THE FLORIDA STATE UNIVERSITY

COLLEGE OF SOCIAL SCIENCES

QUANTIFICATION, ANALYSIS, AND MANAGEMENT OF INTRACOASTAL
WATERWAY CHANNEL MARGIN EROSION IN THE GUANA TOLOMATO MATANZAS NATIONAL ESTUARINE RESEARCH RESERVE, FLORIDA

By
FRANKLIN D. PRICE

A Thesis submitted to the Department of Urban and Regional Planning in partial fulfillment of the requirements for the degree of Master of Science

Degree Awarded: Spring Semester, 2005The members of the Committee approve the thesis of Franklin D. Price defended on March 29, 2005

.
Robert Deyle Professor Directing Thesis

Sergio Fagherazzi Outside Committee Member

John Thomas Committee Member

The Office of Graduate Studi es has verified and approved the above named committee members.

iiACKNOWLEDGEMENTS

I would first like to thank my wife, Kadee, for her tolerance and assistance over the past three years and for being the most understand ing, supportive friend a nd the best lover I could ever imagine.

I would also like to thank my parents for having me. Now that I am finishing my Master’s, I cannot believe how hard it must have been to have a kid while in grad school.

I would finally like to thank the Matanzas Ri ver for giving me the in spiration I needed to make myself work, my boss, Helen Light , who allowed me the time to work, my committee for being available to answer que stions, Melanie Darst for her editing assistance, my brother Samuel for letting me use his boat for field work, and the helpful staffs of the GTMNERR, the FDOT, the FIND, the USCOE, the FDEP, the FFWCC, the SJRWMD, the USGS, NOAA, the St. Johns County GIS office, and Florida Sea Grant.

iiiTABLE OF CONTENTS

List of Tables ................................................................................................................. ................ vi List of Figures................................................................................................................ ............... vii
Abstract.......................................................................................................................................... ix
INTRODUCTION .......................................................................................................................... 1
1. QUANTIFICATION AND ANALYSIS OF EROSIVE TRENDS........................................... 4 Background......................................................................................................................... 4 Methods........................................................................................................................ ..... 14 Results........................................................................................................................ ....... 24 Discussion......................................................................................................................... 31 Further Research ............................................................................................................... 32
2. EROSION MANAGEMENT ALTERNATIVES ................................................................... 33
Introduction................................................................................................................... .... 33 The Goals of Inshore Erosion Management ..................................................................... 33 Stabilization Based Alternatives....................................................................................... 34 Regulation Based Strategies ............................................................................................. 37
3. POLICY GOVERNING IMPLEMENTATION OF MANAGEMENT ALTERNATIVES... 39
Introduction................................................................................................................... .... 39 Implementation of Stabilization Plans.............................................................................. 39 Implementation of Regulation Plans................................................................................. 40
CONCLUSION..................................................................................................................... ........ 45
GLOSSARY ................................................................................................................................. 46
APPENDIX................................................................................................................................... 47
REFERENCES ............................................................................................................................. 64

ivBIOGRAPHICAL SKETCH ........................................................................................................ 70

vLIST OF TABLES

1. Summary of 1970/1971 channel margin classification..................................................... 10
2. Indicators of factors affecting erosion and accretion........................................................ 19
3. Summary of area eroded 1970/1971 to 2002.................................................................... 24
4. Summary of lateral moveme nt from 1970/1971 to 2002.................................................. 25
5. Regression of lateral movement on significant causal factors and margin type............... 28
6. Correlations of causal factors a nd channel margin movement ......................................... 30

viLIST OF FIGURES

1. Study area – Southern portion of Guana Toloma to Matanzas National Estuarine Research Reserve (GTMNERR) ........................................................................................................ 2
2. Factors affecting erosion and accretion along an estuarine channel margin ...................... 4
3. Alterations in the vicinity of Matanzas Inlet....................................................................... 9
4. Digitizing the channel margin in th e vicinity of a side channel ....................................... 16
5. Estimation of error ............................................................................................................ 16
6. Classification of channel margin types............................................................................. 17
7. Methods used to measure erosion and accretion............................................................... 18
8. Coding of exposure to waves caused by predominant winds ........................................... 20
9. Determination of exposure to navigation channel boat wakes ......................................... 21
10. Measurement of distance from edge of 1999 navigation channel to channel margin ...... 22
11. Coding of curvature variable and dete rmination of radii of curvature ............................. 23
12. Minimum, maximum and quartile rates of lateral movement from 1970/1971 to 2002 classified by margin type .................................................................................................. 26
13. Minimum, maximum and quartile rates of lateral movement from 1970/1971 to 2002 classified by exposure to causal factors............................................................................ 27
14. 1970/1971 to 2002 change in area estimated from rates of lateral movement ................. 29
15. Project Greenshores in Pensacola, Florida........................................................................ 36
16. Boat registrations in Flagler a nd St. Johns Counties, 1977 to 2001 ................................. 38
17. Index of plates................................................................................................................... 47
18. Plate 1........................................................................................................................ ........ 48
19. Plate 2........................................................................................................................ ........ 49

vii20. Plate 3........................................................................................................................ ........ 50
21. Plate 4........................................................................................................................ ........ 51
22. Plate 5........................................................................................................................ ........ 52
23. Plate 6........................................................................................................................ ........ 53
24. Plate 7........................................................................................................................ ........ 54
25. Plate 8........................................................................................................................ ........ 55
26. Plate 9........................................................................................................................ ........ 56
27. Plate 10....................................................................................................................... ....... 57
28. Plate 11....................................................................................................................... ....... 58
29. Plate 12....................................................................................................................... ....... 59
30. Plate 13....................................................................................................................... ....... 60
31. Plate 14....................................................................................................................... ....... 61
32. Plate 15....................................................................................................................... ....... 62
33. Plate 16....................................................................................................................... ....... 63

viiiABSTRACT

The Guana Tolomato Matanzas National Estuarine Research Reserve is one of twenty-six such reserves in the United States established wi th the intent of protecting coastal estuaries. GIS-based analysis of aerial photographs of the sout hern half of the reserv e reveals high rates of erosion along the margin of the Atlantic Intracoastal Waterway which runs through the reserve. From 1970/1971 to 2002 nearly 70 hectares (approxi mately 170 acres) of shoreline habitat were degraded by erosion along the 64.8 kilometers of channel margin analyzed. Wakes generated by vessels in the Intracoas tal are hypothesized to be the primary cause of this erosion. An examination of the relationships between lateral movement of the channel margin and factors with the potential to affect erosion and accre tion supports this hypothesis. Exposure to boat wakes was found to be the causal factor most str ongly correlated with ra te of lateral margin movement. Margin movement rates were also fo und to vary significantly with exposure to wind waves and with the type of channel margin eroded. A reduction in nearshore wave energy appears to be necessary to allow the recovery of impacted ecosystems. Approaches to erosion management based on nearshore st abilization and regula tion of navigation are discussed, and the intricacies of the implementation of such plans are described.

ixINTRODUCTION

Coastal wetlands worldwide are increasingly valued for buffering the capacity of coastal storms to flood or erode upla nds, filtering urban runoff, provi ding wildlife habitat, and supporting coastal fisheries (Bea tley, Brower, & Schwab, 2002). Rapid development of coastal regions has led to the establishment of an array of local, state, and national regulatory efforts to protect these values. Among the national pr ograms in the United States which support conservation of coastal wetlands is the National Estuarine Research Reserve (NERR) system. The NERR program was created by the Coasta l Zone Management Act of 1972 (National Estuarine Research Reserve System, 2004) to en courage “long-term re search, water-quality monitoring, education, and coastal stewardship” (Guana Tolo mato Matanzas Reserve, 2004, February 18). The reserves, which constitute the system, are selected from areas nominated by states to represent distinct bioge ographic regions. If chosen fo r incorporation into the national program, the reserves enter into a federal-stat e partnership in which the National Oceanic and Atmospheric Administration ( NOAA) provides 50% of fundi ng for reserve operation and a cohesive, system-wide management structure. State partners are responsible for providing the remaining 50% of funding and for management of resources and administration of programs at the local level. The federal government does not purchase or as sert direct management authority over the reserve lands, but instead relies on the states to provide resource protecti on to “ensure a stable environment for research" (Natio nal Estuarine Research Reserve System, 2005(a)). Still, conservation is a significant focus of the NERR system. This is well-reflected in one of the stated objectives of the reserve program— to “m aintain and enhance the integrity of reserve habitats through stewardship and restoration” (National Estuar ine Research Reserve System, 2004). The emphasis on resource protection is fu rther emphasized in the fact that NOAA is authorized to withdraw the designation of a rese rve if a stable resear ch environment is not maintained (National Estuarine Research Reserv e System, 2005(b)). With this in mind, it is clear that any degradatio n of habitat within a re serve would be an issue of concern. This study addresses one such issue of concern in the Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR)— the issue of habitat degradation due to erosion along the

1margin of the Atlantic Intracoas tal Waterway (AICW). Not only is such habitat degradation an issue of concern given the reserve management objectives, but it also co ntradicts the desired trend of “no net loss of wetla nds” supported by local regula tions (Flagler County, 2004 ) and federal commitments (U.S. Environmental Protection Agency, 2004). The GTMNERR is divided into two secti ons, together comprising approximately 24,000 hectares (60,000 acres) in St. Johns and Flagler c ounties in northeastern Florida. The Guana, Tolomato, and Matanzas Rivers are the major estuar ine bodies of the reserve; together they form a string of relatively narrow “bar bounded” estuaries behind the barrier islands which line the Atlantic coast. This study focuses on the AICW in the southern portion of the GTMNERR (Figure 1). The AICW in the st udy area consists of a marked ch annel in the Matanzas River, portions of which have been deepened and stra ightened to provide fo r navigation, and several reaches of completely man-made channel.

St. Johns County

Flagler County Atlantic Ocean 

# ¢

012345 Kilometers Legend Study area GTMNERR

GTMNERR GTMNERR

Figure 1: Study area – Southern portion of Gu ana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR)

2Habitats found in the reserve include salt ma rsh and mangrove tidal wetlands, oyster bars, estuarine lagoons, creeks and rive rs, dredge spoil dis posal areas, upland, and a section of the adjoining Atlantic Ocean. It is of interest th at the mangrove wetlands in the reserve constitute “the northern-most extent of mangrove habitat on the east coast of the United States” (Guana Tolomato Matanzas Reserve, February 18, 2004). Although the reserve is described as relatively undeveloped, the hydrology of the estuaries has b een significantly altere d by human activities, including the construction of th e AICW (Guana Tolomato Matanzas Reserve, 2004, February 18) which was first dredged as early as 1883 (F lorida Inland Navigation District, 1967). Years of personal observations and a brief pilot study conduc ted in the fall of 2003 made apparent the process of erosion and subsequent habitat degradation in the GTMNERR. Although erosion is a natural process, th e high rate of erosion observed in the GTMNERR appeared to be degrading natural habitats at a ra te far faster than they could re build. Studies have shown that lateral erosion of salt ma rsh channels, such as that of the AICW and its tidal tributaries, is naturally offset by deposition in other areas (L etzsch & Frey, 1980). Thus, any observation of widespread erosion, not offset by accretion el sewhere, warrants careful examination. The margin of the AICW channel which runs through the reserve has eroded considerably over the past thirty years. As a result, productive habita ts, including salt marsh, mangroves, and oyster bars, are being eroded and replaced by intertidal sand flats which are considerably less productive (Montague & Wiegert, 1990) and t hus, also considerably less valuable from an anthropocentric perspective. The channel of the AICW in the GTMNERR is lined with tidal creeks, oyster bars, salt a nd mangrove marshes, dredge spoil islands, and developed uplands. The intent of this study is to quantify the extent of habitat loss due to channel margin erosion from 1970 to 2002, examin e correlations between erosion rates and possible causal factors, investigat e management alternatives which could be used to limit habitat degradation, and examine the regulatory fram ework surrounding the implementation of such alternatives.

3CHAPTER 1

QUANTIFICATION AND ANALYSIS OF EROSIVE TRENDS Background

The process of habitat loss to erosion in the GTMNERR can be described as erosion along the margin of a major estuarine channe l which has been modified to provide for navigation. Sediment transport in estuaries has been widely studi ed, and the basic mechanics of it are well understood. While the majority of studies concerned with erosion and accretion within estuaries have focused specifically on salt marsh channels, the findi ngs have applications to channels of other margin types. Along estu arine channel margins, erosion and accretion are regulated by the interaction of fo rces that add energy to the near shore environment with variables which regulate the input of new sediment and wh ich govern sediment mobility (Figure 2).

Sediment

Supply

Biological Stabilization and Destabilization Sediment

Type Waves

and Wakes

Tidal Currents

Dredging and Filling Sediment Movement

Sediment

Input

Sediment Mobility Erosion or Accretion of Channel Margin

Figure 2: Factors affecti ng erosion and accretion along an estuarine channel margin

4As displayed in Figure 2, the primary forces re sponsible for the movement of sediment are waves, currents, and human dredging and filling. Waves and currents affect shoreline sedimentary processes by adding energy to the nearshore environment. Dredging and filling physically add or remove sediment. Sediment s upply regulates the amount of sediment available for accretion, and the sediment type and level of biological stabilization or destabilization govern the mobility of channel margin sediments. Of these factors, several can be disregarded as potential causes of the erosion in the GTMNERR and several are likely contributing causes. The role of sea level is also addre ssed below due to its connection to the global climate change debate and frequent associati on with coastal erosion.

Waves and Wakes In modern estuarine systems, the two majo r sources of wave energy are wind waves and boat wakes. Both are recognized as capable of causing significant sediment transport in a variety of aquatic environments. The shoreline impact of waves generated in estuaries is influenced by a number of factors, but two of the most si gnificant of these are nearshore bathymetry and bottom friction. Because waves break and lose energy when they enter sufficiently shallow water, the wave energy at impact, and thus the erosive capacity of a wave, is significantly affected by the bathymetric profile of nearshore areas. A gently sloping profile a llows wave energy to dissipate gradually because waves break farther from the shore, while a steep profile focuses a larger portion of the wave energy directly on the shorelin e. In a similar manner, submerged bars off a shoreline can significantly reduce the impact of waves approachi ng from open water. Increased bottom friction also leads to a decrease in wave energy. Quantification of the effects of bathymetry and bottom friction in the GTMNERR is difficult; however, these factors are certainly of importance. Even a cursory observation of shorelines in the study ar ea reveals a great deal of variation in nearshore depths and substrate types. The level of variation makes measuremen t and analysis of the role of this variation difficult. Wind waves are cited as a cause of marsh er osion in a number of studies (Day, Scarton, Rismondo, & Are, 1998; Doane, Wells, & Merma n, 1998; Downs, Nicholls, Leatherman, & Hautzenroder, 1994; Phillips, 1986b; Schwimmer, 2001). Waves cause marsh erosion directly

5by undermining the stabilizing root mat of smooth cordgrass, Spartina alterniflora , the dominant marsh vegetation in the GTMNERR. Non-marsh channel margins are eroded more gradually. The prediction of the extent of wind wave erosion is difficult due to the number of factors which influence wave energy at bank impact. These factors include wind sp eed, duration and fetch (distance that winds blows over water), as well as water depth and angle of wave impact. Previous studies (Hershberger & Ting, 1996) have shown that even complex models of inshore wave propagation can encounter cons iderable error. Hershberger and Ting’s research in the Gulf Intracoastal Waterway compared field measurements of wave height and period with those predicted by the U.S. Army Corps of Engi neers (USCOE) Automated Coastal Engineering System model and found the model to over-predi ct waves when wind was blowing along the channel and under-predict waves when wind was blowing across the channel. Considerable expertise is necessary to accura tely predict wind wave-caused er osion through the prediction of wave energy in a channel such as the AICW. A simpler predictor of channel margin erosion may be the presence or absence of exposure to causal factors such as wind waves. Wind wave erosion has been found to be most severe downwind of the prevailing wind and largest local fetch (Day et al., 1998; Doane et al., 1998; Downs et al., 1994; Schwimmer, 2001). National Oceanographic and Atmospheric Ad ministration data from a coastal automated weather station approximately 2 km east of the study area show the predominant direction of winds over 10 knots to be from 345 o to 45 o (National Oceanographic and Atmospheric Administration, 2003). The Beaufo rt wind scale defines 10 knots as the wind velocity at which small waves generally start to form and thus wi nd wave erosion can be expected to begin to occur. Given the results of pr evious studies, wind wave erosi on can be expected to be most severe along the Matanzas Ri ver downwind of this wind dir ection, or along river channel margins facing from 90 to 300 degrees. Boat wakes are also widely recognized as a cause of bank erosion in inland bodies of water (Grossfeld, 1997; Kennish, 2002; Maynord et al., 2001; Raines, 2003; Wilcox, n.d.; Williams, 1993; Zabawa, Ostrom & Byrne, 1980). Factors influencing the erosive impact of boat wakes include the size of the wake, the wate r depth, the current dire ction and velocity, the morphology of the impacted bank, the presence of wind waves, and the distance of the vessel from the shore (Macfarlane & Renilson, 1999). The size of the wake is governed by vessel speed, hull form, draft, loading, and trim. Ge nerally, fast moving vessels displacing large

6volumes of water produce the largest wakes wh ile vessels displacing less water and moving slowly or at planing speed pr oduce the smallest wakes. Although boat wakes and wind waves affect the channel margin in a similar manner, wake-caused erosion can be distinguished from wind wave-caused erosion in that it occurs in areas sheltered from wind waves and may be most severe where the AICW channel is closest to the channel margin. Wakes can be expected to be a much more significant problem in the GTMNERR than in wider bodies of water such as the nearby St. Johns River. The relatively narrow channel of the AICW does not allow significant distance for wake energy to subside before wakes impact the margin. The narrow cha nnel also does not provide as large a fetch for the development of wind waves as wider channels do; thus, ecosystems along the margins of the AICW are adapted to significantly lower energy levels than those along channels where larger wind wave propagation is possi ble. Personal observations supported by consultation with knowledgeable locals and experts in the fiel d of coastal geomorphology (Sergio Fagherazzi, personal communication, 2004) have led to the hypothesis that boat wakes in the AICW are the primary case of erosion in the GTMNERR.

Tidal Currents Tidal currents are capable of causing erosi on along estuarine channels in the same manner that riverine currents erode river banks . Generally, channels erode on the outside of bends, where current velocity and resultant shear stress is highes t, and accrete on the point bars on the inside of bends. Tighter bends, with sma ller radii of curvature, erode on the outside and accrete on the inside faster than wider bends with larger radii of curvature (Leopold, Wolman, & Miller, 1992). In stable systems lateral, current -induced erosion in one area is offset by accretion in another (Letzsch & Frey, 1980).
Dredging and filling Dredging and filling for navigational or other purposes can cause erosion or accretion in several ways. Most obviously, channels can be dredged directly thr ough an area or existing channels can be filled. This results in apparent erosion or accreti on in a map or aerial photograph. According to Brian Brodehl of the USCOE Jacksonville district (personal communication, September 10, 2004), dredging can al so cause channel widening when a channel

7is dredged to such a depth that when channel be d sediments reach their natural angle of repose, the bank is under cut. If the dimensions of a channel and the angle of repose of constituent sediments are known, it is possible to calculate the potential for eros ion due to this mechanism. Considering that the planned dimensions for th e AICW navigation channel are 125 feet wide by 12 feet deep and that the approximate angle of repose of bed sediments is 1:2.5 (according to B. Brodehl.), the current mean widt h of the entire tidal channel, over 1000 feet, is more than sufficient to accommodate the construction of the channel without under cutting banks. Mr. Brodehl acknowledged that although the USCOE consid ers this calcul ation in the dredging of the AICW channel, it is likely that historically dredging efforts we re not as carefully engineered. It is also possible for dredgi ng to alter depth or fetch available for wave propagation, or to alter current directi on or velocity and thus indirectly influence local erosion rates. One mechanism through which channel dredging may increa se current velocities and increase erosion rates is through alteration of th e tidal prism (the difference in the volume of water in a water body between low and high tides) (Cox, Wadswort h, & Thomson, 2003). It is likely that dredging associated with the creat ion of the AICW altered the local tidal prism, but it is difficult to determine the magnitude of the change or to relate this change to sedimentary processes. A second manner in which navigation related dr edging and filling may have affected tidal currents, and thus affected sedimentation, is th rough the alteration of na tural channels in the vicinity of Matanzas Inlet, bo th during the initial construction of the AICW and again in the 1970’s. Figure 3 allows the comparison of the modern channel configuration with the unmodified channel, as depicted in United States Coast Survey maps created in 1867 and 1872. The channel to the north of the inlet was reali gned during construction of the AICW channel as was the smaller channel running south from the inle t. The thin strip of land dividing the inlet and the navigation channel was also fortified to prevent tidal currents from depositing sediment in the channel. Together these modifications dr amatically altered the natural tidal channels in the vicinity of the inlet and are likely to have caused substantia l changes in sediment transport processes.

80 400 800 Meters Channel margin from ~1870 UCS maps AICW channel margin from 2002 photography

Back ground is 2002 SJC ph otography Shorelines in this area fortified after dredging of AICW M a ta

n z a s I

n l e t

Figure 3: Alterations in the vicinity of Matanzas Inlet

The precise effect of such alterations is agai n difficult to discern. However, a portion of the study area, from the State Road 206 Bridge to the north end of the study area, has apparently never been dredged (judging from the absence of dredge spoil islands) and can be viewed as a control for the examination of dredging impacts.
Sediment supply The primary condition which must be met fo r accretion to occur is the existence of a sufficient supply of sediment. The primary sour ces of allocthonous sediment for most marsh systems are (1) riverine sources, (2) off-shore sources, (3) barrier wash -over, (4) erosion of coastal cliffs, and (5) wind-blown sediments. Biogenic organic aggreg ates provide the major source of autochthonous sediments (Frey & Basa n, 1978). The AICW in the study area does not receive significant input of sediment from riverine sources or experience substantial barrier island wash over and is not located near any coastal cliffs. Off-s hore sources, wind-blown sediments, and organic aggregates are most probably the major potential sources of new

9sediment (personal observations , 1980-present). Dredged bed sediment also may contribute considerably to the sediment supply, both durin g the dredging process and later as dredged sediment is eroded from shoreline disposal areas. There is no indi cation of a change in sediment supply levels during the study period.
Sediment type Channel margin sediments in the study area vary from coarse oyster shells to fine organic sediments. According to this variation in sediment, any location along the AICW channel margin can be placed into one of five differe nt categories: intertidal bars, salt marsh, sandy dredge spoil disposal areas, upl ands, or water (the mouths of tributaries or off-channel areas which join the main channel). Although these ca tegories are somewhat subjective, they can be viewed as an indicator of both channel margin sediment type and the level of biological stabilization or destabilization. Intertidal bars contain mostly disarticulated oyster shells; marshes contain very fine sediments; spoil is generally sandy with some shell; uplands are sandy, but are usually reinforced with tree roots or se awalls. The 64.8 kilomete rs of channel margin examined in this study were classified as displa yed in Table 1 below. Each sedimentary class can be expected to respond differently to erosive forces due to both the physical structure of the sediment and the levels of biological stabilization or destabilization.

Table 1: Summary of 1970/1971 ch annel margin classification Margin classification Margin length (km) Proportion of margin length intertidal bars 8.7 13% marsh 24.8 38% dredge spoil 19.3 30% upland 6.1 9% water 5.9 9% Total 64.8 100%

10Biological stabilizati on and destabilization Estuarine organisms can have both positive and negative influences on the stability of channel margins. The major species responsible for shoreline and nearshore stabilization in the GTMNERR are smooth cordgrass, Spartina alterniflora , and the eastern oyster, Crassostrea virginica . Atlantic coast salt marshes, such thos e found in the GTMNERR, commonly consist of extremely fine unconsolidated silts and clays (F rey & Basan, 1978), the t op several inches of which are reinforced by the rhizomatic mat of Spartina alterniflora . Personal observations suggest that marsh erosion in the reserve follows the general pattern de scribed in the seminal work of Redfield (1972). Erosion of the sedi ment from under the root mat leaves the marsh surface unsupported and results in the mass wastin g of large blocks of the vegetative mat and coherent sediment. This erosive process makes clear the fact that although Spartina roots do reinforce marsh sediments, they cannot preven t erosion in a high energy environment. Oysters protect fine marsh sediments from erosive forces in a manner similar to cordgrass, but oysters are also not immune to dama ge from waves. Grizzle, Adams and Walters (2002) conducted a study of aerial photography in the Indian River Lagoon, on Florida’s east coast, and observed widespread death of oyster ba r margins, an occurrence they attributed to the action of boat wakes. Wakes ha ve the potential to inhibit the se ttlement of larval oysters and physically move or smother adu lt oysters with sediment. Dead oyster bar margins similar to those discussed by Grizzle et al . (2002) are common in the GTMNERR. They appear much lighter in color than healthy bars and can be distinguished in aerial photographs. Informal analysis of aerial photos of the reserve suggests that all oyster bar margins with direct exposure to the navigation channel of the AICW could be classified as dead us ing Grizzle’s criteria. Biological destabilization, or bioturbation, involves physical disturbance of sediment by living organisms, such as the fiddler crab, Uca pugnax (Letzsch & Frey, 1980). Fiddler crab burrows penetrate marsh sediments and thus increas e their susceptibility to erosion by waves or currents. Although native organisms such as U. pugnax may decrease the stability of sediments in stable ecosystems, lateral erosion and deposition are roughly equal even in their presence (Letzsch & Frey, 1980). Thus, in the absence of any drastic ecosystem changes, bioturbation should not be viewed as a primary cause of erosio n. The same holds true for other examples of ecosystem change with the potential to alte r marsh erosion rates. Periwinkle snails, Littorina sp., have been observed to feed on Spartina ; and in the absence of predation by blue crabs,

11Callinectes sapidus , populations of snails may ha ve the potential to devastate Spartina marshes, destabilizing sediments and lo wering deposition rates (Bertness & Silliman, 2002). Again, overall sedimentation rates should not be expect ed to change significantly unless there is a substantial change in trophic structure. Alteration of the trophic structure of an ecosystem can cause otherwise innocuous processes, such as bioturbation or predation, to have drastic effect s on the stability of the system. However, determination of the role of such pr ocesses in marsh erosion is difficult due to the natural complexity of ecosystems and the larg e amount of observationa l data necessary to ascertain if a change is occurring. No major change s in trophic structure, with clear potential to alter erosion rates, have been reported in the GTMNERR.

The role of sea level
Relative sea level rise can result from either an increase in eustatic sea level (the level of the ocean in relation to the land) or from subsid ence of the land. Mean sea level is measured through analysis of tidal gauge data corrected to account for seasonal and interannual variation and change in land elevation. The lack of tidal data for any one location in the study area for any significant portion of the study peri od negates the possibility of c onducting this type of analysis. However, a NOAA sea level trend analysis for a tidal gauge approximately 48 miles north of the study area reported an average rate of sea leve l rise of 2.43 millimeters/year, from 1928 to 1999 (NOAA, n.d. a). This rate is at the high end of the range of the estimated current global average rate of sea level rise of 1.0 to 2.4 millimeters/year (NOAA, n.d. b). Sea level rise has been impli cated as a causal factor in a number of studies of marsh erosion (Day et al., 1998; Downs et al., 1994; Hartig, Gornitz, Kolker, Mushacke, & Fallon, 2002; Kastler & Wiberg, 1996; Kearney, Grace, & Stevenson, 1988; Phillips, 1986a; Reed, 1988; Salinas, DeLaune, & Patrick, 1986). In these studies, subsidence and eu static sea level rise often function in concert to increa se erosion rates; but in several locations including Venice, Italy (Day et al., 1998) and Louisiana, (Salinas et al., 1986) subsidence appear s to be the underlying cause of observed erosion. Subsidence is the decr ease in elevation of sedi ments due to extraction of subsurface resources or geolog ic processes. There have b een no recorded observations of subsidence in the reserve.

12In cases of erosion exacerbated by eustatic sea level rise and those involving subsidence, the response of the marsh appear s to be essentially the same. A simplified relationship of marsh elevation to relative sea level was presented by Re dfield (1965), who found that if salt marsh surface accretion keeps pace with relative sea level rise, then the marsh will remain stable. This view was amended by Orson, Panageotou, and Leatherman (1985) and again by Schwimmer and Pizzuto (2000) who studied a ra pidly eroding marsh in which the aggradation (vertical building) rate exceeded the rate of relative sea level rise. Schwimmer and Pizzuto propose that in the face of relative sea level rise a marsh can either (1) erode (retreat laterally), (2) prograde (build laterally), or (3) drown depending on local rates of relative sea level rise and marsh surface and nearshore sedimentation rates. Nearshore sediment ation is critical because it has the potential to alter bathymetry and thus affect the erosive impact of waves. A marsh shoreline erodes, in the presence of relative sea level rise, when the nearshore sedimentation rate is less than the local rate of relative sea level rise and the rate of marsh aggradation is greater than the rate of relative sea level rise (i.e. the marsh builds upward fast enough to stay above water but er odes laterally). A shoreline pr ogrades, in the presence of relative sea level rise, when the nearshore sedime ntation rate and the rate of marsh aggradation are both greater than the local rate of relative s ea level rise (i.e. the marsh not only builds upward fast enough to stay above water, but high nearshore deposition rates allow it to build laterally). A marsh drowns when the near shore sedimentatio n rate and the rate of marsh aggradation are both less than the local rate of relative sea leve l rise (i.e. the marsh cannot build upward fast enough to stay above water). The first indicat or of drowning is the deterioration of the vegetative marsh mat due to exce ssive inundation. Where mat dete rioration occurs, new areas of open water form and are then enlarged by waves in the direction of the predominant wind (Stevenson, Kearney, & Pendleton, 1985). Considering these statements, if, in the presen ce of relative sea level rise, erosion is observed but drowning is not observed, as is th e case in the GTMNERR, the marsh must be aggrading and erosion must theref ore be caused by relatively low n earshore sedimentation rates. Nearshore sedimentation rates ar e influenced by wave climate and sediment supply (Schwimmer & Pizzuto, 2000), so erosion can be expected to be most severe in locations where sediment supply is lowest and wave energy is highest. Considering this re lationship, sea level rise should

13not be considered a primary cause of erosion, but rather a secondary factor with the potential to increase the rate of erosion due to waves or nearshore currents.

Methods The commonly used methods of measuring er osion rates can be grouped into two main classes, on-site data co llection and measurement from compiled historical sources. The main advantage of on-site data collection is that chan ge rates can be measured precisely, and change over short time periods can be quantified accurately; however, this method requires significant field work and, therefore, is not well suited to research involvi ng time constraints or large study areas. Measurement from historical sources is a process which allows the intrusion of considerable error; however, this method allows for the relatively rapid assessment of change over large areas and time spans and does not re quire intensive field work. Due to time and budgetary constraints and the desire to study as large an area as po ssible, this study used methods involving measurement from complied historical sources. Analysis of aerial photography, a method routin ely used to analyze coastal geomorphic trends (see Cox, Wadsworth & Thomson, 2003, for a recent example), was used to measure the extent of erosion along the AICW in the southern section of th e GTMNERR over the past thirtyone years. The Florida Department of Tran sportation (FDOT) Surv ey and Mapping Office provided digital versions of 1:24,000 scale, black and white ae rial photography of the Flagler County portion of the study area ta ken in November and December of 1970 and in February of 2002. FDOT also provided 1:24,000 scale, black and white photography of the St. Johns County portion of the study area taken in April of 1971. Photography of the St. Johns County portion of the study area taken in 2002 was purchased from St. Johns County. Both sets of 2002 photography were received as dig ital orthophotos pre-rectified to ge ographic coordinate systems. All photo sets were scanned usi ng a resolution of 2000 dots per inch to yield dig ital photo sets with a 0.3-meter pixel resolution. Environmen tal Systems Research Institute (ESRI) Arc Geographic Information System (GIS) software was used to georec tify the 1970 and 1971 photos using the pre-rectified 2002 images . A minimum of 9 links was used in the rectific ation of each image and the mean root-mean-square (RMS) error for all rectified images was 3.3 meters. RMS error is the measure of uncertainty in geographi c data promoted by the Federal Geographic Data Committee (FGDC, 2004). It is th e square root of the mean s quared differences in location

14between the data set being r ectified (1970 and 1971 photography) a nd the established data set used as a base for rectifica tion (2002 photography). The F GDC does not establish a specific threshold by which to judge RMS error; it in stead suggests that users develop a standard sufficient for the purposes for which the data will be used and adhere to that standard. Once photos were rectified, the channel ma rgin in both the 2002 and the 1970/1971 photo sets were digitized to yield a digital line file. The channel margin was defined as the border of the major tidal channels of the GTMNERR. The margin should be distinguished from the edge of the navigation channel and from the channel shoreline. While the channel margin and the shoreline are often in the same location, there are also many locations in the study area where practically all of the energy gene rated in the channel dissipates on intertidal bars which can be over a hundred meters from dry land. When the shoreline and the channel margin were in the same place, the vegetation line was used to locat e the channel margin. In unvegetated areas, margin definition was less precise. When gaps, such as tributary mouths or openings between dredge spoil islands were encountered, the shor eline was followed away from the main channel until the end of the erosive margin, as indicate d by a white, sandy shoreline, was encountered (Figure 4). The methods used by Kastler and Wiberg (1996 ) were used to ascertain the uncertainty involved in this digitization process. Three ra ndomly selected, vegetated, one-kilometer margin reaches were digitized three times each and the mean distance between each successive digitization was calculated. This calculation yielded a mean di gitization error of 3.9 meters. This number was combined with the 3.3 meter RMS error as the square root of the two squared numbers following the methods of Gaeuman, Schmidt, and Wilcock (2003 ), to yield a total estimated error of 5.1 meters (Figure 5). While this error makes precise location of i ndividual points difficult, it is essentially randomly distributed, so widespread changes in a single general dir ection are likely to be real. Additionally, this error only applies to vegetate d margin types, including marsh, most dredge spoil disposal areas, and uplands. As exposure of in tertidal bars varies with the tide, the degree to which they are distinguishable in aerial photographs varies depending on when the photos were taken. It was found that dead shell bars, which were si gnificantly more common in the 2002 photographs, were much easier to discern than live oyster bars. Water margins, found in the mouths of tributaries along the channel, ar e also imprecise. Due to these differences,

15estimation of a reliable error rate in the delin eation of intertidal bar and water margins is difficult.

0 50 Meters When a side channel was encountered, digitzing proceeded up the channel to the end of the light, sandy erosive margin.

Background is 2002 SJC photographyMarsh / BackwaterIntracoastal Waterway Tidal cree k entering chan nel

Figure 4: Digitizing the channel margin in the vicinity of a side channel

m error estimated Total error RMS error digitizing

1.5)3.3()9.3( _ _)_()_(

2 2 2 2

=+ = +

Figure 5: Estimation of error The channel margin lines were manually attri buted as water, intertidal bars, marsh, spoil or upland by referencing the 1970/1971 photo set, as displayed in Figure 6. Where margin type was uncertain, on-site ground truthing inspections were conducted. The margin classes are subjective; however, they are indicators of the predominant sediment type in the area and the level of biological stabilization.

160 200 Meters 1971 channel margin classification

intertidal bars marsh spoil upland water

Background is 1971 FDOT photograph y Figure 6: Classification of channel margin types

Once digitization and margin classification we re complete, change in margin location was assessed using two separate methods: a poly gon-based analysis of change in area, and a point-based analysis of lateral margin movement.
Polygon-based analysis The polygon-based analysis was used to determine the total change in area of each margin classification as a result of erosion or accretion. Following th e classification of the channel margin, the channel margin lines were used to create two polygons representing the major tidal channels in 1970/1971 and 2002. Using the methods of Gaueman et al. (2003), these polygons were clipped to create two new polygon files. One file contained all areas which were not part of the channel in 1970/1971 but were part of the channel in 2002, and thus represented erosion. The second file contained areas which were part of the channel in 1970/1971 but were not in 2002 and thus represented accretion. Exam ples of erosion and accretion polygons are displayed in Figure 7. Using GI S software, erosion polygons were manually categorized as one of the five margin types by spatially joining them to the file containing channel margin classification types. Accretion polygons, whic h were much less numerous, were categorized

17manually while referencing the 2002 photos (Figures 18-33). The total area of erosion and accretion of each margin classification was calculated.
Point-based analysis The point-based method of analysis was structur ed to determine the rate of lateral erosion or accretion along the channel and to allow examination of rates of change in relation to a suite of indicator variables developed to ascertain the role of the various causal factors in erosion or accretion. Point files were constructed through an automated process which located points every 10 meters along the 64.8 kilometers of digitized channel margin in the study area for both the 1970/1971 and 2002 channel margin line files. This created two point files of approximately 6,480 points each (examples of which are displayed in Figure 7). If the points were found to lie on the margins of the previously create d erosion polygons, the distance from each 1970/1971 point to the nearest point in th e 2002 layer was recorded as a ne gative number. If the points were found to lie on the margins of the accretion polyg ons this distance was recorded as a positive number.

0 10 20 Meters 1970/1971 channel margin 2002 channel margin accretion polygon erosion polygon

Background is 1971 FDOT photography D D

D D 5.8 meters of accretion

3.2 meters of erosionIntracoastal WaterwayMarsh / Backwater

Figure 7: Methods used to m easure erosion and accretion

18The points, at which lateral movement of the channel margin was measured, were classified according to their characteristics wh ich have the potential to influence erosion and accretion using automated geopro cessing techniques. Each point in the 1970/1971 file was dichotomously classified according to its expos ure to wind waves formed by prevailing winds, its exposure to boat wakes generated by vessels in the AICW channel, its exposure to tidal currents likely to cause erosion, and its location north or south of the State Road 206 Bridge (as an indicator of dredging activity). Points were al so classified according to channel margin type. In addition, the width of the entire 1970/1971 cha nnel, as well as the distance between the 2002 channel margin and the edge of the AICW in 1999, were calculated. These indicator variables are summarized in Table 2.

Table 2: Indicators of factors affecting erosion and accretion

Continuous value Variable mean ± stdev (min, max) Category Intended to quantify erosion due
channel margin classification N/A 0 (water) 1 (intertidal bars) 2 (marsh) 3 (dredge spoil) 4 (upland) sediment type and biological stabilization

exposure to wind waves N/A 1 (margin facing predominant wind direction ) 0 (margin not facing predominant wind direction) wind waves

exposure to AICW channel N/A 1 (exposed to boat wakes generated in AICW) 0 (unexposed to boat wakes generated in AICW) boat wakes
entire 1970/1971 channel width (m) 426.2 ± 687.9 (91.1, 1290.5) N/A boat wakes

distance from 1999 AICW channel (m) 272.4 ± 711.1 (7.8, 773.0) N/A boat wakes

exposure to tidal currents N/A 1 (likely to be effect ed by tidal currents) 0 (unlikely to be effected by tidal currents) currents
radius of curvature (m) of the nine identifiable bends 789.1 ± 268.6 (439.3, 1195.1) N/A currents

location relative to SR206 bridge N/A 1 (south of bridge - along dredged channel) 0 (north of bridge - along undredged channel) dredging

19Points were coded 1, as exposed to wind wa ves formed by the prevailing winds, if the margin faced any direction from 300 to 90 degree s. Unexposed points, where the margin faced from 90 to 300 degrees, were coded as 0. Figure 8 displays an example of wind exposure coding and presents a conceptual diagram used to es timate margin angle and subsequent exposure. Exposure was determined based on photographs at a scale of approximately 1:5,000 so minor variations, on the scale of several meters, are not reflected in this variable. Such precision would be prohibitively time consuming and would likel y exceed the precision of the digitized channel margins.

0 200 Meters exposure

0 1

Predominant winds > 10kts from 345 0 to 45 0

Channel margins facing from 300

0 to 90 0 coded as exposed to predominant wind waves

Background is 1971 FDOT photography Figure 8: Coding of exposure to waves caused by predominant winds

Points were coded 1, as exposed to boat wa kes, if a line drawn perpendicular to the centerline of the AICW navigation channel coul d pass through them without crossing a second channel margin (Figure 9). If points did not meet this condition they were coded 0 for this attribute. The same lines used in this test were used to measure the width of the 1970/1971 channel. Channel width was measured perpendicu lar to the centerline of the AICW at 10 meter intervals. Since the width measurement lines usually did not intersect the points where change

20was measured, channel margin points were assi gned the width measurement which intersected the channel margin closest to their location. Po ints unexposed to boat wakes were excluded from the analyses involving channel width. Because bo at wakes decay with distance from the sailing line of the boats which produce them, wake-caused erosion can be expected to be most severe when the entire tidal channel is narrower and wakes have less distance over which to dissipate before they impact the channel margin.

0 200 Meters A I C W n a v i g a t i o n c h a n n e l c e n t e r l i n e

Back ground is 1971 FDOT photo graph y Channel margin

unexposed to boat wakes Channel margin exposed to boat wakes Lines used to measure 1971 channel width

Figure 9: Determination of exposure to navigation channel boat wakes and measurement of 1970/1971 channel width

The distance from the edge of the naviga tion channel, as defined by the location of United States Coast Guard navigation markers in 1999, to the channel margin was measured as displayed in Figure 10. This measurement serves as a third indicator of the influence of boat wakes on erosion rates. As with the cha nnel width variable, poi nts were assigned the measurement which intersected the channel margin closest to their loca tion and points coded as unexposed to boat wakes were excluded. Eros ion rates influenced by boat wakes can be expected to be highest where the navigation channel runs clos est to the channel margin and wakes have the least time to dissipate.

210 200 Meters A I C W n a v i g a t i o n c h a n n e l c e n t e r l i n e

Background is 2002 SJC ph otography Lines used to measure distance from edges of 2002 navigation channel

to channel margin

Figure 10: Measurement of distance from edge of 1999 navigation channel to channel margin

Points were coded 1, as exposed to tidal curren ts, if they were on the outside of one of the nine identifiable bends in the AICW channel in the study area. Points on the inside of bends or on straight reaches of margin were coded as 0. The radius of curv ature, of all identifiable bends, was also recorded to serve as a secondary measure of erosion caused by tidal currents. The radius of curvature of a bend can be interpreted as the radius of the largest circle which fits the curve of a bend smoothly. In this study, Arc GIS so ftware was used to fit an arc to each curve and determine its radius. In addition to these tw o indicators of tidal current-caused erosion, the bathymetric cross sections of the nine bends (t aken from data provided by the St. Johns Water Management District) were examined for signs of active outer bank erosion, mainly a significant increase in depth towards the outside of the be nd. Such erosion can be expected to be most severe in the tightest bends. Figure 11 shows an example of coding of the tidal current exposure variable and measurement of radius of curvature.

22curvature 0 1

radius = 645.3 m D D

0 200 Meters

Back ground is 1971 FDOT photograp hy

Figure 11: Coding of curvature variable and determination of radii of curvature

In addition to the variables discussed previous ly, the location of each point relative to the State Road 206 Bridge was also recorded as a bina ry variable to indicate presence or absence of dredging (south of bridge = 1, north = 0). The 1970/1971 points, where lateral margin mo vement was measured, were analyzed to detect and examine relationships between accreti on or erosion rate and each of the potential contributing factors in Table 2. Linear regressi on was used to examine the correlation between margin movement rates and causal factors measured on a continuous scale. The Kruskal-Wallis test, Tukey’s studentized range test, and the Wilcoxon rank sum test were used to examine differences in rates of channel margin move ment for independent variables measured on a categorical scale. All significant variables were entered into a multiple linear regression model to allow estimation of channel margin movement rates given different site characteristics. Kendall’s Tau-b was calculated to overcome th e weaknesses of least-squares regression as a measure of correlation between binary indepe ndent variables and a continuous response.

23Results

Both polygon and point-based analysis techni ques revealed high rates of channel margin erosion in the study area. Channel margins classified as intertidal bars, marsh, dredge spoil, and uplands all experienced ne t erosion. Channel margins classifi ed as water were excluded from analyses due to the ambiguities involved in the interpretation of accreti on and erosion of these areas. Exposure to wakes generated by vessels in the AICW was the causal factor most strongly correlated with higher rates of erosion. Detailed results of th e polygon and point-based analyses further illustrate the extent of erosion and the relationship of erosion rates with causal factors.
Polygon-based analysis The area of channel margin lost to eros ion in the study area from 1970/1971 to 2002 was found to far exceed the area replac ed through accretion. Instead of an accretion/erosion ratio of approximately 1 that would be e xpected in light of previous wo rk (Letzsch & Frey, 1980), from 1970/1971 to 2002 the ratio of accreti on to erosion in the study area was 0.13. The total tidal channel area, as defined by the digitized cha nnel margins, expanded 11.4% from 656.0 hectares (1621.0 acres) in 1970/1971 to 730.7 hectares (1805.7 acres) in 2002. Excluding channel margins attributed as water, 68.2 hectares (168.6 acres) of marsh, intertidal bars, marsh, spoil areas, and uplands were lost to erosion and not replaced through accretion. These findings are summarized in Table 3 below.

Table 3: Summary of area eroded 1970/1971 to 2002 Area in hectares [acres] Margin classification Proportion of margin length Erosion Accretion Net change intertidal bars 15% 21.0 [51.8] 0.1 [0.1] -20.9 [-51.7] marsh 42% 26.4 [65.2] 10.2 [25.2] -16.2 [-40.1] dredge spoil 33% 28.7 [71.0] 0.1 [0.2] -28.7 [-70.8] upland 10% 2.7 [6.7] 0.3 [0.8] -2.4 [-6.0] Total 100% 78.8 [219.1] 10.6 [26.2] -68.2 [-168.6]

24Point-based analysis While information concerning the area of channel margin habitat eroded is useful in the evaluation of the ecological impacts of erosion, th e approach used in this analysis obscures the impacts of specific causal factors. In order to discern the relative imp act of individual potential causes, it is necessary to eliminate the spatia l variability in exposure which occurs within individual polygons. Comparison of points along the channel margin in 1970/1971 and 2002 allows association of rates of cha nge with discrete sets of causal factors. Table 4 summarizes the lateral erosion data obtained from point comparisons along all non-water margin types.

Table 4: Summary of lateral movement from 1970/1971 to 2002

Margin classification Proportion of margin length Count of measurement points Mean linear movement (m) intertidal bars 15% 870 -23.2 marsh 42% 2477 -9.3 dredge spoil 33% 1930 -16.7 upland 10% 613 -4.6 Total 100% 5890 -13.4

Comparison of Tables 3 and 4 reveals that a lthough the largest loss to erosion in terms of area was from dredge spoil margins, intertidal ba rs were subject to a hi gher rate of lateral erosion. Upland areas experienced both the lowest level of loss of area and the lowest rate of lateral erosion. Marsh margins ra nked third in both in terms of ar ea eroded and lateral rate of movement. In Figure 12, rates of lateral erosi on are depicted graphically according to margin classification.

25-125 -100

-75 -50 -25

0 25 50 75

Intertidal Bars (n=870) Marsh (n=2,477) Dredge Spoil (n=1,930) Upland (n=613) MARGIN CLASSIFICATIONLINEAR CHANGE 1970/1971 - 2002 (m)

Figure 12: Minimum, maximum and quartile rates of latera l movement from 1970/1971 to 2002 classified by margin type

A Kruskal-Wallis test showed that the rate of ch annel margin movement of at least one of the margin classifications was significantly different (p < 0.0001) than the others. A subsequent Tukey’s studentized range test was used to cond uct pair-wise comparisons among all of the mean ranks of all of the margin cla sses. All comparisons showed si gnificant differences (p<0.05). Wilcoxon rank sum tests revealed significant differences (p < 0.0001) in the amount of lateral movement at points exposed and not exposed to both the AICW channel and waves generated by predominant winds. To discern the relative impact of these two factors, lateral rates of movement for points exposed to no si gnificant causal factors, to only wind waves generated by predominant winds, to only boat wake s generated in the AICW channel and to both boat wakes and wind waves were compared. A Kr uskal-Wallis test showed that the rate of movement for at least one of th e causal factor combinations was significantly different (p < 0.0001) than the others. A Tukey’s studentized range test revealed significant differences (p<0.05) in channel margin movement in all possi ble causal factor, pair-wise comparisons except

26the “exposed to no apparent causal factors” and the “exposed to wind waves only” categories (see dashed box in Figure 13). The fact that this comparison was not statistically significant may be associated with the relatively small sample size and limited fetch available at points exposed only to wind waves. These points were locate d along secondary channels and were protected from boat wakes and the longer fetch found in the AICW.

-125 -100

-75 -50 -25

0 25 50 75 100

No apparent causal factors (n=277) Wind waves only (n=86) Boat wakes only (n=3,182) Boat wakes and wind

waves (n=2,345) CAUSAL FACTOR COMBINATIONSLINEAR CHANGE 1970/1971 - 2002 (m)

Figure 13: Minimum, maximum and quartile rates of latera l movement from 1970/1971 to 2002 classified by exposure to causal factors

In order to develop estimates of 1970/1971 to 2002 lateral movement, given variations in and interactions between margin type and exposure to causal factors, dichotomous variables for each margin type, for exposure to boat wakes generated in the AICW channel, and for exposure to wind waves generated by the predominant wind were entered into a least squares linear regression model (see Table 5).

27Table 5: Regression of lateral movement on significant causal fact ors and margin type

Source DF F value Pr > F model 5 255.69 <0.0001 total 5889 R-Square 0.18

Variable Coefficient t value Pr > |t| intercept 8.30 8.57 <0.0001 intertidal bars -17.56 -23.11 <0.0001 marsh -5.65 -8.60 <0.0001 spoil -10.88 -15.91 <0.0001 exposure to wind waves -1.98 -5.04 <0.0001 exposure to boat wakes -13.03 -16.29 <0.0001

All coefficients in this model are significant and the very large overall F-value reveals that the variance explained by the model is signi ficantly greater than th e variance due to model error. However, the R 2 value of 0.18 reveals that much of th e variation in the rate of channel margin movement remains unexplained by the model. This unexplained variation may be due to the fact that the regression attempts to explai n all of the variation in a continuous dependent variable with binary independent variables. It also could be a reflection of the use of blunt measures which do not capture small scale variati on in bathymetry and sediment type, and thus do not precisely reflect the level of eros ive energy at the channel margin. Due to this unexplained variation, the m odel may not be suitable for predicting movement at individual points; however, it can be used to estimate mean rates of lateral movement based on exposure to causal factors a nd margin type. The data in Figure 14 were calculated using the regression coefficients. Me an rates of lateral movement for each exposure and margin combination, as estimated by the re gression model, were multiplied by the total margin length. These products were then multip lied by the proportion of the entire margin classified as each margin type and as exposed to each combination of causal factors. The result is an estimate of the change in area of each margin type associated with each causal factor. This figure indicates that due to the number of points susceptible to boat wake erosion, the total loss

28in area associated with boat wake exposure is mu ch greater than that asso ciated with exposure to other factors.

-50.0 -40.0 -30.0 -20.0 -10.0

0.0 10.0

No apparent causal factors Wind waves only Boat wakes only Boat wakes and wind waves (n=227) (n=86) (n=3,182) (n=2,345) CAUSAL FACTOR COMBINATIONSESTIMATED CHANGE IN AREA (hectares).

-123.6 -98.8 -74.1 -49.4 -24.7 0.0 24.7ESTIMATED CHANGE IN AREA (acres).

upland spoil marsh intertidal bars

Figure 14: 1970/1971 to 2002 change in area es timated from rates of lateral movement

In order to circumvent the problem of the low explanatory power of the regression model resulting from the use of binary independent variables to explain a continuous dependent variable, the Kendall’s Tau-b correlation coeffi cients were calculated for channel margin movement rate and all points exposed to each of the causa l factor combinations (Table 6).

29Table 6: Correlations of causal fa ctors and channel margin movement

Variable Kendall's Tau b coefficient p value exposure to wind waves -0.14 <0.0001 exposure to boat wakes -0.20 <0.0001

Kendall’s Tau-b can be interpreted as a measure of the percentage of variation in the dependent variable explained by the independe nt variable. While this non-parametric statistic is a more effective measure of correlation with binary independent variable s than ordinary least-squares regression, it is limited in that it fails to acc ount for interaction among the causal factors and the margin classification. It also does not help to overcome the coarseness in the measurement of the binary independent variables. These data constitute further evidence that simple exposure to boat wakes explains approximately 20% of the variation in channel margin movement.
Insignificant and marginally significant variables Simple linear regression analysis revealed no significant correlations between channel margin movement and any of the th ree continuous causal variables, radius of curvature, distance from the 1999 AICW channel, and 1970/1971 ch annel width. A Wilcoxon rank sum test revealed no significant difference in the rates of movement for points coded as exposed or unexposed to significant tidal currents. Examinati on of bathymetric cross sections of the nine identifiable bends in the study area also provided no strong evid ence of tidal current caused erosion. The binary variable involvi ng location relative to the State Road 206 Bridge, intended as an indicator of the impact of dredging, was foun d to be related to a small (2m over study period), but significant difference in margin movement. Ho wever, instead of erosion being more severe in dredged areas, it was actually less severe. There is no obvious explanation for this finding, but it could be related to the difference in the sedime nt type and level of s horeline stabilization in areas north and south of the bridge. The variab le was not included in the final regression model because, although the coefficient was significant (p <0.05) its inclusion resulted in only a 0.0025 increase in the R 2 value.

30Discussion

Channel margin erosion in the southern half of the GTMNERR from 1970/1971 to 2002 was severe and has most likely caused significant changes in the estuarine ecosystem. Lateral erosion was found to be significan tly related to exposure to boat wakes generated in the AICW channel. Erosion was also found to be significan tly related to exposure to wind waves generated by predominant winds; however, the effect of wind waves was significantly less than that of boat wakes. The relatively low levels of correlation between the causal factors and erosion rates detected using linear regression and Kendall’s Tau- b should not be viewed as an indication that boat wakes are not a primary cause of erosion. As stated, the re liance on binary variables and bluntness of measurement are tw o possible causes of the low R 2 of the regression model and these factors may also explain the relativ ely low Kendall’s Tau-b coefficients. A process of elimination of the likely causal factors also implicates boat wakes as the most significant cause of erosion. Because more erosion was estimated to have occurred in areas not exposed to waves generated by the predomin ant wind than in areas exposed to these wind waves, wind waves cannot be assumed to be the ma in cause of erosion. Since curvature was not significantly correlated with erosio n rates and visual analysis of erosion patterns and bathymetric cross-sections did not reveal si gnificant evidence of meander mi gration, currents can be rejected as a cause of erosion. The sligh tly lower rate of erosion in dre dged areas south of the State Road 206 Bridge, suggests that dredging, too, does not exacerbated erosive processes. Variation in sediment type, as indicated by channel margin cla ssification, significantly influences erosion rates, but is not, in itself, a cause of erosion. Fina lly, biological change does not appear to be a major factor in high erosion rates because erosion was found to have occurred in all channel margin classification categories. This leaves boat wakes as the primary causal factor of erosion in the reserv e. As displayed in Figure 14, a bove, the widespread susceptibility to boat wakes, alone, demonstrates the potential for vessel traffic to contribute significantly to erosion.

31Further Research

Further research on channel margin eros ion in the GTMNERR can take two main directions: (1) application of the methods used in this study to other areas of the reserve or other time periods or (2) a more in-depth study in the current study area aime d at establishing a stronger correlation between causal factors and erosion rates. Wo rk using present methods could make use of photography from the 1990s, 1980s, 1970s, and 1940s and possibly T-sheet maps created by the United States Coast Survey in the early 1870s before the AICW was created. Such studies could also be extended to cover the northern portion of the re serve. More in-depth work aimed at establishing a stronger causal correlation could involve field measurement of wave energy and an attempt to correlate wave energy with fetch, nearshore bathymetric profile, local sediment type, and erosi on rates. Such a study could develop a comparison of the net volumes of sediment transported by relatively small but frequent wind waves and larger but less frequent boat wakes. In light of the evidence which suggests that overall high levels of erosion in the GTMNERR are related to exposure to boat wakes, the following chapter discusses strategies for managing erosion due to wake impacts.

32CHAPTER 2

EROSION MANAGEMENT ALTERNATIVES
Introduction

Erosion management in coastal areas is most frequently discussed in relation to beach erosion. While the processes of beach and inshor e channel margin erosion are similar, the low energy inshore environment and the distinct management goals make options which are generally undesirable in beach settings quite vi able for inshore shoreline protection. With implementation in mind, methods of inshore er osion management are best grouped into two classes: (1) regulation-based alternatives, which address the cause of erosive forces and (2) stabilization-based alternatives, which address the e ffect of erosive forces. In the case of beach erosion, the human causes of erosion, frequen tly inlet stabilization, are often too firmly established to allow for regulatory management. Along inland waterways the main controllable cause of channel margin erosion is wake-produci ng vessel traffic. While dredging activity is also controllable, dredging does not presently appear to be a major cause of erosion in the GTMNERR. Regulatory options for erosion control in the GTMNERR must involve the regulation of navigational activitie s. Stabilization options include structural and non-structural measures. Structural stabilization includes the construction of physical structures, while nonstructural alternatives involve moving sediment or increas ing natural stabi lization. While structural options can exacerbate erosion and inte rrupt longshore sediment transport on a beach, they are less detrimental when used in contro lling inshore erosion. The selection of erosion control strategies most well suited for use in an area depends mainly on the goal of erosion management in the locale.

The Goals of Inshore Erosion Management

Inshore erosion in the GTMNERR is an issu e of concern because erosive processes are altering ecosystems of economic and envir onmental importance. The goal of erosion management activities depends to some degree on what interests are be ing represented. For

33example, pleasure boaters, fishermen, and waterfront homeowners may each have different feelings from one another, regarding erosion ma nagement. In order to develop a strong erosion management plan, it is important to involve all concerned parties. Not only is this type of planning process essential to ensure public acceptance of a management plan, it will also help to gain the cooperation of owners of submerged la nd in any stabilization efforts and will ease the enforcement of any regulation of boating activity. Given the necessary involvement of these and other local interests, a suitable management goal would be to “minimize channel margin erosion to the extent necessary to allow the recovery of altered shoreline a nd nearshore ecosystems, while accommodating the needs of diverse local inte rests to the extent possible.” As evidence suggests, increased channel margin wave energy levels are the main cause of erosion in the GTMNERR; the key to limiting erosion is decr easing these energy levels. Achieving such a decrease on a scale as large as the entire GTMN ERR is likely to involve the incorporation of both stabilization and regulation.

Stabilization Based Alternatives

As mentioned, stabilization ba sed options include structural and non-structural measures. Non-structural strategies include less perman ent structures which commonly make use of vegetation and other naturally occurring material. Structural measures invol ve the construction of permanent stabilization works. Both types of st abilization have advantages and disadvantages. Non-structural, or soft, stabilization options are probably the most widely promoted and possibly the most widely used means of contro lling inshore erosion. They are intended to physically resist erosive forces by stabilizing shoreline sediments. In estuaries, some of the first tools of those planning soft st abilization efforts are the organisms which naturally provide stabilization— the marsh grass, Spartina alterniflora (Knutson & Woodhouse, 1983), and oyster shells (Meyer, Townsend, & Thayer, 1997). The most obvious shortcoming of these strategies is the fact that they rely on the sa me biota that are being impacted by erosion to provide stability. If well-established marsh grasses and oyster bars are being eroded, then it is unlikely that new plantings of either will establish themselves be fore they, too, are eroded away. Stabilizing only the shoreline also fails to protect nearshore habi tat, such as oyster bars , from increased wave energy.

34Two studies which recognize the impermanen ce of vegetative plantings in areas of elevated wave energy are the works of Broome , Rogers & Seneca (1992) and Rogers (1994). Both of these reports provide extensive discussi ons of the combined use of vegetation and low cost, wooden breakwaters in cont rolling erosion in a North Caro lina estuary. Breakwaters are structures built in the water, parallel to an eroding shoreline for the purpose of reducing wave energy. They present the main structural option for controlling erosi on in the GTMNERR. Erosion control structures, such as groins and jetties, which are built perpendicular to the shoreline, are of little use in the inshore envi ronment because these structures are designed to reduce longshore transport of sediment ra ther than to reduce wave energy. With a few exceptions, breakwate rs are a type of permanent stabilization, usually built from wood or stone. They extend from the botto m of a body of water to just below or well above the surface of the water. In addition to protecting shorelin es, breakwaters also provide a hard substrate for the attachment of oysters a nd a refuge and foraging ground for fish. However, they have the potential to have unintended adverse effects on se dimentation or other ecological processes, and so they should be pilot tested before construction and used with caution. According to Dale Campbell, of the USCOE Pana ma City office, stone breakwaters are often opposed by boaters because of the potential hazards they pose to those who inadvertently leave the marked navigation channel (personal communication, September 10, 2004). One example of a nonpermanent breakwater is the new product called WhisprWave®, developed by Wave Dispersion Technologies, Inc.. This stru cture is a floating plastic breakwater, which serves the same purpose as a permanent breakwater but has the advantages of being quicker to install and easier to relocate. Such a structure w ould also have the advantage of being less damaging in case of a vessel impact. An example of a large, traditional, ins hore breakwater project is offered by the 11,700 foot long stone breakwater constructed in Louisi ana to protect eroding marshes bordering the Gulf Intracoastal Waterway from wake damage (Louisiana Coastal Wetlands Conservation and Restoration Task Force, 2001). An example from Florida, involving the same regulatory agencies which would be involved in a stabilizat ion project in the GTMNERR, is Project Green Shores in Pensacola (Florida Department of Environmental Protection, 2005) (Figure 15).

35Figure 15: Project Greenshores in Pensacola, Florida

While these projects are expect ed to significantly decrease ma rsh loss to erosion, they are costly. The Louisiana project co st about $137 per linear foot of br eakwater. Although this cost also includes construction of stone terraces, to reduce available fetch in a portion of the protected marsh, building a similar protective structure for only half of the study area would cost about $15 million. Breakwater construction at lower cost has been shown to be possible. In both coastal Louisiana (S teller, 1991) and Italy’s Venice Lagoon (Scarton, Cecconi, Are, Day, & Rismondo, 2000), an innovative technique has been used to construct fence-type breakwaters from wood and brush. Both of these pr ojects involved the cons truction of a sort of wooden bin between posts set into the bottom. In Italy, the fences were filled with willow and poplar bundles. In Louisiana, the fences were filled with discarded Christmas trees. This innovative reuse effort won a participating parish a national award for environmental

36sustainability (Kratch, 1996). High levels of volunt eer participation result ed in the construction of 7,000 meters of fence for only $190,000 in 1991. The obvious drawback of these less costly fences is their durability. The breakwater in It aly received severe damage during a storm and a large portion of the sediment which had accumula ted behind it was lost. Before construction of this type of breakwater, careful study should be undertaken to dete rmine if the low cost is worth the lower durability and resulting higher maintenan ce costs. It is possible that a breakwater of this design could be an excellent pilot project to study the effect s of breakwaters on local erosion rates before construction of a more permanent structure. The high cost and potential ad verse ecological impacts associ ated with stabilization, such as breakwaters, makes it unlikely that a sign ificant portion of the GTMNERR channel margin environment will ever be protected by struct ures. This emphasizes the need for regulatory protective strategies.

Regulation Based Strategies

Regulation-based erosion management strate gies address the caus e of erosion without permanent physical alteration of the nearshore ec osystem. These strategies focus primarily on the reduction of boat wakes. The role of boat wakes in channel margin erosion rates can be expected to increase as the level of boat traffic in the reserve increases. There has been increase in boat registration in St. Johns and Flagler counties of over 400% since 1977 (Figure 16). Boat traffic can be regulated in several ways to reduce margin erosion caused by wakes. As previously stated, factors influenc ing the erosive impact of boat wakes include the size of the wake, the water depth, the current direction and velocity, the morphology of the impacted bank, the presence of wind waves, a nd the distance of the vessel from the shore (Macfarlane & Renilson, 1999). F actors which can potentially be regulated include the distance of vessels from shore and factors such as vesse l speed, hull form, draft, loading and trim which influence the size of the wake. Vessel speed and distance from shore are th e most obvious opportuni ties for regulation. Development of precise regulati ons may need to be supported by additional research linking wakes to habitat degradation in the GTMNERR. Such research w ould also help to clarify which vessels and what activities should be regulated. For example, is it more important to regulate

37less common displacement-hulled vessels that produce huge wakes or more common planing vessels that produce smaller wa kes? Although such studies ha ve been conducted elsewhere (Wilcox, n.d.), it is important to understand the imp acts of the specific distribution of vessel types found in the GTMNERR.

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000FY 77-78FY 78-79FY 79-80FY 80-81FY 81-82FY 82-83FY 83-84FY 84-85FY 85-86FY 86-87FY 87-88FY 88-89FY 89-90FY 90-91FY 91-92FY 92-93FY 93-94FY 94-95FY 95-96FY 96-97FY 97-98FY 98-9920002001VESSEL REGISTRATIONS Flagler County commercial St. Johns County commercial Flagler County private St. Johns County private

Figure 16: Boat registrations in Flag ler and St. Johns Counties, 1977 to 2001 (Florida St atistical Abstract, 1977-2001) Implementation of both stabilization-based plans and regulation-based plans will require significant planning. Before such a planning effort is undertaken, an attempt should be made to establish which private and governme ntal entities will need to be involved in the implementation process.

38CHAPTER 3

POLICY GOVERNING IMPLEMENTATI ON OF MANAGEMENT ALTERNATIVES
Introduction

Given the evidence which implicates wakes from boat traffic as the primary factor in the observed channel margin erosion in the GTMN ERR and the preceding discussion of possible measures which could be used to mitigate the ef fects of navigation on the AICW, it is useful to understand how such measures could be implemented. The options for implementation of stabilization plans and regulation plans differ c onsiderably. Implementation of stabilization plans involves public participation and envi ronmental permitting, while implementation of regulation is mainly a matter of law enforcement.

Implementation of Stabilization Plans

Implementation of stabilization plans is co mplicated by the fact that the AICW in the GTMNERR is constructed in waters of the Unite d States within a right-of-way, composed of federally owned easements on state and privat e land. Although shoreline protection is a permitted activity for property owners within the right-of-way, a large scale public margin stabilization project, partially on privat e land, would be an involved process. First, the project must be permitted under applicable federal and state regulations. Federal permitting authority to regulate construc tion in waters of the AICW stems from two main sources, Section 404 of the Clean Water Act (2005) and Section 10 of the Rivers and Harbors Act (2005). The Clean Water Act regulates placement of any type of fill, including materials used to build stabilization works, in the navigable waters of the United States. The Rivers and Harbors Act applies to projects which have the potentia l to obstruct navigation in the navigable waters of the United States. The US COE is charged with the implementation of both of these statutes. If federal funding is used in the completion of a project or a federal permit is issued, completion of an Environmental Impact Statement, in compliance with the National Environmental Policy Act (2005) , may also be required.

39The State of Florida maintains an Envi ronmental Resource Permitting (ERP) system, independent of the federal system. The ERP system, which is implemented by the Florida Department of Environmental Protection and the Florida Water Management Districts, regulates most major land alterations within the state in cluding projects involving dredging and filling of waters or wetlands. Statutory au thorization of the ERP program to regulate activity in wetlands is contained in Part IV of Chap ter 373 of the Florida Statutes ( 2004). Issuance of an ERP permit from the state certifies not only that a project is compliant with state wetlands regulations, but also that it is consistent w ith the goals of the Florida Coastal Zone Management Program (Coastal Planning and Management, 2004). Although the USCOE issued a Statewide Programmatic General Permit to the State of Flor ida to avoid duplication in federal and state permitting procedures, regulation of breakwaters is specifically excluded from the scope of this permit (State of Florida, n.d.). Separate applicat ions to the USCOE and the state are required to ensure compliance with the Clean Water Act (20 05) and the Rivers and Harbors Act (2005). As nearshore and shoreline stabiliz ation projects have been cons tructed in Florida (Florida Department of Environmental Protection, 2005), m eeting the federal and state requirements is clearly possible with proper project design. In addition to regulatory permits , proprietary authorization mu st also be obtained from involved parties. If the work is to take place within the AICW right-of-way, then the USCOE Real Estate Branch must authorize the use of an easement. If the work is to take place on submerged lands owned by the State of Florida, th e state must issue a proprietary authorization for use as required in Chapter 253 of the Florida Statutes (2004). If the work is to take place on privately owned lands, consent must also be ob tained from these land owners. According to David Roach, of the Florida Inland Navigati on District (personal communication, January, 2005), the owners of the AICW right-of-way retain all rights to the land except those interfering with the navigation project. Once the consent of property owners and the USCOE Real Estate Branch is obtained and all applicable permits are acquired, construction can begin.

Implementation of Regulation Plans

Implementation of new navigation regulations is mainly a matter of enforcement, which is discussed below under Regulati on of Navigation. Before disc ussing the implementation of a

40new set of regulations, it is important to understand the existing regulatory framework which establishes and supports the right to inshore navigation in the AICW.
The Right to Inshore Navigation in Florida In Florida, and the United States as a whol e, the right to navigate is protected by expressions of the Public Trust Doctrine which is rooted in the Roman Co de of Justinian (Robert Deyle, personal communication, March, 2005) under which publicly useful bodies of water are preserved as public property. In Florida this auth ority is defined in a c onstitutional provision (FL Const. art. X, § 11) which declares that land bene ath navigable waters is to be publicly held, and not for sale (Reimer, 2001). Navigable water bodies are defined in case law as any bodies, which in 1845, at the time of statehood, were “capable of bei ng used” for transportation. The ordinary high water line defines the extent of public ownershi p. In the case of saltwater bodies, this high water line is statutorily defined as the “mean high water line,” a location that can be established from local tidal gages (Reimer, 2001). The Atlantic Intracoastal Waterway, which is of particular concern, is a fede ral waterway, and so the right to navigation is based on federal navigational servitude as established in the Co mmerce Clause of the United States Constitution (U.S. Const. art. I, §8). As demonstrated, the righ t to navigate is firmly based in both the federal and state constitutions.
Support of Inshore Navigation Governmental support of navigation mainly consists of developing, marking, and maintaining inshore channels. The 1927 Rivers and Harbors Act (2005) assigned the federal government the role of constructing and maintain ing the navigation channe l of the Intracoastal Waterway (Florida Inland Navigation Dist rict, 1967a). The USCOE is assigned the responsibility for the physical construction wo rk and for cooperating with state and local authorities in planning and project development (Florida Inland Naviga tion District, 2002). In Florida, the Florida Inland Navigation District (FIND), esta blished by the state legislature as an independent sp ecial district in 1927, helps to provide necessary rights-of-ways and land for channel dredging spoil disposal areas, to the federa l government, free of charge (Florida Inland Navigation Distri ct, 2002). FIND is composed of eleven Florida east coast counties: Duval, St. Johns, Flagler, Volusia, Brevard, Indian River, St . Lucie, Martin, Palm

41Beach, Broward, and Miami-Dade. The district is governed by an eleven member Board of Commissioners, one from each county in the distri ct, appointed by the Governor (Florida Inland Navigation District, 2002). Accord ing to Franklin Morrison, with the Jacksonville District of the USCOE, the local port authorities cooperate with both the USCOE and FIND in funding local navigational projects and the acquisition of dr edge material management sites (personal communication, November 20, 2003). Supported by an array of state and fe deral legislation, the channel of the Intracoastal Waterway forms the backbone of inland marine navigation along Florida’s east coast.
Regulation of Navi gational Activities Once the right to navigate is established a nd the creation and maintenance of a waterway, which can support modern navigation, is ensured, the conditions are such that the environmental conflicts begin to occur. As boat traffic on Florida’s waterways continues to increase, the need to regulate boating in order to moderate environm ental degradation will increase. Federal, state, and local authorities share an interest in th e regulation of marine navigation, but the legal authority of these entities to enact su ch regulation differs substantially.
Federal Regulation The ability of the federal government to regul ate marine navigation is established jointly in the Commerce Clause of the United States Constitution, previously cited as establishing the federal right to navigation, and the Property Clause of the Constitution (U.S. Const. art. IV, §3). The Commerce Clause gives the government the right to regulate maritime activity in waters of the United States based on the “federal navigatio nal servitude” and this basis for regulation has been supported by the courts (G ibbons v. Ogden, 1984). The aut hority to restrict navigation based on the reasoning that the U.S. has the ri ght to make rules governing conduct on federal property and adjacent non-federal property, as desc ribed in the Property Clause, has also been upheld (McGrail v. Babbitt, 1997). The implementa tion of these constitutional authorities has been delegated to a number of federal agencies. Brooks (2000) discusses six fede ral agencies with potential power to regulate navigation in Florida waters, the United States Coast Guar d (USCG), the USCOE, the Fish and Wildlife Service (USFWS), the National Marine Fisherie s Service (NMFS), the National Park Service

42(NPS), and NOAA. The powers of NOAA and th e NPS are restricted to national marine sanctuaries and national parks, respectivel y (Brooks, 2000). Although the Fort Matanzas National Monument borders the study area, its small size make s any regulation within its boundaries insignificant in terms of protecting the resources of the GTMNERR as a whole. While the GTMNERR is administered jointly by NOAA and the State of Florida, it is not a marine sanctuary, and thus NOAA is also unlikely to have significant regulatory authority over activities in the reserve. The USFWS and the NMFS derive broad authority from the Endangered Species Act (2005) and the Marine Mammal Protection Ac t (2005) to regulate activity which may impact endangered species or marine mammals. This authority has been largely delegated to the State of Florida, which makes use of it in regula tion of boating activities for the protection of the West Indian Manatee (F lorida Manatee Sanctuary Act, 2004). However, regulation related to endangered species does not appear to have immediate application to the current issue of channel margin protection. The power of the USCOE to restrict navigation is generally limited to issues of military operati ons and national security (Brooks, 2000). The limitations on the previously discussed agencies leave the USCG as the federal body with the most power to affect meaningful regulation within the GTMNERR. The Coast Guard has authority to restrict vessels operating in th e navigable waters of the United States for “environmental purposes” (Ports and Waterways Safety Program, 2005) and to restrict vessels from “safety zones” for safety or environm ental purposes (Navigation and Navigable Water Rule, 2005).
State Regulation State regulation of inshore navigation in Florida is accomplished through the statutory grant of police powers and the Public Trust Doct rine, as defined in the State Constitution (FL Const. art. X, §11). Such regulation is implem ented by the Board of Trustees of the Internal Improvement Trust Fund, the Florida Fish a nd Wildlife Conservation Commission (FWCC), and the Florida Department of Environmental Pr otection (FDEP). However, only the FWCC and FDEP have power to restrict naviga tion for environmental purposes. The FWCC uses its statutory authority, under the Florida Manatee Sanctuary Act (2004), to restrict and exclude vessels to ensure manat ee protection. This authority has been upheld in

43court (Marine Industries Ass’n of South Florida, Inc. v. FDEP, 1996). Perhaps this power has the potential to be extended to ensure the protection of other envi ronmental entities. The FDEP has the authority to restrict motorized watercraft within state-defined canoe trails (Recreational Trails System , 2004), but at this time there ar e no such trails within the study

area.
Local Regulation Local governments in Florida, through exercise of their police power , have the authority to restrict the operation of vessels, within water bodies in their jurisdiction, through local law or ordinance. These local regulations cannot conflict directly with state or federal laws and cannot pertain to vessels operating within the AICW (Vessel Safety, 2004). The restriction on local laws regulating activ ities in the Intracoastal Waterway makes significant local regulation of in shore boating activity along much of Florida’s east coast very difficult. Particularly in regi ons such as northern Flagler Count y or southern St. Johns County, where practically all inshore na vigation takes place in the Wate rway, local governments are left with few means to restrict boating activity. In situ ations such as these, any significant restriction on navigation on the AICW will have to occur on the federal or state level.

44CONCLUSION

Erosion along the margin of the Atlantic Intracoastal Waterway channel in the Guana Tolomato Matanzas Estuarine Research Reserve is drastically altering nearshore habitat and resulting in substantial ecologi cal degradation. From 1970/1971 to 2002 nearly 70 hectares (170 acres) of nearshore intert idal bars, marsh, dredge spoil disposal areas, and uplands have been lost to erosion. Analysis of erosiv e trends suggests that increased nearshore wave energy caused by boat wakes is the primary cause of this erosion; however, further research may be necessary to accurately relate wake energy to erosion rates. Such work should be followed by the development and implementation of a plan inte nded to address the problem of erosion. A management plan develope d to address the problem of margin erosion in the GTMNERR should focus primarily on minimizing nearshore wave energy levels and perhaps using nearshore stabiliza tion techniques as a remediation to ol where impacts have been most severe. Regulation of navigation on the Intr acoastal Waterway w ould most likely be implemented by the State of Florida and thus involve enforcement by the Florida Fish and Wildlife Conservation Commission. As no clear statutory authority for such regulation exists, extension of existing legislation or introduction of new state legislation may be necessary. Implementation of the stabilization portion of such a plan would invol ve meeting federal and state permitting requirements and obtaining the c onsent of involved land owners. Failure to implement such a plan is likely to allow current rates of habitat degradation to continue and, therefore, has the potential to undermine the intent of the GT MNERR as a National Estuarine Research Reserve (National Estuarin e Research Reserve System, 2005(b)).

45GLOSSARY

accretion The process of accumulation of sediment deposited by wind or water accretion polygons A closed, two-dimensional figur e with at least three sides representing an area where accretion has occurred aggradation The process of a vertical incr ease in the elevation of a landform due to sediment deposition AICW Atlantic Intracoastal Waterway allochthonous sediment Sediment introduced from outside the system autochthonous sediment Sediment generated within the system bathymetric profile A cross section showing the el evation of the bottom of a body of water bioturbation Disruption caused by biological activity erosion Removal of sediment by wind or water erosion polygons A closed, two-dimensional figur e with at least three sides that represents an area where erosion has occurred eustatic sea level rise A worldwide fluctuation in s ea-level; as opposed to local or regional change fetch The distance wind blows acr oss the surface of a body of water to generate waves GTMNERR Guana Tolomato Matanzas National Estuarine Research Reserve longshore sediment transport The physical movement of sediment along a shoreline by currents running parallel to the shore NERR National Estuarine Research Reserve organic aggregates Macroscopic particulate matte r of biological origin predation An interaction which involves one organism eating another rhizomatic mat A structure formed by the interwoven underground stems of plants riverine Of or related to a river subsidence The decrease in the el evation of a landform surface accretion Synonymous with aggradation tidal prism The difference in the volume of water in a body between high and low tides trophic structure The network of interrelat ionships in a biological community based on the transfer of energy

46APPENDIX



### 3 8

2

1 4 5 7
6 9 11 14

10

13

12 15 16

GTMNERR Atlantic Ocean

GTMNERR

0 1 2 3 4 5 Kilometers 

# ¢

Figure 17: Index of plates

470 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1970 FDOT photography

Figure 18: Plate 1

480 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1970 FDOT photography

Figure 19: Plate 2

490 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1970 FDOT photography

Figure 20: Plate 3

500 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1970 and 1971 FDOT photography

Figure 21: Plate 4

510 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 22: Plate 5

520 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1970 and 1971 FDOT photography

Figure 23: Plate 6

530 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 24: Plate 7

540 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 25: Plate 8

550 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 26: Plate 9

560 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 27: Plate 10

570 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 28: Plate 11

580 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 29: Plate 12

590 100 200 300 400 500 Meters 

# ¢ Legend Accretion intertidal bars
marsh spoil upland 

### Erosion intertidal bars
marsh spoil upland



### Background is 1971 FDOT photography

Figure 30: Plate 13

600 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 31: Plate 14

610 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 32: Plate 15

620 100 200 300 400 500 Meters 

# ¢ Legend Accretion
intertidal bars
marsh spoil upland 

### Erosion
intertidal bars
marsh spoil upland


### Background is 1971 FDOT photography

Figure 33: Plate 16

63REFERENCES

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64FL Const. art. X, § 11.
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. Annapolis, MD: Tidewater Administration, Maryland Dept. of Natural Resources.

69BIOGRAPHICAL SKETCH

Frank Price was born in Tallahassee Memorial Hospital in 1978. In 1980 he moved to St. Augustine where he grew up surfing at Butler Beach and fishing in the Matanzas River. He moved back to Tallahassee in 1996 to earn a bach elor’s degree in Enviro nmental Studies with a minor in Biology. He has been employed by Florida State University, North Carolina State University, and Environmental Planing and Analysis (a private environmental consulting firm). Currently he works for the U.S. Geological Su rvey in Tallahassee where he assists with interdisciplinary research on the Apalachicola Ri ver. Upon graduation he plans to pursue a career in coastal resource management in the southeastern U.S.

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