SHIP SHOAL: SAND RESOURCE SYNTHESIS REPORT

Prepared by:
Mark Kulp, Shea Penland, and Karen Ramsey
Coastal Research Laboratory Department of Geology and Geophysics University of New Orleans
2000 Lakefront
New Orleans, LA 70148
Submitted to:
Lee Wilson and Associates
105 Cienga St.
Santa Fe, New Mexico 87501
July 2001

TABLE OF CONTENTS

List of Tables .................................................................................................................... ii List of Figures................................................................................................................... iii List of Appendices ............................................................................................................ iv
Introduction ...................................................................................................................... 1
Purpose of Report ............................................................................................................. 3
Regional Geologic Framework......................................................................................... 3
Ship Shoal: Location and Morphology .............................................................................. 7
Ship Shoal: Geologic Framework...................................................................................... 13
Available Geologic Data .............................................................................................. 13
Surficial Sedimentary Character ................................................................................... 16
Stratigraphy and Depositional Environments................................................................ 21
Shoal crest .............................................................................................................. 21
Shoal front ............................................................................................................. 24
Shoal base .............................................................................................................. 24
Sand sheet .............................................................................................................. 25
Stratigraphic Cross Sections ......................................................................................... 25
Isopachous Map of Ship Shoal ..................................................................................... 30
Risks and Factors to Consider ........................................................................................... 30
Overfill Calculations .................................................................................................... 30
Infrastructure of Proposed Dredge Areas ...................................................................... 34
Archeological Resource Considerations ....................................................................... 38
Environmental Impacts ................................................................................................ 40
Hydrodynamic Impacts ................................................................................................ 42
Dredging ........................................................................................................................... 46
Hydraulic dredging ...................................................................................................... 48
Hopper Dredges ...................................................................................................... 48
Sidecasting Dredge.................................................................................................. 49
Plain Suction and Dustpan Dredges .......................................................................... 50
Mechanical Dredges..................................................................................................... 50
Clamshell Dredges .................................................................................................. 50
Combination Dredges................................................................................................... 50
Cutterhead Dredge .................................................................................................... 50
Ship Shoal Cost Analysis .................................................................................................. 51
Dredging Configuration ............................................................................................... 53
Projected Cost Estimate ............................................................................................... 57
Conclusions ...................................................................................................................... 60
References and Bibliography ............................................................................................ 61
Appendix A ...................................................................................................................... A-1
Appendix B....................................................................................................................... B-1
i

List of Tables

Table I Sorting classification scheme ........................................................................... 17

Table 2 Characteristics of dredge types ...................................................................... 47

Table 3 Task I cost estimate ............................................................................................ 58

Table 4 Task 2 cost estimate ............................................................................................ 59

11

List of Figures

Figure 1 Satellite image of southern Louisiana ............................................................. 2
Figure 2 Inner-continental shelf shoals of south-central Louisiana ................................ 4
Figure 3 Distribution and chronology of Holocene deltaic complexes .......................... 6
Figure 4 Plan-view of three-stage transgressive barrier model ...................................... 8
Figure 5 Cross-sectional vies of transgressive barrier model......................................... 9
Figure 6 Bathymetric map of the Ship Shoal area ....................................................... 10
Figure 7 Bathymetric profiles of eastern and western Ship Shoal................................ 11
Figure 8 Distribution of high-resolution seismic data in the Ship Shoal area............... 14
Figure 9 Distribution of vibracore data in the Ship Shoal area .................................... 15
Figure 10 Grain-size classification chart....................................................................... 18
Figure 11 Surficial textural data of Ship Shoal area ...................................................... 19
Figure 12 Sedimentary facies map of the Ship Shoal area............................................. 20
Figure 13 Stratigraphic log of Ship Shoal..................................................................... 22
Figure 14 Cross section of Ship Shoal facies ................................................................ 23
Figure 15 Cross section location map ........................................................................... 26
Figure 16 Cross section A-A’....................................................................................... 27
Figure 17 Cross section B-B’ ....................................................................................... 28
Figure 18 Cross section C-C’ ....................................................................................... 29
Figure 19 Isopachous map of Ship Shoal sand .............................................................. 31
Figure 20 Mean-grain size data for MMS lease blocks SS88, PL12, PL13.................... 32
Figure 21 Sorting data for MMS lease blocks SS88, PL12, PL13 ................................. 33
Figure 22 Grain-size data for Isles Dernieres beach sediment ....................................... 35
Figure 23 Fill-ratio chart .............................................................................................. 36
Figure 24 Hydrocarbon infrastructure for lease blocks PL12, PL13 .............................. 37
Figure 25 Hydrocarbon infrastructure for lease block SS88.......................................... 39
Figure 26 Map showing Ship Shoal transport distances ............................................... 52
Figure 27 Inshore rehandling facility............................................................................ 54
Figure 28 Offshore rehandling facility.......................................................................... 56
iii

List of Appendices

Appendix A. Hydrodynamic impact ............................................................................ A-1

Appendix B Cost Analysis Tabulations ........................................................................ B-1

IV

INTRODUCTION

A subsiding delta plain and regional absolute sea-level rise have collectively made the Mississippi River delta of southern Louisiana the site of the highest relative sea-level rise rates (RSLR) in the Gulf of Mexico basin (Penland et al., 1989). A consequence of the high RSLR rates, in conjunction with lower delta plain sediment starvation imparted by upstream damming and diversions, is an average long-term coastal erosion rate of 4.2 m yr-1 (Williams et al., 1991) and land loss of as much as 25 km2 yr-1 (Britsch et al., 1993). Coastal deterioration of this magnitude suggests a dire future for coastal Louisiana.
Much attention is currently focused on the coastal change and habitat loss of southern Louisiana. Several state- and federally-funded programs (e.g., Coastal Wetlands Planning Protection Restoration Act (CWPPRA) and Coast 2050) are currently active and directed toward coastal ecosystem restoration in south Louisiana. Current Gulfside shoreline solutions to this problem include beach nourishment and barrier-island restoration. However, the success of these initiatives requires large volumes of texturally appropriate sediment and consequently, are feasible only if sand supply is sufficient and environmental impacts of removing this sediment minimal. A recently completed Coast 2050 project by the U.S. Geological Survey (Coastal Marine Geology Program) and University of New Orleans Coastal Research Laboratory, in conjunction with the U.S. Army Corp of Engineers, identified a relatively limited supply of high- quality sand resources on the inner-continental shelf of the Barataria Barrier Shoreline Feasibility Study (Fig 1). This survey concluded that there is not a sufficient quantity of nearshore sand resources to satisfy the needs of planned and proposed CWPPRA barrier shoreline projects and the proposed Coast 2050 Barataria Barrier Shoreline restoration project. As a consequence, large marine sand bodies such as Ship Shoal must be evaluated and integrated into the CWPPRA and Coast 2050 barrier-shoreline restoration programs. Therefore, shoreline restoration and
1

Lake

Pontchartrain

Atchafalaya

Bay

Ship Shoal

Figure 1. Satellite image showing features of south-central Louisiana that are discussed in the text.
renourishment projects within Louisiana are now confronted with finding and investigating more distally located offshore continental-shelf sand deposits. Additionally, exploitation of these potentially valuable resources will likely require the development of efficient and innovative dredging methodologies and nearshore sediment-delivery systems.

PURPOSE OF REPORT

This report focuses on the Ship Shoal area of the central Louisiana inner-continental shelf (Figs. 1 and 2). Ship Shoal has been the focus of numerous studies and previously suggested as a viable sediment source for barrier shoreline beach, dune, and back-barrier restoration projects along coastal Louisiana (e.g. Penland et al., 1989; Ramsey and Penland, 1991). The purpose of this report is to provide to a synthesis of current geologic knowledge about Ship Shoal, as well as address the suitability and feasibility of using Ship Shoal sediment for beach nourishment and restoration along Louisiana’s rapidly deteriorating barrier shorelines.

REGIONAL GEOLOGIC FRAMEWORK

The geomorphologic and shallow stratigraphic framework of the Mississippi River delta plain and Louisiana inner-continental shelf is the product of fluvial and marine depositional processes that have been operative for at least the last 7,000 years (Frazier, 1967). During this time the Mississippi River and associated distributaries have been the primary conduits delivering sediments to the region. Current models describe the Holocene history (~ last 10 ky) of the Mississippi River delta as a multi-stage process reflecting the complex interplay between changing rates of sea-level rise and sediment dispersal paths (Frazier 1967; Penland and Boyd,
1985; Penland et al., 1988). Deltaic growth is an episodic process, fluctuating between periods of seaward progradation of deltaic depocenters (regressive deposition) and the landward retreat of the deltaic coastline as depocenters are abandoned, reworked, and inundated by marine waters
(transgressive deposition).
3

N

W E

S

New Orleans

Marsh

Island

Point au

Fer

Terrebonne

Bay

Trinity Shoal

Ship Shoal

50 0 50 Miles

50 0 50 100 Kilometers

Figure 2. Regional map of south-central Louisiana coastline and inner-continental shelf. Ship Shoal is the easternmost shoal of a series of coast-parallel offshore shoals that are the transgressed remnants of earlier-formed deltaic headlands. Shoreline data from LOSCO (2000); bathymetric data from LOSCO (1999).
Regressive depositional episodes are characterized by the seaward advance of distributaries, resulting in the construction of deltaic headlands and a progressively more seaward-located coastline. Deltaic headlands are however subject to marine processes such as wave and tidal currents that disperse sediment laterally and contribute toward the construction and nourishment of flanking beaches, beach ridges, and chenier plains. In the Ship Shoal area the most recent phase of constructional deposition is primarily attributed to progradation of the Maringouin deltaic complex (Fig. 3; Frazier, 1967). Distributary pathways are, however, ephemeral; seaward progradation results in lengthened distributary networks a reduction in their gradient, and ultimately, abandonment of the active distributary networks in favor of shorter, more hydraulically efficient routes. Distributary switching is a naturally occurring event and a fundamental process that has contributed to the overall geomorphology and geographic extent of the modern Mississippi River delta plain.
Distributary abandonment, coupled with the combined effects of substrate subsidence and absolute sea-level rise (collectively called relative sea-level rise), results in erosional headland retreat and the landward migration of the shoreline as earlier deposited sediment is reworked and redistributed by marine processes. Regressive deposition is recognized as an important contributing process to the vertically stacked and laterally offset deltaic depocenters preserved within the shallow Holocene stratigraphic framework of the Mississippi River delta plain and adjacent continental shelf (e.g. Scruton, 1960; Coleman and Gagliano, 1966; Frazier, 1967). Penland et al. (1981) and Penland and Boyd (1981) emphasized however the role and
significance of transgressive events in the stratigraphic architecture of the deltaic system, and presented a conceptual model that accounts for the genesis of transgressive stratigraphy. Their
three-stage model depicts the evolution of an active deltaic headland to an inner-shelf shoal
5

32° N

31°

ST.BERNARD

30°

TECHE

29°

MARINGOUIN

LAFOURCHE

PLAQUEMINE/BALIZE

28°

27°

0 km 100 km 200 km

-94° -93° -92° -91° -90° -89° -88°

Plaquemine/Balize

Outer shelf deltaic complexes?

Maringouin

Teche

Lafourche

St.Bernard

14C years B.P.

Figure 3. Geographic distribution and proposed chronology for Holocene delta complexes of the Mississippi River (modified from Frazier, 1967).
through processes of marine reworking and relative sea-level rise.
Transgressive deposition begins when marine processes transform an abandoned deltaic depocenter into a stage-1 erosional headland with flanking headland barriers and recurved spits built by longshore drift of headland sand sources (Figs. 4 and 5). A limited sediment supply from the abandoned distributaries coupled with continued relative sea-level rise and shoreface erosion eventually, leads to separation of the stage-1 barrier shoreline from the mainland and formation of a stage-2, barrier-island arc. The final stage occurs during transgressive submergence of the barrier-island arc as ongoing relative sea-level rise and storm processes prevent the barrier-island arc from maintaining subaerial integrity. Eventually, complete submergence and marine reworking generates a sand-rich marine shoal that is detached from the deltaic coastline and isolated on the inner shelf (Figs. 4 and 5).

SHIP SHOAL: LOCATION AND MORPHOLOGY

Ship Shoal is the easternmost and largest of a group of inner-shelf shoals that have developed on the Louisiana continental shelf as a result of deltaic abandonment and marine transgression (Figs. 2 and 6). The shoal is an asymmetric, landward-skewed sedimentary body approximately 50-km long, marking the minimum seaward extent of early to mid-Holocene Maringouin deltaic deposition. Widths across the central part of the shoal range between 4 and 8 km, whereas on the eastern and western ends shoal width ranges between 5 and 10 km (Fig. 6). Relative to the surrounding shelf, relief of the shoal varies from between approximately 7 m on the western end to approximately 5 m in the central and eastern portions of the shoal; water depths above the shoal range between approximately 3 m over the western end to 8 m on the eastern-edge (Figs. 6 and 7).
A 15- to 20-km wide platform lies seaward of Ship Shoal and forms the base of Ship
Shoal between the 12- and 20-m isobaths (Fig. 6). Approximately 25-km seaward of Ship Shoal
7
!TRANSGRESSIVE MISSISSIPPI DELTA BARRIER MODEL\

REGRESSIVE

ENVIRONMENTS

E:J Fresh N•rol>

-;;? &each lil!dg<!

TRANSGRESSIVE

ENVIRONMENTS

Subaerial

&nier Sands,

Su:baqt.UH.Jns

!latrler

D Sand Sh<!el

Salt Marsh

••• R"tu""d

,.., Sbell R••f

f Tldol CllanMI

Figure 4. Plan view of a three-stage conceptual model illustrating the construction of transgressive stratigraphic intervals within the Mississippi River deltaic framework. Evolution of deltaic headlands to an inner-shelf shoal progresses from stage 1: erosional headland and flanking barriers to stage 2: transgressive barrier-island arc to stage 3: inner-shelf shoals (modified from Penland et a!., 1988).

STAGE I-EROSIONAL HEADLAND

0 MSL

5

I

0

Sand 5

Sheet

5

Distance (km )

REGRESSIVE FACIES

Distributary

Elll Delta Front/Prodelta

----. Sediment Dispersol Pathway

25 35

TRANSGRESSIVE FACIES

f;W?W?:J Barrier

[@Marsh

Lagoon

Figure 5. Cross sectional view of a stratigraphic framework illustrating the development of sand-rich shoals on the inner continental shelf from an abandoned deltaic headland (from Penland eta!., 1985).

N

W E

S

study area

Point au Fer

2

Isle Denieres

Islands

Terrebonne

Bay

4

6

10 8

1412

18 16

20

24 22

28 26

6 4

Ship Shoal

Timbalier Islands

Outer Shoal

10 0 10 20 Miles

10 0 10 20 30 Kilometers

Figure 6. Detailed bathymetric map of the Ship Shoal area. Dashed lines across Ship Shoal mark location of cross sections displayed in figure 7. Contour interval every two meters. Shoreline data from LOSCO (2000). Bathymetric data from LOSCO (1999).

EASTERN SHIP SHOAL SHELF COMPONENTS

DISTANCI! !ltml

Figure 7. Bathymetric profiles illustrating the primary geomorphologic components of eastern and western Ship shoal (modified from Penland eta!., 1986).

on the seaward edge of this platform is another shore-parallel shoal with an inner-shelf relief of only 1 to 2 m and water depths of approximately 12 to 15 m above its crest. This feature, termed the Outer Shoal (Penland et al., 1988) is approximately 35-km long and 5 to 10- km wide. The platform and Outer shoal are best defined on the inner shelf, offshore of the western end of Ship Shoal.
Toward the west along the crest of the shoal there is a reduction in the seaward slope of the shoal and an increase in the landward slope (Figs. 6). This variation in shoal-crest asymmetry and westward orientation occurs concurrently with a decrease in water depth over the crest and an increase in shoal relief. This westward trending increase of the landward-directed crest slopes and water depths reflects the influence of a nearshore protuberance defined by a 6-m bathymetric protuberance extending southeast out of the Calliou Bay and Point Au Fer areas
(Fig. 6). The Calliou Bay protuberance, Ship Shoal, and the seaward platform constitute the shelf components of the easternmost portion of the transgressed Maringouin delta. Bathymetric profiles extending across the shoal illustrate the geomorphic components across the western and eastern components of the shoals-platforms complex (Fig. 7).
The landward asymmetry of Ship shoal as well as seafloor bathymetric change (List et al., 1994) suggest that Ship shoal is migrating north-northwest onto the Calliou Bay platform. Sea-floor change analysis conducted for the time period 1880’s to 1930’s indicates the landward edge of Ship Shoal accreted 42.5 x 106 m3 of sediment. For the analysis period between 1930
and 1980 the landward edge accreted 43.3 x 106 m3 and the seaward slope eroded 62.1 x 106 m3.
Accretion along the landward edge was most likely the result of redeposition of sediment that had been moved from the seaward face of the shoal. The deficit between eroded and accreted material is likely attributable to offshore-onshore transport and dispersal of sediment that has been reworked by storm events impacting the shelf.
12

SHIP SHOAL: GEOLOGIC FRAMEWORK

Available Geologic Data

Numerous researchers have previously investigated the sedimentology, stratigraphy, and morphology of Ship Shoal (e.g. Kraweic, 1960; Frazier, 1974; Penland et al., 1981; Penland and Boyd, 1981). A variety of methods, including vibracores, surface grab samples, and high- resolution seismic profiling have been utilized in these investigations. Figures 8 and 9 show the distribution of high-resolution seismic profiles and vibracores collected around Ship Shoal in the
1980’s by the Louisiana Geological Survey; these datasets were used in this report to verify the conclusions of previous workers and construct new diagrams and maps displaying the stratigraphy and morphology of Ship Shoal. These vibracore and high-resolution seismic profiles are archived at the University of New Orleans Coastal Research Laboratory.
High-resolution seismic data available for the Ship Shoal area was collected with a Datasonics 3.5-khz subbottom profiler and an Ocean Research Equipment Geopulse system. The subbottom profiler is a high-frequency system that offers high resolution (~0.5 m) within shallow sediments, however penetration depth is limited to the approximately upper 15 m of stratigraphy. Alternatively, the Geopulse system has poorer resolution in the upper stratigraphy but a penetration depth generally in excess of 25 m. Typically, both of these high-resolution seismic profiles are available in the Ship Shoal area along any single seismic track line.
Vibracores used in this study were collected, through contracts with the Louisiana Geological Survey, between 1983 and 1993 by Alpine Ocean Seismic Surveys. Each vibracore was 7.5 cm in diameter and 10- to 12-m long. Along the eastern end of Ship Shoal, five 6-m long vibracores were taken in the year 2001 from the U.S. Geological Survey R/V Gilbert. Most
of the vibracores used in this report were described in detail and analyzed for grain-size
13

N

W E

S

Lacoss III-83

Acadiana-86

Laser-88

Figure 8. Distribution of high-resolution seismic coverage for the Ship Shoal area. These seismic surveys were acquired during the
1980's by the Louisiana Geological Survey and are currently archived at the University of New Orleans Coastal Research Laboratory.

N

W E

S

2

86-18

86-1

4

86-2

86-19

86-20

86-23

86-22

86-9

83-14

83-18 83-17

83-10 83-11

83-7

92-11 92-12

83-6

83-1

83-2

86-3 92-6 92-5

86-4

92-4

83-12

92-2

83-15

86-28

86-25

00-2

00-5

00-4

00-1

6

83-5

8

83-4

83-3

86-26

86-32

92-7 92-8

92-9

92-10

86-11

86-12

83-13

92-3

86-13

83-16

86-29

86-30

86-31

00-3

86-24

83-19

10

86-5

12

14

16

18 86-6

86-21

86-17

86-16

20 0 20 Miles

20 0 20 40 Kilometers

86-15

1992 vibracores

2000 vibracores

Figure 9. Distribution of vibracores for the Ship Shoal area. Vibracores were acquired during the 1980s by the Louisiana Geological
Survey and currently archived at the University of New Orleans Coastal Research Laboratory.
distributions by Louisiana Geological Survey personnel now employed by UNO. Figure 10 and
Table 1 display the grain-size classification scheme used throughout this text.

Surficial sedimentary character

Krawiec (1966) examined the textural character and mineralogy of Ship Shoal and the adjacent shelf wit h grab samples taken along south-trending transects of the western and eastern shoal (Fig 11). Compositional analysis and grain-size statistics indicated that Ship Shoal consists predominantly of fine-grained, quartz sand and is substantially more sand rich than adjacent parts of the shelf (Fig. 11). Krawiec (1966) concluded, on the basis of grain size, sorting, and bulk composition, that Ship Shoal formed from the deterioration of a barrier shoreline associated with
a formerly active Mississippi River delta.
Cuomo (1984) investigated the surficial shoal sediments and concluded that grain size decreases from east to west along the shoal crest and toward the south away from the shoal crest; sorting also decreases away from the shoal crest. Cumo (1984) suggested that grain-size distributions for the shoal crest were similar to the well-sorted (0.28 - 0.44 ?units), fine to very- fine grained sand (2.7-3.9 ?) that is characteristic of beach environments.
Frazier (1974) mapped the subaqueous lithofacies in the Ship Shoal region on the basis of percent sand. Between the 7- to 8-m isobaths, Ship Shoal was indicated to contain between 75-
100% sand. Locally, seaward protruding areas of the western shoal contained zones of between
75 - 100% and 50 - 75% sand. Much of the surrounding shelf was indicated to consist of silty clay.
Williams et al. (1989) combined previous datasets with their own to map seven major lithofacies in the Ship shoal area that were distinguished on the basis of sand content (Fig. 12).
Quartz sand, consistent with the results of Krawiec (1966) and Mazullo (1986), was found to be
16

Table 1. Measures of sorting used in grain-size analysis. Phi units represent a non- dimensional description of the measure of dispersion about the mean grain size; low values are representative of well-sorted sediments (modified from McManus, 1988).

Phi value

mm size

Wentworth

Classification

Boulder

Cobble

Pebble

Gravel

very coarse
3.0 0.125
coarse

S

medium a n

d

fine
very fine

Silt

Clay

Figure 10. Diagram displaying the equivalence of the dimensionless phi grain-size scale, metric measurements, and the Wentworth grain-size classifications (modified from Hobson, 1979).

N

0 20 Miles

0 20 Kilometers W E

S

2

95 75

97 77

98

4 79

215

99

6 100 81

82

8 103 83

105

10

12

10

clay

8

6 silt

4 vfs

2 fs ms

0

95 97 98 215 99 100 103 105 107 108 109

sample

107

108

109

10 84

clay

8

6 silt

4 vfs 85

2 fs

0 86

75 77 79 81 82 83 84 85 86

sample

Figure 11. Map of surficial textural data collected by Krawiec (1966); vfs = very fine sand, fs = fine sand, ms = medium sand.

N

0 20 Miles

0 20 Kilometers W E

S

2

sm

4

ms ms

6

8 sm sm

10

12 ms

14

sm

m m

sm

16

18

sandy

silty sand

silt

sm sandy mud ms muddy sand

sandy silt

m mud

Figure 12. Map of major sedimentary facies in the Ship Shoal area (modified from Williams et al., 1989).
a primary constituent of the surficial sediment with an average, but highly variable, sand content of 54%; however much of Ship Shoal contained 90 to 99% sand.

Stratigraphy and Depositional Environments

The stratigraphy of the Ship Shoal area has been extensively studied. Previous workers divided the stratigraphy of the area into two primary suites of genetically related depositional units: a transgressive suite and regressive suite (Penland et al., 1991). Figure 13 is a stratigraphic log displaying the generalized transgressive-regressive stratigraphy of Ship Shoal. Of primary interest for sand resources is the transgressive component of the Ship Shoal stratigraphy, consisting of a shoal crest, shoal front, and shoal base. A generalized stratigraphic cross section illustrates the facies relationships between the overlying transgressive deposits and the
underlying regressive deposits (Fig. 14). The shoal crest, shoal front, shoal base, sand-sheet, and lagoonal stratigraphy are deposited above the regressive units as Ship Shoal migrates landward. The subjacent deltaic interval, consisting of distributary, delta front, and prodelta sediments, represents regressive deposition associated with the earlier progradational phase of Magingouin deposition. Because sand-rich deposits suitable for restoration efforts are primarily located within the transgressive suite of deposits this report focuses on a description of the sedimentary
character of the shoal crest, shoal front, and shoal base. Much of the following discussions about the transgressive, sand-rich facies of Ship Shoal are extracted from Penland et al. (1986).
Readers are referred to Penland et al. (1986) and Ramsey and Penland (1991) for a thorough discussion on the character and distribution of the regressive stratigraphy of the Ship Shoal area.

Shoal Crest

The shoal crest environment is a shore-parallel accumulation of sand and shell that has been deposited in response to reworking by wave and tidal currents crossing the shoal ramp and
adjacent continental shelf. This segment of the shoal is the highest energy environment where
21

Shoal Crest

Shoal Front

Shoal Base

Lagoon

Distributary

Delta Front

Prodelta

Transgressive stratigraphy

Regressive stratigraphy

Figure 13. Representative stratigraphic log for the Ship Shoal area. Regressive stratigraphic intervals represent deposition during the progradation of deltaic headlands, whereas transgressive stratigraphic intervals reflect reworking and inundation of abandoned headlands (Penland
et al., 1986).

North

5

back shoal

Ship Shoal Facies Model

shoal crest

lower shoal shoal front

shoal migration

South

10 lagoon

15

deltaic deposits

sand sheet

0 5 10 15 20 distance (km)

Figure 14. Generalized stratigraphic cross section of Ship Shoal showing the relationships between the sedimentary facies of Ship Shoal (Penland et al., 1986).
currents and waves winnow, sort, and abrade the available sediment into a uniform grain size. The shoal crest is typically within the upper 4 meters of stratigraphic section. Sediment consists of very well-sorted, well-rounded, quartz sand with parallel, horizontal to subhorizontal laminations. Whole and reworked shells (Mulinia, Olivella, Rangia, Crassostrea) are heavily concentrated within this interval, which generally displays a coarsening upward grain size. This section of the shoal locally consists of as much as 99% sand. Mean grain size in this
sedimentary facies ranges between 1.5 and 2.7 , with a sorting value of 0.5 to 1.6 units.

Shoal front

The shoal-front facies borders the shoal crest facies along the seaward edge, consisting of moderately sorted, fine- to very fine-grained sand. Mean grain size in this facies ranges between
2.7 and 3.1 , with a sorting value of 0.5 to 0.9 . The shoal front through most of the area has been suggested to be approximately 75 to 95% sand. Sedimentation along the shoal front is primarily the result of storm events that pass over the shoal crest and transport sediment into deeper, off-shoal waters.

Shoal base

Sediments of the shoal base typically consist of interbedded silty clay and lenticular-to- wavy bedded, poorly sorted, very fine-grained sands. Mean grain size of these sediments ranges between 3.1 and 3.6 with a sorting value of 1.2 to 1.5 units. The shoal base contains 50 to
75% sand. The low-energy, shoal-base environment marks the advancing edge of the landward migrating Ship Shoal depositional surface. The shoal base lies between the 8- to 9-m isobath in the west and the 11- to 12-m isobath in the east. Because of greater water depths in the shoal base area than in the shoal-front and shoal-crest environments, sedimentation is even more
episodic and primarily the product of storm events.
24

Sand Sheet

A discontinuous sand sheet covers much of the seaward slope of Ship Shoal marking the path of the shoal’s landward migration. Grain size of the sediment within the sand sheet ranges between 2.7 and 3.2 with sorting values of 1.7 to 2.3 ?units. Thickness of the sand sheet is variable but may be as much as one meter. The sand sheet likely represents the amalgamated deposits of storm events that have mobilized sediment and transported them seaward from more landward located locations.

Stratigraphic Cross Sections

Three stratigraphic cross sections illustrate the strike- and dip-parallel architecture of Ship Shoal (Fig. 15). South-trending cross-sections A-A’ and B-B’ provide an excellent overview of the overall facies relationships and geometry of the shoal (Figs. 16 and 17). On both cross sections the Ship Shoal sand body consists of shoal crest, shoal front, and shoal base deposits sitting unconformably upon a regressive deltaic sedimentary package. Cross-section A- A’ indicates a thickness of sand-rich shoal sediment in excess of 4 meters locally, whereas cross- section B-B’ indicates a thickness of approximately 3 meters. The subjacent regressive sequence is approximately 8- to 12-m thick and consists primarily of fine-grained lagoonal and delta-front deposits. Lagoonal muds directly below the transgressive shoal deposits are persistent throughout the Ship Shoal area but are not synchronous with the overlying transgressive
deposits. Lagoonal deposits on the landward side of the shoal are however, temporally equivalent to parts of the shoal body and reflect low-energy deposition taking in the back shoal area.
Cross section C-C’ trends parallel along the shoal axis and similarly reveals the relationship of the transgressive shoal deposits to underlying regressive deltaic deposits (Fig. 18).
Basal shoal sands sit disconformably atop the underlying lagoonal deposits. A large distributary
25

N

W E

S

2

A 86-18

86-1

4

86-2

86-19

86-20

86-23

86-22

83-14

83-18

83-17

86-9

83-10 83-11

83-7

83-6

83-2

83-1

86-3

92-6

92-5

92-4

86-11

83-12

83-15

86-29

00-3

86-25

00-2

00-4

C'

92-11 92-12

6

83-5

C83-4

8

83-3

86-4

86-26

86-32

92-7 92-8

92-9

92-10

86-12

83-13

92-2

92-3

86-13

83-16

86-28

86-30

86-31

86-24

00-5

83-19

00-1

10

12 A'

14

16

18

86-5

86-6

B' 86-21

86-17

86-16

1983 vibracores

1986 vibracores

20 0 20 Miles

20 0 20 40 Kilometers

86-15

1992 vibracores

2000 vibracores

Figure 15. Location of cross sections discussed in the text.

A

SS-86-18

4

6 1 Bay

2

A'

sea level sea level

SS-86-1

1

8 2

3

SS-86-2

SS-86-4

SS-86-32

10 3

4

12 5 4

5

1

1

2

2 SS-86-3

3

Shoal 1

2

SS-86-5

1

14 6

7

16

8

18

9

20 10

22 11

12

24

0 50 100

% sand

26

28

ve = 1087X

6

7

8

9

0 50 100

% sand

0

3

4

5

6

7

8

9

10

5 10 km

0 50 100

% sand

1 4

2 5

3 6

4 7

5 8

6 9

7 10

8 11

9 12

10

0 50 100

% sand

0 50 100

% sand

3

4

5

6

7

8

9

0 50 100

% sand

2

3

4

5

6

7

8

9

10

0 50 100

% sand

Figure 16. Cross section A-A'.

B B'

sea level sea level

SS-86-19

4

1

6 2

SS-86-11

3

8

SS-86-20

5

1

10

6

2

7

1

SS-86-10 2

3

1

4

Shoal

SS-86-12

1

12

8

9

14

10

16 11

18

20

22

0 50 100

% sand

3

4

5

0 50 100

% sand

2

3

4

5

6

7

8

0 50 100

% sand

2

5

3

6

4

7

5

8

6

9

10 7

8

11

12 9

0 50 100

% sand

10

SS-86-21

1

2

3

4

24 0

ve = 960X

2.5 5 km

11

12

0 50 100

% sand

5

0 50 100

% sand

Figure 17. Cross section B-B'.

C sea level

sea level C'

5

6

SS-83-5

7 1

2

8

3

9 4

5

10

6

11

7

12 8

9

13

10

14 11

12

15 0 50 100

% sand

ve = 2747X

16

seafloor

Shoal

SS-83-2

1

2

3

4

5

6

7

8

9

10

11

12

0 50 100

% sand

SS-86-26

1

2

3

4

5

6

7

8

9

10

11

0 50 100

% sand

SS-92-7SS-92-8

1 1

2 2

3 3

4 4

0 50 100

% sand

0 50 100

% sand

SS-86-11

1

2

3

4

5

6

7

8

9

10

11

12

0 50 100

% sand

Shoal

SS-92-3

1

2

3

0 50 100

% sand

SS-86-30

1

2

3

4

5

6

7

8

0 50 100

% sand

Shoal

0

SS-00-2

1

2

0 50 100

% sand

2.5 km

SS-00-4

1

0 50 100

% sand

5

Figure 18. Cross section C-C'.
body is suggested to be present along much of the cross section, extending from vibracore 86-26 to 86-11, to the east this sedimentary body appears to pinch out into the overlying lagoonal and underlying delta-front deposits. Although typically separated from the overlying shoal sediments by clay-rich lagoonal sediments, distributary sediments as much as 2-m thick are present below portions of the western shoal. These distributary networks potentially hold a considerable quantity of sand-rich sediment but further study is required to isolate their distribution and thickness. Penland et al (1991) suggested that the volumetric measure of Ship Shoal sand
contained within shoal front, shoal base, and shoal crest facies is approximately 1.2 billion m3.

Isopachous Map of Ship Shoal

Figure 19 is an isopachous map of the Ship Shoal area, constructed from the available vibracore data and high-resolution seismic profiles. Maximum thickness of the shoal, including the shoal crest, shoal front, and shoal base is on the western and eastern ends along the shoal axis, locally the thickness exceeds 4 meters. Figure 19 also identifies the U.S. Minerals
Management Service (MMS) lease blocks, Ship Shoal 88 (SS 88), Pelto 12 (PL 12), and Pelto 13 (PL 13), that are being considered as areas from where sediment can be dredged and used as borrow material. Estimated borrow quantities for these lease blocks, also shown on figure 19, range between 34,000,000 m3 (PL 12) and 57,000,000 m3 (SS 88). Grain-size statistics indicate that the upper 4 meters of sediment within these lease blocks consists of predominantly well- sorted, fine-grained sand (Figs. 20 and 21).

RISKS AND FACTORS TO CONSIDER

Overfill Calculations

The textural character of stable shorelines is a reflection of the hydrodynamic conditions along the shoreline. Ideally, borrow material used for a beach/shoreline restoration and re- nourishment project is texturally equivalent to the native shoreline sediment it is replacing.
30

N

Lease block estimated volume

45,000,000 m3 W E

Pelto 12

Pelto 13

Ship Shoal 88

4

(58,000,000 yd3)

34,000,000 m3

(44,000,000 yd3)

57,000,000 m3

(74,000,000 yd3)

Ship Shoal 88

S

6 4

8

10

Pelto 12 and 13

12

1

14

4 4

6 1 4 16

2 1 1

8 18

10

12

14

16 20

18

20 0 20 Miles

20 0 20 40 Kilometers

c.i. = m

Figure 19. Isopachous map of the Ship Shoal sand body. Proposed areas of sediment removal lease blocks Ship Shoal 88, Pelto 12, and Pelto 13 -- are indicated. Volumetric measures of available sediment within the proposed areas are estimated using the currently available stratigraphic data and rounded down to the nearest millionth.

N

92-6

0

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

fine sand

92-5

v. fine sand

0

1

2

3

4 fine

92-8

W E S

v. fine

2.0 2.5 3.0 3.5

1 mean size (phi)

sand

5

sand

2.0 2.5 3.0 3.5

2 mean size (phi)

3

4 fine sand

5

v. fine sand

2.0 2.5 3.0 3.5 1

mean size (phi)

4 4

1 4

2 1 1

0

1

2

3

4 fine sand

5

92-7

v. fine sand

0

1

2

3

4 fine sand

86-25

v. fine sand

2.0 2.5 3.0 3.5

mean size (phi)

5

2.0 2.5 3.0 3.5

mean size (phi)

20 0 20 Miles

20 0 20 40 Kilometers

c.i. = m

Figure 20. Map showing mean grain size versus depth charts for cores within the proposed areas of sediment removal; Ship Shoal 88, Pelto 12, and Pelto 13. Data suggests that sediments of the upper approximately four meters within the targeted areas consist predominantly of fine sand.

0

1

2

3

4

0

vws ws

5

1

N

0 W E

1

S

2

3

mws ms 4

0.0 0.5 1.0

vws ws

5

mws ms

2 sorting (phi units)

3

0.0 0.5 1.0

sorting (phi units)

4

vws ws

5

mws ms

1

0.0 0.5 1.0

sorting (phi units) 4 4

4

2 1 1

0

1

2

3

4

vws ws

5

0

1

2

3

mws ms

0.0 0.5 1.0

sorting (phi units)

4

5 vws ws

mws ms

20 0 20 Miles

0.0 0.5 1.0

sorting (phi units)

20 0 20 40 Kilometers

c.i. = m

Figure 21. Map showing sorting verses depth charts for cores within the proposed areas of sediment removal; Ship Shoal 88, Pelto 12, and Pelto 13. Vws = very well sorted, ws = well sorted, mws = moderately well sorted, ms = moderately sorted. Sand resources of the upper approximately four meters within the targeted areas are primarily well sorted.
Otherwise, fine-grained borrow material added to a relatively coarser-grained deposit will tend to be winnowed from the shoreline by marine processes; and volumes of sediment fill added to a shoreline will eventually be reduced if the fill material does not closely match the native beach sediment. Overfill factors provide an estimate of the cubic meters of borrow material required to produce one cubic meter of sediment with the specific native grain-size characteristics, assuming that the comparatively fine-grained component of the fill will be lost. James (1975) demonstrated a methodology for calculating overfill ratios using mean grain size
and sorting values of proposed borrow material in comparison to the same grain-size statistics for the native material it is replacing.
Grain-size samples from the Isle Dernieres barrier islands indicate that the sediment along this section of the Louisiana coastline consists of 99%, moderately to very well-sorted, fine-grained, quartzose sand with an average grain size of 2.7 ?and sorting value of 0.49 ?units
(Fig. 22). Overfill values were calculated for the Isle Dernieres assuming borrow material would be taken from the previously mentioned MMS lease blocks. A mean grain size of 2.5 and sorting value of 0.47 for PL 13 and a mean grain size of 2.7 and a sorting value of 0.34 for SS 88 were used in the methodology presented by James (1975). These preliminary calculations indicate an overfill ratio of 2.0 for the upper 4 m of sediment in SS 88 and that sediment from PL 13 would be stable along the Isle Dernieres, approximating an overfill value of 1.0 (Fig. 23).

Infrastructure of Proposed Dredge Areas

Dredging in the shallow Gulf waters of coastal Louisiana presents a unique challenge because of the preponderance of offshore hydrocarbon infrastructure. The presence of offshore platforms and pipelines could inhibit the ability to efficiently dredge potentially favorable sections of Ship Shoal. Figure 24 shows the known hydrocarbon infrastructure of lease blocks PL 12 and PL 13. Large sections of these lease blocks are relatively free of hydrocarbon with
34

N

W E

S

Calliou Bay

Raccoon

Lake Pelto

16 17 19

Wine Island

Pass

3.00

sample location

0 5 10 15 20

vfs

2 5

4 6 7

8 9 10

2.50

2.00

1.50

0.50

0.00

2.6 2.6 2.7

2.8

2.5

3.1 3.0

2.4

2.9

2.7 2.5 2.7 2.6

2.8

2.4

2.9 2.8

2.7 2.6

2.8 fs ms

cs

1.00

0.75

0.50

sample location

0 5 10 15 20

.95

ms mws

10 0 10 Miles

0.25

0.00

.28

.45 .46

.51

.44

.58 .54

.42

.52

.34 .38

.51 .51 .49

.59

.52

.44

.37

.54 ws

vws

10 0 10 Kilometers

Figure 22. Grain-size data for beach samples from the Isles Dernieres barrier islands. From Williams et al. (1989).

Ship Shoal 88

Pelto 13

mean b - mean n

n

Figure 23. Plot of fill ratios for Isles Dernieres beach samples using sediment from Ship Shoal
88 and Pelto 13. Cut to fill ratio for Isles Dernieres beaches using Ship Shoal 88 sediment is
approximately 1.75, whereas Pelto 13 sediment is approximately 1.0. Method and graph from
(USACE, 1977).

N

W E

S

Pelto 12 Pelto 13

platforms pipelines

lease-block

boundaries

2 0 2 4 Miles

2 0 2 4 Kilometers

Figure 24. Hydrocarbon infrastructure of the Pelto 12 and Pelto 13 lease blocks on the eastern end of Ship Shoal (Fig. 20). Infrastructure data taken from the U.S. Department of the Interior Mineral Management Service (2001).
most of the current platforms located on the periphery of the lease blocks. However, multiple pipelines do cross the lease blocks. Figure 25 shows the known infrastructure for SS 88, which according to currently available data consists of one pipeline in the extreme southwest corner of the block. Although data used to map the location of infrastructure within the lease blocks was the most current available from the MMS more detailed mapping and magnetometer surveying of the lease blocks will be necessary prior to dredging.

Archeological Resource Considerations

The federally mandated National Historic Preservation Act of 1966 (NHPA) ensures the recognition and preservation of historical and archeological properties of the United States. The MMS is therefore responsible for ensuring that significant archeological sites are not damaged or altered in areas of the outer continental shelf where it has permitted activity. The following section provides an overview of the requirements established by the MMS for archeological surveys of outer-continental shelf lease blocks. Information presented below was taken from the MMS website for archeological studies (Gulf of Mexico Archeological Information, 2001).
An archeological resource refers to material remnants of human life and activities, which are at least 50 years old and possess archeological interest. Scientific and scholarly investigations of archeological resources provide a scientific and/or humanistic understanding of past human behavior, cultural adaption, and similar topics. Probable archeological resources of
the Louisiana continental shelf include: 1) prehistoric Native American cultural sites dating from the time when sea level was lower than modern sea level and thus the continental shelf was subaerially exposed and 2) historic shipwrecks. Guidelines for conducting archeological
surveys and generating resultant reports are implemented by the MMS and available in
publication “Notice to Lessees 98-06.” Specific archeological-survey requirements vary
38

N

W E

S

SS 88

platforms

pipelines

2 0 2 4 Miles

2 0 2 4 Kilometers

Figure 25. Map showing the hydrocarbon infrastructure of the Ship Shoal 88 lease block on the central part of Ship Shoal (Fig. 19). Infrastructure data taken from the U.S. Department of the Interior Mineral Management Service (2001).
depending upon whether the block has been determined to have a probability for historic shipwrecks or for submerged prehistoric cultural sites.
Archeological investigations of the continental shelf are conducted utilizing an array of remote sensing instruments such as a magnetometer, dual-channel side-scan sonar, sub-bottom profiler, and depth sounder. Additional investigative techniques that may be required include the use of underwater television, still and video cameras, archeological divers, and remote or
manned submersibles. Geophysical instrumentation utilized in these investigations is required to be state-of-the-art technology and used in a fashion as to minimize intra-system interference. Moreover, data recorders must be interfaced with a continuous positioning navigation system capable of a 5 m or less accuracy. Final reports, providing details of the collected data and resulting interpretations, must be presented and signed by an archeologist and geophysicist with appropriate credentials and experience.
Survey-line spacing depends upon the suspected type of archeological resource; lease blocks with a high probability for historic shipwrecks are surveyed with a line spacing of 50 m, whereas lease blocks with a high probability for containing prehistoric sites must be surveyed at a line spacing of 300 m. Information currently provided by MMS indicates that lease block Ship Shoal 88 would have to be surveyed with 50-m line spacing and lease blocks Pelto 12 and 13 with a survey spacing of 300 meters.

Environmental Impacts

Dredging redistributes sediments, modifies bottom topography, disrupts habitats, and potentially alters water-circulation patterns. Although the environmental effects of estuarine dredging elsewhere have been studied (e.g., Jeane et al., 1975; Kenkel et al., 1976; Johnston,
1981) large-scale dredging of the Louisiana inner-continental shelf is a new endeavor and the
40
possible environmental side affects of open-water dredging have not been well documented. Deleterious effects are possible both in the area being dredged as well as the area of sediment placement.
In estuarine environments, circulation changes resulting from dredging have been shown to affect natural chemical regimes and thus the availability of nutrients and dissolved gases to aquatic fauna (Johnston, 1981). Moreover, increased turbidity in marine waters at both the removal and dispersal sites may affect aquatic biota by disrupting normal photosynthetic processes, smothering benthic fauna, or inhibiting substrate re-colonization upon completion of dredge operations (Johnston, 1981). The result, either immediately or over a longer period of time, is a change in species composition, a loss of biodiversity, and potentially a reduction in commercial and recreational fisheries. Although primarily lacking in the Ship Shoal area, cohesive clays may be nuclei for adsorption of many pollutants, radioisotopes, petroleum products, pesticides, and metals (Wells, et al., 1981). As such, disposal of dredged material constitutes an environmental perturbation and depending upon the environmental quality of the material may result in ecosystem-level damage.
The uncertain environmental impacts of removing large volumes of Ship Shoal sediment and disposing it onto shoreline environments will likely necessitate a thorough and detailed environmental management plan. Additional permitting in accordance with state and federal
laws may be required with the extent of documentation determined by the quantity and biological and chemical quality of sediment proposed for dredging. Probable methods of analysis include subsurface investigations, surface grab samples, sediment testing, probing, and additional
methods of habitat analysis.
41

Hydrodynamic Impacts

In a numerical modeling effort, removal of the entire shoal was simulated and the impact on wave propagation and energy levels discussed (Stone et al., 2001; Appendix A). It is important to note that an additional numerical modeling effort will be required, using state-of-the-art models (e.g., SWAN) when the volume and dimensions of the borrow site are designed.
Removal of Ship Shoal will alter the wave propagation, dissipation and the wave energy distribution. The magnitude and spatial distribution of the alteration depend on the initial wave conditions. During severe storms (Case 1) and strong storms (Case 2), propagating waves reach breaking conditions seaward of the western flank of Ship Shoal. Therefore, removal of Ship Shoal causes a maximum increase of the significant wave height by 90% - 100% (i.e., almost double the present value) in Case 1, and 40% - 50% in Case 2, over the shoal and immediately adjacent to the lee of the complex. Wave breaking does not occur on the east flank of the shoal because of much deep water, and the magnitude of the wave height increase due to shoal removal is significantly less on comparison with that on the west flank.
During weak storms (Case 3) and fair weather conditions (Case 4), waves do not reach breaking conditions over any part of Ship Shoal. The magnitudes of the significant wave height increase due to the removal of the shoal is considerably smaller, only 10% - 20% on the west part of the shoal. The values of wave height change on the east part of the shoal are minimal.
The nearshore wave fields are largely dependent on the offshore wave conditions. Under high energy conditions in Case 1 and Case 2, removal of Ship Shoal results in higher nearshore breaking wave heights, however, the breaker zone is displaced between 0.5 – 1.0 Km offshore. Ultimately, wave in the surfzone eventually collapse to the same energy level on comparing with and without shoal scenarios, suggesting that shoal removal will not have a significant impact on
wave energy conditions along the Isles Dernieres. The nearshore impact is even less noticeable
42
under the weaker energy conditions in Case 3 and Case 4, particularly along the east of the study area.
Wave approach direction exerts significant control on the wave climate leeward of Ship Shoal for stronger storm conditions (Case 1 and 2) but not weak storms or fairweather waves. Inclusion of the wind function increases wave height in all simulations. The magnitude of the increase is dependant on the deep water wave height and the slope of the shoreface profile. In Case 1, the surfzone is widened by almost 1.0 Km whereas in Case 4, the change is minimal. Removal of Ship Shoal results in a 50% increase of the significant wave height. This is much larger than the magnitude (between 25% to 30%) when wind forcing is neglected. The magnitude of wave height increase due to the wind forcing over the east part of the shoal is as much as 0.8m. While inclusion of the wind forcing function allows for an increase in the wave height, the effects attributable to the removal of Ship Shoal are limited to the periphery of the leeward flank of the system, particularly along its western boundary.
Changes in wave approach direction redistributes the increase in wave height in the lee of the shoal complex. This does not, however, impact breaker wave heights in the nearshore along the Isles Dernieres. Simulation of long wave propagation landward during Hurricane Andrew indicates near total wave energy dissipation, as opposed to breaking, over Ship Shoal. A much smaller percentage of low amplitude waves crossed the shoal complex. Peak wave energy dissipation rates occurred, however, seaward of Ship Shoal in approximately 25 – 30 m water depths.
The data presented suggest that the entire removal of Ship Shoal will not significantly influence the wave climate beyond the leeward periphery of the complex, such as the nearshore zone along the Isles Dernieres. The data suggest that this conclusion is valid for winter storm
conditions and hurricanes similar to that of Hurricane Andrew. This conclusion implies that
43
given the unlikely situation that the entire volume mass of sediment be removed from Ship Shoal during a single dredging event, wave climate changes peripheral to the shoal will be substantially reduced given the removal of significantly lower volumes of sediment than that simulated here.
Field research on hydrodynamics and sediment transport in the vicinity of Ship Shoal, has for the most part been conducted exclusively by researchers from the Coastal Studies Institute at Louisiana State University, and is discussed in Pepper et al. (1998), Pepper et. al. (1999), Pepper (2000), and Pepper and Stone (submitted, 2001). The region is generally characterized by low- energy processes, including low waves (mean significant wave height less than 0.7 m), weak
near-bottom currents (generally less than 10 cm s-1) and fairly low rates of sand transport (on the
order of 0.1 g cm-1 s-1). However, winter cold front passages, and presumably, tropical storms and hurricanes, are forcing mechanisms which provide an input of energy to the inner-shelf system which may cause increases of more than an order of magnitude in hydrodynamic parameters and sediment transport rate. Winter storm (cold front) passages were found to consist of two distinctive end-member types in terms of their associated inner-shelf response, although other types of frontal passages may undoubtedly occur. Type 1 storms were characterized by weak southerly pre-frontal and strong northeasterly post-frontal winds. They generally resulted
in strong post-frontal responses that included high, short-period, southerly waves, strong, southwesterly currents, and moderately high sediment transport that was southwesterly overall. Type 2 storms included periods of both strong southerly pre-frontal winds and strong northerly post-frontal winds. They generated high, long-period northerly swell waves prior to the frontal passage that persisted throughout most of the post-frontal phase, during which time energetic southerly storm waves developed, creating a complex, bimodal wave spectrum. Currents prior to the frontal passage were fairly strong and northerly, while subsequent to the frontal passage, they
became rotational, likely as a result of inertial effects, but were southeasterly in direction overall.
44
Shear velocity was elevated during both the pre- and post-frontal phases, while sediment transport occurred predominantly during the post-frontal phase, when mean sediment transport was directed southeasterly, and low-frequency and wind-wave flows produced northerly transport.
It is apparent that Ship Shoal influences these processes measurably. During a two-month winter period, mean wave height and period on the landward side were 36% and 9% lower, respectively, than on the seaward side, due to attenuation, while across-shelf currents were offshore on the seaward side and onshore on the landward side, where flow speed was10% higher. During a subsequent one-month period, mean significant wave height decreased from its seaward value by 15% and 25% as measured on the middle and the landward portions of the shoal, respectively. Sediment transport direction was also predicted to differ considerably between the seaward and landward sides of the shoal, with fair-weather transport directed towards the west on the seaward side and towards the northeast on the landward side, while during cold front passages, transport was toward the southeast on the seaward side, and variable, but generally southward on the landward side. Sediment flux across Ship Shoal appears to have been divergent during fair weather conditions, potentially causing shoal erosion, and convergent during cold front passages, potentially causing accretion. It appears, therefore, that removal of sand from Ship Shoal would likely result in a modification of hydrodynamic and sediment transport processes on what is currently the landward side of the shoal, including an increase in wave height and wave period, an increase in offshore current flow, and potentially, a decrease in landward transport of sediment during fair weather. The magnitude of these effects is difficult to predict however, since the bathymetry of the shallow inner shelf would undoubtedly influence these processes, even discounting the influence of Ship Shoal itself, and the possible change in
bottom substrate (from fine sand to other materials) would change bottom boundary layer
45
characteristics and resuspension processes.

DREDGING

There have been many dredging and beach fill projects in the United States. However, very few of these have utilized borrow sites with distances of more than a few miles from the restoration location. In Louisiana, the U.S. Army Corps of Engineers routinely dredges navigation channels using the dredge spoil to crate new habitats. Barrier island restoration has historically occurred using sands from nearshore borrow areas and channels or inland ridges. Most of the offshore aggregate mining occurs in Europe due to the advance dredging technology and equipment. In the United States, the two largest offshore aggregate mining operations are in New Jersey and California. McCormack Aggregates in Amboy, New Jersey and Tidewater Sand and Gravel in Oakland, California produce concrete sand, a medium grain-sand that is mined by hopper barges propelled by integrated tugs. Tidewater mines approximately 400,000 yd3 per year, while McCormick mines approximately 800,000 yd3 per year (Kraut, 1986).
The availability of detailed information regarding dredge operations and costs in the United States has been limited due to industry competition. However, research indicates that pipelines are most appropriate for short distances (less than 3 mi) between borrow sites and fill locations. Hopper dredges are better suited for borrow areas 3 to 5 miles away and tugs and scows are the best alternative for longer distances (Chisholm, 1989).
There are three basic types of dredging operations: 1) hydraulic, 2) mechanical, and 3) a combination of hydraulic and mechanical (Table 2).
Hydraulic dredging techniques include the hopper, sidecaster, and dustpan dredges along with hydraulic-pipeline and plain-suction dredges. This method is favored by the U.S. Corps of Engineers (USACE) for channel dredging in navigation channels and restoration through dredge
spoil. Mechanical dredging moves material by removal and relocation. Clamshell, dipper, and
46
Table 2. Characteristics of Dredge Types

Table 2. Characteristics and features of dredges discussed in the text.
ladder dredges are examples of mechanical dredging. Combination dredges loosen material mechanically and then transport it hydraulically. Cutterhead dredges are an example of a combination dredge. This type of technique limits dredging to the capacity of the barge and is efficient on upland disposal sites. However, cutter dredges are designed to operate in calm water and not offshore.
The selection of which dredging equipment is best suited for restoration depends on the physical characteristics, quantity, and dredging depth of the material, as well as the distance to disposal area. More detailed information on the different types of dredging equipment is listed below.

Hydraulic Dredges

Hopper Dredges

Hopper dredges are probably the most effective dredges in rough open water. They can operate in water depths of 3 to 30 m and have a carrying capacity of approximately 300 to
16,000 yd3. Production rates range from 500 - 22,000 cubic yards per hour. Hopper dredges are
self-propelled, with molded hulls. They are equipped with propulsion machinery, dredging equipment, and sediment containers called hoppers that are required to remove and transport material from a channel bottom or sea floor. Hydraulic dredges draw the borrow material and water slurry through drag arms into the hoppers. The hoppers are then transported to the restoration site where the dredge material is unloaded. However, the vessel draft ranges from 12 to 31 ft depending on sediment load. Many newer hopper dredges have split hulls instead of doors allowing the vessel to open along a center line with faster unloading rates in shallow water. Many hoppers pump out their loads through a discharge pipe to allow disposal to upland restoration sites. The hopper is unloaded and then returns the borrow site to resume dredging. A major advantage of using this type of dredge is that is can move quickly and economically to the
48
dredging project under its own power. They travel at approximately 9 to 16 knots and do not generally interfere with other channel traffic. However, the disadvantage of this dredging method is a deep draft that inhibits shallow water operations. Moreover, this type of dredge excavates with less precision than other dredges and is inefficient in hard-packed sands and side banks.
The Hopper dredge appears to be the most suitable equipment for dredging Ship Shoal. Cost estimates to move sand from Ship Shoal onto Isles Deniers ranges between $5.00 and
$12.00 per yd3. As a result of draft restrictions, the hopper dredge would require moving lighter
loads and thus more frequent trips between the borrow site and the placement location.

Sidecasting Dredge

The sidecasting dredge is another variation of hydraulic dredging. It differs from the hopper dredge in that it operates continuously and has a shallow draft. In this dredging technique, the sediment is picked up from the bottom through two drag arms and pumped through a boom-supported discharge pipe. The vessel can independently travel the entire length of a shoaled area, excavating between 6 and 25 ft below the seafloor. Sidecasting dredges have been used to deposit material into hopper barges traveling parallel to the dredge. The advantage
of using a sidecasting dredge is that it can work in relatively exposed water and is self sustaining, so it can perform work in remote locations. It can also be rapidly mobilized between projects. However, most sidecasting dredges in the United States are small with relatively low-production rates of approximately 325 to 650 yd3. The only sidecast dredges in the United States are owned and operated by the USACE. Due to its low production rates, it would be costly to operate this
type of dredging system on Ship Shoal.
49

Plain Suction and Dustpan Dredges

The plain suction dredge is the same as the cutterhead described later in the combination section only the cutter is removed. It transports through a pipe line so it operates continuously and is not easily damaged by wave action. However, the plain suction dredge is uncommon in the United States. The dustpan dredge is similar to the suction dredge but is mainly designed for dredging shoals on the Mississippi River. It is not commonly used in exposed waters.

Mechanical Dredges

Clamshell Dredge

A clamshell dredge is a mechanical cable excavator dredge that uses a single bucket. The bucket is attached to the dredge crane with cables. This type dredge operates by lifting the
bucket, or the clamshell, dropping it into the bottom sediments, lifting the bucket and dredged material to the surface, and emptying the dredged material into a nearby disposal facility, scows, or barges for transportation to a disposal facility. The use of clamshell bucket dredging and transfer by bottom-release scow maintains much of the integrity of the sediments. This method usually produces positive relief features in the placement area. The deposited sediment occupies a volume only about 1.1 times greater than it did in the channel, and the slope of the deposit is considerably greater than for hydraulically dredged and deposited sediments. Clamshell dredges are suited more for channel dredging and not for offshore mining.

Combination Dredges

Cutterhead Dredge

The most efficient and versatile dredge type is the hydraulic-pipeline with a motorized cutter known as a cutterhead-suction dredge. This type of dredge has a centrifugal pump mounted on a barge. A pipe supported by a framework, called the ladder, is mounted on
the front of the barge and extends down to the bottom. Cables lift the ladder to control the depth
50

cutter at the end of the ladder and hence the depth of cut. Dredging depths of the cutterhead dredge range between 3 and 65 ft. Production rates range from 25 to 10,000 cubic yd3. The cutterhead has a limited open-area carrying capacity and is designed to operate in calm water rather than offshore. A cutter section dredge was successfully used in 1984 for placing renourishment material from Cat Island Pass onto Isles Dernieres (Jones and Edmonson, 1987). SHIP SHOAL COST ANALYSIS

The following cost-analysis sections are excerpted from a report completed by Picciola and Associates, Inc. (1996). This report was originally constructed as a cost analysis for utilizing Ship Shoal borrow material along the Fourchon headland adjacent to and east of Belle Pass.
There are many ways to obtain sand from offshore. However, the extreme distance, between the borrow and deposit sites, pose many logistical problems and represented the challenge in making this project feasible (Fig. 26). Additionally, the fact that Ship Shoal is located in exposed waters represents a serous factor in determining acceptability of equipment to be considered for this project.
Another difficulty for dredging at Ship Shoal is draft restrictions imposed on dredges by the shoal waters of south Louisiana. Deeper draft dredges will not be able to dredge on top of Ship Shoal or get very close to shore. They would likely dredge on the landward side of Ship Shoal and to take advantage of calmer water conditions.
The estimate developed herein provides the cost per yd3 of sand on the beach, ranging
between $8.70 per yd3 and $10.00 per yd3. It is recommended that the higher end of the range be used for estimated purposes. Initial project costs will likely tend to be higher than estimated, but will probably decrease as contractors become familiar with the area.
Maintaining a hopper at Port Fourchon may be a feasible solution to providing borrow
material to the beach. This would certainly be an economic advantage, provided that the initial
51

N Approximate transport distances

W E S

Marsh

Island

1 Pelto 12 to Cheniere

Ronquille

2 Pelto 12 to Belle Pass

3 Pelto 12 to Timbalier

Island

4 Pelto 12 to Whiskey

Pass

5 Ship Shoal 88 to

Whiskey Pass

~95 km

(~60 mi)

~64 km

(~40 mi)

~25 km

(~15 mi)

~20 km

(~ 12 mi)

~20 km

(~12 mi)

Atchafalaya

Bay

Barataria

Bay

Terrebonne

Bay

1

5 4 3

Ship Shoal 88 Pelto 12

Figure 26. Map showing approximate transport distances from areas of suggested borrow removal to restoration project areas.
costs and annual operational/maintenance costs can be overcome. Most significant is the cost estimate for purchasing and maintaining a permanent first year dredging operation at the Port. The initial cost (first year) are projected to be approximately $17.38 /yd3 of material on the
beach. However, yearly costs thereafter reduce to $4.27 /yd3. If mining of Ship Shoal for
Fourchon Beach or any of the other barrier islands in the area (i.e. Isle Dernieres or Timbalier Islands) prove feasible, specific dredging equipment can be developed which would be better suited to operating efficiently for this particular project. Tailoring equipment to the specific site would certainly decrease the cost per unit of material moved over that estimated herein. A way to make this project more credible would be to pair multiple restorations with that project. If a dredge or dredges were to be permanently maintained at Port Fourchon or another nearby port, it could be utilized to supply material from Ship Shoal to Isle Dernieres, Timbalier Islands, Wine Islands, or any other nearby barrier islands.

Dredging Configuration

The proposed configuration of dredging operations for the project is to dredge on Ship Shoal with hopper dredges, either tug/barge combination or self propelled vessels. The dredging vessel will then travel to Port Fourchon, up Belle Pass to a rehandling facility just offshore of the beach at Fourchon.
The first scenario will have a rehandling facility where the material in the hopper will be pumped out via pipeline onto the beach (Fig. 27). If the vessel does not have self pumped-up capability, a barge unloader will be used to pump the material to the replenishment area by pipeline where it will be shaped into the final profile.
Part of the mobilization will be the installation of a rehandling station in Belle Pass. This
could consist of a barge moored along the shores of Bayou Lafourche against pilings. The barge
53

Rehand ling Fac ility

0

Port Fourchon Beach

Gulf Of Mexico

Belle Pass

Figure 27. Dlustration of onshore handling facility

will house rehandling pumps and generators for power to run the pumps. The discharge pipe will depart from this location and run onto the beach.
The advantages of this proposed method, are that the rehandling facility is within protected waters, moored onshore, and can be reached by vehicles. However, one disadvantage is that the hopper dredge will be limited in draft by the depth of the navigation channel at Fourchon.
To alleviate this problem, permits can be obtained to dredge Belle Pass to a depth suitable to the loaded draft of the hopper dredge. This can be completed first and material dredged from the channel dumped onto the beach or offshore.
The second scenario involves mooring a work barge just offshore of the beach replenishment area (Fig. 28). The work barge would hold the seaward end of the discharge pipeline. The discharge pipeline would come off the barge and run shoreward along the bottom up to the beach.
The advantage of this method is that the work barge could be moored far enough offshore such that the hopper dredge could operate at maximum draft when full. Disadvantages are that the rehandling facility would be isolated from shore and only accessible by boat. Additionally,
the station would be exposed in adverse weather and possibly have to be demobilized during extreme weather conditions. It is not recommended to pursue this option unless permits cannot be obtained to dredge Belle Pass.
On the beach where the dredged material is being placed the pipeline will be identical for both rehandling facility configurations. The pipeline will have Y-branch discharge lines, controlled by gate valves, to the main pipeline in order to stage the placement of each fill. The
importance of this procedure can be appreciated when one understands that along the
55

Belle Pass

Port Fourci'\On Beach

Gulf Of Mexico

Rehandling Fac Ill ty

Hopper Dredge _..J-r-r-r-r-.-- .......J-,

D

Figure 28. illustration of offshore handling facility

approximate seven miles of the replenishment area the contractor can direct material onto the beach for distribution by dozers. Along the beach the pipeline will be run above ground to each of the distribution points.

Projected Cost Estimate

The cost estimate for this study is based on actual information provided by the U.S. Corp of Engineers from previous projects in which hopper dredges were used to dredge navigational channels (mostly the Mississippi River) and deposit the sediment offshore. For these projects, the deposit material was dumped offshore using split hull hopper dredges or from doors beneath the hopper bins. Therefore, an estimate was made for the approximate time required to offload the dredge using a pumping system.
Project Costs are split into several items including Mobilization and Demobilization, Pipeline Construction, Sand Fill, and Engineering (Table 3). Mobilization and Demobilization was based on examining the average cost from contractor’s bids for five projects consisting of dredging the Mississippi and Calcasieu rivers. These bids averaged approximately $230,000 and included moving the dredge and equipment to and from the site. In addition to this, the Ship Shoal/Fourchon Project would require the construction of a rehandiling facility on or near shore. It is assumed that the assembly of the Rehandling Facility, including all associated equipment, would cost approximately $320,000.
Pipeline construction was estimated by reviewing bid abstracts from the USCAE for previous jobs where a pipeline was constructed on the beach for restoration projects. Estimates are based on $30 per foot and a project length of seven miles (36,960 ft). Bid abstracts from the
Grand Isle Beach Restoration Project were used in deriving this estimate.
57

Table 3. Cost estimates for task 1.

Sand fill for this project was computed using results of previous projects administrated by US Army Corps of Engineers. Production rates were tabulated and averages calculated for percentage of hopper capacity (Table 4). Additionally, the parameters such as excavation time, down time, and travel time were examined to reasonably estimate project time based on the capacity of each dredge.
Hourly rates for different hopper dredge sizes were estimated from bid abstracts on several projects administrated by the USACE. Three different sizes of hopper dredges were considered for determining costs for this project. Sizes of 27" diameter pipe and 3600 yd3
hopper capacit y, 28"diameter pipe and 4000 yd3 hopper capacity, and a 33.5" diameter pipe 6300
yd3 hopper capacity were estimated form information provided by the USACE. Total cost varies depending upon the size of the dredge used, but in general the results from the three estimates ranged less then $1 per yd3 of material on the beach. It would make sense that the larger dredges
58
should be more cost effective because of they require fewer trips to deliver similar quantities of material. Details of the cost analysis are presented in Appendix B.

Table 4. Cost Estimates for Task 2.

TASK 2 COST ESTIMATE

The engineering estimate is listed as a lump-sum effort which includes developing beach profiles, surveying, rehandling facility design, obtaining permits, soil borings, and construction supervision. The cost estimate for maintaining a full-time dredge at Port Fourchon to continually move sand from Ship Shoal to Fourchon was developed utilizing the same information established in Task 1. It was assumed that pipeline construction would be deferred as a yearly
cost based on the movement of the work along the beach. Also, construction or purchase of a
59
dredge would be absorbed in the initial year cost of equipment in the size range required for the project. Yearly operation and maintenance considers the cost of fuel, crew salaries, groceries and supplies, as well as equipment maintenance.

CONCLUSIONS

Ship Shoal is a shore-parallel sand body located approximately 15-km offshore of the Isle Dernieres Islands of south-central Louisiana. Ship Shoal is the remnant of a former deltaic headland and barrier shoreline that has been progressively inundated by marine waters due to relative sea-level rise and transgressive submergence (Penland et al., 1988). Previously, the recoverable sand of Ship Shoal has been estimated to be 1,200,000 billion m3. However, large areas of Ship Shoal are also the sites of extensive hydrocarbon infrastructure, presenting a technical difficulty for the efficient removal of sediment. Currently suggested areas of sediment removal are offshore lease blocks SS 88, PL 12, and PL 13. Volumes, not considering the presences of infrastructure within these blocks, are estimated at 57,000,000 m3, 45,000,000 m3, and 34,000,000 m3 respectively. Factors that need to be considered prior to dredging include the:
1) environmental and hydrodynamic impacts of dredging Ship Shoal, 2) possibility of archeological sites within proposed dredge areas, 3) most suitable dredging method, 4) the associated economics of dredging, and 5) the performance of Ship Shoal sediments in contract to poorer quality nearshore sediment as it relates to project construction and maintenance costs.
The development of new innovative dredging technologies will be required to deliver offshore
sediment resource over long distances to shallow water project construction sites.
60

REFERENCES AND BIBLIOGRAPHY

Berryhill, H.L., Moslow, T.F., Penland, S., and Suter, J.R., 1985. Shelf and Shoreline Sands, Northwest Gulf of Mexico. American Association of Petroleum Geologists Short Course Notes, Tulsa, OK.
Boyd, R. and Penland, S. 1984. Shoreface translation and the Holocene stratigraphic record in Nova Scotia, southeastern Australia, and the Mississippi River delta plain. Marine Geology, 63: 391-412.
Boyd, R. and Penland, S., 1988. A geomorphic model for Mississippi River delta evolution.
Gulf Coast Association of Geological Societies. Annual meeting. New Orleans, LA., October 19-21 (abstract).
Boyd, R., Suter, J.R., and Penland, S., 1988. Implications of modern sedimentary environments for sequence stratigraphy. In: D.P. James and D.A. Leckie (editors), Sequences, Stratigraphy, Sedimentology: Surface and Subsurface, CSPG Memoir 15, p. 33-36.
Boyd, R., Suter, J.R., and Penland, S. 1989. Sequence stratigraphy of the Mississippi delta. Gulf
Coast Associate of Geological Societies Transactions, v. 39:331-340.
Britsch, L.D., and Dunbar, J.B., 1993, Land loss rates: Louisiana coastal plain: Journal of
Coastal Research, v. 9, no. 2, p. 324-338.
Byrnes, M. R., Penland, S., Ramsey, K. E., Crawford, T.G., Kelly, R. F., and Rowland, J., 1991.
Offshore sand resources for coastal erosion in Louisiana: physical environmental considerations and economic feasibility. MTS 91, Marine Technology Society, Washington, D.C., p. 755-761.
Byrnes, M.R., Penland, S., Ramsey, K.E., Crawford, T.G., Kelly, R.F., and Chisholm, T.A.,
1991. Characterization of the Development Potential of Ship Shoal Sand for Beach
Replenishment of Isles Dernieres. Final Report to the U.S. Minerals Management
Service, Office of Marine Minerals International Affairs, Herndon, VA.
Chisholm, T.A., 1991. Dredging Aspects of Aggregate Mining from Ship Shoal, in Characterization of the Development Potential of Ship Shoal Sand for Beach Replenishment of Isles Dernieres. Report prepared by Louisiana Geological Survey for U.S. Minerals Management Service under cooperative agreement #14-12-0001-30404.
Circe’, R.C., Wertz, R.R., Harrison, D.G. and Williams, S.J., 1988. Map showing distribution of surficial sediments on the inner continental shelf off central Louisiana: U.S. Geol. Survey Open-File Report 88-411.
Circe’, R.C., Wertz, R.R., Harrison, D.G. and Williams, S.J., 1989. Surficial sediment isopleth maps of sand, silt, and clay offshore the Isles Dernieres barrier islands, Louisiana: U.S. Geol. Survey Misc. Invest. Map I-2004.
61
Coleman, J.M, and Gagliano, S.M., 1996, Cyclic sedimentation in the Mississippi River deltaic plain: Gulf Coast Association of Geological societies Transactions, v. 14, p.67-80.
Frazier, D.E., 1967, Recent deltaic depositions of the Mississippi River: their development and chronology, Gulf Coast Association of geological societies Transactions, v.27, p. 287-
315.
Gulf of Mexico Environmental information (GMEI), 2001, www.gomr.mms.gov/homepg/regulate/environ/archaeological/introduction.html
Hobson, R.D., 1979, Definition and use of the phi grade scale: U.S. Army Corp of Engineers Coastal Engineering Research Center, Fort Belvoir, Virginia, Coastal Engineering Technical Aid no. 79-7,18 p.
Inman, D.L., 1952, Measures for describing the size distribution of sediments: Journal of
Sedimentary Petrology, v. 22, no.3, p. 125-145.
Jeane, G.S., II., and Pine, R.E., 1975, Environmental effects of dredging and spoil disposal: Journal of Water Pollution Control Federation v.47, p. 553-561.
John, C. J., Penland, S., and Ramsey, K. E., 1989, Preliminary assessment of non-fuel mineral resources in the Louisiana continental shelf, in Gulf Task Force, Preliminary assessment on non-fuel mineral resources in the outer continental Shelf Exclusive Economic Zone of the Gulf of Mexico. Report prepared by the Louisiana Geological Survey for the U.S. Mineral Management Service under cooperative agreement 14-12-0001-30404.
John, C. J., Penland, S., Ramsey, K. E., and Groat, C. G., 1989. Preliminary evaluation of sand resources offshore Louisiana. IEEE Oceans ‘89, New York, NY, v. 1, p. 1-16.
Johnston, S.A., Jr., 1981, Estuarine dredge and fill activities: a review of impacts: Environmental
Management, v. 5, no. 5., p. 427-440.
Kenkel, P.A., Harrison, J., Burdick, J.C., III, 1976, Dredging and its environmental effects: Proceedings of a specialty conference, American Society of Civil Engineers, New York.
Kindinger, J.L., Penland, S. Williams, S.J., and Suter, J.R., 1989. Inner shelf deposits of the Louisiana-Mississippi-Alabama region, Gulf of Mexico. Gulf Coast Association of Geological Societies Transactions, 39: 413-420.
Kindinger, J.L., Penland, S., Williams, S.J., Suter, J.R., McBride, R.A., Brooks, G.R., and Locker S., 1991. Nearshore Holocene stratigraphy, Northern Gulf of Mexico: Integration of regional geologic studies. Modern Coastal Depositional System in the Gulf of Mexico: Quaternary Framework and Environmental Issues. 12th Annual GCSSEPM Foundation Research Conference. Houston, TX, December 8-10, (Abstract).
Kindinger, J. L., Penland, S., Williams, S.J., Brooks, G.R., Suter, J.R., and McBride, R.A., 1991.
Late Quaternary geologic framework, north-central Gulf of Mexico. Coastal Sediments
‘91, ASCE, p. 1096-1110.
62
Kindinger, J. L., Penland, S., Williams, S. J., Suter, J. R., McBride, R. A., Brooks, G. R., and Locker, S., 1991. Nearshore Holocene stratigraphy, northern Gulf of Mexico: Integration of regional geologic studies. Coastal Depositional Systems in the Gulf of Mexico: Quaternary Framework and Environmental Issues. GCSSEPM Foundation, p. 96-102.
Krumbein, W.C., 1938, Size frequency distribution of sediments and phi normal curve: Jounal of
Sedimentary Petrology, v. 18, p. 84-90.
List, J.H., Jaffe, B.E., Sallenger, Jr., A.H., Williams, S.J., McBride, R.A., and Penland, S, 1994.
Louisiana Barrier Island Erosion Study: Atlas of Sea Floor Changes from 1878 to 1989. U.S. Geological Survey, Miscellaneous Investigations Series I-2150-B, 81 p.
Louisiana Oil Spill Coordinator’s Office (LOSCO), 1999, Louisiana offshore bathymetry, geographic NAD83, [bathymetry].
Louisiana Oil Spill Coordinator’s Office (LOSCO), 2000, Land and water interface of the
Louisiana coastal region, geographic NAD83, LOSCO, [landwater].
Maciasz, E., McBride, R. A., McLaughlin, T. M., Nakashima, L. N., Penland, S., Ramsey, K. E., Scott, D. B., Suter, J.R., Taylor, B. G., and Westphal, K. A., 1988, Database Compilation for Nearshore Sand Resources: Marsh Island to Sandy Point: Technical Report to the Louisiana Department of Natural Resources, 89 p.
Mazzullo, J., 1986, Sources and provinces of late Quaternary sand on the east Texas-Louisiana continental shelf: Geological Society of America Bulletin, v.97, p. 636-647.
McManus, J., 1988, Grain size determinations and interpretation, in Tucker, M. (ed.), Techniques in Sedimentology: Oxford, Blackwell scientific Publications, p. 63-85.
Mossa, J., 1986. Analysis of the environmental effects of nearshore sand resource utilization on the Louisiana continental shelf. Louisiana Geological Survey Technical Report for U.S. Minerals Management Service, 65 p.
Nummedal, D., Cuomo, R.F., and Penland, S., 1984. Shoreline evolution along the northern coast of the Gulf of Mexico. Shore and Beach, 52(1): 11-17.
Penland, S., and Boyd, R., 1982. Genesis and evolution of Mississippi delta barrier systems.
Geological Society of America, southeastern section. 31st annual meeting. Washington, D.C., March 25-27 (abstract).
Penland, S. and Boyd, R., 1982. Mississippi delta coastal sand barriers: an overview. In: Deltaic Sedimentation on the Louisiana Coast. Gulf Coast Section, Society of Economic Paleontologists and Mineralogists, Tulsa, OK, p. 71-91.
Penland, S., and Boyd, R., 1982. Evolution of transgressive deltaic environments on the Loui- siana coast. Association of American Petroleum Geologists. 67th annual meeting. Cal- gary, Alberta, June 27-30 (abstract).
63
Penland, S., and Boyd, R., 1982. Transgressive facies relationship of Mississippi delta coastal barrier systems. International Association of Sedimentologists. Eleventh congress. Hamilton, Ontario, August 22-28 (abstract).
Penland, S., Suter, J.R., and Moslow, T.F., 1984. Sand shoal development on the muddy Mis- sissippi River delta shelf. American Association of Petroleum Geologists. 69th annual meeting. San Antonio, TX., May 20-23 (abstract).
Penland, S., Suter, J.R., and Moslow, T.F., 1984. Act 41 nearshore sand inventory for the Cheniere Ronquille, Isles Dernieres, and Holly-Peveto Beach pilot protection projects. Louisiana Department of Natural Resources, 3 maps.
Penland, S., Suter, J.R., and Moslow, T.F., 1984. Generation of inner-shelf sand bodies.
American Geophysical Union. Ocean sciences meeting. New Orleans, LA., January 23-
26 (abstract).
Penland, S., and Suter, J.R., 1984. Depositional model for transgressive shelf deposits offshore of the Mississippi River delta plain. Society of Economic Paleontologists and Mineralo- gists. First annual mid-year meeting. San Jose, CA., August 10-13 (abstract).
Penland, S. and Boyd, R., 1985. Transgressive Depositional Environments of the Mississippi River Delta. Guidebook Series 3, Louisiana Geological Survey, Baton Rouge, LA, 262 p.
Penland, S. and Boyd, R., 1985, Mississippi delta shoreline development, in Penland, S., and Boyd, R. eds., Transgressive depositional environments of the Mississippi River delta plain: A guide to the barrier islands, beaches, and shoals in Louisiana: Louisiana Geological Survey, Guidbook Series no. 3, p. 53-122.
Penland, S., Suter, J.R., and Moslow, T.F., 1985. Stratigraphic development of Ship Shoal, northern Gulf of Mexico. Geological Society of America. 98th annual meeting. Orlando, FL., October 28-31 (abstract).
Penland, S., and Suter, J.R., 1986. Stratigraphic signature of transgressive submergence: criteria for testing the origin of inner-shelf shoals. Society of Economic Paleontologists and Mineralogists, Gulf Coast Section. 7th annual research conference. Corpus Christi, TX., December 7-10 (abstract).
Penland, S., and Suter, J.R., 1986. Criteria for distinguishing submerged barrier islands and inner-shelf shoals, northern Gulf of Mexico. Society of Economic Paleontologists and Mineralogists. Fourth mid-year meeting. Raleigh, N.C., September 25-28 (abstract).
Penland, S., and Suter, J.R., 1986. Transgressive barrier submergence, northern Gulf of Mexico.
International Association of Sedimentologists. 12th international sedimentological con- gress. Canberra, Australia, August 25-29 (abstract).
Penland, S., and Suter, J.R., 1986. Criteria for distinguishing submerged barrier islands and
64
inner-shelf shoals, northern Gulf of Mexico. Society of Economic Paleontologists and
Mineralogists. Fourth mid-year meeting. Raleigh, N.C., September 25-28 (abstract).
Penland, S., and Suter, J.R., 1986. Transgressive barrier submergence, northern Gulf of Mexico.
International Association of Sedimentologists. 12th international sedimentological con- gress. Canberra, Australia, August 25-29 (abstract).
Penland, S., Suter, J.R., and Boyd, R., 1986. Inner-shelf shoal formation through transgressive barrier submergence. American Association of petroleum Geologists. 71st annual convention. Atlanta, GA., June 15-18 (abstract).
Penland, S., Suter, J.R., and Moslow, T.F., 1986. Inner-shelf shoal sedimentary facies and sequences: Ship Shoal, northern Gulf of Mexico. In: T.F. Moslow and E.G. Rhodes (editors), Modern and Ancient Shelf Clastics: A Core Workshop, Society of Economic Paleontologists and Mineralogists Core Workshop 9, Tulsa, Ok, p. 73-123.
Penland, S., Suter, J.R., and Moslow, T.F., 1986. The Holocene geology of the Ship Shoal region, northern Gulf of Mexico, Louisiana Geological Survey, Baton rouge, 114 p..
Penland, S., Suter, J.R., and McBride, R.A., 1987. Delta plain development and sea level history in the Terrebonne coastal region, Louisiana. Coastal Sediments '87, ASCE, p. 1689-1705.
Penland, S. and Suter, J.R., 1988. Barrier island erosion and protection in Louisiana: a coastal geomorphological perspective. Gulf Coast Association of Geological Societies Transactions, 38: 331-342.
Penland, S., and Suter, J.R., 1988. Coastal and Shallow Marine Sedimentation on the Missis- sippi River Delta Plain and Chenier Plain. Field Trip Guide. Society of Economic Pale- ontologists and Mineralogists, 132 p. Christi, TX., December 7-10 (abstract).
Penland, S. and Suter, J.R., 1988. Barrier island erosion and protection in Louisiana: a coastal geomorphological perspective. Gulf Coast Association of Geological Societies. Annual meeting. New Orleans, LA., October 19-21 (abstract).
Penland, S. 1988. Preliminary evaluation of aggregate mineral resources, offshore Louisiana.
9th MMS-ITM: Marine Mineral Resources, Northern Gulf of Mexico. Annual meeting,
October 24-26 (abstract).
Penland, S., and Suter, J.R., 1988, Nearshore sand resources in the eastern Isles Dernieres Barrier island arc: Louisiana Geological Survey, Open-File Series 88-08, 177 p.
Penland, S., Suter, J.R., and Boyd, R., 1988. The transgressive depositional systems of the Mississippi River delta plain: a model for barrier shoreline and shelf sand development. Journal of Sedimentary Petrology, 58(6): 932-949.
Penland, S., Suter, J.R., and McBride, R.A., 1988. Reconnaissance investigation of shoreface and inner-shelf sand resources in Terrebonne Parish: Point Au Fer to Timbalier Island. Louisiana Geological Survey Open-File Series no. 88-06, 73 p.
65
Penland, S., Suter, J.R., and McBride, R.A., 1988. A new depositional model for the Mississippi River delta plain. Sequences, stratigraphy, sedimentology: surface and subsurface. Canadian Society of Petroleum Geologists. Core conference and meeting, Calgary, Alberta, September 14-15 (abstract).
Penland, S., Suter, J.R., and Boyd, R., 1989. The development of inner shelf shoals offshore of the Mississippi River delta plain through the process of transgressive submergence. 28th International Geological Congress. Washington, D.C., August 10-18 (abstract).
Penland, S., Suter, J.R., McBride, R.A., Williams, S.J., Kindinger, J.L., and Boyd, R., 1989.
Holocene sand shoals offshore of the Mississippi River delta plain. Gulf Coast
Association of Geological Societies Transactions, 39: 417-480.
Penland, S., Mossa, J., McBride, R.A., Ramsey, K.E., Suter, J.R., Groat, C.G., and Williams, S.J., 1990. Offshore and onshore sand resource delineation and usage for coastal erosion control in Louisiana: Isles Dernieres and Plaquemines barrier systems. Proceedings of Second Symposium on Studies Related to Continental Margins. University of Texas - Bureau of Economic Geology, Austin, TX, p. 74-86.
Penland, S., Suter, J.R., Ramsey, K.E., McBride, R.A., Williams, S.J., and Groat, C.G., 1990.
Offshore sand resources for coastal erosion control in Louisiana. Gulf Coast Association
of Geological Societies Transactions, v. 40:721-731.
Penland, S., (project coordinator), 1991, Historical shoreline change in the northern Gulf of Mexico , 1:2,000,000 map: prepared for the U.S. Environmental Protection Agency, Louisiana Geological survey, Baton Rouge, LA.
Penland, S., McBride, R.A., Suter, J.R., Boyd, R., and Williams, S.J., 1991. Holocene development of shelf-phase Mississippi River delta plain. Coastal Depositional Systems in the Gulf of Mexico: Quaternary Framework and Environmental Issues. GCSSEPM Foundation, p. 182-185.
Penland, S., Williams, S.J., Davis, D.W., Sallenger, A.H., Jr., and Groat, C.G. 1992. Barrier island erosion and wetland loss in Louisiana. Atlas of shoreline changes in Louisiana From 1985 to 1989. U.S. Geological Survey, Miscellaneous Investigations Series I-
1250A, p. 2-7.
Penland, S., Williams, S.J., Sallenger, A.H., Jr., Byrnes, M.R., McBride, R.A., and Kindinger, J.L., 1992. Formation and evolution of Late Quaternary river deltas of the northern Gulf of Mexico. Association of American Geographers. 88th Annual Meeting. San Diego, CA, April 18-22 (Abstract).
Penland, S., 1992. Coastal land loss in Louisiana - Status of the Louisiana Geological Survey research activities. Proceeding of the 54th Meeting of the Coastal Engineering Research Board, U.S. Army Corps of Engineers, p. 63-66.
Penland, S., McBride, R.A., Suter, J.R., Boyd, R., and Williams, S.J., 1992. Facies architecture
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and sequence stratigraphy of the Late Quaternary Incised Valley Fill of the Mississippi
River. American Association of Petroleum Geologists Meeting. Calgary, Alberta, June
21-24 (Abstract).
Penland, S., 1993. Transgressive Deltaic Sands Workshop. Phillips Petroleum Company, 255 p.`Geological Society of America, southeastern section. 31st annual meeting. Washington, D.C., March 25-27 (abstract).
Penland, S., Suter, J.R., and Boyd, R., 1993. Sea level control on the evolution of the Mississippi River delta plains during the Holocene Transgression. International Large Scale Coastal Behavior (LCSB) Conference. U.S. Geological Survey. St. Petersburg, FL, November 16-19 (Abstract).
Penland, S., and Williams, S.J., 1995. Holocene development of the Mississippi River delta plain: Sea level history, incised valley-fill and sequence stratigraphy. Geological Society of America. Annual Meeting. New Orleans, LA, November 6-9 (Abstract).
Penland, S, Wayne, L.D., Britsch, L.D., and Williams, S.J., 2000, The geomorphology of coastal land loss in the Mississippi River delta plain, Investigative Map Series, Map I-0417.
Penland, S, Wayne, L.D., Britsch, L.D., and Williams, S.J., 2000,The processes of coastal land loss in the Mississippi river delta plain, Investigative Map Series, MapI-0418.
Pepper, D.A., Stone, G.W., and Wang, P., 1988. Bottom boundary layer parameters and sediment transport on the Louisiana inner-shelf during cold front passages. Gulf Coast Association of Geological Societies: Conference Proceedings, 49: 432-439.
Pepper, D.A., and Stone G.W. (Submitted). Atmospheric forcing of fine sand transport on a low- energy inner shelf: south-central Louisiana, USA. Geo-Marine Letters.
Pepper, D.A., Stone, G.W., and Wang, P., 1999. A preliminary assessment of wave, current, and sediment interaction on the Louisiana shoreface adjacent to the Isles Dernieres, Recent Research in Coastal Louisiana Proceedings: 35-45.
Pepper, D.A., Stone, and Wang, P., 1999. The significance of mid-latitude cyclones on the Inner continental shelf of the northern Gulf of Mexico (abstract): The Impact of Hurricane Camille: A Storm Impact Symposium to Mark the 30th Anniversary: New Orleans.
Pepper, D.A., 2000. Hydrodynamics, bottom boundary layer processes and sediment transport on the South-Central Louisiana Inner Shelf: the influence of extratropical storms and bathymetric modification. Ph.D. dissertation. Department of Oceanography and Coastal Sciences, Louisiana State University, Baton rouge, LA 159 p.
Picciola and Associates, Inc., 1996. Ship Shoal reconnaissance study. Prepared for Louisiana State University Center for Coastal, Energy, and Environmental Resources (CCEER), Baton Rouge, Louisiana, 27 p..
Pope, D.L., Penland, S., Suter, J.R., and McBride, R.A., 1991. Holocene geologic framework of
67
Trinity Shoal Region, Louisiana. Coastal Depositional Systems in the Gulf of Mexico: Quaternary Framework and Environmental Issues. GCSSEPM Foundation, p. 191-201.
Ramsey, K. E., Penland, S., Suter, J.R., McBride, R.A., and Williams, S.J., 1990. Offshore sand resources for coastal erosion control in Louisiana. Gulf Coast Association of Geological Societies. Annual meeting. Lafayette, LA., October 17-19 (abstract).
Ramsey, K. E., Penland, S., 1991, Geologic framework and sand resources of Ship Shoal, northern Gulf of Mexico exclusive economic zone, in Characterization of the development of Ship Shoal sand for beach replenishment of Isle Dernieres: prepared for US Mineral Management Service agreement# 14-12-0001-30404 by Louisiana Geological Survey, p. 29-47.
Ramsey, K.E., 1999, Sand Resource Inventory Offshore Grand Terre, Louisiana: prepared for
National Marine Fisheries Service, Coastal Restoration Division, Baton Rouge, LA.
Ritchie, W., Westphal, K., Mc Bride, R.A., Penland, S., 1989, The coastal sand dunes of
Louisiana-Isles Dernieres: Coastal Geology Technical Report No. 5, Louisiana
Ritchie, W., Westphal, K., Mc Bride, R.A., Penland, S., 1990, Coastal sand dunes of Louisiana: The Plaquemine shoreline: Coastal Geology Technical Report no. 6, 90 p.
Ritchie, W., Westphal, K., Mc Bride, R.A., Penland, S., 1990, Coastal sand dunes of Louisiana:The Plaquemine shoreline: Coastal Geology Technical Report no. 6, Louisiana Geological Survey, Baton Rouge, LA, 120 p.
Scruton, P.C., 1960, Delta building and the deltaic sequence, in Shepard, F.P., Phleger, F.B., and Van Andel, T.H., eds., Recent sediments, northwest Gulf of Mexico: Tulsa, Oklahoma, American Association of Petroleum Geologists, p. 82-102.
Stright, M.J., 1990, Archaeological sites on the North American continental shelf, in Lasca, N.P., and Donahue, J., eds., Archaeological geology of North America: Boulder, Colorado, Geological Society of America, The Geology of North America, v. K-, p. 439-465.
Stone, G.W., and Xu, J.P., 1996. Wave climate modeling and evaluatin relative to sand mining on Ship Shoal, Offshore Louisiana, for Coastal and barrier island restoration. OCS study, Minerals Management Service, report 96-0059.
Stone, G.W., 2000. Wave climate and bottom boundary layer dynamics iwth implications for offshore sand mining and barrier replenishment in south-central Louisiana. OCS study, Minerals Management Service, MMS, 20000-053.
Stone, G.W., 2001. Mining of Ship Shoal for large-scale barrier island restoration along the Isles
Dernieres, Coastal Studies Institute, LSU, Baton Rouge, LA 70803.
Suter, J.R., Penland, S., and Berryhill, H.L., 1984. Stratigraphic evidence for sea level changes, Louisiana continental shelf. Society of Economic Paleontologists and Mineralogists. First annual midyear meeting. San Jose, CA., August 10-13 (abstract).
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Suter, J.R., Penland, S., and Moslow, T.F., 1984. Geologic framework of sand shoals on the muddy Mississippi River delta shelf. American Association of Petroleum Geologists.
69th annual meeting. San Antonio, TX., May 20-23 (abstract).
Suter, J.R. Penland, S., and Moslow, T.F., 1985. Ship and Trinity Shoals: Submerged deltaic barriers on the Louisiana continental shelf. Society of Exploration Geophysicists. Annual meeting. Alexandria, VA., October 6-10 (abstract).
Sutter, J.R., Berryhill, H.L., and Penland, S., 1985, Environments of sand deposition on the southwest Louisiana continental shelf. Gulf Coast Association of Geological Societies Transactions, v. 35, p. 495-504.
Suter, J.R., and Penland, S., 1986. Continental shelf sands: northern Gulf of Mexico. Inter- national Association of Sedimentologists. 12th international sedimentological congress. Canberra, Australia, August 25-29 (abstract).
Suter, J. R., and Penland, S., 1986. Nearshore sand resources of beach nourishment in Louisiana.
The Coastal Society. Annual convention. New Orleans, LA., October 12-15 (abstract).
Suter, J. R., Berryhill, H.L., and Penland, S., 1987. Delineation of late Quaternary depositional sequences by high resolution seismic stratigraphy, Louisiana continental shelf. American Association of Petroleum Geologists. 72nd annual convention. Los Angeles, CA., June
7-10 (abstract).
Suter, J. R. and Penland, S., 1987. A preliminary assessment of the sand aggregate resources of three areas of the Louisiana inner continental shelf: Timbalier Islands, Chandeleur Islands, and Trinity Shoal. Louisiana Geological Survey, Open-File Series 87-04, 58 p.
Suter, J. R., and Penland, S., 1987. Louisiana nearshore sand resource inventory. P. 8-1 through
8-14 in S. Penland and J. R. Suter, eds., Barrier shoreline geology, erosion, and protection in Louisiana. Field trip guide. New York: American Society of Civil Engineers.
Suter, J. R., Penland, S., Ramsey, K. E., and McBride, R. A., 1987. Mapping Nearshore Sand Resources in Coastal Louisiana: Raccoon Point to Belle Pass, LA. to Louisiana Department of Natural Resources, 30 p.
Suter, J.R., Mossa, J., and Penland, S., 1988. Preliminary assessments of the occurrence and effects of utilization of sand and aggregate resources of the Louisiana inner shelf. First Symposium in Studies Related to Continental Margins, Texas Bureau of Economic Geol- ogy, Austin, TX p. 80-90.
Suter, J. R., Morton, R.A., and Penland, S., 1989. Coastal Depositional Systems, Northwestern Gulf of Mexico. International Geological Congress Field Guidebook T370, American Geophysical Union, 52 p.
Suter, J.R., Mossa, J., and Penland, S., 1989. Preliminary assessments of the occurrence and effects of utilization of sand and aggregate resources of the Louisiana inner shelf. Marine
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Geology, v. 90:31-37
Sutter, J.R., Mossa, J. and Penland, S.,and Ramsey, K.E., 1991, Nearshore sand resources of the Mississippi River delta plain: Marsh Island to Sandy Point: Louisiana Geological Survey, Coastal Geology Technical Report no. 8, 130 p.
U.S.Army Corp of Engineers, 1977, Shore Protection Manual Volume II: U.S. Army Coastal
Engineering Center, Fort Belvoir, Virginia, Chapter 5, p. 1-59.
Wells, J.T., Crout, R.L., and Kemp, G.P., 1981, An assessment of coastal processes, dredged sediment transport and biological effects of dredging, coast of Loisiana: Coastal Studies Technical Report no. 34, 36 p.
Wentworth, C.K., 1922, A scale of grade and class terms for clastic sediments: Journal of
Geology, v. 30, p. 377-392.
Williams, S.J., Jaffe, B.E., Wertz, R.W., Holland, T., and Sallenger, A.H., 1989. Map showing precision bathymetry of the south-central Louisiana nearshore, Isles Dernieres and ship Shoal region: U.S. Geol. Survey Open-File Report 89 - 150.
Williams, S.J., Penland, S., and Circe', R.C., 1989. Distribution and textural character of surficial sediments, Isles Dernieres to Ship Shoal region, Louisiana. Gulf Coast Association of Geological Societies Transactions, 39: 571-576.
Williams, S. J., Penland, S., McBride, R.A., Sallenger, A.H., and Kindinger, J.L., 1991. Geologic controls on the formation and evolution of Quaternary coastal deposits of the northern Gulf of Mexico. Coastal Sediments 91, ASCE, p. 1082-1095.
Williams, S.J., Cichon, H.A., Westphal, K.A. and Ramsey, K.E., 1992. Representative Publications from the Louisiana Barrier Island Erosion Study. Results from a cooperative five-year study (1986 - 1990) of Geological Framework and Processes conducted by the U.S. Geological Survey and the Louisiana Geological Survey. U.S. Geological Survey Open File Report 92-530.
Williams, S.J., Penland, S. and Sallenger, A.H., Jr., Editors, 1992. Louisiana Barrier Island Erosion Study - Atlas of Barrier Shoreline Changes in Louisiana from 1853 to 1989. U.S. Geological Survey Miscellaneous Investigations Series I-2150-A, 103 p.
70

Appendix A

Supplemental Hydrodynamic Impact Contributions

This is the executive summary of a two-part report capturing the efforts of a comprehensive program funded by the Minerals Management Service and conducted by Dr. Greg Stone and other scientists in the Coastal Studies Institute, Louisiana State University, to
evaluate the physical processes and sediment transport at Ship Shoal. The first part documents a detailed numerical wave modeling effort designed to assess the potential impacts of removing Ship Shoal through dredging, and subsequent impacts on the wave field. The second deals with
a physical measurement program focusing on measuring the bottom boundary layer physics and sediment transport at the shoal. In both reports a considerable literature is reviewed that pertain to previous efforts pertinent to Ship Shoal and sediment transport processes. Given the length of the report, only the executive summary is provided here. The report is available on the web at http://erin.csi.lsu.edu/projects.
In a numerical modeling effort, removal of the entire shoal was simulated and the impact on wave propagation and energy levels discussed (Stone et al., 2001). It is important to note that an additional numerical modeling effort will be required, using state-of-the-art models (e.g.,
SWAN) when the volume and dimensions of the borrow site are designed. Removal of Ship Shoal will alter the wave propagation, dissipation and the wave energy distribution. The magnitude and spatial distribution of the alteration depend on the initial wave conditions. During severe storms (Case 1) and strong storms (Case 2), propagating waves reach breaking
conditions seaward of the western flank of Ship Shoal. Therefore, removal of Ship Shoal causes a maximum increase of the significant wave height by 90% - 100% (i.e., almost double the present value) in Case 1, and 40% - 50% in Case 2, over the shoal and immediately adjacent to
the lee of the complex. Wave breaking does not occur on the east flank of the shoal because of
1
much deep water, and the magnitude of the wave height increase due to shoal removal is significantly less on comparison with that on the west flank.
During weak storms (Case 3) and fair weather conditions (Case 4), waves do not reach breaking conditions over any part of Ship Shoal. The magnitudes of the significant wave height increase due to the removal of the shoal is considerably smaller, only 10% - 20% on the west part of the shoal. The values of wave height change on the east part of the shoal are minimal.
The nearshore wave fields are largely dependent on the offshore wave conditions. Under high energy conditions in Case 1 and Case 2, removal of Ship Shoal results in higher nearshore breaking wave heights, however, the breaker zone is displaced between 0.5 – 1.0 Km offshore. Ultimately, wave in the surfzone eventually collapse to the same energy level on comparing with and without shoal scenarios, suggesting that shoal removal will not have a significant impact on wave energy conditions along the Isles Dernieres. The nearshore impact is even less noticeable under the weaker energy conditions in Case 3 and Case 4, particularly along the east of the study area.
Wave approach direction exerts significant control on the wave climate leeward of Ship Shoal for stronger storm conditions (Case 1 and 2) but not weak storms or fairweather waves. Inclusion of the wind function increases wave height in all simulations. The magnitude of the increase is dependant on the deep water wave height and the slope of the shoreface profile. In Case 1, the surfzone is widened by almost 1.0 Km whereas in Case 4, the change is minimal. Removal of Ship Shoal results in a 50% increase of the significant wave height. This is much larger than the magnitude (between 25% to 30%) when wind forcing is neglected. The magnitude of wave height increase due to the wind forcing over the east part of the shoal is as much as 0.8m. While inclusion of the wind forcing function allows for an increase in the wave
height, the effects attributable to the removal of Ship Shoal are limited to the periphery of the
2
leeward flank of the system, particularly along its western boundary.
Changes in wave approach direction redistributes the increase in wave height in the lee of the shoal complex. This does not, however, impact breaker wave heights in the nearshore along the Isles Dernieres. Simulation of long wave propagation landward during Hurricane Andrew indicates near total wave energy dissipation, as opposed to breaking, over Ship Shoal. A much smaller percentage of low amplitude waves crossed the shoal complex. Peak wave energy dissipation rates occurred, however, seaward of Ship Shoal in approximately 25 – 30 m water depths.
The data presented suggest that the entire removal of Ship Shoal will not significantly influence the wave climate beyond the leeward periphery of the complex, such as the nearshore zone along the Isles Dernieres. The data suggest that this conclusion is valid for winter storm conditions and hurricanes similar to that of Hurricane Andrew. This conclusion implies that given the unlikely situation that the entire volume mass of sediment be removed from Ship Shoal during a single dredging event, wave climate changes peripheral to the shoal will be substantially reduced given the removal of significantly lower volumes of sediment than that simulated here.
Field research on hydrodynamics and sediment transport in the vicinity of Ship Shoal, has for the most part been conducted exclusively by researchers from the Coastal Studies Institute at Louisiana State University, and is discussed in Pepper et al. (1998), Pepper et. al. (1999), Pepper (2000), and Pepper and Stone (submitted, 2001). The region is generally characterized by low- energy processes, including low waves (mean significant wave height less than 0.7 m), weak
near-bottom currents (generally less than 10 cm s-1) and fairly low rates of sand transport (on the
order of 0.1 g cm-1 s-1). However, winter cold front passages, and presumably, tropical storms and hurricanes, are forcing mechanisms which provide an input of energy to the inner-shelf system which may cause increases of more than an order of magnitude in hydrodynamic
3
parameters and sediment transport rate. Winter storm (cold front) passages were found to consist of two distinctive end-member types in terms of their associated inner-shelf response, although other types of frontal passages may undoubtedly occur. Type 1 storms were characterized by weak southerly pre-frontal and strong northeasterly post-frontal winds. They generally resulted
in strong post-frontal responses that included high, short-period, southerly waves, strong, southwesterly currents, and moderately high sediment transport that was southwesterly overall. Type 2 storms included periods of both strong southerly pre-frontal winds and strong northerly post-frontal winds. They generated high, long-period northerly swell waves prior to the frontal passage that persisted throughout most of the post-frontal phase, during which time energetic southerly storm waves developed, creating a complex, bimodal wave spectrum. Currents prior to the frontal passage were fairly strong and northerly, while subsequent to the frontal passage, they became rotational, likely as a result of inertial effects, but were southeasterly in direction overall. Shear velocity was elevated during both the pre- and post-frontal phases, while sediment
transport occurred predominantly during the post-frontal phase, when mean sediment transport was directed southeasterly, and low-frequency and wind-wave flows produced northerly transport.
It is apparent that Ship Shoal influences these processes measurably. During a two-month winter period, mean wave height and period on the landward side were 36% and 9% lower, respectively, than on the seaward side, due to attenuation, while across-shelf currents were offshore on the seaward side and onshore on the landward side, where flow speed was10% higher. During a subsequent one-month period, mean significant wave height decreased from its seaward value by 15% and 25% as measured on the middle and the landward portions of the shoal, respectively. Sediment transport direction was also predicted to differ considerably
between the seaward and landward sides of the shoal, with fair-weather transport directed
4
towards the west on the seaward side and towards the northeast on the landward side, while during cold front passages, transport was toward the southeast on the seaward side, and variable, but generally southward on the landward side. Sediment flux across Ship Shoal appears to have been divergent during fair weather conditions, potentially causing shoal erosion, and convergent during cold front passages, potentially causing accretion. It appears, therefore, that removal of sand from Ship Shoal would likely result in a modification of hydrodynamic and sediment transport processes on what is currently the landward side of the shoal, including an increase in wave height and wave period, an increase in offshore current flow, and potentially, a decrease in landward transport of sediment during fair weather. The magnitude of these effects is difficult to predict however, since the bathymetry of the shallow inner shelf would undoubtedly influence these processes, even discounting the influence of Ship Shoal itself, and the possible change in bottom substrate (from fine sand to other materials) would change bottom boundary layer characteristics and resuspension processes.

Part 1: Wave Climate Modeling and Evaluation Relative to Sand Mining on Ship Shoal

By
Gregory W. Stone, Ph.D.
ExxonMobil Professor of Marine Geology
Coastal Studies Institute and
Department of Oceanography & Coastal Sciences
312 Howe-Russell Geoscience Complex
Louisiana State University
Baton Rouge, LA 70803
Gregory W. Stone
and
Jingping Xu, Ph.D.
United State Geological Survey
USGS MS-999
345 Middlefield Road
Menlo Park, CA 94025
OCS Study, MMS 96-0059
5

Part 2: Wave Climate and Bottom Boundary Layer Dynamics with Implications for

Offshore Sand Mining and Barrier Island Replenishment, South-Central Louisiana

By
David Pepper, Ph.D.
Coastal Studies Institute
117 Howe-Russell Geoscience Complex
Louisiana State University
Baton Rouge, LA 70803
and
Gregory W. Stone, Ph.D.
ExxonMobil Professor of Marine Geology
Coastal Studies Institute and
Department of Oceanography & Coastal Sciences
312 Howe-Russell Geoscience Complex
Louisiana State University
Baton Rouge, LA 70803
OCS Study MMS 2000-053
6

Appendix B

BELLE PASS COST ESTIMATES (from Picciola and Associates, 1996)

STANDARD BEACH PROFILE~ 125 cu. yd/ft
RF CRIT =1.03
= 128.75 cu. yd/ft
Borrow Material = 5,000,000 yd3
Linear Ft. of Beach 7 mi. (36,960 ft)

PIPELINE

30 $/ft. * 36,960
$1,108,800.00

MOB&DEMOB

$450,000.00
1

INSHORE DREDGE APPLICATION

(27" / 3,600 yd3)
Hopper Yield = 65%
One (1) Trip = 3,600*0.65
= 2,340 cu. yd. Number. of Trips =5,000,000 / 2,340
=2,137
Down Time =7.5%
* Total Hours = (2,137 / 1.75) * 1.075* 24
=31,506 hrs
*Assume 1.75 trips per day i.e.
2.5 hours extraction
7.5 hours travel
3.5 hours off load
Cost per Hour = 1,325 $/hr
Total Cost = 1,325* 31,506

=$41,745,450.00

OFFSHORE DREDGE APPLICATION

(28" / 4,000 yd3)
Hopper Yield = 65%
One (1) Trip = 4,000*0.65
= 2,600 cu. yd.
Nb. of Trips =5,000,000 / 2,600
=1,923
Down Time =7.5%
* Total Hours = (1,923 / 1.75) * 1.075* 24
=28,351 hrs
*Assume 1.75 trips per day i.e.
2.5 hours extraction
7.5 hours travel
3.5 hours off load
Cost per Hour = 1,650 $/hr
Total Cost = 1,650* 28,351

=$46,779,150.00

2

DREDGE

(33.5" / 6,300 yd3)
Hopper Yield = 65%
One (1) Trip = 6,300*0.65
= 4,095 cu. yd.
Number of Trips =5,000,000 / 4,095
=1,221
Down Time =7.5%
* Total Hours = (1,221/ 1.75) * 1.075* 24
=18,001 hrs
*Assume 1.75 trips per day i.e.
2.5 hours extraction
7.5 hours travel
3.5 hours off load
Cost per Hour = 2,250 $/hr
Total Cost = 2,250* 18,001

=$40,502,250.00

3