OCS Study 

MMS 96-0059 

Wave Climate Modeling and Evaluation 

Relative to Sand Mining on Ship Shoal, 

Offshore Louisiana, for Coastal and Barrier 

Island Restoration 

Final Report 

October 1996 

LABORATORY 

//~~ US. Department of the Interior Louisiana State University 

Am Minerals Management Service pepartrrred of Geography and Anthropology 
OCS Study 

MMS 96-0059 

Wave Climate Modeling and Evaluation 

Relative to Sand Mining on Ship Shoal, 

Offshore Louisiana, for Coastal and Barrier 

Island Restoration 

Final Report 

October 1996 

Authors: 

Gregory W. Stone 

and 

Jingping Xu 

Prepared under MMS Cooperative 

Agreement 14-35-0001-30660 through 

the MMS/LSU Coastal Marine Institute 

UeorznTOxr 

U.S . Department of the Interior Louisiana State University 

~r~n~~ Minerals Management Service Department of Geography and Anthropology 
DISCLAIMER 

This report has been reviewed by the Minerals Management 

Service and approved for publication . Approval does not signify 

that the contents necessarily reflect the views and policies of the 

Service, nor does mention of trade names or commercial products 

constitute endorsement or recommendation for use . 
11 

Contents 

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .i 

Program Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Program P.I . and Supporting Personnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

Report Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 

2 Regional Setting and Study Site Description . . . . . . . . . . . . . . . s 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Site Description and Regional Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 

Climatology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 

Waves, Tide and Sea-Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

3 Wave Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

RCPWAVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 

REF/DIF1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

REF/DIFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

STWAVE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Comparison of the Models and Selection . . . . . . . . . . . . . . . . . . . . 15 

Wave Transformation During Hurricane Andrew . . . . . . . . . . . . . . . . . . . . . . 16 

4 Data Acquisition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Bathymetric Grid Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 

Deep Water Database for Winter Storms and Fairweather . . . . . . . . . . . . . . . . . 21 

Deep Water Database for Hurricane Andrew . . . . . . . . . . . . . . . . . . . . . . . . . 33 

5 Technical Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

Wave Transformation Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

Configurations of Model Input and Bathymetric Grid . . . . . . . . . . . . . . . . . 41 

Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 

Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 

Case 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 

Effect of Wind Forcing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 
iii 

Hurricane Andrew Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 

Wave Height and Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 

_ Maximum Near-Bottom Orbital Velocity . . . . . . . . . . . . . . . . . . . . . . . . . 80 

Energy Dissipation Across the Continental Shelf . . . . . . . . . . . . . . . . . . . . 83 

6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ss 

Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 

Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 

Appendix C . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 

Appendix D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : . . . 150 
IV 

List of Figures 

Figure 1 Map of the study area. Bathymetric contours in meters . . . . . . . . . . . . . . . . . 2 

Figure 2 Primary factors responsible for barrier island deterioration in Louisiana . . . . . . 3 

Figure 3 Sedimentary facies of Ship Shoal (modified from Penland et al., 1986) . . . . . . . 7 

Figure 4 Low resolution bathymetric grid used in Hurricane Andrew simulations . . . . . 20 

Figure 5 High resolution bathymetric grid across the inner shelf incorporating Ship Shoal 22 

Figure 6 High resolution bathymetry of Ship Shoal and its vicinity, surveyed by USGS in 

1986 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 

Figure 7 Map of Wave Information Study stations in the Gulf of Mexico . . . . . . . . . . . 25 

Figure 8 Map of National Data Buoy Center stations in Gulf of Mexico . . . . . . . . . . . . 26 

Figure 9 Time series of Hs from NDBC 42017, April - September 1989 . . . . . . . . . . . 27 

Figure 10 Time series of Tp from NDBC 42017, April - September 1989. . . . . . . . . . . 28 

Figure l 1a Time series of Hs from NDBC 42001 August 1991. - January 1992 . . . . . . . . 29 

Figure l lb Time series of Hs from NDBC 42001 February 1992 - July 1992. . . . . . . . . 30 

Figure 12a Time series of Tp from NDBC 42001 August 1991 - January 1992 . . . . . . . . 31 

Figure 12b Time series of Tp from NDBC 42001 February 1992 - July 1992 . . . . . . . . . 32 

Figure 13a Time series of Hs from Latex 16, 6 - 24 December 1993 . . . . . . . . . . . . . . 34 

Figure 13b Time series of Hs from Latex 16, 15 February - 3 June 1994. . . . . . . . . . . . 35 

Figure 14a Time series of Tp from Latex 16, 6 - 24 December 1993 . . . . . . . . . . . . . . 36 

Figure 14b Time series of Tp from Latex 16, 15 February - 3 June 1994. . . . . . . . . . . . 37 

Figure 15a Time series of Direction from Latex 16, 6 - 24 December 1993 . . . . . . . . . . 38 

Figure 15b Time series of Direction from Latex 16, 15 February - 3 June 1994. . . . . . . 39 

Figure 16 3D view of the bathymetric grid, with Ship Shoal . . . . . . . . . . . . . . . . . . . . 42 

Figure 17 3D view of the bathymetric grid, without Ship Shoal . . . . . . . . . . . . . . . . . . 43 

Figure 18a Image of modeled significant wave height, HS . Case 1, 8=0°, with Ship Shoal . 44 

Figure 18b Image of modeled significant wave height, HS. Case 1, 8=0°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 

Figure 18c Image of percentage of HS increase due to shoal removal. Case 1, 8=0°. . . . . 46 

Figure 19a Image of modeled significant wave height, HS . Case 1, 8=45°, with Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 

Figure 19b Image of modeled significant wave height, H5 . Case 1, 8=45°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 

Figure 19c Image of modeled significant wave height, HS . Case 1, 0=45., percentage of HS 

increase due to shoal removal . . . . . . . . . . . . . .

. . . . . . . . . . . . .

. . . . . 49 

Figure 20a Image of modeled significant wave height, HS . Case l, 8=-45°, with Ship 

Shoal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 

Figure 20b Image of modeled significant wave height, HS . Case 1, 8=-45°, without Ship 

Shoal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 

Figure 20c Image of percentage of HS increase due to shoal removal . Case 1, 8=-45°. . . 52 

Figure 21a Cross-sectional profiles of significant wave height, HS along J=150 in Case 1 . 54 
V 

Figure 21b Cross-sectional profiles of percentage of HS increase due to shoal removal along 

J=150 in Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 

Figure 21c Cross-sectional profiles of significant depth-limited wave breaking index, H/h, 

along J=150 in Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 

Figure 22a Cross-sectional profiles of significant wave height, HS along J=400 in Case 1 57 

Figure 22b Cross-sectional profiles of percentage of HS increase due to shoal removal along 

J=400 in Case l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 

Figure 22c Cross-sectional profiles of depth-limited wave breaking index, H/h, along J=400 

in Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 

Figure 23a Modeled wave rays when 8=0° in Case 1 with Ship Shoal. . . . . . . . . . . . . 60 

Figure 23b Modeled wave rays when 0=0° in Case 1 without Ship Shoal. . . . . . . . . . . 61 

Figure 24a Modeled wave rays when 8=45° in Case 1 with Ship Shoal. . . . . . . . . . . . . 62 

Figure 24b Modeled wave rays when 8=45° in Case 1 without Ship Shoal. . . . . . . . . . . 63 

Figure 25a Modeled wave rays when 8=-45° in Case 1 with Ship Shoal. . . . . . . . . . . . 64 

Figure 25b Modeled wave rays when 8=-45° in Case 1 without Ship Shoal . . . . . . . . . . 65 

Figure 26 Modeled percentage of HS increase due to shoal removal. Case 2, 0=0 . . . . . . . 67 

Figure 27 Modeled percentage of HS increase due to shoal removal. Case 2, 8=45° . . . . 68 

Figure 28 Modeled percentage of HS increase due to shoal removal. Case 2, 8 =-45° . . . . 69 

Figure 29 Modeled percentage of HS increase due to shoal removal. Case 3, 8=0° . . . . . 71 

Figure 30 Modeled percentage of HS increase due to shoal removal . Case 3, 0=45' . . . . 72 

Figure 31 Modeled percentage of HS increase due to shoal removal . Case 3, A=-45° . . . . 73 

Figure 32 Modeled percentage of HS increase due to shoal removal . Case 4, 0=0 ° . . . . . 75 

Figure 33 Modeled percentage of HS increase due to shoal removal . Case 4, 0=45' . . . . 76 

Figure 34 Modeled percentage of HS increase due to shoal removal . Case 4, 8 =-45° . . . 77 

Figure 35 Contour plot of the simulated wave height across the Louisiana shelf during 

Hurricane Andrew . Contour intervals are 1 meter . . . . . . . . . . . . . . . . . . . . 81 

Figure 36 Contour plot of the simulated maximum near-bottom orbital velocities across the 

Louisiana shelf during Hurricane Andrew . Contour intervals are 1 m/s . . . . . . 82 

Figure 37 Contour plot of the simulated wave energy dissipation rates across the Louisiana 

Shelf during Hurricane Andrew . Contour intervals are 0 .2 jl/m3.

. . . . . . . . . . 84 

Figure 38 Wave height - energy relationships from two wave rays west (Ray 24) and east 

(Ray 80) of the Mississippi Canyon. The respective bathymetric profiles are 

also shown for comparison . . . . . . . . . . . . . . . .

.

. . . . . . . . . . . . . . . . . . 85 

Figure A-1 Image of modeled significant wave height, Case 2, 8=0°, with Ship Shoal . . 94 

Figure A-2 Image of modeled significant wave height, Case 2, a= 0°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 

Figure A-3 Image of modeled significant wave height, Case 2, 8=45°, with Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 

Figure A-4 Image of modeled significant wave height, Case 2, 8 =45°, without Ship 

Shoal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 

Figure A-5 Image of modeled significant wave height, Case 2, 8 =-45°, with Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 
V1 

Figure A-6 Image of modeled significant wave height, Case 2, 8 =-45°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 

Figure A-7 Cross-sectional profiles of significant wave height, HS, along J=150 in 

Case 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 

Figure A-8 Cross-sectional profiles of percentage of Hs increase due to shoal removal 

along J=150 in Case 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 

Figure A-9 Cross-sectional profiles of depth-limited wave breaking index, H/h, 

along J=150 in Case 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 

Figure A-10 Cross-sectional profiles of significant wave height, HS, along J=400 in 

Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 

Figure A-11 Cross-sectional profiles of percentage of Hs increase due to shoal removal 

along J=400 in Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 

Figure A-12 Cross-sectional profiles of depth-limited wave breaking index, H/h, along 

J=400 in Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 

Figure A-13 Modeled wave rays, Case 2, 8=0°, with Ship Shoal . . . . . . . . . . . . . . . 106 

Figure A-14 Modeled wave rays, Case 2, 8 =0°, without Ship Shoal . . . . . . . . . . . . . 107 

Figure A-15 Modeled wave rays, Case 2, 8 =45°, with Ship Shoal. . . . . . . . . . . . . . . 108 

Figure A-16 Modeled wave rays, Case 2, 8 =45°, without Ship Shoal . . . . . . . . . . . . . 109 

Figure A-17 Modeled wave rays, Case 2, 8=-45°, with Ship Shoal . . . . . . . . . . . . . . 110 

Figure A-18 Modeled wave rays, Case 2, 8 =-45°, without Ship Shoal . . . . . . . . . . . . 111 

Figure B-1 Image of modeled significant wave height, Case 3, 8=0°, with Ship Shoal . . 113 

Figure B-2 Image of modeled significant wave height, Case 3, 8 =0°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 

Figure B-3 Image of modeled significant wave height, Case 3, 8 =45°, with Ship Shoal. 115 

Figure B-4 Image of modeled significant wave height, Case 3, 8 =45°, without Ship 

Shoal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 

Figure B-5 Image of modeled significant wave height, Case 3, 8 =-45°, with Ship Shoal . 117 

Figure B-6 Image of modeled significant wave height, Case 3, 8 =-45°, without Ship 

Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 

Figure B-7 Cross-sectional profiles of significant wave height, HS, along J=150 in 

Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 

Figure B-8 Cross-sectional profiles of percentage of Hs increase due to shoal removal 

along J =150 in Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 

Figure B-9 Cross-sectional profiles of depth-limited wave breaking index, H/h, along 

J =150 in Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 

Figure B-10 Cross-sectional profiles of significant wave height, H5, along J=400 in 

Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 

Figure B-11 Cross-sectional profiles of percentage of Hs increase due to shoal removal 

along J=400 in Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 

Figure B-12 Cross-sectional profiles of depth-limited wave breaking index, H/h, 

along J=400 in Case 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 

Figure B-13 Modeled wave rays, Case 3, 8=0°, with Ship Shoal . . . . . . . . . . . . . . . . 125 

Figure B-14 Modeled wave rays, Case 3, 0 =0°, without Ship Shoal . . . . . . . . . . . . . . 126 
vii 

Figure B-15 Modeled wave rays, Case 3, 8=45°, with Ship Shoal . . . . . . . . . . . . . . . 127 

Figure B-16 Modeled wave rays, Case 3, 8=45°, without Ship Shoal. . . . . . . . . . . . . 128 

Figure B-17 Modeled wave rays, Case 3, 8 =-45°, with Ship Shoal. . . . . . . . . . . . . . 129 

Figure B-18 Modeled wave rays, Case 3, 8=-45°, without Ship Shoal. . . . . . . . . . . . 130 

Figure C-1 Image of modeled significant wave height, Case 4, 8 =0°, with Ship Shoal . 132 

Figure C-2 Image of modeled significant wave height, Case 4, 0=0', without 

Ship Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 

Figure C-3 Image of modeled significant wave height, Case 4, 0 =45°, with 

Ship Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 

Figure C-4 Image of modeled significant wave height, Case 4, 0=450, without 

Ship Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 

Figure C-5 Image of modeled significant wave height, Case 4, 8=-45°, with 

Ship Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 

Figure C-6 Image of modeled significant wave height, Case 4, 8 =-45°, without 

Ship Shoal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 

Figure C-7 Cross-sectional profiles of significant wave height, H5, along J=150 

in Case 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 

Figure C-8 Cross-sectional profiles of percentage of Hs increase due to shoal 

removal along J=150 in Case 4 . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . 139 

Figure C-9 Cross-sectional profiles of depth-limited wave breaking index, H/h, 

along J=150 in Case 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140 

Figure C-10 Cross-sectional profiles of significant wave height, HS, along J=400 in 

Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 

Figure C-11 Cross-sectional profiles of percentage of Hs increase due to shoal 

removal along J=400 in Case 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 

Figure C-12 Cross-sectional profiles of depth-limited wave breaking index, H/h, 

along J=400 in Case 4. . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . 143 

Figure C-13 Modeled wave rays, Case 4, 8=0°, with Ship Shoal . . . . . . . . . . . . . . . 144 

Figure C-14 Modeled wave rays, Case 4, 0 =0°, without Ship Shoal. . . . . . . . . . . . . 145 

Figure C-15 Modeled wave rays, Case 4, A=45°, with Ship Shoal. . . . . . . . . . . . . . . 146 

Figure C-16 Modeled wave rays, Case 4, 8 =45°, without Ship Shoal. . . . . . . . . . . . . 147 

Figure C-17 Modeled wave rays, Case 4, 8=-45°, with Ship Shoal. . . . . . . . . . . . . . 148 

Figure C-18 Modeled wave rays, Case 4, 8 =-45°, without Ship Shoal . . . . . . . . . . . . 149 

Figure D-1 Wind effect on the wave height distribution in Case 1, sectional profiles at 

J=150. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 

Figure D-2 Wind effect on the wave height distribution in Case 1, sectional profiles at 

J=400 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 

Figure D-3 Wind effect on the wave height distribution in Case 2, sectional profiles at 

J=150. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 

Figure D-4 Wind effect on the wave height distribution in Case 2, sectional profiles at 

J=400. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 

Figure D-5 Wind effect on the wave height distribution in Case 3, sectional profiles at 

J=150. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 
viii 

Figure D-6 Wind effect on the wave height distribution in Case 3, sectional profiles at 

J=400. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156 

Figure D-7 Wind effect on the wave height distribution in Case 4, sectional profiles at 

J=150. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 

Figure D-S Wind effect on the wave height distribution in Case 4, sectional profiles at 

J=400. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 

Figure D-9 Modeled percentage of HS increase under effect of wind forcing. Case 1, 

Vwind-1.O m/s, 8=0° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 

Figure D-10 Modeled percentage of HS increase under effect of wind forcing . Case 1, 

Vwind-ZO m/s, 8=45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 

Figure D-11 Modeled percentage of HS increase under effect of wind forcing . Case 1, 

Vwind-ZO m/s, 8=-45. . . . . . . . . . . . . . . . . . . . . . . . . . '. . . . . . . . . 161 

Figure D-12 Modeled percentage of HS increase under effect of wind forcing . Case 2, 

Vwind-ZO m/s, 8=0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 

Figure D-13 Modeled percentage of HS increase under effect <>f wind forcing . Case 2, 

VWina=20 m/s, 8=45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 

Figure D-14 Modeled percentage of HS increase under effect of wind forcing . Case 2, 

VWi,,a=20 m/s, 8=-45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 

Figure D-15 Modeled percentage of HS increase under effect of wind forcing . Case 3, 

VWina=20 m/s, 8=0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 

Figure D-16 Modeled percentage of HS increase under effect of wind forcing . Case 3, 

Vwind-ZO m/s, 8=45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 

Figure D-17 Modeled percentage of HS increase under effect of wind forcing . Case 3, 

Vwind-LO m/s, 8=-45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 

Figure D-18 Modeled percentage of HS increase under effect of wind forcing . Case 4, 

Vwind-1.O m/s, 8=0° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 

Figure D-19 Modeled percentage of HS increase under effect of wind forcing . Case 4, 

VWind=20 m/s, 8=45° . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 

Figure D-20 Modeled percentage of HS increase under effect of wind forcing . Case 4, 

Vwind-ZO m/s, 0 =-45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 
ix 

List of Tables 

Table t . Sources of wave climate data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 

Table 2 . Incident wave parameters used for deep water wave boundary conditions . . . . . . 33 

Table 3 . Input to Wavenrg obtained from the hindcasts of Cardone and Cox (1992) . . . . . 40 

Table 4. Wind speeds and directions used to test the wind forcing term . . . . . . . . . . . . . 79 
1 

1 Introduction 

Program Overview 

It is now well established in the literature that the barrier islands comprising the Isles 

Dernieres (Figure 1) have been experiencing among the highest rates of shoreline retreat in the 

United States (McBride et al ., 1992; Williams et al., 1992 ; Stone and Penland, 1992) . As 

summarized in Figure 2, the primary factors responsible for deterioration of these islands includes 

(1) eustatic sea-level rise ; (2) compactional and geological subsidence ; (3) wave erosion; (4) wind 

deflation; (5) reduction in sediment supply and (6) anthropogenic activity . Historical erosion rates 

along the Isles Dernieres ranged from 4.8 m/yr. (East Island) to 22.9 m/yr. (Wine Island) over 

the last century or so (McBride et al., 1992) . Recent evidence indicates an apparent acceleration 

in erosion, approximating 213% over the last decade (Williams et al., 1992) . Based on these 

data, it is estimated that several of the islands will disappear within the next decade or two 

(McBride et al., 1992) . Given the recent impact of Hurricane Andrew along this coast (Stone et 

al., 1993; Stone et al., 1995 ; Grymes and Stone, 1995), it is highly probable that this time period 

is less . 

With the degradation of barrier systems, it is likely that mainland shoreline erosion and 

wetland loss will occur in response to a more energetic, local wave field (Penland and Suter, 

1988 ; McBride et al., 1992)--although, the critical links have not yet been fully investigated (List 

and Hansen, 1992) . Recent data indicate that land loss in the Terrebonne Bay area averaged 0.86 

km2/yr . between 1932 and 1990 (Britsch and Dunbar, 1993). Although preliminary, work carried 

out by van Heerden et al . (1993) indicates a large-scale relationship between degradation of the 

Isles Dernieres, increasing tidal prism, and, subsequently, enhancement of wetland loss . 

The work of van Heerden et al. (1993) indicates that approximately 11 .6 million cubic 

meters of sand would be required to restore the Isles Dernieres to a configuration indicative of the 

late 1800's . Their work indicates that with such a configuration, there will be an increase in 

wetlands of 30,000 acres, in addition to reductions in salinity, tidal current velocity and shoreline 

erosion. Several studies, funded largely by the U.S . Minerals Management Service, have 

indicated the potential use of Ship Shoal (Figure 1) as a source of clean quartz sand 

(approximately 1 .2 billion cubic meters) for beach nourishment along Isles Dernieres (Mossa, 

1988; Suter et al., 1989) . Although dredging of the material appears both technically and 

economically feasible (Byrnes and Groat, 1991), a detailed evaluation of the potential impacts 

associated with such an undertaking has not yet been undertaken. The data presented here build 

on the findings of Mossa (1988), and Byrnes and Groat (1991) which pertained to the impact of 

dredging portions of Ship Shoal on wave refraction patterns, and qualitative assessments of the 

resultant wave energy distribution along the Isles Dernieres . 
a' 

.6 

SHOAL 

SHIP 

~ . N 

/or' ~ 

III ' TERREBONNE 

BAY 

CAILLOU ~ + I ~ nIAsALIER 

BAY ~~ 

LAKE PEl:TO 

ISLAND 

~ EAST ISLAND ~e 

RACCOON TR"Ty wKsKEr IrSSwro + ,N ISLAND ' A e~s~`p a ---~ 6-

DRN~ERE E 

GULF OF MEXICO 

N 

0 5 10 

91*10, 91,00, 9o ;5o 9o "4o~ 

LOU 

rip 

90.30' 

N 

Figure 1 Map of the study area. Bathymetric contours in meters . 
BEACH NOURISHMENT 

AND RENOURISHMENT 

OVERWASH/ 

OFFSHORE 

TRANSPORT 

BREACHING/ 

INLET 

FORMATION 

ANTHROPROGENIC 

INFLUENCES 

RATE 

OF 

DETERIORATION 

REDUCTION IN 

SEDIMENT SUPPLY 

APERIODIC 

ATMOSPHERIC 

FORCINGS 

RELATIVE 

SEA-LEVEL 

RISE 

Figure 2 Primary factors responsible for barrier island deterioration in Louisiana. 
4 

The degree to which Ship Shoal mitigates the wave climate along the Isles Dernieres has not 

yet been established. Consequently the potential impacts associated with large-scale extraction of 

sediment from Ship Shoal should not be attempted prior to a detailed evaluation of the wave and 

current field in this area. Specifically, a combination of wave and current data obtained from in 

situ measurement and numerical modeling is necessary to understand more completely the effects 

of Ship Shoal on the wave and current field. The objective of this project is to numerically model 

the wave field and quantify the effects of shoal removal on wave conditions in the study area. 

Although total removal of the shoal is an unlikely scenario, this approach will permit an evaluation 

of the importance of Ship Shoal on the wave field during a variety of fairweather, storm and 

hurricane-generated wave scenarios . 

Program Principal Investigators and Supporting Personnel 

All aspects of this program (including this report) have been carried out by the principal 

investigators : 

Dr . Gregory W. Stone (Louisiana State University) 

Dr . Jingping Xu (Louisiana State University) 

Mr . Xiongping Zhang was responsible for digitizing, some computer programming, and 

other technical support . 

Report Organization 

In this report we present background to the problem, methodological techniques and results 

in a structured and detailed form so that readers may have direct access to the relevant 

information. There are 6 chapters in total : 

Chapter 1---project introduction and overview. 

Chapter 2---regional setting and study site description. 

Chapter 3---wave models . 

Chapter 4---data acquisition . 

Chapter 5---technical discussion . 

Chapter 6---conclusions . 
5 

2 Regional Setting and Study Site Description 

Introduction 

This chapter provides a general description of the geological, climatological and 

oceanographic setting of the study area and background information pertaining to the wave climate 

in the study area. It also reviews and summarizes previous work and available data for the area. 

Site Description and Regional Setting 

The study site is located off the coast of Terrebonne Parish, south central Louisiana (Figure 

1) . The morphology of the study area is the product of a process combining relative sea-level rise 

with regressive (delta building) sequences, and transgressive (delta abandoning) sequences of the 

Mississippi River (Penland, 1990) . Over the last 7000 years the Mississippi River has built six 

major delta lobes (Frazier, 1967) . Except for the Modern delta and Atchafalaya delta complexes, 

all other abandoned deltas have responded to the Holocene transgression by undergoing erosion, 

subsidence, sediment redistribution, and landward migration . Isle Dernieres, Timbalier islands, 

and Ship Shoal are all products of these processes. Ship Shoal is a marine sand deposit located 

15 km offshore of Isles Dernieres near the 10 m bathymetric contour and was formed by the 

erosion of a submerged barrier shoreline. The shoal is approximately 50 km long, comprised of 

well-sorted, clean quartz sand and is the easternmost member of a group of Holocene inner shelf 

shoals located southwest of the Mississippi River delta plain (Penland et al., 1986). Bathymetric 

comparisons covering a time span of over a century since 1853 indicate that Ship Shoal has 

migrated landward by approximately 1 .5 km (Penland et al., 1986; List et al., 1994). 

Penland et al . (1986) identified seven major sedimentary facies in the study area and its 

vicinity based on lithology, texture, sedimentary structures, faunal assemblages and stratigraphic 

position. Of the seven facies, the first three are the most significant with regards to 

characterization of the surficial sediment and the environments of deposition . The first facies, 

representing the crest of Ship Shoal, is located within the upper 5 m of the shoal and is 

characterized as a very well-sorted, well-rounded 99% quartz sand that coarsens upward within 

the unit from 0.13 mm at the base to about 0 .16 mm at the top. The second facies, which 

represents the central body (or shoal front) of Ship Shoal, is a 1 .2 to 3 .4 m thick, moderately 

sorted and very fine to fine (0 .12 to 0.15 mm), sand that underlies facies 1 . Facies 3 is 

characterized by poorly sorted, very fine sand (0.1 to 0.13 mm), with interbedded layers of silty 

clay . It represents the lower extent, or shoal base, of Ship Shoal . The shoal crest contains 112 

million m3 of sand and resides within the zone of active normal and storm wave processes. Water 

depths over the shoal crest range from 2.7 m in the west to 7.0 m in the east . The shoal front and 

shoal base environments contain approximately 430 and 640 million m3 of sand respectively . 

Because these two facies are in deeper water, they are subjected to a lower energy environment. 
6 

A block diagram illustrating shoal facies and depositional environment (Penland et al., 1986) is 

shown in Figure 3 . 

Climatology 

Coastal Louisiana has a climate classified as humid subtropical (Muller and Fielding, 1987) 

with a significant amount of well distributed rainfall (Faiers et al., 1994) . The governing controls 

on the climate are the subtropical location of Louisiana and proximity to the Gulf of Mexico 

resulting in long hot summers, and short, mild winters (Muller and Fielding, 1987) . The airflow 

for the area is dominated by the semi-permanent, North Atlantic, high pressure cell . Airflow into 

the Louisiana coastal region, emanating from the tropical Gulf of Mexico, Caribbean and south 

Atlantic, follows the occurrence of this high pressure system during spring, summer and early 

autumn. The high moisture content of the dominant maritime air tends to reduce the temperature 

range from day to night by approximately 20°F, with highs and lows approximating 90 and 70° 

(Muller and Fielding, 1987) . Average annual temperatures range between 67 and 70°F, although 

freezing temperatures have been experienced in the winter . 

High pressure systems over the North American continent play an important role along the 

Louisiana coast. During the winter season, three distinct end-member type cold fronts impact the 

northern Gulf of Mexico: (1) the Arctic surge ; (2) the Gulf cyclone; and (3) the mid-latitude 

cyclone. These extratropical weather systems produce local variations in wind direction, intensity 

and duration and thereby significantly affect wave and sediment transport processes along the 

Louisiana coast. Intense winter surface anticyclones are associated with outbreaks of Arctic and 

polar air which surge southward out of northern Canada to the Gulf of Mexico coast when a 

highly amplified PNA ridge-trough pattern occurs (Rohli and Rogers, 1993) . This distinct polar 

jet stream configuration guides polar anticyclones into the Gulf region . There are two distinctive 

anticyclone paths: one track guides polar anticyclones into Texas while the other track guides 

polar anticyclones into Florida (Rogers and Rohli, 1991) . In the south-eastern USA, relationships 

are strongest between circulation and the number of storms, probably caused by the ability of 

large-scale flow to steer frontal storms into an area (Henderson and Robinson, 1994) . Locally, 

arctic surge type cold fronts produce short-lived pre-frontal southerly winds and strong postfrontal northerly winds which last for several days. 

Gulf cyclones periodically develop in the northwest Gulf of Mexico and impact much of the 

northern Gulf including Louisiana. Cyclogenesis in this region has been studied by several 

investigators (Heclanan and Thompson 1978; Atlas et al ., 1983 ; Murty et al ., 1983 ; Lewis and 

Hsu 1992). Atlas et al. (1983) suggested that cold air outbreaks in the northwest Gulf can 

produce cyclonic vorticity in the lower levels of the atmosphere which can lead to the formation 

of a Gulf cyclone . Perturbations in the jet stream enhance development of extratropical storms 

and if only one mechanism is in place, cyclogenesis may be weak or may not even occur . The 

authors further contended that during El Nino years the southward displaced polar jet results in 

an abnormally large number of Gulf cyclones . 
SHIP SHOAL DEPOSITIONAL MODEL 

SE 

NE 

SW 

TRANSGRESSIVE REGRESSIVE 

., . Shoal crest Back Shoal ~ Distributary Prodelta UnS dimentsed 

Lower Shoal - Lagoon Delta Front 

Figure 3 Sedimentary fades of Ship Shoal (modified from Penland et al., 1986) . 
8 

The migrating mid-latitude type cold front is the most common of the three and perhaps 

produces the most significant changes at the coast. Periodically a teleconnection between the 

eastern Pacific and North American continent exist producing stormier conditions in the Gulf of 

Mexico . This teleconnection can be linked to large-scale circulation changes associated with 

warming events in the eastern tropical Pacific. A vigorous low-latitude mean flow across the Gulf 

of Mexico and increased frontal activity result in stormier weather in this region as mid-latitude 

cyclones are steered to lower latitudes. Migrating mid-latitude cyclones can produce strong prefrontal winds which raise water levels in Louisiana bays. With the passage of a front, strong postfrontal northerly winds increase wave energy conditions. Storm waves propagate landward on a 

super-elevated water surface thereby concentrating wave energy higher on the foreshore profile 

causing erosion . 

Summer temperatures of 100° F or more are not uncommon in the northern portions of the 

state. This is particularly apparent during prolonged dry periods when a reduction in cloud cover 

allows significant increases in solar radiation reaching the earth's surface. Daytime highs have 

occasionally reach 110° F with an all-time high reaching 114 F in Bossier Parish . Along the 

coast, higher humidity and more consistent cloud-cover reduces insolation thereby moderating 

daytime temperatures in the 90's . The combination of high humidity and temperatures produces 

heat index values of 110° F on a regular basis . Such high values frequently occur in conjunction 

with reduced air quality. 

Freezing temperatures are a relatively common component of winters in Louisiana, although 

occur seldom along the coast. In the northern parishes, several running days of freezing 

temperatures are not uncommon. A minimum temperature of -16 ° F was recorded in Webster 

Parish . By contrast, along the coastal parishes, temperatures rarely fall below zero and when they 

do, the freeze does not exceed 48 hours . During cold front events, particularly "Arctic 

Outbreaks", strong northerly winds may reduce temperatures to 0 OF . 

Although a number of large rainfall events have been associated with frontal passages, 

tropical storms and hurricanes induce, by far, the highest rates of precipitation, particularly in the 

coastal parishes (State Climatologist, personal communication, 1995) . Unpublished data from the 

Southern Regional Climate Center at Louisiana State University show that single totals of 

approximately 1050 mm are common across the state annually. Historical reviews (Faiers et al., 

1994) suggest that several sites have experienced one-day totals over 380 mm and the state's 

maximum of 559 mm recorded in Cameron Parish in 1962. Monthly accumulations of 760 mm 

have been recorded at several sites around the state . In the north this can be attributed to frontal 

activity and to tropical cyclone activity in the coastal parishes . Annual rainfall in excess of 203 

cm has been reported on numerous occasion around the state with an all time record of near 2850 

mm set in New Orleans in 1991 (State Climatologist, personal communication, 1995). 
9 

Cyclones 

One of the most important causes of shoreline erosion on Louisiana's barrier islands is the 

frequent occurrence of hurricanes and major storms . Striking the Louisiana coast approximately 

once every three years (Neumann et al ., 1992), hurricanes account for as much as 90% of 

shoreline retreat. Based on the analysis of historic maps and storm records, Kahn (1980) showed 

that the hurricanes accounted for 50-90% of total shoreline retreat in the Chandeleurs . Hurricane 

Camille (1969) and Frederic (1979) each caused between 40 and 80 m of shoreline erosion. 

Hurricane Audrey (1957) accounted for dune crest retreat of between 15 and 91 m along the 

Chenier Plain coastline (Morgan et al., 1957) . Muller and Fielding (1987) noted that the peak 

frequency (13%) for hurricanes and tropical storms occurs in September. While the Atlantic Basin 

hurricane season officially extends from June 1 to November 30, a review of past tropical events 

indicates that Louisiana has experienced storms as early as late May, with the state's season 

essentially ending in October. No storm has made landfall in the state during the month of 

November in over one hundred years with only three systems extending west of 90° longitude in 

the Gulf of Mexico during that month. During the 20th century, approximately seventy tropical 

storms have made landfall in or near the state (Neumann, 1992), including more than two dozen 

hurricanes . The earliest recorded hurricane to impact the area was in 1711 when a three-day 

storm was reported in September in the general area of modern-day New Orleans (Dr. Donald 

Davis, Louisiana State University, personal communication, 1995) . 

Neumann et al. (1992) presented tropical cyclone tracks and statistical summaries for storm 

systems traversing the North Atlantic during the period 1871 through 1992 . The report showed 

that Louisiana experienced among the fewest hurricane landfalls over a period of one hundred 

years when compared with the remainder of the northern Gulf from Texas to Florida. Grymes 

(1995) provides a map of Louisiana showing frequency of hurricane and tropical storm landfall 

between 1886 and 1993 . The western half of the Isle Dernieres was the worst affected coastal 

segment which experienced five hurricanes and four tropical storms . Chandeleur Islands, because 

of their shoreline orientation, has the lowest incidence of storm landfalls. Of all hurricanes to 

impact Louisiana, only two have been classed as "major", i .e ., category 4 or 5 . These were 

Audrey (1957) and Camille (1969) . 

The most recent hurricane to have impacted the coast was Andrew in 1992 . Stone et al. 

(1993) provide a comprehensive chronological overview of the climatological and hydrological 

aspects associated with Hurricane Andrew and its morphological impacts along the Louisiana 

coast. The initial storm surge effects in Louisiana's coastal marshes were experienced when the 

system was over 150 miles offshore . Storm surges were found to exceed 1 .2 m in the marshes 

that coincided with the front right quadrant of the system. In addition, the vast majority of storm 

wave inundation and morphological change occurred east of the storm track along the barriers east 

of Point Au Fer Island to Grand Isle . A more detailed account of the climatology and 

meteorology of Hurricane Andrew has been provided by Grymes and Stone (1995) . Stone and 

Finkl (1995) provide a collection of research papers dealing with the meteorology, sea state and 

biophysical impacts of Hurricane Andrew on the Florida and Louisiana coastal zones. Impacts 
10 

of Hurricane Andrew on tree mortality and nutrient flux as well as the structural impact on the 

forested wetlands of the Atchafalaya Basin have also been identified in this report . 

In the Atchafalaya, Terrebonne, and Timbalier bay systems, evidence indicating two 

contrasting effects of the storm surge was presented by Halford (1995) : first a period of rapid 

water level increase (or decrease depending on location relative to the storm tracks) within a short 

period of time (3 to 6 hours) during which most marsh destruction took place, and most of the 

coarse-grained sediments were deposited on the marsh surface; second, relaxation of the water 

surface occurred after the storm moved inland over an approximate 24 hour period, during which 

the fine-grained sediment was distributed across the marsh surface. 

On synthesizing the data obtained from various authors on the impacts of Andrew on 

Louisiana, Stone and Finkl (1995) made some important conclusions that have direct significance 

to this study. Firstly, while the barrier systems underwent a phase of destruction during the 

hurricane, particularly those along the Isle Dernieres, some post-storm recovery was apparent 

during over flights three years later . Secondly, the pre-storm condition of the rriarshes 

pre-determined the severity of response to Andrew. Stable marshes showed evidence of vertical 

accretion after the storm in many areas, whereas unstable marshes underwent severe destruction. 

A model elucidating the linkage between atmospheric forcing and coastal morphosedimentary 

response has not yet been developed for regions of the Louisiana coast. In addition, while the 

historical record of shoreline change has been established a detailed evaluation of the role of 

hurricanes in long-term shoreline migration has not yet been established. 

Waves, Tides and Sea-Level 

The study area and its vicinity can be categorized as a low energy environment . In a 20 

years (1956-1975) hindcast Wave Information Study (WIS) conducted by the U.S . Army Corps 

of Engineers (Hubertz and Brooks, 1989), statistics from the hindcast stations adjacent to the study 

area indicated an annual-mean significant wave height of 1 .0±0.2 meters and mean peak period 

of 4 .5 - 6 .0 seconds. The maximum hindcast wave heights at the same stations exceeded 5 m, and 

the wave peak period associated with the largest wave exceeded 11 seconds. The monthly mean 

significant wave heights in winter months (Dec. - Mar.) were 0 .2 - 0.6 m higher than that of the 

rest of the year . The data also show that the predominant wave directions were from the 

southeastern quadrant. 

Despite the dominant low wave energy environment in the study area, tropical storms and 

hurricanes influence sea state significantly . The 20-year hindcast of hurricane waves shows that 

the significant wave height for a 50-year return period is greater than 15 m. The 5-year return 

period significant wave height approximates 6-7 m. Fair weather wave conditions can be estimated 

using data from the Wave Information Study for the period 1956-1975 (Hubertz and Brooks, 

1989) . At hindcast stations 18 (28 .SN, 91 .SW), 19 (28.SN, 91 .UW), 19 (28.SN, 90.SW), located 
11 

south of the Isle Dernieres and Timbalier Islands, the data show an average wave height of 

1 .0±0 .2 meters and period of 4 .5-6 .0 seconds. The dominant wave directions are from the 

southeast quadrant (90°-180°), the percentages of occurrence of hindcast waves in this quadrant 

are 42% (station 18), 67% (station 19) and 68% (station 20) . Additional discussion of these data 

is presented in Chapter 4 of this report . 

Tidal patterns in the Gulf of Mexico differ markedly from other ocean basins in that tidal 

range extremes are determined by the astronomical declination of the moon rather than the 

cumulative gravitational effects of the moon and sun on the earth . When the moon reaches 

maximum declination, the diurnal (daily) tidal producing forces reach a maximum and the 

resulting Tropic tides achieve a relatively large range (typically 60 cm in the Louisiana area) . 

Conversely, at minimum declination when the moon lies on the equatorial plane, tide producing 

forces are reduced resulting in lower Equatorial tides (typically less than 15 cm) having a 

semidiurnal or mixed pattern around the Louisiana coast. Over a lunar month, two periods of 

Tropic and Equatorial tides are evident around the Louisiana coast, although this may be 

significantly influenced by local conditions including freshwater discharge to the coast . The 

dominantly diurnal tidal pattern in the Gulf may be attributed to the system having a period of 

oscillation which closely approaches the diurnal harmonic of 24 hours (Mariner, 1954) . This 

hypothesis has been questioned because of independent findings showing significantly smaller 

resonant periods in the Gulf, and the necessary inclusion of a non-existent amphidromic point in 

the middle of the Gulf to satisfy Mariner's argument (Royer and Reid, 1966 ; Zetler and Hansen, 

1970) . 
12 

3 Wave Models 

Introduction 

Several numerical models exist with the general capabilities of wave height prediction from 

deep water to the break point. These models define the wave field as monochromatic or single 

period waves, one-dimensional spectral waves, two-dimensional spectral waves or shallow water 

waves. As presented earlier, the objectives of wave modeling in this project are two-fold: (1) 

large-scale (or global scale) modeling that provides the wave characteristics across the southcentral Louisiana shelf, including the study area; and (2) local wave modeling that outputs higher 

resolution information (e .g . wave breaking) to evaluate the potential impacts of shoal removal on 

nearshore wave conditions . Several of the more commonly used models are presented below and 

evaluated for the use in this study . Additional model reviews may be found in Holthuijusen et al., 

1989; O' Reilly and Guza, 1991, 1993) . 

RCPWAVE 

RCPWAVE is a short-wave numerical model used to predict linear, plane wave propagation 

over an open coast region of arbitrary bathymetry (Cialone et al., 1992) . The model solves finite 

difference approximations of an elliptical equation (Berkhoff, 1972, 1976) in a significantly 

simplified form to estimate the complete linear wave transformation process with the restriction 

of a mild bottom slope . This is accomplished using the following three equations 

1 a2 a + a2a + 1 (Da~V(CCg)) +k2-IVs1Z=O 

a ax 2 ay 2 ccg 

(JVsJ sin6 ) + ((OsJsin6 ) = 0 

y 

a (a Z ccgIvsI pose ) + (a Z CCgIOsI sin6 ) = 0 (3) ~ 

y 
13 

In the above equations, 

x,y =two orthogonal horizontal coordinate directions 

a(x,y) =wave amplitude function 

C(x,y) =wave celerity 

Cs(x,y) =group velocity 

k(x,y) =wave number 

s(x,y) =wave phase function 

8 =local wave direction 

RCPWAVE uses linear wave theory because it has been shown to yield fairly accurate first-order 

solutions to wave propagation problems and at a relatively law cost. Refractive and bottominduced diffractive effects are included in the model; however, the model can not treat diffraction 

caused by structures extending above the water surface. Application of this model does not 

include nonlinear effects nor a spectral representation of irregular waves. 

REF/DIF 1 

This combined refraction-diffraction wave model (Kirby and Dalrymple, 1993) is a weakly 

nonlinear numerical model that is based on a parabolic equation governing the complex amplitude 

A of the fundamental frequency component of a Stokes wave . The governing parabolic equation 

is given by : 

2ikCCgAz + 2k(k ko)CCgA + i(kCCg)A + (CCgA y)y - k(CCg)K 'o 1ZA = 0 (4) 

where (x,y) are horizontal coordinates, lco is a reference wavenumber related to the initial 

conditions of the incident wave, C is phase speed, Cs is group velocity, and 

Kl=k3 C cosh4kh+8-2tanh2kh 

Cg 8 sinh4kh 

(5) 

This model applies a nonlinear approach to compute wave propagation, dissipation and breaking . 

It includes both refraction and diffraction effects explicitly, thus permitting the modeling of waves 

in regions where the bathymetry is irregular and where diffraction is important. Unlike the wave 

tracing technique, it computes wave heights and directions on a model grid rather than on 

irregularly spaced rays. Therefore, regions where wave rays cross due to local focussing or where 

caustics are caused by other means are treated correctly, and no infinite wave heights are predicted 

(Kirby and Dalrymple, 1993) . REF/DIF 1 assumes a mild bottom slope (< 1 :3) and weak 
14 

nonlinearity . In dealing with nonlinearity, REF/DIF 1 applies a hybrid model which provides a 

smooth patch between the Stokes dispersion relationship, valid in deep water, and Hedges'(1976) 

dispersion relationship that is used in shallow water where the Stokes relationship becomes invalid 

when the Ursell parameter exceeds 40. It is capable of simulating the energy dissipation in the 

following forms : (1) Laminar surface and bottom boundary layer; (2) Turbulent bottom boundary 

layer; (3) Porous sand ; and (4) Wave breaking. 

Although REF/DIF 1 can compute numerous frequencies per computer run, it can only 

calculate waves at a single frequency per calculation because the wave-wave interactions between 

different frequencies are not included . Therefore, REF/DIF 1 is an efficient model to be used for 

monochromatic waves. 

REF/DIF S 

REF/DIF S (Kirby and Ozkan, 1994) is a weakly nonlinear combined refraction and 

diffraction model that simulates the behavior of a random sea over an irregular bottom 

bathymetry, incorporating the effects of shoaling, refraction, energy dissipation and diffraction. 

It includes most features present in the model REF/DIF 1 so it can also be used to model the 

behavior of monochromatic waves. 

REF/DIF S is used with two-dimensional wave spectra. The input frequency spectrum in 

conjunction with a directional spreading function are divided into discrete wave components 

characterized by a certain frequency and direction . REF/DIF S stacks parabolic models for the 

individual wave components, propagating them simultaneously through the domain. After each 

step, the complex amplitudes for all wave components are known and the significant wave height 

H 3 can then be computed in the following manner 

N 

Hvs(xxY)= 81: O(x~Y) 

n=1 

(6) 

where N is the total number of wave components and A(x,y),, is the amplitude of the wave 

component n . The authors of REF/DIF S are continuing to develop the spectral capabilities of 

the model. A new version that will include the wave generation (wind forcing) was being 

developed at the time of writing . 

STWAVE 

STWAVE is a finite-difference model for near-coast time-independent spectral wave energy 
15 

propagation simulations (Cialone et al., 1992) . It is based on a simplified spectral balance 

equation 

N 

a (cc E~;+ a (cc UB)) +ES;=o 

E 

ax g ay i=1 ' 

where E(f,6) =spectral energy density 

f =frequency of spectral component 

B =propagation direction of spectral component 

S; =source terms (shoaling, refraction, wind forcing, wave-wave 

nonlinear interactions, bottom interaction, etc.) 

STWAVE simulation requires a wave energy spectrum specified for the input boundary of the 

computational grid . It transforms the spectrum across the grid, including refraction and shoaling 

effects . The spectrum is modified to include the effects of bottom diffraction and the 

convergence /divergence of energy influenced by the local bathymetry. Wind-wave generation, 

nonlinear energy transfer, wave field and wave-bottom dissipation and wave breaking are 

considered. The model is computationally efficient because of its assumption that only wave 

energy directed into the computational grid is significant, i .e ., wave energy not directed into the 

grid is neglected. STWAVE has been successfully used in several projects (Kraus et al., 1994; 

Dr . Don Resio, personal communication) . 

Comparison of the Models and Selection 

The models described previously are compared against the following criteria : representation 

(scale), efficiency, accuracy, spectral capability, computational grid size requirement, breaking 

criteria, and wind-wave generating . The performance of each model against the criteria is shown 

in the matrix overleaf . 

It is apparent from the matrix that STWAVE has the highest composite score because of its 

spectral capability, inclusion of a wind-forcing function, high accuracy, and high efficiency . Thus, 

considering the objectives of the study, STWAVE was selected for use in this study. 
16 

RCPWAVE STWAVE REF/DIF 1 REF/DIF S 

Representation Global Global Local Local 

Efficiency High High High Moderate 

Accuracy N/A Documented 

Yes' 

Documented 

Yes' 

Documented 

Yes2 

Spectral Capability No Yes No Yes 

Grid Size 

Requirement 

Restricted by 

ox/0y, not 0x 

or Ay 

0 x < 0.5 L 

Recommended 3 

O x < 0 .2 L 

Required ° 

0 x < 0.2 L 

Required 4 

Breaking Criteria Weggel(1972) Resio(1987) Dally et al. 

(1985) 

Thornton and 

Guza(1983) 

Wind-Wave 

Generating 

No Yes No YesS 

1 - Kraus et al., 1994 

2 - Vincent and Briggs, 1989 ; Berl:hoff et al., 1982 

3 - Dr. Resio, personal communication, 1995 

4 - Kirby and Ozkan, 1994 

5 - In a new version being worked on at the time of writing 

Wave Transformation During Hurricane Andrew 

Deep water wave boundary conditions obtained from a calibrated hindcast model were used 

to simulate the rate of energy dissipation of long waves across the Louisiana continental shelf 

during Hurricane Andrew. The simulation represented deep water wave conditions off the 

Louisiana coast when Hurricane Andrew reintensified prior to landfall, and transformation of these 

waves during shoreward propagation and breaking along the coast using a standard depth-limiting 

instability ratio (McCowan criterion) . 

A wave-energy dissipation model (WAVENRG) was used in this study to simulate wave 

propagation and decay across the Louisiana shelf during Hurricane Andrew . The model, written 

by May (1973) and modified by Stone (1991), applies linear wave theory to simulate the first 

order wave field across a bottom slope by computing wave refraction, shoaling and bottom 

friction . The model was adopted for use in this study because it readily provided output by which 

near bottom maximum orbital velocities could be calculated in addition to two dimensional 

changes in wave-energy dissipation and attenuation . By assuming that there is no significant 

energy loss due to internal friction, friction at the free surface, adverse currents, or percolation 
17 

into the bottom (May, 1973), the wave height at a specific location (i .e . water depth) can be 

described given a known deep water wave height, by 

H~ =K~KSHo (g) 

In (8), K, is the refraction factor, KS is the shoaling factor and Ho is the wave height . 

In addition to K~and K5, the bottom friction also causes decay of the wave height . The time 

rate of energy dissipation due to bottom friction is 

dE -cfp u 

dt 

(9) 

where cr (-0.03, see May, 1973) is a dimensionless friction coefficient, p is water density and 

u is the near-bottom horizontal wave orbital velocity whose linear expression is 

u = 

TE H cos(kx -c) t) 

Tsinh(kD) 

(10) 

where T is wave period, w is the radian frequency, and x denotes the direction of wave travel 

direction. Since u in (10) is periodic, the mean rate can be computed by 

dH _ 1 T 4c~u 3 

(' dt (11) 

dt T~ gH 0 

The change of wave height in space (along a ray) will be: 

ax _ 2Tcfw3H2 

- - (12) 

3 L n g sinh3(kD) 

Therefore, the wave height loss due to bottom friction is : 

TC W3H2 

SH= -0 .67 f f dx (13) 

L n gsinh3(kD) 

xo 
18 

Combining (8) and (13) gives the estimated wave height, i .e . 

H~ =K,KSHo + SH (14) 
19 

4 Data Acquisition 

Introduction 

Computational bathymetric grids and deep water wave conditions (directional amplitude and 

period weighted by frequency of occurrence) are necessary inputs for numerical modeling of 

surface wave behavior across the study site . Three different types of bathymetric grid were 

generated for application in this study. The grids differed in resolution, and underwent embedding 

of "local" (high resolution) in "global" (coarser resolution) grids. A quantitative inventory and 

assessment of the wave climate in the vicinity of the study area is presented in addition to 

quantification of wave parameters at the offshore boundary of the computational grids . 

Bathymetric Grid Development 

Multiple bathymetric data sources were acquired to establish the computational grids . These 

data sources included National Ocean Service (NOS) bathymetric charts and U.S . Geologic Survey 

(USGS) field surveys conducted in 1984 and 1986 (List et al., 1994) . Two types of NOS charts 

(Scale 1 :80,000, Mean Lower Low Water North American Datum of 1983 ; and Scale 1 :458,596, 

Gulf Coast Low Water Datum of 1927) were digitized to produce respective grids. The USGS 

survey data were then embedded in the lower resolution digitized data set to reflect the most recent 

bathymetry . Modular GIS Environment (MGE) software was used to digitize, manipulate, 

analyze, and display data on creating the bathymetric grid file . The software includes MGE 

Nucleus, MGE Coordinate System Operations, MGE Projection Management, MGE Grid 

Generation, and MGE Terrain Analyst2 . All work was carried out on the Microstation 

environment which is a CAD product from Bently Systems Incorporated . Hardware support was 

Intergraph's Clix and TD workstation systems. Two three-dimensional seed files with two 

different projections for the study site were generated using the MGE Coordinate System. One 

seed file was a UTM (Universal Transverse Mercator) projection with the North American Datum 

in zone 15 . The second seed file was a Mercator projection with the North American 1983 datum. 

There are two main methods that can be used to convert a base map to a design file . One 

is to create a design ale from scanned base-map features and the other is to digitize base-map 

features . In this project, the digitizing method was selected, because water depths were more 

easily digitized directly from the map than scanned and converted to text in the design file . A 

blank design file called lafourch.dgn, based on the Mercator projection seed file was created. The 

central Meridians and parallels were set. The map was affixed to the digitizing table and a design 

file setup based on at least four selected control points on the map. When the error was less than 

a given value (0.02%), the setup was accepted and digitizing to a graphic design file commenced. 

On completion of the digitizing procedure, the MGE Terrain Analyst module was used to 

manipulate the file . 
20 

The MGE Terrain Analyst is a specialized software package developed by Intergraph 

Corporation for the analysis, manipulation, modification, and graphical display of computerized 

terrain-modeling data. Graphic design files are used for loading features (elements), placing 

terrain displays, and performing analysis . The 3-D design file features, which include coastline 

position and water depth, were loaded into a TIN (Triangular Irregular Network) model using 

Import Design File Features . The TIN model was created from the terrain features using Convert 

Feature. A TIN model consists of a set of triangular facets formed from the coordinates of point, 

linear, and area features. Because each feature coordinate defines a triangle vertex, it maintains 

triangular-neighborhood and feature-type relationships and all input data points are preserved . This 

method provides an efficient, yet precise, method of representing the terrain surface . The model 

is stored in a file with .TIN extension. Because the regular ASCII grid file requires the Grid 

model, the TIN model is converted to the grid model . 

A grid model is defined as ~a regular matrix of elevation/depth values referenced to a 

common datum. Data in the grid model were formatted in a binary data storage format that 

conformed to Intergraph corporation's standard grid format . The Grid model was converted from 

the TIN model using the function TIN to GRID and the appropriate grid spacing defined. 

A lower resolution grid was developed for purposes of simulating wave propagation and 

energy dissipation during Hurricane Andrew. The bathymetric grid (Figure 4) used in this phase 

was generated from digitizing NOS Chart 1116A (Scale 1 :458,596) which covers the area from 

26 .85 °N to 29 .82 N and from 89 .2 W to 93 .52 W. Grid dimensions of 180 x 240 were 

established with a square grid size of 2 .293 km . 

The core component of this project necessitated a substantially higher resolution grid 

representing bathymetric configurations in intermediate and shallow water. The grid developed 

has dimensions of 432 x 910 with a square grid size of 100 m. The data were digitized from 

NOS Charts 11356 and 11357 (Scale 1 :80,000; North American Datum of 1983) covering the area 

from 28° 35'N to 29 20'N and 90 11' W to 9''1 30'W (Figure 5) . The digitized database was 

updated by embedding the data from a USGS field survey conducted in 1984 and 1986 (List et al., 

1994) (Figure 6) . The vertical datum for the soundings is Mean Lower Low Water (MLLW), 

determined from the Grand Isle tide gauge from 1960 to 1978. A high resolution gridding interval 

was established for more detailed work on the shoreface with spacing on the Y axis (onshoreoffshore) of 22 .5 m and 135 m in the X (alongshore) direction. 

Deep Water Database for Winter Storms and Fairweather 

The deep water wave inputs representing winter storms and fairweather conditions were 

obtained from three sources (Table 1) : (1) 20 years (1956-1975) of hindcast data obtained from 

the Wave Information Study (WIS) (Abel et al., 1989 ; Hubertz and Brooks, 1989) ; (2) National 

Oceanic and Atmospheric Administration (NOAA)'s National Data Buoy Center (NDBC) buoy 

42017 (25 .9°N, 89.7°'vV) ; and (3) Louisiana-Texas Shelf Physical Oceanography Progra (LATEX) 
LA Barrier Island Study Bathymetry 

110 

100 

90 

so 

70 

60 

50 -

40 -

30 

20 

10r 

21 

Figure 4 Low resolution bathymetric grid used in Hurricane Andrew simulations . 

20 40 60 80 100 120 140 160 180 200 

Km 
22 

Study Area 

40 

85 

30 

n. ca~ 

~Ie 20 

20 

r

: : :. . . 

.: t' r'~= 

~ i r i w- : I 

:.rf' :s~v.,r 

30 25 20 15 10 5 0 

m eters 

Figure 5 High resolution bathymetric grid across the inner shelf incorporating Ship Shoal. 

1 D 30 40 50 60 70 80 90 

km 
23 

Isles Dernieres, USGS 

8000 L 

6000 -_i 

VONA 

4000 

E 

2000 

:

. 

40 

a+ " 

0 0 .5 1 1 .5 2 2 .5 

m eters 

10 9 8 7 6 5 4 3 

3 

2 1 

3 .5 

x 104 

0 

Figure 6 High resolution bathymetry of Ship Shoal and its vicinity, surveyed by USGS in 

1986. 
24 

station 16 (28.9°N, 90.5°VV) (unpublished data supplied by Dr. Steven F. DiMarco, Texas A&M 

University) . 

Table 1 . Sources of wave climate data 

Sources Lat. (N) Long. (VV) Water Depth (m) 

WIS 19 28 .5° 91 .0° 33 

WIS 20 28 .5° 90.5° 38 

WIS 21 28 .5° 90.0° 91 

NDBC 42017 27 .5° 90.5° 407 

LATEX 16 28 .9° 90.5° 21 

Among the three sources, the WIS data set provides the most complete information. 

Statistics from three hindcast stations 19, 20, and 21 (Figure 7 for locations) had shown an annualmean significant wave height of 1.0±0 .2 meters and mean peak period of 4.5 - 6 .0 seconds. The 

maximum wave heights from these stations exceeded 5 m, and the wave peak period associated 

with the largest wave exceeded 11 seconds. The monthly mean significant wave heights in winter 

months (Dec . - Mar.) were 0.2 - 0.6 m higher than that of the rest of the year. The predominant 

wave directions were from the Southeastern quadrant (135 .0°, 112.5°, and 90.0° for Stations 19, 

20 and 21 respectively). The average directions associated with the largest waves were also 

mostly from this quadrant (125°, 117°, and 112° for the three stations) . If the percentages of 

occurrence of wave directions being in the range of 90° - 180° are summed, the percentages for 

the four stations are 76 %, 85 %, and 85 % respectively . 

Among the buoys that NDBC has administered within the Gulf of Mexico, 42017 (27 .5°N, 

90.5°VV) is more significant for the purpose of the current project because of its close location to 

the study area (Figure 8). However, only 6 months (Apr. - Sep. 1989) of data are available from 

NDBC 42017. Although limited, the time series shows that the monthly mean significant wave 

heights ranged from 0.6 to 1 .4 m (Figure 9) and peak periods from 4.5 to 5 .3 seconds (Figure 

10) . A storm at the end of July, 1989 generated the maximum significant wave height of 5 .1 

meters for the 6-month period . The peak period corresponding to the largest wave was almost 8 

seconds. The 12-month (Aug. 1991 - Jul. 1992) time series from buoy 42001 (25.9°N, 89.7°W) 

showed that the monthly mean significant wave heights ranged from 0.6 to 1 .8 m and monthly 

mean peak periods from 4.3 to 5 .5 seconds (Figures 11 and 12) . The monthly mean significant 

wave heights, which also show a decreasing trend from winter to summer months, compared 

reasonably well with the WIS hindcast data. No wave directions were recorded during both 

periods . 
25 

Figure 7 Map of Wave Information Study stations in the Gulf of Mexico . 

100°W 5 10 15 20 25 30 35 48oa~ '~ 
26 

1 42009 

---30oN--------------- -- 

4201 0 -------- ' - ------- A---- 42005---------- 

42008 42011 42007 42012 

4201? ; 42004 ~42036 

~ 4006 

~ ;42001 ~ 

------- ~--4~0~-2=------- -----------4~Ofl3------------------- ---

9a°W 90°W 86°W 

Figure 8 Map of National Data Buoy Center stations in Gulf of Mexico. 
27 

5 

N 

NDBC 42017 

apr 89 

1 11 111 1 11 I I IIII I I I 

0 120 240 360 480 600 720 840 

5 

E may 89 

y 

I ~ V 

O C !1 V11 I11 III - 1 I ~ I I l I I 

0 120 240 360 480 600 720 8 40 

5 

jun 89 

H 

0 I I~ I i ~ I i I ! 6 

0 120 240 360 480 600 720 84 0 

5 

j 1 89 

y 

0 

0 120 240 360 480 600 720 84 0 

5 

z 

aug 89 

0 u r n r i r~^ i I ~-~ I 

0 120 240 360 480 600 720 840 

5 

E 

y 

z 

0 

sep 89 

0 120 240 360 480 600 720 - 840 

hours 

Figure 9 Time series of Hs from NDBC 42017, April - September 1989 . 
10 

N 

5 

00 

10 

N 

5 

00 

10 

,. 5 

00 

10 

`n 5 

00 

10 

CA 

5 

00 

10 

H 

~: 5 

0~ 

NDBC 42017 Zs 

120 240 360 480 600 720 840 

May 89 

120 240 360 480 600 720 840 

360 480 600 720 

120 240 360 480 600 720 840 

Aug 89 

120 240 360 480 600 720 840 

Sep 89 

120 240 360 480 600 720 840 

Hours 

Figure 10 Time series of Tp from NDBC 42017, April - September 1989 . 
NDBC 42001 

4 

x 

0 

Aug 91 

29 

0 

4 

N 

2 

O 

4-

E 

x 

00 

4 

E 

vi 2 

x 

00 

4 

x 

0 

0 

4 

N ` 

lzu 24o 360 480 600 720 840 

120 240 360 480 600 720 840 

360 480 600 720 840 

120 240 360 480 600 720 840 

120 240 360 480 600 720 840 

Jan 92 

0 120 240 360 480 600 720 840 

Hours 

Figure l la Time series of Hs from NDBC 42001 August 1991 - January -1992 . 

a 
NDBC 42001 30 

4 rev az 

x w 

0 0 120 240 360 480 600 720 840 

q Mar 92 

0 0 120 240 360 480 600 720 840 

4 Apr 92 

E 

vi 2 

0 0 120 240 

4 

N 

Z 

120 240 0 0 

4-

E 

z 

00 

720 840 

Jun 92 

360 480 600 

No data for May 92 

360 480 600 720 840 

120 240 360 480 600 720 840 

Hours 

Figure 1 lb Time series of Hs from NDBC 42001 February 1992 - July 1992 . 
NDBC 42001 

10 31 

Aug 91 

N 

~ 5 

0 0 120 240 360 480 600 720 8 40 

10 

Sep 91 

fl- 5 

0 0 120 240 360 480 600 720 8 40 

10 

' Oct 91 

N 

c:z 5 - `~ .MJ 

0 

0 120 240 360 480 40 

10 

Nov 91 

N 

0 0 120 240 360 480 600 720 8 40 

10 

Dec 91 

5 

0 0 - 120 240 360 480 600 720 840 

10 

Jan 92 

N 

5 

00 120 240 360 480 600 720 840 

Hours 

Figure 12a Time series of Tp from NDBC 42001 August 1991 - January 1992 . 
32 

10 

N 

5 

0 

0 

10 

Vl 

5 

0 

0 

10 

N 

5 

0 

0 

10 

5 

0 

0 

10 

N 

~- 5 

0 

0 

NDBC 42001 

feb 92 

120 240 360 480 600 720 

mar 9e 

120 240 360 480 600 720 

apr 92 

120 240 360 480 600 

no data for may 92 

720 

120 240 360 480 600 720 

120 240 360 480 600 720 

hours 

Figure 12b Time series of Tp from NDBC 42001 February 1992 - July 1992 . 
33 

LATEX station 16 (28.9°N, 90.5°VV) is located within the general study area. The wave data 

recorded by MiniSpec (Coastal Leasing, Inc.) directional wave gauges during a 6-month period 

(Dec. 1993 and Feb. - Jun. 1994) show that the monthly-mean wave heights varied from 0.3 to 

1.3 m and period from 5 .5 to 6 seconds (Figures 13 and 14). The dominant wave directions agree 

with the previous data sets showing the importance of southeasterly approaching waves (Figure 

15). On synthesizing these data, four scenarios are presented which represent the respective deep 

water wave conditions for fairweather through severe storms--excluding hurricanes (Table 2) . 

Table 2 . Incident wave parameters used for deep water wave boundary conditions 

Case HS(m) Tp(s) APPROACH 

DIR. 6(deg.)' 

DESCRIPTION 

1 6 11 -45,00, +45 Severe Storm 

2 4 9 -45,00, +45 Strong Storm 

3 2 6 -45,00, +45 Weak Storm 

4 1 5 -45,00, +45 Fairweather 

1-45 = SOUTHWEST APPROACH 

45 = SOUTHEAST APPROACH 

00 = SOUTH APPROACH 

Deep Water Database for Hurricane Andrew 

Measured deep water wave conditions do not exist for Hurricane Andrew with the exception 

of NDBC data obtained from two buoys located in the left quadrants of the cyclone (see Stone et 

al, 1993, 1995 ; Grymes and Stone, 1995) . Maximum significant wave heights approached 6 m 

at one of the buoys located closest to the storm center, however, this is an underestimation of 

wave conditions in the front right quadrant. Several approaches have been used to estimate the 

significant wave height during hurricanes (Long, 1979 ; Abel et al, 1989 ; Hsu, 1991 ; 1994) . The 

Hsu (1991) method relates maximum significant wave height in deep water to sea-level pressure 

(PO) at the storm center by, 

H =0 .2(1013-Po) (15) 

The equation appears reliable on comparison with measured wave heights during Hurricanes 

Gloria and Kate (Hsu, 1991) and when compared with data sets obtained by Abel et al (1989) (see 
.'T7 ~F~+ 

VV 

C 

M 

CD 

w 

w 

H Ir 

CD 

F+ 

O 

x 

O 

r 

N 

N 

d 

n 

~-1 

W 

Sig. Wave Height, m 

0 

15:00 

12/6/93 - --~--~---~---

18:00 

1217/93- : 

21 :00 :- 

12/8/93 --

0:00 

12/10/93 

3:00 

12/11/93 :-

6:00 

12/12/93 . 

d(A. 

9:00 t 

12/13/93 :-

12:00 

12/14/93 

15:00 

12/15/93 

18:00 - 

12/16/93 --

21 :00 _ 

12/17/93 : - 

0:00 

12/19193 

3:00 

12/20/93 

6:00 

12/21/93

-- 

- 9:00 

12/22/93 --

12:00 

12/23/93 

15:00 -

12/24/93 

N 

N <n 

k 

N 

O 

J 
Uo 

G 

cu 

w 

H 

~~i 

lY 

O 

x 

O 

r 

N 

177 

N 

w 

C 

CD 

Sig . Wave Height, m 

0 

0:00 ° °' ~ °' ^' 

2/15 - --{- 

0:00 

2/21 

0:00 

2/27 --

0:00 

3/5 

o:oo 

3/11 

0:00 

3/17--

0:00 -

/23-- 3 

2:00 

3/29--

2:00 

4/4 

2:00 

41 10 

2:00 

4/16 :--

2:00 : : 

4/22 

2:00 

4128 

2:00 _ 

5l4 

2:00 

5/10 :-

2:00 : : 

5/16 --

2:001 

5/22 

2:00 

5/28 

3:00 

6/3 

N 

tll W 

K 

y 

0 
'T7 

Or~o 

c 

H F+ 

(u 

FJ " 

H 

H 

cD 

x 

N 

t7 

n 

(v 

a' 

w 

15:00 ° -' 

12/6/93 -} 

18:00 

12/7/93 

21 :00 

12/8/93 

0:00 

12/10/93 

3:00 

12/11/93 

6:00 

12/12/93 

12/13193 

12:00 

12/14193 

15:00 

12/15/93 

18:00 

12/16/93 

21 :00 

12!17/93 

0:00 

12119193 

3:00 

12120/93 

6 :00 

12/21/93 

9:00 

12/22/93 

12:00 

12/23/93 

15:00 

12/24/93 

Peak Wave Period, sec. 

n~ w 4 cn o) v oo cn 

-+--++--+ -i iT-i 

k 

O 
Or"o 

., 

v' 

F+ " 

Cu 

O 

y 

b 

O 

N 

x 

N 

w 

C 

co 

~1O 

.P1 

Peak Wave Period, sec. 

00 f0 O 0:00 0 

-+ N 0 4 Ch 0) -4 

2/15 

0:00 

2/21 

0:00 

2/27 

0:00 

3/5 

o:oo 

3/11 

3/17 

0:00 

3/23 

2:00 

3/29 

2:00 

4/4 

Q 2 :00 

4110 

2 :00 

4/16 

2:00 

4/22 

2:00 

4/28 

2:00 

5/4 

2:00 

5/10 

2:00 

5/16 

2:00 

5122 

2:00 

5128 

3:00 

6/3 

ID 

K 

y 

O 

7 

J 
ITI 

w 

N 

CD 

O 

d 

OR 

M 

O 

W 

ON 

N 

C 

n 

CD 

M 

110 

w 

15 :00 ° 

12/6/93 

-- ---- i 

18 :00 

12/7/93 - - 

21 :00 

12/8/93 

0:00 

12/10/93 

3:00 

12/11/93 " x 

6:00 

12/12/93 - - 

9:00 

12/13/93 

12:00 

12/14/93 

X` 

15:00 

12/15/93 = X 

_ 

18:00 

12/16/93 

21 :00 

12/17/93 

0:00 XC 

12!19/93 

x 

3:00 

12/20/93 

- 

x 

s:oo 

12/21/93 

X 9:00 

12/22/93 

12/23/93 

15:00 

12/24/93 

Wave Direction, deg. 

pp N 

O O 

-~--- 

n 

Xx 

~ x* 

x X 

X `x 

XX 

X 

X 

X 

r 

CSC 

ST 

A 

K 

N 

Sir 

X 

J 

X 

x X 

X 

X 

X 

X 

X n 

~X 

X 

x, X 

~X 

XX 

>~ 

x X 

X >~ 

X 
Uv 

C 

v' 

Frrr+yyy " 

N 

cu 

O 

~-h 

n 

r+ " 

M 

d 

r w 

k 

N 

w 

C 

cu 

.A. 

0:00 0 

2/15 -

0:00 

2/21 

0:00 

2/27 -

0:00 

315 

0.00 

3/11 

0:00 

3/17 

0:00 

3123 

z:oo 

3/29 

2:00 

aia 

2 :00 

4/10 -- 

2 :00 

4/16 

2 :00 

4/22 

2:00 

4/28 

2:00 

5l4 

2:00 

5/10 

2:00 

5116 

2:00 

5/22 

2:00 

5/28 

3:00 

6/3 

Sig. Wave Height, m 

fD 

x 

O 

3 

v> 

~p N Wp~ 

O O O O 
40 

Hsu, 1994) . Applying equation (15) off the Louisiana coast implies that HS in deep water, 

approximated 14 m. This is in agreement with observations of inferred wave heights made on 

several platforms off the Louisiana coast (Bothelo et al, 1994) and hindcast data obtained by 

Cardone and Cox (1992) . In the latter, a wave hindcast model was used to generate a twodimensional wave spectrum at hourly intervals for the Gulf. The hindcast data show significant 

wave heights increasing from 8 m off the Florida coast, to 13 .3 m south of the Mississippi River 

delta where the cyclone strengthened before landfall (Stone et al, 1993, 1995 ; Grymes and Stone, 

1995). The hincast data show good agreement when compared with the NDBC buoy tune series, 

although a small phase lag does exist (Cardone and Cox, 1992). 

To simulate peak intensity wave conditions off the Louisiana coast, the hindcast data 

generated by Cardone and Cox (1992) were used as input to the WAVENRG model providing the 

opportunity to incorporate decreases in wave height outward from the storm center, as a function 

of a decaying wind field. The input data are presented in Table 3, and consist of seven sectors 

in which the significant deep water wave height ranges from 11 to 13 .3 m, and the significant 

wave period approximates 14 secs. Water depths in which wave propagation began varied from 

300 m to 1200 m, a location 30 km to 230 km south of Main Pass . A deep water wave approach 

angle of 135 degrees was selected to simulate the storm track of Hurricane Andrew as it moved 

across the Louisiana continental shelf (Stone et al, 1993) . A hindcast storm surge of 0.5 m was 

used for deep water conditions as calculated by Cardone and Cox (1992) . 

Table 3 . Input to Wavenrg obtained from the hindcasts of Cardone and Cox (1992) . 

Section Rays Latitude (°N) Sig. Wave Height 

(m) 

Wave Period (s) 

1 2-14 26.91 - 27 .18 11 .0 14 

2 15-21 27.18-27 .33 12 .0 14 

3 22-35 27.33 - 27 .62 13 .0 14 

4 36-52 27.62 - 27 .97 13 .3 14 

5 53-66 27.97 - 28 .26 13 .0 14 

6 67-73 28.26 - 28 .40 12 .0 14 

7 74-83 28.40 - 28 .50 11 .0 14 

Longitude = 89 .25 ° W 
41 

5 Technical Discussion 

Introduction 

To quantify numerically, the impacts of Ship Shoal on wave climate, the approach taken 

centered on removal of the entire shoal complex from the bathymetric grid. By comparing the 

wave fields obtained from running the wave model over these two grids, the significance of Ship 

Shoal in affecting the wave climates under different conditions was examined. Figures 16 and 17 

show the three-dimensional images of the two bathymetric configurations . As much as 6 m thick 

of sand was removed at the west portion of the shoal, and the total volume of sand extracted from 

Ship Shoal was 1 .1 x 109 m3. It is important to note that this approach was necessary to determine 

the role Ship Shoal plays in mitigating the wave climate. Total removal of Ship Shoal is highly 

unlikely in the foreseeable future given recent estimates of the volume of sand required to restore 

the Isles Derrieres, i.e ., 11 .6 x 106 m3 (van Heerden et al, 1993) . Considering this statistic, Ship 

Shoal could provide enough source material for approximately 95 nourishment/renourishments . 

Wave Transformation Analysis 

Configuration of Model Input and Bathymetric Grid 

As discussed previously, three deep water wave approaches are considered for this project: 

0° (approach direction from the south, 45 (southeast), afld -45 (southwest) with the 

corresponding deep water wave statistics (Table 2). Given a set of input significant wave heights 

HS, peak wave periods TP, and wave directions 8, STWAVE generates a JONSWAP spectrum, 

an input wave energy matrix of 15 frequencies and 35 directions . 

Case 1 (HS=6 m, Tp=11 sec.) 

Case 1 represents a severe storm in the Gulf of Mexico. Three wave directions are simulated 

(southeast, south and southwest) although directional spectra indicate that the main approach 

during storms of this nature in the study area is from the southeast. Figures 18 through 20 

represent the image contour plots of the significant wave height generated by STWAVE for the 

three directions . A sequence of figures is presented for each wave approach where "a" represents 

the wave height distribution with the Ship Shoal in place, "b" represents shoal removal, and "c" 

the percentage difference in significant wave heights attributable to the effects of the shoal on 

wave climate. Interpretation of these figures leads to the following conclusions: 

(1) . Significant wave height increases from west to east across Ship Shoal as a function of a 

commensurate increase in water depth. 

(2). The removal of Ship Shoal results in a significant increase in wave height during this storm 

simulation, although restricted to the leeward flank of the western segment of the shoal. 
42 

SOUTH-CENTRAL LOUISIANA SHELF 

0 

E 

~ -10 

,.. 

a CD 

-u-20 

~ -30 

0 

~0 

Figure 16 3D view of the bathymetric grid, with Ship Shoal. 

J, 100 m/grid 0 I, 100 m/grid 
43 

HYPOTHETICAL SOUTH-CENTRAL LOUISIANA SHELF 

0 

E -10 

a 

d 

L 

~ -30 

0 

.p 

Figure 17 3D view of the bathymetric grid, without Ship Shoal. 

J, 100 m/grid 0 I, 100 m/grid 
44 

Hs=6 m, Tp=11 sec ., theta=0 [S] 

400 

350 

300 

v .` 

~0)2so 

0 200 

r 

- 150 

100 

50e 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 

1 2 3 4 5 6 

Hs, m 

Figure 18a Image of modeled significant wave height, Hs . Case 1, 0 =0°, with Ship Shoal . 
45 

Hs=6 m, Tp=11 sec., theta=0 [NS] 

400 

350 

300 

:i 

X250 

10200 

r 

- 150 

100 

50 

1 2 3 4 5 6 

Hs, m 

Figure 18b Image of modeled significant wave height, Hs. Case 1, 0 =0°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
46 

H s=6 m, Tp=11 sec ., theta=0 

400 

351 

300 

-o .` 

X250 

E 

0 200 

r 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H[S] 

Figure 18c Image of Percentage of HS increase- due to shoal removal . Case 1, 0 =0°. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
47 

400 

- No, 

F

" . .~.~' 

5% 

, . 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 

1 2 3 4 5 6 

Hs, m 

Figure 19a Image of modeled significant wave height, Hy. Case 1, 0 =45°, with Ship Shoal. 

Hs=6 m, Tp=11 sec., theta=45 
48 

Hs=6 m, Tp=11 sec ., theta=45 [NS] 

400 

350 

300 

X250 

F 

Q 200 

r 

- 150 

~ra 100 

5 0 

1 2 3 4 5 6 

Hs, m 

Figure 19b Image of modeled significant wave height, HS. Case 1, 8=45°, without Ship 

Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
49 

Hs=fi m, Tp=11 sec ., theta=45 

400 

350 

300 

v .` 

X250 

E 

0 200 

---7150 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H [S] 

Figure 19c Image of modeled significant wave height, Hs . Case 1, 8 =45°, percentage of HS 

increase due to shoal removal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
50 

Hs=6 m, Tp=11 sec., theta=-45 

400 

350 

300 

i 

X250 

0 200 

r 

-150, 

t 

100 

5 0 

1 2 3 4 5 6 

Hs, m 

Figure 20a Image of modeled significant wave height, Hy. Case l, 8=-45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
51 

H s=6 m, Tp=11 sec., theta=-45 [NS] 

400 

350 

300 

-o .` 

X250 

E 

0 200 

r 

-1501 

100 

50~ 

1 2 3 4 5 6 

Hs, m 

Figure 20b Image of modeled significant wave height, HS . Case 1, 8=-45°, without Ship 

Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
52 

Hs=6 m, Tp=11 sec ., theta=-45 

400 

351 

300 

-v .` 

X250 

E 

0 200 

--:,l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H[S] 

Figure 20c Image of percentage of Hs increase due to shoal removal . Case 1, 8=-45°. 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
53 

(3) . Although the patterns of wave transformation (the west-east increasing wave height gradient) 

and wave height increase (the locality of the most significant increase) due to shoal removal are 

very similar for each wave approach direction simulated, directionality does have important 

implications (Figures 18c, 19c, and 20c) . The magnitude of wave height increase and the area 

within which wave height increases more than 60% are greatest when the wave approach is 

southeast (8=45°) . For example, the greatest value of wave height increase in Figure 19c is 

100 %. Waves propagating from the south (8 =0°) result in a smaller wave height increase--

approximately an order of magnitude less than that associated with southeast waves. Southwest 

(0=45') waves undergo the lowest wave height change in both magnitude and geographical 

extent . This is a direct function of higher rates of energy dissipation and wave attenuation 

seaward of the western flank of the shoal where the inner shelf slope decreases markedly in 

comparison to the east flank. 

Two longitudinal sections (J=150 and J=400) corresponding to a geographic position west 

of Racoon Point and Whiskey Island respectively, are plotted in Figures 21 and 22. The top-most 

panel in each figure is the sectional bathymetric profile pertaining to the inclusion and exclusion 

of Ship Shoal. The three panels below are the plots of the sectional profiles representing the 

outputs for the three incident wave directions in which "a" is a plot of the significant wave height 

generated by STWAVE over the two bathymetric configurations ; "b" shows the change in 

significant wave height due to the removal of Ship Shoal; and "c" represents the depth-limited 

wave breaking index. The data demonstrate that the magnitude of the wave height increase (40-

60%) due to the removal of the shoal on the west flank of the shoal area (Figure 21 a) is much 

larger than that at the east flank (10-20%) (Figure 22a) . The directionality of the changes can also 

be recognized, especially in Figure 21 . Since the unit-width volumes of sand removed from the 

shoal at these two sections are approximately the same, the magnitude of wave height increase is 

more dependent on among other things the local water depth, rather than the removed volume of 

sand . This is because the water depth dictates where wave breaking occurs . The depth-limited 

breaking criteria used in STWAVE is 0 .65 . In Figure 21c, waves from all three directions break 

over the west portion of Ship Shoal. As shown in Figure 22c, wave breaking does not occur over 

the eastern flank of the shoal due to much deeper water depths, although the breaking wave index 

increases substantially . 

It is apparent in both sectional profiles that waves break further inshore (the second breaking 

phase for section J=150) for both simulations with and without the shoal complex . The data 

suggest that removal of Ship Shoal does not impact the nearshore wave field along the Isles 

Dernieres during this particular storm simulation . 

The distribution of wave energy was evaluated qualitatively through wave refraction 

diagrams. Wave orthogonals or rays, were generated for scenarios including and excluding Ship 

Shoal for the three deep water wave approaches (Figures 23, 24 and 25) . In each of the figures, 

"a" represents wave ray patterns for the bathymetry containing Ship Shoal and "b" excludes the 

shoal . Refraction is clearly evident over the western portion of the shoal and is not evident on 

removal of the entire complex . It is worthy of note that laboratory work (Vincent and Briggs, 
J=150, Hs=6 m, Tp=11 sec . 

0 

E 

=-10 

n. 

~ -20 

CO 

: 'r 0--qn 

0 50 100 150 200 250 300 

theta=0 

6 

4 

E 

N 

i 

i 

^ ( I I 

V 

0 50 100 150 200 250 300 

theta=45 

350 400 

350 400 

6 

E4 I 

22 

0 50 100 150 200 250 300 350 400 

theta=-45 

b 

. . 22~ 

C 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure 21a Cross-sectional profiles of significant wave height, Hs along J=150 in Case 1 . 
J=150, Hs=6 m, Tp=11 sec . 

0 

~ -10 

.r 

a 

~ -20 

3: _.Q n 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

a~ 5 0 L . . . 

U 

C 

N 

I 

00 50 100 150 200 250 300 350 400 

theta=45 

a0 50 100 150 200 250 300 350 400 

theta=-45 

100 

0 

50 

U 

C 

N 

0 

~ I 1 I _- I ' ' \ 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure 21b Cross-sectional profiles of percentage of HS increase due to shoal removal along 

J=150 in Case 1 . 
0 

J=150, H s=6 m, Tp=1 i sec . 

~ -10 

a 

~ -20 

m 

3: _ .q n 

1 

. . 

0 50 100 150 200 250 300 350 400 

theta=45 

0 50 100 150 200 250 300 350 400 

theta=0 

i ---v 

0 .5 r 

1 

0 .5 

0L 

0 

1 

50 100 150 200 250 300 350 400 

theta=-45 

0 .5 L 

01 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure 21c Cross-sectional profiles of significant depth-limited wave breaking index, H/h, 

along J=150 in Case 1 . 
J=400, Hs=6 m, Tp=11 sec . 

0 

E 

~ -10 

Q 

~ -20 

.. 

~ _qn 

0 50 100 150 200 250 300 350 400 

theta=0 

6 

4 ~ 

1 

E 

N 

. . . . . 

a l 

0 50 100 150 200 250 300 350 400 

theta=45 

6 

I 

i 

2 

1 

i 

0 

0 50 100 150 200 250 300 350 440 

theta=-45 

6 

4 E j 

c 

s 2~ I 

0 

0 

1 

50 

e 

100 

. 

150 

i 

200 250 300 350 400 

I, 100 m/grid 

Figure 22a Cross-sectional profiles of significant wave height, Hs along J=400 in Case 1 . 
0 

E 

J=400, Hs=6 m, Tp=11 sec . 

~ -10 

Q 

m 

~ -20 

3~ _ .qn 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

T 50- U 

C 

0 50 100 150 200 250 

theta=45 

t 

300 350 400 

100 i 

o 

i 

m 

i 

~0 50 100 150 200 250 300 350 400 

theca=-45 

100 

i 

m 5d . . 

U F 

C 

- f 

i 

r 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure 22b Cross-sectional profiles of percentage of H9 increase due to shoal removal along 

J=400 in Case 1 . 
,i-40u, Ha=6 ill, TP=1I see . 

d 

J7 

i 

t -1di . . . 

4+ 

Q 

-20 

~ -30 

I I I 

S3 5n 10 3 1r'n 233 2 5, ~ ~~~ 7'~~J 4 L 

th eta=0 

1 

0 .5 

0 50 100 150 200 X50 300 350 400 

th eta=45 

1 

T u .~ 

.r j 

I 

1 1 I I ! .rte, so ; oA i se ~~o 250 :;e ;; ~5o 4 0 

theta=-45 

1 

? .5 

~0 so 100 150 200 250 300 350 400 

I, 100 mlgrid 

Figure 22c Cross-sectional profiles of depth-limited wave breaking index, H/h, along J=400 

in Case 1 . 
60 

H s=6 m, Tp=11 sec., theta=0 [S] 

400 

350 

300 

v .` 

X250 

E 

c200 

r 

--:'l 50 

100 

50 

Figure 23a Modeled wave rays when 0 =0° in Case 1 with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
61 

Hs=6 m, Tp=11 sec ., theta=0 [NS] 

400 

350 

300 

i. 

E 

0 200 

r 

'150 

100 

50 

Figure 23b Modeled wave rays when 0 =0° in Case 1 without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
62 

Hs=6 m, Tp=11 sec ., theta=45 [S] 

400 

350 

300 

v .` 

X250 

E 

Q° 200 

r 

= 150 

100 

50 

Figure 24a Modeled wave rays when 0 =45° in Case 1 with Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
63 

Hs=6 m, Tp=11 sec ., theta=45 [NS] 

400 

350 

300 

v .` 

X250 

E 

0 200 

T 

= 150 

100 

50 

_ . r . -- ' -- 1 vh?1° ~1~. 

~~] f,~,~FJ r 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 

Figure 24b Modeled wave rays when 0 =45° in Case 1 without Ship Shoal . 
64 

Hs=6 m, Tp=11 sec ., theta=-45 [S] 

400 

350 

300 

i 

E 

0 200 

--:'l 50 

100 

50 

I Y ~'. `~` : RI {~ 

1 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 

Figure 25a Modeled wave rays when 0 =-45° in Case 1 with Ship Shoal . 
65 

H s=6 m, Tp=11 sec., theta=-45 [NS] 

400 

350 

300 

i 

250 

0 200 

r 

= 150 

100 

50 

Figure 25b Modeled wave rays when 0 =-45° in Case 1 without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
66 

1989) and numerical studies (Kirby and Ozkan, 1994) suggest that the transformation of spectral 

waves displays much less of a refraction effect than when using a monochromatic one. Thus, the 

refraction patterns derived by STWAVE over the shoal are less pronounced than would be evident 

from models using monochromatic waves and first order wave theory (cf RCPWAVE used by 

Byrnes and Groat, 1991) . 

Case 2 (H5=4 m, TP=9 sec.) 

Case 2 represents a storm condition weaker in magnitude than Case 1 . To make reading this 

report easier, the image contour plots of significant wave heights for each deep water direction 

are presented in Appendix A along with refraction diagrams . The plots showing percentage 

change in significant wave height due to shoal removal are presented in the main body of the text 

in Figures 26, 27 and 28 . Interpretation of the data leads to the following conclusions: 

(1) . Similar gradients in nearshore significant wave height (HS increasing from west to east) are 

observed in all plots for the three incident wave directions . The gradients are caused by the water 

depth difference between the east and west portion of the study area (water depth increasing from 

west to east). However, the gradients in this case are smaller than those in Case 1 . This implies 

a reduction in the influence of water depth as exerted on wave height and period, and, more 

specifically, wave transformation and dissipation owing to the increase in relative water depth, 

h/L, where h is water depth and L is the local wave length (cf., Kundu, 1990). 

(2) . The removal of Ship Shoal also results in a significant increase of the wave height, however, 

as expected, the magnitudes of wave height increase are smaller than those determined for Case 

1 . For example, while the highest value in Figure 18c is more than 80%, the maximum in Figure 

26 is only 40%. The wave height increase is restricted to the shoal area, especially along the 

western portion of Ship Shoal where the water depths are less . 

(3). The directionality within the wave transformation as well as the wave height variation due 

to the removal of Ship Shoal can also be clearly seen in Figures 26, 27 and 28 . Both the 

magnitude of wave height increase and the lobe area within which wave height increases more 

than 30% are the largest when the wave approach is southeast (A=45°) . For example, the greatest 

value of wave height increase in Figure 27 is 50% . When waves propagate from the south 

(8=0°), the magnitude of wave height increase is smaller, and propagation from the southwest 

(8=-45() results in the lowest value of both the magnitude and the lobe area . 

Similar to case 1, longitudinal profiles are presented (J=150 J=400) (Appendix A-7 

through A-12) and display the following: bathymetric configurations with and without Ship Shoal; 

significant wave height distribution generated by STWAVE for respective bathymetries ; increase 

of the significant wave height due to the removal of Ship Shoal and the depth-limited wave 

breaking index . Comparisons with the corresponding plots in Case 1, indicate that the magnitude 

of the wave height increase is much smaller, although the spatial variation in the increase is 

similar to that found in the previous case . As discussed previously, the relative water depth is 

the controlling factor in wave propagation, dissipation and breaking . As shown in Appendix A-9, 
67 

Hs=4 m, Tp=9 sec., theta=0 

400 

350 

300 

v .` 

250 

0 200 

r- 

--:,l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H[S] 

Figure 26 Modeled percentage of H$ increase due to shoal removal. Case 2, 0 =0°. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
68 

Hs=4 m, Tp=9 sec ., theta=45 

400 

350 

300 

v .` 

X250 

E 

0 200 

r 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H[S] 

Figure 27 Modeled percentage of HS increase due to shoal removal. Case 2, 0 =45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
69 

Hs=4 m, Tp=9 sec ., theta=-45 

400 

350 

300 

v 

L. 

250 

Q 200 

r 

- 150 

100 

50 

rs . . ,a~ 

s'i'f'S -i. .-'1' 1 I I .1, . 

10 20 30 40 50 60 70 80 90 100 

of Hs change ;(H[NS]-H[S])/H[S] 

Figure 28 Modeled percentage of Hg increase due to shoal removal . Case 2, 0 =-45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
70 

though waves from all three directions did not break over the west portion of Ship Shoal, the 

breaking index is still much greater than that in Appendix A-12. Both sectional profiles show 

waves breaking further inshore for both present and hypothetical bathymetric scenarios. 

Consequently the significant wave height collapses to the same value in the nearshore (Appendix 

A-7) or the land boundary (Appendix A-10) for both scenarios. Thus, the removal of Ship Shoal 

does not alter the nearshore significant wave height under storm conditions in Case 2 . The 

nearshore breaker zone in Case 2 is approximately 1 - 2 km further inshore when compared to that 

generated in Case 1 . 

Wave refraction patterns are shown in Appendix A-13 through A-18 for the three incident 

wave approach directions . Refraction is particularly pronounced over the western portion of Ship 

Shoal during oblique approaches . 

Case 3 (HS =2 m, TP=6 sec.) 

Case 3 was selected to represent a weak storm condition. The format adopted for Case 2 is 

used here and the relevant data presented in Appendix B. The plots showing percentage change 

in significant wave height due to shoal removal are presented in the main body of the text in 

Figures 29, 30 and 31 . Similar to the previous cases, the same three incident wave directions 

were used in the simulations . Interpretation of the data leads to the following conclusions: 

(1) . An increasing nearshore wave height gradient from west to east is apparent but is much 

less than that observed in Case 1 and Case 2. This is because, for a shorter and smaller wave, the 

relative water depth, h/L, is very high, when compared to those values in Case 1 and Case 2, 

throughout the study area except the surfzone . Thus, the significant wave heights become 

insensitive to the differential water depth across the shoal (i .e ., west-east orientation) . 

(2) . In the area where the significant wave height increases substantially on removing Ship 

Shoal for stronger storms, the magnitudes of wave height increase becomes minimal in all three 

directions simulated in Case 3 (Figures 29, 30 and 31). For example, the maximum value of 

percent increase in significant wave height is approximately 20% (Figure 29), significantly less 

than for storms previously discussed (40% and 80%) . The wave height increase is restricted to 

the western margin of the shoal complex where water depths are significantly less . 

(3) . The data suggest that varying wave direction plays a minor role on wave-shoal 

interaction and, therefore, resultant wave climate . 

Section profiles are plotted in Appendix B for bathymetric configurations including and 

excluding Ship Shoal showing the increase of the significant wave height due to shoal removal and 

the depth-limited wave breaking index. On comparison with previous cases, as expected, the 

magnitude of the wave height increase becomes much smaller, although the spatial variation is 

similar to those in the previous cases. Differential water depths from the west and east flanks of 

the shoal continues to exercise control on the magnitudes of significant wave height increase and 

wave breaking index, although the degree of control is considerably less than found in cases 1 and 
71 

Hs=2 m, Tp=6 sec., theta=0 

400 

350 

300 

.v `

X250 

E 

0 200 

T 

--:'l 5U 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure 29 Modeled percentage of HS increase due to shoal removal. Case 3, 0 =0° 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
72 

Hs=2 m, Tp=6 sec., theta=45 

400 

350 

300 

-o .` 

-a-)2so 

Q 200 

r 

--:,150 

goo 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[N S]-H[S])/H[S] 

Figure 30 Modeled percentage of HS increase due to shoal removal. Case 3, 0 =45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
73 

Hs=2 m, Tp=6 sec., theta=-45 

400 

350 

300 

-v .` 

-m-2so 

0200 

:'l 50 

100 

50 

---°----~----i. 

~N, IJ ~r ~u". 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S ])/H[S] 

Figure 31 Modeled percentage of HS increase due to shoal removal. Case 3, 0 =-45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
74 

2 . Waves propagating landward in Case 3 do not break over the western portion of the shoal, 

a condition not met in either Cases 1 or 2. Because of this, the significant wave height from the 

model run over the hypothetical bathymetry (shoal removed) is always slightly greater than the 

wave height derived from the model run over the present bathymetry . On the east flank of the 

shoal, wave breaking occurs in the nearshore (Whiskey Island, in this section), and the breaker 

zone is further inshore relative to the position of the breaker zone in Case 1 and Case 2. 

Consequently, the significant wave height from both runs (with and without Ship Shoal) attains 

the same value at the landward boundary . Thus, the data suggest that the removal of Ship Shoal 

does not affect the nearshore significant wave height . Notable impacts on the entire significant 

wave height distribution across the inner shelf landward of the shoal are negligible (Appendix B11) . 

Wave refraction diagrams for bathymetric configuration including and excluding Ship Shoal 

are shown in Appendix B-13 through B-18 for three incident directions. Refraction effects are 

noticeable over the western flank of the shoal during oblique wave approaches. However, as 

expected, the signal is significantly weaker than observed in previous cases . 

Case 4 (HS=1 m, Tp=S sec.) 

Case 4 represents fair weather wave conditions . As in the previous cases, incident waves 

from three directions are propagated over the same bathymetry in the numerical simulations and 

the data are presented in Appendix C. The percentage change in significant wave heights due to 

shoal removal are presented in the main body of the text in Figures 32, 33 and 34 . The following 

conclusions are presented: 

(1) The longshore gradients of nearshore significant wave height (HS increasing from west 

to east) are negligible on comparison with previous scenarios . This can be explained as follows ; 

for the shortest and smallest wave, the relative water depth, h/L, is also the highest (among the 

4 cases discussed in this report) everywhere in the study area except the surfzone . Thus, the 

significant wave heights become insensitive to the differential water depth in the west-east 

orientation. 

(2) In the area where the significant wave height increased dramatically due to the removal 

of Ship Shoal in both Case 1 and Case 2, the magnitudes of wave height increase due to shoal 

removal also becomes negligible for all three wave approaches in Case 4 (Figures 32, 33 and 34), 

representing incident wave directions of 0°, 45°, -45° respectively) . For example, the maximum 

values in Figures 32, 33 and 34) are all smaller than 10%, comparing the highest values of 80 

in Figure 18c and 40% in Figure 26 . The wave height increase is also restricted to the shoal area, 

especially at the west-most part of Ship Shoal where the water depth is the shallowest . 

(3) As noted in previous Case 3, directionality has a minimal effect on the wave climate. 

The cross-shore sections at the same two locations are plotted in Appendix C-7 through C12) to display the sectional profiles of the present (with Ship Shoal) and hypothetical (without Ship 
75 

Hs=1 m, Tp=5 sec., theta=0 

40 

350 

300 

-v .` 

X250 

E 

10 200 

r 

- 150 

100 

50 

16 r . ' 1 I I I ' ' ~e '` 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure 32 Modeled percentage of H9 increase due to shoal removal. Case 4, 0 =0° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
76 

Hs=1 m, Tp=5 sec ., theta=45 

400 

350 

300 

-v .` 

m250 

E 

Q 200 

r 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure 33 Modeled percentage of Hg increase due to shoal removal. Case 4, 0 =45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
77 

Hs=1 m, Tp=5 sec,, theta=-45 

400 

350 

300 

.v 

~=2so 

E 

0 200 

T 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H [S])IH[S] 

Figure 34 Modeled percentage of HS increase due to shoal removal. Case 4, 8=-45°' 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
7s 

Shoal) bathymetric configurations; the significant wave heights generated from running the model 

over the two bathymetric configurations ; the increase of the significant wave height due to the 

removal of Ship Shoal and the depth-limited wave breaking index. Comparing with the 

corresponding plots in the three previous cases, it is apparent that the magnitude of the wave 

height increase becomes much smaller, although the spatial variation and directionality of this 

wave height }ncrease are similar to those in the previous cases . The difference in water depths 

between the section J=150 and section J=400 causes the differential magnitudes of significant 

wave height increase and wave breaking index, although these differences are almost negligible. 

In cross-shore section J=150, waves do not reach the breaking stage . Consequently, the 

significant wave height from the model run over the hypothetical bathymetry remains slightly 

greater than the wave height derived from the model run over the present bathymetry . However, 

in section J=400 (Appendix C-7 through C-9) wave breaking occurs at the landward boundary 

(Whiskey Island, in this section), and the breaker zone is further inshore relative to its position 

in previous cases. The removal of the shoal does not have an impact on the nearshore significant 

wave height. 

Wave refraction diagrams are presented in Appendix C-13 through C-18 for both 

bathymetries and respective wave approaches. Refraction over the shoal complex is minimal. 

Effects of Wind Forcing 

Towards the end of this project, the National Data Buoy Center released wind data for 

station 42001 that could for the first time, be used in conjunction with the deep water wave 

climate to test the importance of including the wind forcing function on wave climate. In this 

section we present the model output for the same four cases discussed above with the wind forcing 

term included . 

In Appendix D-1 through D-8 the effect of including the wind function on wave height is 

demonstrated along sectional profiles J=150 and 400 for the deep water wave boundary conditions 

used in the previous discussion . As discussed earlier, it is more appropriate to use the eventspecific rather than the average parameters in modelling the cases presented in this study. The 

time series of wind speed was examined with respect to the events that were selected from the time 

series of wave height to represent the 4 cases . The selected values of wind speed are listed in 

Table 4. 

The two cross-shore sectional profiles of the modeled significant wave height for each of the 

listed 4 cases are plotted in Appendix D for a southeast wave approach . The topmost panel in each 

figure shows the present and hypothetical bathymetric profiles. The second panel shows the 

comparison of the wave height profiles over the present bathymetry with and without the wind 

forcing term. The third panel shows the comparison of the wave height profiles over the 

hypothetical bathymetry (Ship Shoal removed) with and without the wind forcing term. In the 

bottom panel, the two wave height profiles generated with and without the wind forcing term are 

plotted for both bathymetries . 
79 

Table 4. Wind speeds and directions used to test the wind forcing term 

Case HS(m) Tp(s) Wind 

Speed (ms-') 

Wind Direction 

6(deg.)1 

1 6 11 20 -45,00,45 

2 4 9 15 -45,00,45 

3 2 6 10 -45,00,45 

4 1 5 5 -45,00,45 

1 -45 = SOUTHWEST APPROACH 

45 = SOUTHEAST APPROACH 

00 = SOUTH APPROACH 

In Case 1, the 20 m/s wind blowing in the direction of wave propagation maintains a 0.5 m 

higher significant wave height seaward of the west portion of Ship Shoal (section J=150) . Waves 

are reduced to slightly higher than 2 m over the shoal, a value which is equal on comparing it with 

and without the wind forcing function. Over the hypothetical bathymetry inclusion of the wind 

forcing function results in a gradual increase in wave height difference due to increasing fetch. 

The maximum value of the increase is < 1 m. Thus the wind-present wave height at this 

location increases by as much as 2 m, a 90% increase, after Ship Shoal is removed compared to 

the 40% shown in the wind-free simulation . The nearshore breaking wave height is more than 

0.5 m higher, and the nearshore breaker zone is 0.5 - 1 .0 Km further offshore when the wind 

function is included. Over the eastern part of the shoal where the water depth is greater, the 

magnitude of wave height increase due to the wind forcing is relatively higher . The significant 

wave height is increased by as much as 1 m seaward of Ship Shoal. The locations of nearshore 

wave breaking either before or after Ship Shoal removal are less than 0.5 Km further offshore 

because of the increase of the breaking wave height . As in the wind-free simulations, the effect 

of Ship Shoal removal on the wave height is limited to the leeward periphery of the shoal itself . 

In the nearshore, shoal removal does not increase the wave height with or without the wind 

forcing function . Additionally, the differential water depths over the shoal show similar impacts 

on the wave height distribution with the wave height increase due to Ship Shoal removal being 

significantly smaller along the eastern part of the shoal than along the west. 

In all three of the remaining cases, the properties and patterns of the wave height increase 

due to the addition of the wind forcing term in the numerical model are similar to what have been 

described above, although the magnitudes of these changes are different from case to case. In 

Case 2, the magnitude of the significant wave height increase due to the addition of a 15 m/s wind 

is also approximately 0.5 m seaward of the west part of Ship Shoal prior to breaking. Unlike in 

Case 1, however, the significant wave height after breaking does not collapse to the same value 

as in the wind-free simulation . Over the hypothetical bathymetry this magnitude continually 
80 

increases shoreward until the waves reach the breaking condition. Removal of Ship Shoal will 

result in a 50% increase of the significant wave height . This is much larger than the magnitude 

(between 25% to 30%) where wind forcing was neglected. The magnitude of wave height 

increase due to the wind forcing over the east part of the shoal is as much as 0.8 m. Cases 3 and 

4 represent a weak storm and a fair weather condition respectively . Although wave breaking does 

not occur when the waves approach Ship Shoal, higher energy dissipation in this area results in 

a larger degree of significant wave height change due to the removal of Ship Shoal . The 10 m/s 

wind in Case 3 causes more than 0.5 m of significant wave height increase, and the 5 m/s wind 

in Case 4 causes a 0.2 m increase . 

The distribution of the percent change in significant wave heights due to shoal removal for 

each deep water wave boundary condition, and associated wind speed, is plotted for the three 

wave approach directions in Appendix D-9 through D-20 . As expected, while the 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 the 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. 

Hurricane Andrew Simulation 

Wave Height and Attenuation 

Wave heights decreased from approximately 11 m in 150-200 m of water, to 2 m in 15-20 

m of water off the Isles Dernieres (Figure 35) . The rate of attenuation decreased significantly 

across Ship Shoal, where the majority of long waves underwent total energy dissipation rather than 

breaking . Shoreward propagation of waves across Ship Shoal was limited . West of Main Pass, 

12 and 13 m waves began attenuating in depths of around 200 m, and experienced a generally 

higher attenuation rate than those simulated off the Isles Dernieres . The higher energy portion 

of the attenuated wave spectrum was shifted closer to the coast around the eastern terminus of 

Timbalier Island and further east (Figure 35) . The variability in this distance is a direct function 

of continental shelf slope and not deep water wave boundary conditions . As discussed below, 

differential attenuation across the shelf had a significant impact on wave energy conditions along 

the adjacent coast . 

Maximum Near-Bottom Orbital Velocity 

Calculated maximum near-bottom orbital velocities became weakly-developed in water 

depths of around 200 m, and approached 20 cm sec' in approximately 150 m of water (Figure 

36) . Since sediment comprising this portion of the shelf is generally fine-grained clay transported 

from the Mississippi Delta proper (cf Treadwell, 1955 ; Shepard, 1956; Coleman, 1982), it is 

unlikely that sediment resuspension due to surface gravity waves occurred at this depth. However, 

based on the relationship between threshold velocities, quartz grains and longer period waves 
81 

off 

~ 2.f o . .o 

N 

- 

VN~, 

0 30 KM 

TVVWaQW MW 

.44 

2 \ l 

X ~9 S 

V " 8 ^v\ \V vJ N 

V 

10 

r 

aff 

- 

3 

1S 

r ^l\ 6~/ 

i 

%. \ CI = lm 

Figure 35 Contour plot of the simulated wave height across the Louisiana shelf during 

Hurricane Andrew . Contour intervals are 1 meter. 
82 

Figure 36 Contour plot of the simulated maximum near-bottom orbital velocities across the 

Louisiana shelf during Hurricane Andrew . Contour intervals are 1 m/s. 
83 

proposed by Komar and Miller (1975), it is apparent that velocities had achieved the critical 

threshold for entrainment of medium sand (20 cm sec') at 150 m depths . Near-bottom orbital 

velocities increased significantly across the shelf due to a rapid decrease in water depth, and were 

typically 150-200 cm sec-' in approximately 30 m of water . Two current meters deployed in 20.5 

and 37 m depths south of Terrebonne Bay at LATEX moorings 14 and 16 (see DiMarco et al, 

1995), recorded near bottom velocities in excess of 100 and 80 cm sec-' respectively, prior to 

instrument failure or movement, during the peak of Hurricane Andrew. (It is perhaps worthy of 

note that the calculated orbital velocity in 30 m water depths would have exceeded the entrainment 

velocity for particles well within the gravel range .) Bottom velocities decreased gradually across 

the lower gradient inner shelf incorporating the Ship Shoal complex, due to a gradual decrease in 

depth and incident wave height . East of the Mississippi Canyon, bottom orbital velocities 

increased at a greater rate than on the west flank, due to a steeper shelf slope . On attaining a 

maximum of approximately 200 cm sec-' in 40 m of water, bottom velocities decreased only 

slightly to approximately 140 cm sec' in shallow water. 

Energy Dissipation Across the Continental Shelf 

A two-dimensional distribution of wave energy dissipation across the shelf is shown in 

Figure 37. Since the energy dissipation gradient is a direct function of the effects of shoaling, 

refraction and friction on wave height, it is expected that the variable shelf slope would 

differentially impact the rate of wave energy dissipation across the Louisiana shelf during 

Hurricane Andrew . 

Wave energy dissipation became apparent in water depths of approximately 150-200 m. The 

rate of wave energy decay (dE/dR) varied considerably across the shelf due to differential bottom 

slope-wave height effects . Given the significance of wave height in computing dE/dR, the 

distribution of both are plotted in Figure 38 for two locations across the shelf; west and east of 

the Mississippi Canyon, with the former extending across Ship Shoal . West of the Canyon, a 

larger proportion of the wave energy dissipation occurred approximately 100 km offshore reaching 

a peak near 5 jl m-3 in water depths between 25-30 m. Waves decreased in height to 

approximately 7 m and with additional shoreward propagation, continued to loose energy at a 

significantly slower rate . On moving across the Ship Shoal complex, the rate of energy decay 

increased from < 0.5 jl M-3 to 2 jl m 3 before final peaking during breaking. East of the Canyon, 

the shorter, steeper nature of the shelf reduced it's ability to absorb wave energy during shoreward 

propagation. Consequently, although the decay gradient is similar to that west of the Canyon, the 

peak decay value of 3 jl m 3 was significantly less and located considerably closer to shore--

approximately 20 Ian offshore in 25-30 m of water. Prior to breaking, the energy dissipation rate 

decreased only slightly, resulting in considerably higher wave energy conditions along this portion 

of the coast than further to the west. 

A more detailed account of the wave field during Hurricane Andrew and morphological 

changes along the south-central Louisiana coast are presented in Stone et al. (1995) . 
84 

Figure 37 Contour plot of the simulated wave energy dissipation rates across the Louisiana 

shelf during Hurricane Andrew . Contour intervals are 0.2 jl/m3 . 
85 

Rav 80 

E 

x 

F 

d 

w O 

w 

E 

x 

a 

c 

W 

15 10 

10 

WAVE HEIGHT 

5

- DE/DR 

5 

0 50 100 150 200 250 300 

DISTANCE FROM POINT OF PROPAGATION (Km) 

E 

x 

H 

a 

W 

O 

W 

a 

3 

o 

w 

F 

DISTANCE FROM POINT OF PROPAGATION (Km) 

15 

10 

WAVE HEIGHT 

- DE/DR 

5 

T 

0 50 100 150 200 250 30 

DISTANCE FROM POINT OF PROPAGATION (Km) 

10 

0 

v 

5~ 

0 

Figure 38 Wave height - energy relationships from two wave rays west (Ray 24) and east (Ray 

80) of the Mississippi Canyon. The respective bathymetric profiles are also shown for 

comparison . 

DISTANCE FROM POINT OF PROPAGATION (Km) 
86 

6 Conclusions 

The following main conclusions can be made from the research conducted on the significance 

of Ship Shoal regarding wave climate off the Isles Derrieres. 

(1) The removal of Ship Shoal will alter the wave propagation, dissipation and the wave 

energy distribution. The magnitude and the spatial distribution of the alteration depend on the 

initial wave conditions . 

(2) . During severe storms (Case 1) and strong storms (Case 2), the 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. 

(3) During the 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. 

(4) The nearshore wave fields are largely dependent on the offshore wave conditions . 

Under the 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, waves 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. 

(5) Wave approach direction exerts significant control on the wave climate leeward of Ship 

Shoal for stronger storm conditions (Cases 1 and 2) but not weak storms or fairweather waves. 

(6) Inclusion of the wind function increases wave height in all simulations . The magnitude 

of the increase is dependent 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 
87 

of wave height increase due to the wind forcing over the east part of the shoal is as much as 0.8 

m. 

(7) While the 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. 

(8) Changes in the 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. 

(9) 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 . 

(10) The data presented in this report 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 Derrieres. The data suggest that this conclusion is valid for winter 

storm conditions and hurricanes similar to that of Hurricane Andrew. 

(11) Conclusion (10) 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. 
88 

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93 

APPENDIX A. Case 2: HS = 4 m, Tp = 9 seconds 
94 

Hs=4 m, Tp=9 sec ., theta=0 [S] 

400 

350 

300 

.` 

X250 

E 

0200 

r 

--:'l 50 

100 

50 

g, 5 

0 .4 0.8 1 .2 1 .6 2 .0 2 .4 

I 

2

1 

.8 3

I 

.2 

A

3

M 

.6 4.0 

Hs, m 

Figure A-1 Image of modeled significant wave height, Case 2, 8=0°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
95 

Hs=4 m, Tp=9 sec ., theta=0 [NS] 

400 .. 

350 i- . ., . 

300 

.` 

X250 

0200 

r 

:'l 50 

goo 

50 

0 .4 0 .8 1 .2 1 .6 2 .0 2 .4 2 .8 3 .2 3 .6 4 .0 

Hs, m 

Figure A-2 Image of modeled significant wave height, Case 2, 0 =0°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
96 

Hs=4 m, Tp=9 sec ., theta=45 [S] 

400 

350 

300 -o 

.` 

250 

E 

Q 200 

r 

--:'l 50 

100 

50 

0 .4 0 .8 1 .2 1 .6 2 .0 

Hs, m 

_-

-----_ _---1-- .y t 

2 .4 2 .8 3 .2 3 .6 4.0 

Figure A-3 Image of modeled significant wave height, Case 2, 8 =45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
97 

Hs=4 m, Tp=9 sec., theta=45 [NS] 

400 

350 

300 

v .` 

X250 

E 

Q 200 

T 

= 150 

goo 

50 

0 .4 0.8 1 .2 1 .6 2 .0 

Hs, m 

2 .4 2 .8 3 .2 3 .6 4 .0 

Figure A-4 Image of modeled significant wave height, Case 2, 0 =45°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
98 

Hs=4 m, Tp=9 sec ., theta=-45 [S] 

400' 

350 

300 -Q .` 

X250 

E 

10200 

T 

---:150 

100 - 

50 L 

100 200 300 400 500 

J, 100 m/grid 

oo 800 900 

;. 

0 .4 0.8 1 .2 1 .6 2.0 2 .4 2 .8 3 .2 3 .6 4 .0 

Hs, m 

Figure A-5 Image of modeled significant wave height, Case 2, 0 =-45°, with Ship Shoal. 
99 

Hs=4 m, Tp=9 sec ., theta=-45 [NS] 

400 

350 

300 -o .` 

X250 

E 

a 200 

--:'l 50 

100 

50 

0 .4 0 .8 1 .2 1 .6 2 .0 

Hs, m 

1,II I 

I I 1 

2 .4 2 .8 3 .2 3 .6 4.0 

Figure A-6 Image of modeled significant wave height, Case 2, 8=-45°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
0 

E 

J=150, H s=4 m, Tp=9 sec. 

M-10 

Q 

m 

~ -20 

m 

3: _qn 

0 50 100 150 200 250 300 350 400 

theta=0 

4 

3~ 

E .,, 

_

,A 2 -

z 

1 ~-

0 i 

0 50 100 150 200 250 300 

th eta=45 

4 

3 

i 

z 

O I I f I I 

0 50 

350 400 

100 150 200 250 300 350 400 

theta=-45 

4 

3 

E 

. . . . 

y 

L'F 

1 

I 

0 50 100 150 200 250 300 350 400 

i, 100 mJgrid 

Figure A-7 Cross-sectional profiles of significant wave height, HS, along J=150 in Case 2. 
b 

E 

Z-10 

~° -2a m . . 

3~ _qn 

J=150, H s=4 m, Tp=9 sec . 

0 50 100 1 b0 200 250 300 350 400 

theta=0 

100 

0 

p , . . . 

._ i 

z 

i 

0 

0 50 100 150 200 250 300 350 400 

th e to=4 5 

100 

0 

m 0 , . ; . . . . . . . . . . . 

V 

G 

N 

1 

i 

~0 50 100 150 200 250 300 350 400 

theta=-45 

100 

0 

H 

fb 

m 50 

L 

C1 

C 

N 

0 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure A-8 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J =150 in Case 2 . 
0 

~ -10 

J=1 5a, Hs=4 m, Tp=9 sec. 

m 

~ -20 

3~ _.qn 

50 100 150 200 250 300 350 400 

theta=0 

1 

0 .5 ~-

I 

i 

-------------- 

0' 

0 50 100 150 200 250 300 350 400 

theta=45 

1 

~.J 1 

. . \\ 

i 

o f 1 I 1 1 t 

0 58 100 150 200 250 300 350 400 

theta=-45 

1 

0 .5 

I i i i 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure A-9 Cross-sectional profiles of depth-limited wave breaking index, H/h, along 7=150 

in Case 2. 
0 

E 

,~ -10 

J=4d0, Hs=4 m, Tp=9 sec . 

~ -20 

m 

3~ _an 

0 54 100 150 200 250 300 350 A40 

theta=0 

4 

I 

E 3 _2 ~ 

~ . 

` I 

1 ~- 

0 1 1 

0 50 100 150 200 250 300 350 400 

theta=45 

4 

3 i i 

E 2 ~ 

N 

. 

1 r 

I I I I i 

V 

0 50 100 150 200 250 300 350 400 

theta=-45 

4 

3 

1 i 

0 1 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure A-10 Cross-sectional profiles of significant wave height, Hs, along J= 400 in Case 2. 
0 

E 

~ -10 

J=4D0, Hs=4 m, Tp=9 sec . 

Q 

m 

'a -20 

m r 

3: An 

100 

0 

N 

ca 

~' 50 U 

C 

S 

o L 

50 100 150 200 250 300 

theta=45 

1 

i 

i 

50 100 150 200 250 300 350 400 

theta=-45 

100 -T--

a 

i i 

7 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure A-11 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J=400 in Case 2 . 

0 5d 100 150 200 253 300 350 400 

theta=0 

350 400 
J=400, Hs=4 m, Tp=9 sec . 

0 

E 

J_-10 

Q 

~ -20 

m 

0 50 100 150 200 250 300 350 400 

theta=0 

1 

0 50 100 150 200 250 300 350 400 

theta=45 

1 

s 

0 .5 z 

~0 50 100 150 200 250 300 350 400 

theta=-45 

1 

= 0.5'r0 

I 

50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure A-12 Cross-sectional profiles of depth-limited wave breaking index, H%h, along J=4.00 

in Case 2. 
106 

Hs=4 m, Tp=9 sec ., theta=0 (Sj 

400 

350 

300 

v 

L. 

~0)ZrJa 

E 

a 200 

:"150 

100 

50 

Figure A-13 Modeled wave rays, Case 2, 0 =0°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
Hs=4 m, Tp=9 sec ., theta=0 [NS] 

400 

350 

300 

v 

L 

-tD250 

10200 

T 

--:150 

100 

50 

107 

Figure A-14 Modeled wave rays, Case 2, 0 =0°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
Hs=4 m, Tp=9 sec ., theta=45 [S] 

400 

354 

aao 

i 

X250 

Q 200 

r 

= 150 

100 

54 

108 

Figure A-15 Modeled wave rays, Case 2, 0 =45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
109 

Hs=4 m, Tp=9 sec ., theta=45 [NS] 

400 

350 

300 

v .` 

250 

r 

Q 240 

-150 

100 

so 

Figure A-16 Modeled wave rays, Case 2, 0 -45°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
110 

Hs=4 m, Tp=9 sec., theta=-45 [S] 

40( 

350 

Sao 

fr 

~25 0 

200 

r- 

--:'l 50 

100 

50 

Figure A-17 Modeled wave rays, Case 2, 6 =-45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
111 

Hs=4 m, Tp=9 sec., theta=-45 [NS] 

400 

350 

300 

:2 

L 

M'ZJ0 

a 200 

r c' 

= 15G - 

10 4 

50 1; 

Sao 

Figure A-18 Modeled wave rays, Case 2, 0 =-45°, without Ship Shoal. 

200 300 400 500 600 700 800 900 

J, 100 m/grid 
112 

APPENDIX B. Case 3 : HS = 2 m, Tp = 6 seconds 
113 

Hs=2 m, Tp=6 sec ., theta=0 [S] 

400 

350 

300 

-o .` 

X250 

E 

0 200 

T 

= 150 

100 

50 

=71 1 1 1 

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 

Hs, m 

Figure B-1 Image of modeled significant wave height, Case 3, 0 =0°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
114 

Hs=2 m, Tp=6 sec ., theta=0 [NS] 

400 

350 

300 

.v 

X250 

E 

0200 

r 

- 150 

100 

50 

_ ,-----

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 

Hs, m 

Figure B-2 Image of modeled significant wave height; Case 3, 0 =0°, without Ship Shoal., 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
115 

Hs=2 m, Tp=6 sec ., theta=45 [S] 

400 

350 

300 

-v 

-i 

X250 

E 

0 200 

T 

:'l 50 

goo 

50 

-- - 

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 

Hs, m 

Figure B-3 Image of modeled significant wave height, Case 3, 0 =45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
116 

Hs=2 m, Tp=6 sec ., theta=45 [NS] 

400 

350 

300 

v .` 

X250 

E 

0 200 

r- 

--:'l 50 

100 

50 

_r .r------,-- _ 

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 

Hs, m 

Figure B-4 Image of modeled significant wave height, Case 3, 0 =45°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
117 

Hs=2 m, Tp=6 sec., theta=-45 [S] 

400 

350 

300 -Q .` 

X250 

E 

10200 

T 

---:,l 50 

100 

50 

0.2 0 .4 0 .6 0 .8 1 .0 1 .2 

Hs, m 

1 .4 1 .6 1 .8 2 .0 

Figure B-5 Image of modeled significant wave height, Case 3, 0 =-45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
118 

Hs=2 m, Tp=6 sec., theta=-45 [NS] 

400 --

350-

300 -

.e250 

v 

E 

0 200 

T 

--:'l 50 

100 

50 

0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6 1 .8 2 .0 

Figure B-6 Image of modeled significant wave height, Case 3, 6 =-45°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
J=150, H s=2 m, Tp=fi sec . 

0 

E 

~ -10 

t+ 

Q 

N 

~ -20 

m 

~ _qn 

0 50 100 150 200 250 300 350 400 

theta=0 

2 

N ' 

. . ., . . . . . . . . . . 

0 .5 

D i 

0 50 100 150 200 250 300 350 400 

theta=45 

2 

1 .5 

E i 

z 

0 .5 ~ . 0 50 100 150 

I I I I 1 

200 250 300 350 400 

theta=-45 

r 

1 .5F 

F 

I 

0 .5 

D . ~ . i 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-7 Cross-sectional profiles of significant wave height, Hs, along J=150 in Case 3 . 
0 

E 

~ -10 

J=150, Hs=2 m, Tp=6 sec . 

Q CD 

~ -20 

m 

.. 

3~ _.qn 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

y 

ED 50 - 

. . . . . . . . . . 

U 

C 

N 

~ _ I 1 1 _ _ 1 O 1 i 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

N 

TO 50- 

U 

C 

N 

---- 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

c o~ 

50 ; . 

C7 

C 

O (- - - - -- - - - -- - 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-8 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J=150 in Case 3 . 
0 

E 

J=150, H s=2 m, Tp=6 sec . 

M-10 .r Q 

~ -20 

m 

\V 

~ _.q n 

1 

0 50 100 150 200 250 300 350 400 

theta=0 

0.5 r 

i oL 

0 

1 

50 100 150 200 250 

theta=45 

300 350 400 

=0.5F 

i 

0 50 100 150 200 250 300 350 400 

theta=-45 

1 

t 

= 0 .5 

I r i 

0 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-9 Cross-sectional profiles of depth-limited wave breaking index, H/h, along J=150 

in Case 3 . 
J=400, Hs=2 m, Tp=6 sec . 

0 

E 

~ -10 

.. 

a 

m 

-° -20 

3~ _,q n 

0 50 100 150 200 250 300 350 400 

theta=0 

2 

, .5 

E 

1 

z 

0 .5 

D i 

0 50 100 150 200 250 300 350 400 

theta=45 

2 

i 

0.5 

p i 

0 50 100 150 200 250 300 350 400 

theta=-45 

2 

1 .5~ 1 

1 r . . . 

0 .5 r ' 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-10 Cross-sectional profiles of significant wave height, Hs, along J =400 in Case 2 . 
0 

E 

~ -10 

J=400, Hs=2 m, Tp=6 sec . 

.. 

a d 

~ -20 

3: __Qn 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

I 

0 

0 

U 

C 

N 

i 

0 

0 50 100 150 200 250 300 350 400 

theta=45 

z 

0 50 100 150 200 250 300 850 400 

theta=-45 

100 

0I \ I 

i CO m 50 . . . . . . . 

U 

i 

0 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-11 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J=400 in Case 3 . 
0 

E 

~ -10 

m 

~ -20 

m 

J=400, Hs=2 m, Tp=6 sec . 

3~ _an 

1 

0 50 104 150 200 250 300 350 400 

th eta=0 

= 0.5 

I ! 

0 50 100 150 200 250 300 350 400 

theta=45 

t 

I 

=0 .5~- . 

o ~ r . i 1 

0 50 100 150 200 250 300 350 400 

theta=-45 

1 

0 .5 

I I I ri 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure B-12 Cross-sectional profiles of depth-limited wave breaking index, H/h, along J=400 

in Case 3 . 
125 

Hs=2 m, Tp=6 sec., theta=0 [S] 

400 

350 

300 

v 

X250 

E 

0 200 

r 

-= 15 0 

100 

50 

Figure B-13 Modeled wave rays, Case 3, 0 =0°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
126 

Hs=2 m, Tp=6 sec ., theta=0 [NS] 

400 

350 

300 

-o 

X250 

200 

r 

--:'l 50 

100 

50 

Figure B-14 Modeled wave rays, Case 3, 0 =0°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
127 

Hs=2 m, Tp=6 sec ., theta=45 [S] 

400 

350 

300 

v .` 

X250 

E 

2 200 

= 150 

100 

50 

Figure B- 15 Modeled wave rays, Case 3, 0 =45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
128 

Hs=2 m, Tp=6 sec., theta=45 [NS] 

400 

350 

300 

.` o 

250 

E 

0200 

r 

= 150 

100 

50 

Figure B-16 Modeled wave rays, Case 3, 0 =45°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
Hs=2 m, Tp=6 sec., theta=-45 [S] 

400 

350 

300 

.` 

X250 

E 

0 200 

r 

= 150 

100 

50 

129 

Figure B-17 Modeled wave rays, Case 3, 0=450, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
130 

Hs=2 m, Tp=6 sec., theta=-45 [NS] 

400 

350 

300 

-o .` 

X250 

E 

0 200 

r 

---:150 

100 

50 

Figure B-18 Modeled wave rays, Case 3, 0 =-45°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
131 

APPENDIX C. Case 4 : H$ = 1 m, TP = 5 seconds 
132 

Hs=1 m, Tp=5 sec., theta=0 [S] 

400 

350 

300 

:L X250 

a 200 

r 

---: 150 

1 00 

so 

0 .1 0 .2 0 .3 0 .4 0 .5 0.6 

Hs, m 

0 .7 0 .8 0.9 1 .0 

Figure C-1 Image of modeled significant wave height, Case 4, 0 =0°, with Ship Shoal. 

100 200 340 400 500 600 700 800 900 

J, 100 mlgrid 
133 

Hs=1 m, Tp=5 sec ., theta=0 [NS] 

400 

350 

300 

i 

X250 

F 

Q 200 

- 150 

Boa 

50 

0.1 0.2 0.3 0.4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0 

Hs, m 

Figure C-2 Image of modeled significant wave height, Case 4, 6 =0°, without Ship Shoal. 

100 200 300 400 504 600 700 800 900 

J, 100 mlgrid 
134 

Hs=1 m, Tp=5 sec., theta=45 [S] 

400 

350 

30U~ 

.` 

m250 

F 

0 200 ~~ 

- 150 

100 

50 

---,---

' 

0 .1 0 .2 0 .3 0 .4 0 .5 0.6 0 .7 0 .8 0 .9 1 .0 

Hs, m 

Figure C-3 Image of modeled significant wave height, Case 4, 6 =45°, with Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
135 

400 

35U j 

G 

300 

X250" 

Q 200 

r 

-150 1 

10G 

50 

0 .1 0 .2 0 .3 0 .4 0.5 0 .6 0 .7 0.8 0 .9 1 .0 

Hs, m 

Figure C-4 Image of modeled significant wave height, Case 4, 0 =45°, without Ship Shoal. 

Hs=1 m, Tp=5 sec ., theta=45 [NS] 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
136 

Hs=1 m, Tp=S sec ., theta=-45 [NS] 

4001 

356 C 

3Dd' 

.` 

X250 

a 200 

15C 

16u 

5G 

0 .1 0.2 0 .3 0 .4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0 

Hs, m 

Figure C-5 Image of modeled significant wave height, Case 4, 0 =-45°, with Ship Shoal. 

100 200 300 400 500 600 704 800 900 

J, 100 mlgrid 
137 

Hs=1 m, Tp=5 sec ., theta=-45 [S] 

400 

350 

300 

i 

X250 

E 

a 200 

T 

-150 

100 

50 

0 .1 0 .2 0.3 0.4 0 .5 0 .6 0 .7 0 .8 0 .9 1 .0 

Hs, m 

Figure C-6 Image of modeled significant wave height, Case 4, 0 =-45°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
J=150, Hs=1 m, Tp=5 sec . 

0 

,~ -10 

Q aD 

~ -20 

m .. 

3: _ .qn 

0 50 100 150 200 250 380 350 400 

theta=0 

1 

E 

y 0 .5 

z 

00 50 100 150 200 250 300 350 400 

th eta=45 

.~-

0 50 100 150 200 250 3t30 s5~? -*~i: 

theta=-45 

c 

o .5 

o f i 1 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure C-7 Cross-sectional profiles of significant wave height, H9, along J=150 in Case 4 . 
0 

~ -10 

n 

~ -20 

m 

J=150, Hs=1 m, Tp=5 sec . 

3: _qn 

0 50 100 150 200 250 300 350 400 

theta=0 

100 

0 

N 

0 

U 

C 

W 

-- - - ' - 

0 50 100 150 200 250 300 350 400 

theta=45 

100 

0 

50 - 

U 

N 

i 

n l I _ 1 ~~L~ . ~ .1. 

tl 

0 50 100 150 200 250 300 350 400 

theta=-45 

100 

0 

N 

p 

U 

C 

H 

0 1 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure C-8 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J=150 in C ase 4 . 
J=150, Hs=1 m, Tp=5 sec. 

0 

s -10 

4-CL a) 

-a -20 

-30~- 

I ~ ~ 

0 50 100 150 200 250 300 350 400 

theta=0 

1 

0 .5 I n 

o f ~ i 

0 50 100 150 200 250 300 350 400 

theta=45 

1 

0.5 ~-- 

n 

v0 50 100 150 200 250 300 350 400 

theta=-45 

1 

0.511- 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure C-9 Cross-sectional profiles of depth-limited wave breaking index, H/li, along J=150 

in Case 4 . 
0 

E 

-1-10 

J=400, Hs=1 m, Tp=5 sec . 

.. 

m 

~ -20 

3~ _zn 

0 50 100 150 200 250 300 350 ~i00 

theta=0 

1 

J 

y 0.5 (- 

01 

0 50 100 150 200 250 300 350 400 

theta=45 

i 

y 0 .5 ~-

F 

0 50 100 150 200 250 300 350 40v 

theta=-45 

1 

I 

~; 0.5 

z 

i 

~0 5,0 100 150 200 250 340 350 400 

I, 100 m/grid 

Figure C-10 Cross-sectional profiles of significant wave height, Hs, along J=400 in Case 2 . 
J=400, H s=1 m, Tp=5 sec . 

0 

E 

s -10 

a 

m 

_° -20 

3~ _,an 

0 50 100 150 200 250 3o0 350 400 

theta=0 

0 

100 

j 

U 

50 

4 0 50 100 150 200 250 300 350 400 

theta=45 

goo 

0 1 

z 

0 50 100 150 200 250 300 350 400 

theta=-45 

100 

o ~ i 

v. 

m 

L 50

C 

0 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure C-11 Cross-sectional profiles of percentage of Hs increase due to shoal removal along 

J=400 in Case 4 . 
J=400, Hs=1 m, Tp=5 sec . 

0 

E 

~ -10 

a 

m 

~ -20 

m 

3~ _,an 

1 

0 50 100 150 200 250 300 350 40 u 

theta=0 

0 .5 

i 

a ~_ 

0 

1 

0 .5 

i 

i 

o L 

0 

1 

50 100 150 

50 100 

200 250 300 

theta=45 

350 400 

i 

150 200 250 300 350 400 

theta=-45 

~ 0 .5i 

i 

0 5a 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure C-12 Cross-sectional profiles of depth-limited wave breaking index, H/h, along J=400 

in Case 4. 
400 

350 

300 

v 

X250 

a 200 

-150 

Boa 

5 0 

Hs=1 m, Tp=5 sec ., theta=0 [S] 

Figure C-13 Modeled wave rays, Case 4, 8=0°, with Ship Shoal. 

144 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
400 

350 

300 

v 

250 

E 

Q 200 

r 

-150 

100 

50 

Hs=1 m, Tp=S sec ., theta=a [NS] 

i 

1, s 

y 7 7" 

300 400 500 

J, 100 m/grid 

145 

Figure C-14 Modeled wave rays, Case 4, 0 =0°, without Ship Shoal . 

100 200 600 700 800 900 
Hs=1 m, Tp=5 sec ., theta=-45 [S] 

400 

350 

340 

v 

X250 

F 

0200 

-f50 

100 

50 

146 

Figure C-15 Modeled wave rays, Case 4, 0 =45°, with Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
Hs=1 m, Tp=5 sec ., theta=-45 [NS] 

400 

350 

300 

v 

m250 

E 

0 200 

r 

---:150 

100 

50 

147 

Figure C-16 Modeled wave rays, Case 4, 0 =45°, without Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
Hs=1 m, Tp=S sec ., theta=45 [S] 

400 

350 

300 

m 250 

E 

0 200 

T 

100 

50 

148 

Figure C-17 Modeled wave rays, Case 4, 0 =-45°, with Ship Shoal . 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
400 

350 

300 

v 

X250 

E 

0200 

rJ0 

100 

50 

Hs=1 m, Tp=5 sec ., theta=45 [NSj 

149 

Figure C-18 Modeled wave rays, Case 4, 8=-45°, without Ship Shoal. 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
150 

APPENDIX D. Wave height distribution with wind forcing function included 

for cases 1 through 4. 
0 

E 

~ -10 

.. Q 

m 

~ -20 

F+ m 

J=150, Hs=6 m, Tp=11 sec . 

3: _an 

0 50 100 150 200 250 300 350 400 

6 

4 -

E 

N 

2 

t 

a ' ' 

0 50 100 150 200 250 300 350 400 

[NS] 

6 

E 

4~ 

f 

N 

. 

0 50 100 150 200 250 300 350 400 

s i 

i 

I 

I 

i 

< < 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-1 Wind effect on the wave height distribution in Case 1, sectional profiles at J=150. 
J=400, Hs=6 m, Tp=11 sec . 

0 

~ -10 4-CL 

~ -20 

~ _~n 

0 50 100 150 200 250 300 350 400 

[S] 

6 

4~ 

E 

z 

2~ 

i 

-~ 

I 

0 50 100 150 200 250 300 350 400 

[NS] 

6 

i 

i 

z 

2~ 

i . , 

0 

50 100 150 200 250 300 350 400 

° f 

I 

j . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

r 

i 

r0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-2 Wind effect on the wave height distribution in Case 1, sectional profiles at 7=400. 
0 

s -10 

a 

m 

~ -20 

: 'r' *--Qn 

J=150, Hs=4 m, Tp=9 sec . 

0 50 100 150 200 250 300 350 400 

[S] 

4 

3~ -

i 

E 

_ _---

H

2 

O I 1 I I I I I i I 

0 50 100 150 200 250 300 350 400 

[NS] 

4 

_2L i 

i 

i 

j -; 

Q i i 

0 50 100 150 200 250 300 350 400 

4 

e 

3 

E 

z 

i 

Q I 1 I 1 1 i i i 

0 50 100 150 280 250 300 350 400 

I, 100 m/grid 

Figure D-3 Wind effect on the wave height distribution in Case 2, sectional profiles at J=150 . 
0 

E 

~ -10 

r 

d 

m 

~ -GO 

m 

3~ _,a n 

J=400, Hs=4 m, Tp=9 sec . 

0 50 100 150 200 250 300 350 400 

4 

3i 

H 

0 50 100 150 200 250 300 350 400 

[NS] 

4 

3~ -

E 

z ! 

0 

0 50 100 150 200 250 300 350 400 

4! 

z . 

i 

1r 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-4 Wind effect on the wave height distribution in Case 2, sectional profiles~at 7=400. 
0 

E 

~ -10 

c 

m 

~ -20 

3~ _an 

J=4f34, Hs=2 m, Tp=B see . 

0 50 1011 150 200 250 300 350 

IS) 

2 

i 

z 

0 .5 :; 

I I I I 1 

0 50 100 150 200 250 300 350 400 

[NS] 

2 

1 .5 -; 

I 

i 

s F + 

0 .5 

a i 

0 50 100 150 200 250 300 350 400 

2 

vi i~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

2 ! I 

Q I i a c i 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-5 Wind effect on the wave height distribution in Case 3, sectional profiles at J=150. 
0 

E 

~ -10 

J=150, Hs=2 m, Tp=6 sec. 

f. Q 

m 

~ -20 

m 

~ _ .q n 

0 50 100 150 200 250 380 350 400 

[S] 

2 

1 .5r 

E f 

m 1 {_ 

S I 

0 .5 

0 50 100 150 200 250 300 350 400 

[NS] 

i 

z 

°-

0 50 100 150 200 250 300 350 400 

z 

z ~! 

i 

Q .S 

o 

0 50 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-6 Wind effect on the wave height distribution in Case 3, sectional profiles at J=400. 
J=150, Hs=1 m, Tp=5 sec . 

0 

E 

~ -10 

Q 

~ -20 

m 

3~ _,an 

0 50 100 150 200 250 300 350 400 

1 

y 0 .5 

z 

0' ' 

0 50 100 150 200 250 300 350 400 

[NSJ 

, . . . . . 

0 50 104 150 200 250 300 

E ! 

y 0.5 ~ 

z 

0 5 0 100 150 200 250 300 350 400 

I, 100 m/grid 

Figure D-7 Wind effect on the wave height distribution in Case 4, sectional profiles at J=150.. 
J=400, Hs=1 m, Tp=S sec. 

0 

~ -10 

Q 

~ -20 

3: _qn 

1 

0 50 100 154 200 250 380 350 400 

,~ 0 .5 ~ j 

0 50 100 150 200 250 300 350 400 

[NS] 

f 

0 54 100 150 200 250 300 350 400 

i 

. 

_ 

i0

. 5 

0 50 100 150 200 250 300 350 400 

I, 100 mlgrid 

Figure D-8 Wind effect on the wave height distribution in Case 4, sectional profiles at J=400. 
159 

Hs=6 m, Tp=11 sec ., theta=45, Vwind=20 m/s 

400 

350 

300 

-o .` 

~o)25U 

E 

o° 200 

r 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-9 Modeled percentage of Hs increase under effect of wind forcing. Case 1, 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrici 
160 

Hs=6 m, Tp=11 sec ., theta=0 

400 

350 

300 

v .` 

X250 

F 

0200 

r 

--:'l 50 

goo 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change, (H[NS]-H[S])/H[S] 

Figure D-10 Modeled percentage of H$ increase under effect of wind forcing. Case 1, . 

VWi,d=20 m/s, 8=45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
161 

Hs=6 m, Tp=11 sec ., theta=-45 

400 

350 

300 

v .` 

X250 

0 200 

r 

- 150 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change, (H[NS]-H[S])/H[S] 

Figure D-11 Modeled percentage of Hg increase under effect of wind forcing . Case 1, 

Vw;.a=20 m/s, 8=-45° 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
162 

Hs=4 m, Tp=9 sec ., theta=45, Vwind=i5 min 

400 

350 

300 

v .` 

X250 

°0 200 

r 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-12 Modeled percentage of Hg increase, under effect of wind forcing . Case 2, 

VW;nd=20 m/s, 8=0° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
163 

Hs=4 m, Tp=9 sec., theta=0 

400 

350 

300 

v 

X250 

0 200 

r- 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-13 Modeled percentage of HS increase under effect of wind forcing. Case 2, 

VW~d=20 m/s, 8=45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
164 

Hs=4 m, Tp=t9 sec ., theta=-45 

400 

350 

300 

-v .` 

X250 

E 

0200 

--:'150 

100 

50 

164 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])IH[S] 

Figure D-14 Modeled percentage of HS increase under effect of wind forcing. Case 2, 

VW; d=20 m/s, 6=-45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
165 

Hs=2 m, Tp=6 sec ., theta=45, Vwind=lD mis 

400 

350 

300 

v .` 

X250 

F 

0 200 

--- :150 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[N S]-H[S]j/H[S] 

Figure D-15 Modeled percentage of HS increase under effect of wind forcing . Case 3, 

VW;,,d=20 m/s, 8=0° 

100 200 300 400 500 600 700 800 900 

J, 100 mlgrid 
166 

Hs=2 m, Tp=6 sec ., theta=G 

400 

350 

300 

v .` 

X250 

E 

0 200 

--:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-16 Modeled percentage of HS increase under effect of wind forcing . Case 3, 

VWi,d=20 m/s, 8=45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
167 

Hs=2 m, Tp=6 sec., theta=-45 

400 

350 

300 

-v 

250 

E 

a 200 

r 

--:'l 50 

100 

50 

' I III 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NSj-H[S])/H[S] 

Figure D-17 Modeled percentage of H$ increase under effect of wind forcing . Case 3, 

VWind=20 m/s, 0=-45' 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
168 

Hs=1 m, Tp=5 sec ., theta=45, Vwind=5 mis 

400 

350 

300 

-o .` 

X250 

E 

0 200 

r 

:'l 50 

100 

50 

r 

r . 

10 20 30 40 50 60 70 80 90 10G 

of Hs change ; (H(NS]-H[S])IH[S] 

Figure D-18 Modeled percentage of Hg increase under effect of wind forcing . Case 4, 

VWi,,d=20 m/s, 0 =0° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
169 

Hs=1 m, To=S sec. . theta=L 

400 

350 

300 

.`-v 

X250 

a 200 

T 

--- :150 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-19 Modeled percentage of HS increase under effect of wind forcing. Case 4, 

VWi,d=20 m/s, 8=45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
170 

Hs=1 m, Tp=5 sec ., theta=-45 

400 

350 

300 

.`-v 

X250 

E 

Q 200 

:'l 50 

100 

50 

10 20 30 40 50 60 70 80 90 100 

of Hs change ; (H[NS]-H[S])/H[S] 

Figure D-20 Modeled percentage of H$ increase under effect of wind forcing . Case 4, 

VWi,,d=20 m/s, 8=-45° 

100 200 300 400 500 600 700 800 900 

J, 100 m/grid 
The Department of the Interior Mission

As the Nation's principal conservation agency, the Department of the Interior has responsibility 

for most of our nationally owned public lands and natural resources. This includes fostering 

sound use of our land and water resources; protecting our fish, wildlife, and biological diversity; 

preserving the environmental and cultural values of our national parks and historical places; 

and providing for the enjoyment of life through outdoor recreation. The Department assesses 

our energy and mineral resources and works to ensure that their development is in the best 

interests of all our people by encouraging stewardship and citizen participation in their care. 

The Department also has a major responsibility for American Indian reservation communities 

and for people who live in island territories under U.S. administration. 

The Minerals Management Service Mission 

As a bureau of the Department of the Interior, the Minerals Management Service's (MMS) 

primary responsibilities are to manage the mineral resources located on the Nation's Outer 

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and Indian 

lands, and distribute those revenues. 

Moreover, in working to meet its responsibilities, the Offshore Minerals Management Program 

administers the OCS competitive leasing program and oversees the safe and environmentally 

sound exploration and production of our Nation's offshore natural gas, oil and other mineral 

resources. The MMS Minerals Revenue Management meets its responsibilities by ensuring the 

efficient, timely and accurate collection and disbursement of revenue from mineral leasing and 

production due to Indian tribes and allottees, States and the U.S. Treasury. 

The MMS strives to fulfill its responsibilities through the general guiding principles of: (1) being 

responsive to the public's concerns and interests by maintaining a dialogue with all potentially 

affected parties and (2) carrying out its programs with an emphasis on working to enhance the 

quality of life for all Americans by lending MMS assistance and expertise to economic 

development and environmental protection.