US Army Corps
f Engineers

NTO S

National Oceanic
and Atmospheric
Administration

ws Lie he Ted Rep. CURE 89 ~ |
TECHNICAL REPORT CERC-83-1

SHORELINE MOVEMENTS

Report 1
CAPE HENRY, VIRGINIA, TO
CAPE HATTERAS, NORTH CAROLINA, 1849-1980
by
Craig H. Everts

Coastal Engineering Research Center
U. S. Army Engineer Waterways Experiment Station
P. O. Box 631, Vicksburg, Miss. 39180

and
Jeter P. Battley, Jr., and Peter N. Gibson

National Ocean Service
National Oceanic and Atmospheric Administration
U. S. Department of Commerce
6001 Executive Blvd., Rockville, Md. 20852

WHO!

DOCUMENT
COLLECTION

July 1983
Report 1 of a Series

Approved For Public Release; Distribution Unlimited

Prepared for Office, Chief of Engineers, U. S. Army
Washington, D. C. 20314

and National Oceanic and Atmospheric Administration
Rockville, Md. 20852

Destroy this report when no longer needed. Do not return
it to the originator.

The findings in this report are not to be construed as an official
Department of the Army position unless so designated.
by other authorized documents.

The contents of this report are not to be used for

advertising, publication, or promotional purposes.

Citation of trade names does not constitute an

official endorsement or approval of the use of
such commercial products.

MBL/WHOI

OLOMOUC

0 0301 0090105 4

Unclassified

SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)
READ INSTRUCTIONS
1. REPORT NUMBER 2. GOVT ACCESSION NO, 3. RECIPIENT'S CATALOG NUMBER
Technical Report CERC-83-1

4. TITLE (and Subtitle) 5. TYPE OF REPORT & PERIOD COVERED
SHORELINE MOVEMENTS; Report 1: CAPE HENRY, Report 1 of a series
VIRGINIA, TO CAPE HATTERAS, NORTH CAROLINA,

1849-1980

6. PERFORMING ORG. REPORT NUMBER

7. AUTHOR(s) 8. CONTRACT OR GRANT NUMBER(s)

Craig H. Everts
Jeter P. Battley, Jr.

Peter N. Gibson
9. PERFORMING ORGANIZATION NAME AND ADDRESS

U. S. Army Engineer Waterways Experiment Station
Coastal Engineering Research Center

P. 0. Box 631, Vicksburg, Miss. 39180 and

U. S. Department of Commerce

National Oceanic and Atmospheric Administration
National Ocean Service

6001 Executive Blvd., Rockville, Md.

10. PROGRAM ELEMENT, PROJECT, TASK
AREA & WORK UNIT NUMBERS

12. REPORT DATE

July 1983

13. NUMBER OF PAGES
113

15. SECURITY CLASS. (of thie report)

20852

- CONTROLLING OFFICE NAME AND ADDRESS

W

Office, Chief of Engineers, U. S. Army
Washington, D. C. 20314
National Oceanic and Atmospheric Administration
6001 Executive Blvd., Rockville, Md. 20852

14. MONITORING AGENCY NAME & ADDRESS(if different from Controlling Office)

Unclassified

1Sa. DECLASSIFICATION/ DOWNGRADING

SCHEDULE

16. DISTRIBUTION STATEMENT (of this Report)
Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (of the abstract entered in Block 20, if different from Report)

18. SUPPLEMENTARY NOTES

Available from National Technical Information Service, 5285 Port Royal Road,
Springfield, Va. 22161.

19. KEY WORDS (Continue on reverse side if necessary and identify by block number)

Atlantic coast
Beach erosion
Coastal morphology
Shorelines

20. ABSTRACT (Continue en reverse side if necessary and identify by block number)
Shoreline position changes between about 1850 and 1980 along the ocean

coastal reach from 12 km west of Cape Henry, Virginia, to 8 km west of Cape
Hatteras, North Carolina, are documented in this report. In places where the
ocean shoreline is on an island or spit, shoreline changes in the sound or bay
are also given. Shoreline movement maps at a scale of 1:24,000 constitute the
basic data set included in the report. Composite reproductions of these maps

are shrinkwrapped separately. In addition, ocean and sound shoreline changes
(Continued)

FORM
DD , jan 73 1473 EDITION oF 1 Nov 65 1S OBSOLETE

SECURITY CLASSIFICATION OF THIS PASE (When Data Entered)

Unclassified
SECURITY CLASSIFICATION OF THIS PAGE(When Data Entered)

20. ABSTRACT (Continued).

averaged for 1-minute-latitude- (or longitude-) distance increments are pro-
vided.

Consistent alongshore trends in the shoreline change rate are evident
only from Virginia Beach south to the Virginia-North Carolina border and for
about 15 km north of Cape Hatteras. Other areas experienced variable rates of
shoreline change. The highest average shoreline change rate, about -2.0 m/year,
occurred between 1917 and 1949. From about 1850 to 1917, the shoreline change
rate averaged -0.1 m/year, and for the past 30 years it has averaged about
-0.8 m/year.

Unclassified
SECURITY CLASSIFICATION OF TH!IS PAGE(When Data Entered)

PREFACE

This report is the result of a cooperative effort of the National Ocean
Service (NOS), National Oceanic and Atmospheric Administration, U. S. Depart-
ment of Commerce, and the Coastal Engineering Research Center (CERC) of the
U. S. Army Engineer Waterways Experiment Station (WES). The study, based on a
comparison of historic survey data contained in the archives of NOS, was
funded jointly by the Office, Chief of Engineers, and the National Oceanic and
Atmospheric Administration. All survey data reduction and quality control
were performed by NOS; data analyses and report preparation were accomplished
primarily by CERC.

The report was prepared by Dr. Craig H. Everts, CERC, and
Messrs. Jeter P. Battley, Jr., and Peter N. Gibson, NOS. The work was car-
ried out under the general supervision of Mr. N. E. Parker, Chief, Engineer-
ing Development Division, CERC; Mr. R. P. Savage, Chief, Research Division,
CERC; and Dr. R. W. Whalin, Chief, CERC. At CERC, Mr. Edward Hands developed
a computer program to analyze shoreline change data and Mr. Jon Berg reduced
the data. The section on historic inlets was researched by Ms. Marie Ferland,
CERC. Reviewers included Drs. Robert Byrne and Robert Dolan and
Messrs. William Birkmeier, Edward Hands, Thomas Jarrett, James Melchor,

Neill Parker, and S. Jeffress Williams.
Commander and Director of WES during the publication of this report was

COL Tilford C. Creel, CE. Technical Director was Mr. F. R. Brown.

CONTENTS

PREFACE .
LIST OF TABLES
LIST OF FIGURES .

CONVERSION FACTORS, INCH-POUND TO METRIC (sD
UNITS OF MEASUREMENT. :

INTRODUCTION .

PART II: STUDY AREA.

Geographical Setting
Historic Inlets .
Inlet location 5s
Accuracy of inlet location.
Continental Shelf .
Tides, Winds, and Waves .
Tides and other sea evel Aimeeoatsens.
Wind conditions .
Waves .
Coastal Storms.
Coastal Structures

PART III: DATA REDUCTION .

Data Sources.
Shoreline Deminntstont

Methods Used to Revise the 1980 Mean High | Water Line

Data Reduction Procedures .
Quality Control and Potential BEROES

PART IV: DATA ANALYSIS AND DISCUSSION

Analysis Methodology.

Shoreline Change Rates
Listing of shoreline chenee aa 2e8 :
Ocean shoreline change rates.
Sound shoreline change rates.
Oregon Inlet.
Cape Hatteras and Gane ‘Wena.

Variation in shoreline change rates ofa time 6

Changes in island width and position

PART V: PREDICTION OF FUTURE SHORELINE CHANGES .

Temporal Predictions

Spatial Predictions . , ‘ :
Barrier island miesenezom and aninantine
Alongshore sediment transport reversal.
Sound shoreline change.
Inlets and shore erosion
Capes and shoreline change.

Shoreface-connected ridges and anomelane: chanee :

Page
DARE WIC. SUMAN ANID). (COMMGIQUSIUOMS 6 6 os 6 6 o 6 6 & © GS 6 6 6 6 6 6 106
REERRENGCES), 32a se chs tars dete Ae Meet ee hae een yy eee ah, 109

NOAA/NOS shoreline movement maps, 1852-1980, are shrink-
wrapped as a separate enclosure to this report.

No.

Mm fF WwW HN &

Oo Co N OD

10

11

12

LIST OF TABLES

References to Maps and Charts Used to Establish Historic
Inlet Locations . SOMES SoMa Oe KoNIenE OL “c Reeth Sut

History of Rudee Inlet, Virginia .

Coastal Structures, Cape Henry to Cape Hatteras.

Historic Shoreline Surveys, Cape Henry to
Cape Hatteras, 1847-1980. Soto hse

Ocean Shoreline Changes in Virginia West of Cape Henry .
Ocean Shoreline Changes in Virginia South of Cape Henry.

Ocean Shoreline Changes in North Carolina North of
Cape Hatteras .

Ocean Shoreline Changes West of Cape Hatteras.
Sound Shoreline Changes, Cape Henry to Cape Hatteras .
Pamlico Sound Shoreline Changes West of Cape Hatteras.
Summary of Mean Shoreline Changes, Oceanside .
Summary of Mean Shoreline Changes, Soundside .

Combined Ocean- and Soundside Shoreline Changes.
LIST OF FIGURES

Location map .

Cape Hatteras viewed toward the northwest

Frontal dune along the Atlantic Ocean side of Hatteras Island.

Jockey's Ridge at Nags Head, N. C., rises almost 50 m

Sand dunes encroaching on cottages and a forest at Kill
Devil Hills, N. C.

Pea Island, N. C., viewed south across Oregon Inlet
Relic beach ridges at Cape Henry, Va.

View north across Oregon Inlet .

Locations of persistent inlets reported open on maps and charts

between Cape Hatteras and Cape Henry from 1585 to 1980

Inlet channel, possible related to the now-closed Trinity Harbor
Inlet, in Currituck Sound west of the CERC field research

facility

Barrier Island width versus duration of time inlets were open

after 1585 between Cape Hatteras and Cape Henry .

Probable site of a large pre-1585 inlet at Kitty Hawk, N. C.

Page

18
20
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Continental shell profiles taken between Virginia Beach, Va.,
and Hatteras Island, N. C., to 30 km from shore .

Tide ranges, Cape Henry to Cape Hatteras .

Tide frequencies for ocean shoreline at Kitty Hawk, N. C., for
several classes of storms: (a) landfalling, (b) alongshore,
(c) inland, (d) exiting hurricanes, (e) winter storms,

(£) all storms

Surface wind roses, Cape Henry and vicinity, from data
collected 1850-1960 . ;

Surface wind roses, Cape Hatteras and vicinity, from
data collected 1850-1960

Annual cumulative significant wave height distribution based
on 20 years of hindcast data measured at 10-m water depth
off Kitty Hawk, N. C.

Wave rose diagram showing the significant wave height and direc-
tion of wave propagation for combined 20-year hindcast data in

10-m water depth at station 81 off Kitty Hawk, N. C.

Yearly storm surge return period for extratropical storms at
Hampton Roads, Va.

Number of tropical cyclones reaching the North Carolina
coast, by sector, for the period 1886-1970

Recreational Pier at Virginia Beach, Va., a typical fishing
pier for the study area . 6 Bh

View toward north of groins near Cape Hatteras Lighthouse
Weir jetty system at Rudee Inlet, Virginia Beach, Va.

U. S. Geological Survey 1:24,000 haa sincaaiies used as base
maps in the study . 6 RE pe

Digitization procedure for correcting shoreline position loca-
tion when original shoreline movement map distortions exist .

Definition sketch illustrating parameters used to obtain
shoreline change rates for a north-south-trending ocean
shoreline .

Ocean shoreline change rates from near Cape Henry to Cape
Hatteras, from about 1850 to 1980 . Aare tas

Standard deviation of ocean shoreline position changes between
Cape Henry and Cape Hatteras

Average ocean shoreline change rates for the 36-km-long reach
south of Cape Henry in the periods 1859-1925 and 1925-1980

Average ocean shoreline change rates for two survey periods in
the reach between Duck, N. C., and Cape Hatteras :

Page

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38)

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Average ocean shoreline change rates at Virginia Beach for four
successive surveys between 1925 and 1980: (a) 1925-1942(44),

(b) 1942'(44)=1962) (ec) Pl962 10 BON ay sep eee nan LOS
Extreme ocean shoreline excursions from about 1850 to 1980,
Cay Niaiiay TO CANS HENERERAS 66 6 6 6 6 6 6 6 0 6 ooo 70

Sound shoreline change rates for the reach between Back Bay, Va.,
Evaval 72 Jam Wrasie oie (Ceyoea ENCES 675 o 6 6 5 o 0 6 6 oO 0 6 6 6.0 Oo 72

Standard deviation of sound shoreline position changes between
Cape Henry and Cape Hatteras .........5.....:.~- 13

Average sound shoreline change rates, for the periods from about
1850 to 1915 and from about 1915 to 1980, between Poa Head

and'\Caper Hattexa's|,0N Com rus ecuese pine : : Such Ge:
Changes in ocean and sound shorelines adjacent to Oregon Inlet,

N. C., for five surveys between 1852 and 1980 .......... 715
Migration rates of Oregon Inlet throat for five survey intervals
between? 1849)"and) 1980!" DS. DSN.Lolneg So) Gis aaa Re a OT EE a6
Relative locations and orientations of the narrowest section

Oe Teary Opeeyaorn Ila tearonies MVNO) 6 5 5 6 66 5,60 6 ooo ol)
Plan view changes in land area in the vicinity of Oregon Inlet,

1 feel Coestromeaal eo /42)-n WS) 10S te aie CR ee GU silo e Nan h Go ami Vo 77
Changes in mean high-water shoreline at Cape Point, Cape

Hatteras ibetweent 1852) amcdigl9S Ome sien ent -f tintin) ere -IIn 719
Relative plan area of the subaerial projection for Cape

Hatteras eles 2=10808S 77 vat SER, FOO, Beet aae, ERE tenn eet eee. Peer 80
Location of Cape Hatteras point between 1852 and 1980 ...... 80
Changes in mean high-water shoreline at Cape Henry between

T8525 arid’ OBO) eR ES ace BEE cal ee ace Mean hel re eA me ato 81
Shoreline change rates, averaged by survey period, for east-

facing ocean shorelines and west-facing sound shorelines ... . 83
Shoreline change rates, averaged by survey period, for west-

facing ocean and sound shorelines ........+.-+.-++-++.+:+4.-. 83
Island width changes between about 1850 and 1980, from Pe

Henry to west of Cape Hatteras ...... : : MAH. ABN
Island width change rates, 1852-1917 and 1917-1980, between

Kitty Hawk and Cape Hatteras, N. C. ..... , : ORAS 488
Rates of position change of island axis between about 1850 to

1980, Cape Henry to west of Cape Hatteras .......-+.:+--.- 89

Rates of position change of island axis, 1852-1917 and
1917-1980, between Kitty Hawk and Cape Hatteras, N. C. ..... 90

Relationship of apparent ocean shoreline change to Capes,
_shoreface-connected ridges, and Oregon Inlet ......+..-.-. 94

No.

52

53

54

55

Ocean shoreline changes from about 1850 to 1980, Cape Henry
to Cape Hatteras, as a function of island width in 1980 .

Sound shoreline changes from about 1850 to 1980, Cape Henry to
Cape Hatteras, as a function of island width in 1980

Bathymetry seaward of the ocean shore between Cape Henry and
Cape Hatteras .

Shoreline orientation referenced to true north between Cape
Henry and Cape Hatteras .

Page
98
99

104

105

CONVERSION FACTORS, INCH-POUND TO METRIC (SI)
UNITS OF MEASUREMENT

Inch-pound units of measurement used in this report can be converted to metric

(SI) units as follows:

Multiply By To Obtain
cubic yards 0.7645549 cubic meters
feet 0.3048 meters
inches 0.0254 meters
knots (international) 0.514444 meters per second
miles (U. S. statute) 1.609347 kilometers
miles per hour 1.609347 kilometers per hour

SHORELINE MOVEMENTS

Report 1

CAPE HENRY, VIRGINIA, TO CAPE HATTERAS, NORTH CAROLINA, 1849-1980

PART I: INTRODUCTION

1. This report describes results of a cooperative National Oceanic and
Atmospheric Administration (NOAA), National Ocean Service (NOS), and U. S.
Army Engineer Waterways Experiment Station, Coastal Engineering Research
Center (CERC), study of shoreline changes. The study area comprises the ocean
coast south from Cape Henry, Virginia, to west of Cape Hatteras, North Caro-
lina, and the sound-side coast of the barrier islands between each of the
Capes (Figure 1). Changes in shoreline position from 1852 to 1980 are treated
using survey data from NOS and its predecessor, the U. S. Coast and Geodetic
Survey (C&GS). (NOAA/NOS-CERC shoreline movement maps, 1852-1980, are in-
cluded as a separate enclosure to this report.)

2. Shoreline changes of a quantifiable nature are presented covering
what is probably the longest period of historic survey record of the area
available. Although maps exist dating back to 1585 (Cumming 1966), prior to
1849 the position of the shoreline was not located with sufficient accuracy to
allow a comparison of that feature on different maps. The early maps, however,
do provide a valuable reference for locating inlets that were open during the
past 400 years. Langfelder et al. (1970), in a study of coastal erosion in
North Carolina, used aerial photographs dating from 1945, for which measure-
ments were made at approximately 300-m intervals along the beach. Dolan
et al. (1979) also using aerial photographs but measuring at 100-m intervals,
established erosion rates in Virginia, North Carolina, and elsewhere, based
upon data spanning 30 years or more for over half the area and over 15 years
for the whole area. Dolan et al. (1979, p 603) note their total measurement
error as potentially as much as +25 m for rate-of-change calculations. The
frequency of the aerial survey was much greater than that of shoreline surveys
used in this study, but the total aerial study duration was less than 25 per-
cent that of this study. This longer data span (130 years) allows a more

extended analysis of temporal variations in shoreline change rates.

LONGITUDE

eS 76 07
5 {= —————
wo | 2 z
37°00 + CHESAPEAKE + Se 75°59
Bay i LATITUDE
CAPE HENRY 36°55
VIRGINIA BEACH 50°
RUDEE INLET
>
Zn -N 36 45
= i
2
3) 40
ro)
35
NORTH CAROLINA ‘
3630 + a
25:
COROLLA
S 20
ro)
S
36 15°
zm
10°
KITTY HAWK 05°
CROATAN SHORES
(KILL DEVIL HILLS) 36=00'

NAGS HEAD

BODIE |S.

OREGON INLET

35°45
PEA IS.
40
RODANTHE 35°
WAVES
SALVO
35°30!
25°
AVON 50!
BUXTON 6 1S

CAPE HATTERAS

HATTERAS INLET————___ LO NeTUeE
OCRACOKE |S. Kaien andaie Wad

75°36"
OCRACOKE

RT + + INLET +

Figure 1. Location map (the study area shoreline is shown as

a heavy line; data are not available where the heavy line is

dashed. The northwest boundary of the study area is 12 km

west of Cape Henry at the Chesapeake Bay entrance; the south-
west boundary is 8 km west of Cape Hatteras)

10

3. This report provides a long-term basic data set for use in manage-
ment and engineering decisions related to the coastal zone. In the absence of
other data, past shoreline changes usually provide the best available basis
for predicting future changes. An extrapolation of past changes is not with-
out risk, though. Man's actions may have affected the natural coastal change
processes and thereby altered the rates of change. Probably more importantly,
the material processes themselves may have altered over time thereby varying
the shoreline change rate; Hayden (1975), for example, has identified rela-
tively large changes in storm-wave climate in this century at Cape Hatteras.

4. Historic shoreline change data are direct, believable, and explicit
and can be updated as new data become available. Shoreline changes obtained
from historic charts for a specific time period also are invariant. Past
shoreline changes based on NOS surveys can be supported in a court of law.

5. Coastal engineers use past shoreline changes in the design of proj-
ects for shoreline stabilization, flood prevention as a result of storm surges,
and maintenance of navigable depths in coastal waterways. A knowledge of past
changes in shoreline position is a useful and often necessary basis from which
to predict the effects of natural processes and proposed modifications on the
coastal zone.

6. This is an empirical report. It serves to explain and enhance the
shoreline change maps which go with it. Since it is sometimes difficult to
determine trends from maps alone, average changes have been calculated for
each minute of latitude (north-south-trending shoreline) and longitude (east-
west-trending shoreline). Relationships are established between the shoreline
change rates and (a) shore orientation, (b) location of capes, (c) proximity
to present inlets and inlets that were historically open, (d) shore-connected
ridges, and (e) an alongshore sediment transport nodal reach. A brief de-
scription of wind, wave, tide, and sedimentological parameters in the study
area is provided in Part II for readers interested in those factors; however,
because their records are insufficiently detailed or too short with respect to

shoreline changes, these parameters are not used further in this report.

11

PART II: STUDY AREA

Geographical Setting

7. The study area encompasses 210 km of Atlantic Ocean barrier island
coast. It begins in the north 12 km west of Cape Henry, Virginia, and extends
south to 8 km west of Cape Hatteras, North Carolina (Figure 1). A bay and
four sounds back the barrier islands along the southern 175 km of ocean shore.
These include Back Bay, Currituck Sound, Albermarle Sound, Roanoke Sound, and
Pamlico Sound. Presently, only Oregon Inlet connects a sound and the ocean
in the study area. Rudee Inlet provides ocean access from a small lake near
Virginia Beach.

8. Currituck Banks now extends south from Back Bay, Virginia, to
Oregon Inlet, North Carolina. A past segment of the Banks from the vicinity
of Kitty Hawk, North Carolina, to Oregon Inlet is still called Bodie Island.
Beyond Oregon Inlet, the barrier is known as Pea Island about as far south as
Rodanthe, North Carolina, and as Hatteras Island from Rodanthe to Hatteras
Inlet, North Carolina; the boundary between the two lies at the site of now-
closed New Inlet. Hatteras Island is sharply angled to the southwest at Cape
Hatteras. The Cape is one of the most conspicuous cuspate headlands along the
Atlantic Coast (Figure 2).

9. The barrier islands vary in width from 0.5 to almost 5 km. A
frontal dune backs most of the barrier beach (Figure 3). Dunes west of the
frontal dune, most notably Jockey's Ridge, North Carolina (Figure 4), also are
found along some sections. Hennigar (1979) found these dunes to be moving to
the southwest at Kill Devil Hills, North Carolina (Figure 5), and elsewhere.
In most locations, aeolian, overwash, and relict flood-tidal delta flats ex-
tend from the dunes to the sound (Figure 6). Relic beach ridges exist in the
flats area at Kitty Hawk, west of Cape Hatteras, and at Cape Henry (Figure 7).

10. Sand size varies in an alongshore direction, across the beach and
from season to season. From the Virginia-North Carolina line to Cape Hatteras,
the median foreshore sand size is 0.44 mm, with a slight average increase from
north to south (Shideler 1973). Within this area, the beach from between
Corolla and Duck to Kitty Hawk, North Carolina, is composed of anomalously
large, iron-stained quartz and feldspar sand in the 1-mm-diameter range.

Beach sand north of the States boundary is finer. Average dune sand size in

12

Figure 2. Cape Hatteras viewed toward the northwest (the Atlantic
Ocean is in the foreground; Pamlico Sound is in the background)

‘

Figure 3. Frontal dune along the Atlantic Ocean side of
Hatteras Island between Salvo and Avon, N. C.

13

Figure 4. Jockey's Ridge at Nags Head, N. C., rises almost 50 m (the
Atlantic Ocean shore is in the foreground; Albemarle Sound is in the
background) (Hennigar 1979)

Figure 5. Sand dune encroaching on cottages and a forest at Kill Devil
Hills, N. C. (dune movement is to the southwest; i.e., toward the left
background of the photograph)

14

Figure 6. Pea Island, N. C., viewed south across Oregon Inlet (overwash

and flood-tide delta flats comprise most of the western two-thirds of

the island; the Atlantic Ocean is at the left; Pamlico Sound is at the
right of this photograph)

Figure 7. Relic beach ridges at Cape Henry, Va. (these ridges formed in
the past as the cape built north and eastward; Virginia Beach is at the
foreground)

US

the study area is 0.27 mm and does not vary from north to south.

Historic Inlets

11. Inlets have played and continue to play an important role in shore-
line evolution in the study area. At present only two inlets, Rudee and
Oregon, are open; in the past as many as seven have been open simultaneously.
The inlets act as traps for littoral sediments which move into the lagoons
from adjacent ocean beaches and in this way contribute to ocean shoreline re-
treat. The sound shoreline is often moved toward the mainland by sand accre-
tion in flood-tidal deposits behind the islands and adjacent to open inlets
(Figure 8). Closed inlet locations are frequently distinguishable by a bulge
in the sound shoreline.

Inlet location

12. Figure 9 shows the extent of inlets reported open since 1585 on

Figure 8. View north across Oregon Inlet (most of the

large shoreline lobes and islands in Pamlico Sound at

the left are relic flood-tidal shoals and other inlet

features created as Oregon Inlet migrated south; the

sound shoreline, therefore, moved west as the inlet
trapped beach sand)

16

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Table 1
References to Maps and Charts Used to Establish

Historic Inlet Location (Figure 9)

Reference

Number

(Fig. 9) Date Author Secondary Reference
1 1585 White Cumming (1966)
2 1590 White-DeBry Cumming (1966)
3 1606 Mercator-Flordius Cumming (1966)
4 1657. Comberford Cumming (1966)
5 1672 Ogilby-Moxon Cumming (1966)
6 1733 Moseley Cumming (1966)
7 yO Colikete Cumming (1966)
8 1775 Mouzon Cumming (1966)
9 1808 Price-Strother Cumming (1966)
10 1833 MacRae-Brazier Cumming (1966)
11 1852 NOAA/NOS-CERC shoreline change maps*
12 1859 NOAA/NOS-CERC shoreline change maps
13%* 1861 Bachman Cumming (1966)
14%% 1861 Colton Cumming (1966)
15 1865 U. S. Coast Survey Cumming (1966)
16 1882 Kerr-Cain Cumming (1966)
17*“* 1896 Post Route Map . Cumming (1966)
18 1917 NOAA/NOS-CERC shoreline change maps
19 1949 NOAA/NOS-CERC shoreline change maps
20 1962 NOAA/NOS-CERC shoreline change maps
al 1975 NOAA/NOS-CERC shoreline change maps
22 1980 NOAA/NOS-CERC shoreline change maps

* Published as a separate inclusion to this report.

** Maps not discussed in Fisher (1962).

18

the maps and charts of the times found in Cumming (1966), on NOAA/NOS-CERC
shoreline change maps dating from 1852, or, in the case of Caffeys Inlet, ac-
cording to data collected by Fisher (1962). The following inlets warrant
specific comment on their locations as shown in Figure 9.

13. Rudee Inlet. The inlet shown at approximately 36°48' in several of
the very early maps (1585, 1590, and 1606) was located by position in relation
to geomorphic features rather than by latitude, since latitude was less ac-
curate for location purposes prior to the late 1700's. The inlet was possibly
open in 1682 (Cumming 1966, figure on p 14); however, on a copy of a 1682 map
"Rudee" was written next to a lake which has the same general configuration of
Rudee Lake today. A history of Rudee Inlet after 1927 is given in Table 2.

14. "Back Bay" Inlet at latitude 36°33'-34' (1590, 1606). On the
original maps, this inlet did not open into a large sound or bay but instead
appeared as a small indentation in the coastline. Comparing geomorphological
features and the mainland shoreline shows that this inlet sequence actually
existed just south of Back Bay, opposite Knotts Island. It was most likely
the precursor to Old Currituck Inlet which was shown in later years as having
closed at approximately this location (1833, 1861 (Colton), 1865, 1882); the
1882 map states that Old Currituck Inlet closed in 1775.

15. Caffeys Inlet at latitude 36°915'. Early mention of this inlet in
a report by the North Carolina Fisheries Commission Board (1923, p 33) shows
that the inlet was open for a short time between 1780 and 1800. The location
can be deduced from the text to be south of Currituck Inlet, but no map was
included in the report.

16. Dunbar (1958, p 218) placed the inlet at approximately 36°13',
calling it Carthys Inlet and showing it open from at least 1798 to 1811. He
concluded that the inlet opened at the site of Trinity(e) Harbor (1585-?) and
that the same location was later called South Inlet (1808, 1833, 1861), though
the inlet had actually closed by that time.

17. Fisher (1962, p 90) shows Caffeys Inlet to be north of the town of
Duck at 36°15' and open from 1770 to 1811, maximum. He bases this location
on the existence of a large, relict, flood-tidal delta feature which he felt
was a more likely site than the relatively narrow segment of the island at
36°13' where the Caffeys Inlet Coast Guard Station is now located. Fisher's
location is shown in Figure 9.

18. The Price-Strother map of 1808 shows an unnamed inlet at 36°11’,

19

Date
pre-1927
1927

1933
ISS

1952

1953
1954-1962

1962
1962-present

1968

1975
1975
1979-spring

1980-spring

Table 2

History of Rudee Inlet, Virginia (from U. S. Arm
Engineer District, Norfolk (1982))

Event
Shallow drainage ditch that opened and closed frequently

Virginia Highway Department constructed a concrete culvert and
built a highway over it

Hurricane destroyed both the culvert and the highway

Inlet open but less than 18 in. deep (and meandering to some
degree)

Virginia Beach Erosion Commission organized

Virginia Beach Erosion Commission constructed two short jet-
ties on either side of the inlet and a sheet pile wall on
north side

A fixed dredge was installed on the end of the south jetty to
bypass sand

"Ash Wednesday" storm destroyed the bypassing plant

Small dredges have operated periodically with limited suc-
cess. Several commercial dredging operations have also
been completed to +6 ft* mean low water (mlw) project depth

Existing jetties were extended north, by 560 ft, and south, by
280 ft, in addition to a 477-ft-long timber weir. Also, a
100,000-cu yd sand trap was dredged to -16 ft

Waterways Experiment Station (WES) installed a test jet-pump
bypassing system

Virginia Beach purchased the system from WES. This system was
operating through 1982

A commercial dredge opened the filled sand trap and removed
approximately 100,000 cu yd of material

A commercial dredge opened the sand trap and removed approxi-
mately 100,000 cu yd of material

* A table for converting the inch-pound units of measure in this report to
metric (SI) units is found on page 8.

20

but placement by geomorphic features corresponding to current maps indicates
that the latitude is actually 36°14'-15'. This is most likely the inlet known
as Carthys and Caffeys (and perhaps South in 1861 maps).

19. South Inlet at latitude 36°16'-18'. Dunbar (1958, p 138) makes two
references to South Inlet (1830, 1833); he states that the inlet had actually

closed by the referenced time and was "

...probably an example of cartographic
perpetuation of a feature no longer in existence." He gives no reason for the
change in name from Caffeys to South Inlet, though he considers them to be at
the same location.

20. South Inlet appears at approximately 36°16'-17' on the 1861 maps
that Cumming (1966) considered during his study. It is probably not signifi-
cant that South Inlet appears on the Bachman map because the map is inaccurate.
Colton also shows South Inlet on his 1861 map, but it is quite possible that
all inlets on his map should be shifted to the north by approximately 5' of
latitude; if South Inlet were shifted northward, it could be considered part
of the Currituck Inlet system found between 36°26'-27' at that time. South
Inlet is shown in Figure 9, but it may not represent a single event at that
location.

21. Trinity Harbor Inlet at latitude 36°12'. Dunbar (1958, p 216)
placed Trinity Harbor (1585-?) at approximately 36°13' and regarded it as the
precursor to Carthys Inlet, now the site of Caffeys Inlet Coast Guard Station,
which was open from at least 1798 to 1811. Interestingly, Dunbar's location
of Caffeys Inlet is 1'-2' south of the large flood-tidal delta sequence at a
harrow section of the barrier beach mentioned in paragraph 17.

22. Fisher (1962, p 110) discussed the location of Trinity Harbor and
concluded that Dunbar's assumption of its location was incorrect because it
would be unusual for an inlet to open on the site of an earlier inlet. He
goes on to say that Trinity Harbor was most likely located further to the
north at 36°17' where there is a relict inlet feature (presently called
Beasley Bay).

23. The White-DeBry map of 1590 (Figure 9) shows Trinity Harbor to be
north of the wide Kitty Hawk/Southern Shores feature, directly east of a small
embayment and just south of an unnamed inlet with associated islands. Close
examination of this 1590 map and comparison with current maps suggests that a
location of 36°11'-12' is more accurate; Fisher's placement to the north by

almost 5' of latitude seems to be based almost entirely on the relict inlet

21

feature. In addition to the 1590 and 1606 maps, strong evidence for the
existence of Trinity Harbor Inlet at the more southerly location includes:

a. A channel of 5- to 7-ft depths (where adjacent water depths are
2-3 ft on the average) in Currituck Sound (Figure 10).

b. Inlet/channel fill sediments recorded (Field 1973) from cores
taken when the CERC Field Research Facility was constructed.

c. A slight westward bulge in the Currituck Sound shoreline which
could be the remnant of a reworked flood-tidal delta.

24. 1657 Comberford map. This map depicts two large unnamed inlets
open in the stretch of coast between Currituck Sound and present-day Oregon
Inlet. The two inlets extend for the equivalent of at least 5' and 2', re-
spectively, of latitude fronting Roanoke Island for most of its length; this
is probably a distortion, since earlier and later maps showed much narrower
inlets. Placement of both of these class B inlets in Figure 9 (possibly
Roanoke and Gunt) at the midpoint of the location listed on the 1657 map is
subjective.

25. Kitty Hawk Bay region at latitude 36°00' to 36°15'. Three distinc-
tive features suggest a prehistoric inlet in this region:

a. A wide "field" of long beach ridges (Figure 11), recurving and
ending abruptly to the south at Kitty Hawk Bay, which could
have been formed during the migration of an inlet.

b. Kitty Hawk Bay itself and the narrow section of the barrier
island which separates the bay from the Atlantic Ocean.

|o

Collington Island, a large feature composed of both sandy
areas and salt marsh, which closely resembles a relict flood-
tidal delta.

Early maps (1585, 1590, and 1606, to name the earliest) delineate this multi-
ple feature quite clearly. Therefore, depositional processes that formed the
feature were active before 1585, and the area has (approximately) maintained
its present configuration through historic time.

26. Chacandepeco Inlet at latitude 35°16'-17'. In 1923, the North
Carolina Fisheries Commission Board (1923, p 17) suggested that an inlet be
opened 3 miles north of the Hatteras Lighthouse to increase the fishing poten-
tial of Pamilco Sound. This was considered to be an optimum location for an
inlet because of (a) the existence of "Cape Channel," a deep channel in
Pamlico Sound; (b) the narrowness of the island; and (c) the distance from
another major inlet. Previous existence of an inlet, however, was not

mentioned.

De.

LATITUDE

36°14' 7

36°12’ og 88
JARVISBURG

COASTAL
ENGINEERING
RESEARCH
CENTER

FIELD RESEARCH
FACILITY

36°10’

36°08’

36°06"

Figure 10. Inlet channel, possibly related the now-closed Trinity
Harbor Inlet, in Currituck Sound west of the CERC Field Research
Facility (contour lines show depth in feet)

23

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27. Dunbar (1958, p 217) stated that the inlet was open from 1585 to
1687 and called Chacandepeco by the Indians. He also noted that, although
the inlet was shown on Comberford's 1657 map, it could have been copied from
earlier maps and not actually open at that time.

28. Fisher (1962, p 92-93) concluded that an inlet was open from pre-
1585 to 1672 at 36°16.5'; his conclusion was based largely on the presence of
Cape Channel and the island's low and narrow profile in 1961. He showed that
this inlet was recorded as open on 11 maps between 1585 and 1657. On four of
those maps (1585, 1590, 1606, 1657), which were analyzed in this study, how-
ever, evidence of an open inlet was lacking. During the 1962 (Ash Wednesday)
storm, an ephemeral inlet was opened at this site; because of the conflicting
evidence it was not included in Figure 9 as a persistent inlet.

Accuracy of inlet location

29. Use of past and present inlets in an attempt to develop a relation-
ship between inlets and shoreline change requires that historic, and if pos-
sible, prehistoric inlets be identified and accurately located. NOS shoreline
maps were used to compare inlet locations after 1852 with those on maps used
in Cumming's (1966) report. The locations of inlets on the NOS maps are con-
sidered accurate.

30. In Figure 9, the two positions listed for Oregon Inlet in 1861
(Bachman and Colton in Cumming 1966) are included to show the possible varia-
tion due to (a) cartographic mislocation of the inlets or (b) mislocation dur-
ing the original survey work. The Bachman map is entitled "Panarama [sic] of
the Seat of War, Birds Eye View of North and South Carolina, a part of
Georgia." It is an oblique map, very schematically drawn, lacking latitude
and longitude coordinates, and the location and existence (or nonexistence)
of particular inlets on it should be viewed with caution. The Colton map of
the same year is more accurately drawn, though its description emphasized the
railroad and overland transportation routes and no discussion of the coastline
is included. There is an obvious lack of correlation between the general
trend of Oregon Inlet's present position and the 1861 positions; however, if
the entire sequence of inlets shown on the Colton Map (i.e., Oregon, New, un-
named, and Loggerhead) are shifted to the north by 3'-5' of latitude, this
dramatic offset is eliminated. This seems to be a more reasonable solution
than keeping the inlets in their 1861-mapped position and assuming a "zig-zag"

migration pattern.

25

31. Navigation accuracy increased through time. Evidence of this grow-
ing sophistication in positioning tools and techniques can be seen in the
noticeable decrease in the width of the inlet sequences. Prior to the 19th
century, New Currituck, Roanoke, and Chickinacommock Inlet sequences are all
at least 5' of latitude wide, while the sequences of Oregon (assuming that
the offset of 1861 is a distortion), New, and New/Loggerhead Inlets are all
approximately 3' of latitude wide. With time, more accurate measurements re-
sulted is less lateral variation in the map position of inlets. Inlet loca-
tions on maps other than those produced by NOS are potentially inaccurate by
up to +5 minutes of latitude (i.e., the approximate amount by which early
measurement methods could vary and still produce a map with the general con-
figuration of the existing shoreline). This reasoning could help to explain
the dramatic change in location of Roanoke Inlet between 1657 and 1770 shown
in Figure 9.

32. Another explanation for the variation over time of inlet locations
is north or south inlet migration. The NOS maps show, for example, that
Oregon Inlet has migrated south over the past 130 years, at the rate of 29 m/
year, for almost 2 minutes of latitude. If the migration sweep of other
inlets falls within the same range, an inlet remaining open for 100 years or
so could move +2 minutes in latitude.

33. A large shoreline bulge into the sound is often a good geomorphic
clue to the presence of an inlet which was open in the past. Currituck Inlet
is clearly related to a wide section of the island (Figure 11). Musketo
Inlet, however appears to be located several minutes north of a large island
bulge (Figure 9); quite likely, the bulge is the site of historic Musketo
Inlet. The very large width change from Kitty Hawk to Nags Head is likely re-
lated to prehistoric Kitty Hawk Inlet (Figure 12). Roanoke Inlet, shown as
having varied widely in an alongshore distance (Figure 9), is centered at a
shoreline bulge; possibly more than one inlet existed in this reach. An
island bulge is also associated with the sites of the now-closed New and

Loggerhead Inlets shown on NOS shoreline maps (Figure 11).
Continental Shelf

34. A barrier island shoreline is to a large extent shaped by ocean

waves which move across the continental shelf onto the shoreface and break

26

Figure 12. Probable site of a large pre-1585 inlet at Kitty Hawk,
N. C. (Inlet was located in the left-central part of the picture
(Fisher 1962). Note the longshore bar as evidenced by breaking
waves in the Atlantic Ocean at the right side of the photograph.
The Wright Brothers Memorial is located in the left foreground)

near the beach. The shoreface, or inner part of the continental shelf, has a
concave profile; seaward of the shoreface, the continental shelf is planar

and dips away from the coast. Because wave form is modified and wave energy
is dissipated in shallow water, the width of the continental shelf is a factor
in regulating the amount of wave energy which reaches and is expended at the
coast. The shelf width to the 180-m (100-fathom) isobath narrows from 126 km
east of Cape Henry to 48 km east of Cape Hatteras.

35. Because of its decreasing width, the slope of the continental shelf
increases from north to south. The depth at the base of the steep, concave
shoreface also increases in that direction (Figure 13). The profiles shown
in the figure are averages of nine profiles, spaced 1.5 km apart, at each
location. An analysis of seismic data from the study area suggests the shore-
face may be resting unconformably upon older sediments of the planar and
seaward-dipping continental shelf; this implies the concave shoreface is

shaped by processes (waves, currents) active today or in the recent past.

27

10 @
R %
ry e
5 lg
PROFILE
10 NUMBER
| 1
5 A
E 10 ®
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25
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30 a)
e7;.4
35
0 5 10 15 20 25 30
DISTANCE, km
NOS
PROFILE PROFILE CHART PROFILE
NUMBER LOCATION NO. AZIMUTH LATITUDE LONGITUDE
1 VIRGINIA BEACH, 1227 717° 36°49.18' 75°58.06’
VIRGINIA
2 SOUTH OF FRESH POND 1227 80° 36°29.38' 75°51.34'
HILL, NORTH CAROLINA
3 NAGS HEAD, 1229 65° 35°54.60' 75° 35.82’
NORTH CAROLINA
4 WRECK-HATTERAS ISLAND - GULL 1232 95° 35°28.17' 75° 28.86’

ISLAND BAY, NORTH CAROLINA
Figure 13. Continental shelf profiles taken between Virginia Beach, Va.,
and Hatteras Island, N. C., to 30 km from shore (the averaged profile is
a solid line; dotted profile is a mathematical fit to the average pro-
file) (after Everts 1976)

36. Bathymety further seaward on the continental shelf reflects both
past and present processes. In the study area, the shelf is a broad sand plain
molded into north-south-trending sand ridges and troughs of up to 10-m relief
(Swift et al. 1978a, p 21). Two shelf-valley complexes were generated by the
landward displacement of the Chesapeake Bay and Albemarle Sound estuaries as
sea level rose in the Holocene epoch. Each complex has left an imprint on the
inner shelf: one lies seaward of the shoreface of Virginia Beach, Virginia,

and the other off Nags Head, North Carolina (Swift et al. 1978a, p 20).

28

37. Four clusters of closely spaced ridges trend oblique to the shore-
line and tie to the shoreface between Cape Henry and Cape Hatteras. They are,
from north to south, False Cape Shoals, Oregon Shoals, Wimble Shoals, and
Kinakeet Shoals. Swift et al. (1978b, p 270-271) note these characteristics
of shoreface-connected ridges: (a) the ridges rest on surfaces exposed as
the shoreface retreats to the west, (b) shoreface-connected ridges form angles
with the coast opening into the direction of prevailing flow (i.e., from north
to south), (c) sand on the seaward (downcurrent) flanks is finer than sand on
the landward (upcurrent) flanks, (d) ridges tend to be steeper on the seaward
side except next to their shoreface connection, and (e) ridges tend to migrate
downcoast and offshore. These ridges are emphasized because they appear to

have an influence on adjacent shoreline retreat rates.

Tides, Winds, and Waves

38. The data in paragraphs 39-46 are presented for reference only and
are not used in the analysis section; they provide background on the dynamic
conditions which have existed in recent times.

Tides and other sea level fluctuations

39. An astronomical tide is the periodic rising and falling of the
water surface resulting from the gravitational attraction of the moon and sun
on the rotating earth. The period of a complete tidal cycle in the study
area is 12.4 hours; the mean and spring tide ranges from NOS Tide Tables for
1981 are shown in Figure 14.

40. Sometimes superimposed on the astronomical tides is storm surge;
i.e., wind and wave setup and water surface differences caused by barometric
variations. Wind setup is the vertical rise in water level at a lee shore
caused by wind shear stresses on the water surface. Wave setup is another
superelevation of the water surface, caused by the onshore mass transport of
water by waves. In the sounds 20 km or more away from Oregon Inlet, the
astronomical tide range is less than 0.3 m, but the wind setup may raise the
water surface a meter or more for a l-year wind event. Return periods for
storm surge along the ocean shore at Kitty Hawk are shown in Figure 15 (Ho
and Tracey 1975).

41. A changing sea level occurring over a period of years may have a

profound effect on shoreline position. Changes on the order of years in sea

29

LONGITUDE

2 S oF 7¢°07'
° SS ooo
co} { o wo
x Kn i é & TIDE RANGE, M
37 00’ + CHESAPEAKE F _+ 75 59°
BAY
CAPE HENRY CATITODE to) 0.5 1.0 1.5
36 55’
VIRGINIA BEACH 50’
WOREOUR RUDEE INLET
°
Bs uy) 36 45’
=
y
= 40
Tay
35’
° NORTH CAROLINA
36 30° 4 “° or ery
25’
° 20’
ray
wy °
2 36 15
10’
KITTY HAWK 05’
CROATAN SHORES °
(KILL DEVIL HILLS) 36 00’
NAGS HEAD
55’
BODIE IS
50’
OREGON INLET ©
PEA IS 35 45
40'
20 RODANTHE 35’
WAVES
SALVO °
35 30’
25°
AVON 20’
ice me BUXTON 35°15°
ep HATTERAS CAPE HATTERAS \~ SPRING
ee HATTERAS INLET ——— EONGITUDE
OCRACOKE !S Perr meen es 31°
75.36’
a OCRACOKE
35 00’ 4 + INLET +
Figure 14. Tide ranges, Cape Henry to Cape Hatteras (from NOS tide
tables, 1981, for ocean sites (above mlw))

30

TIDE HEIGHT, FT MSL

RETURN PERIOD, YEARS

Figure 15. Tide frequencies for the ocean shoreline at Kitty Hawk, N. C.,
for several classes of storms: (a) landfalling, (b) alongshore,
(c) inland, (d) exiting hurricanes and tropical storms, (e) winter

storms, (f) all storms (from Ho and Tracey 1975)

surface elevation may cause a reshaping of the beach, nearshore, and inner
continental shelf profile; a rising sea relative to land will probably cause
the shoreline to retreat.

42. Sea level change data are not available in the study area. How-
ever, tide gage records (Hicks 1981) from Norfolk, Virginia, and Charleston,
South Carolina, exist, respectively, for the periods 1928 through 1978 and
1922 through 1978. The average rate of sea level rise relative to land at
Norfolk was +4.4 mm/year, but the trend may be one of a declining rise rate
(Everts 1981); from 1940 to 1978 the average was +3.7 mm/year, or about
15 percent less than the 1928 to 1978 average. At Charleston the 1922-to-
1978 average was +3.6 mm/year, but Hicks' (1981) data show a 1940-to-1978
rate of only +2.5 mm/year and indicate a decline in the rate of sea level

rise relative to land.

3

Wind conditions

43. Wind direction and mean scalar speed in the study area are given
in Figures 16 and 17. Mean annual velocities increase slightly to the south.
A velocity of 16 km/hour, 10 m above the ground, is required to initiate sand
movement. Speeds of 25 km/hour are required to sustain transport (Bagnold
1941). Winds at or above these speeds are predominantly onshore from the
northeast and occur most frequently during the winter months. The effects of
northwest winds, which are potentially important, may be lessened because of
local sheltering due to forests on the west side of the barriers (Hennigar
1979).

Waves

44. Changes in shoreline configuration result from a combination of
(a) wave action which mobilizes sediment and (b) wave-, wind-, and tide-
induced currents which transport the mobilized sediment.

45. Wave data are available from gages situated at Virginia Beach,
Virginia, and Nags Head, North Carolina (Thompson 1977). The Virginia Beach
gage, located at a depth of 5.5 to 6 m of water msl on the north side and near
the seaward end of the 15th Street fishing pier, was a step resistance, staff
relay gage in noncontinuous operation between 1962 and 1971. At Nags Head a
step resistance, staff relay gage was in operation, with some short periods of
inoperation, between 1963 and 1972. In 1972 a continuous wire staff gage was
installed at a depth of 5 m of water msl on the north side and 50 m from the
end of Jeannettes Fishing Pier. A third gaging site, recently operational,
is the CERC Field Research Facility, just north of Duck, North Carolina. Wave
data have been available from that site since 1979.

46. The Wave Information Study, Phase III (Jensen 1983), provides hind-
cast wave data for 20-year time periods for the study area. Using those hind-
cast results, Figure 18 shows the annual cumulative significant wave height
distribution for waves which approach from all directions at station 81 at a
10-m water depth off Kitty Hawk, North Carolina. The mean and maximum sig-
nificant wave heights are, respectively, 0.89 m and 4.70 m. Figure 19 is a
wave rose diagram for the same location off Kitty Hawk showing the significant
wave height and direction of wave propagation for the combined 20-year hind-

cast data.

32

JANUARY FEBRUARY MARCH

APRIL MAY JUNE

JULY AUGUST SEPTEMBER

NOVEMBER DECEMBER

DIRECTION FREQUENCY:
BARS, EACH CIRCLE = 20%.

25% OF ALL WINDS
WERE FROM NORTH-
EAST

MEAN SPEED (KNOTS)
IS INDICATED BY THE
PRINTED NUMBER AT
THE END OF EACH
BAR

MEAN SCALAR SPEED
OF ALL OBSERVED EAST
WINDS WAS 10 KNOTS

SCALAR MEAN SPEED
(KNOTS)

OBSERVATION COUNT
PERCENT OF CALMS

Figure 16. Surface wind roses, Cape Henry and vicinity,
from data collected 1850-1960

33

JANUARY FEBRUARY

DIRECTION FREQUENCY:
BARS, EACH CIRCLE = 20%.

25% OF ALL WINDS
WERE FROM NORTH-
EAST

MEAN SPEED (KNOTS)
IS INDICATED BY THE
PRINTED NUMBER AT
THE END OF EACH
BAR

MEAN SCALAR SPEED
OF ALL OBSERVED EAST
WINDS WAS 10 KNOTS

SCALAR MEAN SPEED
(KNOTS)

OBSERVATION COUNT
PERCENT OF CALMS

Figure 17. Surface wind roses, Cape Hatteras and vicinity,
from data collected 1850-1960

34

WAVE HEIGHT, M

10-1 10° 10! 102
PERCENT GREATER THAN INDICATED

Figure 18. Annual cumulative significant wave height distribution based on

20 years of hindcast data measured at 10-m water depth off Kitty Hawk, NewiGe
(after Jensen, draft report)

35

LEGEND
WAVE HEIGHT
OVER 2.99 M 5
E PERCENT
2.50-2.99 M ta OF WAVES
ae
ce
2.00-2.49 M ora
tw
Ow <a
oo
a oO
1.50-1.99 M <i
S
¢
=
1.00-1.49 M
0.50-0.99 M
STATION 81
0.00-0.49 M JAN-DEC

58440 CASES

EX PERCENT OF WAVES AN
OCCURRING FROM

THIS DIRECTION FOR
THE 20 YEARS

Figure 19. Wave rose diagram showing the significant wave height

and direction of wave propagation for combined 20-year hindcast

data in a 10-m water depth at station 81 off Kitty Hawk, N. C.
(from Jensen 1983)

Coastal Storms

47. Extratropical (northeasters) and tropical (hurricanes) storms play
a major role in changing the position of the shoreline. Figure 20 from Eber-
sole (1982) shows the frequency of occurrence of storm surge for extratropical |
storms at Hampton Roads, Virginia, the closest tidal reference station to the
study area (about 20 km west of Cape Henry). The figure was produced nsdn
hourly values of water level data from 1952 to 1971. Ebersole (1982) found
that about 20 years of data provided a relatively stationary tidal probability

36

RETURN PERIOD, YEARS

1.01 1.1 2 5 10 20 50 100 200
2 7
6
5
ke
uw
uw
C)
oc
a 4
=
c
fe)
=
w
3
2
1
0.001 0.1 0.3 05 0.7 08 0.9 0.95 0.98 0.99 0.995

FREQUENCY OF OCCURRENCE

Figure 20. Yearly storm surge return period for extratropical

storms at Hampton Roads, Va. (after Ebersole 1982)

density function. Figure 20 illustrates the yearly return period for extra-
tropical storms which produce the given storm surge elevations.

48. Hayden (1975) studied secular variations in storm occurrence. Ina
hindcast study of extratropical storms (i.e., with waves greater than 1.6 m),
he found that storm occurrences were at a maximum in March between 1942 and
1960, but that the maximum had moved to January by 1974. The mean annual
number of storms with waves over 1.6 m did not vary significantly (the annual
average was about 34); however, Hayden (1975, p 982) found the number of
events in which the waves exceeded 2.5 m had increased 1.9 times between the
1942-1965 period and the 1965-1974 period. Hayden notes that the increased
frequency of large stormwaves is consistent with observed trends in shoreline
erosion.

49. Hurricanes generally move from southwest to northeast in the study
area (Ho and Tracey 1975), with an increase in the frequency of hurricanes
from Cape Henry to Cape Hatteras (Figure 21). Simpson and Riehl (1981, p 109,
292) show below-average frequencies predominated from 1895 to 1930; in 1931

Sif

VIRGINIA

ELIZABETH CITY |S

WASHINGTON Os,” gs

MOREHEAD “py tle
JACKSONVILLE@.” CITY,

WILMINGTON: 5

N, .
. : BR;
SOUTHPORT: “)};
NO Cy
SOUTH CAROLINA ‘‘y.--fmee

Tc LEGEND
GH TC - ALL TROPICAL CYCLONES (40 MPH OR HIGHER)

H - ALL HURRICANES (74 MPH OR HIGHER)
GH - GREAT HURRICANES (125 MPH OR HIGHER)

Figure 21. Number of tropical cyclones (hurricanes) reaching the North
Carolina coast, by sector, for the period 1886-1970

hurricane frequency rose to an above average level and remained there until

1960 when another decline began.

Coastal Structures

50. Various types of structures have been constructed on the beach and
in the nearshore zone along the study area coast (Table 3). They were con-
structed to serve four general needs: recreation and research (piers, Fig-
ure 22), coastal protection (bulkheads), coastal stabilization (groins, Fig-
ure 23), and navigation improvements (jetties, Figure 24). Jetties and groins
modify the directional distribution of energy approaching the adjacent shore-
line and act as barriers to longshore sand transport; piers also modify the
movement of sand in an alongshore direction.

51. In addition to fixed coastal structures, beach fills and dunes or

38

Figure 22. Recreational pier at Virginia Beach, Va., a typical

fishing pier for the study area (note the shoreline bulge

created at the pier by a decrease in the rate of sediment

transport parallel to shore. The decrease probably occurred

because the pier piles created a partial obstruction to shore-

parallel flow and because the pier piles in the water dissipate
some of the wave energy)

39

Figure 23. View toward north of groins near Cape Hatteras
Lighthouse; Cape Hatteras Point is about 1 km south of the
lighthouse (note the change in shoreline orientation at
the groin system. Sand moving from north to south is
partially trapped and held north of the groins. The beach
to the south (bottom of photograph) consequently receives
less sand than it loses, and erosion is accelerated)

40

Table 3
Coastal Structures, Cape Henry to Cape Hatteras*

Location Structure Number Remarks

West of Lynnhaven

Inlet, Va. Fishing pier 1
Virginia Beach, Va. Fishing pier 1
Virginia Beach, Va. Bulkhead 1
Virginia Beach, Va. Jetties 2 Rudee Inlet, South Structure, is

a weir jetty

Duck, N. C. Research pier 1 550 m long or 2 to 3 times as long

as the fishing piers located
south of Kitty Hawk, N. C.

Kitty Hawk to South

Nags Head, N. C. Fishing pier 5
Rodanthe, N. C. Fishing pier 1
Salvo, N. C. Fishing pier 1

Cape Hatteras
Light, N. C. Groins 3

ay

* Oceanfront only, 1980 conditions.

41

Figure 24. Weir jetty system at Rudee Inlet, Virginia Beach, Va.

(Sand movement at this location is predominantly south to north

(left to right in the photograph). Sand moves over the low weir

section and is periodically pumped to nourish the recreation
beaches north of the north jetty)

sand fences have been constructed to prevent flooding from the Atlantic Ocean
and to slow or halt shoreline retreat. The most extensive beach fill efforts
have taken place at Virginia Beach, where sand has been placed on the beach
for the last 25 years: between 1952 and 1976, over 4.5 million cu m of sand
were placed along 8 km of shoreline, mostly within the 5.5-km reach north of
Rudee Inlet (Goldsmith et al. 1977). Sand sources were (a) a stockpile at
Cape Henry where material dredged from Thimble Shoal Channel in the Chesapeake
Bay entrance was stored, (b) Lakes Rudee and Wesley and Owl Creek, (c) Lynn-
haven Waterway, and (d) upland borrow sources (currently from south of Rudee
Inlet). The net alongshore movement is about 200,000 cu m of sediment/year to
the north at Rudee Inlet. Bypassing is presently accomplished using the weir
jetty system shown in Figure 24: sand passes over the low weir crest into a
sheltered depositional basin from which it is periodically pumped north across
Rudee Inlet to the Virginia Beach problem area.

52. In response to rapid shoreline retreat north of Cape Hatteras, the

42

National Park Service contracted to have 240,000 cu m of sand placed on the
beach in 1966 (Dolan 1972a). That fine-grained sand, taken from Pamilico
Sound, was soon lost. Three groins were then constructed by the U. S. Navy
in 1970. Further erosion north of the groins was addressed by a beach-
replenishment project in 1972 when 170,000 cu m of beach sand from Cape Point
was placed; in 1973, 750,000 cu m were added from the same source.

53. Between 1936 and 1940, sand fences were built along various reaches
of the study area by the Civilian Conservation Corps to create and maintain
continuous dunes (Dolan 1972b). Over 900,000 m of fencing was erected on
Bodie, Pea, and Hatteras Islands, most of it near the beach. Following a
severe storm in March 1962, a dune was constructed along 30 km of oceanfront
between Nags Head and Kitty Hawk. In the 1950's and 1960's the U. S. Depart-
ment of the Interior, National Park Service, constructed and stabilized dunes
in the Cape Hatteras National Seashore (i.e., from South Nags Head to past the

southern limit of the study area).

43

PART III: DATA REDUCTION
Data Sources

54. Forty-two historical NOS and C&GS shoreline surveys and maps, at
scales varying from 1:5000 to 1:40,000 and dating from 1849 through 1975,
exist for the study area. The earliest surveys (up to around 1927) were
"topographic surveys" and were practically all completed by planetable. Since
1927, aerial photography and photogrammetric methods (thus photogrammetric
surveys) have been used increasingly to provide topographic information along
the coast (Shalowitz 1964, p 52).

55. Eighteen 1:24,000-scale U. S. Geological Survey (USGS) quadrangles
were selected to be the base maps for this project (Figure 25). They were re-
vised by the Cartographic Revision Section of the Photogrammetry Division of
NOS with 1:24,000-scale color photography, taken on 16 March 1980 at near high
water, covering both sides of the barrier island and all of the ocean coast
within the project. This procedure is described more fully below. The
historical sheets available for each base map, with their scales and dates of
survey, are listed in Table 4. A particular sheet may often be listed on more
than one base map; each base map usually comprises sheets of varying scales

and area limits.

Shoreline Definition

56. Topographic surveys, in support of hydrographic surveys, have been
compiled by NOS since the early 1800's. These surveys are the basis for the
delineaton of the shoreline on the nautical charts published by the Agency.
According to Shalowitz (1964), the authority on the historical significance
of early topographic surveys of NOS, "The most important feature on a topo-
graphic survey is the high-water line." High-water line (HWL) is a general
term; because it is used in this report as the shoreline, it must be defined
as actually surveyed through the years by NOS and its predecessors.

57. About 1840, Ferdinand Hassler, the first Superintendent of the
Survey, issued the earliest instructions for topographic work. Those instruc-
tions (Volume 17, Coast Survey, Scientific, 1844-1846, handwritten) included
the following:

44

Figure 25.

LONGITUDE

=) = =

% ieee < :
© =

3700 + CHESAPEAKE va Et

NORTH CAROLINA

36 30 +

'
ia BUXTON

D CAPE HATTERAS

OCRACOKE !S a

OCRACOKE

ae a + mer +

nd

U. S. Geological Survey 1:24,000 quadrangles used as base

in this study

*6 07
1559

LATITUDE

‘6 55

50

LONGITUDE

75 3)

75 36

17. On the sea shore and the rivers subject to the

tides, the high and low water lines are to be surveyed

accurately; and the kind of ground contained between

them, whether sand, rock, shingle or mud marked

accordingly. The low water line is taken by offsets
whilst running the high water, and when not too far

apart from each other, but when their distance is

great they must be surveyed separately: a couple of

hours before the end of the ebb, and the same time

45

maps

Sheet Name*

Cape Henry

Virginia Beach

North Bay

Knotts Island

Barco NW

Barco NE

Barco SE

Powells Point NE

Kitty Hawk NW

L

Table 4

Historic Shoreline Surveys, Cape Henry to Cape Hatteras, 1847-1980

T-Sheet

T-507

T5753}

T-3647

T-4139, Sect 1
T-8301

T-11704
T-11705
T-11706

Base map 43

LE7/53}

T-4139, Sect 1
T-8299

e709

Base map 44

T-743

T-4139, Sect 2
T-4139, Sect 1
Base map 45

T-736

T-743

T-4139, Sect 2
Base map 46

T-657
Base map 47

W015} 7/
Base map 48

a

T-381, Sect
T-381, Sect 2
Base map 49

T-381, Sect 2
Base map 50

T-292
Base map 51

Date of Survey

1852

Apr-May 1859
1916

Oct 1925

1944

May 1962

May 1962

May 1962

16 March 1980

Apr-May 1859
Oct 1925
1942

Mar, May, Sept 1962

16 March 1980

Feb, Mar 1859
Oct 1925
Oct 1925
16 March 1980

Nov, Dec 1858
Feb, Mar 1859
Oct 1925

16 March 1980

1857
16 March 1980

1857
16 March 1980

1852
1852
16 March 1980

1852
16 March 1980

1849
16 March 1980

(Continued)

*« U. S. Geological Survey quadrangle; see Figure 25.

46

Scale

20K
20K
30K
20K
20K

Map Number

WONDAUW Whe

fe
ow ft

(Sheet 1 of 3)

Sheet Name T-Sheet Date of Survey Scale Map Number
Kitty Hawk SW T-292 1849 20K 15
T-3538 1915 4OK 20
Base map 52 16 March 1980 24K 52
Manteo T=351 1851 20K 16
T=3558 1915 40K 20
T-9159 Dec 1949 20K 17
Base map 53 16 March 1980 24K B)S)
Roanoke Island NE T-354 Jan 1849 20K 18
T-3538 1915 40K 20
T-9160 May 1949 20K 19
Base map 54 16 March 1980 24K 54
Oregon Inlet T-354 Jan 1849 20K 18
T-3538 1915 40K 20
T-9278 Dec 1949 20K 21
T-11672 1963-64 10K 22
T-11665 1963-64 10K 23
T-12140 1963-64 10K 24
TP-00887 1975 5K 25
TP-00889 1975: 5K 26
Base map 55 16 March 1980 24K 59
Pea Island = 3 Oy Mar, Apr 1852 20K 27
T-3707 1917 40K 28
TeSys Seer il 1946 10K 29
TEST ace Z 1946 10K 29
T-12147 May 1962 10K 30
T-12562 Oct 1963 10K Si
Base map 56 16 March 1980 24K 56
Rodanthe T-367 Mar, Apr 1852 20K 27
T-3707 1917 4OK 28
T-8712, Sect 1 1946 10K 32
T-8712, Sect 2 1947 10K 32
T=12437 April 1963 20K 33
Base map 57 16 March 1980 24K 7)
Little Kinnakeet WSSi7/7/ Jan, Feb 1852 20K 34
T-3707 1917 40K 28
T-8713, Sect 1 1946 10K 35
T-8713, Sect 2 1946 10K 35
T-12438 April 1963 20K 36
Base map 58 16 March 1980 24K 58
(Continued)

Table 4 (Continued)

47

(Sheet 2 of 3)

Table 4 (Concluded)

Sheet Name

Buxton

Cape Hatteras

T-Sheet

WS3y7/7)

T-790

T-1246

T-3707

T-8714, Sect 1
T-8714, Sect 2
TP-00507

Base map 59

W8}7/ 7/

T-790
T-1246
T-3707
T-8718
T-12442
TP-00507
Base map 60

Date of Survey

Jan, Feb 1852
1860

1872

1917

1946

1946

April 1974

16 March 1980

Jan, Feb 1852
1860

1872

1917

1947

April 1963
April 1974

16 March 1980

48

Scale Map Number

20K
20K
20K
40K
10K
10K
20K
24K

20K
20K
20K
40K
10K
20K
20K
24K

(Sheet 3 of 3)

during the commencement of the flood tides will be the
proper time for taking the low water line, and your
operations must be so timed, as to be on the shore on
those periods.

18. You will establish points along the shores, and
mark them securely by means of stakes, at suitable
distances, for the use of the hydrographical parties
in taking their sounding--and also furnish them with
the high and low water line, from your map, they may
require.

58. The first specific instruction regarding the nature of the line to
be surveyed is contained in the Plane Table Manual (Wainwright 1889), which
states: 'In tracing the shoreline on an exposed sandy coast, care should be
taken to discriminate [sic] between the average high-water line and the storm
water line." Still later, Shalowitz (1964, p 174) elaborated by stating:

The mean high-water line along a coast is the inter-
section of the plane of mean high water with the shore.
This line, particularly along gently sloping beaches,
can only be determined with precision by running spirit
levels along the coast. Obviously, for charting pur-
poses, such precise methods would not be justified,
hence, the line is determined more from the physical
appearance of the beach. What the topographer actu-
ally delineates are the markings left on the beach by
the last preceeding high water, barring the drift cast
up by storm tides. On the Atlantic coast, only one
line of drift would be in evidence....If only one line
of drift exists, as when a higher tide follows a lower
one, the markings left by the lower tide would be
obliterated by the higher tide and the tendency would
be to delineate the line left by the latter, or pos-
sibly a line slightly seaward of such drift line.

In addition to the above, the topographer, who is an
expert in his field, familiarizes himself with the tide
in the area, and notes the characteristics of the beach
as to the relative compactness of the sand (the sand
back of the high-water line is usually less compact

and coarser), the difference in character and color

of the sun cracks on mud flats, the discoloration of
the grass on marshy areas, and the tufts of grass or
other vegetation likely along the high-water line.

59. Historical references are included to emphasize that it was the
intention of all the agency's topographic surveys to determine the line of
mean high water (MHWL) for delineation on maps. With the exception of tidal
marsh areas, where in most cases the outer limit of vegetation is mapped,

the MHWL delineated on the surveys by the experienced topographer or

49

photogrammetrist was that line at the time of the survey or the date of
photography.

60. With the advent of precision aerial photography, the compilation
of a 'T-sheet" for photohydro support opened a new dimension in shoreline
compilation. When stereoscopic instruments and known tide data were used, the
MHWL could be accurately determined by aerial photography. This method was
supplemented, when possible, by profile points run from vertical bench marks
to verify the photointerpretation. When beach profiles were run on the more
contemporary surveys, they were referenced to the nearest tide station. If
this was a tertiary (i.e., temporary) station, the readings were referenced

to a primary station.

Methods Used to Revise the 1980 Mean High Water Line

61. To make this study as current as possible, USGS quadrangle maps
were revised to show a 1980 MHWL. The revision was made using 1980 color
aerial photographs flown for this study. Date and time of the photography
were correlated with the stage of the tide, and a detailed stereoscopic ex-
amination of the photographs was made to determine the 1980 MHWL. This pro-
cess was completed by the Cartographic Revision Section of the Photogrammetry
Division of NOS. Their method was by direct transfer of the photointerpreted
line (see paragraph 60) from 1:24,000-ratioed film positives to the USGS base
maps. Using the ratioed photography, the base maps (manuscripts) were held
planimetrically to local physical features. In absence of triangulation sta-
tions to position the manuscript accurately against the photographs, it is
possible to use "hard" planimetric features, such as road intersections or
other permanent physical structures without great relief, to assure good photo-
graphic positioning. In areas where there were not enough features to assure
proper positioning, stereomodels were set on the National Ocean Survey Analyt-
ical Plotter (NOSAP). NOSAP is a high-precision stereoscopic plotter that
allows the operator to bridge over areas of sparse control and accurately
determine the correct relationship between photographic models and the base
maps. Due to time restraints, no field check of the office-determined 1980
MHWL was made. All shorelines compiled by this method were reviewed to assure

a uniformity of the photointerpreted shoreline, accuracy of compilation, and

50

proper symbolization. These maps were then digitized, checked, and reviewed

in the manner identical to that used for all historical source maps.
Data Reduction Procedures

62. Copies of all historical maps used as source data in this study
were obtained from the NOS vault in Riverdale, Maryland, through the NOS Re-
production Division. Copies were initially bromide prints (a photographic
process which provides a long shelf-life copy) and were later made into more
stable matte-finish film positives. Historical sheets covering the study area
were examined to determine which sections of shoreline would be included in
the study, and those were highlighted using a yellow felt marker. Only those
areas and sections of shoreline for which data from other NOS historical maps
would be available for comparison were used.

63. Digitizing of the shoreline on each historical map and each base
map, revised for contemporary shoreline, was the next task. This procedure
was completed by the Data Translation Branch, Environmental Data and Informa-
tion Service, Asheville, North Carolina. The digitizing was completed on a
Calma-graphics III system, with a repeatability factor of +0.001 in. and a
maximum absolute error of +0.003 in. The digitized data tapes were then pro-
cessed using a program developed by the NOS Marine Data Systems Project for
use with the NOAA UNIVAC computer (GPOLYT2); this program allows for the con-
versions of the digitized data to geographic positions (GP's). Since many of
the historic sheets used in the study were completed before the North American
Horizontal Datum of 1927 (NA 1927) was established, the GP's for these sheets
were converted to that datum so that accurate comparisons between pre- and
post-NA 1927 surveys could be made. Conversion was completed mathematically,
based on the conversion factors for triangulation stations in the area, on a
program also written by the NOS Marine Data Systems Project.

64. After processing of the data was completed, plot tapes were gen-
erated using the NOS McGraphics program, and the plot tapes were used, with a
Calcomp 748 plotter and Calcomp 925 Controller, to plot the shoreline movement
maps. This task was completed with the assistance of the NOS Automated
Cartography Group.

pil

Quality Control and Potential Errors

65. All sections of shoreline from the source maps were digitized so
that all shoreline points could be converted into GP's and replotted at any
desired scale (before the final portrayal scale of 1:24,000 for the shoreline
movement maps was chosen, other scales were tested to determine which map
scale would portray the data in the most readable form). Digitizing also re-
moved inherent media distortion caused by the age of the original manuscripts.
The mechanics and mathematics of the digitizing system required that all pro-
jection (latitude and longitude) intersections completely enclose the data to
be digitized. By assigning known and true values for each projection inter-
section, the GPOLYT2 program adjusted each of the shoreline points enclosed
within a projection cell, based on the true values of the intersections versus
the digitized and computed values for those same intersections. The values
for each shoreline point are thus correct in their position relative to the
known (true) projection intersections and to known triangulation data
(Figure 26).

es 2a

+ DIGITIZED VALUES

-+- CORRECTED VALUES

' ADJUSTED TO TRUE
VALUES FOR
INTERSECTIONS

aes “S a

Figure 26. Digitization procedure for correcting shoreline position
locations when original shoreline movement map distortions exist

66. Following the digitizing process, each sheet was reviewed visually
with the use of a raw data plot in which shoreline positions were shown at the
same scale as the original map. The plotted shoreline was superimposed on the
original map and checked for completeness and accuracy of tracking during dig-
itization. This review helped to minimize a potential source of human error

that could occur during the digitizing process.

52

67. Other sources of potential error also were considered. The most
difficult of these to determine accurately was the location accuracy of the
MHWL on the source surveys and maps, on either (a) the early surveys prior to
approximately 1930 and (b) the group of maps based on photogrammetric surveys.
In discussing the early surveys, Shalowitz (1964, p 175) has stated:

The accuracy of the surveyed line here considered is
that resulting from the methods used in locating the
line at the time of survey. It is difficult to make
any absolute estimates as to the accuracy of the early
topographic surveys of the Bureau. In general, the
officers who executed these surveys used extreme care
in their work. The accuracy was of course limited by
the amount of control that was available in the area.

With the methods used, and assuming the normal control,
it was possible to measure distances with an accuracy
of 1 meter (Annual Report, U. S. Coast and Geodetic
Survey 192 (1880)) while the position of the plane-
table could be determined within 2 or 3 meters of its
true position. To this must be added the error due to
the identification of the actual mean high water line
on the ground, which may approximate 3 to 4 meters.

It may therefore be assumed that the accuracy of loca-
tion of the high-water line on the early surveys is
within a maximum error of 10 meters and may possibly
be much more accurate than this. This is the accuracy
of the actual rodded points along the shore and does
not include errors resulting from sketching between
points. The latter may, in some cases, amount to as
much as 10 meters, particularly where small indenta-
tions are not visible to the topographer at the
planetable.

The accuracy of the high-water line on early topo-
graphic surveys of the Bureau was thus dependent upon
a combination of factors, in addition to the personal
equation of the individual topographer. But no large
errors were allowed to accumulate. By means of the
triangulation control, a constant check was kept on
the overall accuracy of the work.

On aerial photographs, the MHW line is located to within 0.5 mm at map scale
(USC&GS 1944). This translates to less than 5 m on the ground for a map scale
of 1:10,000, or 9.99 m on the ground for a map scale of 1:20,000. Since the
great majority of source maps were of a larger scale than the 1:24,000 base
maps, the 0.5-mm accuracy of source maps made using aerial photography was at
least maintained by reducing most of the source maps to the common base scale
of 1:24,000. Present NOS survey maps are even more accurate. In a recent

shoreline mapping project in the state of Florida using NOS charts, 36 random

dg}

features such as road intersections and shoreline features, including points
of marsh, were scaled from the map compiled from aerial photography. Where
these features were then located by field traverse and the geodetic coordinate
values compared, the check revealed a maximum error of +3.0 m. This accuracy
is not claimed for all surveys, but it does serve as an indicator of the ac-
curacy of surveys conducted within NOS.

68. The last source of potential error is the conversion of digitized
values to GP's. Digitizing equipment automatically recorded 1,000 coordinate
values for every inch of shoreline traced, which values were then corrected
to true latitude and longitude positions, as previously discussed. The
GPOLYT2 program printout provided a final error column each for "Latitude Y"
and "Longitude X," which were examined on each printout. In the event any of
the figures exceeded 0.5 mm (at map scale), the digitizing effort was rejected
and the original sheet was redigitized. Although the maximum allowable error
from this source was 4.99 m on the ground for a 1:10,000-scale map and 9.99 m
on the ground for a 1:20,000-scale map, rarely were the error column values as
high as 0.5 mm; in most cases, they were 0.2 mm or smaller. As such, the
possible errors from this source were more likely to be in the vicinity of
1.99 m on the ground for a 1:10,000-scale map and 3.99 m on the ground for a
1:20,000-scale map. Since most data were finally portrayed at a scale smaller
than the map being digitized, the shoreline movement maps produced are well

within map accuracy standards.

54

PART IV: DATA ANALYSIS AND DISCUSSION

69. Reproductions of composite shoreline movement maps are enclosed
separately. These maps are useful in a qualitative way; i.e., they provide an
easy means of observing the changes that have occurred in the past. Because
of slight variations in shoreline position created in the printing process,
however, they should not be digitized for quantitative use in coastal manage-
ment, engineering, or research. To enable the data these maps represent to
be so used, the following paragraphs describe the techniques used in this
study to quantify shoreline change.

70. An analysis routine was used to average shoreline change parameters
for specified longshore distances. Because geographic point analyses were
based on latitude and longitude, a reasonable distance to use was one keyed to
those measures. Based on shore orientation, a 1-minute-latitude (about 2 km)
or -longitude (about 1.5 km) distance was selected to average long-term shore-
line changes. It deserves mention that the shoreline change rate given is
the average for the entire shoreline within the 1l-minute coastal reach, not
the rate at particular sites 1 minute apart. The distinction is an important
one because measurements made at a constant alongshore interval seem to be
subject to a bias depending upon the particular interval chosen (Hayden et al.
1979).

Analysis Methodology

71. Shoreline change rates resulting from the following analyses,
although averages in space, are based on particular points in time. Nothing
is included that identifies what happened to the shoreline in the interval
between shoreline surveys; the analyses simply distribute the change uniformly
over the separating time increment. The rates given in this report are the
shore-normal rates of movement averaged for a fixed shore-length increment,
they were obtained using changes in plan area between successive latitude or
longitude boundaries 1 minute apart. For each survey set from time t a plan
area A(t) was specified using fixed latitude and longitude boundaries (three
of the boundaries used) and the shoreline (the fourth boundary) (Figure 27).
The latitude and longitude boundaries were invariant in time; only the shore-

line boundary changed. That change in shoreline position between surveys

2)

1’ LONG: TUDE

7

1’ LATITUDE

SHORELINE
sh

. “J OCEAN
/ SHORELINE

Figure 27. Definition sketch illustrating parameters used to obtain
shoreline change rates for a north-south-trending ocean shoreline
(a north-south trend is defined as 315° < a > 45°)

created a change in plan area. The difference in plan area for each time

interval, divided by the shoreline length 2 and the number of years between

surveys, produced an annual shoreline change rate Si for a particular survey

interval

56

Te (te cee ie (1)

where i varies from 2 to n _, and n equals number of surveys. This shore-
line change rate is the average shore-normal movement landward (-) or seaward
(+) of the shoreline. This approach was used to quantify changes in both the
ocean and sound shoreline between survey dates.

72. A straight-line shoreline length 2 was used because the average
shore-normal rate of change in shoreline position was desired. Generally, the
ocean and sound shoreline orientation, a (Figure 27), did not vary at any
site by more than a degree during the study period. This indicates that shore-
line changes within l-minute increments were mostly shore-normal; i.e., the
coastline in the interval did not pivot a great deal. Therefore, the length
2 between latitude or longitude boundaries 1 minute apart remained almost
constant. The use of the straight-line distance 2 rather than the actual
shoreline distance was preferred on the sound side because (a) that shore was
often very irregular and (b) one objective of the study was to compare ocean
and sound shoreline changes. The sound shoreline change must, therefore, be
viewed as the average rate of shore-normal movement based on changes in plan
area and including nearshore islands. The straight-line shoreline length 2
is thus a fairly constant, easily measured, and reasonable scaling factor to
transform changes in area to shore-normal shoreline changes.

73. Areas, as shown in Figure 27, were digitized at NOS for each
l-minute increment. In the sound, islands immediately off the coast were in-
cluded in the area computations because they had often been part of the coast
at an earlier time; the islands were included only when they were clearly near
the barrier island and when the sound beyond the island was open and wide.

74. The least-squares shoreline change rate So is the slope of the
best fit line to a plot of shoreline positions A, /2 (Equation 1) versus time

of each of the surveys in that 1-minute shoreline reach, or

is ew JN
2p ==
=
Sy°= = Waimea Saekatie (2)
pa Geek = t)
n=1

57

where

n

Sl

Oe t. (3)
=|

and

n

an

Mes ony (4)
n=1

It is immaterial whether time is consistently taken as the date of the earlier
or the later of the two surveys compared. The standard deviation SD of

annual rates of shoreline change is

(5)

where

n

aie 1

See OL (6)
=a

1

Shoreline Change Rates

Listing of shoreline change rates

75. Shoreline changes, averaged (a) by varying shoreline distances
(b) over the total survey period and parts of that period, are presented
without interpretation in this section. Reasons for shoreline changes and
relationships between shoreline changes and shelf bathymetry, inlets, capes,
and shore orientation are discussed in the next section.

76. Tables 5-8 are listings of shoreline change rates for the period of
approximately 1850 to 1980 for the following ocean shoreline reaches:

Table 5: Virginia, west of Cape Henry

58

Table 5
Ocean Shoreline Changes in Virginia West of Cape Henry*

Shoreline Longitude
76°06'

Lynhaven Inlet
76°04'

76°03'

76°02'

76°01'

76°00'

sey

Cape Henry

1852-
1859

Wo8)

-6.8

1852-
1980%%

-0.4

10)
Nes
Nod
elie
Piloil
0.2

Survey Dates
185 2—Wews59 =
19161916

S12
0.8
aul
0.5
=lets)
-0.7
-0.5

1916-
1944

0.1

Wats}
1.0
38)
-0.7
3 )4/74
1.1

1944-
1962

-0.9

0.6
lel
PG
-0.6
0.5
0.2

1962-
1980

Sho!

0.8
Phen?
Soil
eal
0.4
2.0

J

value indicates shoreline retreat.

tote

«x Least-squares estimate of shoreline change rate.

Ocean Shoreline Changes in Virginia South of Cape Henry*

Table 6

Survey Dates

* Shoreline change averaged between survey dates shown, in m/year; negative

T852- 1852- 1858- 1858- 1859- 1859- 1859- 1916- 1925- 1925- 1925- 1942- 1942- 1944- 1962-
Shoreline Latitude 1916 1980** 1925 1980** 1925 1944 1980** 1944 1942 1944 1980 1962 1980 1962 1980
Cape Henry
36°55' =O sn Oli2: 1. 0.2 2.0
36°54! 0.5 0.7 0.4 2.9
36°53' 0.2 0.1 0.3 0.2 0.9 1.2
36°52" , -0.1 0.0 0.2 0.1 0.5 0.7
Virginia Beach
36°51' -0.3 -0.2 -0.3 SN Wes) 1.4
36°50' 0.0 0.0 S57) 0.2 0.6 1.4
36°49' -0.6 -0.5 0.5 =0°4 -0.9 -0.8
Rudee Inlet
36°48' =O -0.7 -0.5 -0.1 0.1
36°47' -1.0 = OF So? -0.2 0.3
36°46' -0.9 -0.9 P53) -0.8 -0.1
36°45' -0.8 Sia =Bha7/ -1.4 -0.3
36°44! -1.4
36°43'
36°42' -2.3 -2.4 = 2
36°41' -3.4 -3.0 -2.5
36°40' =2e3) S251 ail)
36°39' -1.2 S55} -1.8
36°38' Silos} -0.8 -0.1
36°37' -1.5 -0.9 -0.1
36°36'
36°35' -0.4 -0.4 -0.3
36°34' =O Oe Oe 0.2
36°33' 1.4 0.9 0.2
36°32' 1.3 1.0 0.6
36°31" 2.0 3} 0.5
36°30' 1.6 1.1 0.4
* Shoreline change averaged between survey dates shown, in m/year; negative value indicates shoreline retreat.

** Least-squares estimate of shoreline change rate.

x

59

Table 7

Ocean Shoreline Changes in North Carolina North of Cape Hatteras*

Cape Hatteras

Survey Dates

1849- 1849- 1849- 1852- 1852- 18)72=HPLOS=Ielg 15S — 1949- 1949- 1963- 1963- 1975-
Shoreline Latitude 1872 1915 1980** 1946 1980** 1915 1949 1980 1963 1980 1975 1980 1980
Southern Shores
36°09' 0.
36°08' 0.
36°07' -0.
36°06" 0.0 -0.5 Coiling k
36°05" 0.1 0.6 -1.4
Kitty Hawk Beach
36°04' 0.7 0.6 1.9
36°03" 0.7 -0.5 ONG 7/
36°02' 1.5 0.4 2.3
Croatan Shores
36°01" =-1.7
36°00" -2.3
35°59! er2) 0.7 4.0 =i) 0.4
35°58" -0.2 -0.8 Mo7/ —=1'33 =0).
35°57" =l.7 -1.4 -1.1
Nags Head
35°56" — 12. =1.3 -1.4
B55 51 ileal -0.7 -0.2 -0.5 -0.9
35°54" 13) 0.7 0.1 0.3 0.5
35530 -1.4 -1.2 -0.9 -1.0 oil
B5252" 0.0 0.7 -1.8 103) 0.7
35°51' -0.8 -0.8 -0.8 -0.9 1.2 -2.8
35°50" -2.0 10515) 0.0 =l'.3 3.3 -2.3
35°49" -3.6 -3.0 -0.8 a7 -6.3 -3.2 -3.9
Oregon Inlet
SEAMAGY 0.1 4.3 -7.0
35°44" 2.8 2.9 —=2ia2 -4.9
35°43" —)29 -1.8 0.1 =)
35°42" -1.7 1.3 1.0 =1.2
35°41" 0.1 0.0 0.5 NG7/
35°40! 0.0 0.2 -1.4 0.5
35°39! 0.1 4.8
35°38" -3.2 -1.0 0.1 1.7
35°37' -3.7 -3.8 4.5 3.3 5.3 0.7
35°36" -1.5 -3.2 -4.6 -4.5 =—7.1 =2.2
35°35" 0.3 =1'.6 -1.9 4.3 -2.0 io 22
Rodanthe
35°34! 0.4 0.2 0.1 0.2 1.1 -1.4
35°33" 0.4 0.3 -0.8 0.4 3.2 0.4
35°32" 0.2 0.3 -1.0 0.4 =2\ei/) 2.6
BS oly -0.6 0.0 -0.2 0.7 1.3 2.1
35°30" 0.2 0.5 0.9 0.8 0.2 Noe
35°29" 1.5 0.2 -1.5 -0.8 P55) 1.9
35°28' 1.4 0.1 Mo7/ 0.8 =2.5 2.1
35°27" -0.3 -0.3 0.5 -0.1 -2.6 0.8
35°26' 1.2 0.5 2.4 -2.0 2.6 0.7
35°25' 1.5 -0.5 -4.1 =2i3) =1\.3) 0.5
Little Kinnakeet
35°24" 2.0 0.3 3.9 -2.6 -1.6 0.8
35°23" 5.0 1.2 -5.8 =2.5 3 1.8
35°22" 4.0 0.2 8.5 3.9 1.2
35°21" 0.8 -0.5 -1.9
Avon
35°20" 0.1 0.3 -1.3 0.6 0.1
35°19! 0.3 -1.0 -3.2 -2.0 -l.1 1.2
35°18" 0.4 -2.0 5.6 -3.7 -1.4 0.0
35°17" -2.4 -3.3 -5.2 -4.2 -3.2 =2.2
35°16' 2.5 4.2 Jos) -3.7 —8}55) Jo 74
BS may -10.2 -5.2 -6.3 -4.0 -3.2 -2.3 =—).9
35°14"

* Shoreline change averaged between survey dates shown, in m/year; negative value indicates shoreline retreat.
** Least-squares estimate of shoreline change rate.

60

Table 8
Ocean Shoreline Changes West of Cape Hatteras*

Survey Dates
1860- 1860- 1872- 1917- 1946- 1963- 1975-
Shoreline Longitude 1872 1980** 1917 1946 1963 1975 1980

Cape Hatteras

BS od Ts 11.5 10.1 =o) BoM = Geel
USPS Tol 5.6 Do 10.5 -5.4 Zh jifde§)
USS oy 24.0 8.6 2s’) 15.7 LORS —6)0 Zaha U
WD) 35), 9.6 We Sle Soe) ine) PlleZ D352)
TSI" SO ae OS kes) -0.8 eG -O)ol& Bo)

* Shoreline change averaged between survey dates shown; in m/year, negative
value indicates shoreline retreat.
wx Least-squares estimate of shoreline change rate.

61

Table 6: Virginia, south of Cape Henry

Table 7: North Carolina, north of Cape Hatteras

Table 8: North Carolina, west of Cape Hatteras
For the same period, Tables 9 and 10 list shoreline change rates for the fol-
lowing soundside shoreline reaches:

Table 9: Cape Henry to Cape Hatteras

Table 10: Pamlico Sound, west of Cape Hatteras
Ocean shoreline change rates

77. 1850 to 1980. The mean rate of change for the ocean shoreline over
the approximately 130-year study period is shown in Figure 28. For those
ocean reaches without rates shown, either no shoreline change values were
available (i.e., the Corrolla to Duck, North Carolina, reach), or a major
change in shore orientation (i.e., Capes Henry and Hatteras) or a break in the
barrier island system (i.e., Oregon Inlet) precluded the determination of a
usable ocean shoreline change rate. Between about 1850 and 1980 where data
were available, approximately 28 percent of the ocean shore prograded, 68 per-
cent retreated, and 4 percent did not change position.

78. Average shoreline change rates should be used with caution for
planning and design purposes because large temporal and spatial variations in
the rates have occurred in the past and can be anticipated to occur in the
future. The standard deviation of shoreline position changes with time is a
measure of these temporal variations. Large standard deviation values indi-
cate a large variability in shoreline change rates between different surveys;
smaller values indicate the shoreline change rate has been more nearly con-
stant from one survey interval to the next. Figure 29 shows the standard
deviation and the number of surveys used to calculate it for the east-facing
ocean shore. Shoreline changes north of Oregon Inlet were relatively constant
from 1852 to 1980 when compared to the changes south of Oregon Inlet to Cape
Hatteras. Greater variations in shoreline position are the norm for the
latter 60-km-long reach.

79. Partial study period. Dates of survey allow a separation of the
data set into two nearly equal time intervals. It is useful to compare ocean
shoreline changes for those two periods for several reasons. During the
period from about 1850 to 1915-1925, the shoreline underwent mostly natural
changes, except for the dune vegetation loss caused by grazing animals. Dur-

ing the period from 1915-1925 to 1980, human intervention in the form of

62

Table 9
Sound Shoreline Changes, Cape Henry to Cape Hatteras*

Survey Dates
Shoreline [849- 1849- 1852- 1852- 1852- 1857- = 1858- 1859- 1915- 1917—- 1917— 1946- 1946- 1949- 1949- 1963- 1963- 1975-
Latitude 1915 1980** 1917 1946 1980** 1980** 1980** 1980 1949 1946 1949 1963 1980 1963 1980. 1975 1980 1980

36°42" 0.

36°41" =i,

36°40! -6.

36°39! -10.

36°38! 4.

36°37" -7.

36°36! -1.

36°34" +.

36°33"

36°32"

36°31"

36°30"

36°28" 0.9

36°27' 23}

36°26! -1.0
0.1
1.3

+
FUNK @Enw

Bro
Seo

b

36°25"
36°24"
36°21" 0.
36°20' 0
36°19" =l.
36°18! 1
36°17" 2
36°16" 1.
36°15' =I".
36°14" -0.
36°13" 0.
36°08" -0.
36°05"

36°04"

36°03"

36°02'

35°58" 0.7
35°57!" -0.2
35°56"

B5e5 5 2.
35°54" “5
35053) =2..
Sey! 2.
SOS Y 13. -0.4 -0.1
35°50' 3. 0.7 0.2
35°49" 0. -1.2 0.3
Oregon Inlet -0.5

35°45! -1.4 -5.8 12.2
35°44"

35°43!

35°42"

35°41" 1
35°40!

35°39!

haste 21.
35°37" 4.
35°36" Ne
35°35! -0.
35°34! 0.
35°33" =0!
35°32" 0.
35°31" 0.
35°29! =On
35°28" -0.
35°27" 0.
35°26" =e
35°25" -1.
35°24" =f
35°23" =e
35°22" -0.
35°21"
35°20" Sino)
35°19! -1.3
35°17" -0.2

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ae Shoreline change averaged between survey dates shown, in m/year; negative value indicates shoreline retreat.

Least-squares estimate of shoreline change rate.
t+ Some latitudes not included because data were unavailable.

63

Table 10

Pamlico Sound Shoreline Changes West of Cape Hatteras*

Survey Dates

1860- 1860- 1872- 1917- 1946-

Shoreline Longitude 1872 1980%* LOM 1946 1980
U5? 32" -0.5 -0.3
19°33" -0.9 oil, il =1.0 =1.4 -0.8
75°34! 4.1 2255) -4.1 So Ml -0.6
USO35)" 0.5 =1.5 oi. 7/ Nef =e
S236. 25M 211.5 -4.0 1.6 1/4

Shoreline change averaged between survey dates shown, in m/year; negative
value indicates shoreline retreat.
“wx Least-squares estimate of shoreline change rate.

64

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artificial dune-building occurred along much of the ocean shore; it was also
in this latter period that recreation became the dominant industry in the area.
Figure 30 shows average ocean shoreline change rates for the two periods in
the 36-km-long coastal reach south of Cape Henry; Figure 31 illustrates the
same parameters for the reach between Duck and Cape Hatteras, North Carolina.
The study area was divided into two areas because of the long intervening
reach for which shoreline position data were unavailable. Shoreline change
rates at Virginia Beach, Virginia, for the most recent 55 years of survey data
are illustrated in Figure 32; they are included separately because the influ-
ence of man in recent times at Virginia Beach has increased significantly.

80. Extreme shoreline position excursion is another measure of shore-
line change variability (Figure 33). Taken over the 130-year period of record
this provides the maximum landward and seaward position to which the shoreline

moved, based on infrequently-taken survey data; the actual extreme shoreline

LATITUDE
36°55’ CAPE HENRY

LEGEND
VIRGINIA
@——® ABOUT 1858 TO BEACH
ABOUT 1925
@—-8 ABOUT 1925 TO
1980 Ao:
RUDEE INLET

FALSE CAPE

-4 -3 =O, =1| 0 1 2
AVERAGE SHORELINE CHANGE RATES, M/YEAR

Figure 30. Average ocean shoreline change rates for the 36-km-long
reach south of Cape Henry in the periods 1859-1925 and 1925-1980

67

LATITUDE
36°10’

SOUTHERN SHORES
B

KITTY HAWK —~

BEACH x

CROATAN r

SHORES ae

NAGS HEAD LeGene

@— ABOUT 1850 TO

ABOUT 1915
35°50’ @-—-@ ABOUT 1915 TO
1980

OREGON

Pe ee
CAPE HATTERAS ~~

AVERAGE OCEAN SHORELINE CHANGE RATES, M/YEAR

Figure 31. Average ocean shoreline change rates for two survey

periods (about 1850 to about 1915 and about 1915 to 1980) in

the reach between Duck, N. C. (latitude 36°06'), and Cape
Hatteras (latitude 35°15')

68

LATITUDE

CAPE HENRY
S<
35°55’ ee
a> _>
—_—
=— - ae
‘ _
x a
\ va LEGEND
7 —_ 1925-1942(44)
y aN =-= 1942(44)-1962
\ = = 1962-1980
“y
|
oe
ee at
RUDEE INLET
35°48"
-2 -1 i) 1 2 3

AVERAGE OCEAN SHORELINE CHANGE RATES, M/YEAR

Figure 32. Average ocean shoreline change rates at

Virginia Beach for four successive surveys between

1925 and 1980: (a) 1925-1942(44), (b) 1942(44)-1962,
and (c) 1962-1980

69

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excursion probably was larger than appears because only a few shoreline posi-
tions were measured. In over one-half the surveyed shore reach, the extreme
shoreline position change occurred between the first and last surveys, in-
dicating a relatively continuous shore retreat or advance. Because of this
trend, patterns shown in Figure 33 are similar to mean shoreline change rate
patterns shown in Figure 28. Areas of retreat are more numerous than areas
of advance.

Sound shoreline change rates

81. 1850 to 1980. Shoreline changes on the sound side of the barrier

islands exhibit few consistencies in an alongshore direction (Figure 34).

The largest retreat rates occurred in the Back Bay area, a constricted fresh-
water region reported to be free of inlets in historic time (Figure 9).
Accretionary trends adjacent to and south of Oregon Inlet appear to be inlet-
associated. The consistent 0.5- to 1.5-m/year retreat of the sound shore-
line south of Salvo, North Carolina, also occurs in an area where inlets
persistent in historic times have not been reported. Figure 35 illustrates
the standard deviation of shoreline position change in the sounds through
time.

82. Partial study period. Figure 36 shows changes in the sound

shoreline for the same periods illustrated for the ocean shoreline in Fig-
ure 31. The 1852-1980-averaged sound shoreline change rate was -0.1 m/year,
a retreat which is 13 percent of the average retreat rate (-0.8 m/year) of
the ocean shore.

83. In the sound adjacent to Oregon Inlet the standard deviation of
shoreline change (Figure 35) is very large, suggesting fluctuations that are
likely inlet-related. South of Rodanthe, the shoreline retreated in a rela-
tively continuous manner. Infrequent and severe storms probably caused the
changes in this area. However, the storm effects, which are usually localized
in time and location, were probably lost in spatial averaging, especially con-
sidering the large survey interval of this study.

Oregon Inlet

84. Oregon Inlet was opened in 1846 by a severe coastal storm. Ini-
tially, large quantities of water moved through New Inlet (Figure 9) into
Pamlico Sound. Precipitation and runoff further increased the volume of
water in the sound; when the wind direction changed to the west, some of this

ponded water was carried seaward north of the site of present-day Oregon Inlet

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LATITUDE

36°00" CROATAN SHORES

NAGS HEAD

13.1
LEGEND
@—— ABOUT 1850 TO OREGON INLET
ABOUT 1915
@-——@ ABOUT 1915 TO
980
RODANTHE
Pal
St
as AVON
CAPE HATTERAS

-4 -2 0 2 4
AVERAGE SOUND SHORELINE CHANGES, M/YEAR

Figure 36. Average sound shoreline changes, for the periods from
about 1850 to about 1915 and from about 1915 to 1980, between
Nags Head and Cape Hatteras, N. C.

(Cumming 1966). With time, a channel was cut and deepened. Tidal currents
through the inlet throat have since kept it from filling with littoral sedi-
ments carried in a shore-parallel direction.

85. The inlet has not remained fixed in its original position, nor has
its shape nor the shape of the adjacent islands remained constant. Figure 37
shows the changes that have occurred since the inlet opened. (The dashed line
is the 1849 shoreline included for comparison purposes; note that a short
reach of shoreline south of Oregon Inlet was not surveyed during the 1915-1917
period.) Between about 1849 and 1980 the average inlet migration rate (i.e.,
the shore-parallel (north-south) movement of the midpoint of the narrowest
part of the inlet throat) to the south for Oregon Inlet was approximately
29 m/year. As shown in Figure 38 this rate varied greatly from one survey
interval to the next. The most rapid movement of the midpoint, 87.5 m/year
south between 1963 and 1975, occurred just after a severe storm on 6 and

7 March when the inlet widened and migrated north.

74

LATITUDE
35°55"

36°50°

35°45"

INLET

Figure 37. Changes in ocean and sound shorelines adjacent to
Oregon Inlet, N. C., for five surveys between 1852 and 1980

a5

TO NORTH

TO SOUTH

- MEAN INLET MIGRATION RATE BETWEEN SURVEYS, M/YEAR

1975
1849 1915-17 1946 1963 1980 SURVEY DATES

1850 1900 1950
DATE MIDWAY BETWEEN SURVEYS

Figure 38. Migration rates of Oregon Inlet throat for five
survey intervals between 1849 and 1980

86. Figure 39 shows the relative locations and orientations of the
narrowest section of the Oregon Inlet throat measured during six surveys
between 1849 and 1980. Also shown are changes in narrowest inlet throat
width, the relative location of the center of the inlet throat, and the di-

rection of inlet throat migration. This figure emphasizes three interesting

features:

a. The width of the inlet throat in 1963, about 2.5 km, was over
twice as large as the width average which is about 1.2 km. The
throat was expanded during the storm of March 1962, mostly at
the expense of the island to the north.

b. With the exception of the 1962 storm period (1963 survey) when
the center of the inlet throat moved north, migration was in a
generally south direction.

c. Except for immediately after the 1962 storm, the orientation

of the channel at the narrowest section was approximately
north-south; i.e., a line connecting the two sides of the
inlet at its narrowest section was oriented east-west.

87. The change in land area adjacent to Oregon Inlet very likely re-
flects the inlet influence on the nearby shorelines. This land area (Fig-
ure 40) above mean high water has been declining since the inlet opened;

with the exception of the 1963-1980 interval, the loss has averaged about

76

Ta ate 1849 (1.05)

—
=—_—

1963 (2.50)

9) THLINE OF
\

INLET MIGRATION

1915 (1.22)

NORTH-SOUTH DISTANCE, KM

1949 (1.27)

foene fi cae 1980 (0.90)

EAST-WEST DISTANCE, KM

Figure 39. Relative locations and orientations of the narrowest section of
Oregon Inlet throat, 1849-1980 (dates given are dates of survey; numbers in
parentheses are inlet widths in kilometers)

10

LEGEND

@ TOTAL AREA
® AREA NORTH OF INLET
@ AREA SOUTH OF INLET

OREGON INLET

PLAN AREA, SQ M x 10®

1849 1915 1949 1963 1980
SURVEY DATE

Figure 40. Plan view changes in land area in the
vicinity of Oregon Inlet, N. C., 1849-1980

77

-36,000 sq m/year. The land region included in the analysis extended 8 km
north and 8 km south of the inlet as it existed in 1849 (Figure 37). The net
loss for the total system, which may include some effects of New Inlet, re-
sulted from shoreline retreat adjacent to the inlet; this probably represents
a transfer of sand from the ocean shoreline region to the sound by inlet cur-
rents. Note that the decrease in plan area was continuous south of the inlet
but the variable plan area changed north of the inlet. The increase to the
north occurred as the result of a spit which built south as the inlet migrated
south.

Cape Hatteras and Cape Henry

88. The land protrusion of Cape Hatteras (Figure 2) has changed sig-
nificantly in plan area and shape since the first survey in 1852 (Figure 41).
Figure 42 shows that a decrease in land area occurred as the east-facing coast
retreated (eroded) to the west and the south-facing coast prograded (accreted).
Figure 28 shows evidence of the ocean shoreline retreat at the Cape Hatteras
lighthouse. In 1870, when the lighthouse was built, the shoreline was 600 m
east of its 1980 position. Retreat has been continuous except for a brief
period in the 1940's where a slight progradation occurred. Figure 43 shows
that Cape Point moved about 0.5 km in a net southwesterly direction between
1852 and 1980. The figure also shows that Cape Point fluctuated greatly in
position during that period and that the present position is likely a tempo-
rary site.

89. Cape Henry, during the same period, changed in a different way
(Figure 44). The east-facing shore moved east (prograded), while the
north-facing Chesapeake Bay shore moved south (eroded). The changes at Cape
Henry were nearly an order of magnitude smaller than the changes at Cape
Hatteras.

Variations in shoreline change rates with time

90. Shoreline change rates varied greatly with time. The extent of
this variation is illustrated in Tables 11 and 12. The periods shown on the
tables, 1852-1917, 1917-1949, and 1949-1980, are expedients based on available
survey data. The shoreline change data, when averaged by reach (Figures 45
and 46) suggest these trends:

a. Shoreline retreat on the east-facing ocean coast was at a maxi-
mum during the 1917-1949 period (Figure 45). Greatest shore
stability occurred between 1852 and 1917.

78

75 32’ 75°31’ 75°30’
35°15"

35°14’

CAPE HATTERAS

SCALE 1:24,000

1 1/2 0 1/2 1 MI
ar EEE)
1000 0 1000 2000 3000 4000 5000 6000 7000 FT
Pe ce eee)
1 0.5 0 0.5 1KM
aS

Figure 41. Changes in the mean high-water shoreline at Cape Point,
Cape Hatteras, between 1852 and 1980 (dates indicate the year of
the shoreline survey)

79

1.25

AREA IN REGION: LONG - 75°30-31’
LAT - 35°13-14'
(INCLUSIVE)

1.0

o
N
a

RELATIVE PLAN AREA, SQ M x 108
i=)
oa
(=)

0.25

1850 1900 1950 1980
SURVEY DATE

Figure 42. Relative plan area of the subaerial projection for
Cape Hatteras, 1852-1980

2KM

SQ) <—<————— NO

0 1 2KM
Sn IEA

Figure 43. Location of Cape Hatteras point between 1852 and 1980

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81

Table 11
Summary of Mean Shoreline Changes, Oceanside

Mean Shoreline Change for These Survey Periods, m/year*

Coastal Reach 1852-1917 1917-1949 1949-1980 1852-1980
West of Cape Henry 0.2 (5)** 0.5 (7) 132 GW) 0.2 (7)
Cape Henry to

Oregon Inletf -0.0 (20) -1.2 (18) -0.3 (21) -0.6 (40)
Oregon Inlet to

Cape Hatterasft 0.4 (21) -2.9 (23) -1.3 (30) -1.1 (28)
West of

Cape Hatteras LSS) S365) 2.0 (3) lS) (S))
Average 0.6 (51) -0.8 (53) -0.4 (63) -0.4 (80)
Mean N-S ocean coast = -0.8 m/year; n = 75

Mean E-W ocean coast = +2.0 m/year; n = 12

Table 12
Summary of Mean Shoreline Changes, Soundside

Mean Shoreline Change for These Survey Periods, m/year*
Coastal Reach 1852-1917 1917-1949 1949-1980 1852-1980

West of Cape Henry 2 -- 20 bo
Cape Henry to

Oregon Inlet 2.0 (9)** 0.1 (10) -0.2 (10) -0.5 (40)
Oregon Inlet to

Cape Hatterasf 0.7 (24) 0.3 (20) -0.2 (27) 0.3 (19)
West of

Cape Hatteras} -1.9 (4) Sils0) (G)) -0.9 (5) -1.7 (4)
Average 0.7 (37) 0.1 (35) -0.3 (42) -0.3 (63)

Mean N-S sound shore = -0.1 m/year; n = 70

Mean E-W sound shore = -1.2 m/year; n = 5

ny
"

Positive = shoreline moves seaward; negative = shoreline moves toward
mainland.

** Number in parentheses is number of 1l-minute reaches included in analysis;
number varies for different time periods because surveys are not continuous
for entire coast.

~ Data coverage = approx. 60 percent of total shoreline.

tt Data coverage = approx. 90 percent of total shoreline.

t Data coverage (1852-1980) = approx. 80 percent of total shoreline.

82

2 N SOUNDSIDE
_ GC HENRY TO
\ OREGON INLET

N

ona NU SOUNDSIDE
= av OREGON INLET
x QT Ta 70.6 HATTERAS
\ ae
0 . >.

OCEANSIDE
C. HENRY TO
OREGON INLET

MEAN SHORELINE CHANGE RATE, M/YEAR

OCEANSIDE
-2 OREGON INLET
TO C. HATTERAS

1852-1917 1917-1949 1949-1980
SURVEY PERIOD

Figure 45. Shoreline change rates, averaged by survey period, for east-
facing ocean shorelines and west-facing sound shorelines

8
OCEANSIDE Vea \

WEST OF C. HA ay As \

| ve i"
\
\

OCEANSIDE
WEST OF C. HENRY

MEAN SHORELINE CHANGE RATE, M/YEAR

SOUNDSIDE eee
WEST OF ace
C. HATTERAS

1852-1917 1917-1949 1949-1980
SURVEY PERIOD

Figure 46. Shoreline change rates, averaged by survey period, for
west-facing ocean and sound shorelines

83

b. The temporal trend, but not the magnitude, of east-facing ocean
coast changes was similar north and south of Oregon Inlet
(Figure 45).

North- and south-facing ocean coasts (Figure 46) were accre-
tional in the 5- to 10-km study reaches west of the capes for
all survey periods. The trends of change were not similar;
however, the small number of reaches sampled in each area
(Table 11) may preclude a realistic comparison.

Ke)

| Qu

The west-facing shoreline trend in the sounds was one of con-
tinuous change from progradation (movement into the sounds)

to retreat (movement toward the ocean) between 1852 and 1980
(Figure 45). The trends were similar north and south of Oregon
Inlet.

|o

Between 1852 and 1980, the north-facing shoreline west of Cape
Hatteras decreased its net retreat (Figure 46). This trend was
the opposite of that measured for the west-facing sound shore-
line (Figure 45).

f. Ocean and sound shoreline changes generally did not follow
similar trends through time. While the east-facing ocean
shoreline retreated at a maximum rate between 1917 and 1949,
the west-facing sound shoreline (i.e., the shoreline on the
other side of the barrier island) reached a maximum retreat
rate in the 1949-1980 period. Only the north-facing ocean
shoreline at Cape Henry and the north-facing sound shoreline
at Cape Hatteras (Figure 46) showed similar behavioral trends
through time.

Changes in island width and position

91. Where data covering both ocean and sound shorelines are available,
an analysis of island width and position provides useful information on the
particular ways in which the islands have changed shape. When averaged for
the period of about 1850 to 1980, the east-facing ocean shore retreated an
average 0.8 m/year. In the same period the average retreat rate of the west-
facing sound shoreline was 0.1 m/year. This resulted in an average island
narrowing of 0.9 m/year.

92. Because the average ocean shore retreat exceeded the average rate
of sound shore retreat, the island axis (i.e., the midpoint between shore-
lines) moved landward (west) an average 0.35 m/year. However, as Table 13
shows, in most time periods and along most reaches, the island axis moved sea-
ward at more locations than it moved landward. This island axis movement,
though, should not be confused with the classical definition of barrier island
migration which assumes that both oceanside and soundside shorelines move
toward the continental land mass. Island migration occurs when the ocean

shoreline erodes and, concurrently, the sound shoreline progrades as sand is

84

Table 13

Combined Ocean- and Soundside Shoreline Changes

Number of 1-minute Latitude/Longitude Shoreline
Increments Which Moved

Survey Period North of South of West of No
1852-1980 Oregon Inlet Oregon Inlet Cape Hatteras Total Change
Island* widens 8 4 2 14
Island narrows 16 15 2 33
Island axis moves
toward sound 12 7 0 19
Island axis moves =
toward ocean 10 12 4 26
Survey Period
1852-1980
Island widens 4 9 2 15
3
Island narrows 4 7 2 13
Island axis moves 4
toward sound 6 6 0 UW
Island axis moves
toward ocean 2 13 4 19
Survey Period
1946-1980
Island widens 1 7 2 10
1
Island narrows 9 18 3 30
Island axis moves
toward sound 9 12 0 21
4

Island axis moves
toward ocean 0 12 4 16

Island as shown here also includes the peninsula or spit north of Oregon
Inlet.

85

transported (a) across the island by overwash or wind or (b) through inlet
openings directly to the sound shoreline.

93. A general indication of island behavior is shown in Table 13 for
three regions (i.e., north and south of Oregon Inlet and west of Cape Hat-
teras) in the study area. Note that island narrowing, by portion of the
coast, is the most common change, while island widening is the least common
behavior. Slightly more segments of the island system moved seaward than
landward. Table 13 references direction of movement by 11-minute latitude or
longitude increments. The following four changes are noteworthy:

a. For the measured segments, island narrowing greatly exceeded
island widening when averaged for the 130-year study period.
However, during the 1852-1917 period, island widening and nar-
rowing were almost equal. Between 1946 and 1980, three times
as much of the measured island system narrowed as widened.

b. Island-narrowing-to-widening ratios were generally similar
north and south of Oregon Inlet. This suggests that the con-
ditions which led to the island width changes, while they
varied through time, were consistent throughout the study area.

Over the study period, the island axis moved seaward at slightly
more places than it moved landward. This situation, however,
varied by survey period. Between 1852 and 1917 seaward move-
ment prevailed, while between 1946 and 1980 landward movement

of the axis prevailed.

ike)

d. For the measured portions of the study area, trends in island
narrowing or widening did not indicate particular movements of
the island axis.

94. Figures 47-50 show the rates of island width change and the rates
of change in position of the island axis for different time periods. Fig-
ures 48 and 50 are limited to the section between Kitty Hawk and Cape Hatteras,
North Carolina, because that is the only area in which data were available for
both the periods 1852-1917 and 1917-1980. These figures illustrate the fol-
lowing alongshore changes in island width and position through time:

a. The largest island width changes occurred near Back Bay, Vir-
ginia (Figure 47). This is an area of large ocean (Figure 28)
and sound (Figure 34) shoreline retreats.

b. Increases in island width between Kitty Hawk and Oregon Inlet
(Figure 47) came as a result of progradation of the sound
shoreline (Figure 34) during a period of ocean shore retreat
(Figure 28) (the area near Croatan Shores was not influenced
by an inlet during the study period). The south-facing ocean
coast west of Cape Hatteras was also an area of island width
increase; however, here the increase occurred because of ocean
shore progradation (Figure 28).

86

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Island narrowing south of Oregon Inlet (Figure 47) generally
occurred as a result of combined ocean and sound shore retreat
(Figures 28 and 34).

Island width changes varied greatly in time in both magnitude
and direction (Figure 48). The period 1852-1917 was one of
slightly greater island widening; between 1917 and 1980,
island narrowing predominated.

Island axis migration rates (Figure 49) may be positive
(seaward-moving) in Back Bay but, because island narrowing
along both shorelines predominated here (Figure 47), to con-
sider this axis migration as island migration is misleading.
It is best thought of as island narrowing, with retreat of the
sound shoreline greater than the ocean shoreline.

Changes directly north and south or Oregon Inlet are the result
of inlet processes: the ocean shoreline has retreated and the
sound shoreline has prograded (Figures 28 and 34). Processes
associated with Oregon Inlet and New Inlet (Figure 9) are
responsible.

Island migration was similar in direction for the 1852-1917 and
1917-1980 survey periods, with one exception (Figure 50): the
island axis in the region centered on Avon, North Carolina,
moved seaward in the former period and toward the mainland in
the latter period. This change in direction is primarily the
result of a shifting ocean shoreline (Figure 28).

91

PART V: PREDICTION OF FUTURE SHORELINE CHANGES

95. The NOS shoreline change maps show what happened between Cape Henry
and Cape Hatteras from 1850 to 1980. An analysis of the maps quantifies the
changes both spatially and temporally. Data regarding historical shoreline
changes can provide useful information with which to predict future changes.
When the causes of change are imperfectly known, however, it is difficult to
predict future changes by extrapolating past trends because the future may
not mimic the past. It is not apparent from the results of this study that
the magnitude of future changes in shoreline behavior can be forecast. How-
ever, future changes at specific sites can probably be estimated for any given
time period relative to the average changes which have occurred in the rest of
the study area. This section treats these aspects of shoreline change pre-

diction separately.

Temporal Predictions

96. Great variability was found in change rates within the 1850-1980
survey period. It is not unreasonable to assume future changes will be dif-
ferent from the 1850-1980 average. The survey record of shoreline changes in
the study area is relatively short, intermittant, and nonuniform in frequency;
it also lacks noticeable trends through time (Tables 11 and 12, and Figures 45
and 46). Consequently, there is limited shoreline change data available with
which to extrapolate shoreline changes into the future. In addition, because
of the multiplicity of processes involved, it is impossible to evaluate the
relative importance of man's impact relative to changes in the natural pro-

cesses that caused the shore to accrete or erode.
Spatial Predictions

97. Many changes in shoreline position are likely related to local
conditions. Because wave, wind, and current data are unavailable over the
130-year survey period and throughout the study reach, a direct causal rela-
tionship cannot be established to predict those changes. However, most of the
alongshore variations in shoreline change appear to be influenced by the prox-

imity of the shoreline to inlets, capes, and nearby shore-connected ridges

92)

(Figure 51). The relationship between shoreline change and these features
appears reasonable and informative, but the relationship does not consider the
actual processes causing the changes. Extrapolation of future shoreline
changes using both past shoreline change data and the relationships between
those changes and local features improves the forecasts, but even these pre-
dictions must be treated with caution. Clearly, an effort to establish the
causes of the shoreline changes related to local features is warrented.
Barrier island migration and narrowing

98. Barrier islands along the mid-Atlantic coast very likely formed on
the Continental Shelf considerably east of their present positions during a
period when sea level was much lower than it is today (Swift et al. 1972).
As sea level rose, the islands are thought to have migrated toward the con-
tinental land mass--or west in the study area. For this migration to have oc-
curred, the ocean side of the islands must have retreated and the sound side
must have prograded. During migration the islands likely had alternating
periods of net island narrowing and widening superimposed on the longer term
landward migration. Conditions favoring island migration are those that move
sand from the ocean side of the islands to the sound side. In the study area,
this would mean one or more of the following conditions:

a. Overwash transport. The optimum conditions are a narrow island
(probably less than 1 km in width, and maybe quite a bit less);
a low island where dunes are absent, or low and discontinuous;
minimum vegetation, especially those shrubs and trees that
would hinder overwash; and storm surges of long duration in
which the water level exceeds the island elevation.

b. Aeolian transport. The optimum condition is a strong onshore
wind that exceeds 25 km/hour (that necessary for sand transport)
for long periods of time; a wide, dry beach area that serves as
a source for wind-carried sand; and an absence of vegetation so
that the windblown sand can be carried to the sound side of

the island. (A low, narrow island would probably allow a more
speedy trip for a sand grain from ocean to sound but is not
necessary for effective aeolian sand transport. )

Ke)

Inlet-related transport. Most important to island migration is
the presence of many large and relatively permanent inlets
which intercept sand moving in the littoral zone and move it

in a net westward direction. An inlet is capable of removing

a large portion of the sand moving in an alongshore direction
and transferring it to shoals in the sound or to the sound
shoreline adjacent to the inlet. As the number, size, and
persistence of the inlets increase, the amount of sand moved

in a landward direction increases and the probability of island
migration increases.

93

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94

99. The data presented herein have shown that although islands in the
study area narrowed over the 130-year study period (Figures 47 and 48), they
did not migrate in the classic sense toward the mainland because both the
ocean and sound shorelines retreated toward the island. The reasons island
migration has ceased are not clear. Quite likely, overwash has not been an
important mechanism in sound shoreline progradation for the last several
hundred years. Today, the islands are probably too wide in most places for
overwash penetration across the entire island (Leatherman and Fisher 1976).

In addition, prior to about 1800 the islands were well vegetated with trees
and shrubs (Hennigar 1979) which would have either inhibited overwash or been
destroyed had frequent or severe overwash conditions existed. In the nine-
teenth and early twentieth centuries, aeolian transport may have been of some
local significance because poor land practices had left the island barren
(Hennigar 1979). However, at other times wind-transported sand probably did
not account for much sound shoreline progradation. If island migration oc-
curred in the study area between 1585 and 1850, it was probably the result of
inlet processes. Figure 9 shows that the number and permanency of inlets have
decreased in the study area from 1585 to the present time; if migration is not
occurring today, it is probably because the impact of inlets is too small.
Only Oregon Inlet now acts as a sediment trap in the study area; significantly,
the barriers adjacent to it are migrating in a westerly direction.

100. The reasons for island narrowing are also not clear; nor is it
clear when the narrowing cycle began or when it will end. Sand losses from
the front and back of the islands in the recent past may have been partially
caused by a rise of sea level relative to land--a vertical rise of probably
4 mm/year in the study area since 1930 (Hicks 1981) (on a static shore slope
of 1:40, for example, this would translate to an apparent shore retreat of
0.1 m/year). Quite likely a relative sea level rise would also have caused
dynamic changes in the beach that would have increased the shore retreat rate;
this effect cannot be quantified at present. Long-term changes in wave and
wind conditions also could have forced the ocean and sound shores to retreat
or accrete, especially if the frequency and duration of storms had changed
substantially. An added factor, frequently not considered, is that unconsoli-
dated marine coasts may retreat under "normal" conditions. Whether the rate
of relative sea level rise will increase or decline and whether wind and wave

conditions will produce more or less erosion in the future are unknown.

101. Island narrowing must have begun before 1850. It will, of course,
end when the islands disappear or when one or both shorelines begin to pro-
grade. At the present average rate of island narrowing (0.9 m/year), it will
take almost 1700 years for a 1500-m-wide island to narrow to nothing. Before
that happens, though, overwash, if allowed, will likely begin to transport
sand to the sound shoreline and island migration will commence. A reasonable
forecast based on past behavior is that narrowing will probably continue in
the foreseeable future.

Alongshore sediment transport reversal

102. Waves approaching shore at acute angles and winds with a shore-
parallel component create alongshore currents. Sediment mobilized by wave
activity is moved by these currents. Over the period of a year the amount of
sand moved one way is rarely balanced by that which is moved the other way; the
difference is the net volume of littoral sand which moved preferentially in one
direction. This net volume and the direction it is moved may change from year
to year and over longer time periods as the wave and wind climate changes.

103. Study results tell us little about the net volume moved; however,
they provide some indication of the direction of net sediment transport. Other
studies have suggested that, on the long-term average, 2 X 10° cu m/year of
sediment moves north at Rudee Inlet* and 5 xX 10> cu m/year moves south at Ore-
gon Inlet (U. S. Army Engineer District, Wilmington 1980). This net transport
indicates that a change in the net alongshore sediment transport direction--
i.e., a transport reversal--occurs somewhere between the two inlets. Evidence
from this study suggests that the reversal occurs near latitude 36°41' (Fig-
ure 28 shows a very uniform decrease in the shoreline retreat rate north and
south of that site (the north end of Back Bay)) to create a divergent long-
shore sediment transport nodal zone; i.e., a place where sand moves alongshore
to both the north and the south away from the site. Losses north and south
of latitude 36°41' are nearly equal and decrease progressively with distance.
Shoreline retreat rates are expected to decrease if a divergent nodal zone
exists because sediment moving away from the node will reach adjacent beaches
and thereby reduce the loss rates there.

104. The large shoal complex east of the Chesapeake Bay entrance

EGR Tet A I Td SE SN a RR OL a

* Personal Communication, James Melchor, 1981, Oceanographer, U. S. Army
Engineer District, Norfolk, Va.

96

influences the refraction path of waves approaching the coast from north to
east. The effect of the topographic high is to bend waves approaching from
north of shore-normal to approach from the south. This mechanism tends to
create a northward-directed current, which supports the inference that an
alongshore sediment transport nodal zone exists near latitude 36°41'.

105. At Rudee Inlet, the net alongshore transport rate of 2 X 10° cu m/
year based on recent dredging records, is 60 percent of an estimated
3.4 x 10°

latter value is based on long-term shoreline change rates (Figures 28), the

cu m/year cummulative volume loss north of the nodal zone. The

alongshore distribution of those rates, and a 10-m shoreface depth (Haller-
meier 1977). Therefore, in recent times 60 percent of the sediments lost from
the beaches appear to have moved in an alongshore direction primarily inshore
of the ends of the Rudee Inlet jetties (Figure 24). Loss rates in the nodal
zone area are based on 130 years' record and variations from one survey to the
next were small (Figure 29), indicating that conditions have not varied as
much there as elsewhere in the study area. Some of the unaccounted-for 40 per-
cent of lost sediment may have been moved west by overwash or wind transport,
or east and offshore into water that is deeper than the jetty ends. In addi-
tion, the static effect of sea level rise relative to land at 0.4 mm/yr (Hicks
1981) on a beach sloping at 1:30 would be a yearly loss of 26,000 cu m, or
about 20 percent of the unaccounted-for sediment. Rising sea level may have
had an additional, unquantifiable effect on the dynamics of the system.

Sound shoreline change

106. Dune construction, either by natural or artificial means, is
usually accomplished at the expense of sand in the littoral zone. To compen-
sate for the lost sand, the shoreface and beach profile, and, consequently,
the shoreline, will retreat. This was probably the case following construc-
tion of the continuous dune between South Nags Head and Cape Hatteras which
was begun artificially, using sand fences, between 1936 and 1940. Dune pro-
file data and rates at which the dune grew are unavailable; however, if a
final 5-m-high-by-60-m-wide dune with about a 3-m-high. overwash platform re-
sulted and a shoreface depth (i.e., the depth from mean sea level (MSL) to
base of shoreface) of 10 m is assumed, the removal of that volume of sand from
the littoral zone would result in a shoreline retreat of 11m. Dune-building
may be a factor in the increased shore erosion between Oregon Inlet and Cape

Hatteras between 1917 and 1949 (Figure 45).

97

107. Driven by storm surges (Figure 15), overwash probably occurred
frequently in the study area before dune construction; however, it likely had
only a minor effect on the ocean and sound shorelines (Figures 52 and 53).
Shoreline position changes do not seem to be related to island width for either
the ocean or sound shorelines, except near existing or recently closed inlets.
Away from inlets, the sound shoreline where the island was less than 900 m
wide retreated at an average rate of 0.6 m/year (Figure 53), which is greater
than the average retreat rate for island sections where the width was greater.
Accordingly, overwash probably did not significantly affect the sound shore-
line during the period from 1850 to 1980. If the effect were important, the
sound shoreline at narrow places on the island would have likely prograded as
sand moved from the beaches into the sound.

108. Away from inlets, the retreat of the sound shoreline can be ac-
counted for mostly by sea level rise. At an average surface gradient of 1:100
near the sound shoreline, and a sea level rise of 0.004 m/year (Hicks 1981),
the sound shoreline retreat rate would be 0.4 m/year, or nearly the actual
rate measured. This rate will vary in the future as the sea level change

rate relative to the island varies.

LEGEND
@
z 2 @OPEN N-S FACING COAST
Ww @ NEAR PAST OR PRESENT
8 ® INLET
{e)
eR

MEAN SHORELINE CHANGE, OCEAN, M/YEAR

TO MAINLAND

3
500 1000 1500 2000 2500 3000 3500 4000 4500
ISLAND WIDTH, M

Figure 52. Ocean shoreline changes from about 1850 to 1980, Cape Henry
to Cape Hatteras, as a function of island width in 1980 (shoreline
changes are shown in Figure 28)

98

@
+7.94b+9.8 643.9 b+6.8 LEGEND
BS

a ea @ OPEN N-S FACING COAST

2 @ NEAR PAST OR PRESENT
INLET

TO OCEAN
MEAN SHORELINE CHANGE, SOUND, M/YEAR

TO MAINLAND

0 500 1000 1500 2000 2500 3000 3500 4000
ISLAND WIDTH, M

Figure 53. Sound shoreline changes from about 1850 to 1980, Cape Henry to
Cape Hatteras, as a function of island width in 1980 (shoreline changes
are shown in Figure 34)

Inlets and shore erosion ;

109. Inlets affect both sides of a barrier island or spit and have had
a major impact on shoreline behavior in the study area. Shoreline changes
that have occurred as a result of open inlets during the 130-year period of
this study provide a basis to extrapolate shoreline changes caused by inlet
processes backward in time to 1585 (Figure 9) and earlier. In some cases the
effect of an inlet on adjacent shorelines is only one of a number of causes
of the change in those shores.

110. Present inlets. Rudee Inlet, one of the two inlets presently open
in the study area, is a small and stabilized feature that has only a small
effect on adjacent shorelines; the recent history of Rudee Inlet is listed in
Table 2. Oregon Inlet, unstabilized and many times larger than Rudee, is the
only inlet that has been open continuously for the length of the study period.
Since it opened just 4 years before the first shoreline survey was made, the
survey data presented in this paper provide an excellent sequence with which
to detail the inlet's behavior.

111. Oregon Inlet today is flanked by erosional ocean shorelines for
about 8 km on either side of the inlet throat (Figures 28 and 31). Shore

erosion, which is greatest near the inlet, decreases as distance from the

99

inlet increases. (The past site of New Inlet (Figure 9), just north of
Rodanthe, also has experienced major erosion since 1850 (Figure 31).) The
sound shoreline has been affected to a lesser extent (Figures 34 and 36), but
the net change has been one of progradation. This shoreline adjustment adja-
cent to Oregon Inlet is related to the normal alongshore sediment transport
(see paragraph 103) of beach sand. When this sand reaches the inlet throat,
some is carried landward by flood-tidal currents and deposited within the in-
let system. The large shoal area in Pamlico Sound west of the throat at Oregon
Inlet is evidence of that inlet's trapping capacity. The sand composing those
shoals is coarser than the sound sands upon which the shoal area rests. In-
lets such as Oregon Inlet probably trap sand until the sound shoals have grown
to attain a quasi-equilibrium condition, at which time the volume of beach
sand which enters the inlet on a flood tide is balanced by the volume carried
out on the subsequent ebb tide. The trapping rate of an inlet normally de-
creases with time after the inlet opens. However, when an inlet moves paral-
lel to shore as Oregon Inlet has done (29 m/year on the average, Figure 38)
the entrapment rate may not decrease very rapidly because the flood-tidal
shoals never attain a quasi-equilibrium state of development.

112. An analysis of Oregon Inlet sand gains relative to adjacent ocean
shore sand losses provides an approximate means to illustrate that most of
the adjacent shoreline retreat is inlet-caused. Approximately 32,000 sq m/
year (4.2 Xx 10°
since 1849 within 8 km of Oregon Inlet (Figure 40) (to some extent, these

sq m, total) of barrier island surface area has been lost

values have also been influenced by previously open New Inlet (Figure 9)).

To calculate the volume of sand moved, the depth to which the shoreface
profile has been modified must be considered; a reasonable depth (Hallermeier
1977) is about 10 m. Using the surface area lost (Figure 40) and the assumed
10-m depth to which erosion occurred, approximately 4 x 10! cu m of sediment
was lost from the barrier islands adjacent to Oregon Inlet between 1852 and
1980. The ebb- and flood-tide shoals in Oregon Inlet cover an estimated

2.5 X 10! sq m of Pamlico Sound. At an average estimated thickness of 2 m,

j cu m of sands transported from the ad-

these inlet deposits contain 5 X 10
jacent islands. Thus, according to this very crude analysis, the sands lost
from the beaches near Oregon Inlet can be accounted for within the inlet sys-
tem, primarily in Pamlico Sound flood-tide deposits. Of course, superimposed

on the inlet-caused ocean shoreline change, is the long-term 0.8-m/year

100

retreat which exists for the entire study reach.

113. It is interesting to note that the sand entrapment rate has re-
mained relatively constant since 1849 (Figure 40). The only perturbation
occurred during the 1949-1963 period when the March storm of 1962 greatly
changed the inlet (Figures 38, 39, and 40). Poststorm recovery, however, re-
turned the system to its prestorm condition; Oregon Inlet is apparently still
trapping sand (1980) at about the rate it trapped it in the first 66 years
after it opened. As long as Oregon Inlet remains open and unstructured and
continues to migrate south, the sand entrapment rate should remain near its
1852-1980 average value of 3 X 10°

havior should remain similar to that shown in Figure 28. As the inlet mi-

cu m/year. Adjacent ocean shoreline be-

grates south, the inlet-influenced ocean shoreline 8 km north and south of
the throat also will migrate south.

114. Small, structured Rudee Inlet is presently not acting as a sand
trap; littoral sand that is moved into the inlet throat is returned to Vir-
ginia Beach by hydraulic means. In the future this inlet will not likely
affect adjacent beaches as long as present (1980) conditions prevail.

115. Past inlets. Inlets have been located, in historic times, in two
regions: in northern Currituck Sound and centered around Oregon Inlet (Fig-
ure 9). Probably the largest prehistoric inlet (pre-1585), as evidenced
primarily by beach ridges, was located at Kitty Hawk, North Carolina (Fig-
ure 11). Small ephemeral inlets have been opened during storms, but natural
movements of sand along the coast have caused them to close within a few years.
Only relatively stable passages through the barrier spits and islands are in-
cluded in Figure 9.

116. Sands are deposited in flood-tidal shoals within the sound, on
adjacent sound shorelines, and in ebb-tidal shoals in the ocean after an inlet
opens. The net sand loss from adjacent beaches is reflected in an increase
in the rate of ocean shoreline recession. Conversely, the sound at the inlet
gains sand. If the inlet subsequently closes, the flood-tidal shoals fre-
quently form a new shoreline or islands in the sound (Figure 37). Inlet
closure is usually accompanied by ocean shoreline readjustment such that is-
land width at the site of the former inlet increases; i.e., the ocean shore-
line builds seaward.

117. An anomalously wide portion of a barrier island is often a clue to

the previous existence of an inlet. In Figure 11, which plots island width

101

with inlet location and the length of time the inlet was open, the anomalous
island widths shown near latitudes 36°15' and 36°00' most likely reflect pre-
1585 inlets. The existence of these sites indicates that the islands have
existed in or near their present locations for at least the past 400 years.

118. Wide portions of barrier islands are usually less susceptable to
a new inlet opening than are narrow portions. Thus, while the existence of
an anomalously wide island reach often reflects the past site of an inlet, it
probably is not a prime site where a new inlet will open. However, ocean and
sound hydraulic characteristics, which were once maximized at the previous
inlet location, probably did not change much; therefore, that general region
remains a potential site for a new inlet. These sites can be identified in
Figure 11.

119. Inlet effects on the ocean coast are rapidly muted after the inlet
closes. Within a decade after closure, the effect of an inlet on the adjacent
shorelines is no longer noticeable (see New Inlet, for example, in Figure 37).
This occurs because alongshore sediment transport and the landward transport
of ebb-tidal shoal material act to straighten the ocean side of the previously
inward-flaired coast.

120. Conversely, the effects of an inlet on the sound shoreline may per-
sist for hundreds of years (see Kitty Hawk Inlet, for example, in Figure 11).
In the years after the inlet closes, the flood-tidal shoals may become islands,
or may weld to the adjacent sound shores and spread and become less pronounced
with time.

Capes and shoreline change

121. Cape influence is reflected in the behavior of adjacent ocean
beaches. It appears that changes in the east-facing ocean shoreline at least
14 km south of Cape Henry and 10 km north of Cape Hatteras are dominated by
the respective capes (Figures 28 and 31).

122. At Cape Henry the east-facing shoreline prograded while the nearby
north-facing shoreline retreated (Figure 44), a situation that will likely
continue into the future. The progradation could increase if additional arti-
ficial beach fill is placed on Virginia Beach. Some of the recently placed
fill material moved north and was deposited along the east-facing shoreline
(Figure 28).

123. The position of Cape Point at Cape Hatteras is highly variable

(Figure 41), and its year-to-year movements do not appear to be predictable.

102

In general, though, the longer trend term appears to be to the south and west,
as reflected in changes on the nearby shoreline (Figure 28). North of the
cape, the shoreline movement has been one of retreat to the west, with the
greatest westward retreat nearest the cape. West of the cape, the shoreline
has prograded; this movement has occurred for a long time and is referenced in
a large number of east-west-trending ridges. Future shoreline changes north
and west of Cape Hatteras will likely be similar to those that have occurred

in the past.

Shoreface-connected
ridges and shoreline change

124. Shoreface-connected ridges also appear to significantly influence
the ocean shoreline in the study area. These linear ridges with a maximum of
10-m relief extend up to 10 km offshore from the shoreface in a northeast
direction; side slopes are usually not more than a few degrees. Fields of
such ridges are common from Long Island to Florida (Swift et al. 1972). Loca-
tions of the four shoreface-connected ridges along the east-facing ocean in

the study area are shown in Figure 54 and listed in the tabulation below.

Name Latitude
False Cape Shoal SOe3on
Oregon Shoal Booze
Wimble Shoal Si) S18)
Kinekeet Shoal S523)

125. The ridges intersect the shoreface about 5 km south of some of the
most prominant concave seaward shorelines in the study area (Figure 55).
Except at inlets, these are the major sites along the east-facing ocean reach
where the shore orientation varies greatly. The shoreline at and south of the
ridge intersection is generally convex in a seaward direction. In all cases
the site of the intersection is along a reach where the shoreline is rapidly
changing from a northwesterly to a northerly direction.

126. Shoreline changes associated with the shoreface-connected ridges
are predictable. Shorelines north of ridge intersections retreated, while
those to the south usually prograded. One exception is south of Oregon Shoal
where the shoreline retreated, probably because of the influence of Oregon
Inlet. Shoreline changes adjacent to the ridge intersections appear to vary
with time in a relatively consistent manner. Data shown in Figures 30 and 31

suggest the ridge influence is moving south.

103

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105

PART VI: SUMMARY AND CONCLUSIONS

127. Shoreline change maps of the ocean and sound shorelines from west
of Cape Henry to west of Cape Hatteras were produced using historic NOS shore-
line maps. The accuracy of the shoreline change maps is estimated to be at
least within +10 m. Using a digitizing procedure, average shoreline change
rates were quantified for 2-km-long reaches of the study coast. Predicting
the magnitude of shoreline change rates for future years is difficult because
of undefined temporal changes in the processes which produce the changes.
Relative shoreline change rates, however, can be forecast with some confidence
in an alongshore direction; that is, the relative rates at adjacent shore
locations can be forecast based on relationships with geomorphic features at
or near the locations. The following characteristics of shoreline change in
the study area can be concluded from this study:

a. Shoreline change rates have varied greatly from one time period
to another (Tables 11, 12). Because of these variations and
the difficulties encountered in attempting to account for them,
accurate quantitative forecasts of the absolute magnitude of
shoreline change decades into the future are not possible using
data acquired in this study. However, very likely the general
erosional trend which existed between 1850 to 1980 will
continue.

b. Barrier spits and islands generally narrowed between about 1850
and 1980. This narrowing contrasts with geological evidence
that the barriers have migrated landward in the past thousands
of years. Island migration, in the classic sense, is ocean
shore retreat and simultaneous sound shore progradation; i.e.,
island movement toward the continental landmass. Island nar-
rowing in the 130-year study period may be a higher frequency
trend within the longer term trend of island migration which
occurs in association with sea level rise relative to land.

The barrier islands appear to be too wide (1980) to migrate as
the result of overwash processes. Overwash-transported beach
sands rarely reach the sound side of the islands.

lo

Island width (Figure 12) correlates well with two inlet systems
that existed before 1585 (geomorphic evidence) and inlets that
existed after 1585 (evidence in maps and charts).

{Qu

Inlets in the study area have tended to open and close in
specific regions, but not in the same places in these regions.
Because inlets often (but not always) caused the island to
widen after the inlet closed, the historic inlet area became
less susceptible as a site for a new inlet. But because the
hydraulic characteristics of the ocean and sound caused the
region to remain susceptible as a new inlet site, new inlets

io)

106

[Hs

tended to open near the sites of past inlets. Sites where
inlets existed in the past 400 years (see Figure 9) are
(1) Nags Head to Rodanthe and (2) Duck, North Carolina, to
the Virginia State line.

Oregon Inlet, the only unstructured inlet that has been open

in the study area for the entire study period, apparently af-
fected the ocean coastline at least 8 km north and probably

8 km south of its 1980 location (Figure 37). Shoreline changes
to the south were masked by the opening and closing of New
Inlet. Shore erosion decreased exponentially away from the
inlet (Figure 28). A rough calculation of ocean shoreline
losses and Pamlico Sound sand gains indicates that nearly all
the Atlantic Ocean sand lost from 8 km north and south of the
inlet was deposited in Pamlico Sound. This net movement of
sand in a westerly direction could, on a time scale of hundreds
or thousands of years, be a major factor in island migration.
Today, inlet processes are the major mechanism for moving lit-
toral sand in a westward direction. Wind is probably second in
importance.

Because of near-continuous southward migration of Oregon Inlet
(about 29 m/year), the amount of littoral sand trapped in the
flood-tidal shoals of Pamlico Sound appears to have been con-

stant through time (about 3 X 10° cu m/year (Figure 40)).

Evidence of inlets that closed before 1585, most notably at
Kitty Hawk, suggests the islands have not moved appreciably
(i.e., not more than one-fourth the island width) in at least
the past 400 years (Figure 12).

Capes affect adjacent beaches. In the past 130 years, the
east-facing beach south of Cape Henry accreted, while the east-
facing beach north of Cape Hatteras eroded (Figure 28). Con-
currently, the north-facing beach west of Cape Henry eroded

and the south-facing beach west of Cape Hatteras accreted. The
net change is a very slight clockwise rotation and southward
movement of the cape boundaries. The eastward progradation of
Cape Henry and the southward progradation of Cape Hatteras are
similar to longer term geologic changes in these areas as re-
flected in the orientation of beach ridges (Figures 2 and 7).
Erosion north of Cape Henry and north of Cape Hatteras does not
reflect past geologic changes; however, because these changes
have occurred for at least 130 years, they can be expected to
continue into the future.

A divergent alongshore transport nodal zone, identified using

shoreline change data, exists near latitude 36°41'. This ap-

pears to be the only site of net alongshore sediment transport
reversal along the east-facing ocean coast between Capes Henry
and Hatteras.

Overwash probably has not been a major factor in producing
changes in the sound shoreline. Most of the retreat in the
sounds away from inlet influences can be accounted for by
considering sea level rise on a gently sloping shore.

107

|B

Shoreface-connected ridges intersect the ocean coast at four
places. In each location, the shoreline north of the ridge
intersection retreated, while the shoreline prograded south of
the intersection. The ridge intersections are about 5 km south
of the most prominent concave shore reaches (Figure 55) away
from inlets. At and south of the ridge intersections, the
shoreline changes rapidly from a northwesterly to a northerly
orientation.

Characteristics of the shoreface-connected ridges are not
dependent upon the net alongshore sediment transport direction.
The False Cape Shoal is near a transport reversal; other ridges
are located in areas where the net transport is to the south.

108

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111

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