and on -going
maintenance of the AIWW. The AIWW initially was dredged out
approximately fifty years ago. Maintenance dredging of the AIWW
occurs at variable frequencies, ranging from annual dredging in
inlet areas to essentially no dredging needed in certain areas
between inlets.
The Corps acquired a perpetual 1,000 foot wide easement for
disposal of initial construction of the AiW7W. The disposal of
dredged materials has created approximately fifty circular
islands ranging in height up to 20-30 feet. In certain areas
these islands are so close as to have merged into one long island
with several circular plateaus or are separated by only a narrow
band of water or wetland vegetation. These islands appear to
exhibit erosion and slumping due to such causes as boat wakes and
the natural instability of the dredged materials. The total area
of these islands is approximately 454 acres, based on examination
of 1986 (1" = 4001) aerial photographs. These islands are
inventoried in Exhibit 1.
For the most part, these islands are contained within the
Corps' easements, which basically precludes their use for
anything but disposal. Of the 454 acres, 161 acres or 35% are
located outside the easement boundaries. In addition, much of
these 161 acres consist of narrow slices of islands that
otherwise lie mainly within the easement.
Vegetation associated with -the islands ranges from Spartina•
alterniflora (smooth cordgrass) below mean high water to
established woody species such as Myrica cerifera (wax myrtle)
and Juniperus virginiana (red cedar) on the higher islands. A
number of the islands represent significant nesting habitat for
colonial waterbirds.
b. Development limits
The development potential appears to be fairly limited. As
noted above, most of the island acreage lies within the Corps
easement and is restricted from development. In addition, those
parts of the islands outside- the easement would be severely
impacted by any dredged material disposal activities on the parts
of the islands within the easement. Disposal activities
generally require construction of a large dike thatwould be
Q

disrupting to development. More importantly, disposal severely
disrupts the groundwater of ,the entire island by the raising of
the water table with an infiltration of saltwater from the
dredged materials. This impact would disrupt. wells and septic
systems. Development of these islands would also be limited by
local regulations. These include the requirement of a 75 ft.
setback from the mean high water line by the County Zoning
Ordinance (Sec. 59.4-5). In addition, the Wilmington
Hanover County'Land Use Plan includes a policy.that states:
"1.2(2) Development of estuarine system islands shall be
permitted only i= proper measures are taken for hurricane
evacuation, utilities provision, access on and off the
island, pollution: control, and other design considerations
that will insure compatibility of the development with the
estuarine systems."
Although this policy presently is not entirely implemented
by local regulations, the issuance of certain permits, primarily
Coastal Area Management Act (LAMA) permits, must be consistent
with it.
It should be noted that the Corps may be willing to trade
lands with persons interested in developing a dredged spoil
island, so long as the Corps will benefit from the land swap in
terms of improving its dredged disposal program. .This
possibility has been rarely pursued anywhere and is probably
unlikely in New Hanover County, due to the lack of mainland or
island sites. suitable for trade to the Corps that meet
environmental constrai:its, and that are not presently surrounded
by development that would be impacted by groundwater disruption.
One possible use of the islands, however, could be for
marinas. Considering the fairly. stringent State regulations
regarding the location: of marinas, a high spoil island adjacent
to the AIW'W may present an environmentally attractive
alternative. Minimal dredging, if any, would likely be required
and natural tidal flushing of the marina waters would likely be
adequate.
One major drawback to residential development .of these
islands would be the difficulties encountered in their evacuation
in case.of a hurricane. The time required for evacuation would
be significantly extended because the first step would be
evacuation by boat .which would be hampered by the adverse water
conditions that often precede a hurricane long before the severe
winds and flooding of a hurricane are felt. In addition,
adequate docking facilities and parking would be required on the
mainland. It should be noted that the County has adopted a
stringent policy (1.1(2)) in its .Land -Use Plan that eliminates
the use of barrier islands for residential development if the
island does not have an adequate evacuation network of roads and
bridges. The County h-as also adopted subdivision regulations for.
barrier islands requiring establishment of parking and community

boating facilities on the mainland sufficient to serve
subdivisions on the islands [Sec. 41-1(11)1."
The Corps presently is performing a study with a fifty-year
planning horizon for the dredging program in the AIWW. Although
it has not been completed, it likely will conclude that the Corps
will not relinquish its control of the spoil islands and may even
be forced to examine such alternatives as pumping sand from the
AIWW to the beaches and combining spoil islands into larger
islands to increase disposal capacity.
2. Natural islands - Natural estuarine islands are considerably
more limited for development tnan are .the dredged spoil islands.
These islands tend to be formed during periods of increased wave
swash and are associated with inlets. These conditions allow for
sand to be deposited over marshes in the shape of narrow berms.
(Cleary et al, 1979).
These islands in New Hanover County are generally quite low,
around one foot in height and no higher than three feet. In
addition, these islands appear to .be sinking, due to both sea
level rise and compaction of the organic layer covered over by
the sand deposition. These islands are considered to have
generally insignificant development potential because of these
factors. It is interesting to note, however, that Harbor Island
in Wrightsville Beach may, have originally been one of these
islands and then expanded by fill.
D. Riverine Islands
The islands of the Cape Fear River have been characterized
by the disposal -of spoil by the Corps for the maintenance of the
navigation channel. The few remaining natural islands appear to
be the result of meanders in the Rivers. These natural islands
tend to be fairly small and low. These islands, which tend to be
dominated by wetland vegetation, are unsuitable for development.
The spoil islands in the Cape Fear River are higher than the
natural islands in the River due to disposal of dredged
materials; however, they share many of the physical
characteristics possessed by the previously discussed AIWW
islands. They tend to be circular in shape and up to 25 feet in
height, depending upon the amount of spoil deposited and the
height of the dike. The vegetation is also similar, ranging from
salt marsh species to woody species. The Rivers contain
approximately twenty islands for a total of 199 acres of high
ground and/or associated marsh. Certain of these islands,
however, appear to be located in Brunswick County rather than New
Hanover County. All of these islands with high ground are the
property of the State of North or the U.S. Government Generally
for use as spoil disposal.
The Corps of Engineers will be completing in 1988 a draft
Environmental Impact Statement on its maintenance plan'for the
4

next fifty years for the Wilmington Harbor and navigation
channel. If current practices were to continue,. approximately
500 acres of estuarine bottoms in the River would be filled by
expansion of the spoil islands in the next fifty years. One
alternative being examined includes.' disposal on the mainland,
which is probably not feasible, due to increasing development and
groundwater restrictions. Another alternative includes disposal
of the dredged materials as part of a beach renourishment program
when suitable material is found, or perhaps disposal in the
ocean.
The apparent continued importance of the riverine islands to
the Harbor and channel maintenance program and particularly the
fee simple ownership of the islands by the State and Federal
governments appear to preclude possible development of these
islands. The Corps, for instance, has rejected a proposal by a
developer who wished to purchase and construct a bridge over to
one island in the River for purpose of residential development.
It should also be noted that residential development of these
islands would be impacted by the lack of an adequate road and
bridge evacuation network as similarly discussed for AIWW
islands.
III. CONCLUSIONS
The estuarine islands of New Hanover County likely will
remain undeveloped, at least for residential purposes, due to
existing regulatory and ownership constraints. This likelihood
is desirable considering the potential impacts that could be
suffered by development in these islands. The following
recommendation, however, could be implemented to control
development:
A. A memorandum of understanding would be signed by the U_.S.
Corps of Engineers and New Hanover County .as shown in
Exhibit 2.
1. The Corps will continue to keep the County informed of
its dredging and disposal activities.
2. The Corps will not allow any land swaps involving spoil
islands or otherwise relinquish any control over the
islands without informing the County and allowing the
County an opportunity for review and comment.
3. The County will continue to utilize regulations and
Land Use Plan policies that preclude any development
that may interfere with the Corps dredging program.
A draft letter is attached as Exhibit 2.
B. The Subdivision regulations that require adequate community
boating and parking facilities on the mainland for barrier
5

islands [Sec. 41-1(11)1 could be
estuarine islands.
expanded to include
0

ACKNOWLEDGMENT
The help of Barry Holiday, Phil Payank, Frank Yelverton, and
others from the Wilmington, NC regional office of the U.S. Corps
of Engineers is gratefully appreciated. The assistance provided.
by Dr: William Cleary of UNC-W was also of considerable help.
REFERENCES
Cleary, W.J., P.E. Hosier, and G. R. Wells, 1979
"Genesis and Significance of Marsh Islands within
Southeastern North Carolina Lagoons", Journal of
Sedimentary Petrology, 49(3): 703-710
7

EXHIBIT I
INVENTORY OF ISLANDS
AIWW-ISLANDS
(Tax Map No.
(Tax Map No.
Island No.)
Acreage
Island No.)
Acreage
37-1
1.8
-5
2.5
-2
3.0
.77-1
3.0
-3
15
-2
28.9
-4
3.6
-3
7.5
-5
4
-4
5.0
38-1
18
-5
5.5
-2
2.5
-6
5.4
-3
2.6
79-1
15.5
-4
2.6
-2
30.7
45-1
2.5
80-1
6.0
-2
9.0
-2
9.0
-5
5.0
-3
5.8
-6
1.2
82-1
6.0
-7
1.4
-2
5.8
-8
7.5
-3
6:0
-9
4.2
-4
1.0
-10
7.5
-5
1.2
52-1
49
-6
1.4
-2
30
-7
4.8
67-1
8
-2
44
TOTAL
454.4
-3
33
68-1
10
72-1
18
-2
16.5
-3
1
-4
2.5
RIVERINE ISLANDS
(Tax Map No.
(Tax Map No.
Island No.)
acreage
Island No.)
Acreage
24-1
6.4
84-1
4
69-1
82.6
89-1
2.7
-2
6.6
-2
17
-3
3.5
91-1
2.5
75-1
43.6
-2
2.8
-2
"
6.3
93-1
2.5
78-1
2.0
-2
12.0
TOTAL
199.0
81-1
1
_7
1
-3
2.5
*Aerial photos referencing each
island are on file in
the County
Planning Department.

r
1\
EXHIBIT 2
DRAFT
MEMORANDUM OF UNDERSTANDING
DATE:
SUBJECT: Use of Estuarine Spoil Islands
FROM: G. Felix Cooper, New Hanover County Manager
Colonel Paul Woodbury, Wilmington District Engineer,
U.S.C.O.E
The following provisions of this Memorandum of Understanding
shall assist in the governing of uses of dredge spoil islands
within the. jurisdiction of New Hanover County.and the U.S. Army
Corps of Engineers:
1. The Corps shall notify the County of its dredging and
spoil disposal activities.within the County;
2. The Corps shall not allow any land swaps involving spoil
islands or otherwise relinquish any control over the islands
within the County' without allowing the County adequate
opportunity for review and comment.
3. The Countv shall maintain and implement regulations and
Land -Use Plan policies that preclude any development that
may interfere with the Corps' dredging program.
W