Effects of Inlet Migration on Barrier Island Planform and Oceanfront Change: New Topsail Inlet, N.C

EFFECTS OF INLET MIGRATION ON BARRIER ISLAND PLANFORM AND OCEANFRONT CHANGE: NEW TOPSAIL INLET, N.C.

Merritt Ross Willingham McLean

A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment of the Requirements for the Degree of Master of Science

Department of Geography and Geology

University of North Carolina Wilmington

2009

Approved by

Advisory Committee

Paul A. Thayer Michael S. Smith

William J. Cleary Chair

Accepted by

Dean, Graduate School This thesis has been prepared in a style and format

consistent with

The Journal of Coastal Research

TABLE OF CONTENTS

ABSTRACT ...... vi LIST OF TABLES ...... vii LIST OF FIGURES ...... viii INTRODUCTION ...... 1 Background ...... 2 Tidal Inlets ...... 2 Study Area ...... 3 Regional Geology ...... 7 Regional Tidal Inlets ...... 7 Sediment Bypassing ...... 8 Inlet Hazard Zones ...... 10 OBJECTIVES ...... 13 Inlet Migration ...... 13 Shoreline Change ...... 13 Ebb Delta: ...... 14 Bypassing Events ...... 14 Management and Inlet Hazard zones ...... 14 METHODS ...... 15 Rate of Change Database ...... 15 Channel Orientation and Barrier Morphology Database ...... 18 Ebb-Tidal Deltas ...... 19 Area and Volume ...... 19 RESULTS ...... 22 Total Inlet Migration ...... 22 Long-term Inlet Characteristics ...... 23 Short-term Inlet Changes ...... 31 Inlet Bypassing Cycles ...... 31 Inlet Migration Patterns ...... 33 Oceanfront Change ...... 37 Net Change 1938-2006 ...... 40

iii

Topsail Island ...... 40 Hutaff Island ...... 41 Net Change Intervals...... 41 Net Change 1938-1949 ...... 41 Hutaff Island ...... 42 Net Change 1949-1962 ...... 44 Topsail Island ...... 44 Hutaff Island ...... 46 Net Change 1962-1974 ...... 46 Topsail Island ...... 46 Hutaff Island ...... 48 Net Change 1974-1999 ...... 48 Topsail Island ...... 49 Hutaff Island ...... 49 Net Change 1999-2006 ...... 51 Topsail Island ...... 51 Hutaff Island ...... 53 Cumulative Shoreline Change ...... 53 Topsail Island ...... 54 Northern Shoreline Reach (T-1 through T-16) ...... 54 Southern Shoreline Reach ...... 54 1974-1999 ...... 58 1999-2006 ...... 63 Hutaff Island ...... 63 1938-1962 ...... 63 1962-2006 ...... 66 DISCUSSION ...... 73 Effects of Inlet Migration: ...... 74 Direction of Migration: ...... 74 Rate of Inlet Migration: ...... 78 Long-term Rates of Migration: ...... 78

Short-term Rates of Migration: ...... 79 Tidal Delta Changes:...... 86 Flood Tidal Delta ...... 86 Ebb Tidal Delta ...... 90 Oceanfront Shoreline Change ...... 100 Shoreline Change Intervals ...... 101 1938-1949 ...... 101 1949-1962 ...... 103 1962-1974 ...... 107 1974-1999 ...... 108 1974-1982 ...... 109 1982-1990 ...... 110 1990-1999 ...... 112 1999-2006 ...... 117 Future Changes and Implications...... 119 CONCLUSIONS...... 121 LITERATURE CITED ...... 124

ABSTRACT

New Topsail Inlet, located 40 km northeast of Wilmington, NC, separates Topsail Island, a developed barrier from Hutaff Island, an undeveloped barrier. Since the inlet opened in the late 1720’s the inlet has migrated ~11 km to the southwest. A GIS based analysis of 61 sets of historic aerial photographs (1938-2006) provided data on migration rates, the morphologic changes, the periodicity of ebb delta breaching events and oceanfront changes associated with migration.

Since 1938, New Topsail Inlet has migrated southwest at an average rate of 26 m/yr. Migration rates have varied from 95 m/yr (1945-49), to 11m/yr (1956-62). Four ebb delta-breaching events occurred between 1978 and 2007. During the largest event (1978-1986) the outer segment of the ebb channel was repositioned by 68º. Prior to channel reorientation, the inlet was migrating at 62 m/yr. Immediately prior to the breaching event, the ebb channel briefly reversed its direction of movement, migrating at 23m/yr to the northeast. Subsequent to shoal breaching, migration accelerated to 73 m/yr to the southwest due to the large volume of material by-passed to the updrift Topsail Beach shoulder.

As a consequence of the southwesterly migration and ebb channel deflection, the southern portion of Topsail Beach has been characterized by complex temporal and spatial oceanfront changes. Increased rates of accretion (34 m/yr) and erosion (-15 m/yr) were common. This is due in part to the development and movement of a large shoreline protrusion and in part to the truncation of the trailing shoreline as the inlet moves south. The shoreline bump, which develops when the inlet is oriented to the north, accretes rapidly as bypassed shoals weld to the updrift beach. However, when the channel switches, the large bump soon becomes an erosion hotspot. Both the shoreline bump and the erosion hotspots migrate with the inlet, leaving behind a beach with typical erosion rates.

LIST OF TABLES

Table 1. Summary of Inlet Bypassing Episodes ...... 34

Table 2. Summary of Yearly Migration Rates and Channel Orientation ...... 36

vii

LIST OF FIGURES

Figure 1. Location map of the study area...... 4

Figure 2. Map illustrating the migration pathway of New Topsail Inlet ...... 5

Figure 3. Map showing the current Inlet Hazard Areas...... 12

Figure 4. Map depicting the location of the transects ...... 17

Figure 5. Bathymetric maps of New Topsail Inlet ...... 21

Figure 6. Map showing historic island outlines of Topsail and Hutaff Islands...... 24

Figure 7. Line plot illustrating possible inverse relationship between ebb-tidal delta volume and channel orientation...... 27

Figure 8. Composite images show the bypassing episode from 1982 – 1987 ...... 32

Figure 9. Composite image illustrating the 4 bypassing episodes during the short-term study ... 35

Figure 10. Map illustrating the study area and the portion of Topsail Island that is zoned as an Inlet Hazard Area ...... 38

Figure 11. Line plot depicting cumulative channel migration from 1938 to 2006...... 39

Figure 12. Map illustrating historic shorelines and inlet positions during 1938 and 1949...... 43

Figure 13. Map depicting historic shorelines and inlet positions during 1949 and 1962 ...... 45

Figure 14. Map of the study area depicting historic shorelines and inlet positions from 1962 and 1974...... 47

Figure 15. Map of the study area, inlet positions and net oceanfront changes between 1974 and 1999...... 50

Figure 16. Image of the study area in 2006 ...... 52

Figure 17. Bar graph showing the total cumulative changes for the transects located in the northern shoreline reach...... 55

Figure 18a. Two line plots illustrate the movement of the shoreline between 1938 and 1974 .... 56

viii

Figure 18b. Two Line plots illustrate the shoreline movement of the southern transects ...... 57

Figure 19. Bar graph displaying the cumulative shoreline change experienced by transects in the southern shoreline reach from1974-1999 ...... 59

Figure 20. Line plot illustrating shoreline movement over the southern shoreline reach during the period between 1974 and 1982 ...... 60

Figure 21.Two line plots display the movement of the shoreline across transects in the southern shoreline reach from 1982-1990 ...... 61

Figure 22. Two line plots illustrating changes in the shoreline during the mini period from 1990- 1999...... 62

Figure 23. Bar graph showing the cumulative change data for transects 18-27 for the time period between 1999 and 2006...... 64

Figure 24. Two line plots show the various positions of the oceanfront shoreline during the period 1999-2006...... 65

Figure 25. Bar graph displaying cumulative shoreline loss across all transects within the Hutaff shoreline reach from 1938-1962 ...... 67

Figure 26. Bar graphs showing cumulative shoreline change data on Hutaff Island for all other time periods between 1962 and 2006 ...... 68

Figure 27. Line plot illustrating shoreline position change on Hutaff Island between 1938 and 1982 for transects 30-31...... 69

Figure 28. Line plot showing the movement of the shoreline across transects 32-34 on Hutaff Island for the time period 1982-1990 ...... 70

Figure 29. Line plot displaying shoreline position for transects 34 and 35 on Hutaff between late 1990 and 1999 ...... 71

Figure 30. Line plot shows shoreline change for transects 35 and 36 for the time interval 1999- 2006...... 72

Figure 31. Images serve as photographic documentation of re-curved dune ridges on the southern portion of Topsail Island ...... 76

Figure 32. Composite image illustrating changes to the inlet’s morphology incurred over the course of the study ...... 80

Figure 33. Composite image showing the movement of the flood ramp (illustrated by the orange triangles) from 1962 to 1974. During this period, ...... 81

Figure 34. Composite image showing the completed migration ...... 82

Figure 35. Composite image showing the final position of the flood ramp ...... 83

Figure 36. Bar and line graph that illustrates the connection between channel migration and the orientation of the ebb channel ...... 85

Figure 37. Line plots illustrate the inverse relationship between inlet minimum width and migration rate...... 87

Figure 38. Line plots for the inlet’s minimum width and the acreage of the ebb delta ...... 93

Figure 39. A) Line plots illustrate the inverse relationship between the overall slowing migration of the inlet and the increase in ebb delta siz ...... 94

Figure 40. Map of the study area illustrating the ideal ebb delta and channel configuration for accelerated shoreline advancement on Hutaff Island...... 96

Figure 41. Map of the study area showing positions of the ebb delta and channel orientation prior to the large protrusion build out on Hutaff Island...... 98

Figure 42. Map of the study area showing the ebb delta configuration subsequent to the configuration favored for shoreline advancement on Lea/ Hutaff...... 99

Figure 43. Composite image illustrates changes to the Hutaff Island planform incurred due to inlet migration ...... 116

INTRODUCTION

During the past several decades, all coastal communities in North Carolina have become important tourist destinations that have experienced rapid growth and increased land values. The single most important variable affecting development is the presence of a wide oceanfront beach.

Most of these developed shorelines are situated within chronic erosion zones and the greatest hazards are associated with contemporary inlets. All developed barrier island oceanfronts experiencing problems related to inlet-induced erosion, have erosion rates10-15 times the average annual erosion of the mid-barrier oceanfront segments. During the past two decades,

80% of the insurance claims for erosion threatened buildings were related to erosion along inlet shorelines. Currently many additional structures are threatened. As a result, inlets have drawn the attention of coastal managers as communities continue to develop and attempt to mitigate land loss within these erosion hot spots.

The designation of inlets as areas of environmental concern necessitates special consideration. Coastal regulators have recognized detailed site-specific studies are needed to effectively manage areas influenced by inlets. Currently the N.C. Division of Coastal

Management is attempting to redefine the areas falling within inlet hazard zones. However, the lack of a sufficient database and an under-developed appreciation of the processes that determine the short and long-term changes of the associated oceanfront shorelines have limited re-zoning procedures. The intent of this paper is to present the effects New Topsail Inlet exhibits on its adjacent barrier islands, and how the inlets movement plays a role in the shoreline change on both islands. Background

Tidal Inlets

Tidal inlet systems are breaks in the shoreline, which provide a connection between the ocean and the back barrier bays, marshes, lagoons and tidal creek systems. In addition to flushing out these areas, tidal inlets play a major role in the sediment budget, retaining large volumes of sand impounded from the littoral system. Inlets also control the erosion and accretion patterns over extensive shoreline stretches. Various factors such as, throat size, ebb shoal geometry, bypassing events, and migration habit contribute to the length of an inlets influence, however the width of influence is typically many times the current dimension of the specific inlet (SEABERGH and KRAUS, 2003; FENSTER and DOLAN, 1996; BRUUN, 1990,1996).

The main features associated with tidal inlets are, tidal deltas and recurved spit-inlet-fill sequences related to inlet migration (HAYES, 1980). HAYES (1980) proposed the following terms for tidal deltas: ebb-tidal delta (seaward shoal) and flood tidal delta (landward shoal). Each of these deltas is composed of a series of morphologic features. Common features of a typical ebb tidal delta include a main ebb channel, flanked on either side by channel-margin linear bars, a large broad sheet of sand called the swash platform, large swash bars formed by breaking and shoaling waves and a large, steep, seaward slope called the terminal lobe. Depending on the location on the ebb channel, the inlet system may have one or more marginal flood channels. The morphology of the ebb tidal delta is a function of local tidal regime and wave energy.

Less than one percent of North Carolina’s shoreline is currently occupied by inlets; however, inlets have had a significant influence in the shaping of the current shoreline. 13 of the

2 inlets found within North Carolina’s shoreline are located in Onslow Bay. During the past 200 years these inlets have influenced 65% of the barrier shorelines within the bay and up to 100% of some shoreline stretches. The 13 inlets found within Onslow Bay are a mixed group of stable and migrating inlet systems (CLEARY, 1996). Eight of these inlets border developed shorelines, six of which have been somewhat modified. Generally, stable inlet systems occur in the regressive shorelines of the northern bay while migrating systems are found within the transgressive barrier segment.

Study Area

Topsail Beach is the southernmost town of three communities located along Topsail

Island in Pender County N.C. The town is located updrift (NE) of New Topsail Inlet, which is located 70 km north of Cape Fear and 40 km northeast of Wilmington (Figure 1). The inlet separates developed Topsail Island from undeveloped Hutaff Island. During the early 1990’s, the

2 inlet was approximately 400 m wide and had a cross-sectional area of 675 m (CLEARY, 1994), currently the inlet is 700m wide and has an unknown cross sectional area.

New Topsail Inlet has historically influenced the morphology and sedimentology of this coastal segment through a long history of migration (Figure 2). After opening just south of Sloop

Point in the late 1720’s, the inlet has migrated nearly 11km in a southwesterly direction

(CLEARY, 1994). Recent migration has occurred at rates of nearly 30 m/yr, migrating approximately 1.6 km between 1938 and 2006. Previous inlet migration is evidenced

Figure 1. Location map of the study area. Red boxes on image inlays indicate position of blown up study area. Base image from PENDER COUNTY GIS DEPT (2006).

Figure 2. Map illustrating the migration pathway of New Topsail Inlet, several historic inlet positions are shown. Inlet migration evidenced by long back barrier channel (Banks Channel) and the presence of several strings of marsh islands. Base image from PENDER COUNTY GIS DEPT (2006), 1849-1873 shoreline from NCDCM (2006).

5 within the back barrier by a long (10km) channel (Banks Channel) paralleling the landward side of the island (Figure 2). Accompanying this feature are a series of narrow marsh islands, built from previous flood tidal deltas as storm waves and flood currents reworked the sediments

(CLEARY et al., 1996). The hydrography of the inlet was modified in the 1930s with the dredging of the Atlantic Intracoastal Waterway (AIWW) and the associated channel that connects the estuary and the inlet (CLEARY et al.,2003).

New Topsail Inlet lies in a mixed energy setting with a mean tidal range of 0.91 m and an average wave height of 0.73 m (CLEARY, 1994). The island is oriented northeast to southwest, exposing the inlet to waves propagating from these directions. According to a US Army Corps of

Engineers study (1989) the dominant direction of wave approach is from the south-southwest, accounting for over half the annual wave energy. Based on these data it was assumed that the dominant direction of sediment transport was northward. It was estimated by the US Army Corps of Engineers that 55 % of the 500,000 m3/yr gross rate of sediment transport moves in a northerly direction across the inlet (CLEARY, 1994.; JARRETT, 1976).

Due to the migration of New Topsail Inlet and the periodic ebb-tidal breaching events, its ebb-tidal delta rarely conforms to the previously discussed standardized models. It is common for the outer portion of the ebb channel to be oriented at varying angles to adjacent barrier islands. The deflection and reorientation of the ebb channel plays a significant role in shoreline change along adjacent barriers. Due to the breakwater effect of the ebb-tidal delta, slight changes in its morphology can affect adjacent oceanfront shoreline changes.

Regional Geology

The barrier islands of Onslow Bay are situated in the southeastern part of the North

Carolina coastal zone, causing the majority of shoreline features to be controlled by the pre-

Holocene stratigraphic framework of the shore-face (RIGGS, CLEARY and SNYDER, 1996).

Tertiary and Cretaceous stratigraphic units characterize the shore-face stretch between

Cape Lookout and Cape Fear. These units, along with interlaying Quaternary sediments form a platform that many of the barriers are built upon. The underlying stratigraphy controls the morphology of the shore-face while influencing sediment composition and fluxes as well as modern beach dynamics (RIGGS, CLEARY and SNYDER, 1996). The perched barriers are composed of thin assorted layers in which surficial beach sands top older eroding stratigraphic units such as unconsolidated sands and muds, compacted muds, limestones, and sandstones. The composition of individual barriers as well as the underlying geology also affects the position of regional inlets and their ability to migrate.

Regional Tidal Inlets

Historically, the area south of Topsail Island has been influenced by several inlets. Maps and charts from the 1880’s show three inlets occupying areas of what is now Hutaff Island. The inlets responsible for modifying the shoreface of this area where: Old Inlet, Old Topsail Inlet, and Sidbury Inlet. An 1880 T-sheet survey map placed Old Inlet 1 km northeast of Old Topsail

Inlet’s location at that time. Old Inlet has not been recorded on any maps or viewed in any aerials

7 since the 1880’s; its previous location is now an area that is being modified by New Topsail

Inlet’s southwestern shoulder.

Old Topsail Inlet, the most prominent of the three historic inlets, previously separated

Hutaff Island into two smaller islands, Lea Island to the northeast and Coke Island to the southwest. Similar to many inlets in the region, Old Topsail inlet was migratory, moving 1.3 km to the southwest between 1938 and 1998 (MCGINNIS, 2004). The inlet continually reduced in size during this time, eventually closing between September 1997 and June 1998.

Historically, Sidbury Inlet has shown a transient nature. The small inlet was located 2.1 km northeast of Rich Inlet and has been recorded four times. The inlet is shown on T- sheets from 1857 and 1880, and has also been recorded more recently opening from1909 - 1925 and from 1959 – 1962 (GAMMILL, 1990).

A study by MCGINNIS (2004) showed that between 1938 and 2002, variations in inlet position at Rich and Sidbury Inlets, and the migration of Old Topsail Inlet suggested that 35 % of

Hutaff Island, in 2002, would have been underlain by inlet fill. In addition to this data, identification of previous inlet features, such as marsh islands, coupled with recorded locations on T-sheets suggest that the entire Hutaff Island shoreline, in 2002, was underlain by inlet fill.

Sediment Bypassing

Inlet sediment bypassing is the process by which sediment moves from one side of the inlet to the other. Generally, the direction of movement is from the updrift to the down drift side of the inlet throat (FITZGERALD et al., 2001). BRUUN and GERRITSEN (1959) who originally

8 described this process identified two primary modes of transport: 1) bar bypassing- sand bypasses inlets by wave action, moving around the inlet, along the terminal lobe; and 2) tidal bypassing- sediment is transported into the channels during a flood current and subsequently moves seaward through the channel system during ebb flow conditions.

Since BRUUN and GERRITSEN’S (1959) pioneering work, a number of additional models of natural bypassing have been proposed by FITZGERALD et al., (2001) that pertain to the study area include: ebb delta breaching, outer channel shifting and spit platform breaching.

Ebb-delta breaching occurs at inlets with stable throat positions (FITZGERALD et al., 2001;

FITZGERALD and PENDLETON, 2002). At these inlets, longshore transport produces sediment accumulation on the updrift margin, promoting the deflection of the main channel. In time, breaching of the ebb shoals leads to a realignment of the ebb channel and subsequent bypassing of large quantities of sediment to the down drift shoulder (KOMAR and INMAN, 1970; GAUDIANO and KANA, 2001.).

The second model that pertains to the conditions at New Topsail Inlet involves the shifting of the outer ebb channel that initiates a bypassing episode similar to ebb tidal delta breaching but is limited to the extreme seaward position of the ebb channel. The main portion of the ebb channel remains in a fixed position while the outer channel is deflected in a down drift direction. As in the ebb tidal-delta breaching model, the channel will realign along a new path with time and the cycle begins anew.

The third model applicable to the study area involves spit platform breaching. This type of bypassing commonly occurs at migrating inlets where the updrift spit is fronted by a large intertidal platform (FITZGERALD et al., 2001). Large quantities of sand are bypassed when a new

9 channel breaches the protruding platform leading to down drift bypassing of the segmented shoal.

An extensive analysis of aerial photographs indicates sediment bypassing at New Topsail

Inlet is complex and differs from the aforementioned models. In addition to wave related transport of sediment around the periphery of the shoals, ebb delta breaching and outer channel deflection are the principal mechanisms of bar bypassing. Spit platform breaching is rare and only occurs during large storm events. Examination of several photographic sets indicates ebb delta breaching and channel deflection events can lead to either updrift or down drift bypassing as the inlet migrates along its pathway. Changes along the adjacent oceanfront shorelines sometimes occur quite rapidly whereas others are slow and lag relative to the movement of the inlet. Morphologic planform changes occur at varying distances from the main inlet channel and are directly connected to the alignment of the ebb channel.

Inlet Hazard Zones

According to the N.C. Division of Coastal Management Handbook (2003), inlet hazard zones cover ranges from 75 m for stable inlets, to 1.3 km for migrating inlets. Studies of nearby

New River Inlet and Rich Inlet (Cleary, 2002., CLEARY et al., 2003, and CLEARY et al., 2004) indicate that the shoreline change patterns related to the respective inlets can extend 2-3.5 km along the adjacent shorelines. A study of the mixed energy barrier islands of Virginia (FENSTER and DOLAN 1996) suggested that the zone of inlet influence could extend for as much as 6.8 km along the bordering barrier shorelines. The data from the above-mentioned investigations clearly point to the fact each inlet has unique site-specific characteristics that are important in the

10 determination of the inlet hazard zone. Important parameters include the size of the inlet, its migration habit, the ebb channel’s alignment history, the associated shape changes of the ebb- tidal delta and the local wave climate (FITZGERALD et al., 1983). Figure 3 shows the current inlet hazard zone for New Topsail Inlet, which is approximately 825m long (NCDCM, 2006), and encompasses a small portion of the inlet’s zone of influence.

Figure 3. Map showing the current Inlet Hazard Areas. Image illustrates the extent of the study area and current inlet hazard zones. Base image from PENDER COUNTY GIS DEPT(2006), inlet hazard area shapefile from NCDCM (2006).

OBJECTIVES

The primary objective of this study is to examine the long-term effects of inlet migration on adjacent barrier island morphology. This issue has been addressed through the development of a robust data set consisting of spatial and temporal shoreline changes as well as changes in inlet components responsible for oceanfront change. The main objective has been supported with a suite of sub-objectives that aid in the understanding of the migrating inlet system and subsequent shoreline change. These sub-objectives have been broken into five sections: inlet migration, shoreline change, ebb delta, bypassing events, and management and inlet hazard zones.

Inlet Migration:

Determine length of total inlet migration.

Determine migration rates since the advent of aerial photography (1938).

Find out if current migration rates are consistent with previous time periods.

Reveal how varying migration rates affect the shoreline.

Shoreline Change:

Determine long-term shoreline change rates.

Determine short-term changes in shoreline position with respect to inlet behavior.

Determine change in shoreline morphology with respect to inlet behavior.

Ebb Delta:

Determine how the position, size and shape of the ebb delta affect erosion and accretion

patterns along the shoreline.

How do ebb-tidal breaching events affect the shorelines morphology?

Determine periods for the various cycles of ebb-tidal delta symmetry changes.

Bypassing Events:

Determine how frequently large-scale bar bypassing events occur.

Determine the change in shoreline morphology due to shoal welding events.

What is the related time frame for the attendant shoreline change to occur?

Management and Inlet Hazard zones:

Determine the length of inlet influence on the updrift and down drift shorelines.

Find out how the zone of inlet influence changes with channel deflection, re-orientation

of the ebb channel, welding of large swash bars and ebb delta symmetry.

Is the current delineation of the inlet hazard zone appropriate for Topsail Beach?

METHODS

The investigation relied primarily on data derived from a large photogrammetric database. Vertical aerial photographs were used to track changes in inlet position, inlet shoulder positions, inlet width, ebb channel orientation, and ebb delta position. The photographs were also used to observe bypassing cycles and determine migration history, migration rate, and shoreline change rates. Two databases were developed through the rectification and digitization of the aerial photos, one to monitor shoreline change, and the other to monitor inlet processes.

Rate of Change Database

Seventeen sets of historical aerial photographs from 1938-2006 were used to compile the

GIS database. Photos were obtained from the USACE Wilmington District, NCDCM, the

UNCW coastal geology laboratory and Coastal Planning and Engineering. The images were scanned between 300 and 600 dpi (yielding approximately 3ft./pixel) using an Epson Perfection

1650 scanner and exported as uncompressed TIFF files. Simple rectification of the photographic sets was completed using ERDAS ARC GIS 9.1 software, geo-referencing to a base layer of

2002 digital orthophotos. The photos were rectified in the North Carolina State Plane 1983 coordinate system using between 8 and 15 ground control points per photograph. The variation in number of ground control points was due to the lack of identifiable features in photos prior to the island development. The target root-mean-square (RMSE) value remained below 3 yielding less than 10 ft. of error.

After rectification, the photos were imported into ArcView 3.1 for analysis. Once in

ArcView, shorelines were traced and digitized, using the high-water line (HWL) as the primary shoreline indicator (DOLAN et al., 1980; Moore, 2000; PAJAK and LEATHERMAN, 2002). This feature is often used to digitize shoreline positions due to its ease of recognition on historical aerial photographs (CROWELL et al., 1991). The use of the HWL as an indicator has several inherent sources of error including photographic quality, digitizing techniques and operator error.

CROWELL et al. (1991) determined worst-case error estimates for rectified aerial photos at ~ 25 ft, including distortion of photos, error in the delineation of the HWL from good quality photos, digitizer error, and digitizer-operator error in the calculations (ANDERS and BYRNES, 1991).

Shoreline change rates were determined by positional comparison of historical high water lines. Measurements were taken with the use of an offshore baseline, which paralleled the coast and had 41 shore normal transects spaced 152.4 m (500 ft) apart attached to it (Figure 4) The

SCARPS! (Simple Change Analysis of Retreating and Prograding Systems) extension of

ArcView, created by C.W. JACKSON (2004), was used to collect shoreline change data along each transect. SCARPS! generates several different shoreline change rates commonly used by the state and local government, including, end point rate (EPR), linear regression rate (LRR), and average of end point rates (AER). For a summary of various shoreline change methods please refer to DOLAN et al., 1991.

Figure 4. Map depicting the location of the transects used in the SCARPS! shoreline change data analysis.

For this study it was determined that EPR was the easiest and most effective way of measuring both long-term and short-term shoreline change. As the primary disadvantage of using EPR is the loss of data between the endpoint shorelines, cumulative shoreline change rates were also calculated. This improved the ability to recognize important shoreline change patterns and trends as well as beach nourishment projects on Topsail Beach.

In addition to shoreline change data, the photo sets were subjected to several other measurements including minimum width, channel migration rate and inlet shoulder migration rate. Inlet minimum width was measured using the measurement tool in ArcView where as the other two measurements were completed though the construction of another baseline, which crossed the inlet perpendicular to the inlet channel. The base line was constructed as an extension of the adjacent islands centerlines. Ebb channel migration, or inlet migration was completed using digitized ebb channels, starting with the earliest channel (1938) as the zero point.

Migration was noted as the distance along the baseline, between the zero point and the channel being measured. Distances between individual ebb channels were also recorded to determine variations in migration rate. The same process was completed for the inlet shoulders.

Channel Orientation and Barrier Morphology Database

In addition to the 16 sets of photographs used for shoreline change analysis, 45 more sets of photographs were used in the observation of inlet processes. These photos were examined at

¼ year, ½ yr and 1 yr intervals over a twenty-two year period (1982 -2003). The photos were selected based on availability, quality and amount of change occurring since the prior image set.

All of the air photos used to compile the database were subjected to the same processing steps described for the shoreline change analysis photo sets.

These images were primarily used to calculate short-term shoreline change rates and observe the temporal scale of the inlet’s cyclic bypassing and bar welding events. This was completed through the digitization of the ebb channels and input into the GIS for analysis.

Channel orientations were calculated using SCARPS! with output as azimuth values.

Ebb-Tidal Deltas

Ebb-tidal deltas were hand digitized using the breaker line as a guide for the seaward portion of the ArcGIS polygon. The interior portion of the ebb-tidal deltas were digitized along the High Water Line (HWL) and then brought to a baseline inside the inlet, which acted as the landward cutoff of the delta. While this is an unorthodox definition of the ebb tidal delta, it provided constancy in the computation of the ebb delta footprint.

Area and Volume

The area of the polygon was then calculated using the ArcGIS extension X-tools. The extension output yields the area in a number of measurements including square yards, square meters and acres. X-tools also calculates the perimeter of the polygon based on the measurement selected.

Estimated volumes were calculated based on a conversion factor developed by Coastal

Planning and Engineering (Pers. Com. JARRETT, 2008). The conversion factor is simply:

The Approximate Ebb Delta Volume was calculated by CPE using fathometer data collected in 2007. The data was entered into MATLAB and the difference between two sets of bathymetry was calculated (Figure 5). Based on surface estimates in MATLAB, the ebb shoal volume was approximately 5,454,031 cubic yards (Pers. Com. DAY, 2008). Therefore:

The approximate volumes of historic ebb-tidal deltas were calculated by multiplying the area of the ebb-tidal delta by 4.27 yards. In order to maintain consistency, cubic yards were converted to cubic meters.

Figure 5. Bathymetric maps of New Topsail Inlet. The purple line marks the area used for calculating ebb delta volume. The white lines indicate the location of a CPE sand resource area. (A) Shows bathymetry of New Topsail Inlet with current ebb-tidal delta, (B) Show bathymetry of the same area with the ebb- tidal delta removed.

RESULTS

The results of this study are presented in two separate parts, a long-term study from 1938-

2006 and a short-term study from 1982-2006. The long-term study consists of 17 photo sets, which exhibit long-term traits and patterns. The image sets in this study are spaced sporadically and depend on availability. The long-term study focuses on both inlet change and shoreline change; however, it was primarily used to calculate shoreline change rates. The short-term study consists of 44 photo sets and mainly focused on short-term inlet changes. The photo sets cover changes in time periods ranging from 4 months to 1 year, sufficient for in depth analysis of inlet change patterns.

Total Inlet Migration

From the opening of New Topsail Inlet during the late 1720’s until the completion of the study period in 2003 the inlet migrated a total distance of 11.5 km. The average migration rate over the inlet’s lifespan was 41.8 m/yr. It is likely this migration occurred in several stages of varying migration rates; however, this data covering the time period from the 1720’s to 1849 have not been analyzed in any detail.

The earliest data incorporated in this section of the study is a shoreline which was mapped from 1849-1873 (NCDCM, 2007). From 1849-1873 until the advent of aerial photography (1938) New Topsail Inlet migrated 2.27km to the southwest yielding an average migration rate between 25.5 m/yr and 34.9 m/yr (Figure 2). From 1938 through 2006 (the detailed study period) the inlet migrated 1.66 km at an average rate of 25.5 m/yr. These data

22 produce a total migration distance of 3.93 km over a period of 130 to 153 years and yield a migration rate between 25.5 m/yr to 30.2 m/yr (Figure 6).

The migration distance and migration rate during the study period (1938-2003) were calculated using 17 inlet positions. The migration rate during each of these eras varied considerably ranging from a low of 1.1 m/yr. to a high of 73.7 m/yr.

Long-term Inlet Characteristics

During the base year of 1938, New Topsail Inlet had a minimum width of 398 m. The main ebb channel had a shore normal orientation of 148.9º and was located in the southern portion of the inlet, directly adjacent to Hutaff Island. The resulting ebb-tidal delta occupied

191.4 acres and contained approximately 3,029,110 m3. The ebb shoal was positioned almost directly in front of the inlet corridor.

In the 6.58 years between the 1938 and 1945 photograph sets, the main ebb channel of

New Topsail Inlet migrated 111.6 m to the northeast. The northward trend was also followed by the inlet’s northern shoulder eroding 114 m; however, the southern shoulder of the inlet also eroded 140 m, producing a significantly wider inlet corridor with a minimum width of 548.1 m.

Although still in a shore normal orientation, the main ebb channel has reoriented itself to an azimuth of 129.8º, with the outer portions of the channel in a more central location within the inlet corridor. Because of channel orientation, the ebb tidal delta had an elongated shape, with the majority of the sediment north of the inlet’s centerline. Although the minimum width increased by 150 m, the area occupied by the ebb-tidal delta only increased by 1.5 acres.

Figure 6. Map showing historic island outlines of Topsail and Hutaff Islands. Note how the morphology of the islands has changed through time. Base image from PENDER COUNTY GIS DEPT (2006).

From 1945 to 1949, New Topsail Inlet reversed direction and migrated 346 m to the south at an average rate of 73 m/yr, the highest rate of movement during the study period. The southern inlet shoulder eroded 116 m while the northern shoulder accreted 78 m, primarily the result of a bypassing cycle taking place during this time. The main ebb channel has moved directly adjacent to Hutaff Island and is in a near shore parallel position with the southern island.

As a result of the bypassing episode and the alignment of the main ebb channel, the inlet’s minimum width increased to 564 m and the ebb-tidal delta stretched into a flat, elongated shoal protecting 1065 m of the Hutaff shoreline. The elongated shape of the ebb-tidal delta also caused its area and volume to increase dramatically. The ebb shoal covered 225.58 acres and had an approximate volume of 3,568,790 m3.

From 1949 to 1956 (6.3 years) the main inlet channel migrated 19 m to the southwest at an average rate of 3 m/yr. The slow rate of migration may have been the result of a large bypassing event initiated by the jump in channel position during 1949. Although the main ebb channel has barely moved, the inlet shoulders both changed dramatically. The northern inlet shoulder accreted at 40.3 m/yr and developed a large spit protruding into the interior portion of the inlet throat. While the northern shoulder accreted, the southern shoulder eroded a rate of 32 m/yr for a total of 207 m of net erosion. Although both inlet shoulders have responded in a similar fashion, the inlet’s minimum width has decreased from 564 m to 324 m, a result of the formation of the spit. The exterior portion of the main ebb channel has reoriented itself to a more central location and exited the shoal at 144º. Because of channel realignment, decreased inlet minimum width and the previous bypassing episode, the ebb-tidal delta decreased in both area and volume, covering 151.5 acres and containing 2,397,900 m3 of sediment.

Over the next 3.5 years, the main ebb channel migrated 49 m to the southwest along the inlet baseline; however the exterior portion of the channel deflected to a position further south than in 1956, exiting the main ebb shoal at a more northern orientation of 137º. Although there was 124 m of accretion on the northern shoulder, this was primarily a result of the erosion of the spit and the repositioning of the sediment contained within. The erosion of the spit also led to a

150 m increase in the inlet’s minimum width. The new channel orientation and increase in inlet width may have caused an increase in the size of the ebb delta shoal (Figure 7). The shoal covered an area of 220.28 acres and had an approximate volume of 3,485,035 m3.

Between 1959 and 1962 there was very little movement of the interior portion of the main inlet channel, however, buildup of the ebb-tidal delta caused the outer portion of the channel to shift northward and exit the ebb shoal at 145º. Even though the main ebb channel only migrated 2.9 m (a measurement within the margin of error), the southern inlet shoulder eroded

155 m due to the formation of a marginal flood channel. The channel likely served as an exit point for the main ebb channel, and was the beginning of a large bypassing event. The orientation of the main ebb channel and previous welding of ebb shoal swash bars caused a reduction in the size of the ebb-tidal delta, which occupied 209.7 acres and had an approximate volume of 3,318,790 m3.

Unfortunately, due to the lack of available aerial photographs, the next observation period was quite large and little interpretation can be done for the 11.6 years. Between 1962 and 1974

Figure 7. Line plot illustrating possible inverse relationship between ebb-tidal delta volume and channel orientation. Correlation between the two first starts in 1962 after the inlet recovered from several large storms destroying the ebb shoal and the outer portion of the inlet channel was deflected to the north.

27 the main ebb channel migrated 569 m to the southwest at an average rate of 49 m/yr. Both the northern and southern inlet shoulders responded accordingly. The northern shoulder accreted 391 m and the southern shoulder eroded 267 m. The inlet’s minimum width reduced 22 m to 367 m.

The main ebb channel was oriented in a near shore perpendicular position, exiting the ebb shoal at 174º. The ebb delta volume has decreased to 3,162,230 m3.

Between 1974 and 1978, the main inlet channel migrated 111 m at a rate of 31.4 m/yr.

The inlet channel was pressed against Hutaff Island and maintained a shore perpendicular orientation. The channel exited the ebb shoal at 180º. The northern inlet shoulder accreted at 20 m/yr, building 73 m of beach, where as the southern inlet shoulder eroded nearly 100 m. The position of the channel near Hutaff Island caused the formation of a large protrusion on the northern end of the island (discussed further in shoreline change section of results). A bypassing event occurred during the period between photographs and formed a small spit on the southern end of Topsail Island. The orientation of the channel has further reduced the volume of the ebb shoal to 3,126,525 m3.

From 1978 to 1982, the main inlet channel migrated 200 m with the inlet’s northern shoulder accreting 228 m at a rate of 58 m/yr. Meanwhile, the south shoulder eroded 168 m at a rate of 43.2 m/yr. The inlet’s minimum width increased by 10 m to 388 m. The main inlet channel remained pressed against Hutaff Island, with the exterior portion of the channel moving to a more northerly orientation of 173.1º. The position of the main ebb channel caused continual growth of the shoreline bump on Hutaff Island, directly south of the inlet corridor. The reorientation of the inlet channel has caused the ebb tidal delta to increase in volume by 506,090 m3 and to occupy an area of 229.6 acres.

During the 6.6 years between the 1982 and 1989 photographic sets, the inlet migrated 204 m at a rate of 30 m/yr. The northern inlet shoulder trailed behind at a rate of 16 m/yr while the southern shoulder eroded at an accelerated rate of 33 m/yr. The varying rates of migration as well as other factors such as increased water flow, lead to an increase in minimum width by 217 m to a new width of 605 m. The main ebb channel remained pressed against Hutaff Island, however, the outer portion of the channel continued its movement to the north and was oriented at 168.2º. As shown in Figure 7, the ebb tidal delta increased in area and had a volume of approximately 3,801,936 m3.

From 1989 to 1993, New Topsail Inlet migrated 132 m at a rate of 26 m/yr. Both inlet shoulders migrated at slightly faster rates, the northern shoulder accreted at 30 m/yr and the southern inlet shoulder eroded at 36 m/yr. The inlet’s minimum width has decreased to 489 m due to the new shape of the inlet complex. The most dramatic change within the inlet complex was the change in path and location of the main inlet channel. The channel has started flowing in a “C” shape and exited at a very northern orientation of 126.7º. Because of the new channel position, a large channel margin linear bar has formed on the southern side of the main inlet channel. The orientation of the channel has also affected the inlet complex in two ways. 1) The ebb tidal delta increased in size, occupying 291.4 acres and contained approximately 4,610,650 m3 of sediment. 2) The orientation and position of the ebb channel orientation caused the buildup of a large shoreline bump on the southern end of Topsail Island.

Between 1993 and 1999, the main inlet channel migrated 128 m at a rate of 24 m/yr, both the northern and southern shoulders migrated at similar rates of 20 m/yr and 23 m/yr respectively. The inlet’s minimum width increased by 154 m due to the repositioning of sand along the southern end of Topsail Island; the minimum width during 1999 was 643 m. It is likely

29 a bypassing event took place during the time between photographic sets. This was evidenced by a small spit building up on the southern end of Topsail Island and by the relocation and reorientation of the main ebb channel. The exterior portion of the channel moved 465 m to the south and exited at an orientation of 148.6º. As a possible result of the new orientation, the ebb tidal delta volume decreased to 4,552,300 m3.

From 1999 to 2003, the main inlet channel migrated a total of 16 m; however, the inlet shoulders behaved very differently. The northern inlet shoulder accreted 174 m as a result of welding swash bars and spit development. The southern inlet shoulder eroded 99 m in its continual march to the southwest. The inlet’s minimum width has decreased slightly to 614 m.

The main inlet channel has maintained its now characteristic “C” shape although there was a slight linear bar breach during 2002. The exterior portion of the channel exits at the breach site and has an orientation of 131º. It is important to note this orientation caused the channel to exit the inlet corridor pressed against the southern end of Topsail Island and resulted in the buildup of a large shoreline protuberance. The shoreline bump is likely due to the accretion of sand that would otherwise be trapped in the ebb tidal delta. The ebb tidal delta increased in size and occupied 338.5 acres while containing 5,355,935 m3 of sediment.

From 2003 to 2006, the main inlet channel migrated 87 m at a rate of 21 m/yr. The main inlet channel has reoriented itself to a more southerly position of 147.5º. Despite this reorientation, the inlet complex has maintained its “C” shape. The new position of the inlet channel has caused a smoothing of the shoreline on Topsail Island, causing the shoreline bump to be reworked. The channel’s new position has also allowed a large spit or accreting swash bar to form off the southern tip of Topsail Island. The inlet’s minimum width has increased to 701 m, possibly due to the widening planform of Topsail Island. The ebb tidal delta’s volume reduced to

4,172,880 m3, possibly due to large welding events and the repositioning of the main inlet channel.

Short-term Inlet Changes

This section of the study was used to identify trends within the inlet complex that may have been identified during the long-term study, but could not be expanded upon due to the time gap in the data sets. The following presents results on sand bypassing, migration trends, erosion and accretion rates of the inlet shoulders (tied into bypassing events), and how channel orientation, ebb delta volume and migration rate are all interrelated.

Inlet Bypassing Cycles

During the period covered by the short-term portion of the study (April 1982 – October

2003), New Topsail Inlet was subject to 4 sand bypassing\ channel re-orientation periods. Of the

4 bypassing events, only one completed a full cycle. The completed cycle likely began in 1978

(out of the scope of the intensive study period), and reached completion in early 1987. The main inlet channel started at a position of 180.6°, and slowly re-oriented itself to a terminal position of

106.1°, experiencing 74° of change through the cycle. Figure 8 shows the channel orientations throughout 1978-1987. The change in orientation was accompanied by change in ebb delta position and size, as well as the full development of the channel linear bars.

Figure 8. Composite images show the bypassing episode from 1982 – 1987. Blue shapes highlight changing orientation of shoals; the black dotted line illustrates the outer extent of the ebb tidal delta. The highlighted shorelines and channels correspond to the dates of the pictures.

During the cycle, the main inlet channel migrated 153 m to the southwest. However, the migration did not occur in a constant rate or direction. The channel migrated to the south from

1982-1984, then switched, migrating north during 1985-1986, and finally switched back to a southwesterly direction in 1987. The yearly migration rates ranged from -24 m/yr to 72 m/yr.

The inlet’s minimum width and ebb delta volume both increased during the episode; the inlet’s minimum width ranged from 391 m in 1982 to 560 m right before the channel jumped to its new position in 1987, and the ebb delta increased in volume from 3,593,400 m3 in 1982 to 4,052,140 m3 in 1987.

The three other bypassing episodes ranged in length of time and degrees of change, with two of the cycles ending with pre-mature breaching events. The third episode began at the end of

1994 and has not yet reached completion. A summary of results from all the bypassing episodes can be seen in Table 1, whereas channel locations of the 4 episodes are displayed in Figure 9.

Inlet Migration Patterns

In addition to the migration rates calculated during the long-term study, migration rates were recorded in detail over the span of the short-term study. Although data may have been collected on a sub-yearly basis, this data was compiled to represent rate of migration and therefore distance traveled per year. The data collected during the short-term study are similar to those collected during the long-term study; however, they present a more accurate representation of how the inlet complex migrates and how its components are tied together. A summary of the migration data for the main inlet channel, northern inlet shoulder, and southern inlet shoulder is presented in Table 2.

Table 1. Summary of Inlet Bypassing Episodes Migration Migration Change in Period ° Of Change ° Of Jump Rate (m/yr) Distance (m) Ebb Delta Volume Notes

1978 to 01/13/1987 74° 62° 31.8 153 + 535,000 m3 Channel moved through complete cycle.

Pre-mature breaching 01/13/1987 to 1/11/1990 28° 24° 25.9 77.7 - 267,500 m3 episode.

Pre-mature breaching 1/11/1990 to 11/3/1994 26.8° 40.6° 23.3 91 + 841,000 m3 episode.

11/3/1994 to 10/13/2006 32.7° Unknown 17.1 152.2 + 535,000 m3 Channel in re-orientation process.

Figure 9. Composite image illustrating the 4 bypassing episodes during the short-term study. A) Shows complete bypassing cycle from 04/7/2982 to 01/13/1987. B) Shows small and incomplete cycle from 01/13/1987 to 1/14/1991. C) Illustrates channel position during incomplete cycle from 1/11/1990 to 11/13/1994. D) Channel orientations during current bypassing episode, the cycle began near 11/13/1994.

Table 2. Summary of Yearly Migration Rates and Channel Orientation Migration Rate (m/yr) Year Inlet Channel N. Shoulder S. Shoulder Azimuth 1982 68.76 84.7 61.0 174.02 1983 68.78 84.7 61.0 160.32 1984 31.4 -91.8 24.0 143.4 1985 -17.0 11.7 4.8 110.5 1986 -24.2 -46.0 29.0 105.1 1987 72.1 -44.0 -9.6 157.4 1988 7.5 26.1 42.8 148.4 1989 8.0 97.8 38.8 139.4 1990 -8.8 140.4 76.5 158.6 1991 57.5 1.2 28.0 151.2 1992 33.8 59.0 85.1 140.6 1993 17.4 -80.2 10.2 129.7 1994 -2.7 13.3 55.6 133.4 1995 95.4 -25.6 10.4 168.2 1996 -62.1 145.1 -41.1 161.3 1997 101.9 41.8 74.9 161.0 1998 34.0 94.5 29.7 155.0 1999 32.6 185.5 33.7 142.9 2000 -10.9 84.0 158.1 131.6 2001 -13.9 72.0 -28.1 132.8 2002 3.9 41.6 50.7 141.8 2003 -18.8 29.8 68.9 141.2

The relationship between migration of the inlet channel and how the inlet shoulders respond will be explained in the discussion, as will the relationship between channel orientation and migration rate.

Oceanfront Change

The next phase in determining New Topsail Inlet’s influence on its adjacent barrier islands was to determine long and short-term oceanfront change rates and patterns. The primary focus of the study was to gather an extensive database of shoreline change rates within the current Inlet Hazard Areas (IHA), which extends from Transects 18 to 28 on Topsail Island

(Figure 10). However, change rates were also calculated for the shorelines, which continued past the IHA. As the dataset outside the IHA is not as complete, various temporal periods were used to group the data. These data were split into periods, which coincide with changes in inlet migration rate.

Figure 11 illustrates cumulative inlet migration. The variations in slope indicate periods of faster and slower migration and interval time periods were based on these changes, yielding

EPR’s for 1938-1949, 1949-1962, 1962-1974, 1974-1999 and 1999-2006. In addition to the interval time periods, EPR was calculated for the whole study area from 1938-2006.

Cumulative shoreline change data was also calculated for the study area. Due to the migration of the inlet and the lack of aerial photographs, cumulative change could not be calculated for the entire study area. As previously stated, the IHA portion of the study area has the most comprehensive data set, but other sections of the shoreline were also selected to illustrate the presence of “erosion hotspots” and bump progradation. These results are primarily presented in the DISCUSSION.

Figure 10. Map illustrating the study area and the portion of Topsail Island that is zoned as an Inlet Hazard Area. The transects within the IHA were the primary focus for shoreline change analysis. Please note green lines that indicate the portion of the study area which has been in continuous existence since 1938. IHA shapefile from NCDCM (2006). 38

Figure 11. Line plot depicting cumulative channel migration from 1938 to 2006. Red lines illustrate changes in migration rate and intervals for shoreline change analysis.

Net Change 1938-2006

Of the 6,097 m (20,000 ft) of shoreline analyzed, only 2,439 m (8000 ft) or 40% of the shoreline has been in continual existence since 1938 (Figure 10). The other 60% of the shoreline either has been subject to inlet influence (inlet shoulder or re-worked material) or has been the location of Old Topsail or New Topsail Inlets.

Topsail Island

Transects 1-28 covered the Topsail Island portion of the study area, however, only transects 1 -17 had continuous shoreline change data during 1938-2006. Net erosion occurred along the majority of the oceanfront, from transects 1-15. This shoreline reach experienced an average loss of -38.4 m at a rate of -0.57 m/yr. The greatest amount of erosion occurred along transect 9, which lost 65.2 m of beachfront at a rate of -0.96 m/yr. The transect with the least amount of erosion was transect 15, which lost -2.95 m of beachfront at a rate of -0.04 m/yr. The extremely slow rate of erosion was likely due to the transect’s proximity to the 1938 inlet position and the pattern of island widening occurring at the southern end of Topsail Island.

The two southern most transects 16 and 17 in the shoreline reach both experienced net accretion from 1938 -2006. The accretion experienced at transect 17 was largely due to its position on the 1938 inlet shoulder and cannot be considered true oceanfront change. However, transect 16, which represents true oceanfront change gained 30.6 m of beach front at a rate of

0.45 m/yr. The accretion at transect 16 is likely due to its proximity to the 1938 inlet position and the previously mentioned pattern of island widening.

Hutaff Island

On Hutaff Island only 2 transects were in continuous existence from 1938 -2006.

Transects 35 and 36 both experienced an average net erosion of -147.5 m at a rate of -2.2 m/yr.

All other transects covering the Hutaff Island shoreline (23-41) are either now re-worked material forming the southern tip of Topsail Island or were in a position that overlaid New

Topsail or Old Topsail Inlet.

The five transects which overlap both the 1938 Hutaff Island shoreline and the 2006

Topsail Island shoreline can be used to exhibit the idea of shoreline straightening. Transects (23-

27) have prograded an average of 230 m. However, because the transects overlap two different islands, this data is erroneous and cannot be used for more than speculation.

As a side note, it is important to remember that these data represent only the changes which occurred between 1938 and 2006 and do not incorporate any of the changes that took place between the two dates. Those changes will be discussed in another section of the

RESULTS and in the DISSCUSSION.

Net Change Intervals

As previously mentioned, oceanfront change was also calculated for five interval periods corresponding to inlet migration rates. These data were calculated to see if any relationship between inlet migration rate and oceanfront change rates exist.

Net Change 1938-1949

Of the 6,097m (20,000 ft) of shoreline analyzed, 4,420 or 72.5% was in continual existence between 1938 and 1949. The other 27.5% was either the location of an inlet or part of an inlet shoulder (Figure 11).

Topsail Island

During the period from 1938 to 1949, transects 1-16 recorded shoreline change data on

Topsail Island. Transects 1-10 all had net erosion occur along them, losing an average of -23.8 m at a rate of -2.11 m/yr. The greatest amount of erosion took place at T-3 where -36.8m of beachfront was lost at a rate of -3.26 m/yr. The slowest rate of change occurred at T-10, which eroded at -0.71 m/yr for a net loss of -7.98 m.

Transects 11-17 (See Figure 12) all experienced net accretion during the time period. An average of 38.9 m was gained across the shoreline reach at a rate of 3.4 m/yr. The smallest amount of accretion occurred at T-11, the most northern portion of the shoreline reach. T-11 gained 5.2 m of beachfront at a rate of 0.46 m/yr. Transect 17, located in the southernmost part of the shoreline reach and therefore closest to the 1949 inlet corridor, accreted at a rate of 11.6 m/yr and gained 131.6 m of beachfront.

Hutaff Island

From 1938 to 1949, transects 23-36 recorded shoreline change along Hutaff Island. The

2,134 m shoreline reach experienced net erosion along all transects. The average loss along the shoreline was -64.4 m, which eroded at a rate of -5.72 m/yr. These rates however, are not an accurate reflection of how the island changed. Both the northern and southernmost transects (T-

23 and T-36) had very high oceanfront losses of -165.7 m and -143.3 m respectively. T-23 eroded at a rate of 14.6 m/yr where as T-36 eroded at a slightly lesser rate of -12.7 m/yr. The smallest rate of change took place near the middle of the island along T-29, which eroded at a rate of -0.38 m/yr. The morphological changes, which occurred to Hutaff Island are displayed in

Figure 12. The erosion that took place effectively changed the islands shape from a concave drumstick shape into a linear, straighter shoreline.

Figure 12. Map illustrating historic shorelines and inlet positions during 1938 and 1949. T-17 was did not record data as it was part of the inlet shoulder in 1938.

Net Change 1949-1962

During this time interval, shoreline change data was collected from 4,115.8 m of oceanfront. Transects 1-17 collected data on Topsail Island and Transects 27-36 collected data on Hutaff Island (Figure 13). 67.5% of the study area was part of a continuous shoreline during this time period. The remaining transects were subject to inlet influence or inlet position.

Topsail Island

From 1949-1962 T1-17 recorded shoreline changes along Topsail Island, however, the pattern, which was recorded, was different during this time period. Instead of having two distinct shoreline reaches, one which suffered from net erosion and the other experiencing net accretion, there are three shoreline reaches; two zones of accretion, separated by a zone of erosion.

Transects 1-4 and 14-17 all experience net accretion, where as transects 5-13 experienced net erosion.

The accretion zones consisted of a large shoreline bump surrounding the Topsail Beach pier, and an area in close proximity to New Topsail Inlet. The average rate of change over both accretion zones was 1.37 m/yr, gaining 16.9 m of beachfront over the 12.3-year period. The transects with the highest accretion rates were T-3 and T-16; both transects prograded 28.8 m at a rate of 2.3 m/yr. The least amount of shoreline change occurred at T-17, which gained only

4.1 m of beach at a rate of 0.33 m/yr.

The erosion zone, which was located 405 m south of the pier had an average zone wide loss of -14.1 m, which occurred at a rate of -1.1 m/yr. The highest rate of erosion took place at T-

11, this section of shoreline lost -30.7 m of material at a rate of 2.38 m/yr. The area least

Figure 13. Map depicting historic shorelines and inlet positions during 1949 and 1962. Note that not only has New Topsail Inlet migrated, but Old Topsail Inlet has also migrated, extending the length of Hutaff Island past T-39.

45 effected by erosion was just north of the southern accretion zone, at T-13, where -0.39 m of beachfront was eroded during the 12.3 year period.

Hutaff Island

During the period from 1949-1962, net erosion occurred at all transects but one along the

Hutaff Island shoreline. Transects 27-35 all recorded net erosion where as T-36 recorded net accretion. The beachfront gained at this location was a result of Old Topsail Inlet’s migration south and the subsequent island building that occurred. The rest of Hutaff Island eroded an average of -38.1 m at a rate of -3.08 m/yr. The highest recorded loss took place at T-32 where -

65.5 m of beach was eroded at a rate of -5.3 m/yr.

Net Change 1962-1974

During the period from 1962-1974, 30 out of 41 transects recorded shoreline changes over 70% of the study area. Transects 1-19 recorded changes on Topsail Island and transects 29-

39 recorded shoreline changes on Hutaff Island (Figure 14).

Topsail Island

Nearly all transects on the Topsail Island shoreline reach recorded net erosion; T-2, T-5 and T-19 recorded net accretion. T-2 and T-5 had minimal gains of 2.3 m and 2.7 m respectively.

T-19 had a much higher rate of accretion and gained 44.3 m of beachfront at a rate of 3.8 m/yr.

This large accretion rate was likely due the proximity of the inlet complex and its influence.

Figure 14. Map of the study area depicting historic shorelines and inlet positions from 1962 and 1974.

Topsail Island lost an average of 9.29 m of beachfront material at a rate of 0.80 m/yr. The shoreline reach, which excluded T-19, had an average net change of -12.2 m and eroded at a rate of 1.05 m/yr. The greatest loss occurred at T-16, the previous site of a large accretion zone during the 40’s and 50’s. The beach at T-16 eroded 30.1 m at a rate of 2.6 m/yr. Transects 14 and

15 were also heavily eroded and lost 22.8 m and 25.9 m of beach respectively. The lowest rate of erosion took place at T-7, which lost 0.21 m/yr and had a total loss of -2.41m.

Hutaff Island

The transects along the Hutaff Island reach (T-29 – T-39) recorded both net erosion and net accretion. Similar to previous years the flanks of the island were more dramatically affected by shoreline change processes than the center of the island. Overall, Hutaff Island accreted an average of 40.0 m at a rate of 3.4 m/yr. The transects closest to New Topsail Inlet changed the most, building out 111.9 m and 113.6 m at T-29 and T-30. These transects had accretion rates of 9.6 m/yr and 9.7 m/yr respectively. The net erosion that occurred on the southern portion of the island was a result of Old Topsail Inlet’s migration to the south. T-38 lost the most material eroding 20.7 m at a rate of 1.78m/yr.

Net Change 1974-1999

Unfortunately, the extent of aerial photographs during 1999 did not cover the entire study area and limited the amount of shoreline change data collected. As a result, transects 1-8 did not record any changes between 1974 and 1999 or between 1999 and 2006. However, data was recorded along the rest of the Topsail and Hutaff Island shoreline reaches, accounting for 50% of

48 the study area; the other 50% was either previous or current inlet position or unavailable (Figure

15).

Topsail Island

In similar fashion to previous time periods, the Topsail Island shoreline can be divided into two shoreline reaches based on net change. Transects 8-17, the northern shoreline reach, experienced net erosion, losing 7.7 m of material at a rate of 0.32 m/yr over all transects.

Minimal accretion took place at T 8-10 where the largest gain was 1.8 m. The highest erosion rate occurred at T-15, which lost 21.6 m of beachfront at a rate of 0.9 m/yr.

The southern shoreline reach (transects 18-22) gained an average of 52 m, pushing seaward at 2.14 m/yr, however the shoreline reach did not accrete in a uniform fashion. Instead, accretion rates ranged from a minimum of 0.39 m/yr at T-18 to a maximum of 5.48 m/yr at T-22.

Once again, accelerated rates were likely due to the proximity of the inlet complex during 1978.

Hutaff Island

Two transects , T-34 and T-35, recorded net accretion from 1962 to 1974; both transects gained 24.2 m of beachfront at a rate of 1.0 m/yr. All other transects on Hutaff Island recorded net erosion. As a whole, Hutaff Island eroded and average of 36.6 m at a rate of 1.5 m/yr.

Transect 40, the farthest transect from New Topsail Inlet to record oceanfront change, lost 82.9 m of beach at a rate of 3.41 m/yr.

Figure 15. Map of the study area, inlet positions and net oceanfront changes between 1974 and 1999. Note that due to the length of the time period nearly 600 m of shoreline on Topsail Island was not analyzed.

Net Change 1999-2006

The 1999-2006 data period is the best record of changes, which occurred on the southern end of Topsail Island. 3,506.1 m of shoreline or 57.5% of the study area was used to calculate shoreline change data between 1999 and 2006. Of that, 2,743.9 m of the shoreline was part of the

Topsail Island reach (not including transects 1-8). Essentially this resulted in 762.1 m of new shoreline being analyzed that did not exist in 1974 (Figure 16).

Topsail Island

Once again, the Topsail Island shoreline can be divided into two sections based on net change. The northern section was comprised of transects 8- 19 and was subject to net erosion.

This portion of the Topsail shoreline lost an average of 12.6 m of beachfront at a rate of 1.5 m/yr.

T-11 suffered the highest loss of 19.8 m at a rate of 2.42 m/yr.

The southern shoreline reach, comprised of transects 20-27 accreted at the accelerated rate of 11.5 m/yr, gaining an average of 94.6 m across all transects. However, the same pattern of increasing accretion rates tied to the proximity of the inlet complex was present in the data set.

The smallest beachfront gain occurred at T-20, which gained 10.2 m at a rate of 1.26 m/yr. The largest seaward progression took place at T-27, which gained 224.5 m of material at an astounding rate of 27.4 m/yr. The rates of change between T-20 and T-27 increased steadily as

T-27 was approached.

Figure 16. Image of the study area in 2006. Shorelines from 1999 and 2006 show inlet position and oceanfront change during the time period. Topsail Island shoreline south of T-20 had not been included in previous time periods.

Hutaff Island

Transects 35-40 recorded shoreline change data along Hutaff Island; all transects but T-

35 recorded net accretion. The average rate of accretion along all transects was 0.93 m/yr for a total progression of 7.6 m. The average rate of change for the transects that recorded net accretion was 2.6 m/yr, gaining 12.7 m of beachfront material. The erosion that occurred at T-35

(6.4 m) was likely a factor of the transect’s proximity to the inlet complex.

Cumulative Shoreline Change

In addition to net change, cumulative shoreline change data was also collected for the study area. This data gave insight into the processes occurring between the net change interval dates. As the shoreline is constantly changing, cumulative change data is essential in tracking day to day changes related to storm events, beach nourishment projects and the everyday movement of the shoreline.

This dataset combines shoreline change rates from the long-term study (17 shorelines) and the more temporally intensive short-term study (45 shorelines). When compiling this data several problems presented themselves. First, the migration of New Topsail Inlet makes it impossible to attain cumulative shoreline data from 1938 to 2006 as over 1.6 km of shoreline analyzed did not exist in 1938. Second, by combining the long-term and short-term studies, the number of transects with change data for every date interval was greatly reduced. Transects that had data during the long-term study may not have data available during the short-term study simply because of the limited nature of the short-term photographic database. A large number of photograph sets used during the short-term study only had 1 or 2 photos as the sets were taken to track inlet changes.

Topsail Island

As a result of the problems described above, data from 1938-1974 will be used to discuss the northern portion of the island (T-1 to T-16). The more recent data will focus on the current inlet hazard zones, which cover the southern reach of Topsail Island (T-17 to T-27).

Northern Shoreline Reach (T-1 through T-16)

Data for this section of Topsail Island was compiled from the following dates: 1938,

1945, 1949, 1956, 1959, 1962, and 1974. All transects within this shoreline reach experienced periods of both erosion and accretion, however at most locations, erosion outweighed accretion.

Transects 1-13 recorded a cumulative landward movement of the shoreline where as transects

14-16 recorded a cumulative seaward movement of the shoreline. Figure 17 shows the net cumulative change experienced by each transect in the northern shoreline reach. In addition to

Figure 17, Figure 18A and 18B illustrate how shoreline advance and retreat took place during

1938 to 1974. The first and last points on the data plots represent the net change of the shoreline between 1938 and 1974 for the representative transect. As can be seen in the graphs, there are several positions on the beach that were subject to large movements in the shoreline, Figure 18B is a particularly good example. Reasons behind the shorelines movement for this position as well as others will be explained in the DISCUSSION.

Southern Shoreline Reach

As previously discussed, the southern portion of the Topsail Island shoreline presented several problems that made it difficult to present the data in a consecutive and understandable

Figure 17. Bar graph showing the total cumulative changes for the transects located in the northern shoreline reach. These changes illustrate the balance of erosion or accretion that has occurred at each transect location.

Figure 18a. Two line plots illustrate the movement of the shoreline between 1938 and 1974. Positive values denote regressive shoreline and negative values denote a transgressive shoreline.

Figure 18b. Two Line plots illustrate the shoreline movement of the southern transects located in the northern shoreline reach. Notice how transects located next to each other react to events in a similar fashion.

57 matter. As most of the problems have been spatial, the southern shoreline reach was divided into several spatial limits based on different time periods. The goal was to use as much data as possible while keeping it organized in manageable chunks and similar time intervals as the net change data.

1974-1999

In order to include as much data as possible, the period from 1974 to 1999 was broken into several smaller intervals. The mini intervals were: 1) 1974-1982, this time period had data from three shorelines and covered transects 14-22, 2) 1982-1990, which had data available from

16 shorelines and covered transects 17-24, and 3) 1990-1999, which included data from 22 shorelines and spanned from T-18 to T-25. Figure 19 illustrates the total cumulative shoreline changes that occurred at each transect during the mini time intervals. Notice that trends seen in the net change data, such as an increase in accretion as the inlet complex is approached and an apex point, which indicates a shift between accretion and erosion, are prevalent in this data set.

Unfortunately, the limited shoreline data from 1982 did not allow data to be collected outside the inlet’s zone of influence, limiting what can be determined about how the inlet effected shoreline change during the early 1980’s. The data displayed in Figure 19 does not represent how the shoreline behaved during the period, just the total amount of erosion or accretion that occurred.

Figures 20-22 illustrate the habits of shoreline position by transect. The line plots in Figures 20-

22 show that although cumulative shoreline change was either dominated by erosion or accretion, both processes occur along each transect within the shoreline reach.

Figure 19. Bar graph displaying the cumulative shoreline change experienced by transects in the southern shoreline reach from1974-1999. The cumulative change for transects with more than one column can be determined by adding the respective changes.

Figure 20. Line plot illustrating shoreline movement over the southern shoreline reach during the period between 1974 and 1982. Accretion of transects 14-18 and erosion of T-19 was likely related to the New Topsail Inlet’s migration to the southwest.

Figure 21.Two line plots display the movement of the shoreline across transects in the southern shoreline reach from 1982-1990. The more dramatic movements recorded by T-21 through T-24 are related to the proximity of New Topsail Inlet and the repositioning of the main ebb channel.

Figure 22. Two line plots illustrating changes in the shoreline during the mini period from 1990- 1999. Again changes in the southern part of the shoreline reach were more dramatic than changes occurring along the more northern transects.

1999-2006

The most current period, incorporated 11 shorelines and spanned an area from T-18 to T-

27 (the area of Topsail Island covered by the current inlet hazard zones). Figure 23 shows the total cumulative change, which occurred within the shoreline reach. As can been seen in Figure

19, this shoreline reach was dominated by accretion during the time period. However, Figure 24, which illustrates the movement of the shorelines within this reach, shows that large erosional events also take place along this section of the beach.

Hutaff Island

Several of the problems that occurred in presenting the cumulative data for the Topsail shoreline were also present in the data for Hutaff Island. The two main problems within this data set were the lack of historic aerial photographs, and the substantial amount of erosion that occurred on the northern end of the island. Unlike the situation on Topsail Island, where the island out grew the 1938 shoreline, the opposite has happened here; erosion has claimed the shoreline on all but two transects. In order to deal with New Topsail Inlet’s migration, the cumulative shoreline change data for Hutaff Island has been split into several time intervals.

1938-1962

The shoreline reach from 1938 to 1962 stretched from T-25 to T-35 and contained the largest shoreline reach on Hutaff Island for computing cumulative change. This time interval dataset is the most comprehensive portion of cumulative shoreline change data as all other time periods were limited to two or three transect spans. All transects within the shoreline reach were characterized by cumulative erosion, however, transects located at the islands extremities were

Figure 23. Bar graph showing the cumulative change data for transects 18-27 for the time period between 1999 and 2006. This shoreline reach is located within the current inlet hazard zone for New Topsail Inlet and is extremely prone to oceanfront change.

Figure 24. Two line plots show the various positions of the oceanfront shoreline during the period 1999-2006. The figure shows that although the area is predominately accretionary, erosion does occur.

65 subject to higher levels of erosion (Figure 25). The proximity of both New Topsail and Old

Topsail Inlets played a dramatic role in how the shoreline moved at these locations.

1962-2006

Cumulative data for several time intervals within this time period were plotted and can be seen in Figure 26. Again, large erosion and accretion events were usually influenced, if not controlled by the proximity of New Topsail Inlet. Typically, large accretion events took place when the main channel of New Topsail Inlet exited the inlet throat directly adjacent to Hutaff

Island. The position of the inlet channel and its protective shoals allowed for the buildup of a large shoreline bump (illustrated in Figure 26) during 1962-1982. As the inlet’s ebb channel shifted northward and the outer portion of the channel was repositioned, the shoals were reoriented and erosion of the shoreline bump took place. In addition to channel shifting, the continual southern migration of the inlet complex caused continual erosion and reshaping of

Hutaff’s inlet shoulder, causing cumulative shoreline loss for much of the period between 1982 and 2006.

Positional changes in the shoreline recorded during the course of the study period are displayed through figures 27-30. As a way of dealing with the continual loss of shoreline and to limit the effect of the inlet shoulder, these graphs were created using transects that were in existence for the entire time period being analyzed and were not in areas being reshaped as part of the inlet complex.

Figure 25. Bar graph displaying cumulative shoreline loss across all transects within the Hutaff shoreline reach from 1938-1962. The higher level of erosion present for transects 25-26 and 34- 35 is due to the proximity of New Topsail Inlet to the north and Old Topsail Inlet to the south.

Figure 26. Bar graphs showing cumulative shoreline change data on Hutaff Island for all other time periods between 1962 and 2006. Limited data displayed for certain time intervals is due to lack of shoreline information.

Figure 27. Line plot illustrating shoreline position change on Hutaff Island between 1938 and 1982 for transects 30-31. There is clear bump development which took place on the northern end of the island from 1962 to1980. This was a direct result which occurred because of location of the main ebb channel and its exit position adjacent to Hutaff Island.

Figure 28. Line plot showing the movement of the shoreline across transects 32-34 on Hutaff Island for the time period 1982-1990. The previous shoreline bump which was built from 1962 to 1980 was eroded during the early 80’s as a result of outer ebb channel repositioning. The small bump developed during 1988- late 1989 was also due to channel repositioning.

Figure 29. Line plot displaying shoreline position for transects 34 and 35 on Hutaff between late 1990 and 1999. The zigzag position of the shoreline during the late 1990’s was caused by New Topsail Inlet’s migration to the south. The position of transects 34 and 35 during these years was starting to be influenced by the erosional aspects of the inlet complex.

Figure 30. Line plot shows shoreline change for transects 35 and 36 for the time interval 1999- 2006. Accretion and erosion during this time period was a result of the change in shape of the southern inlet shoulder and subsequent oceanfront realignment.

DISCUSSION

Increased coastal development up and down the eastern seaboard has lead to the construction of permanent structures in areas sensitive to inlet influence. The dynamic nature of these systems and the resulting oceanfront realignment related to them has lead to the necessity for the development of a large scale inlet management plan. As many of the eastern seaboards inlets remain unmodified, they largely act as individualistic systems. Generally, these inlets have certain similarities and components, but numerous factors influence how the overall inlet complex works as a whole.

The detailed study and analysis of specific inlet systems, such as New Topsail Inlet, will not only further the scientific understanding of how adjacent barrier islands are affected by inlets, but will also allow site specific management plans to be developed. With the use of these management plans, state and local government agencies will be in a more able position to regulate development within sensitive areas, and prevent development that mirrors the mistakes in the past.

This study is currently the most in-depth and complete data set assembled for any inlet system in North Carolina. Several aspects of the study have made this statement to be true, including the long and short-term components as well as the extensive aerial photograph database, which allowed quarterly review of inlet changes on certain occasions. Hopefully the understanding gained through this study can be used in future monitoring of New Topsail Inlet and the information applied to other migrating systems with similar traits.

Effects of Inlet Migration:

The first thing that comes to mind when discussing the New Topsail Inlet system is long periods of migration. And although the migration of the inlet complex has been continuous, it has also been complex. Unfortunately, a detailed history of migration rates pre-1849 was not possible. However, some understanding of the past can be gained by the current conditions taking place within the inlet system. The complexities in the migration of the inlet complex stem from two factors, 1) the direction of migration and 2) the rates at which the system is migrating.

Direction of Migration:

In order to fully understand how the New Topsail Inlet complex migrates, short-term and long-term changes must be taken into account. Over the 68 years which this study analyzed in detail, New Topsail Inlet migrated a total of 1.66 km to the southwest, reversing its direction only once, and indicating that New Topsail Inlet migrates unilaterally. The direction of migration is not only supported through photographic evidence, but also by the presence of Banks Channel, a long, island parallel channel that separates the southern portion of Topsail Island from the mainland (Figure 2). Flanking the marsh side of Banks Channel are a series of marsh islands, created by the stabilization and vegetation of previous, reworked flood tidal delta shoals

(CLEARY et al., 1979).

Another indicator of New Topsail Inlet’s migration is the presence of re-curved dune ridges along the southern portion of Topsail Island. As the inlet migrated, it produced a series of curved beach ridges separated by low lying marshy areas, indicating lateral sedimentation processes (HAYES, 1980). Unfortunately, the development of Topsail Island has made the re-

74 curves difficult to see in recent photographs, however Figure 31 illustrates several re-curves in photos from 1938 and 2008.

A feasibility study conducted by the USACE (1989) estimated the gross rate of sediment transport across New Topsail Inlet to be approximately 500,000 m3/yr, 55% or 275,000 m3 moving across the inlet throat in a northerly direction. More recently, the USACE used their shoreline model GENESIS to predict the sediment transport potential for Topsail Island

(USACE, 2006). The data in this study concluded that the predicted average gross transport along Topsail Beach amounted to 433,500 m3/yr with an average transport of 217,291 m3 to the north.

What is curious and difficult to understand is that despite the predicted gross transport rate to the north, New Topsail Inlet has historically continued its migration to the southwest. In fact, all previous inlets found in the area, including Old Topsail Inlet and Sidbury Inlet, migrated to the south as well. Although inlets typically migrate in the direction of net littoral drift, there are rare instances, in unique settings and conditions, where inlets migrate in the opposite direction of net drift (AUBREY AND SPEER, 1984). It seems a combination of 2 factors proposed by AUBREY AND SPEER (1984) have contributed to New Topsail Inlet’s continual up-drift migration, 1) attachment of ebb tidal delta bars to the down-drift barrier spit (Topsail Island) and,

2) disrupted ebb tide discharge around the channel/barrier bend.

The formation, migration and welding of wave driven ebb delta swash bars as well as the breaching and bypassing of elongated ebb delta channel lobes within New Topsail Inlet has resulted in the episodic accretion of sand on Topsail Island. During the short study period from

1982-2003, no less than 4 bypassing episodes were observed, the largest of which took 9 years to

Figure 31. Images serve as photographic documentation of re-curved dune ridges on the southern portion of Topsail Island. These ridges are one of the main components supporting long-term unilateral migration

76 reach completion and added 180 linear meters of sand to the northern inlet shoulder. Although the shoal did indeed weld itself to the southern tip of Topsail Island, it would be difficult to assume that all 180 m of property were amassed simply by this bypassing episode as the shoal took 3 years to move across the inlet throat. However, for historic perspective it is interesting to note the bypassing episodes as a potential drive mechanism for inlet migration. Therefore, assuming that the inlet opened in 1720, approximately 31 bypassing episodes of a similar nature could have occurred, resulting in 5,700 linear meters of sand transported through the inlet.

In addition to the bypassing episodes, it is thought that another driving factor of New

Topsail Inlet’s up drift migration is a sedimentation pattern similar to what is present in meandering rivers. In this scenario, channel curvature found within the inlet throat provides a mechanism for migration by modifying bed shear gradients, causing the outer bank of the channel to erode and the inner bank to accrete (AUBREY and SPEER, 1984). In this type of depositional environment, the growth of the inner bank stems from the re-worked flood tidal delta. In regards to morphology, New Topsail Inlet has been similar to a meandering river for quite some time, and has both a steep outer bank (eroding shoulder of Hutaff Island) and an accreting point bar on the inner shoulder (Topsail Island). Historically, New Topsail Inlet has exhibited a similar morphologic pattern since the advent of aerial photography. Prior to that, maps and charts of the area have continually shown Topsail Island with a long parallel channel running its length, where previously deposited sediments could have been easily gathered for deposition on the interior shoulder as the water flowed through the bend in the inlet throat.

Rate of Inlet Migration:

Due to the extensive photographic documentation of New Topsail Inlet, both long-term and short-term inlet migration rates have been calculated. Obviously, the long-term rates illustrate more established trends in the inlet’s speed and direction of migration. These changes can then be paired with shoreline change data in order to determine how inlet morphology changes cause changes to adjacent island planforms. On the other hand, the short-term data is more useful in determining how the inlet responds to quick changes, such as bypassing events. It also illustrates the inlet’s highly variable migration rates and frequent reversals in the direction of migration.

Long-term Rates of Migration:

The migration of New Topsail Inlet is complex and it is difficult to speak about different components singularly, however the variation in migration rates likely reflects changes in ebb channel orientation, longshore transport rates, inlet width and changes in the tidal prism.

Between 1938 and 2006, New Topsail Inlet’s rate of migration ranged from 73.75 m/yr to 1.12 m/yr in a southerly direction and 29.75 m/yr to 2.41 m/yr in a northerly direction. The average migration rates for the 16 intervals used within the long study illustrate the extreme variability in migration rates. Despite the complexity of the migration mechanism it is evident that the ebb channel migration rates generally decreased from 1962 to 2003 (Figure 11). Data taken from more recent aerial photographs suggest that the migration rate of the inlet increased from 2003 to

2006. Long-term migration rates were grouped into similar rates of change and averaged in order to understand how the speed of the inlet affected the morphology of the adjacent islands during the study.

The historic aerial photographs collected for the study illustrate the changing configuration of the inlet, ebb channel position, and adjacent oceanfront shorelines during representative years between 1938 and 2006. Figure 7, a composite cartoon of the changing adjacent island morphology, clearly illustrates the changes that have occurred along both Topsail

Beach and Hutaff Island since 1938. However, in order to comprehend the changes occurring to the inlet complex, Figures 32-35 were used to illustrate the morphologic changes that occurred within New Topsail Inlet and likely affected both its migration pattern and rate. Examination of

Figures 32 and 33 show that between 1938 and the late 1950s the morphology of the Hutaff

Island inlet margin was substantially different than in the early 1960s. By 1962, both barriers had achieved a position of relative equilibrium that suffered minimal changes until 1995 when a portion of the Hutaff Island inlet margin was eroded substantially. The erosion lead to the exposure of a relict tidal delta (likely deposited by one of the previous three inlets that occupied this coastal stretch), characterized by sand filled creek mouths and tidal marsh, and may have accounted for decreased channel migration rates.

Short-term Rates of Migration:

As a result of the in-depth photographic documentation available, it was possible to reveal how New Topsail Inlet migrates and changes on a sub-yearly basis. These small-scale

(time frame) changes have lead to an understanding of the relationship between channel orientation, migration rate, and channel width. It has also illustrated how the inlet shoulders respond to migration and bypassing events.

Figure 32. Composite image illustrating changes to the inlet’s morphology incurred over the course of the study. The orange triangles indicate the position of the flood ramp and its migration to its current position behind the Topsail Island spit.

Figure 33. Composite image showing the movement of the flood ramp (illustrated by the orange triangles) from 1962 to 1974. During this period, increased curvature of the main inlet channel began to limit space available in the back barrier.

Figure 34. Composite image showing the completed migration of the flood ramp from behind the inlet throat, to its new position behind the Topsail Island Spit. It continues to change its orientation so that it faces the incoming flood tide.

Figure 35. Composite image showing the final position of the flood ramp within Banks Channel. At this point it has successfully oriented itself to face the incoming flood tide.

Both channel orientation and inlet width seem to have an effect on inlet migration. The orientation of the channel and its migration rate has a direct relationship where the migration rate slows down as the configuration of the channel moves to a lower azimuth (shore parallel orientation). Figure 36 illustrates how the migration rate of the channel continually slows down until a by-passing event occurs and the migration rate jumps back up. During this process, the inlet continuously deposits sand in the ebb tidal delta, which, due to the nature of the inlet is situated off the southern inlet shoulder as an extension of Hutaff Island. Over time, the dominant northerly longshore transport deflects the outer portion/ ebb channel of the inlet to the north, increasing the length of the main inlet channel, shifting the ebb tidal delta to a more central location, and slowing down the rate of migration.

As time passes and the ebb channel continues its northward march, the orientation of the channel causes the development of a large shoreline bump on Topsail Island. The protrusion is built out through a combination of swash bar migration and welding as well as sediment deposition on the leeward side of the ebb tidal delta. These built up portions of the shoreline do not remain permanently, but soon become erosion “hotspots” after the inlet has shifted to the south and no longer supplies sediment. During the buildup process, the channel reaches a near shore parallel orientation and the inlet slows its migration rate.

Once the channel becomes hydraulically inefficient, or some outside factor takes place

(such as a large storm event), the ebb delta is breached, bypassing a large quantity of sand and causing an acceleration in migration rate (Figure 36 and Figure 8). The change in channel curvature not only increases the migration rate of the channel but also increases the accretion rate of the northern inlet shoulder, likely due to the recently by-passed ebb-delta.

Figure 36. Bar and line graph that illustrates the connection between channel migration and the orientation of the ebb channel. Migration rates of the inlet slow as the ebb channels deflection nears Topsail Island. After the cycle of deflection is completed and the ebb channel jumps to its new orientation, the inlet increases its rate of migration.

The inlet’s minimum width seems to have an inverse relationship with the inlet’s migration rate. Although the correlation between these two components of the inlet complex only develops for a short time prior to being interrupted by a bypassing episode, Figure 37 illustrates a clearly developed inverse relationship from 1988 and 1994. Simple physics would tell us that this relationship exists due to the need to get the same quantity of water from the back barrier area through the inlet throat in the same amount of time available as when the inlet has a wider channel. In order to accomplish this, the rate of flow must be increased and thus the amount of friction would increase also. As such, one might think this would result in increased erosion of the southern inlet shoulder and an increased migration rate. Although this scenario has been documented at New Inlet (HASBROUCK, 2008), the direct relationship between inlet width and migration rate is not as noticeably present at New Topsail Inlet. Perhaps the complexity of the migration cycle prevents an easy link being established on a short-term basis.

Tidal Delta Changes:

In addition to location changes of New Topsail Inlet, morphologic changes to both the flood and ebb tidal deltas have also occurred because of inlet migration.

Flood Tidal Delta

Although the flood tidal delta is not as prominent a feature at the ebb tidal delta within the New Topsail Inlet complex, the changes in its location and morphology have been quite dramatic. Initially in 1938, the flood ramp was situated nearly directly behind the inlet throat, in a seaward facing position as illustrated through Figure 32, picture A. However progression of the inlet to the south coupled with changes in the position of the main inlet channel changed the

Figure 37. Line plots illustrate the inverse relationship between inlet minimum width and migration rate. Although the relationship is frequently interrupted by jumps in the channel position, small areas of continuity (from 1988-1994) distinguish its existence.

87 interior morphology of the inlet complex, forcing the flood ramp to shift positions. Inspection of

Figures D2 A, B, C, D and D3 illustrate positional and morphological changes of the flood ramp within the inlet complex. In Figure 32 A, B,C and D, the flood ramp remains in a central position, close to the inlet throat. However changes in the morphology of the Hutaff shoulder starting in 1956 (Figure 32, D) gradually force the flood delta further into the back barrier. The continued elongation of the Hutaff shoulder through 1959 and 1962 (Figure 33, A and B) kept the flood delta in a back barrier position, effectively lengthening the main inlet channel.

Unfortunately, the largest data gap occurs between 1962 and 1974 during which a significant change to the position of the flood ramp occurs, moving from directly behind the inlet throat to a position sheltered by the southern portion of Topsail Island and perched on the previously formed marsh islands. Because of its new position, the orientation of the flood ramp has deflected towards the south, directly facing the incoming flood tide. Speculation into the change to the interior morphology might suggest that as the inlet progressed southward, it moved into an area previously occupied by its predecessor, Old Topsail Inlet. Previously deposited flood deltas (marsh islands) then caused a dramatic change in the shape of northern Hutaff Island and increased resistance to channel migration. In fact, in the 12.38 years prior to 1962 (February

1956 – March 1962) the southern inlet shoulder eroded 98.1 m at a rate of 7.92 m/yr where as in the 11.66 years subsequent to 1962 (March 1962- December 1974) the southern inlet shoulder eroded at a severely decreased rate of 1.96 m/yr for a total of 22.9 m. The resultant shape change

(northern most tip pointing towards Topsail Island, Figure 33, C and D) to northern Hutaff Island and the decreased erosional pattern of the inlet shoulder removed the space previously occupied by the flood ramp (Figure 33, A and B), and forced it into its new position behind Topsail Island

(Figure 33, C and D).

From 1982 onward, the continued migration of the inlet and the resultant changes to both the back barrier and the main inlet channel caused the flood delta to be pushed father behind

Topsail Island (Figures 34 and 35). The increase in channel curvature, which first started in 1962

(Figure 33, B) but was exemplified in the early 1980’s and 1990’s (Figure 34) may have contributed to the location of the flood ramp by limiting back barrier space between the now exposed mash islands behind Hutaff Island and the southern portion of Topsail Island. As a result, the flood ramp was positioned within Banks Channel at the start of the elongated main inlet channel. It is quite evident that’s the increased curvature of the main inlet channel caused the complete realignment of the flood ramp which sits perpendicular to Topsail Island and the inlet throat (Figure 34 and 35). It is quite possible that the repositioning of the flood delta within

Banks Channel has contributed to the decrease in the inlet migration rate experienced in 1962.

Additionally, the movement of the flood ramp may be a contributing factor to the increase in island width experienced by the southern portion or Topsail Island. The interior position of the flood delta has led to the buildup and development of large channel margin bars within and behind the inlet throat. The resultant position of the channel margin bars has lead to bar welding on the interior shoreline of the island and contributed to the trend of island widening seen since the beginning of the study. Maximum island width for the southern end of Topsail

Island has ranged from a minimum of 363m in 1938 to a maximum of 661m in 2003. Obviously, the interior welding of channel margin bars was not the sole component which caused the increase in island width, both sand bypassing episodes and swash bar welding as well as channel position also contributed to the increase seen since 1938. However, the increase in channel curvature and movement of the flood tidal delta contributed to changes in island planform.

Ebb Tidal Delta

Between 1938 and 2006, the ebb tidal delta occupied areas from a minimum of 151 acres in 1956 and a maximum of 336 acres in 2003 and had volumes ranging between 2.4 million m3 and 5.3 million m3. The time averaged surface area of the ebb delta was 256 acres with a volume of 3.9 million m3. Figure 7 illustrates that up until 1978 large fluctuations or increases in the area of the ebb delta were minimal, with the exception of 1956 when the surface area dropped from 225 acres to 151 acres and the volume dropped from 3.5 million m3 to 2.4 million m3. The large fluctuation was likely due to the combined effect of the landfall of Hurricane Hazel in

October 1954, Hurricane Connie on 8/11/1955 and Hurricane Diane on 8/17/1955, and the subsequent readjustment of the inlet complex.

It is however, interesting to note that no other recorded storm events ever triggered such a dramatic response from the inlet. In fact, it seems that other storm events, including, the great

Atlantic Hurricane (9/44), Bertha (7/96), Fran (9/96), Bonnie (8/98), Floyd (9/99) or any of the numerous nor’easters had much impact on the inlet complex at all. The combined effect of

Hurricane Bertha, a category 2 storm, and Hurricane Fran, a category 3 storm, caused a decrease in the surface area from 319 acres to 268 acres and a loss of 764,554 m3 between 6/27/1996 and

2/16/1997. Hurricane Bonnie, a category 3 storm, caused a decrease in surface area of 31 acres between 8/21/1998 and 3/21/1999. Hurricane Floyd a category 2 storm had so little impact that the ebb delta actually increased in size from 287 acres to 292 acres between the time period

3/2/99 and 4/5/2000. This is especially interesting in that storm events are known triggering mechanisms for ebb delta breaching episodes, however in this location, they are not. It is possible that the impact to the inlet complex viewed in 1956 was a result of the close succession of three storms with the initial damage occurring during Hazel (category 3) and then continued

90 by Connie (category 2) and Diane (category 1) which followed 10 months later and were less than a week apart.

Since 1978, changes in the size of the ebb delta have continued to increase, with small fluctuations occurring in recent years as a result of the aforementioned storm interference and bypassing episodes. Prior to 1978, the time averaged surface area of the ebb delta was 198 acres.

Since 1978, the time averaged surface area has been 280 acres, indicating a significant increase in size because of the changing inlet dynamics. Inlet minimum width, migration rate, and channel orientation are the three primary factors that have likely influenced the increase in size of the ebb tidal delta. As the functions taking place at New Topsail Inlet are complex, it is important to note that although the three components are discussed singularly below, minimum width, migration rate and channel orientation are all interlinked and influence the size of the ebb shoal as a complex system.

A direct correlation and two inverse relationships describe how inlet minimum width, migration rate, and channel orientation have affected the changes observed to the ebb shoal. The direct relationship exists between the inlet’s minimum width and the ebb delta, where as migration rate and channel orientation have inverse relationships. As the inlet continued its progression to the south, back barrier areas and tidal prism expanded. The increased tidal flow leads to gradual inlet widening and an increase in the inlet’s minimum width over time. Figure

38 indicates that because of the increased tidal flow, the inlet moved more sand from the back barrier to the ebb shoal or had greater sand trapping abilities for sand entering the inlet complex via longshore transport.

The general decrease in migration rate that has occurred since 1962 has lead to the general increase in size of the ebb tidal delta, while at the same time, the ebb tidal delta has responded to changes in migration rate in an inversely correlated fashion. Figure 39A indicates that typically larger delta sizes are associated with lower rates of migration. This is especially true after the inlet started taking on its modern morphology in 1962. This correlation is of no great surprise as the slower the inlet moves along its migration pathway, the longer it will have to build a larger ebb shoal. There are however a few exceptions, such as the pairing between the smallest ebb delta size of 151 acres and the slowest period of migration which occurred from

1949 – 1962 (Figure 39B). The strange relationship between the very slow migration rate and the small ebb delta was likely due to the previously discussed storm activity during this period and the resultant destruction of the ebb shoal.

The second inverse relationship that exists relates the increase in ebb delta size to main inlet channel orientation. Figure 7 clearly illustrates the relationship between ebb delta size and channel orientation where the ebb delta is larger when the main inlet channel occupies a lower azimuthal position and exits the inlet complex in more shore parallel position. The relationship can then be linked to the migration rate as the lower azimuthal positions occur during the slowest periods of migration (Figure 36). The geometry of the ebb shoal post 1962 was primarily asymmetrical, with the main inlet channel separating the northern and southern portions of the delta. The northern portion of the delta is typically much smaller than its southern counterpart, and portions of it may weld to Topsail Island, forming small shoreline progradations. The shoreline bumps typically build out as swash bars weld to the island and via direct deposition of sand carried out of the inlet throat. The southern portion of the ebb delta is typically and extended shoal which may or may not extend from the northern portion of Hutaff Island, out

Figure 38. Line plots for the inlet’s minimum width and the acreage of the ebb delta show the direct relationship between the increase of the channel minimum width and the size of the ebb delta.

Figure 39. A) Line plots illustrate the inverse relationship between the overall slowing migration of the inlet and the increase in ebb delta size. B) line plots display migration rates to show the corresponding link between inlet migration rate and ebb delta size.

94 across the center line of the inlet throat (not the main inlet channel). The asymmetrical geometry of the ebb shoal acts as a breakwater for Topsail Island and amplifies the progradation taking place on the southern tip of the island.

Changes in the inlet morphology since 1962 have primarily allowed the above to be the dominant configuration of the ebb delta in recent times. Between 1962 and 2006, only one interval from 1974-1982 had a different ebb shoal configuration for an extended period of time.

Between 1974 and 1982, the main inlet channel had an extremely limited amount of curvature, and exited the inlet throat pressed against Hutaff Island, causing the northern portion of the shoreline to build out (Figure 33, C and D, Figure 34, A). In fact, transects on the northern end of

Hutaff Island recorded a net gain across the board, from T-31 to T-37. The highest build out was recorded at T-32 which prograded a total of 192.2 m at a rate of 25.9 m/yr. T-37, which was located 1.1 km away from the main inlet channel in 1982, recorded the smallest amount of accretion, but still prograded 36.8 m at a rate of 4.9 m/yr. The ebb delta orientations which facilitated the large progradation, along with historic shorelines and channel locations are presented in Figure 40. Figures 41 and 42 illustrate previous and subsequent ebb shoal configurations that have been more typically present post 1962 and generally assist accretion on the southern tip of Topsail Island. The extremely short but rapid accretionary period experienced on Hutaff Island is a perfect example of how inlets can dramatically affect shoreline change and why building codes in inlet hazard areas need to be maintained.

Figure 40. Map of the study area illustrating the ideal ebb delta and channel configuration for accelerated shoreline advancement on Hutaff Island.

Figure 41. Map of the study area showing positions of the ebb delta and channel orientation prior to the large protrusion build out on Hutaff Island and illustrates a more typical delta configuration.

Figure 42. Map of the study area showing the ebb delta configuration subsequent to the configuration favored for shoreline advancement on Lea/ Hutaff. These deltas illustrate a more typical orientation of the ebb channel and favor build out on the Topsail Island shoreline.

Oceanfront Shoreline Change

Throughout the course of the study, changes to both Topsail and Hutaff Islands have primarily been related to inlet migration and changes to the inlet’s morphology. Changes in the inlet’s migration rate have not only affected the erosion experienced by the northern shoulder of

Hutaff Island, but have also influenced erosion rates on Topsail Island, where chronic erosion is the norm. Planform changes on both islands have been directly related to the inlet’s southward march, ultimately adjusting the geometry of both the leading and trailing barriers. Figure 6 illustrates the dramatic changes in barrier planform experienced by Hutaff Island and also illustrates how the lengthening of the trailing barrier (Topsail Island) and updrift shoreline truncation has caused erosion to become commonplace along Topsail Beach.

Paired with the migration of the inlet complex, the changing morphology of the inlet, specifically the deflection and realignment of the ebb channel, caused dramatic shoreline change fluctuations to adjacent barriers. Of the varying alignments experienced by the ebb channel, the time limited shore normal alignment lead to a nearly symmetrical ebb shoal, which resulted in accretion occurring on both Hutaff and Topsail Islands. On the other hand, the far more common alignment with the ebb channel deflected to the north favors accretion on Topsail Island and has lead to the buildup of several large shoreline protrusions over the course of the study. Not only does the skewed ebb channel lead to accretion of the northern shoulder, but the associated asymmetrical ebb shoal leaves Hutaff exposed to oncoming wave energy out of the southeast.

Furthermore, because of the skewed morphology of the inlet, the southern marginal flood channel develops off the northern tip of Hutaff and has lead to rapid erosion of the inlet shoulder and adjacent oceanfront shoreline.

100

Changes that occurred during the study period were broken into sections based on both inlet migration rates and major changes seen in inlet morphology. Both net change and cumulative net change were calculated for shoreline changes. Net change intervals for Topsail

Island have shown that for the history of the study, transects outside the zone of direct inlet influence, which ranges from ~1200 m to ~1600 m, are subject to chronic erosion. Net change rates within these shoreline reaches varied from a maximum of -2.1 m/yr from 1938-1949, to a minimum of -0.3 m/yr from 1974-1999. Unfortunately net change intervals do not illustrate a direct relationship to migration rates of the same interval and are generally of no use when measuring shoreline change along the Topsail reach as they do not take into account localized progradation or beach nourishment activities. Accretion and erosion was recorded during all net change intervals on Topsail Island.

Shoreline Change Intervals

1938-1949

It is difficult to speculate as to what caused shoreline change during the early throws of the study. Inspection of the photographic database indicates that the 1938 Topsail shoreline had just been subject to a small period of accretion, which resulted in a shoreline bump near T-16.

Post Topsail build out, the main inlet channel shifted south and caused the buildup of the Hutaff shoreline in a fashion similar to the period from 1974-1982. Between 1938 and 1949 erosion was commonplace along the northern reach of the Topsail shoreline, which spanned T-1 through T-

10 and was located ~1130 m north of the inlet throat. The average erosion rate along the northern reach was 2.1 m/yr during 1938-1949. However, erosion rates varied significantly between 1938-

101

1945, which had an average rate of -3.97 m/yr, and 1945-1949, which had an average rate of -

0.51 m/yr. The increased rates of the 38-45 period and likely linked to the Great Atlantic

Hurricane, which made landfall in the area on 8/1/1944.

Adjustment of the main inlet channel within the inlet corridor between 1938 and 1945 led to a change in symmetry of the ebb tidal delta and may have caused a small bar welding event to occur on Topsail Island, which caused the transgression of the shoreline an average of 10.7 m between T13 and T-16 at a rate of 3.28 m/yr. It is also at this point in time that the trend of island widening, recorded through the rest of the study, begin. The development of the small bulbous shape at the southern tip of Topsail Island caused the shoreline to prograde 15.1 at T-15 and 17.4 m at T-16. Further movement of the inlet channel to the south between 1945 and 1949 lead to a major restructuring of the ebb shoal which facilitated continued progradation of the Topsail shoreline; transects 11-16 experienced as much as 22 m of shoreline change. The expansion of the ebb tidal delta extended its wave sheltering effect as far north as T-11 and allowed T-11 through T-13 to infill shoreline areas previously left behind during the shoreline bump build out of 1938-1945. Development of a large marginal flood channel prevented further accretion from occurring on transects 14 or 15.

Change in the channel position between 1939 and 1945 lead to the complete truncation of the northern tip of Hutaff Island. Areas previously protected by the ebb shoals wave sheltering breakwater effect, were left exposed to oncoming wave energy and were further scoured away by the development of a large marginal flood channel. Shoreline change on Hutaff ranged from a minimum of -6.6 m at a rate of ~ -1 m/yr near the center of the island, to a maximum of -114.5 m at a rate of -17.4 m/yr along both the northern and southern flanks of the island. A shift in the

102 main inlet channel or the ebb channel of Old Topsail Inlet was the likely culprit for the extreme erosion, which occurred on the southern portion of the island.

Further migration to the south by New Topsail Inlet’s main channel between 1945 and

1949 resulted in additional shoreline loss along Lea/ Hutaff Island. Shoreline change was likely accelerated by the location of the inlet channel as it exited the inlet corridor pressed against the southern inlet shoulder in a direction of 165º. Shoreline loss during the period ranged from 15.4 m to 56.8 m. Although extensive shoreline loss was recorded, the extent of the ebb shoal did allow some accretion to occur at T-28 through T-30. The overall realignment of the main inlet channel between 1938 and 1949 had a decimating effect on Hutaff Island geometry and essentially changed the island from a small, concave, drumstick shape to a longer, linear planform model.

1949-1962

Coupled with inlet related changes, several events, which affected shoreline change, took place during this period. Specifically, a sequence of three documented hurricanes made landfall within a ten month period between 10/1954 and 8/1955, and the Jolly Roger fishing pier was first constructed in 1954 (MCALLISTER, 2006).

Shoreline change along the Topsail reach was characterized by three shoreline change zones, two zones of accretion separated by a zone of erosion. The first accretion zone was located along transects 1-4 and encompassed the newly constructed pier; the second zone of accretion was located within direct influence of New Topsail Inlet and occupied transects 14-17.

The shoreline reach between T-5 and T-13 was predominately erosional although some accretion

103 did occur along T-5 and T-6 because of pier construction. The shoreline build out observed at T-

5 and T-6 between 1949 and 1959 was short lived and later reversed between 1959 and 1962, negating nearly all shoreline progradation. Shoreline changes between 1949 and 1962 amounted to -1.6 m at T-5 and less than -0.5 m at T-6. Oceanfront changes at T-13, located at the southern end of the erosional reach, amounted to -0.7 m as a result of inlet induced progradation from

1948-1956 and the resultant truncation as the inlet migrated to the southwest and change in ebb cannel orientation. Ultimately, the change recorded at these two locations was the smallest difference recorded along the Topsail Island reach.

The average total loss of the reach between T-5 and T-13 was -14.1 m at a rate of -1.1 m/yr. Although there was a high frequency storm period from 1954-1955, it was not visible in the record between datasets as erosion rates from 1949-1956 did not differ greatly from those recorded between 1956-1959 or 1959-1962. Interestingly, Figure 18, plots B and C, illustrate that two transects within the reach eroded significantly more than surrounding transects. T-11 suffered a total of -30.7 m of shoreline change and the oceanfront at T-12 was eroded 22.6 m where as the cumulative loss just outside the small reach was 19.9 m and 0.7 m respectively.

This accelerated loss was likely due to the truncation of the trailing shoreline after inlet induced buildup occurred during 1945-1949 and is in effect a mini erosion “hotspot”.

What is interesting about the northern accretion zone is that its development was entirely dependent on the construction of the Jolly Roger fishing pier. Transects 1- 4, which previously experienced erosion rates as high as 4.9 m/yr and an overall average loss of 4.0 m/yr, had accretion rates as high as 3.0 m/yr at T-3 (directly south of the pier) and 2.3 m/yr at T-2 (directly north of the pier). It is obvious that the construction of the pier played a part in the accretion experienced along this shoreline reach, however if the accretion was due to the pilings

104 interrupting longshore sediment transport or if the accretion was a result of material placed on the beach as part of construction remains to be seen. Another interesting bit of information surrounding the pier is that it was completely destroyed by Hurricane Hazel in 1954, and many of the pilings snapped off at or near sand level (MCALLISTER, 2006). It would have been interesting to see if the remaining portion of the pilings the acted at as a groin during Hurricane

Hazel and the subsequent two storms, interrupting longshore transport and facilitating positive shoreline change during these events. By 1962, the accretion zone at T-1 through T-4 had nearly disappeared, and T-3 and T-4 were the only transects to record positive shoreline change from

1959 -1962.

Inlet related changes occurred along the southern portion of the shoreline reach between

T-13 and T-17 from 1949-1956, and between T-13 and T-19 from 1956 -1962. Changes in the orientation of the ebb channel from 1949-1956 caused a decrease in the size of the ebb delta shoal and skewed the position of the shoal in a northerly direction. The new orientation of the ebb channel and the skewed ebb shoal lengthened the period of accretion occurring from T-13 to

T-17 and lead to a 56 m advancement of the shoreline at T-16 and a 42 m advancement at T-15

(Figure 18 plot D). The continual build up of the shoreline reach from T-14 to T-16 will lead to the chronic erosion of this area in the future and the development of the first problematic erosion

“hotspot”.

Continued migration of the inlet complex during 1956-1962, coupled with a shoal bypassing episode during late 1959, extended Topsail Islands measurable shoreline by two transects and caused the northern inlet shoulder to migrate ~390 m to the south. The last period of accretion for the shoreline reach between T-15 and T-16 occurred from 1956-1959 when minimal growth was recorded by both transects. T-14, which was located to the north of the

105 inlet’s protective zone, eroded 15.3 m from 1956-1959. By 1962, the shoreline reach encompassed by transects 5-16 experienced net erosion and the greatest changes were recorded at T-15 and T-16. As illustrated by Figure 18.2 D, the migration south and subsequent shoreline truncation caused the beach at T-15 and T-16 to erode an average of 30.4 m at a rate of -11.7 m/yr. New shoreline growth moved southward with the migration of the inlet complex, and caused an average shoreline advancement of 78.3 m at T-18 and T-19 which accreted at a rate of

12.8 m/yr from 1956-1962.

Near reach wide erosion was experienced along the shoreline reach of Hutaff Island with the exception of T-36 from 1949-1962. The accretion at T-36 amounted to a 48.9 m shoreline advancement that was a direct result of Old Topsail Inlet’s migration and channel realignment.

Transects 27-35 eroded an average of 48.3 m and the greatest loss was experienced at T-25 which was subject to the development of a large marginal flood channel from 1959-1962.

The period from 1938-1962 was the largest length of time that cumulative data could be collected along an extensive shoreline reach on Hutaff Island. The encompassing tidal inlets and their subjective migration pathways severely limited the amount of contiguous shoreline available for data collection. Rapid migration and photographic data limitations from this period forth limited all other datasets to a small number of transects. As illustrated through Figure 25,

Hutaff Island experienced severe erosion across all transects from 1938 -1962, with losses nearing 200 m at the flanks of the island. As the Hutaff Island shoreline tract was limited to ~

1500 m it is difficult to assess the cause of erosion near the center of the island, where as it is quite clear that adjustments to inlet morphology were responsible for the accelerated erosion at the islands flanks.

106

1962-1974

Unfortunately, as previously mentioned, a large gap in the photographic database exists between 1962 and 1974. Not only did this limit observation of inlet change during the period, but it also limits the amount of shoreline change that can be calculated. Because of the data gap, ~

500 m of new oceanfront shoreline could not be analyzed. That being said, the length of the shoreline reach and the lack of significant storm activity during the time period yield typical shoreline change rates.

The shoreline change zone on Topsail Island stretched from T-1 to T-18 and generally experienced net erosion. The average loss over the shoreline reach was 12.2 m at a rate of -1.05 m/yr. Averaged rates included accelerated rates recorded from the erosion hotspot located from

T-14 to T-16 where erosion rates ranged from 1.96 m/yr to 2.59 m/yr and losses totaled 22.8 m to 30.2 m. From 1959-1974 transects within the erosion hotspot lost an average of 49.3 m of beachfront at a rate of -3.47 m/yr. T-16 which suffered the highest loss, suffered 64.8 m of shoreline change at a rate of -4.5 m/yr. Although erosion rates in this area slowed from 1974-

1978 and some accretion occurred on T-14 and T-16 it was not due to natural changes. Instead, the decreased rates of erosion and small periods of accretion were likely linked to the construction of a small groin field on the southern end of Topsail Island or the undocumented placement of beach fill.

Accelerated rates of erosion continued to plague the small transect reach through 1986 when frequent nourishment projects were used to negate the ongoing erosion. However, by this time, cumulative losses experienced from 1959 -1986 resulted in an average shoreline retreat of

95.4 m. The continual erosion of the shoreline reach from T-14 to T-16 continued on through the rest of the 80’s and 90’s and is still a problem for the Sea Vista motel, which was built during the

107 construction boom of the late 60’s. During the time of construction, the beach in front of the motel was more than 100 m wide.

To the south of the 1962-1974 erosional reach, build out of the shoreline caused 44.36m of accretion to occur at a rate of 3.8 m/yr at T-19. The accretion at the area was likely a result of swash bar welding. By 1974 the Topsail Island planform had extended 387 m past the 1962 inlet shoulder and spurred new construction on the southern end of the island. Three finger canals, which exit into Banks Channel, were also excavated into the backside of the extended spit.

Shoreline change data for Lea/ Hutaff Island was recorded over a shoreline reach encompassed by T-29 to T-39. Nearly all transects recorded net accretion during the time period.

The overall average shoreline change recorded was 39.9 m at a rate of 3.4 m/yr. These average changes included the net erosion, which occurred from T-36 to T-38. Shoreline advancement totals for T-29 to T-35 ranged from 13.9 m at T-35 to 113.6 m at T-29. Increased rates of accretion were likely spurred by the realignment of the ebb channel at174º and the resultant positional change of the ebb shoal. Migration of New Topsail Inlet into the previously occupied inlet pathway of Old Topsail Inlet resulted in a dramatic change to the geometry of Hutaff Island

(Figure 6). The progression of the inlet to the south has also lead to the pirating of back barrier tidal creeks which were previously part of the Old Topsail Inlet tidal prism.

1974-1999

In a similar fashion to the RESULTS, the time covered by this interval has been broken down into smaller intervals so shore line changes can be discussed in more detail. The mini intervals are 1974-1982, 1982-1990, and 1990-1999. As stated in the RESULTS section, the

108 changes during the times discussed primarily deal with the southern portion of Topsail Island and the current IHA.

1974-1982

During this time interval, shoreline change data for the Topsail reach was collected along transects 14-22. The migration of the inlet channel 311 m to the south and the southern orientation of the ebb channel, which ranged from 173º to 180º, lead to the extension and truncation of the southern portion of Topsail Island. As previously discussed, extensive shoreline erosion has been the norm for the northern transects located on Topsail Beach, and although this is the southern portion of the Topsail shoreline, cumulative net erosion of 17.1 m was recorded over transects 14 – 19. The transitional apex between erosion and accretion was located between

T-19 and T-20, approximately 1200 m north of the inlet centerline and ~1400 m north of the main inlet channel. Accretion values ranged from 14 m at T-20 to 105.5 m at T-22 and were likely a direct result of inlet proximity and infilling of previous island curvature near the inlet shoulder.

The overall trend of accretion displayed in Figure 20 was likely due to the construction of a small groin field between T-20 and T-15 or undocumented nourishment activities related to maintenance dredging of Old Topsail Creek or Banks Channel. The subsequent trend of erosion from 1978-1982 may have been related to the removal of the groin field, but is more likely due to the natural truncation of the island, stemming from both inlet migration and channel alignment.

109

The southern alignment of the inlet channel during this period led to extensive build up of the shoreline on the Hutaff Island. In a similar fashion to what occurs along the Topsail Island oceanfront, the alignment of the inlet caused a large protrusion to form on the northern tip of the island. The shoreline bump initially spanned transects 29-31 in 1974, but migrated south as the inlet continued along its route and the ebb channel changed orientation. The bump was subsequently positioned between T-30 to T-32 in 1978 and T-31 to T-36 in 1982, when expansion of the bump lead to extensive progradation occurring from 1974 to 1982. The average shoreline transgression during this period was 108.5 m, but ranged from a maximum build up of

192.2 m at T-32 and a minimum build up of 36.8 m at T-37. The period from 1974 to 1982 was the last extensive building period (Figure 26) on Hutaff Island as the inlet’s morphology soon changed completely.

1982-1990

Cumulative changes from 1982-1990 were recorded along the Topsail Island shoreline by transects 17- 24. All transects along the shoreline reach recorded cumulative accretion during the time period. Cumulative net accretion ranged from 16.3 m at T-17 to 200.9 m at T-24; gradual increases in the amount of seaward movement were recorded as the inlet corridor was approached. Although cumulative changes along the shoreline reach resulted in net accretion across the board, shoreline change plots in Figure 21 indicate that erosion is still commonplace

Topsail Island. The up down behavior and sharp increases in shoreline position displayed by the plots is most likely a recorded of small nourishment projects or placement of dredged material on the beach. Information from the USACE indicates that between 1982 and 1988 four small-scale nourishment projects took place on Topsail Beach. Maintenance dredging of Old Topsail Creek,

110

Banks Channel and the AIWW yielded the total disposal of ~ 272,182 m3 of beach fill material along the islands oceanfront shoreline while two small scale nourishment projects from 10/85 -

12/85 and from 1/88-9/88 involved the placement of ~ 45,875 -115,450 m3 along Topsail Beach.

The placement of the above beach fill coupled with several natural events that built out the shoreline, lead to the reversal of previously discussed trend of shoreline retreat.

In addition to the documented nourishment activity a large bypassing episode and complete channel realignment occurred during the time interval. Breif periods of shoreline build up caused by swash bar welding and the northward orientation of the ebb channel were recorded along T-20 and T-21 during 1985 and 1986. Despite the welding events in the record, quantifying shoreline change as a result of inlet influence during this period is nearly impossible as the nourishment projects placed along the shoreline reach are subject to inlet influence and do not sustain extended lifetimes. However, inspection of the photographic database makes it clear that that much of the shoreline advancement during the late 80’s and early 1990 was a result of the bypassed ebb shoal welding to the southern portion of Topsail Island.

Interestingly, in addition to the accelerated accretion, which took place along the shoreline reach, two storms worthy of mention passed through the study area. The first was a large-scale nor’easter, which took place over the 28th and 29th of March, 1984, and was associated with several tornadoes in eastern North Carolina. The second was a category 2 hurricane (Diana) which made landfall south of Cape Fear on 9/12-9/13 1984. The nor’easter caused accelerated erosion rates over the shoreline reach encompassed by T-17 to T-24 and caused time averaged erosion rates ranging from 5.75 m/month to 21.9 m/ month. The average loss over the shoreline reach was 12.2 m/month (Figure 21b), but storm induced damage was the

111 likely culprit for all recorded erosion. On the other hand, accretion was recorded on 7 out of 9 transects during the time in which Hurricane Diana made landfall (04/1984-10/1984).

The Hutaff data set for 1982-1990 was limited to a small shoreline reach of ~ 600 m and

4 transects (T-31 through T-34), a result of limited photographic coverage. Although the shoreline reach was limited, data clearly showed that erosion was the norm for the leading barrier islands oceanfront. Inspection of the photographic database clearly indicates that the erosion suffered by the Hutaff shoreline was related to inlet migration and the changing orientation of the ebb channel. As a result of the previous build out during 1974-1982, transects nearest to the inlet corridor (T-31 and T-32) experienced the largest change in oceanfront position and receded and average of 156.6 m. Time averaged change rates recorded over the shoreline reach ranged from less than -1.0 m/month to -13.1 m/month. As indicated by Figure 28, periods of accretion did occur during the interval; however, they were greatly outweighed by the ongoing erosion.

Shoreline loss on Hutaff during this period was primarily related to inlet migration to the south, channel deflection to the north and the corresponding changes to the morphology of the ebb tidal delta. The limited to non-existent wave sheltering effect of the ebb shoal, paired with the expansion of the marginal flood channel along the Hutaff oceanfront was generally responsible for shoreline retreat on the northern portion of the island. The periods of accretion illustrated in Figure 28 (transects 31 and 32, and 33-34 to a lesser extent) were caused by small bar welding events and the expansion of the ebb shoal off the northern tip of the island.

1990-1999

The continued progression of the inlet throat on its southward trek during this period was paired with both and increase in island width and island length as well as the resultant island

112 truncation along Topsail Island. Coupled with inlet migration, changes to the oceanfront shoreline resulted from ebb channel deflection and its eventual realignment, a small bypassing episode which began in 1994, placement of beach fill from maintenance dredging operations, the land fall of three large hurricanes, and the resultant emergency beach nourishment projects subsequent to storm damage. The cumulative net effects of resultant change were recorded along a shoreline reach ~ 1200 m long and through T-18 to T-25. Shorter periods of shoreline change were recorded over longer reaches but were dependent on photographic documentation.

Over the Topsail shoreline reach, transects 18-24 recorded a net loss of beachfront which ranged from a maximum of 31.8 m at T-21 to a minimum of 7.6 m at T-19. The average loss for the shoreline reach was 19.4 m. Transect 25, the closest transect to the inlet complex was the only transect which recorded cumulative net accretion.

Accretion, which was recorded during the early portion of the time interval, was likely due to the tail end of a large welding event, which occurred near the end of 1989, and the possible placement of dredge materials along the Topsail oceanfront. Subsequent erosion during

1990-1991 was a likely result of changes to the position of the main inlet channel and its average heading of 157º. The ebb channel remained at this heading until late 1991 when it started its cyclic deflection to the north. Reach wide net accretion, which soon followed, was likely caused by the continued deflection of the ebb channel from 11/1993-01/1995 and the accompanied deposition and welding of swash bars. Transects 16-24 recorded a mixture of both accretion and erosion during this short time period. The average shoreline advancement recorded from T-16 to

T-24 was 37.2 m and ranged from a maximum of 56.7 m at T-24 to a minimum of 24 m at T-21.

Time averaged change rates ranged from 12.1 m/month to less than 1 m/month.

113

Reach wide shoreline erosion occurred during two periods during the interval, the first was from 06/1996-09/1996 and the second was from 08/1998-03/1999. Both periods were subsequent to hurricane landfall, hurricanes Bertha and Fran during 06/96-09/96 and Hurricane

Bonnie during 08/19/-03/99. A third period of near reach wide erosion occurred from 10/1991-

05/1992, and was likely due to an undocumented winter storm event. The average shoreline retreat during 06/96-09/96 was 33.8 m and had losses ranging from 78.5 m at T-25 to 12.5 m at

T-21. The time averaged losses during this period ranged from 26.1 m/month to 4.1 m/month.

Storm damage losses for Hurricane Bonnie were not as extensive as the average reach wide loss was 20 m and the maximum amount of shoreline retreat was 33.1 m. In unassociated events, an average retreat of 16.6 m was recorded by the shoreline reach encompassed by T-17 to T-24 from 10/1991-05/1995, at rates, which ranged from -24 m at T-20 to -4.1 m at T-24. Meanwhile the build out of the shoreline occurred at T-25 and T-26 because of swash bar welding and the infill of a previously eroded inlet shoulder.

Data from the USACE indicates that the total documented volume of beach fill placed on

Topsail Beach from 1990-1999 was ~298,940 m3. Inspection of the both the shoreline change data and the photographic database indicate that there were at least two beach fill projects; the first, subsequent to shoreline loss recorded from 10/1991-05/1992, and the second as an emergency fill project post Hurricane Fran. Fill from the first project (10/1991-05/1992) was placed between T-12 and T-17. Unfortunately, data gaps in the shoreline database prohibited the amount of buildup, which occurred from being recorded, but cursory measurements indicate that

~ 45 m of change occurred between the HWL in 1989 and the HWL at the end of the project. As a portion of the project took place within the current IHA, much of it was quickly eroded and inlet influences soon dominated changes in the area. In a situation similar to that described

114 above, much of the fill operation which took place post Hurricane Fran was not documented, however the average progradation over all transects (T-18 to T-25) was 26.5 m during the six month period in which the project took place. It is quite likely that the net loss recorded during

1990-1999 would have been much higher had these operations not taken place.

The shoreline change record for Hutaff Island for 1990-1999 is very limited as T-34 and

T-35 were the only transects in continual existence (with shoreline data) for the period.

Inspection of Figure 29 illustrates that the first shoreline setback corresponds to the start of ebb channel deflection in 10/1991, the subsequent expansion of the marginal flood channel and the shifting of the ebb shoal to the north. The first significant period of shoreline accretion took place during 6/1996 and was a direct result of ebb channel realignment. The channel shift from

136º to 173º, which occurred between 11/1994, and 01/1995 was associated with several bar welding events. The continued periods of accretion and erosion exhibited by the plots in Figure

29, from 1996 to late 1998, were the result of continual changes to the morphology of the ebb delta. When the ebb channel began its second deflection to the north in 08/1998, erosion again became the norm for the shoreline reach.

In addition to the shoreline changes caused by the inlet channel, migration of the inlet throat caused large changes to the planform of Hutaff Island. As the inlet progressed south, continued erosion on the southern inlet shoulder caused a breach between Hutaff and previously deposited, back barrier mash islands (Figure 43). The breach eventually lead to the

115

Figure 43. Composite image illustrates changes to the Hutaff Island planform incurred due to inlet migration and the subsequent breach between Hutaff and previously deposited marsh islands in the back barrier.

116 closure of Old Topsail Inlet in 10/1998 (CLEARY and MARDEN, 1999) as its main feeder channel became part of the New Topsail Inlet tidal prism. The increase in tidal prism had a direct effect on the shape of the inlet throat and increased its minimum width from 483 m in 11/1993 to 700 m in 11/1994.

1999-2006

The most recent period of recorded oceanfront change was similar to previous time periods and was characterized by inlet migration, channel deflection, island truncation and beach nourishment operations. Cumulative oceanfront change observations were recorded over a ~

1200 m shoreline reach and by transects 18-27. Long-term shoreline change data was also available for the period and allowed positional changes to be observed over a longer reach between T-6 and T-26. Unfortunately, the gap between 03/2003 and 01/2005 was too long to record short-term changes which occurred to a nourishment project that was underway in March,

2003.

Near reach wide accretion was the net cumulative change recorded by the shoreline encompassed by T-17 to T-27. Shoreline advancement ranged from 10.1 m at T-19 to 244.8 m at

T-27. The amount of accretion sustained by each transect increased with proximity to the inlet

(Figure 23). Transect 18, which was located on the cusp of inlet influence, was the only transect where net erosion was recorded.

A similar trend was displayed by the long-term shoreline change data, where T-19 through T-26 also recorded net accretion. The long-term accretion values ranged from 10.3 m at

117

T-19 to 163 m at T-26. Shoreline retreat was recorded by all other transects within the extended shoreline reach (T-6 to T-18) despite the fact that as much as 63 linear meters of beach fill was placed along Topsail Beach in 2003. Accelerated erosion values as high as 28 m/yr at T-14 indicate that the project was short lived and likely influenced by the proximity of New Topsail

Inlet.

Limited movement of the ebb channel during this period, which had a directional average of 138º (range of 147º-127º), coupled with a total channel migration of -30.2 m caused a dramatic change to the planform of Topsail Island. Changes facilitated by ebb channel orientation included the buildup of a large shoreline protrusion near T-24/T-25, and caused an increase of 88 m to the islands width from 1999-2003. Accretion on the southern tip of Topsail

Island was likely influenced by both channel position and the wave sheltering effect of the ebb shoal. The accelerated buildup rates may have been further influenced by the placement and immediate erosion of the large beach fill project directly north of T-18. Further advances of the shoreline position from 2003 to 2006 at T-26 and T-27 were the result of infill between the inlet shoulder and the large bump created from 2002-2003.

Changes along Hutaff Island during the period were recorded along a very limited shoreline reach. Cumulative changes were only available for T-35 and T-36 as the shoreline in front of T-34 eroded completely between 10/2003 and 01/ 2005. Although erosion was the dominant shoreline change factor from 1999-2006 small period of accretion also occurred. The shoreline advancement, illustrated by Figure 30, during 2001 was a result of ebb swash bar welding, as was the buildup during 2002. As there were no ebb-channel realignment events during this period, erosion along Hutaff Island was likely caused by the deflection of the ebb channel to the north and the loss of the breakwater effect of the ebb shoal. In a fashion similar to

118 the previous periods, development and expansion of the marginal flood channel was the likely culprit for the recorded erosion along the shoreline reach and the planform changes to the Hutaff inlet shoulder.

Future Changes and Implications

The long history of inlet migration and the increase in migration rate from -29.7 m/ yr during 2002-2003 to 21.4 m/yr during 2003-2006 suggest that New Topsail Inlet will not stop its migration to the southwest anytime soon. It is likely however, that migration rates will remain similar to those of the recent past as it continues to move through areas previously occupied by

Old Topsail Inlet. The continued migration of the inlet will likely lead to an increase in its tidal prism and therefore an increase in the average minimum width; a trend, which has been observed throughout its history. In fact, the inlet’s minimum width increased by ~ 75 m during the last three years of the study. As discussed, the increase in width will lead to an increase in both the inlet’s sand trapping capabilities and the size of the ebb shoal, ultimately leading to a larger area subject to inlet influence.

The deflection and realignment of the ebb channel will continue to affect both the leading and trailing barriers. Although previous bypassing events ranged from 3 to ~7 years it is difficult to predict when the next one might take place. What is clear though is that as the inlet continues to migrate, shoreline truncation of the trailing barrier (Topsail Island) will occur.

The consequence of inlet migration will remain the same as it has in the past and will ultimately result in shoreline retreat. Although erosion has occurred along the length of the

Topsail Shoreline reach, areas of maximum erosion will continue to occur in the same locations as periods of maximum accretion. The issue here is that previously wide stretches of beach front 119 that assured home builders that their houses would be safe will soon erode as shoreline regression continues. Currently, homes built to the southeast of the southernmost finger canal are of concern. These houses will likely face fates similar to the Sea Vista Motel (transect 15), who’s continued presence on the beach has been entirely based on periodic beach nourishment projects.

In fact, several of the homes on the eastern side of the road are already dangerously close to the

2006 HWL. The continued migration and truncation of the island will soon eroded the last of the recurved dune ridges protecting these structures and they will likely be exposed to the open oceanfront in five to ten years.

Erosion mitigation along Topsail Beach will continue to remain a problem for the town as shoreline retreat continues to threaten structures along the oceanfront. Previous mitigation efforts undertaken by the town have proved to be short lived and ineffective as displayed by the complete erosion of the last beach nourishment project in less than two years. The possible reduction in funding from the Federal Government for both navigational and maintenance dredging operations as well as beach nourishment projects could create a severe problem for

Topsail Beach as these procedures would become the responsibility of the state and local government.

The extent of the current IHA clearly does not cover all areas of inlet influence. The continued and accelerated erosion of fill placed on the beach is a clear indication of inlet influence outside the realm of the IHA. Setback limitations and size restrictions to new construction on the island must be applied farther north of the inlet in order to for costly mistakes to be reduced. This is of particular importance for future projects if the Federal Government does indeed reduce or halt funding for aforementioned operations. The extent of the newly proposed

IHA for Topsail Beach is a much more realistic representation of the area subject to inlet

120 influence. These extended restrictions would reduce costs to both local governments and taxpayers as new construction locations, similar to the houses on the southern end of the island, would be subject to tighter regulations.

CONCLUSIONS

The continual and long-term migration of New Topsail Inlet between 1938 and 2006 caused an overall shift of 1750 m in the position of the inlet. Migration rates during this period ranged from a minimum of 1.1 m/yr from 1959 -1962 to a maximum of 73.7 m/yr during 1945-

1949. Although uncommon, two periods of northern migration did occur, the first from 1938-

1945, the second from 2001-2003. Migration rates during these two periods were -16.9 m/yr and

-13.1 m/yr respectively. Migration of the inlet was accompanied by several long lasting changes to the inlet morphology. Changes included variations in the inlet minimum width, which was initially 398.8 m in 1938 but continued to increase with the migration of the inlet and the increase in tidal prism. By 2006, the inlet minimum width was 701.8 m, the widest it had been during the study.

The changes in channel position and orientation of the ebb channel lead to numerous changes in the size, shape, and position of the ebb tidal delta. Ebb channel orientation ranged from a near shore normal position of 148º to a maximum of 180º and a minimum of 104º.

Changes to both the direction of the ebb channel and the position of the main inlet channel caused variations to the size and location of the ebb tidal delta. Ebb delta size ranged from a minimum of ~ 2,394,790 m3 during 1956 to a maximum of ~ 5,348,990 m3 during 2003. The cyclic deflection of the ebb channel often caused the ebb shoal to be skewed to the north and exhibit asymmetrical morphology. Morphology that resembled the classic inlet occurred

121 infrequently, and was only seen when the ebb channel maintained a shore normal position and a symmetrical ebb tidal delta was formed.

Changes to the interior inlet morphology began in 1956 when the inlet main inlet channel started to exhibit increased curvature. The shift in channel orientation with in the back barrier was likely a result of the inlet migrating into a space previously occupied by Old Topsail Inlet and its associated flood shoal. The change to the interior morphology resulted in a lack of space for New Topsail Inlet’s flood shoal and caused it s eventual migration and reorientation with in

Banks Channel, behind the Topsail Island spit. The displacement of the flood shoal started sometime between 1962 and 1974 and ended when the flood ramp had completely reoriented itself in line with Banks Channel and the incoming flood tide during 1982.

Several bypassing events were associated with the migration of the main inlet channel and the cyclic deflection of the ebb channel. During the short-term intensive study, from 1982 to

2003, four bypassing events of various lengths took place. The events ranged from ~ 3 years to greater than 7 years in length and reached various degrees of completion. Only one event moved through the complete cycle; ebb channel orientation ranged from 180º near the start of the cycle to 106º before the ebb shoal was breached. Bypassed sediment amounts ranged from a minimum of 267,590 m3 to a maximum of 841,010 m3 and channel jumps between realignments ranged from 62º to 24º.

Both the Topsail Island and the Hutaff Island shoreline reaches were primarily characterized by net erosion and shoreline retreat. Net accretion did occur along small shoreline tracts within the current zone of inlet influence. Migration of the inlet complex and the deflection of the ebb shoal played a large role in shoreline position. Migration of the inlet resulted in the

122 erosion of the leading barrier and the truncation of the trailing shoreline. Areas that previously experienced accelerated accretion soon became erosion “hotspots” as the inlet migrated and the geometry of the island shifted. Ebb channel deflection and the wave sheltering effect of the skewed ebb shoal were often the cause of accelerated accretion and the buildup of large shoreline protrusions. Typical rates of erosion along the Topsail Island shoreline reach were ~ 1 m/yr, but also experienced accelerated rates that ranged from 2.4 m/yr to 5.6 m/yr. Rates of erosion for the

Hutaff Island reach were typically much higher and compared with storm damage erosion on

Topsail Island; erosion rates as high as 13.1 m/month were recorded on the Hutaff shoreline reach.

Erosion rates were typically higher along the Hutaff Island shoreline due to the exposed nature of the beachfront. The typically skewed geometry of the ebb shoal severely limited the wave sheltering effect of the delta. Also, the geometry of the ebb would typically lead to the development and expansion of a marginal flood channel just off the tip of the island. The position of the marginal flood channel accelerated erosion along the shoreline tract by scouring away the beachfront and portions of the southern inlet shoulder.

123

LITERATURE CITED

ANDERS, F.J. and BYRNES, M.R., 1991. Accuracy of shoreline change rates as determined from maps and aerial photographs. Shore and Beach, 59(1), 17-26.

AUBREY, D.G. and SPEER, P.E., 1984. Updrift Migration of Tidal Inlets. The Journal of Geology, 92(5), 531-545.

BRUUN, P., 1990. Improvement of bypassing and backpassing at tidal inlets. Journal of Waterway, Port, Coastal, and Ocean Engineering, 117(4) 494-500.

BRUUN, P., 1996. Navigation and sand bypassing at inlets: technical management and cost aspects. Journal of Coastal Research, Special Issue 23, 113-119.

BRUUN, P. and GERRITSEN, F., 1959. Natural bypassing of sand at coastal inlets. Journal of the Waterways and Harbors Division , ASCE, 85, 401-412.

CLEARY, W.J., 1994. New Topsail Inlet, N.C. migration and barrier realignment: consequences for beach restoration. Union Geographique Internationale Commission Sur L’Environment Crotier C, Institute de Geographique,116-130.

CLEARY, W.J., 1996. Inlet induced shoreline changes: Cape Lookout – Cape Fear. In: CLEARY, W.J. (ed.), Environmental Coastal Geology: Cape Lookout to Cape Fear, NC. Carolina Geological Society Fieldtrip Guidebook, pp. 49-60.

CLEARY, W., 2002. Variations in inlet behavior and shoreface sand resources: factors controlling management decisions, Figure Eight Island. NC, USA. Journal of Coastal Research, Special Issue 36, 148-163.

CLEARY,W.J., RIGGS, S.R., MARCY, D.C. and SNYDER, S.W., 1996. The influence of inherited geological framework upon a hardbottom-dominated shoreface on a high energy shelf: Onslow Bay, North Carolina, USA. Geology of Siliciclastic Shelf Seas, Geological Society Special Publication 117, pp 249-266

CLEARY, W.J., and MARDEN, T.P., 1999, Shifting Shorelines: A Pictorial Atlas of North Carolina Inlets, UNC SG-99-04, Raleigh, NC, 51 p.

CLEARY, W.J., HOSIER, P.E., and WELLS, G.R., 1979, Genesis and significance of marsh islands within southeastern North Carolina lagoons, Journal of Sedimentary Petrology, 49 (3), pp. 703-709.

124

CLEARY, W.J., JARRETT, J.T., SAULT, M., JACKSON, C.W., and WELSH, J.M., 2003. Inlet-induced shoreline changes: linkage between channel migration and ebb-tidal delta reconfiguration, Bogue and New River Inlets, North Carolina. Coastal Sediments 03, American Society of Civil Engineers, 15p.

CLEARY, W.J.; WILLSON, K.T., and JACKSON, C.W., 2004. Shoreline restoration in high hazard zones: southern North Carolina, USA. Journal of Coastal Research, Special Issue 39, 884-889.

CROWELL,M.; LEATHERMAN, S.P., and BUCKLEY, M.K., 1991. Historical shoreline change: error analysis and mapping accuracy. Journal of Coastal Research, 7(3), 839-853.

DOLAN, R.; HAYDEN,B.P.; MAY, P., and MAY,S., 1980. The reliability of shoreline change measurements from aerial photographs. Shore and Beach, 48(4), 22-29.

FENSTER, M. and DOLAN, R., 1996. Assessing the impact of tidal inlets on adjacent barrier island shorelines. Journal of Coastal Research, 12(1), 294-310.

FITZGERALD, D.M. and PENDLETON, E., 2002. Inlet formation and evolution of sediment bypassing system: New Inlet, Cape Cod, Massachusetts. Journal of Coastal Research, Special Issue 36, 290-299.

FITZGERALD, D.M.; KRAUS, N.C., and HANDS, E.B., 2001. Natural mechanisms of sediment bypassing at tidal inlets. ERDC/CHL CHETN-IV-30, U.S. Army Engineer Research and Development Center, Vicksburg,MS. (http://chl.wes.army.mil/library/publications/chetn) Accessed 11/03/05.

FITZGERALD, D.M.; PENLAND, S., and NUMMEDAL, D., 1983. Control of barrier island shape by inlet sediment bypassing: East Frisian Islands, West Germany. Marine Geology, 60, 355-376.

GAMMILL, S.P., 1990. Coastal saltmarsh development at southern Topsail Sound, North Carolina. Master’s Thesis. University of North Carolina Wilmington, 51p.

GAUDIANO, D.J. and KANA, T.W., 2001. Shoal bypassing in mixed energy inlets: geomorphic variables and empirical predictions for nine South Carolina inlets. Journal of Coastal Research, 17(2), 280-291.

HASBROUCK, E.G., 2008. The influence of tidal inlet migration and closure on barrier planform changes: Federal Beach, NC. Masters Thesis (M.S.), University of North Carolina Wilmington, 80p.

HAYES, M.O., 1980. General morphology and sediment patterns in tidal inlets. Sedimentary Geology, 26, 139-156.

125

JARRETT, J.T., 1976. Tidal prism-inlet area relationships. Vicksburg, Mississippi: U.S. Army Corps of Engineers, GITI Report No. 3, 54p.

JACKSON JR., C.W., 2004. Quantitative shoreline change analysis of an inlet-influenced transgressive barrier system: Figure Eight Island, North Carolina. Master’s Thesis. University of North Carolina Wilmington, 95p.

KOMAR, P.D. and INMAN, D. L., 1970. Longshore sand transport on beaches. Journal of Geophysical Research, 75(30), 5914- 5927.

MCALLISTER, R., 2006. Topsail Island: Mayberry by the Bay. Wilmington, North Carolina: John F. Blair, 228p

MCGINNIS, B.A., 2004. Late Holocene evolution of a retrograding barrier: Hutaff Island , North Carolina. Masters Thesis. University of North Carolina Wilmington, 105pg.

MOORE, L.J., 2000. Shorline mapping techniques. Journal of Coastal Research, 16(1), 111-124.

North Carolina Division of Coastal Management (NCDCM), June 2006. Maps and Spatial Data Page. http://dcm2.enr.state.nc.us/Maps/chdownload.htm Accessed 6/25/06

North Carolina Division of Coastal Management (NCDCM), September 2003. CAMA Handbook for Development in Coastal North Carolina. http://dcm2.enr.state.nc.us/Handbook/contents.htm Accessed 6/25/06

PAJAK, M.J. and LEATHERMAN, S., 2002. The high water line as a shoreline indicator. Journal of Coastal Research, 18(2), 329-337.

Pender County GIS Department, June 2006. Maps and Spatial Data Page. http://gis.pendercounty.com/ConnectGISWeb/%28S%28j0xsknubke1i0j5552ttbv55%29 %29/Default/Default.aspx Accessed 6/25/06.

RIGGS, S.R.; CLEARY, W.J., and SNYDER, S.W., 1996. Morphology and dynamics of barrier and headland shorefaces in Onslow Bay, NC. In: CLEARY, W.J. (ed.), Environmental Coastal Geology: Cape Lookout to Cape Fear, NC. Carolina Geological Society Fieldtrip Guidebook, pp. 33-48.

SEABERGH, W.C. and KRAUS, N.C., 2003. Progress in management of sediment bypassing at coastal inlets: natural bypassing, weir jetties, jetty spurs and engineering aids in design. Coastal Engineering Journal, 45(4), 533-563.

126

USACE, 1990, Final Feasibility Report and Environmental Impact Statement, Hurricane Protection and Beach Erosion Control, West Onslow Beach and New River Inlet, North Carolina (Topsail Beach), U.S. Army Corps of Engineers, Wilmington District, 74 p. plus appendices..

USACE, 2006, Draft GRR and EIS Report on Hurricane Protection and Beach Erosion Control, West Onslow Beach and New River Inlet, (Topsail Beach), NC, U.S. Army Corps of Engineers Wilmington District, 2,076 p.

127