NOAA Technical Memorandum NOS CS 14

VDATUM FOR THE NORTHEAST GULF OF 

MEXICO FROM MOBILE BAY, ALABAMA, TO 

CAPE SAN BLAS, FLORIDA: TIDAL DATUM 

MODELING AND POPULATION OF THE MARINE 

GRIDS 

Silver Spring, Maryland 

August 2008 

noaa National Oceanic and Atmospheric Administration 

U.S. DEPARTMENT OF COMMERCE 

National Ocean Service 

Coast Survey Development Laboratory
Office of Coast Survey 

National Ocean Service 

National Oceanic and Atmospheric Administration 

U.S. Department of Commerce

The Office of Coast Survey (OCS) is the Nation’s only official chartmaker. As the oldest 

United States scientific organization, dating from 1807, this office has a long history. 

Today it promotes safe navigation by managing the National Oceanic and Atmospheric 

Administration’s (NOAA) nautical chart and oceanographic data collection and 

information programs. 

There are four components of OCS: 

The Coast Survey Development Laboratory develops new and efficient techniques 

to accomplish Coast Survey missions and to produce new and improved products 

and services for the maritime community and other coastal users. 

The Marine Chart Division acquires marine navigational data to construct and 

maintain nautical charts, Coast Pilots, and related marine products for the United 

States. 

The Hydrographic Surveys Division directs programs for ship and shore-based 

hydrographic survey units and conducts general hydrographic survey operations. 

The Navigational Services Division is the focal point for Coast Survey customer 

service activities, concentrating predominately on charting issues, fast-response 

hydrographic surveys, and Coast Pilot updates. 
NOAA Technical Memorandum NOS CS 14 

VDATUM FOR THE NORTHEAST GULF OF MEXICO FROM 

MOBILE BAY, ALABAMA, TO CAPE SAN BLAS, FLORIDA: 

TIDAL DATUM MODELING AND POPULATION OF THE 

MARINE GRIDS 

E. A. Dhingra 

K. W. Hess 

Office of Coast Survey, Coast Survey Development Lab, Silver Spring, MD 

S. A. White 

National Geodetic Survey, Silver Spring, MD 

August 2008

noaa National Oceanic and Atmospheric Administration 

U. S. DEPARTMENT National Oceanic and National Ocean Service 

OF COMMERCE Atmospheric Administration John H. Dunnigan 

Carlos Gutierrez, Secretary Conrad C. Lautenbacher, Jr., Assistant Administrator 

VADM USN (Ret.), Under Secretary 

 Office of Coast Survey Coast Survey Development Laboratory 

 Captain Steven R. Barnum, NOAA Mary Erickson 
ii

NOTICE 

Mention of a commercial company or product does not constitute an 

endorsement by NOAA. Use for publicity or advertising purposes of 

information from this publication concerning proprietary products or the 

tests of such products is not authorized.
iii

TABLE OF CONTENTS

LIST OF FIGURES ....................................................................................................................... iv 

LIST OF TABLES .......................................................................................................................... v 

ABSTRACT .................................................................................................................................. vii 

1. INTRODUCTION ...................................................................................................................... 1 

2. DATA SOURCES ...................................................................................................................... 2 

2.1. Coastline Data ...................................................................................................................... 2 

2.2. Tide Station Data ................................................................................................................. 2 

2.3. Bathymetric Data ................................................................................................................. 9 

3. TIDAL DATUM MODELING ................................................................................................. 10 

3.1. Hydrodynamic Model ........................................................................................................ 11 

3.2. Model Grid Development .................................................................................................. 12 

3.3. Incorporating Bathymetric Data ........................................................................................ 12

3.3.1. General Methods ......................................................................................................... 12 

3.3.2. Adding Bathymetric Data ........................................................................................... 13 

3.3.3. Adjusting Data to a Common Vertical Datum ............................................................ 14 

3.4. Model Results .................................................................................................................... 15 

4. INTERPOLATION OF ERRORS ............................................................................................ 17 

5. CREATION OF THE VDATUM MARINE GRID AND POPULATION WITH DATUMS 19 

5.1. Generation of the VDatum Marine Grid ............................................................................ 19 

5.2. Population of the VDatum Marine Grid with Tidal Datums ............................................. 21 

5.3. Potential Errors in the Marine Gridded Data ..................................................................... 21 

6. TOPOGRAPHY OF THE SEA SURFACE ............................................................................. 24 

7. QUALITY CONTROL AND TESTING.................................................................................. 31 

REFERENCES ............................................................................................................................. 33 

APPENDIX A. UNUSED TIDE STATIONS .............................................................................. 35 

APPENDIX B. SOURCES OF BATHYMETRIC DATA ........................................................... 37 

APPENDIX C. TIDE STATION DATA AND MODEL RESULTS........................................... 39 

APPENDIX D. FINAL TIDAL DATUM FIELDS IN THE VDATUM REGION ..................... 45 

APPENDIX E. ESTIMATES OF NAVD88 AT BENCHMARKS ............................................. 47 

APPENDIX F. COMPUTED DELTA VALUES FOR EACH DATUM .................................... 53 

APPENDIX G. COMPARISON OF OBSERVED AND COMPUTED NAVD88 VALUES .... 59 
iv

LIST OF FIGURES 

Figure 1. Tide stations in the northeast Gulf of Mexico region used to the hydro-dynamic 

modeling (red and blue squares) and for VDatum (red squares). The dashed lines 

represent the limits of the area searched for stations, and the purple line represents the 

25 nmi limit. .................................................................................................................... 3 

Figure 2. Tide stations on the Mississippi River Delta (left) and in Mobile Bay (right). ............... 5 

Figure 3. Tide stations in Mississippi (top), Perdido and Pensacola Bays (mid), and 

Choctawachee Bay (bottom). .......................................................................................... 6 

Figure 4. Tides stations in St Andrews Bay (top) and in St Joseph Bay (bottom). ........................ 7 

Figure 5. Bathymetry in the coastal region within 25 nmi of the coastline. Data are from 

NOAA’s Coastal Relief Model. .................................................................................... 10 

Figure 6. Unstructured grid of (a) the entire modeling region and zoomed views of the entrances 

to (b) Perdido Bay and (c) Pensacola Bay. ................................................................... 13 

Figure 7. MLLW sounding values interpolated onto the grid by (a) the cluster averaging 

approach and (b) linear interpolation using the utilities in the SMS software. ............. 14 

Figure 8. Comparison of the MHHW-MSL (squares) and MLLW-MSL (circles) observations 

(m) versus the modeled tidal datums with 5-cm error bands. ....................................... 17 

Figure 9. Subsection of the model grid with the (a) modeled MLLW-MSL (m) datum field (m), 

(b) interpolated MLLW-MSL error field (m), and (c) final corrected MLLW-MSL field 

(m). ................................................................................................................................ 19 

Figure 10. The VDatum bounding polygons for MOBLE, the Mobile Bay region (blue); PCOLA, 

the Perdido, Pensacola, and Choctawhatchee Bays region (cyan); ANDRW, the St. 

Andrews Bay region (red), STJOE, the St. Joseph Bay region (orange); and NEGOM, 

the remaining northeast Gulf of Mexico region (purple). ............................................. 20 

Figure 11. Locations of tidal stations and geodetic benchmarks. ................................................. 24 

Figure 12. The TSS grid for Mobile and Perdido Bays. ............................................................... 28 

Figure 13. The TSS grid for the Northeast Gulf of Mexico.......................................................... 28 

Figure 14. The TSS grid for Perdido, Pensacola, and Choctawhatchee Bays. ............................. 29 

Figure 15. The TSS grid for St. Joseph Bay. ................................................................................ 29

Figure 16. The TSS grid for St. Andrews Bay. ............................................................................. 30 
v

LIST OF TABLES 

Table 1. List of the 100 tide stations in the model domain. Stations from the 1983-2001 National 

Tidal Datum Epoch are marked with an asterisk (*) next to the Station ID. .................... 3 

Table 2. Diurnal tide ranges from the Old (1960-1978) and the New (1983-2001) National Tidal 

Datum Epochs, and the differences. ................................................................................. 8 

Table 3. Absolute average and percent error for each datum for the final series of runs averaged 

for the 74 NOS tide stations in the VDatum region. ....................................................... 16 

Table 4. VDatum grid information for the five regions. ............................................................... 20 

Table 5. Errors for the four tidal datums (m) by VDatum region for the VDatum marine grids. 22 

Table 6. Tidal and geodetic datums at tide stations in the northeast Gulf of Mexico. Tidal datums 

are relative to MLLW. Data are from CO-OPS. Station numbers marked with an asterisk 

have NAVD 88 elevations computed from NGS data, and not by CO-OPS. ................. 25 

Table 7. Differences between known and computed values to the NAVD88-to-MSL offset. ..... 31 
vi
vii

ABSTRACT 

To enable conversion between tidal, orthometric, and three-dimensional datums, a vertical datum 

transformation tool, VDatum, has been designed through a collaboration of NOAA’s National 

Geodetic Survey (NGS), Center for Operational Oceanographic Products and Services (COOPS), and the Office of Coast Survey’s (OCS) Coast Survey Development Laboratory (CSDL). 

The datum transformations already available in the VDatum toolbox include the transformation 

among three-dimensional datums, among orthometric datums, and between the three dimensional 

datums and orthometric datums. This report chronicles the continuing work to determine the 

datum transformations among tidal datums and between the tidal datums and the orthometric 

datums. The focus of this work is on the area from Mobile Bay, Alabama, in the west to Cape 

San Blas, Florida, in the east. A hydrodynamic model was created to simulate the astronomical 

tides in this area. The model results were corrected, using a spatial interpolation method, to 

match the model results to data at NOS tide stations. The final datums were used to populate a 

VDatum marine grid. The sea surface topography, or the difference between local mean sea 

level and the North American Vertical Datum of 1988 (NAVD 88) geopotential surface was 

modeled throughout this region and incorporated in the final VDatum software package. 

Key Words: tides, tidal datums, Mobile Bay, Perdido Bay, Pensacola Bay, Choctawatchee Bay, 

St. Andrew Bay, St. Joseph Bay, Cape San Blas, finite element model, hydrodynamic model, 

ADCIRC, North American Vertical Datum of 1988, mean sea level, spatial interpolation, 

coastline, bathymetry. 
viii
1

1. INTRODUCTION 

This paper documents the continuing work for the VDatum project in the Gulf of Mexico and 

estuaries from Mobile Bay, Alabama, in the west to Cape San Blas, Florida, in the east. This 

VDatum project was conducted as a part of NOAA’s Gulf of Mexico Storm Surge Partnership 

Program, and the model domain and grid will be used for the marine portion of future storm 

surge modeling work. 

The National Ocean Service (NOS) of the National Oceanic and Atmospheric Administration 

(NOAA) requires tidal datum information such as Mean High Water (MHW) and Mean Lower 

Low Water (MLLW) to support nautical charting, navigational safety, shoreline 

photogrammetry, marine boundary determination, and inundation mapping for coastal storms 

(tsunamis and hurricanes) and sea level rise. In addition, tidal datum information is needed for 

referencing NOS’ older bathymetric data from the Chart Datum of Mean Low Water (MLW) to 

the current Chart Datum of MLLW. A bathymetric-topographic Digital Elevation Model (DEM) 

can be created by converting all of the data into one datum using tidal datum and orthometric 

datum transformations. This DEM can be used for a variety of coastal GIS applications (Parker 

et al., 2001; Gesch and Wilson, 2001; Tronvig, 2005). Vertical datum transformation information 

will also be needed for carrying out the kinematic-GPS hydrographic surveying that NOS is 

planning to implement (Hess et al., 2003). 

A software tool under development at NOS called VDatum is designed to transform among 

approximately 30 vertical reference datums (Milbert, 2002; Parker, 2002). These datums fall 

into three categories: ellipsoidal, orthometric, and tidal datums. The ellipsoidal datum and 

orthometric datum fields have already been computed as well as the transformations between 

these two types of datums on a national-scale grid. The transformations among tidal datums 

relative to Local Mean Sea Level (LMSL) and the transformation between LMSL and the North 

American Vertical Datum of 1988 (NAVD 88) are under development. 

The two-dimensional barotropic hydrodynamic tide model ADCIRC (Luettich et al., 1992; 

Luettich and Westerink, 2004) was used to determine the tidal datums in this region of the Gulf 

of Mexico. An unstructured mesh that closely mimicked the MHW coastline was developed and 

bathymetry from NOS sounding data was incorporated into the grid. The model was run and the 

water level was recorded every 6 minutes at every node in the grid. This data was analyzed to 

compute the datums throughout the domain. The model results were compared to datums at 

NOS tide stations throughout the region and the error between the model and the data was 

calculated. The modeled datums were adjusted to match the tide station data by spatially 

interpolating the error throughout the domain. This error field was subtracted from the modeled 

datum fields to produce corrected datum fields that match the data at the NOS tide stations. The 

final corrected datums were used to populate a structured VDatum marine grid that is used in the 

VDatum software package. Finally, the topography of the sea surface, which relates LMSL to 

NAVD 88, was developed, based on leveling connections from geodetic benchmarks to tidal 

benchmarks in the vicinity of each tide station. 
2

2. DATA SOURCES 

This VDatum project includes the development of a hydrodynamic storm surge model whose 

domain and grid cover from region from the Mississippi Delta in the west to Cape San Blas in 

the east. The VDatum portion is intended to cover a smaller area within this domain, namely the 

near-shelf coastal waters out to 25 nmi as well as the bays and estuaries of Alabama and west 

Florida as far east as Cape San Blas. Thus the data acquired must meet both these purposes. 

2.1. Coastline Data 

The MHW coastline was used as a guideline for creating the unstructured grid used for the tidal 

datum modeling and to define the extent of the VDatum marine grid. The MHW shoreline 

derived from Electronic Navigational Charts (ENCs) is the most accurate shoreline available. It 

is based on nautical charts with scales between 1:10,000 and 1:80,000 with emphasis on the 

larger scales. Not all of the charts in U.S. waters are available as ENCs, and, therefore, shoreline 

data was not available for all areas of the domain. Where the ENC data was unavailable, 

NOAA’s Medium Resolution shoreline was used. This shoreline has a nominal mapping scale of 

1:70,000. The Medium Resolution shoreline was created by NOAA’s Special Projects Office 

(SPO) in the 1980’s, and in most places it differs slightly (around 0.1 nmi) from the ENC 

shoreline. This is due in part to actual physical changes in the shoreline, but mostly because the 

newer charts (and therefore newer shoreline) used for the ENCs have revised positions corrected 

with GPS. The shoreline segments were connected manually to produce one continuous 

shoreline segment for the land boundary and additional segments for the islands in the region. 

2.2. Tide Station Data 

The entire model domain extends from southern coastal Louisiana, in the west to Cape San Blas, 

Florida, in the east. All NOS tide stations between 28.80o N and 30.75o N latitude and between 

90.20o W and 85.30o W longitude were selected from the TideSheet1005 (developed in October 

2005) version of the Coast Survey Development Laboratory (CSDL) “TideSheet” data file. This 

data file contains tidal datums and other information as available, such as harmonic constant data 

,and geodetic datums, at existing and historic CO-OPS stations. If more than one station 

occupied the same location, the station with the largest identification number (presumably the 

most recent or longest-running record) was kept and the other stations were eliminated. A total 

of 187 stations were found within this boundary. Next, these stations were compared to the grid 

that was designed for the modeling study (see Section 3). All of the stations that were more than 

500 meters away from a grid node were eliminated. After this test, 117 stations remained. 

Seventeen of these stations were removed for a variety of reasons that are described in Appendix 

A. 

In the end, 100 NOS tide stations were selected for the entire domain. A subset of the 74 stations 

that fall within the VDatum domain (that extends only from Mobile Bay, Alabama, in the west to 

Cape San Blas, Florida, in the east) was selected for the final model comparison and correction. 

The entire set of 100 stations is shown in Figure 1. The 74 stations in the VDatum region are 

shown in blue and the remainder in red. The locations and names are listed in Table 1. 
3

 

Figure 1. Tide stations in the northeast Gulf of Mexico region used to the hydro-dynamic 

modeling (red and blue squares) and for VDatum (red squares). The dashed lines represent 

the limits of the area searched for stations, and the purple line represents the 25 nmi limit. 

Table 1. List of the 100 tide stations in the model domain. Stations from the 1983-2001 

National Tidal Datum Epoch are marked with an asterisk (*) next to the Station ID. 

No. Station ID Latitude Longitude Station Name 

1 8728912 * 29.815001 -85.313332 PORT_ST_JOE_FL 

2 8728942 * 29.668301 -85.360001 CAPE_SAN_BLAS 

3 8728949 * 29.690001 -85.363297 RICHARDSON_HAMMOCK__ST 

4 8728958 * 29.873301 -85.389999 ST._JOSEPH_POINT 

5 8728973 * 30.038300 -85.393303 WETAPPO_CREEK__EAST_BAY 

6 8728995 29.948299 -85.425003 MEXICO_BEACH 

7 8729015 * 30.030001 -85.464996 ALLANTON__EAST_BAY 

8 8729017 * 30.016666 -85.470001 FARMDALE_EAST_BAY 

9 8729039 * 30.136700 -85.516701 PARKER_BRANCH__LAIRD_BAY 

10 8729045 * 30.121666 -85.528336 LAIRD_BAYOU_EAST_BAY_FL 

11 8729063 * 30.136700 -85.571701 CALLAWAY_BAYOU__EAST_BAY 

12 8729071 * 30.245001 -85.605003 MILL_BAYOU__NORTH_BAY 

13 8729084 * 30.126699 -85.611702 PARKER__EAST_BAY 

14 8729085 * 30.098301 -85.613297 PEARL_BAYOU__EAST_BAY 

15 8729101 * 30.283300 -85.646698 SOUTHPORT__NORTH_BAY 

16 8729102 * 30.254999 -85.648300 LYNN_HAVEN__NORTH_BAY 

17 8729105 * 30.091700 -85.648300 BEACON_BEACH__ST_ANDREW 

18 8729108 * 30.151667 -85.666664 PANAMA_CITY 

19 8729117 30.113333 -85.680000 S_OF_DAVIS_POINT 

20 8729119 * 30.094999 -85.684998 SHELL_ISLAND 

21 8729141 * 30.133301 -85.731697 ST._ANDREWS_STATE_PARK 

22 8729149 * 30.129999 -85.743301 ST._ANDREW_STATE_PARK 

23 8729152 * 30.170000 -85.754997 ALLIGATOR_BAYOU 
4

Table 1. (Continued). 

No. Station ID Latitude Longitude Station Name

24 8729155 * 30.158300 -85.768303 GRAND_LAGOON__WEST_END 

25 8729169 * 30.215000 -85.739998 SHELL_POINT__WEST_BAY 

26 8729189 30.186701 -85.833298 PANAMA_CITY_BEACH 

27 8729193 30.230000 -85.833336 WEST_BAY 

28 8729197 * 30.293301 -85.858299 WEST_BAY_CREEK 

29 8729210 * 30.213333 -85.879997 PANAMA_CITY_BEACH 

30 8729332 * 30.428301 -86.136703 JOLLY_BAY 

31 8729333 * 30.468300 -86.138298 LA_GRANGE_BAYOU 

32 8729364 * 30.488300 -86.205002 ALLAQUAY_BAYOU 

33 8729376 * 30.400000 -86.228302 SANTA_ROSA_HOGTOWN_BAYOU 

34 8729387 * 30.486700 -86.253304 BASIN_BAYOU 

35 8729435 * 30.465000 -86.351700 BIG_HAMMOCK_PT 

36 8729479 30.506666 -86.446663 ROCKY_BAYOU_FL 

37 8729501 * 30.503300 -86.493301 VALPARISO__BOGGY_BAYOU 

38 8729505 30.393333 -86.504997 OLD_PASS_LAGOON_FL 

39 8729511 * 30.395000 -86.513298 DESTIN__EAST_PASS 

40 8729538 * 30.434999 -86.586670 GARNIER_BAYOU 

41 8729548 * 30.469999 -86.593300 CAMP_PINCHOT 

42 8729554 30.401699 -86.610001 FORT_WALTON_BEACH 

43 8729567 * 30.428301 -86.631699 CINCO_BAYOU 

44 8729598 * 30.406700 -86.699997 HULBERT_FIELD 

45 8729613 * 30.408300 -86.731697 HARRIS__SANTA_ROSA_SND 

46 8729678 * 30.376667 -86.864998 NAVARRE_BEACH_FL 

47 8729679 * 30.385000 -86.863297 SANTA_ROSA_SOUND 

48 8729702 30.450001 -86.918297 EAST_BAY__HOLLEY 

49 8729736 * 30.386700 -86.991699 WOODLAWN_BEACH 

50 8729747 * 30.581699 -87.014999 SHIELD_POINT__BLACKWATER 

51 8729753 * 30.636700 -87.028297 BLACKWATER_RIVER 

52 8729757 * 30.626699 -87.036697 MILTON 

53 8729791 * 30.455000 -87.099998 HERNANDEZ_POINT_NORTH 

54 8729806 * 30.336700 -87.139999 FISHING_BEND__SANTA_ROSA 

55 8729808 * 30.336700 -87.146698 LITTLE_SABINE_BAY 

56 8729816 30.514999 -87.161697 LORA_POINT__ESCAMBIA_BAY 

57 8729824 * 30.581699 -87.180000 FLORIDATOWN__ESCAMBIA_BAY 

58 8729840 * 30.403299 -87.211700 PENSACOLA__PENSACOLA_BAY 

59 8729849 * 30.401699 -87.251701 BAYOU_CHICO 

60 8729868 * 30.344999 -87.273300 PENSACOLA__NAVAL_AIR_STA 

61 8729871 * 30.375000 -87.276703 WARRINGTON__BAYOU_GRANDE 

62 8729882 * 30.330000 -87.291702 FORT_PICKENS__PENSACOLA 

63 8729889 * 30.370001 -87.318298 HEAD_OF_BAYOU_GRANDE 

64 8729905 * 30.418301 -87.356697 MILLVIEW__PERDIDO_BAY 

65 8729909 * 30.326700 -87.356697 BIG_LAGOON 

66 8729938 * 30.350000 -87.415001 TARKLIN_BAY 

67 8729943 * 30.458300 -87.408302 HURST_HAMMOCK__PERDIDO 

68 8729962 * 30.393299 -87.425003 PERDIDO_BAY 

69 8729974 * 30.299999 -87.448303 PERDIDO_KEY__OLD__RIVER 

70 8730667 * 30.278299 -87.555000 ALABAMA_POINT__PERDIDO 

71 8731269 30.248333 -87.668335 GULF_SHORES_AL 

72 8731952 * 30.303301 -87.735001 BON_SECOUR 

73 8735180 * 30.250000 -88.074997 DAUPHIN_ISLAND_AL 

74 8737048 * 30.708300 -88.043297 MOBILE_STATE_DOCKS 

75 8735587 30.258333 -88.113335 NORTH_POINT_DAUPHIN_ISL 

76 8741196 30.340000 -88.533302 PASCAGOULA_POINT 

77 8742221 * 30.238300 -88.666702 HORN_ISLAND 
5

Table 1. (Continued). 

No. Station ID Latitude Longitude Station Name

78 8743281 * 30.391701 -88.798302 OCEAN_SPRINGS 

79 8743735 * 30.389999 -88.856697 BILOXI_(CADET_POINT) 

80 8744756 * 30.213301 -88.971703 SHIP_ISLAND 

81 8745557 * 30.360001 -89.081703 GULFPORT_HARBOR 

82 8745799 * 30.231701 -89.116699 CAT_ISLAND 

83 8746819 * 30.309999 -89.245003 PASS_CHRISTIAN_YACHT_CLUB 

84 8746943 30.341667 -89.264999 HENDERSON_AVE_BAYOU_PORT 

85 8747131 * 30.326700 -89.288300 MALLINI_BAYOU_NORTH 

86 8747398 * 30.373301 -89.321701 NORTH_SHORE__BAY_OF_ST. 

87 8747437 * 30.325001 -89.324997 BAY_WAVELAND_YC_BAY_ST 

88 8747739 * 30.336700 -89.366699 JOURDAN_RIVER_ENTRANCE__ 

89 8747766 * 30.281666 -89.366669 WAVELAND_MISSISSIPPI_SND 

90 8748525 30.173334 -89.463333 LOWER_POINT_CLEAR 

91 8748842 * 30.186666 -89.506668 WESTERN_CAMPBELL_OUTSIDE 

92 8760551 * 28.990000 -89.139999 SOUTH_PASS_LA 

93 8760595 * 29.493299 -89.173302 BRETON_ISLAND 

94 8760668 * 30.126667 -89.221664 GRAND_PASS_LA 

95 8760742 * 29.823334 -89.269997 COMFORT_ISLAND_LA 

96 8760922 * 28.931700 -89.406700 PILOTS_STATION_EAST_SND 

97 8760943 * 28.924999 -89.418297 PILOT_STATION__SW_PASS 

98 8761305 * 29.868334 -89.673332 SHELL_BEACH_LAKE_BORGNE 

99 8761529 * 29.945000 -89.834999 MARTELLO_CASTLE 

100 8761623 29.166666 -89.900002 HUMBLE_OIL_PLATFORM 

In the following figures the tide stations and their 7-digit NOS identification numbers are shown.

Figure 2. Tide stations on the Mississippi River Delta (left) and in Mobile Bay (right). 
6

 

 

Figure 3. Tide stations in Mississippi (top), Perdido and Pensacola Bays (mid), and 

Choctawachee Bay (bottom). 
7

 

 

Figure 4. Tide stations in St Andrews Bay (top) and in St Joseph Bay (bottom). 

 

Of the 74 stations in the VDatum area (which are the first 74 stations listed in Table 1), all have 

been updated to the 1983-2001 NTDE except for 9 stations, which are referenced to the 1960-

1978 NTDE. The 65 stations that were updated to the 1983-2001 NTDE were compared with 

data at the same location from the 1960-1978 NTDE. The absolute averaged difference in the 

Diurnal Range of Tide (GT), which is the difference between MHHW and MLLW, between the 

datums for adjacent NTDEs averaged over all stations is 0.86 cm, which is 3.2% of the total GT. 

Although several outliers exist, the average difference is low enough that the 9 stations still 

referenced to the 1960-1978 NTDE were deemed acceptable and used for model validation and 

correction. In general, differences of the range of tide between NTDE periods should only be 

expected if the tidal hydrodynamics change significantly over time, such as due to dredging and 

channel deepening (Zervas, 2003). Table 2 lists the range for each of the 65 stations and the 

statistics computed at each station. 
8

Table 2. Diurnal tide ranges from the Old (1960-1978) and the New (1983-2001) National 

Tidal Datum Epochs, and the differences. Percent is 100 times the Difference, divided by 

the mean of Old and New ranges.

Station 

Range (m) 

1960-1978 

NTDE 

Range (m) 

1983-2001 

NTDE 

Ratio 

(New/Old) 

Difference(m) 

(Old – New) 

Percent 

8728912 0.509 0.504 0.99 0.005 0.99% 

8728942 0.424 0.438 1.03 -0.014 3.33% 

8728949 0.530 0.522 0.98 0.008 1.59% 

8728958 0.475 0.475 1.00 0.000 0.10% 

8728973 0.518 0.504 0.97 0.014 2.77% 

8729015 0.471 0.466 0.99 0.005 1.07% 

8729017 0.486 0.476 0.98 0.010 2.08% 

8729039 0.451 0.438 0.97 0.013 2.95% 

8729045 0.456 0.448 0.98 0.008 1.77% 

8729063 0.451 0.438 0.97 0.013 2.95% 

8729071 0.463 0.456 0.98 0.007 1.59% 

8729084 0.439 0.432 0.98 0.007 1.59% 

8729085 0.433 0.428 0.99 0.005 1.12% 

8729101 0.479 0.472 0.99 0.007 1.38% 

8729102 0.457 0.448 0.98 0.009 2.03% 

8729105 0.408 0.402 0.98 0.006 1.59% 

8729108 0.418 0.409 0.98 0.009 2.08% 

8729119 0.402 0.400 0.99 0.002 0.58% 

8729141 0.424 0.418 0.99 0.006 1.35% 

8729149 0.475 0.466 0.98 0.009 2.02% 

8729152 0.421 0.417 0.99 0.004 0.95% 

8729155 0.396 0.392 0.99 0.004 1.08% 

8729169 0.445 0.418 0.94 0.027 6.26% 

8729197 0.460 0.444 0.97 0.016 3.59% 

8729210 0.427 0.418 0.98 0.009 2.13% 

8729332 0.168 0.170 1.01 -0.002 1.40% 

8729333 0.134 0.131 0.98 0.003 2.35% 

8729364 0.155 0.153 0.98 0.002 1.59% 

8729376 0.134 0.178 1.33 -0.044 28.12% 

8729387 0.131 0.123 0.94 0.008 6.35% 

8729435 0.137 0.148 1.08 -0.011 7.60% 

8729501 0.137 0.151 1.10 -0.014 9.61% 

8729511 0.155 0.186 1.20 -0.031 17.90% 

8729538 0.128 0.124 0.97 0.004 3.19% 

8729548 0.152 0.134 0.88 0.018 12.85% 

8729554 0.162 0.156 0.97 0.006 3.49% 

8729567 0.140 0.142 1.01 -0.002 1.27% 

8729598 0.360 0.356 0.99 0.004 1.02% 

8729613 0.381 0.381 1.00 0.000 0.00% 

8729678 0.427 0.421 0.99 0.006 1.35% 

8729679 0.427 0.422 0.99 0.005 1.11% 

8729736 0.421 0.415 0.99 0.006 1.35% 

8729747 0.472 0.484 1.02 -0.012 2.42% 

8729753 0.494 0.505 1.02 -0.011 2.25% 
9

Table 2. (Continued). 

Station

Range (m) 

1960-1978 

NTDE

Range (m) 

1983-2001 

NTDE

Ratio 

(New/Old)

Difference(m) 

(Old – New)

Percent 

8729757 0.491 0.482 0.98 0.009 1.79% 

8729791 0.402 0.397 0.99 0.005 1.34% 

8729806 0.393 0.391 0.99 0.002 0.56% 

8729808 0.396 0.392 0.99 0.004 1.08% 

8729824 0.445 0.442 0.99 0.003 0.68% 

8729840 0.387 0.383 0.99 0.004 1.06% 

8729849 0.381 0.376 0.99 0.005 1.32% 

8729868 0.366 0.364 1.00 0.002 0.48% 

8729871 0.372 0.368 0.99 0.004 1.04% 

8729882 0.357 0.350 0.98 0.007 1.87% 

8729889 0.384 0.376 0.98 0.008 2.12% 

8729905 0.229 0.229 1.00 0.000 0.17% 

8729909 0.311 0.322 1.04 -0.011 3.51% 

8729938 0.189 0.193 1.02 -0.004 2.11% 

8729943 0.238 0.240 1.01 -0.002 0.94% 

8729962 0.219 0.218 0.99 0.001 0.67% 

8729974 0.195 0.247 1.27 -0.052 23.49% 

8730667 0.265 0.262 0.99 0.003 1.14% 

8731952 0.472 0.470 1.00 0.002 0.52% 

8735180 0.372 0.367 0.99 0.005 1.31% 

8737048 0.500 0.479 0.96 0.021 4.26% 

2.3. Bathymetric Data 

All of the bathymetric data for this project came from NOS sounding data archives or were 

digitized directly from the nautical charts. A search of the NOAA National Geodetic Data 

Center’s (NGDC’s) GEOphysical DAta System (GEODAS) yielded a total of 328 NOS 

hydrographic surveys conducted within the model domain. Of these surveys, 125 were 

referenced to MLLW and the other 202 were referenced to MLW. The dates of the MLW 

surveys range from 1899 to 1989, and the MLLW survey dates range from 1935 to 1994. These 

data are saved in file pscola_nos_bathy.tar. Additionally, 6,823 sounding depths were digitized 

from current Electronic Navigation, and these were all referenced to MLLW. These data are 

saved in file dig_bathy.tar. A sample of the depths from NGDC’s Coastal Relief Model in the 

coastal region of the study area is shown in Figure 5. Additional information about the source of 

the bathymetric data is given in Appendix B. 

 
10

 

Figure 5. Bathymetry in the coastal region within 25 nmi of the coastline. Data are from 

NOAA’s Coastal Relief Model. 

3. TIDAL DATUM MODELING 

Throughout the development of the VDatum vertical datum transformation software, several 

approaches have been used for computing the tidal datum fields that are used to populate the 

VDatum marine grids. The simplest method is to spatially interpolate the datum values directly 

from the NOS tide stations. This method works best in an enclosed bay or estuary with a dense 

network of stations. An example of this method was used in the creation of the first version of 

the Delaware Bay VDatum application (Hess et al., 2003). The second method that has been 

employed for the VDatum project is to use data from a pre-existing tidal constituent database. 

The harmonic constant data is re-constituted into water level time series, which are then analyzed 

to calculate the tidal datum fields. The datums are adjusted so that the datums match the NOS 

tide station data at those locations. This method is dependent on the availability of a tidal 

constituent database in the area of interest. This method was used for the creation of the Strait of 

Juan de Fuca VDatum application (Spargo et al., 2006). The third method, which was used for 

this study, is to set up and run a regional hydrodynamic model. This approach is the most 

complex and time consuming as the modeler needs to create a grid for the domain, populate this 

grid with bathymetry, set the model parameters, and run the model several times to converge to 

the best modeled solution. At that point, the error between the model and the station data is 

spatially interpolated to allow the final datum fields to match the station data at those locations. 

The advantage of this approach over using tidal databases is the flexibility in grid design over the 

pre-positioned tidal constituent database grids. Another example of a VDatum application using 

this approach is in the Central North Carolina area (Hess et al., 2005). Whereas the interpolation 
11

of the datums does not address the underlying physical processes, the model will more accurately 

reflect the hydrodynamics in the region. 

3.1. Hydrodynamic Model 

The hydrodynamic model used for this study was the two-dimensional, depth-integrated version 

of the ADvanced CIRCulation (ADCIRC) model (Luettich et al., 1992; Luettich and Westerink, 

2004). This is a barotropic finite element model that has been used in previous VDatum areas 

(Hess et al., 2005; Spargo and Woolard, 2005). The ADCIRC code allows a variety of userspecified input parameters. For these model runs, the full non-linear form of the equations were 

used, which includes non-linear bottom friction, finite amplitude and convection terms. The 

model runs began with a smooth hyperbolic tangent time ramp function, which was applied for 

the first 5 days. The open boundary of the model grid, located in the Gulf of Mexico, was forced 

with a synthetic tide that was generated using the amplitude and phase of six tidal constituents 

(K1, O1, Q1, M2, S2, and N2) extracted from an inverse model (Myers and Baptista, 2001; Myers, 

unpublished document) based on the model grid used to create the EastCoast2001 tidal 

constituent database (Mukai et al., 2001). The node factors and equilibrium arguments were set 

to the values from the middle of 1992 (which is in the middle of the 1983-2001 NTDE). A no 

flow boundary was set for all land segments except at the upstream end of the Perdido River, 

where, to prevent reflection of the tide back into Perdido Bay, a radiation boundary condition 

was used Wetting and drying was allowed for this model run. The lateral eddy viscosity 

coefficient was set to 5 m2/s, which was the lowest possible number that did not produce 

numerical instabilities. 

The ADCIRC model allows for several different methods of implementing bottom stress. 

Generally, bottom stress is expressed as τbx=Uτ* and τby=Vτ*, where U and V are the velocity 

terms and τ* is the bottom friction coefficient. For the linear friction option, τ* = Cf , where Cf is 

the user-specified bottom friction coefficient, and that term is constant in time, but may vary in 

space. For the quadratic friction option, which was used for the model runs discussed in this 

report, a more complex formula is used for τ* such that: 

H

Cf U V 2

1 2 2

*

( + )

τ = (1) 

where H is the bathymetric depth at the node, and the Cf value was set to a standard value of 

0.003. 

For each iteration, the model was run for 40 days with a 3 second time step. The small time step 

was due to the Courant number limitation imposed by the small element sizes. The water surface 

elevation was recorded at every node in the grid every 6 minutes for the last 33 days of the 40-

day model run. This time series data was later used to tabulate the higher-high, lower-high, 

higher-low, and lower-low waters, from which the datums could be computed. 

The ADCIRC model has been parallelized using domain decomposition, a conjugate gradient 

solver and Message Passing Interface (MPI) based message passing. This parallel version of the 

code was compiled and run on NOAA’s Earth System Research Laboratory (ESRL) EJET 
12

computer in Boulder, Colorado. It took approximately 6 wall-clock hours to complete a single 

40-day run utilizing 50 processors. 

3.2. Model Grid Development 

The ADCIRC model takes advantage of unstructured grids, which allow increasing resolution in 

areas of interest or areas with complex hydrodynamics such as over the shelf break or through 

inlets. Knowing that the grid developed for this study would become the base grid of the Gulf of 

Mexico Storm Surge Partnership Project, the domain was expanded beyond the VDatum region 

(from Mobile Bay, Alabama, to Cape San Blas, Florida) to include Chandeleur Sound, Brenton 

Sound and the Mississippi Delta region in Louisiana. 

Figure 6 gives several views of the unstructured grid. The resolution, which is measured as the 

average distance between the nodes in an element, ranges from 24 km at the open ocean 

boundary down to 24 m in sections of the Intracoastal Waterway. Along the coastal areas of 

Louisiana, the resolution is around 350 m, and the average in the Alabama and Florida regions is 

100 m. For model stability, the change in size between elements must be gradual, and great care 

was taken to ensure a smooth transition between areas of low and high resolution. The grid has 

192,889 nodes and 367,019 elements. 

3.3. Incorporating Bathymetric Data 

3.3.1. General Methods 

Two methods were used to interpolate the bathymetric sounding data onto the grid. In most 

locations, the bathymetric data was added to the grid using a so-called cluster averaging 

approach. Each node in the grid is surrounded by a cluster of elements that share that node as 

one of the vertices. (For nodes that are on the edge of the grid, there may be only one or two 

nodes in this “cluster”.) For the cluster averaging method, all of the sounding data points that 

fall within that cluster of elements are linearly averaged and that average is applied as the 

bathymetric depth for the node. This method allows the data to be filtered into the grid at the 

grid scale. In cases where no sounding points fall within the element cluster surrounding a node, 

the null value of -9999 is assigned as the bathymetric depth for that node. 

The second method used was a linear interpolation option available with the Surface-Water 

Modeling System (SMS) software. The sounding data points are read into SMS and the program 

triangulates the data points to create a TIN. The surface is assumed to vary linearly across each 

triangle in the TIN. Since a TIN only covers the convex hull of a scatter point set, extrapolation 

beyond the convex hull does not occur. The nodes in the grid are assigned values based from the 

TIN, but any nodes outside the convex hull of the scatter point set are assigned the null value of 

-9999. 
13

 

Figure 6. Unstructured grid of (a) the entire modeling region and zoomed views of the 

entrances to (b) Perdido Bay and (c) Pensacola Bay. 

3.3.2. Adding Bathymetric Data 

The bathymetry in the final unstructured grid was built up, in a sense, starting with the newest 

and most reliable data and filling in the gaps with older, less reliable data. Initially, all of nodes 

in the grid were given bathymetric depths of -9999. The survey data was added one survey at a 

time by date and datum. First the 126 surveys referenced to MLLW were used in order from 

newest to oldest. All of the data from the newest MLLW-referenced survey were added to the 

grid using the cluster averaging approach. In the areas where no data from that survey was found, 

the nodes retained the -9999 null value. This process continued with the second newest MLLWreferenced survey. In this case, if nodes had a bathymetric value (from the application of the 

more recent survey data), no changes would be made; only the nodes with -9999 null values 

could be populated with bathymetry from the second newest MLLW-referenced dataset. This 

process continued until all of the surveys had been processed, which resulted in a grid file with 

bathymetric data referenced to MLLW where it was available. The digitized soundings 

(referenced to MLLW) were added to this grid to expand the coverage of the MLLW data. A 

visual inspection showed that the recent surveys referenced to MLLW in Mobile Bay were very 

b c

a
14

sparse. Eventually when the older MLW surveys (from the 1960’s) were added to the sparse grid 

with newer surveys (from1987), the resulting bathymetry contours would be very irregular and 

unrealistic. To avoid this problem, the linear interpolation package available with the SMS 

software was used in Mobile Bay to spatially interpolate the sparse soundings. Figure 7 shows 

the soundings interpolated onto the grid using the cluster averaging approach and then with the 

SMS linear interpolation. 

Next, the MLW-referenced survey data were applied to the original blank grid file (where all 

nodes had bathymetry listed as -9999). The data was again added survey by survey from newest 

to oldest. In this way, two separate grids were made where all of the data in one was referenced 

to MLLW and the other referenced to MLW. The data could not be combined until the data was 

referenced to a common datum. 

 

Figure 7. MLLW sounding values interpolated onto the grid by (a) the cluster averaging 

approach and (b) linear interpolation using the utilities in the Surface Water Modeling 

System software. 

3.3.3. Adjusting Data to a Common Vertical Datum 

The adjustment to a common datum is the most complex part of the problem. In fact, this is what 

the VDatum software is designed to do, but without the completed VDatum package, 

determining the tidal datum fields becomes an iterative process. 

The first step is to make an initial guess at the datum differences. For this modeling study, the 

initial adjustment was a 2-step process. First the MLW-to-MLLW difference was examined at all 

100 NOS tide stations throughout the region. The difference was very small, averaging only 

a b
15

about 2 cm. In the ADCIRC model, all depths are positive numbers and heights are negative 

numbers, so to adjust grid with the bathymetry referenced to MLW to a grid with to MLLWreferenced data, the 2 cm offset was added to every node (except the null value nodes). 

At this point, the original MLLW grid and the grid where the MLW bathymetric depths were 

approximately adjusted to MLLW could be combined. At the nodes where the original MLLW 

data was available, those depths were used, and the MLW bathymetry adjusted to MLLW was 

used elsewhere. There were still 6,450 nodes with -9999 null values for the depth. These were 

filled in by interpolation and extrapolation from the surrounding nodes. 

The ADCIRC model zero (MZ) is a geopotential surface. In the open ocean, this is very close to 

MSL, but in the inlets and estuaries, MZ can differ from MSL. For this initial estimate, the two 

were assumed to be equal throughout the domain. The difference between MLLW and MSL was 

calculated to be a spatially varying field. This field was created using the Tidal Constituent And 

Residual Interpolation (TCARI) program (Hess, 2002) which used the MLLW-MSL difference 

from all 100 NOS tide stations located throughout the region to solve the Laplace Equation 

taking landforms into account. The TCARI spatial interpolation program will be discussed in 

more detail in Section 4, below. TCARI was run on the same unstructured grid designed for the 

model runs, so a spatially interpolated MLLW-MSL field was generated with an adjustment 

value at every node in the grid. The grid with bathymetry referenced to MLLW was easily 

adjusted to an estimated MSL-referenced bathymetry by adding the spatially interpolated 

adjustment field to the original bathymetric data. 

After the initial model run (with the grid depths referenced to MSL based on the estimates 

discussed above), the 33-day water surface elevation time series was analyzed at each node to 

calculate the MHHW, MHW, MLW, and MLLW datum fields all relative to MSL. These 

modeled tidal datum fields were used to apply a spatially changing adjustment for the original 

bathymetry (instead of a constant value). The grid with the bathymetry referenced to MLW was 

adjusted directly to MZ (which can now vary from the MSL calculated from the model runs) 

without an intermediate adjustment to MLLW. The grid with the bathymetry referenced to 

MLLW was adjusted directly to MZ, as well. At this point, the depths values in the two grids 

were combined in the manner discussed above, where the depths from the MLLW-to-MZ grid 

were used first and the MLW-to-MZ grid depths were used second. Again, there were 6,450 

nodes with null values that were filled by interpolation and extrapolation from the surrounding 

nodes depths. 

After this initial step, the iterative process continued: after each model run, the original MLW 

and MLLW grid depths were adjusted to MZ and then combined to create a grid for the next 

model run. 

3.4. Model Results 

After each model run, the results were evaluated for accuracy compared to the 74 NOS tide 

stations in the area. Additionally, the tidal datum fields were examined visually for 

discontinuities or abnormalities that would indicate instabilities in the model run. 

After the initial set of runs, the absolute value of the error for each modeled datum compared to 

the station data was generally less than 3 cm, but due to the very small tide range, this absolute 
16

error translated into a percent error of over 25% in some places. The highest errors were in the 

Perdido Bay area where the model results showed an over-prediction trend compared to the data. 

Several attempts to correct this error in this area were made. First, the domain was extended to 

include the lower end of the Perdido River. The results from this grid showed no marked 

improvement over the original results. A radiation boundary condition was added to the upstream end of the river to prevent the tides from being reflected back into the domain. Still, the 

model results showed an overprediction in the tidal datum values in this region. Upon further 

examination, most of the tide appeared to be entering the bay not through the inlet at the entrance 

to Perdido Bay, but through the Intracoastal Waterway (ICW) that connects Perdido Bay to 

Pensacola Bay. Further refinement was added to this section of the ICW, which allowed a more 

accurate representation of the bathymetry in this passage. No major changes were yielded from 

this approach. For experimental purposes, the bathymetry in the channel was artificially 

truncated to create a shallower entrance to the Perdido Bay. Again, no major changes were 

observed. At the conclusion of these experiments, several changes were incorporated. The grid 

used for the final series of runs had the extended section of the Perdido River with the radiation 

boundary condition and increased resolution in the ICW connecting Pensacola Bay to Perdido 

Bay with the regular (non-modified) depths in that channel. Instead of dramatically tuning the 

bathymetry or other model input parameters in this region (which could disrupt the balance in 

other regions of the model), the final model results were accepted and corrections were made 

using the TCARI spatial interpolation program to match the model results to the station data 

located throughout the domain. 

As discussed in Section 3.3 above, the first run of the model used a grid with bathymetry depths 

adjusted to MZ based on an initial estimate of the datum differences and the assumption that MZ 

and MSL were equal. The results from this model run were used to adjust the original 

bathymetry set. Another model run was completed where the grid for this run had bathymetry 

relative to MZ based on the adjustments calculated from the previous run. In total, 5 iterative 

model runs were completed. Negligible improvements were seen after each run indicating that 

the model had converged to a stable solution. Table 3 lists the absolute average and percent error 

for each model run for the MHHW, MHW, MLW and MLLW datums (all relative to Local 

MSL) averaged over all 74 NOS tide stations in the VDatum region. 

Table 3. Absolute average and percent error for each datum for the final series of runs 

averaged for the 74 NOS tide stations in the VDatum region. 

Datum Initial Run Run 2 Run 3 Run 4 Run 5 

MHHWMSL 1.86cm 10.69% 1.88cm 10.64% 1.85cm 10.42% 1.85cm 10.38% 1.86cm 10.44% 

MHWMSL 1.58cm 10.52% 1.58cm 10.42% 1.55cm 10.21% 1.55cm 10.17% 1.55cm 10.23% 

MLWMSL 1.58cm 11.20% 1.58cm 11.05% 1.56cm 10.88% 1.55cm 10.82% 1.56cm 10.87% 

MLLWMSL 2.21cm 12.61% 2.22cm 12.55% 2.19cm 12.34% 2.18cm 12.28% 2.19cm 12.33% 

Total 

Average 1.81cm 11.26% 1.81cm 11.17% 1.79cm 10.96% 1.78cm 10.91% 1.79cm 10.97% 
17

The MHHW-MSL and MLLW-MSL datum results are shown in Figure 8 compared to the 

observations at the 74 NOS tide stations in the VDatum domain. The 45° line shows a one-to-one 

correlation. The error bars (dashed lines) are plotted to show a 5-cm difference between the 

model and the observations. The station name, station identification number, tidal datums at the 

NOS tide stations, hydrodynamic model results at those locations, difference between the two, 

and the absolute average percent difference are listed for all 74 stations in Appendix C. 

Figure 8. Comparison of the MHHW-MSL (squares) and MLLW-MSL (circles) 

observations (m) versus the modeled tidal datums with 5-cm error bands. 

4. INTERPOLATION OF ERRORS 

The datum results from the model matched closely with the NOS tide station data in most 

locations, but did not match exactly at any location. This is expected since the model simulates 

the astronomical tide only, while the station data includes meteorological effects. The VDatum 

project is faithful, in a sense, to the data and it is important that the datum fields used with the 

VDatum software match the published datums at those locations. This match is made possible 

by spatially interpolating the error between the model and the station data and then applying this 

error field to the model results. 

The Tidal Constituent And Residual Interpolation (TCARI) program, which solves the Laplace 

Equation taking landforms into account (so that the results bend around islands and peninsulas), 

was used to spatially interpolate the error. This program has been discussed briefly in previous 

sections, but more details will be given here. TCARI is available in two versions. The first 

version solves the equation using the successive over-relaxation finite difference method. This 
18

version requires a structured grid. The second version solves the equation using the finite 

element method. This program requires a triangulated grid. Since the hydrodynamic model grid 

is triangulated, the finite element version of TCARI was employed so that the same grid could be 

used. The input into the program was the model error at the locations of the NOS tide stations. 

The TCARI model was run once for each datum and the results were a new grid file with the 

spatially interpolated error field listed as the z-value. 

The model grid was designed with emphasis on the VDatum region, so the regions with the 

highest levels of resolution are located in this area. The model error outside that region was not 

evaluated, and corrections were only made in the VDatum region. To speed up the TCARI 

program (by eliminating computational points), a subsection of the grid was selected for the 

interpolation process. The final MLLW-MSL model results on that section of the grid are shown 

in Figure 9. Also, the TCARI interpolation of the MLLW-MSL error and the corrected model 

results on the same grid are shown in Figure 9. 

After the corrected datum fields were created, the MTL and DTL datum fields were calculated 

by taking the average of MHW-MSL and MLW-MSL and the average of MHHW-MSL and 

MLLW-MSL at each node in the smaller model grid (shown in Figure 9) with the corrected 

datum fields, respectively. All of the corrected datum fields are shown in Appendix D. 

a

b
19

Figure 9. Subsection of the model grid with the (a) modeled MLLW-MSL (m) datum field 

(m), (b) interpolated MLLW-MSL error field (m), and (c) final corrected MLLW-MSL 

datum field (m).

5. CREATION OF THE VDATUM MARINE GRID AND POPULATION WITH DATUMS 

5.1. Generation of the VDatum Marine Grid 

The VDatum software requires a regular grid for the vertical datum transformation calculations. 

This grid is called the VDatum marine grid and every node in the grid is identified as either a 

water node or a land node. A computer program (gridder.f) is used to create this marine 

grid, and the program requires both a MHW coastline and a bounding polygon. First, the entire 

array is developed as a rectangular grid with locations within a latitude and longitude window. 

Next, individual nodes are designated as either land or water points. Nodes are defined as water 

if they are (1) completely within the bounding polygon, and are either (2a) not within a land 

mass or island, or (2b) within a land mass or island but are within one half of a cell size of the 

coastline. All nodes not meeting these criteria are defined as land. A further description of this 

process can be found in the paper by Hess and White (2004) describing the creation of the 

marine grid for Puget Sound grid. 

The VDatum area was divided into sub-regions to eliminate a possible problem that can occur 

when a user tries a datum transformation (for example between MLLW and MSL) at a location 

in the middle of a barrier island. If there were no land points between the inner sounds and the 

outer Gulf of Mexico (which could occur if a barrier island were much narrower than the cell 

dimension), the VDatum program would average the value from the water nodes on the sound 

side with the value from the water nodes on the Gulf side and the output datum transformation 

would be too large for the inner sounds and too small for the outer Gulf. 

The sub-regions were created as follows. In Alabama and the western Florida panhandle, the 

separation between the inside sounds and the outside Gulf of Mexico was created by dividing the 

VDatum area into separate regions. In the eastern Florida panhandle, the separation was created 

by increased resolution that produced at least one land cell in the middle of every barrier island. 

Because of the increased resolution, this area was divided into two smaller regions to keep the 

c
20

grid sizes small enough for easy downloads of the VDatum product. In total, five VDatum 

regions were created and they are shown in Figure 10. Details of the VDatum marine grids 

created for each of the five regions, including the limits of the grid, the zonal and meridional 

spacing, the number of nodes in the zonal and meridional directions, and the size of the final 

“gtx” file (discussed in the next section), are listed in Table 4. 

Figure 10. The VDatum bounding polygons for MOBLE, the Mobile Bay region (blue); 

PCOLA, the Perdido, Pensacola, and Choctawhatchee Bays region (cyan); ANDRW, the St. 

Andrews Bay region (red), STJOE, the St. Joseph Bay region (orange); and NEGOM, the 

remaining northeast Gulf of Mexico region (purple). 

Table 4. VDatum grid information for the five regions. 

VDatum 

Region 

Southwestern 

Limit 

Northeastern

Limit 

Horiz. 

Spacing 

deg 

(nmi) 

Vert. 

Spacing 

deg (m) 

No. of 

Horiz. 

Nodes 

No. of 

Vert. 

Nodes 

Size of 

one 

GTX 

File 

MOBLE -88.1660o, 

30.1595o 

-87.3277o, 

30.7424o 

0.0015o 

(146 m) 

0.0010o 

(111 m) 560 584 3.5Mb 

 

PCOLA -87.6867o, 

30.2580o 

-85.86458o, 

30.6490o 

0.0015o 

(146 m) 

0.0010o 

(111 m) 1216 392 5.1Mb 

 

NEGOM -88.1660o, 

29.6500o 

-85.8635o, 

30.3985o 

0.0025o 

(243 m) 

0.0020o 

(222 m) 922 375 3.7Mb 

 

ANDRW -85.8634o, 

29.8918o 

-85.38557o, 

30.3132 0.0006o 0.0004o 

(45 m) 797 829 7.0Mb 

 

STJOE -85.8634o, 

29.6500o 

-85.3006o, 

29.9824o 0.0006o 0.0006o 

(67 m) 989 555 5.5Mb 
21

5.2. Population of the VDatum Marine Grid with Tidal Datums 

The VDatum software program (vpop.f) creates “gtx” files for each tidal datum. In the 

process, the corrected model results are interpolated onto the marine grid by averaging the 

cluster of elements that surround the marine grid node. This is a better approach than averaging 

the nearest model grid nodes, especially near the barrier islands and peninsulas that separate the 

bays of Florida from the Gulf waters in Florida. If the nearest nodes were chosen, it could be a 

mix of the larger datum values from the Gulf and smaller datum values from the bays; the 

average would either be too high if the VDatum node were in the bay or too low if the VDatum 

node were in the Gulf of Mexico. Carefully drawing the bounding polygons along the barrier 

islands and peninsulas also helps guarantee that the VDatum nodes are populated with datums 

from only one region. 

5.3. Potential Errors in the Marine Gridded Data 

Possible errors in the VDatum tidal transformation fields can be traced to three primary sources: 

errors in the hydrodynamic model results, the interpolation of those errors at the tide stations, 

and the interpolation of the model results onto the VDatum marine grid. 

The error in the hydrodynamic model results has been discussed above in Section 3.4. Again, the 

absolute average and percent error for the MHHW-MSL, MHW-MSL, MLW-MSL, and MLLWMSL datums for the final model run compared to the 74 NOS stations in the VDatum area are 

listed in Table 3 (as Run 5). The error at each of these 74 stations (for that final model run) is 

listed in Appendix C. The average absolute error between the hydrodynamic model and the 

observed datums was less than 2 cm. 

 

The second source of errors arises from inaccuracies in the interpolated error field (Section 4). 

As discussed above, errors in the model results were compensated for by subtracting an 

interpolated error field that matched the error value at the tide stations and obeys Laplace’s 

equation in the domain. This makes a nearly exact match of VDatum values at the tide station, 

but the effect on the error throughout the rest of the domain is unknown. It can be noted, though, 

as shown in Figure 9, the error fields are generally smooth, which is desirable when creating the 

final, corrected tidal datum fields. 

The final source of error arises in the process of interpolating the corrected datums onto the 

VDatum marine grids (Section 5.2). One source of error is due to the fact that nodes in the 

triangular grid, which have the corrected values, do not precisely match the actual locations of 

the tide stations. The second source of error is due to the fact that values at two or more the 

closest nodes in the triangular grid are averaged to produce the value at the marine grid’s node. 

Therefore, a check was done to compare the combined datum field results as projected onto the 

VDatum marine grid with datum information at the NOS tide stations in the region. The root 

mean squared error (RMSE) and standard deviation were computed for the four at each station. 

Table 5 lists errors for each VDatum region. 
22

Table 5. Errors for the four tidal datums (m) by VDatum region for the VDatum marine grids. 

 Station ID MHHW MHW MLW MLLW Station Name 

 MOBLE 

 1 8731952 -0.001 -0.002 0.001 0.001 BON SECOUR 

 2 8735180 0.000 0.000 -0.002 -0.003 DAUPHIN ISLAND, MOBILE BA 

 3 8737048 0.001 0.000 0.000 -0.001 MOBILE STATE DOCKS, MOBIL 

 PCOLA 

 1 8729332 0.000 0.000 0.000 0.000 JOLLY BAY, CHOCTAWHATCHEE 

 2 8729333 0.001 0.001 -0.001 -0.001 LA GRANGE BAYOU 

 3 8729364 0.000 0.000 0.000 0.000 ALLAQUAY BAYOU 

 4 8729376 0.000 0.000 0.001 0.001 SANTA ROSA HOGTOWN BAYOU 

 5 8729381 -0.008 -0.006 0.009 0.009 BASIN CREEK 

 6 8729387 0.003 0.004 -0.002 -0.002 BASIN BAYOU, CHOCTAWHATCH 

 7 8729435 0.000 -0.001 0.000 0.000 BIG HAMMOCK PT, CHOCTAWHA 

 8 8729501 0.000 0.000 0.000 0.000 VALPARISO, BOGGY BAYOU 

 9 8729511 0.000 -0.002 0.002 0.000 DESTIN, EAST PASS 

 10 8729538 0.003 0.004 -0.004 -0.003 GARNIER BAYOU, SHALIMAR 

 11 8729548 0.000 0.000 0.000 0.000 CAMP PINCHOT 

 12 8729554 0.000 0.000 0.000 0.000 FORT WALTON BEACH, SANTA 

 13 8729567 0.000 0.000 0.000 0.000 CINCO BAYOU 

 14 8729598 0.000 0.001 0.000 0.000 HULBERT FIELD 

 15 8729613 0.010 0.011 0.011 0.009 HARRIS, SANTA ROSA SOUND 

 16 8729679 0.000 0.000 0.000 0.000 SANTA ROSA SOUND, EAST EN 

 17 8729702 0.000 0.000 0.000 0.000 EAST BAY, HOLLEY 

 18 8729736 0.000 -0.001 0.000 0.000 WOODLAWN BEACH 

 19 8729747 -0.001 -0.001 0.001 0.001 SHIELD POINT, BLACKWATER 

 20 8729753 -0.001 -0.001 0.002 0.001 BLACKWATER RIVER 

 21 8729757 0.001 0.001 -0.001 -0.001 MILTON 

 22 8729791 0.001 0.001 -0.001 0.000 HERNANDEZ POINT NORTH 

 23 8729793 -0.008 -0.016 0.010 0.015 MULLATTO BAYOU 

 24 8729806 0.000 0.001 0.000 0.000 FISHING BEND, SANTA ROSA 

 25 8729808 0.000 0.000 0.000 0.000 LITTLE SABINE BAY 

 26 8729816 -0.002 -0.002 0.002 0.001 LORA POINT, ESCAMBIA BAY 

 27 8729824 -0.001 -0.001 -0.001 0.001 FLORIDATOWN, ESCAMBIA BAY 

 28 8729840 -0.001 0.000 0.000 -0.001 PENSACOLA, PENSACOLA BAY 

 29 8729849 0.000 0.000 0.000 0.000 BAYOU CHICO 

 30 8729868 0.000 0.000 0.001 0.001 PENSACOLA, NAVAL AIR STAT 

 31 8729871 0.001 0.001 -0.002 -0.001 WARRINGTON, BAYOU GRANDE 

 32 8729882 0.002 0.002 0.000 0.000 FORT PICKENS, PENSACOLA B 

 33 8729889 0.000 0.000 0.000 0.000 HEAD OF BAYOU GRANDE 

 34 8729905 -0.013 -0.014 -0.011 -0.014 MILLVIEW, PERDIDO BAY 

 35 8729909 0.000 0.000 0.000 0.000 BIG LAGOON 

 36 8729938 0.001 0.001 -0.001 -0.001 TARKLIN BAY 

 37 8729943 -0.001 0.000 -0.001 0.000 HURST HAMMOCK, PERDIDO RI 

 38 8729962 0.000 0.000 0.000 0.000 PERDIDO BAY 

 39 8729974 0.000 0.000 0.000 0.000 PERDIDO KEY, OLD RIVER 

 40 8730667 0.017 0.017 -0.019 -0.018 ALABAMA POINT, PERDIDO PA 
23

Table 5. (Continued). 

 Station ID MHHW MHW MLW MLLW Station Name 

 ANDRW

 1 8728973 0.000 0.000 0.001 0.001 WETAPPO CREEK, EAST BAY 

 2 8729015 0.000 0.000 -0.001 0.000 ALLANTON, EAST BAY 

 3 8729017 0.000 0.000 0.000 0.000 FARMDALE, EAST BAY, ST. A 

 4 8729039 0.000 0.000 0.000 0.000 PARKER BRANCH, LAIRD BAYO 

 5 8729045 0.000 0.000 0.000 0.000 LAIRD BAYOU, EAST BAY 

 6 8729063 0.000 0.000 0.000 -0.001 CALLAWAY BAYOU, EAST BAY 

 7 8729071 0.000 0.000 0.000 0.000 MILL BAYOU, NORTH BAY 

 8 8729083 0.005 -0.005 0.001 -0.009 DUPONT BRIDGE, EAST BAY 

 9 8729084 0.000 0.000 0.000 0.001 PARKER, EAST BAY 

 10 8729085 0.003 0.009 0.000 -0.003 PEARL BAYOU, EAST BAY 

 11 8729101 0.000 0.000 0.001 0.001 SOUTHPORT, NORTH BAY 

 12 8729102 0.001 0.001 0.000 0.000 LYNN HAVEN, NORTH BAY 

 13 8729105 0.001 0.000 0.000 0.000 BEACON BEACH, ST ANDREW B 

 14 8729107 0.000 0.008 -0.003 -0.012 MASSALINA BAYOU, ST. ANDR 

 15 8729108 0.001 0.000 0.001 0.000 PANAMA CITY, ST. ANDREW B 

 16 8729119 0.000 -0.001 0.000 -0.001 SHELL ISLAND, ST. ANDREWS 

 17 8729136 0.022 0.007 -0.014 -0.010 NEW ENTRANCE CHANNEL, ST. 

 18 8729141 0.000 0.001 0.000 0.001 ST. ANDREWS STATE PARK, G 

 19 8729149 -0.001 -0.001 0.003 0.002 ST. ANDREW STATE PARK 

 20 8729152 0.002 0.002 0.003 0.002 ALLIGATOR BAYOU, PANAMA C 

 21 8729155 0.001 0.000 0.000 0.000 GRAND LAGOON, WEST END 

 22 8729169 -0.001 -0.003 -0.003 -0.003 SHELL POINT, WEST BAY 

 23 8729189 0.000 0.000 0.000 -0.001 PANAMA CITY BEACH 

 24 8729197 0.000 -0.001 0.001 0.001 WEST BAY CREEK WEST BAY 

 STJOE 

 1 8728912 0.001 0.001 0.000 0.001 PORT ST. JOE 

 2 8728942 0.000 0.000 0.000 0.001 CAPE SAN BLAS 

 3 8728949 -0.001 -0.001 0.002 0.001 RICHARDSON HAMMOCK, ST. J 

 4 8728958 0.023 0.031 0.024 0.019 ST. JOSEPH POINT, ST. JOS 

 5 8728995 -0.002 -0.003 0.002 0.002 MEXICO BEACH 

 NEGOM 

 1 8729210 0.001 0.002 -0.002 -0.001 PANAMA CITY BEACH, GULF O 

 2 8729678 0.000 0.000 0.000 0.000 NAVARRE BEACH 
24

6. TOPOGRAPHY OF THE SEA SURFACE 

The Topography of the Sea Surface (TSS) is defined as the elevation of the North American 

Vertical Datum of 1988 (NAVD88) relative to local mean sea level (LMSL). Two 

methodologies were utilized for computing NAVD88-to-LMSL values and the results were 

coupled for creation of the final TSS grid by the National Geodetic Survey (NGS). This grid 

provides compensation for the local variations between a mean sea level surface and the 

NAVD88 geopotential surface over the Mobile Bay to Cape San Blas Vicinity VDatum region. 

A positive value specifies that the NAVD88 reference value is further from the center of the 

Earth than the local mean sea level surface. All data are based on the most recent National Tidal 

Datum Epoch (1983-2001). The location of tide stations and tidal benchmarks used are 

illustrated in Figure 11, and a listing of values at each tide station appears in Table 6. 

Figure 11. Locations of tide stations and geodetic benchmarks. 
25

Table 6. Tidal and geodetic datums at tide stations in the northeast Gulf of Mexico. Tidal 

datums are relative to MLLW. Data are from CO-OPS. Station numbers marked with an 

asterisk have NAVD88 elevations computed from NGS benchmark elevation data, and are 

not published by CO-OPS in the tide station benchmark sheets. 

Station 

ID 

 Latitude Longitude MLLW MLW MSL MHW MHHW NAVD88 

 8728669 29.613330 -84.958330 0.000 0.159 0.343 0.531 0.600 0.410 

 8728690 29.726670 -84.981670 0.000 0.122 0.277 0.461 0.492 0.232 

 8728711 29.763330 -85.033330 0.000 0.094 0.232 0.387 0.412 0.127 

 8728757 29.770000 -85.085000 0.000 0.117 0.213 0.335 0.369 0.157 

 8728786 29.706670 -85.153330 0.000 0.126 0.274 0.468 0.509 0.280 

 8728786 29.706670 -85.153330 0.000 0.126 0.274 0.468 0.509 0.280 

 8728853 29.880000 -85.223330 0.000 0.031 0.163 0.278 0.296 0.005 

 8728853 29.880000 -85.223330 0.000 0.031 0.163 0.278 0.296 0.005 

 8728912 29.815000 -85.313330 0.000 0.062 0.250 0.413 0.504 0.251 

 8728941 30.003330 -85.348330 0.000 0.061 0.262 0.477 0.516 0.191 

 8728942 29.668330 -85.360000 0.000 0.029 0.227 0.422 0.438 0.233 

 8728949 29.690000 -85.363330 0.000 0.046 0.253 0.436 0.522 0.139 

 8728957 29.996670 -85.370000 0.000 0.046 0.245 0.452 0.482 0.174 

 8728958 29.873330 -85.390000 0.000 0.027 0.232 0.381 0.474 0.239 

 8728973 30.038330 -85.393330 0.000 0.004 0.256 0.450 0.504 0.199 

 8729015 30.030000 -85.465000 0.000 0.033 0.231 0.431 0.466 0.192 

 8729022 29.970000 -85.480000 0.000 0.044 0.214 0.389 0.431 0.185 

 8729039 30.136670 -85.516670 0.000 0.025 0.219 0.412 0.438 0.178 

 8729052 30.025000 -85.541670 0.000 0.044 0.206 0.384 0.420 0.179 

 8729063 30.136670 -85.571670 0.000 0.018 0.214 0.412 0.438 0.173 

 8729071 30.245000 -85.605000 0.000 0.032 0.230 0.434 0.456 0.176 

 8729084 30.126670 -85.611670 0.000 0.021 0.217 0.417 0.432 0.188 

 8729085 30.098330 -85.613330 0.000 0.021 0.215 0.398 0.428 0.174 

 8729101 30.283330 -85.646670 0.000 0.032 0.236 0.440 0.472 0.206 

 8729102 30.255000 -85.648330 0.000 0.032 0.220 0.412 0.448 0.173 

 8729105 30.091670 -85.648330 0.000 0.017 0.200 0.388 0.402 0.166 

 8729107 30.151670 -85.660000 0.000 0.008 0.192 0.376 0.400 0.150 

 8729108 30.151670 -85.666670 0.000 0.014 0.203 0.395 0.409 0.170 

 8729136 * 30.125000 -85.721670 0.000 0.021 0.193 0.387 0.394 0.167 

 8729141 30.133330 -85.731670 0.000 0.028 0.206 0.393 0.418 0.182 

 8729149 30.130000 -85.743330 0.000 0.006 0.229 0.442 0.466 0.186 

 8729152 30.170000 -85.755000 0.000 0.016 0.210 0.398 0.417 0.159 

 8729154 30.328330 -85.763330 0.000 0.033 0.205 0.404 0.433 0.156 

 8729155 30.158330 -85.768330 0.000 0.014 0.197 0.378 0.392 0.159 

 8729179 30.308330 -85.811670 0.000 0.031 0.220 0.410 0.449 0.160 

 8729197 30.293330 -85.858330 0.000 0.028 0.222 0.424 0.444 0.168 

 8729210 * 30.213330 -85.880000 0.000 0.020 0.199 0.392 0.418 0.178 

 8729329 30.396670 -86.088330 0.000 0.013 0.080 0.149 0.167 -0.021 

 8729332 30.428330 -86.136670 0.000 0.009 0.086 0.168 0.170 -0.051 

 8729333 30.468330 -86.138330 0.000 0.004 0.067 0.129 0.131 -0.025 

 8729364 30.488330 -86.205000 0.000 0.003 0.073 0.146 0.153 -0.032 

 8729376 30.400000 -86.228330 0.000 0.008 0.094 0.169 0.178 -0.021 

 8729381 30.496670 -86.240000 0.000 0.003 0.075 0.141 0.150 -0.024 

 8729387 30.486670 -86.253330 0.000 0.004 0.062 0.114 0.123 -0.048 

 8729501 30.503330 -86.493330 0.000 0.000 0.076 0.151 0.151 -0.072 

 8729511 30.395000 -86.513330 0.000 0.003 0.086 0.184 0.186 -0.037 
26

Table 6. (Continued). 

Station 

ID 

 Latitude Longitude MLLW MLW MSL MHW MHHW NAVD88 

 8729538 30.435000 -86.586670 0.000 0.008 0.059 0.119 0.124 -0.060 

 8729567 30.428330 -86.631670 0.000 0.011 0.069 0.135 0.142 0.051 

 8729598 30.406670 -86.700000 0.000 0.024 0.175 0.336 0.356 0.079 

 8729613 30.408330 -86.731670 0.000 0.017 0.201 0.364 0.380 0.097 

 8729678 30.376670 -86.865000 0.000 0.016 0.201 0.401 0.421 0.144 

 8729679 30.385000 -86.863330 0.000 0.008 0.206 0.401 0.422 0.118 

 8729736 * 30.386670 -86.991670 0.000 0.007 0.203 0.401 0.415 0.130 

 8729747 30.581670 -87.015000 0.000 0.029 0.240 0.453 0.484 0.144 

 8729753 30.636670 -87.028330 0.000 0.037 0.253 0.467 0.505 0.144 

 8729757 30.626670 -87.036670 0.000 0.042 0.240 0.444 0.482 0.145 

 8729791 30.455000 -87.100000 0.000 0.027 0.198 0.380 0.397 0.104 

 8729793 30.545000 -87.103330 0.000 0.026 0.226 0.442 0.451 0.128 

 8729806 30.336670 -87.140000 0.000 0.016 0.193 0.370 0.391 0.126 

 8729808 30.336670 -87.146670 0.000 0.016 0.193 0.376 0.392 0.140 

 8729824 30.581670 -87.180000 0.000 0.030 0.217 0.423 0.442 0.116 

 8729831 * 30.545000 -87.195000 0.000 0.022 0.197 0.411 0.421 0.092 

 8729840 30.403330 -87.211670 0.000 0.008 0.188 0.374 0.383 0.098 

 8729849 30.401670 -87.251670 0.000 0.014 0.182 0.366 0.376 0.080 

 8729851 30.598330 -87.246670 0.000 0.024 0.223 0.422 0.445 0.082 

 8729868 30.345000 -87.273330 0.000 0.011 0.177 0.354 0.364 0.086 

 8729871 30.375000 -87.276670 0.000 0.016 0.181 0.353 0.368 0.088 

 8729882 30.330000 -87.291670 0.000 0.008 0.169 0.346 0.350 0.077 

 8729889 30.370000 -87.318330 0.000 0.007 0.185 0.366 0.376 0.089 

 8729905 30.418330 -87.356670 0.000 0.004 0.102 0.226 0.229 -0.013 

 8729909 30.326670 -87.356670 0.000 0.013 0.153 0.313 0.322 0.052 

 8729938 30.350000 -87.415000 0.000 0.003 0.091 0.191 0.193 -0.011 

 8729943 30.458330 -87.408330 0.000 0.018 0.113 0.232 0.240 -0.014 

 8729949 30.523330 -87.443330 0.000 0.016 0.121 0.243 0.253 -0.030 

 8729962 30.393330 -87.425000 0.000 0.003 0.105 0.214 0.218 -0.012 

 8729974 30.300000 -87.448330 0.000 0.007 0.115 0.239 0.247 0.008 

 8735180 30.250000 -88.075000 0.000 0.003 0.172 0.361 0.367 0.070 

 8735523 30.443330 -88.113330 0.000 0.017 0.217 0.420 0.438 0.084 

 8737048 30.708330 -88.043330 0.000 0.028 0.241 0.458 0.479 0.062 

 8743735 30.390000 -88.856670 0.000 0.033 0.270 0.505 0.537 0.115 

 8745557 30.360000 -89.081670 0.000 0.038 0.269 0.499 0.532 0.130 

The two methodologies used for creating the NAVD88-to-MSL values are called the indirect 

method and the direct method. The indirect method consists of deriving a value calibrated by 

fitting tide model results to tidal benchmarks leveled in NAVD88. This process used the four 

tidal datum (MHHW, MHW, MLW, and MLLW) marine grids. At each benchmark location in 

the NGS database, we have TBMnavd88, which is the NAVD88 elevation relative to MLLW, and a 

set of four TBMdatum values, each of which is the Datum elevation relative to MLLW (i.e., Datum 

– MLLW). Also, from the four tidal datum grids, we have a set of VDdatum values, which of 

which is the difference between the tidal datum and MSL (i.e., Datum – MSL). 

For the first step of the indirect method, we compute four residuals. The residual, R, for each 

datum is defined as: 

Rdatum = TBMnavd88 – TBMdatum + VDdatum (2)
27

Note that the VD values are interpolated to the location of the benchmark. The four residuals at 

the benchmark are averaged to produce the mean, and this mean is an estimate of the quantity 

MSL – NAVD88. Since the four residuals should be approximately equal, any differences 

indicate inconsistencies in the VDatum gridded data fields. Due to the large extent of the Mobile 

Bay to Cape San Blas Vicinity VDatum region, for testing the region was divided into five subregions. Note that these sub-regions differ from the tidal sub-regions in that for the TSS, Perdido 

Bay is combined with Mobile Bay into the first region. The MSL-to-NAVD88 derived estimates 

can be found in Appendix E. 

In the direct method of obtaining NAVD 88-to-LMSL values, the first step includes calculating 

the orthometric-to-tidal datum relationships at NOAA tide stations where elevation information 

has been compiled. The tide stations and associated elevation information used in the 

computation of the TSS are presented in Table 6. Data for the direct method were supplied by 

CO-OPS and NGS. Next, the mean residuals at all benchmarks are merged with values of the 

quantity NAVD88 – MSL at CO-OPS’ tide stations to produce input data for gridding. Although 

some of the benchmark data has been used in generating values at the tide stations, if was felt 

that the benchmark data may provide information at additional locations where tides are no 

longer measured or where a tide gauge was never installed. 

Then, a continuous surface for the five sub-regions representing inverse sea-surface topography 

was generated as follows. A mesh covering the entire area of benchmarks and tide stations with 

a spatial resolution similar to that of the tidal marine grids is created. Break lines are inserted to 

represent the influence of land. A sea surface topography field is generated using the Surfer© 

software’s minimum curvature algorithm to create a surface that honors the data as closely as 

possible. The maximum allowed departure value used was 0.0001 meters, except for the St. 

Andrews vicinity TSS grid where a maximum residual of 0.0008 meters was used to allow for 

convergence. To control the amount of bowing on the interior and at the edges of the grid, an 

internal and boundary tension of 0.3 was utilized. Once the gridded topography field has been 

generated, null values are obtained from the marine tidal grids and are inserted to denote the 

presence of land. The resulting TSS fields are represented in Figures 12 to 16. 
28

Figure 12. The TSS grid for Mobile and Perdido Bays. 

Figure 13. The TSS grid for the Northeast Gulf of Mexico. 
29

Figure 14. The TSS grid for Perdido, Pensacola, and Choctawhatchee Bays. 

Figure 15. The TSS grid for St. Joseph Bay. 
30

Figure 16. The TSS grid for St. Andrews Bay. 

Quality control was facilitated through several different pathways. After the initial TSS was 

created through interpolation of data compiled through both methodologies, a set of ‘Delta’ 

values are computed. Delta represents the difference between the observed tidal datum and the 

datum as computed by the gridded fields. If S represents the value of the quantity NAVD88 – 

MSL obtained from the sea surface topography grid, then Delta (D) for each tidal datum is 

computed as: 

Ddatum = TBMnavd88 – TBMdatum + VDdatum – S (3) 

The averaged Deltas tabulated for the Mobile Bay to Cape San Blas TSSs are consistent and 

small, and are listed in a table for each region (Appendix F). This provides confidence that grids 

are in agreement. If they are not, the input data and grids are examined, appropriate changes are 

made, and a new TSS grid is computed from the first step. 

In response to the limited amount of data available, the data used to compile the TSS grids for 

both the direct and indirect methods were utilized in comparing against the TSS grid to 

generalize accuracies. The mean difference between known NAVD 88-to-MSL values and that 

calculated for the same point with the individual VDatum region are listed in Appendix G. The 

differences are summarized in Table 7. 
31

 Table 7. Differences between known and computed values to the NAVD88-to-MSL offset. 

SUB-REGION MEAN DIFFERENCE (M) STD. DEV. (M) 

Mobile and Perdido Bays 0.0009 0.0040 

NW Gulf of Mexico -0.0111 0.0188 

Perdido, Pensacola, and 

Choctawatchee Bays 0.0003 0.0039 

St. Joseph Bay -0.0011 0.0036 

St. Andrews Bay 0.0002 0.0020 

7. QUALITY CONTROL AND TESTING 

Before the gtx files can be considered operational, a series of tests was performed on them to 

assess them for quality, consistency, and accuracy of the data. The files tested consist of six for 

tidal datum transformation (mhhw.gtx, mhw.gtx, mlw.gtx, mllw.gtx, mlt.gtx, and dtl.gtx) and six 

for geodetic datum transformation (sst.gtx, ncla.gtx, nclo.gtx, vcn.gtx, g99.gtx, and g03.gtx). For 

further information on these files and on testing procedures, see NOS (in preparation). Testing 

began in February 2007, several months after this report’s primary author, Emily Spargo, had left 

government service to work elsewhere. A record of the tests and their outcomes was kept. 

The first test consisted of comparing the bounding polygons to assure that they enclose an area 

completely within the rectangular area specified by the gtx file header parameters. The program 

used was the latest version of test_poly.f. It was immediately apparent that there were 

some problems with some of the polygons, which had been altered slightly to accommodate a 

request from NGS for the use of preliminary data. To resolve the discrepancy, a few rows and/or 

columns of data were added (by extrapolation) to the gtx files in question. The files includes all 

six tidal plus sst.gtx for the west Florida bays, St. Andrews Bay, and St. Joseph Bay, and the 

g99.gtx and g03.gtx files for St. Joseph Bay. 

The second test looked for overlap in the set of bounding polygons using the program 

test_ovlp.f. It was quickly determined that a major area of overlap existed between the 

Alabama bays and the west Florida bays polygons, which both include Perdido Bay, AL. A 

smaller overlap occurred between the west Florida bays and NE Gulf of Mexico polygons. These 

overlaps were easily rectified by altering the polygons. In particular, the polygon covering 

Alabama was reduced so as to exclude Perdido Bay; this bay is now covered in the west Florida 

bays polygons. Since a large portion of the tidal and TSS gtx files for the Alabama bays covered 

an area outside of the bounding polygon, these files were truncated. The new polygons were then 

used in a repeat of the first test; no problems were encountered. 

Since there were some changes in the polygons and gtx files, a revised set of sub-region names 

was adopted. The sub-region covering Alabama is called MOBLE, the west Florida bays is 

PCOLA, St. Andrews Bay is called ANDRW, St. Joseph Bay is STJOE, and the NE Gulf of 

Mexico is NEGOM (Figure 10). 

For the third test, tidal and TSS datums from the gtx files were compared to those from the 

CO-OPS data base. Data at tide stations used in the development of the hydrodynamic model 

(i.e., from the TideSheet data) were compared with the program test_msf.f, and the largest 

difference in tidal datums (2.2 cm) was found at Station 872-9136 in St. Andrews Bay. The 
32

largest difference in TSS was 13.0 cm at Ft. Walton Beach (Station 872-9554) in PCOLA. The 

NAVD88 value was found to be in error and subsequently revised by CO-OPS. NGS then 

regenerated the TSS files for the five sub-regions; these were retested for polygons (the gridded 

data for PCOLA, ANDRW, and STJOE were expanded by adding rows and/or columns) and 

overlap, and they passed. Then, the largest error in TSS was 0.9 cm. 

In the fourth test, tidal and TSS datums from the gtx files were compared to those from the most 

recent (i.e., latest NTDE) CO-OPS spreadsheet data base, and using the program test_msf.f. 

The data were extracted using the program celect.f and analyzed using test_msf4.f, a 

version modified to read the output from celect3.f as well as in the original (msf) format. 

The largest tidal datum error was 3.1 cm at 872-8958 in STJOE, and the largest error in TSS was 

0.9 cm. 

The fifth test compared values at the interfaces of adjacent sub-regions using the program 

test_cont3.f. A small problem with the TSS values in the PCOLA sub-region was noted. This 

was solved by extrapolating values along the southern edge of the bounding polygon near the 

entrance to Pensacola Bay. 
33

REFERENCES 

Gesch, D. and R. Wilson, 2001: Development of a Seamless Multisource Topographic / 

Bathymetric Elevation Model for Tampa Bay. Marine Technology Society Journal, 35(4): 58-

64, Winter 2001/2002. 

Hess, K.H., 2002: Spatial interpolation of tidal data in irregularly-shaped coastal regions by 

numerical solution of Laplace’s equation. Estuarine, Coastal and Shelf Science, 54(2), 175-

192. 

Hess, K.H., D. G. Milbert, S.K. Gill, and D.R. Roman, 2003: Vertical Datum Transformations 

for Kinematic GPS Hydrographic Surveys. Proceedings, U.S. Hydrographic Conference,

March 24 – 27, 2003. Biloxi, MS. 8 pp. 

Hess, K.W. and S.A. White, 2004: VDatum for Puget Sound: generation of the grid and 

population with tidal datums and sea surface topography. NOAA Technical Memorandum, 

NOS CS 4, 27 pp. 

Hess, K.W., E.A. Spargo, A. Wong, S.A. White, and S.K. Gill, 2005: VDatum for Central 

Coastal North Carolina: Tidal Datums, Marine Grids, and Sea Surface Topography. NOAA 

Technical Report, NOS CS 21, 45 pp. 

Luettich, R.A., J.J. Westerink, and N.W. Scheffner, 1992: ADCIRC: an advanced threedimensional circulation model of shelves, coasts, and estuaries, Report 1: theory and 

methodology of ADCIRC-2DDI and ADCIRC-3DL. U.S. Department of the Army, Technical 

Report DRP-92-6, XXp. 

Luettich, R.A. and J.J. Westerink, 2004: Formulation and numerical implementation of the 

2D/3D ADCIRC finite element model version 44.XX. 

(Http://www.marine.unc.edu/C_CATS/adcirc). 

Milbert, D.G., 2002: Documentation for VDatum (and VDatum Tutorial); Vertical Datum 

Transformation Software. Ver. 1.06 (http://nauticalcharts.noaa.gov/csdl/vdatum.htm). 

Myers, E.P., A.M. Baptista, 2001: Inversion for tides in the Eastern North Pacific Ocean. 

Advances in Water Resources, 24, 505-519. 

Myers, E.P., (in preparation): Tidal Datum Inversion Model of the East Coast of the United 

States. 

Mukai, A.M., J.J. Westerink, and R.A. Luettich, 2001: Guidelines for using the Eastcoast 2001 

database of tidal constituents within the Western North Atlantic Ocean, Gulf of Mexico and 

Caribbean Sea. Department of the Army Technical Note, IV-XX. 

NOS, (in preparation). Standard Procedures to Develop and Support NOAA’s Vertical Datum 

Transformation Tool, VDatum. 
34

Parker, B.P., Milbert, D., Wilson, R., Bailey, J. and Gesch, D., 2001: “Blending bathymetry and 

topography: the Tampa Bay demonstration project.” Proceedings, U.S. Hydrographic 

Conference 2001, Norfolk, VA. 

Parker, B. P., 2002: The integration of bathymetry, topography, and shoreline, and the vertical 

datum transformations behind it. International Hydrographic Review (3) 3 (November 2002). 

Spargo, E.A. and J.W. Woolard, 2005: VDatum for the Calcasieu River from Lake Charles to the 

Gulf of Mexico, Louisiana: Tidal Datum Modeling and Population of the Grid. NOAA 

Technical Report, NOS CS 19, 25 pp. 

Spargo, E.A., K.H. Hess, and S.A. White, 2006: VDatum for the San Juan Islands and the Strait 

of Juan de Fuca with Updates for Puget Sound: Tidal Datum Modeling and Population of the 

Grids. NOAA Technical Report, NOS CS 25, 50 pp. 

Tronvig, K.A., 2005: Near-shore Bathymetry. Geospatial Products and Ecological 

Applications. Hydro International, (9)5, June 2005, 24-25. 

Zervas, Chris E., 2003. Long term changes in tidal response associated with the deepening of 

navigational channels, Proceedings, Coastal Zone 03: Coastal zone management through time, 

Baltimore, MD, July 13-17, 2003, NOAA Coastal Services Center. 
35

APPENDIX A. UNUSED TIDE STATIONS 

One hundred and seventeen tide stations were found in the VDatum region. Twelve of these 

stations were removed from the list due to incomplete datum information. The other stations 

were removed because they were within the 500 m tolerance, but located up creeks, rivers, bays 

and bayous not modeled for this study. Also, the Massalina Bayou station (872-9107) was 

eliminated not only because it was in a bayou not captured in the model grid, but also because it 

is close to the Panama City station (872-9108). 

Table A.1. Tide station identification number, name, location and reason for removal of the 17 

stations eliminated from the final stations list. 

 Station ID Station Name Latitude Longitude Reason for Removal 

1 8729002 St. Andrew Sound -85.480003 29.969999 Off the grid 

2 8729107 Massalina Bayou -85.660004 30.151699 

Close to the Panama 

City station(872-9108) 

and off the grid 

3 8729742 Bay Point -87.004997 30.571667 Incomplete Data 

4 8729793 Mullatto Bayou -87.103302 30.545000 Off the grid 

5 8729887 Fort McRee -87.311668 30.326666 Incomplete Data 

6 8731936 Nelson Landing -87.736664 30.291666 Incomplete Data 

7 8735184 Dauphin Island -88.080002 30.251667 Incomplete Data 

8 8735523 Fowl River -88.113297 30.443300 Off the grid 

9 8747145 Mallini Bayou South -89.286697 30.311701 Off the grid 

10 8760172 Chandeleur Lighthouse -88.871666 30.048334 Incomplete Data 

11 8760579 Port Eads South Pass -89.160004 29.014999 Incomplete Data 

12 8760736 Joesph Bayou -89.271667 29.058332 Incomplete Data 

13 8760841 Jack Bay -89.345001 29.366667 Incomplete Data 

14 8761212 Pelican Island -89.608330 29.250000 Incomplete Data 

15 8761289 Bastian Island -89.663330 29.286667 Incomplete Data 

16 8761557 Bayou Pass -89.853333 29.309999 Incomplete Data 

17 8761687 Barataria Bay -89.945000 29.275000 Incomplete Data 
36
37

APPENDIX B. SOURCES OF BATHYMETRIC DATA 

All bathymetric data came for NOS sources. The oldest data are from NOS hydrographic 

surveys from 1899 to 1989, and have depths referenced to MLW. Locations of these survey 

points (approximately 2.6 million) are shown in Figure B.1. Data from later surveys (1935 to 

1994) are referenced to MLLW (the present NOS chart datum), and the locations of these points 

(approximately 2.0 million) are shown in Figure B.2. 

Inspection of Figures B.1 and B.2 show that there are a few gaps in the data, especially in the 

area centered at 89o 0′ W and 29o 30′ N, just north of the Mississippi River Delta. Bathymetric 

data for this area, as well as for upper Mobile Bay, waterways connecting Mobile Bay with 

Perdido Bay and Choctawatchee Bay with St. Andrews Bay, and the barrier island system 

southeast of the entrance to St. Andrews Bay was obtained from NOS’ Electronic Navigation 

Charts. These charts have depth values (referenced to MLLW) that have been automatically 

extracted from paper charts. Locations of these points are shown in Figure B.3. 

Data from the first two sources is archived in the file pscola_nos_bathy.tar, and data from the 

third is archived in the file dig_bathy.tar. 

 

Figure B.1. Location of NOS hydrographic survey data points with depths referenced to 

MLW. Only every 50th point is shown. 
38

 

Figure B.2. Location of NOS hydrographic survey data points with depths referenced to 

MLLW. Only every 50th point is shown.

 

Figure B.3. Location of depth data points from the Electronic Navigation Charts. 
39

APPENDIX C. TIDE STATION DATA AND MODEL RESULTS 

Table C.1. Tide station information and model results at those locations. 

No. Station ID Station Name Longitude Latitude MHHW MHW MLW MLLW Source 

1 8728912 PORT ST JOE -85.313332 29.815001 

25.4 16.3 -18.8 -25.0 data 

19.2 17.5 -17.6 -18.5 model 

-6.2 1.2 1.2 6.5 difference 

24.4% 7.4% 6.4% 26.0% 

2 8728942 CAPE SAN 

BLAS -85.360001 29.668301 

21.1 19.5 -19.8 -22.7 data 

16.1 16.1 -17.4 -17.4 model 

-5.0 -3.4 2.4 5.3 difference 

23.7% 17.4% 12.1% 23.4% 

3 8728949 RICHARDSON 

HAMMOCK -85.363297 29.690001 

26.9 18.3 -20.7 -25.3 data 

19.4 17.7 -17.9 -18.8 model 

-7.5 -0.6 2.8 6.5 difference 

27.9% 3.3% 13.5% 25.7% 

4 8728958 ST. JOSEPH 

POINT -85.389999 29.873301 

26.8 17.7 -17.7 -20.7 data 

18.9 17.7 -17.8 -18.2 model 

-7.9 0.0 -0.1 2.5 difference 

29.5% 0.0% 0.6% 12.1% 

5 8728973 

WETAPPO 

CREEK 

EAST BAY 

-85.393303 30.038300 

24.8 19.4 -25.2 -25.6 data 

22.7 18.7 -19.3 -21.7 model 

-2.1 -0.7 5.9 3.9 difference 

8.5% 3.6% 23.4% 15.2% 

6 8728995 MEXICO 

BEACH -85.425003 29.948299 

26.2 23.1 -21.7 -25.0 data 

18.5 18.0 -17.8 -17.8 model 

-7.7 -5.1 3.9 7.2 difference 

29.4% 22.1% 18.0% 28.8% 

7 8729015 ALLANTON 

EAST BAY -85.464996 30.030001 

23.5 20.0 -19.8 -23.1 data 

22.2 18.3 -18.7 -21.1 model 

-1.3 -1.7 1.1 2.0 difference 

5.5% 8.5% 5.6% 8.7% 

8 8729017 FARMDALE 

EAST BAY -85.470001 30.016666 

24.0 20.2 -19.8 -23.6 data 

22.2 18.3 -18.7 -21.1 model 

-1.8 -1.9 1.1 2.5 difference 

7.5% 9.4% 5.6% 10.6% 

9 8729039 

PARKER 

BRANCH 

LAIRD BAY 

-85.516701 30.136700 

21.9 19.3 -19.4 -21.9 data 

21.2 17.9 -18.2 -20.0 model 

-0.7 -1.4 1.2 1.9 difference 

3.2% 7.3% 6.2% 8.7% 

10 8729045 

LAIRD 

BAYOU 

EAST BAY 

-85.528336 30.121666 

22.2 19.7 -19.3 -22.6 data 

21.2 17.9 -18.1 -20.0 model 

-1.0 -1.8 1.2 2.6 difference 

4.5% 9.1% 6.2% 11.5% 

11 8729063 

CALLAWAY 

BAYOU 

EAST BAY 

-85.571701 30.136700 

22.4 19.8 -19.6 -21.4 data 

21.1 17.7 -18.0 -19.9 model 

-1.3 -2.1 1.6 1.5 difference 

5.8% 10.6% 8.2% 7.0% 

12 8729071 MILL BAYOU 

NORTH BAY -85.605003 30.245001 

22.6 20.4 -19.8 -23.0 data 

21.3 17.9 -18.3 -20.2 model 

-1.3 -2.5 1.5 2.8 difference 

5.8% 12.3% 7.6% 12.2% 

13 8729084 PARKER 

EAST BAY -85.611702 30.126699 

21.5 20.0 -19.6 -21.7 data 

20.3 18.0 -18.1 -19.0 model 

-1.2 -2.0 1.5 2.7 difference 

5.6% 10.0% 7.7% 12.4% 

14 8729085 

PEARL 

BAYOU 

EAST BAY 

-85.613297 30.098301 

21.3 18.3 -19.4 -21.5 data 

20.6 17.8 -17.9 -19.3 model 

-0.7 -0.5 1.5 2.2 difference 

3.3% 2.7% 7.7% 10.2% 

15 8729101 SOUTHPORT 

NORTH BAY -85.646698 30.283300 

23.6 20.4 -20.4 -23.6 data 

21.2 17.8 -18.1 -20.0 model 

-2.4 -2.6 2.3 3.6 difference 

10.2% 12.8% 11.3% 15.3% 
40

Table C.1. (Continued).

No. Station ID Station Name Longitude Latitude MHHW MHW MLW MLLW Source 

16 8729102 LYNN HAVEN 

NORTH BAY -85.648300 30.254999 

22.8 19.2 -18.8 -22.0 data 

21.2 17.8 -18.1 -20.0 model 

-1.6 -1.4 0.7 2.0 difference 

7.0% 7.3% 3.7% 9.1% 

17 8729105 BEACON 

BEACH -85.648300 30.091700 

20.2 18.8 -18.3 -20.0 data 

18.7 17.1 -16.8 -17.3 model 

-1.5 -1.7 1.5 2.7 difference 

7.4% 9.0% 8.2% 13.5% 

18 8729108 PANAMA 

CITY -85.666664 30.151667 

20.6 19.2 -18.9 -20.3 data 

19.5 17.2 -17.3 -18.2 model 

-1.1 -2.0 1.6 2.1 difference 

5.3% 10.4% 8.5% 10.3% 

19 8729117 S. OF DAVIS 

PT. -85.680000 30.113333 

20.7 17.7 -17.4 -19.8 data 

19.0 17.4 -17.2 -17.7 model 

-1.7 -0.3 0.2 2.1 difference 

8.2% 1.7% 1.2% 10.6% 

20 8729119 SHELL 

ISLAND -85.684998 30.094999 

20.7 19.6 -17.6 -19.3 data 

18.9 17.3 -17.1 -17.6 model 

-1.8 -2.3 0.5 1.7 difference 

8.7% 11.7% 2.8% 8.8% 

21 8729141 ST. ANDREWS 

STATE PARK -85.731697 30.133301 

21.2 18.7 -17.8 -20.6 data 

19.3 17.7 -16.5 -17.0 model 

-1.9 -1.0 1.3 3.6 difference 

9.0% 5.4% 7.3% 17.5% 

22 8729149 ST. ANDREW 

STATE PARK -85.743301 30.129999 

23.7 21.3 -22.3 -22.9 data 

19.5 17.9 -17.2 -17.7 model 

-4.2 -3.4 5.1 5.2 difference 

17.7% 16.0% 22.9% 22.7% 

23 8729152 ALLIGATOR 

BAYOU -85.754997 30.170000 

20.7 18.8 -19.4 -21.0 data 

20.0 17.7 -18.0 -18.8 model 

-0.7 -1.1 1.4 2.2 difference 

3.4% 5.9% 7.2% 10.5% 

24 8729155 

GRAND 

LAGOON 

WEST END 

-85.768303 30.158300 

19.5 18.1 -18.3 -19.7 data 

19.4 17.8 -16.6 -17.1 model 

-0.1 -0.3 1.7 2.6 difference 

0.5% 1.7% 9.3% 13.2% 

25 8729169 SHELL POINT 

WEST BAY -85.739998 30.215000 

24.7 22.9 -13.6 -17.1 data 

20.7 17.9 -18.1 -19.5 model 

-4.0 -5.0 -4.5 -2.4 difference 

16.2% 21.8% 33.1% 14.0% 

26 8729189 

PANAMA 

CITY 

BEACH 

-85.833298 30.186701 

22.5 20.6 -18.5 -19.6 data 

19.6 17.9 -17.2 -17.7 model 

-2.9 -2.7 1.3 1.9 difference 

12.9% 13.1% 7.0% 9.7% 

27 8729193 WEST BAY -85.833336 30.230000 

23.8 17.4 -17.3 -21.0 data 

21.5 18.1 -18.7 -20.6 model 

-2.3 0.7 -1.4 0.4 difference 

9.7% 4.0% 8.1% 1.9% 

28 8729197 WEST BAY 

CREEK -85.858299 30.293301 

22.2 20.2 -19.4 -22.2 data 

21.0 17.6 -17.9 -19.7 model 

-1.2 -2.6 1.5 2.5 difference 

5.4% 12.9% 7.7% 11.3% 

29 8729210 

PANAMA 

CITY 

BEACH 

-85.879997 30.213333 

21.9 19.3 -17.9 -19.9 data 

19.6 18.0 -17.2 -17.7 model 

-2.3 -1.3 0.7 2.2 difference 

10.5% 6.7% 3.9% 11.1% 

30 8729332 JOLLY BAY -86.136703 30.428301 

8.4 8.2 -7.7 -8.6 data 

8.6 8.1 -7.7 -7.9 model 

0.2 -0.1 0.0 0.7 difference 

2.4% 1.2% 0.0% 8.1% 
41

Table C.1. (Continued).

No. Station ID Station Name Longitude Latitude MHHW MHW MLW MLLW Source 

31 8729333 LA GRANGE 

BAYOU -86.138298 30.468300 

6.4 6.2 -6.3 -6.7 data 

8.5 8.0 -7.7 -7.9 model 

2.1 1.8 -1.4 -1.2 difference 

32.8% 29.0% 22.2% 17.9% 

32 8729364 ALLAQUAY 

BAYOU -86.205002 30.488300 

8.0 7.3 -7.0 -7.3 data 

8.4 7.9 -7.6 -7.8 model 

0.4 0.6 -0.6 -0.5 difference 

5.0% 8.2% 8.6% 6.9% 

33 8729376 

SANTA ROSA 

HOGTOWN 

BAYOU 

-86.228302 30.400000 

8.4 7.5 -8.6 -9.4 data 

8.5 8.0 -7.5 -7.7 model 

0.1 0.5 1.1 1.7 difference 

1.2% 6.7% 12.8% 18.1% 

34 8729387 BASIN BAYOU -86.253304 30.486700 

6.1 5.2 -5.8 -6.2 data 

8.5 8.0 -7.5 -7.7 model 

2.4 2.8 -1.7 -1.5 difference 

39.3% 53.9% 29.3% 24.2% 

35 8729435 BIG HAMMOCK 

PT -86.351700 30.465000 

7.7 7.7 -7.0 -7.1 data 

8.2 7.7 -7.3 -7.5 model 

0.5 0.0 -0.3 -0.4 difference 

6.5% 0.0% 4.3% 5.6% 

36 8729479 ROCKY BAYOU -86.446663 30.506666 

7.0 6.4 -6.1 -6.7 data 

7.8 7.5 -7.1 -7.3 model 

0.8 1.1 -1.0 -0.6 difference 

11.4% 17.2% 16.4% 9.0% 

37 8729501 VALPARISO 

BOGGY BAYOU -86.493301 30.503300 

7.5 7.5 -7.6 -7.6 data 

7.8 7.3 -7.1 -7.3 model 

0.3 -0.2 0.5 0.3 difference 

4.0% 2.7% 6.6% 4.0% 

38 8729505 OLD PASS 

LAGOON -86.504997 30.393333 

8.9 7.0 -7.0 -8.2 data 

8.4 8.2 -7.0 -7.2 model 

-0.5 1.2 0.0 1.0 difference 

5.6% 17.1% 0.0% 12.2% 

39 8729511 DESTIN 

EAST PASS -86.513298 30.395000 

10.0 9.8 -8.3 -8.6 data 

8.4 8.2 -7.0 -7.3 model 

-1.6 -1.6 1.3 1.3 difference 

16.0% 16.3% 15.7% 15.1% 

40 8729538 

GARNIER 

BAYOU 

SHALIMAR 

-86.586670 30.434999 

6.5 6.0 -5.1 -5.9 data 

7.5 7.2 -6.8 -6.8 model 

1.0 1.2 -1.7 -0.9 difference 

15.4% 20.0% 33.3% 15.3% 

41 8729548 CAMP PINCHOT -86.593300 30.469999 

6.9 6.9 -6.1 -6.5 data 

7.5 7.2 -6.9 -6.9 model 

0.6 0.3 -0.8 -0.4 difference 

8.7% 4.4% 13.1% 6.2% 

42 8729554 FORT WALTON 

BEACH -86.610001 30.401699 

8.8 8.4 -6.6 -6.8 data 

9.1 8.5 -8.1 -8.4 model 

0.3 0.1 -1.5 -1.6 difference 

3.4% 1.2% 22.7% 23.5% 

43 8729567 CINCO BAYOU -86.631699 30.428301 

7.3 6.6 -5.8 -6.9 data 

7.5 7.2 -6.8 -6.8 model 

0.2 0.6 -1.0 0.1 difference 

2.7% 9.1% 17.2% 1.5% 

44 8729598 HULBERT FIELD -86.699997 30.406700 

18.1 16.1 -15.1 -17.5 data 

17.4 15.3 -14.9 -15.9 model 

-0.7 -0.8 0.2 1.6 difference 

3.9% 5.0% 1.3% 9.1% 

45 8729613 HARRIS SANTA 

ROSA SOUND -86.731697 30.408300 

18.9 17.4 -17.4 -19.2 data 

18.9 16.2 -15.7 -17.3 model 

0.0 -1.2 1.7 1.9 difference 

0.0% 6.9% 9.8% 9.9% 
42

Table C.1. (Continued). 

No. Station ID Station Name Longitude Latitude MHHW MHW MLW MLLW Source 

46 8729678 NAVARRE 

BEACH -86.864998 30.376667 

22.0 20.0 -18.5 -20.1 data 

19.5 17.9 -16.9 -17.4 model 

-2.5 -2.1 1.6 2.7 difference 

11.4% 10.5% 8.7% 13.4% 

47 8729679 SANTA ROSA 

SOUND -86.863297 30.385000 

21.6 19.5 -19.8 -20.6 data 

20.3 17.5 -17.0 -18.8 model 

-1.3 -2.0 2.8 1.8 difference 

6.0% 10.3% 14.1% 8.7% 

48 8729702 EAST BAY 

HOLLEY -86.918297 30.450001 

23.1 20.7 -20.9 -22.6 data 

21.1 18.7 -18.6 -20.0 model 

-2.0 -2.0 2.3 2.6 difference 

8.7% 9.7% 11.0% 11.5% 

49 8729736 WOODLAWN 

BEACH -86.991699 30.386700 

21.2 19.8 -19.6 -20.3 data 

19.9 17.6 -17.2 -18.5 model 

-1.3 -2.2 2.4 1.8 difference 

6.1% 11.1% 12.2% 8.9% 

50 8729747 SHIELD POINT -87.014999 30.581699 

24.4 21.3 -21.1 -24.0 data 

21.7 18.4 -19.1 -20.6 model 

-2.7 -2.9 2.0 3.4 difference 

11.1% 13.6% 9.5% 14.2% 

51 8729753 BLACKWATER 

RIVER -87.028297 30.636700 

25.2 21.4 -21.6 -25.3 data 

21.9 18.6 -19.4 -20.8 model 

-3.3 -2.8 2.2 4.5 difference 

13.1% 13.1% 10.2% 17.8% 

52 8729757 MILTON -87.036697 30.626699 

24.2 20.4 -19.8 -24.0 data 

21.8 18.6 -19.3 -20.7 model 

-2.4 -1.8 0.5 3.3 difference 

9.9% 8.8% 2.5% 13.8% 

53 8729791 HERNANDEZ 

POINT NORTH -87.099998 30.455000 

19.9 18.2 -17.1 -19.8 data 

19.9 18.2 -17.7 -18.7 model 

0.0 0.0 -0.6 1.1 difference 

0.0% 0.0% 3.5% 5.6% 

54 8729806 FISHING BEND -87.139999 30.336700 

19.8 17.7 -17.7 -19.3 data 

19.0 17.3 -16.8 -17.7 model 

-0.8 -0.4 0.9 1.6 difference 

4.0% 2.3% 5.1% 8.3% 

55 8729808 LITTLE SABINE 

BAY -87.146698 30.336700 

19.9 18.3 -17.7 -19.3 data 

18.9 17.9 -17.0 -17.5 model 

-1.0 -0.4 0.7 1.8 difference 

5.0% 2.2% 4.0% 9.3% 

56 8729816 LORA POINT 

ESCAMBIA BAY -87.161697 30.514999 

21.8 20.0 -19.5 -21.1 data 

20.3 18.6 -18.1 -19.1 model 

-1.5 -1.4 1.4 2.0 difference 

6.9% 7.0% 7.2% 9.5% 

57 8729824 FLORIDATOWN -87.180000 30.581699 

22.5 20.6 -18.7 -21.7 data 

20.4 18.7 -18.3 -19.3 model 

-2.1 -1.9 0.4 2.4 difference 

9.3% 9.2% 2.1% 11.1% 

58 8729840 PENSACOLA -87.211700 30.403299 

19.5 18.6 -18.0 -18.8 data 

18.8 17.7 -17.0 -17.5 model 

-0.7 -0.9 1.0 1.3 difference 

3.6% 4.8% 5.6% 6.9% 

59 8729849 BAYOU CHICO -87.251701 30.401699 

19.4 18.4 -16.8 -18.2 data 

18.6 17.5 -16.8 -17.3 model 

-0.8 -0.9 0.0 0.9 difference 

4.1% 4.9% 0.0% 5.0% 

60 8729868 PENSACOLA 

NAVAL AIR STA -87.273300 30.344999 

18.7 17.7 -16.6 -17.7 data 

17.9 16.9 -15.3 -15.8 model 

-0.8 -0.8 1.3 1.9 difference 

4.3% 4.5% 7.8% 10.7% 

 
43

Table C.1. (Continued). 

No. Station ID Station Name Longitude Latitude MHHW MHW MLW MLLW Source 

61 8729871 

WARRINGTON 

BAYOU 

GRANDE 

-87.276703 30.375000 

18.7 17.2 -16.5 -18.1 data 

18.4 17.3 -16.7 -17.2 model 

-0.3 0.1 -0.2 0.9 difference 

1.6% 0.6% 1.2% 5.0% 

62 8729882 FORT PICKENS -87.291702 30.330000 

18.1 17.7 -16.1 -16.9 data 

17.2 17.2 -15.2 -15.2 model 

-0.9 -0.5 0.9 1.7 difference 

5.0% 2.8% 5.6% 10.1% 

63 8729889 

HEAD OF 

BAYOU 

GRANDE 

-87.318298 30.370001 

19.1 18.1 -17.8 -18.5 data 

18.4 17.4 -16.8 -17.3 model 

-0.7 -0.7 1.0 1.2 difference 

3.7% 3.9% 5.6% 6.5% 

64 8729905 MILLVIEW 

PERDIDO BAY -87.356697 30.418301 

11.3 11.0 -11.0 -11.6 data 

15.3 14.0 -13.1 -13.4 model 

4.0 3.0 -2.1 -1.8 difference 

35.4% 27.3% 19.1% 15.5% 

65 8729909 BIG LAGOON -87.356697 30.326700 

16.9 16.0 -14.0 -15.3 data 

16.1 15.6 -14.6 -14.6 model 

-0.8 -0.4 -0.6 0.7 difference 

4.7% 2.5% 4.3% 4.6% 

66 8729938 TARKLIN BAY -87.415001 30.350000 

10.2 10.0 -8.8 -9.1 data 

14.2 13.4 -12.5 -12.5 model 

4.0 3.4 -3.7 -3.4 difference 

39.2% 34.0% 42.1% 37.4% 

67 8729943 HURST 

HAMMOCK -87.408302 30.458300 

12.7 11.9 -9.5 -11.3 data 

15.4 14.1 -13.2 -13.5 model 

2.7 2.2 -3.7 -2.2 difference 

21.3% 18.5% 39.0% 19.5% 

68 8729962 PERDIDO BAY -87.425003 30.393299 

11.3 10.9 -10.2 -10.5 data 

14.7 13.8 -12.9 -12.9 model 

3.4 2.9 -2.7 -2.4 difference 

30.1% 26.6% 26.5% 22.9% 

69 8729974 PERDIDO KEY 

OLD RIVER -87.448303 30.299999 

13.2 12.4 -10.8 -11.5 data 

13.3 12.4 -11.7 -11.7 model 

0.1 0.0 -0.9 -0.2 difference 

0.8% 0.0% 8.3% 1.7% 

70 8730667 ALABAMA 

POINT -87.555000 30.278299 

13.6 12.4 -11.9 -12.6 data 

15.8 14.9 -13.8 -13.8 model 

2.2 2.5 -1.9 -1.2 difference 

16.2% 20.2% 16.0% 9.5% 

71 8731269 GULF SHORES -87.668335 30.248333 

22.9 21.7 -21.6 -21.9 data 

19.0 17.4 -16.7 -17.2 model 

-3.9 -4.3 4.9 4.7 difference 

17.0% 19.8% 22.7% 21.5% 

72 8731952 BON SECOUR -87.735001 30.303301 

23.6 22.5 -22.1 -23.4 data 

21.2 19.4 -19.2 -20.2 model 

-2.4 -3.1 2.9 3.2 difference 

10.2% 13.8% 13.1% 13.7% 

73 8735180 DAUPHIN 

ISLAND -88.074997 30.250000 

19.5 18.9 -16.9 -17.2 data 

18.7 18.7 -15.9 -15.9 model 

-0.8 -0.2 1.0 1.3 difference 

4.1% 1.1% 5.9% 7.6% 

74 8737048 MOBILE STATE 

DOCKS -88.043297 30.708300 

23.8 21.7 -21.3 -24.1 data 

24.2 20.1 -20.3 -23.2 model 

0.4 -1.6 1.0 0.9 difference 

1.7% 7.4% 4.7% 3.7% 
44
45

APENDIX D. FINAL TIDAL DATUM FIELDS IN THE VDATUM REGION 

a

b

c
46

Figure D.1. Final corrected model datum fields on a smaller regional grid for the (a) MHHW, 

(b) MHW, (c) MLW, (d) MLLW, (e) MTL, and (f) DTL tidal datums. 

d

e

f
47

APPENDIX E. ESTIMATES OF NAVD88 AT BENCHMARKS

Estimated values of NAVD 88 at locations of benchmarks in the NGS database in the five subregions (see Figures 12 to 16). 

 

Table E.1. Estimated values of NAVD 88 at benchmark locations in Mobile and Perdido 

Bays. 

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

BH1754 30.24888 -88.07666 -0.1041 -0.1040 -0.1118 -0.1126 -0.1081 0.0047 

BH1752 30.24916 -88.07666 -0.1041 -0.1040 -0.1118 -0.1126 -0.1081 0.0047 

BH1755 30.24916 -88.07583 -0.1069 -0.1068 -0.1145 -0.1153 -0.1108 0.0047 

BH1756 30.24944 -88.07555 -0.1039 -0.1037 -0.1116 -0.1124 -0.1079 0.0048 

BG3643 30.29777 -87.44916 -0.1050 -0.1040 -0.1069 -0.1079 -0.1059 0.0018 

BG3644 30.29861 -87.44777 -0.1083 -0.1073 -0.1093 -0.1103 -0.1088 0.0013 

BG3645 30.29944 -87.44722 -0.1025 -0.1015 -0.1030 -0.1040 -0.1028 0.0010 

BG3646 30.29944 -87.44722 -0.1085 -0.1075 -0.1090 -0.1100 -0.1088 0.0010 

BG3634 30.34916 -87.41388 -0.1042 -0.1041 -0.1032 -0.1010 -0.1031 0.0015 

BG3635 30.34916 -87.41444 -0.1041 -0.1040 -0.1032 -0.1011 -0.1031 0.0014 

BG3636 30.34916 -87.41500 -0.0833 -0.0832 -0.0821 -0.0799 -0.0821 0.0016 

BG3410 30.39500 -87.42361 -0.1143 -0.1139 -0.1123 -0.1149 -0.1139 0.0011 

BG3409 30.39555 -87.42250 -0.1234 -0.1229 -0.1210 -0.1239 -0.1228 0.0013 

BG3647 30.40055 -87.42333 -0.1199 -0.1153 -0.1169 -0.1161 -0.1170 0.0020 

BG3615 30.41805 -87.35527 -0.1275 -0.1239 -0.1275 -0.1271 -0.1265 0.0017 

BG3616 30.41861 -87.35361 -0.1271 -0.1231 -0.1272 -0.1259 -0.1258 0.0019 

BG4595 30.45972 -87.40944 -0.1282 -0.1290 -0.1285 -0.1290 -0.1287 0.0004 

BG4596 30.45972 -87.40888 -0.1251 -0.1256 -0.1254 -0.1263 -0.1256 0.0005 

BG4597 30.45972 -87.40805 -0.1251 -0.1256 -0.1253 -0.1265 -0.1256 0.0006 

BG4594 30.46055 -87.40972 -0.1252 -0.1262 -0.1256 -0.1259 -0.1257 0.0004 

BG4593 30.46111 -87.40972 -0.1282 -0.1292 -0.1287 -0.1290 -0.1288 0.0004 

BH1484 30.70388 -88.04111 -0.2073 -0.2068 -0.2074 -0.2099 -0.2078 0.0014 

Table E.2. Estimated values of NAVD 88 at benchmark locations in the NE Gulf of Mexico. 

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

AA9918 30.21555 -85.87638 -0.0232 -0.0251 -0.0208 -0.0204 -0.0224 0.0022 

BG4570 30.33194 -87.14027 -0.0530 -0.0549 -0.0338 -0.0314 -0.0433 0.0124 

BG4571 30.33388 -87.13972 -0.0740 -0.0759 -0.0488 -0.0494 -0.0620 0.0149 

BG4572 30.33388 -87.13972 -0.0740 -0.0759 -0.0488 -0.0494 -0.0620 0.0149 

BG4573 30.33388 -87.13888 -0.0740 -0.0759 -0.0488 -0.0494 -0.0620 0.0149 

BG4574 30.33388 -87.13666 -0.0711 -0.0729 -0.0458 -0.0464 -0.0590 0.0150 

BG4574 30.33388 -87.13666 -0.0591 -0.0609 -0.0398 -0.0374 -0.0493 0.0124 

BG3467 30.37916 -86.86444 -0.0579 -0.0572 -0.0594 -0.0582 -0.0582 0.0009 

BG3683 30.37916 -86.86611 -0.0579 -0.0571 -0.0593 -0.0581 -0.0581 0.0009 

BG3466 30.37916 -86.86555 -0.0579 -0.0571 -0.0593 -0.0581 -0.0581 0.0009 

BG3465 30.37944 -86.86583 -0.0549 -0.0541 -0.0563 -0.0551 -0.0551 0.0009 

BG3464 30.38083 -86.86500 -0.0579 -0.0572 -0.0594 -0.0582 -0.0582 0.0009 

BG3464 30.38083 -86.86500 -0.0849 -0.0782 -0.0864 -0.0852 -0.0837 0.0037 

BG3463 30.38138 -86.86166 -0.0578 -0.0573 -0.0595 -0.0583 -0.0582 0.0010 
48

Table E.3. Estimated values of NAVD 88 at benchmark locations in Perdido, Pensacola, 

and Choctawatchee Bays.

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

BG3643 30.29777 -87.44916 -0.1048 -0.1038 -0.1072 -0.1082 -0.1060 0.0020 

BG3644 30.29861 -87.44777 -0.1084 -0.1074 -0.1091 -0.1101 -0.1087 0.0011 

BG3645 30.29944 -87.44722 -0.1026 -0.1016 -0.1027 -0.1037 -0.1027 0.0008 

BG3646 30.29944 -87.44722 -0.1086 -0.1076 -0.1087 -0.1097 -0.1087 0.0008 

BG3626 30.32638 -87.36888 -0.1018 -0.1014 -0.1017 -0.1024 -0.1018 0.0004 

BG3625 30.32666 -87.36888 -0.1017 -0.1013 -0.1016 -0.1024 -0.1017 0.0005 

BG3624 30.32694 -87.36888 -0.1016 -0.1012 -0.1016 -0.1024 -0.1017 0.0005 

BG3622 30.32750 -87.36638 -0.1012 -0.1008 -0.1020 -0.1023 -0.1016 0.0007 

BG3623 30.32750 -87.36777 -0.1014 -0.1010 -0.1018 -0.1024 -0.1017 0.0006 

BG1836 30.32888 -87.28805 -0.0943 -0.0917 -0.0939 -0.0855 -0.0913 0.0041 

BG1832 30.33000 -87.29222 -0.0923 -0.0934 -0.0920 -0.0923 -0.0925 0.0006 

BG3613 30.33000 -87.29250 -0.0923 -0.0934 -0.0920 -0.0923 -0.0925 0.0006 

BG4569 30.33416 -87.14083 -0.0531 -0.0524 -0.0568 -0.0548 -0.0543 0.0019 

BG4576 30.33444 -87.13416 -0.0654 -0.0655 -0.0608 -0.0634 -0.0638 0.0022 

BG4568 30.33472 -87.14305 -0.0650 -0.0642 -0.0597 -0.0633 -0.0630 0.0023 

BG4568 30.33472 -87.14305 -0.0500 -0.0492 -0.0507 -0.0513 -0.0503 0.0009 

BG4575 30.33472 -87.13361 -0.0684 -0.0685 -0.0638 -0.0664 -0.0668 0.0022 

BG4567 30.33611 -87.14444 -0.0500 -0.0494 -0.0514 -0.0514 -0.0505 0.0010 

BG4566 30.33638 -87.14361 -0.0501 -0.0496 -0.0539 -0.0517 -0.0513 0.0019 

BG1815 30.34472 -87.26888 -0.0892 -0.0895 -0.0889 -0.0870 -0.0886 0.0011 

BG1814 30.34527 -87.27027 -0.0887 -0.0892 -0.0890 -0.0872 -0.0885 0.0009 

BG1809 30.34638 -87.27944 -0.0888 -0.0888 -0.0944 -0.0918 -0.0909 0.0027 

BG3633 30.34888 -87.41277 -0.1046 -0.1044 -0.1029 -0.1007 -0.1032 0.0018 

BG3634 30.34916 -87.41388 -0.1038 -0.1036 -0.1035 -0.1014 -0.1031 0.0011 

BG3635 30.34916 -87.41444 -0.1037 -0.1036 -0.1036 -0.1015 -0.1031 0.0011 

BG3636 30.34916 -87.41500 -0.0825 -0.0824 -0.0827 -0.0806 -0.0821 0.0010 

BG1823 30.36916 -87.27666 -0.0981 -0.0989 -0.0940 -0.0952 -0.0965 0.0023 

BG3667 30.36944 -87.27666 -0.0950 -0.0959 -0.0910 -0.0923 -0.0935 0.0023 

BG4544 30.37083 -87.32027 -0.0969 -0.0957 -0.0972 -0.0961 -0.0965 0.0007 

BG4543 30.37166 -87.32083 -0.0969 -0.0957 -0.0972 -0.0961 -0.0965 0.0007 

BG3666 30.37361 -87.27500 -0.0947 -0.0953 -0.0915 -0.0925 -0.0935 0.0018 

BG3665 30.38194 -87.27694 -0.0995 -0.1024 -0.0908 -0.0944 -0.0968 0.0052 

BG1692 30.38222 -87.27805 -0.0970 -0.0973 -0.0953 -0.0961 -0.0964 0.0009 

BG3685 30.38638 -86.86222 -0.0579 -0.0632 -0.0637 -0.0622 -0.0617 0.0027 

BG3685 30.38638 -86.86222 -0.0819 -0.0812 -0.0877 -0.0862 -0.0842 0.0032 

BG1892 30.38666 -86.99222 -0.0720 -0.0705 -0.0738 -0.0723 -0.0721 0.0014 

BG3686 30.38777 -86.86277 -0.0594 -0.0648 -0.0622 -0.0606 -0.0618 0.0024 

BG3686 30.38777 -86.86277 -0.0834 -0.0828 -0.0862 -0.0846 -0.0843 0.0015 

BG3410 30.39500 -87.42361 -0.1144 -0.1139 -0.1122 -0.1149 -0.1139 0.0012 

BG3422 30.39527 -86.51388 -0.1227 -0.1207 -0.1239 -0.1235 -0.1227 0.0014 

BG3659 30.39527 -86.51388 -0.1257 -0.1237 -0.1269 -0.1265 -0.1257 0.0014 

BG3660 30.39527 -86.51388 -0.1197 -0.1177 -0.1209 -0.1205 -0.1197 0.0014 

BG3580 30.39861 -86.22861 -0.1141 -0.1153 -0.1141 -0.1143 -0.1145 0.0006 

BG3581 30.39944 -86.22861 -0.1200 -0.1212 -0.1201 -0.1203 -0.1204 0.0005 

BG3582 30.40055 -86.22861 -0.1199 -0.1211 -0.1202 -0.1204 -0.1204 0.0005 

BG3583 30.40055 -86.22861 -0.1199 -0.1211 -0.1202 -0.1204 -0.1204 0.0005 

BG3653 30.40111 -87.25194 -0.1003 -0.1015 -0.1001 -0.0990 -0.1002 0.0010 

BG3670 30.40361 -87.21333 -0.1098 -0.1090 -0.1105 -0.1106 -0.1100 0.0007 

BG3590 30.40833 -86.73305 -0.0984 -0.0981 -0.0949 -0.0977 -0.0973 0.0016 

BG3586 30.40916 -86.70027 -0.0972 -0.0979 -0.0920 -0.0952 -0.0956 0.0026 

BG3589 30.40916 -86.73222 -0.0979 -0.0974 -0.0951 -0.0979 -0.0971 0.0013 
49

Table E.3. (Continued).

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

BG3588 30.40972 -86.73250 -0.0979 -0.0974 -0.0951 -0.0978 -0.0971 0.0013 

BG3615 30.41805 -87.35527 -0.1276 -0.1241 -0.1276 -0.1272 -0.1266 0.0017 

BG3616 30.41861 -87.35361 -0.1272 -0.1233 -0.1273 -0.1261 -0.1260 0.0019 

BG2209 30.42972 -86.13583 -0.1254 -0.1257 -0.1266 -0.1274 -0.1263 0.0009 

BG4613 30.43000 -86.13611 -0.1254 -0.1257 -0.1266 -0.1274 -0.1263 0.0009 

BG4621 30.43055 -86.63333 -0.0568 -0.0580 -0.0560 -0.0581 -0.0572 0.0010 

BG2205 30.43083 -86.13555 -0.1314 -0.1317 -0.1325 -0.1334 -0.1323 0.0009 

BG4620 30.43138 -86.63333 -0.0385 -0.0400 -0.0380 -0.0402 -0.0392 0.0011 

BG4615 30.43194 -86.13500 -0.1255 -0.1257 -0.1265 -0.1274 -0.1263 0.0009 

BG3403 30.43527 -86.58416 -0.1219 -0.1255 -0.1101 -0.1121 -0.1174 0.0075 

BG3402 30.43694 -86.58444 -0.1187 -0.1206 -0.1145 -0.1161 -0.1175 0.0027 

BG4595 30.45972 -87.40944 -0.1281 -0.1287 -0.1285 -0.1294 -0.1287 0.0006 

BG4596 30.45972 -87.40888 -0.1251 -0.1256 -0.1254 -0.1265 -0.1257 0.0006 

BG4597 30.45972 -87.40805 -0.1251 -0.1256 -0.1254 -0.1265 -0.1257 0.0006 

BG3680 30.46027 -87.09583 -0.0972 -0.1010 -0.0900 -0.0878 -0.0940 0.0062 

BG3681 30.46055 -87.09666 -0.1003 -0.1042 -0.0929 -0.0907 -0.0970 0.0063 

BG4594 30.46055 -87.40972 -0.1252 -0.1259 -0.1255 -0.1262 -0.1257 0.0005 

BG4593 30.46111 -87.40972 -0.1282 -0.1292 -0.1287 -0.1290 -0.1288 0.0004 

BG3662 30.46527 -86.13972 -0.0925 -0.0913 -0.0884 -0.0889 -0.0903 0.0020 

BG3663 30.46583 -86.13888 -0.0924 -0.0912 -0.0886 -0.0891 -0.0903 0.0018 

BG2194 30.48500 -86.24444 -0.1185 -0.1175 -0.1050 -0.1068 -0.1120 0.0070 

BG0214 30.48694 -86.25222 -0.1044 -0.1034 -0.0966 -0.0976 -0.1005 0.0040 

BG2181 30.48694 -86.25194 -0.1166 -0.1156 -0.1085 -0.1094 -0.1125 0.0041 

BG3584 30.48694 -86.25083 -0.1051 -0.1041 -0.0956 -0.0967 -0.1004 0.0049 

BG2179 30.48750 -86.25194 -0.1195 -0.1185 -0.1115 -0.1125 -0.1155 0.0041 

BG4608 30.48888 -86.20583 -0.1000 -0.0999 -0.1003 -0.0994 -0.0999 0.0004 

BG4607 30.48972 -86.20555 -0.1030 -0.1029 -0.1033 -0.1024 -0.1029 0.0004 

BG4606 30.49055 -86.20555 -0.1070 -0.1069 -0.1073 -0.1064 -0.1069 0.0004 

BG4600 30.49583 -86.23861 -0.0905 -0.0895 -0.1041 -0.1058 -0.0975 0.0087 

BG4598 30.49638 -86.23805 -0.0905 -0.0895 -0.1041 -0.1058 -0.0975 0.0087 

BG4599 30.49638 -86.23861 -0.0905 -0.0895 -0.1041 -0.1058 -0.0975 0.0087 

BG4601 30.49638 -86.23972 -0.0905 -0.0895 -0.1041 -0.1058 -0.0975 0.0087 

BG4602 30.49666 -86.24000 -0.0875 -0.0865 -0.1010 -0.1028 -0.0945 0.0087 

BG1509 30.50138 -86.49083 -0.1450 -0.1439 -0.1481 -0.1469 -0.1460 0.0019 

BG4635 30.50361 -86.49388 -0.1488 -0.1486 -0.1502 -0.1500 -0.1494 0.0008 

BG4634 30.50416 -86.49277 -0.1487 -0.1483 -0.1504 -0.1500 -0.1494 0.0010 

BG4535 30.54583 -87.10388 -0.0802 -0.0862 -0.1114 -0.1025 -0.0951 0.0144 

BG4536 30.54583 -87.10444 -0.0832 -0.0892 -0.1144 -0.1055 -0.0981 0.0144 

BG4537 30.54583 -87.10583 -0.0832 -0.0892 -0.1144 -0.1055 -0.0981 0.0144 

BG4538 30.54944 -87.10583 -0.0862 -0.0922 -0.1174 -0.1085 -0.1011 0.0144 

BG4539 30.54972 -87.10611 -0.0832 -0.0892 -0.1144 -0.1055 -0.0981 0.0144 

BG3605 30.58055 -87.18000 -0.1030 -0.1050 -0.1063 -0.1056 -0.1050 0.0014 

BG3606 30.58055 -87.17972 -0.1030 -0.1050 -0.1064 -0.1057 -0.1050 0.0015 

BG4533 30.58055 -87.01500 -0.0948 -0.0965 -0.1002 -0.0999 -0.0979 0.0026 

BG4534 30.58083 -87.01444 -0.0948 -0.0965 -0.1002 -0.0999 -0.0978 0.0027 

BG3607 30.58138 -87.17944 -0.1031 -0.1049 -0.1063 -0.1055 -0.1049 0.0014 

BG3608 30.58138 -87.17972 -0.1002 -0.1018 -0.1031 -0.1023 -0.1019 0.0013 

BG3609 30.58250 -87.17888 -0.1000 -0.1020 -0.1033 -0.1026 -0.1020 0.0015 

BG0231 30.62138 -87.03277 -0.0974 -0.1011 -0.0960 -0.0964 -0.0977 0.0023 

BG0232 30.62277 -87.03555 -0.1004 -0.1032 -0.0996 -0.0995 -0.1007 0.0017 
50

Table E.4. Estimated values of NAVD 88 at benchmark locations in St. Andrews Bay.

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

BE1732 30.03083 -85.46472 -0.0517 -0.053 -0.0501 -0.0506 -0.0514 0.0013 

BE1733 30.03083 -85.46444 -0.0399 -0.0413 -0.0381 -0.0385 -0.0394 0.0014 

BE3817 30.03944 -85.39388 -0.0570 -0.0543 -0.0584 -0.0574 -0.0568 0.0018 

BE3815 30.03972 -85.39305 -0.0570 -0.0541 -0.0584 -0.0574 -0.0567 0.0018 

BE3816 30.03972 -85.39388 -0.0567 -0.0533 -0.0582 -0.0575 -0.0564 0.0022 

BE3018 30.09222 -85.64750 -0.0345 -0.0356 -0.0336 -0.0336 -0.0343 0.0009 

BE3019 30.09222 -85.64805 -0.0346 -0.0357 -0.0337 -0.0340 -0.0345 0.0009 

BE3020 30.09222 -85.64805 -0.0346 -0.0357 -0.0337 -0.0340 -0.0345 0.0009 

BE1354 30.09277 -85.68500 -0.0633 -0.0638 -0.0648 -0.0610 -0.0632 0.0016 

BE3011 30.09750 -85.61250 -0.0415 -0.0409 -0.0400 -0.0399 -0.0406 0.0008 

BE3012 30.09861 -85.61250 -0.0471 -0.0442 -0.0347 -0.0396 -0.0414 0.0054 

BE3013 30.09916 -85.61305 -0.0445 -0.0439 -0.0428 -0.0428 -0.0435 0.0009 

BE3015 30.10166 -85.61111 -0.0433 -0.0404 -0.0316 -0.0367 -0.0380 0.0051 

AI3216 30.12388 -85.73333 -0.0306 -0.0339 -0.0214 -0.0058 -0.0229 0.0126 

AI3217 30.12388 -85.73472 -0.0493 -0.0569 -0.0122 0.0069 -0.0279 0.0303 

AI3215 30.12500 -85.73055 -0.0293 -0.033 -0.0172 -0.0012 -0.0202 0.0143 

AI3218 30.12500 -85.73166 -0.0306 -0.0339 -0.0214 -0.0058 -0.0229 0.0126 

BE2976 30.12583 -85.61000 -0.0300 -0.0308 -0.0326 -0.0323 -0.0314 0.0012 

BE2990 30.13027 -85.74305 -0.0437 -0.0423 -0.0473 -0.0471 -0.0451 0.0025 

BE2991 30.13027 -85.74305 -0.0287 -0.0273 -0.0323 -0.0321 -0.0301 0.0025 

BE2988 30.13194 -85.73055 -0.0225 -0.025 -0.0235 -0.0264 -0.0243 0.0017 

BE1720 30.13333 -85.50638 -0.0414 -0.0381 -0.0366 -0.0389 -0.0388 0.002 

BE2956 30.13638 -85.57111 -0.0413 -0.0396 -0.0396 -0.0413 -0.0405 0.001 

BE2957 30.13638 -85.57027 -0.0416 -0.0395 -0.0397 -0.0414 -0.0405 0.0011 

BE2958 30.13638 -85.57027 -0.0416 -0.0395 -0.0397 -0.0414 -0.0405 0.0011 

BE2959 30.13638 -85.57027 -0.0416 -0.0395 -0.0397 -0.0414 -0.0405 0.0011 

BE1719 30.13805 -85.51611 -0.0422 -0.0410 -0.0409 -0.0429 -0.0418 0.0010 

BE0760 30.14750 -85.65888 -0.0556 -0.0474 -0.0335 -0.0407 -0.0443 0.0094 

BE0758 30.15138 -85.66000 -0.0518 -0.0444 -0.0307 -0.0387 -0.0414 0.0089 

BE3029 30.15194 -85.66444 -0.0324 -0.0313 -0.0329 -0.0296 -0.0315 0.0015 

BE3030 30.15194 -85.66444 -0.0384 -0.0373 -0.0389 -0.0356 -0.0375 0.0015 

BE0757 30.15333 -85.65972 -0.0548 -0.0473 -0.0337 -0.0417 -0.0444 0.0089 

BE2994 30.15888 -85.76166 -0.0407 -0.0391 -0.0368 -0.0357 -0.0381 0.0023 

AI3221 30.17000 -85.75555 -0.0464 -0.0447 -0.0475 -0.0475 -0.0465 0.0013 

AI3222 30.17000 -85.75638 -0.0469 -0.0454 -0.0479 -0.0479 -0.0470 0.0012 

BE2969 30.24472 -85.60583 -0.0464 -0.0444 -0.0464 -0.0477 -0.0462 0.0014 

BE2970 30.24472 -85.60583 -0.0554 -0.0534 -0.0554 -0.0567 -0.0552 0.0014 

BE2971 30.24472 -85.60583 -0.0524 -0.0504 -0.0524 -0.0537 -0.0522 0.0014 

BE2972 30.24472 -85.60583 -0.0554 -0.0534 -0.0554 -0.0567 -0.0552 0.0014 

BE1713 30.25277 -85.64805 -0.0426 -0.0407 -0.0399 -0.0419 -0.0413 0.0012 

BE0655 30.25444 -85.64805 -0.0427 -0.0410 -0.0402 -0.0421 -0.0415 0.0012 

BE0657 30.25444 -85.64972 -0.0455 -0.0432 -0.0432 -0.0449 -0.0442 0.0012 

BE0656 30.25472 -85.64944 -0.0426 -0.0403 -0.0404 -0.0420 -0.0413 0.0012 

BE0658 30.25500 -85.65000 -0.0423 -0.0400 -0.0396 -0.0417 -0.0409 0.0013 

BE2963 30.27944 -85.64555 -0.0219 -0.0195 -0.0297 -0.0303 -0.0253 0.0055 

BE2965 30.27944 -85.64555 -0.0249 -0.0225 -0.0327 -0.0333 -0.0283 0.0055 

BE2964 30.27944 -85.64555 -0.0219 -0.0195 -0.0297 -0.0303 -0.0253 0.0055 

BE2961 30.28277 -85.64583 -0.0298 -0.0277 -0.0316 -0.0324 -0.0304 0.0021 

BE2962 30.28277 -85.64583 -0.0268 -0.0247 -0.0286 -0.0294 -0.0274 0.0021 

BE1323 30.29305 -85.85833 -0.0523 -0.0508 -0.0549 -0.0548 -0.0532 0.0020 

BE1324 30.29333 -85.85833 -0.0588 -0.0575 -0.0606 -0.0609 -0.0594 0.0016 
51

Table E.4. (Continued). 

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

BE1325 30.29361 -85.85833 -0.0532 -0.0521 -0.0543 -0.0550 -0.0537 0.0013 

BE1322 30.29388 -85.85833 -0.0523 -0.0511 -0.0549 -0.0556 -0.0535 0.0021 

BE0633 30.29500 -85.85694 -0.0509 -0.0492 -0.0558 -0.0548 -0.0527 0.0031 

Table E.5. Estimated values of NAVD 88 at benchmark locations in St. Joseph Bay.

Benchmark Latitude Longitude 

From 

MLLW 

(m) 

From 

MLW 

(m) 

From 

MHW 

(m) 

From 

MHHW 

(m) 

Average 

(m) 

Std. 

Dev. 

(m) 

AS0930 29.68944 -85.36277 -0.1120 -0.1112 -0.1140 -0.1131 -0.1126 0.0012 

AS0304 29.81722 -85.31222 0.0050 0.0033 0.0079 0.0053 0.0053 0.0019 

AS0956 29.87250 -85.39194 0.0227 0.0285 0.0371 0.0271 0.0289 0.0060 

AS0955 29.87305 -85.39138 0.0236 0.0274 0.0402 0.0258 0.0293 0.0075 

AS0953 29.87416 -85.39055 0.0182 0.0214 0.0474 0.0212 0.0270 0.0137 

AS0954 29.87416 -85.39138 0.0113 0.0140 0.0559 0.0153 0.0241 0.0212 
52
53

APPENDIX F. COMPUTED DELTA VALUES FOR EACH DATUM 

Delta represents the difference between the observed tidal datum and the datum as computed by 

the gridded fields. Differences are computed at each NOS benchmark, denoted by the PID. 

Table F.1. Difference (i.e., Delta) values for the Mobile and Perdido Bays sub-region. 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

BH1754 30.24888 -88.07666 0.0048 0.0049 -0.0028 -0.0036 0.0008 0.0047 

BH1752 30.24916 -88.07666 0.0049 0.0049 -0.0028 -0.0036 0.0009 0.0047 

BH1755 30.24916 -88.07583 0.0008 0.0009 -0.0068 -0.0076 -0.0032 0.0047 

BH1756 30.24944 -88.07555 0.0037 0.0039 -0.0040 -0.0048 -0.0003 0.0047 

BG3643 30.29777 -87.44916 0.0013 0.0023 -0.0007 -0.0017 0.0003 0.0018 

BG3644 30.29861 -87.44777 -0.0027 -0.0017 -0.0038 -0.0047 -0.0032 0.0013 

BG3645 30.29944 -87.44722 0.0003 0.0013 -0.0002 -0.0012 0.0001 0.0010 

BG3646 30.29944 -87.44722 -0.0057 -0.0047 -0.0062 -0.0072 -0.0059 0.0010 

BG3634 30.34916 -87.41388 -0.0080 -0.0079 -0.0070 -0.0049 -0.0070 0.0014 

BG3635 30.34916 -87.41444 -0.0080 -0.0079 -0.0070 -0.0049 -0.0070 0.0014 

BG3636 30.34916 -87.41500 0.0129 0.0130 0.0141 0.0163 0.0141 0.0016 

BG3410 30.39500 -87.42361 0.0008 0.0013 0.0028 0.0003 0.0013 0.0011 

BG3409 30.39555 -87.42250 -0.0067 -0.0061 -0.0042 -0.0071 -0.0060 0.0013 

BG3647 30.40055 -87.42333 -0.0018 0.0028 0.0012 0.0020 0.0011 0.0020 

BG3615 30.41805 -87.35527 -0.0067 -0.0031 -0.0067 -0.0063 -0.0057 0.0017 

BG3616 30.41861 -87.35361 -0.0026 0.0015 -0.0026 -0.0013 -0.0013 0.0019 

BG4595 30.45972 -87.40944 -0.0007 -0.0015 -0.0011 -0.0016 -0.0012 0.0004 

BG4596 30.45972 -87.40888 0.0009 0.0004 0.0007 -0.0003 0.0004 0.0005 

BG4597 30.45972 -87.40805 0.0005 0.0000 0.0003 -0.0009 0.0000 0.0006 

BG4594 30.46055 -87.40972 0.0006 -0.0004 0.0002 -0.0001 0.0001 0.0004 

BG4593 30.46111 -87.40972 -0.0004 -0.0014 -0.0008 -0.0011 -0.0009 0.0004 

BH1484 30.70388 -88.04111 -0.0021 -0.0016 -0.0022 -0.0047 -0.0026 0.0014 

Table F.2. Difference (i.e., Delta) values for the NE Gulf of Mexico sub-region. 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW 

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

AA9918 30.21555 -85.87638 -0.0009 -0.0029 0.0014 0.0018 -0.0002 0.0022 

BG4570 30.33194 -87.14027 0.0356 0.0337 0.0548 0.0572 0.0453 0.0124 

BG4571 30.33388 -87.13972 0.0146 0.0127 0.0398 0.0392 0.0266 0.0149 

BG4572 30.33388 -87.13972 0.0146 0.0127 0.0398 0.0392 0.0266 0.0149 

BG4573 30.33388 -87.13888 0.0146 0.0127 0.0398 0.0392 0.0266 0.0149 

BG4574 30.33388 -87.13666 0.0175 0.0157 0.0428 0.0422 0.0296 0.0150 

BG4574 30.33388 -87.13666 0.0295 0.0277 0.0488 0.0512 0.0393 0.0124 

BG3467 30.37916 -86.86444 0.0006 0.0013 -0.0009 0.0003 0.0003 0.0009 

BG3683 30.37916 -86.86611 0.0021 0.0029 0.0007 0.0019 0.0019 0.0009 

BG3466 30.37916 -86.86555 0.0011 0.0019 -0.0003 0.0009 0.0009 0.0009 

BG3465 30.37944 -86.86583 0.0041 0.0048 0.0027 0.0038 0.0038 0.0009 

BG3464 30.38083 -86.86500 0.0004 0.0011 -0.0012 0.0000 0.0001 0.0010 

BG3464 30.38083 -86.86500 -0.0266 -0.0199 -0.0282 -0.0270 -0.0254 0.0037 

BG3463 30.38138 -86.86166 0.0010 0.0016 -0.0007 0.0006 0.0006 0.0010 

 
54

Table F.3. Difference (i.e., Delta) values for the Perdido, Pensacola, and Chocktawatchee 

Bay sub-region. 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

BG3643 30.29777 -87.44916 0.0012 0.0022 -0.0012 -0.0022 0.0000 0.0020 

BG3644 30.29861 -87.44777 0.0004 0.0014 -0.0003 -0.0013 0.0001 0.0011 

BG3645 30.29944 -87.44722 0.0053 0.0063 0.0052 0.0043 0.0053 0.0008 

BG3646 30.29944 -87.44722 -0.0007 0.0003 -0.0008 -0.0017 -0.0007 0.0008 

BG3626 30.32638 -87.36888 -0.0001 0.0003 0.0001 -0.0007 -0.0001 0.0004 

BG3625 30.32666 -87.36888 0.0001 0.0005 0.0001 -0.0007 0.0000 0.0005 

BG3624 30.32694 -87.36888 0.0001 0.0005 0.0001 -0.0007 0.0000 0.0005 

BG3622 30.32750 -87.36638 0.0004 0.0008 -0.0003 -0.0007 0.0000 0.0007 

BG3623 30.32750 -87.36777 0.0003 0.0007 -0.0001 -0.0007 0.0000 0.0006 

BG1836 30.32888 -87.28805 -0.0030 -0.0004 -0.0026 0.0058 0.0000 0.0041 

BG1832 30.33000 -87.29222 0.0000 -0.0011 0.0003 0.0000 -0.0002 0.0006 

BG3613 30.33000 -87.29250 0.0000 -0.0011 0.0003 0.0000 -0.0002 0.0006 

BG4569 30.33416 -87.14083 0.0055 0.0062 0.0019 0.0038 0.0044 0.0019 

BG4576 30.33444 -87.13416 0.0014 0.0013 0.0060 0.0034 0.0030 0.0022 

BG4568 30.33472 -87.14305 -0.0083 -0.0075 -0.0030 -0.0066 -0.0064 0.0023 

BG4568 30.33472 -87.14305 0.0067 0.0075 0.0060 0.0054 0.0064 0.0009 

BG4575 30.33472 -87.13361 -0.0016 -0.0017 0.0030 0.0004 0.0000 0.0022 

BG4567 30.33611 -87.14444 0.0015 0.0022 0.0001 0.0001 0.0010 0.0011 

BG4566 30.33638 -87.14361 0.0017 0.0022 -0.0021 0.0001 0.0005 0.0019 

BG1815 30.34472 -87.26888 -0.0006 -0.0009 -0.0003 0.0016 -0.0001 0.0011 

BG1814 30.34527 -87.27027 0.0001 -0.0003 -0.0001 0.0016 0.0003 0.0009 

BG1809 30.34638 -87.27944 0.0022 0.0022 -0.0035 -0.0009 0.0000 0.0028 

BG3633 30.34888 -87.41277 -0.0069 -0.0067 -0.0052 -0.0030 -0.0055 0.0018 

BG3634 30.34916 -87.41388 -0.0147 -0.0146 -0.0144 -0.0123 -0.0140 0.0011 

BG3635 30.34916 -87.41444 -0.0171 -0.0170 -0.0170 -0.0149 -0.0165 0.0011 

BG3636 30.34916 -87.41500 0.0007 0.0008 0.0005 0.0026 0.0012 0.0010 

BG1823 30.36916 -87.27666 -0.0034 -0.0042 0.0007 -0.0006 -0.0019 0.0023 

BG3667 30.36944 -87.27666 -0.0003 -0.0012 0.0037 0.0024 0.0011 0.0023 

BG4544 30.37083 -87.32027 -0.0005 0.0007 -0.0007 0.0003 -0.0001 0.0007 

BG4543 30.37166 -87.32083 -0.0004 0.0008 -0.0007 0.0004 0.0000 0.0007 

BG3666 30.37361 -87.27500 -0.0010 -0.0016 0.0022 0.0011 0.0002 0.0018 

BG3665 30.38194 -87.27694 -0.0033 -0.0062 0.0054 0.0018 -0.0006 0.0052 

BG1692 30.38222 -87.27805 -0.0006 -0.0009 0.0011 0.0003 0.0000 0.0009 

BG3685 30.38638 -86.86222 0.0173 0.0120 0.0115 0.0130 0.0135 0.0026 

BG3685 30.38638 -86.86222 -0.0067 -0.0060 -0.0125 -0.0110 -0.0091 0.0032 

BG1892 30.38666 -86.99222 0.0006 0.0021 -0.0013 0.0003 0.0004 0.0014 

BG3686 30.38777 -86.86277 0.0137 0.0083 0.0109 0.0125 0.0114 0.0023 

BG3686 30.38777 -86.86277 -0.0103 -0.0097 -0.0131 -0.0115 -0.0112 0.0015 

BG3410 30.39500 -87.42361 -0.0002 0.0003 0.0020 -0.0007 0.0003 0.0012 

BG3422 30.39527 -86.51388 0.0002 0.0022 -0.0010 -0.0006 0.0002 0.0014 

BG3659 30.39527 -86.51388 -0.0028 -0.0008 -0.0040 -0.0036 -0.0028 0.0014 

BG3660 30.39527 -86.51388 0.0032 0.0052 0.0020 0.0024 0.0032 0.0014 

BG3580 30.39861 -86.22861 0.0033 0.0021 0.0033 0.0031 0.0030 0.0006 

BG3581 30.39944 -86.22861 -0.0036 -0.0048 -0.0037 -0.0039 -0.0040 0.0005 

BG3582 30.40055 -86.22861 -0.0045 -0.0057 -0.0048 -0.0050 -0.0050 0.0005 

BG3583 30.40055 -86.22861 -0.0045 -0.0057 -0.0048 -0.0050 -0.0050 0.0005 

BG3653 30.40111 -87.25194 0.0002 -0.0010 0.0004 0.0015 0.0003 0.0010 

BG3670 30.40361 -87.21333 -0.0026 -0.0018 -0.0034 -0.0034 -0.0028 0.0008 

BG3590 30.40833 -86.73305 -0.0013 -0.0010 0.0021 -0.0007 -0.0002 0.0016 

BG3586 30.40916 -86.70027 -0.0014 -0.0021 0.0038 0.0006 0.0002 0.0026 

BG3589 30.40916 -86.73222 0.0002 0.0007 0.0030 0.0002 0.0010 0.0013 
55

Table F.3. (Continued). 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

BG3588 30.40972 -86.73250 0.0007 0.0011 0.0034 0.0007 0.0015 0.0013 

BG3615 30.41805 -87.35527 -0.0081 -0.0046 -0.0081 -0.0077 -0.0071 0.0017 

BG3616 30.41861 -87.35361 -0.0013 0.0026 -0.0014 -0.0002 -0.0001 0.0019 

BG2209 30.42972 -86.13583 0.0019 0.0016 0.0007 -0.0001 0.0010 0.0009 

BG4613 30.43000 -86.13611 0.0015 0.0012 0.0003 -0.0005 0.0006 0.0009 

BG4621 30.43055 -86.63333 -0.0165 -0.0177 -0.0157 -0.0178 -0.0169 0.0010 

BG2205 30.43083 -86.13555 -0.0042 -0.0045 -0.0053 -0.0062 -0.0051 0.0009 

BG4620 30.43138 -86.63333 0.0065 0.0050 0.0070 0.0048 0.0058 0.0011 

BG4615 30.43194 -86.13500 0.0028 0.0026 0.0018 0.0009 0.0020 0.0009 

BG3403 30.43527 -86.58416 -0.0045 -0.0081 0.0073 0.0053 0.0000 0.0075 

BG3402 30.43694 -86.58444 -0.0011 -0.0030 0.0030 0.0015 0.0001 0.0027 

BG4595 30.45972 -87.40944 -0.0009 -0.0015 -0.0012 -0.0022 -0.0015 0.0006 

BG4596 30.45972 -87.40888 0.0020 0.0015 0.0017 0.0006 0.0014 0.0006 

BG4597 30.45972 -87.40805 0.0017 0.0012 0.0014 0.0003 0.0012 0.0006 

BG3680 30.46027 -87.09583 -0.0008 -0.0045 0.0065 0.0087 0.0025 0.0062 

BG3681 30.46055 -87.09666 -0.0037 -0.0076 0.0037 0.0059 -0.0004 0.0063 

BG4594 30.46055 -87.40972 0.0022 0.0015 0.0019 0.0012 0.0017 0.0004 

BG4593 30.46111 -87.40972 -0.0006 -0.0016 -0.0011 -0.0014 -0.0012 0.0004 

BG3662 30.46527 -86.13972 -0.0022 -0.0010 0.0019 0.0014 0.0000 0.0020 

BG3663 30.46583 -86.13888 -0.0020 -0.0008 0.0018 0.0013 0.0001 0.0018 

BG2194 30.48500 -86.24444 -0.0079 -0.0069 0.0056 0.0038 -0.0014 0.0070 

BG0214 30.48694 -86.25222 0.0012 0.0022 0.0090 0.0080 0.0051 0.0040 

BG2181 30.48694 -86.25194 -0.0107 -0.0097 -0.0026 -0.0036 -0.0067 0.0041 

BG3584 30.48694 -86.25083 0.0019 0.0029 0.0114 0.0103 0.0066 0.0049 

BG2179 30.48750 -86.25194 -0.0136 -0.0126 -0.0057 -0.0066 -0.0096 0.0041 

BG4608 30.48888 -86.20583 0.0011 0.0012 0.0008 0.0017 0.0012 0.0004 

BG4607 30.48972 -86.20555 0.0006 0.0007 0.0003 0.0012 0.0007 0.0004 

BG4606 30.49055 -86.20555 -0.0017 -0.0016 -0.0020 -0.0011 -0.0016 0.0004 

BG4600 30.49583 -86.23861 0.0072 0.0082 -0.0064 -0.0081 0.0002 0.0087 

BG4598 30.49638 -86.23805 0.0068 0.0078 -0.0068 -0.0085 -0.0002 0.0087 

BG4599 30.49638 -86.23861 0.0068 0.0078 -0.0068 -0.0085 -0.0002 0.0087 

BG4601 30.49638 -86.23972 0.0068 0.0078 -0.0068 -0.0085 -0.0002 0.0087 

BG4602 30.49666 -86.24000 0.0096 0.0106 -0.0040 -0.0057 0.0026 0.0087 

BG1509 30.50138 -86.49083 0.0012 0.0023 -0.0020 -0.0007 0.0002 0.0019 

BG4635 30.50361 -86.49388 0.0002 0.0005 -0.0012 -0.0010 -0.0004 0.0008 

BG4634 30.50416 -86.49277 0.0007 0.0011 -0.0010 -0.0006 0.0001 0.0010 

BG4535 30.54583 -87.10388 0.0162 0.0102 -0.0150 -0.0061 0.0013 0.0144 

BG4536 30.54583 -87.10444 0.0147 0.0087 -0.0165 -0.0076 -0.0002 0.0144 

BG4537 30.54583 -87.10583 0.0149 0.0089 -0.0163 -0.0074 0.0000 0.0144 

BG4538 30.54944 -87.10583 0.0143 0.0083 -0.0169 -0.0080 -0.0006 0.0144 

BG4539 30.54972 -87.10611 0.0173 0.0113 -0.0139 -0.0050 0.0024 0.0144 

BG3605 30.58055 -87.18000 0.0015 -0.0005 -0.0018 -0.0011 -0.0005 0.0014 

BG3606 30.58055 -87.17972 0.0016 -0.0005 -0.0019 -0.0011 -0.0005 0.0015 

BG4533 30.58055 -87.01500 0.0031 0.0014 -0.0023 -0.0020 0.0000 0.0026 

BG4534 30.58083 -87.01444 0.0031 0.0014 -0.0024 -0.0021 0.0000 0.0027 

BG3607 30.58138 -87.17944 -0.0001 -0.0020 -0.0033 -0.0025 -0.0020 0.0014 

BG3608 30.58138 -87.17972 0.0028 0.0012 -0.0001 0.0007 0.0012 0.0012 

BG3609 30.58250 -87.17888 0.0013 -0.0008 -0.0021 -0.0014 -0.0007 0.0015 

BG0231 30.62138 -87.03277 0.0005 -0.0032 0.0018 0.0015 0.0002 0.0023 

BG0232 30.62277 -87.03555 0.0002 -0.0026 0.0010 0.0011 -0.0001 0.0017 
56

Table F.4. Difference (i.e., Delta) values for the St. Joseph Bay sub-region. 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

AS0930 29.68944 -85.3628 -0.0011 -0.0003 -0.0030 -0.0021 -0.0016 0.0012 

AS0304 29.81722 -85.3122 0.0050 0.0033 0.0079 0.0053 0.0054 0.0019 

AS0956 29.8725 -85.3919 -0.0024 0.0034 0.0119 0.0019 0.0037 0.0060 

AS0955 29.87305 -85.3914 -0.0027 0.0012 0.0139 -0.0004 0.0030 0.0074 

AS0953 29.87416 -85.3906 -0.0020 0.0012 0.0273 0.0011 0.0069 0.0137 

AS0954 29.87416 -85.3914 -0.0166 -0.0139 0.0280 -0.0126 -0.0038 0.0212 

Table F.5. Difference (i.e., Delta) values for the St. Andrews Bay sub-region. 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW 

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

BE1732 30.03083 -85.46472 -0.0075 -0.0088 -0.0059 -0.0063 -0.0071 0.0013 

BE1733 30.03083 -85.46444 -0.0001 -0.0015 0.0016 0.0012 0.0003 0.0014 

BE3817 30.03944 -85.39388 -0.0003 0.0024 -0.0017 -0.0007 -0.0001 0.0018 

BE3815 30.03972 -85.39305 -0.0003 0.0025 -0.0017 -0.0007 0.0000 0.0018 

BE3816 30.03972 -85.39388 -0.0002 0.0032 -0.0017 -0.0010 0.0001 0.0022 

BE3018 30.09222 -85.64750 -0.0002 -0.0013 0.0007 0.0007 0.0000 0.0009 

BE3019 30.09222 -85.64805 -0.0002 -0.0012 0.0008 0.0005 0.0000 0.0009 

BE3020 30.09222 -85.64805 -0.0002 -0.0012 0.0008 0.0005 0.0000 0.0009 

BE1354 30.09277 -85.68500 -0.0026 -0.0031 -0.0041 -0.0003 -0.0025 0.0016 

BE3011 30.09750 -85.61250 -0.0009 -0.0003 0.0006 0.0007 0.0000 0.0008 

BE3012 30.09861 -85.61250 -0.0060 -0.0031 0.0064 0.0015 -0.0003 0.0054 

BE3013 30.09916 -85.61305 -0.0011 -0.0005 0.0007 0.0006 -0.0001 0.0009 

BE3015 30.10166 -85.61111 -0.0051 -0.0023 0.0066 0.0014 0.0001 0.0051 

AI3216 30.12388 -85.73333 -0.0077 -0.0110 0.0015 0.0171 0.0000 0.0126 

AI3217 30.12388 -85.73472 -0.0223 -0.0299 0.0149 0.0340 -0.0008 0.0304 

AI3215 30.12500 -85.73055 -0.0091 -0.0127 0.0030 0.0190 0.0001 0.0143 

AI3218 30.12500 -85.73166 -0.0076 -0.0109 0.0016 0.0172 0.0001 0.0126 

BE2976 30.12583 -85.61000 0.0014 0.0006 -0.0012 -0.0009 0.0000 0.0012 

BE2990 30.13027 -85.74305 -0.0050 -0.0036 -0.0085 -0.0084 -0.0064 0.0025 

BE2991 30.13027 -85.74305 0.0100 0.0114 0.0065 0.0066 0.0086 0.0025 

BE2988 30.13194 -85.73055 0.0018 -0.0007 0.0008 -0.0021 -0.0001 0.0017 

BE1720 30.13333 -85.50638 -0.0026 0.0007 0.0022 -0.0001 0.0001 0.0020 

BE2956 30.13638 -85.57111 -0.0007 0.0010 0.0010 -0.0008 0.0001 0.0010 

BE2957 30.13638 -85.57027 -0.0010 0.0010 0.0008 -0.0009 0.0000 0.0011 

BE2958 30.13638 -85.57027 -0.0010 0.0010 0.0008 -0.0009 0.0000 0.0011 

BE2959 30.13638 -85.57027 -0.0010 0.0010 0.0008 -0.0009 0.0000 0.0011 

BE1719 30.13805 -85.51611 -0.0005 0.0007 0.0008 -0.0012 -0.0001 0.0010 

BE0760 30.14750 -85.65888 -0.0114 -0.0032 0.0107 0.0035 -0.0001 0.0094 

BE0758 30.15138 -85.66000 -0.0104 -0.0030 0.0107 0.0027 0.0000 0.0089 

BE3029 30.15194 -85.66444 0.0019 0.0030 0.0014 0.0047 0.0028 0.0015 

BE3030 30.15194 -85.66444 -0.0041 -0.0030 -0.0046 -0.0013 -0.0032 0.0015 

BE0757 30.15333 -85.65972 -0.0106 -0.0031 0.0105 0.0025 -0.0002 0.0089 

BE2994 30.15888 -85.76166 -0.0026 -0.0010 0.0013 0.0024 0.0000 0.0023 

AI3221 30.17000 -85.75555 0.0001 0.0018 -0.0010 -0.0010 0.0000 0.0013 

AI3222 30.17000 -85.75638 0.0000 0.0015 -0.0011 -0.0011 -0.0002 0.0012 

BE2969 30.24472 -85.60583 0.0067 0.0087 0.0067 0.0054 0.0069 0.0014 

BE2970 30.24472 -85.60583 -0.0023 -0.0003 -0.0023 -0.0036 -0.0021 0.0014 

BE2971 30.24472 -85.60583 0.0007 0.0027 0.0007 -0.0006 0.0009 0.0014 

BE2972 30.24472 -85.60583 -0.0023 -0.0003 -0.0023 -0.0036 -0.0021 0.0014 

BE1713 30.25277 -85.64805 -0.0014 0.0005 0.0013 -0.0007 -0.0001 0.0012 
57

Table F.5 (Continued). 

PID Latitude 

(deg) 

Longitude 

(deg) 

MHHW 

Deltas 

(m) 

MHW 

Deltas 

(m) 

MLW 

Deltas 

 (m) 

MLLW 

Deltas 

 (m) 

Avg. 

(m) 

Std. 

Dev. 

(m) 

BE0655 30.25444 -85.64805 -0.0011 0.0006 0.0014 -0.0005 0.0001 0.0011 

BE0657 30.25444 -85.64972 -0.0042 -0.0019 -0.0019 -0.0036 -0.0029 0.0012 

BE0656 30.25472 -85.64944 -0.0011 0.0012 0.0011 -0.0006 0.0001 0.0012 

BE0658 30.25500 -85.65000 -0.0013 0.0010 0.0014 -0.0007 0.0001 0.0013 

BE2963 30.27944 -85.64555 0.0045 0.0069 -0.0034 -0.0040 0.0010 0.0055 

BE2965 30.27944 -85.64555 0.0015 0.0039 -0.0064 -0.0070 -0.0020 0.0055 

BE2964 30.27944 -85.64555 0.0045 0.0069 -0.0034 -0.0040 0.0010 0.0055 

BE2961 30.28277 -85.64583 -0.0005 0.0016 -0.0023 -0.0031 -0.0011 0.0021 

BE2962 30.28277 -85.64583 0.0025 0.0046 0.0007 -0.0001 0.0019 0.0021 

BE1323 30.29305 -85.85833 0.0019 0.0034 -0.0007 -0.0006 0.0010 0.0020 

BE1324 30.29333 -85.85833 -0.0042 -0.0030 -0.0060 -0.0063 -0.0049 0.0016 

BE1325 30.29361 -85.85833 0.0011 0.0022 -0.0001 -0.0007 0.0006 0.0013 

BE1322 30.29388 -85.85833 0.0011 0.0023 -0.0014 -0.0022 -0.0001 0.0021 

BE0633 30.29500 -85.85694 0.0018 0.0035 -0.0031 -0.0021 0.0000 0.0031 
58
59

APPENDIX G. COMPARISON OF OBSERVED AND COMPUTED NAVD88 VALUES 

The following tables contain the comparison of the values of observed NAVD88-to-MSl offset at 

both NOS benchmarks (referenced by NGS PID) and tide stations (referenced by CO-OPS 7-

digit Station ID, or SID) and the offsets computed at the same location using the VDatum TSS 

fields. The difference is the computed minus the observed. 

Table G.1. Comparison of observed and computed values of NAVD88-to-MSL and their 

differences for the Alabama Bays sub-region. 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BH1754 30.24888 -88.07666 -0.1081 -0.1090 -0.0009 

BH1752 30.24916 -88.07666 -0.1081 -0.1090 -0.0009 

BH1755 30.24916 -88.07583 -0.1108 -0.1077 0.0031 

BH1756 30.24944 -88.07555 -0.1079 -0.1076 0.0003 

BG3643 30.29777 -87.44916 -0.1059 -0.1062 -0.0003 

BG3644 30.29861 -87.44777 -0.1088 -0.1056 0.0032 

BG3645 30.29944 -87.44722 -0.1028 -0.1028 0.0000 

BG3646 30.29944 -87.44722 -0.1088 -0.1028 0.0060 

BG3634 30.34916 -87.41388 -0.1031 -0.0961 0.0070 

BG3635 30.34916 -87.41444 -0.1031 -0.0961 0.0070 

BG3636 30.34916 -87.41500 -0.0821 -0.0962 -0.0141 

BG3410 30.39500 -87.42361 -0.1139 -0.1152 -0.0013 

BG3409 30.39555 -87.42250 -0.1228 -0.1168 0.0060 

BG3647 30.40055 -87.42333 -0.1170 -0.1181 -0.0011 

BG3615 30.41805 -87.35527 -0.1265 -0.1208 0.0057 

BG3616 30.41861 -87.35361 -0.1258 -0.1246 0.0012 

BG4595 30.45972 -87.40944 -0.1287 -0.1275 0.0012 

BG4596 30.45972 -87.40888 -0.1256 -0.1260 -0.0004 

BG4597 30.45972 -87.40805 -0.1256 -0.1256 0.0000 

BG4594 30.46055 -87.40972 -0.1257 -0.1258 -0.0001 

BG4593 30.46111 -87.40972 -0.1288 -0.1278 0.0010 

BH1484 30.70388 -88.04111 -0.2078 -0.2052 0.0026 

BH1484 30.70388 -88.04111 -0.2078 -0.2052 0.0026 

BH1484 30.70388 -88.04111 -0.2078 -0.2052 0.0026 

8735180 30.25000 -88.07500 -0.1020 -0.1044 -0.0024 

8737048 30.70833 -88.04333 -0.1790 -0.1800 -0.0010 

8729974 30.30000 -87.44833 -0.1070 -0.1048 0.0022 

8729962 30.39333 -87.42500 -0.1170 -0.1170 0.0000 

8729943 30.45833 -87.40833 -0.1270 -0.1270 0.0000 

8729938 30.35000 -87.41500 -0.1020 -0.0988 0.0032 

8729905 30.41833 -87.35667 -0.1150 -0.1199 -0.0049 
60

Table G.2. Comparison of observed and computed values of NAVD88-to-MSL and their 

differences for the Northeast Gulf of Mexico sub-region. 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

AA9918 30.21555 -85.87638 -0.0224 -0.0222 0.0002 

BG4570 30.33194 -87.14027 -0.0433 -0.0886 -0.0453 

BG4571 30.33388 -87.13972 -0.0620 -0.0886 -0.0266 

BG4572 30.33388 -87.13972 -0.0620 -0.0886 -0.0266 

BG4573 30.33388 -87.13888 -0.0620 -0.0886 -0.0266 

BG4574 30.33388 -87.13666 -0.0590 -0.0886 -0.0296 

BG4574 30.33388 -87.13666 -0.0493 -0.0886 -0.0393 

BG3467 30.37916 -86.86444 -0.0582 -0.0585 -0.0003 

BG3683 30.37916 -86.86611 -0.0581 -0.0600 -0.0019 

BG3466 30.37916 -86.86555 -0.0581 -0.0590 -0.0009 

BG3465 30.37944 -86.86583 -0.0551 -0.0590 -0.0039 

BG3464 30.38083 -86.86500 -0.0582 -0.0582 0.0000 

BG3464 30.38083 -86.86500 -0.0837 -0.0582 0.0255 

BG3463 30.38138 -86.86166 -0.0582 -0.0588 -0.0006 

8729678 30.37667 -86.86500 -0.0570 -0.0579 -0.0009 

8729210 30.21333 -85.88000 -0.0210 -0.0212 -0.0002 

Table G.3. Comparison of observed and computed values of NAVD88-to-MSL and their 

differences for the Perdido, Pensacola, and Chocktawatchee Bays sub-region. 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BG3643 30.29777 -87.44916 -0.1060 -0.1060 0.0000 

BG3644 30.29861 -87.44777 -0.1087 -0.1088 -0.0001 

BG3645 30.29944 -87.44722 -0.1027 -0.1080 -0.0053 

BG3646 30.29944 -87.44722 -0.1087 -0.1080 0.0007 

BG3626 30.32638 -87.36888 -0.1018 -0.1017 0.0001 

BG3625 30.32666 -87.36888 -0.1017 -0.1017 0.0000 

BG3624 30.32694 -87.36888 -0.1017 -0.1017 0.0000 

BG3622 30.32750 -87.36638 -0.1016 -0.1016 0.0000 

BG3623 30.32750 -87.36777 -0.1017 -0.1017 0.0000 

BG1836 30.32888 -87.28805 -0.0913 -0.0913 0.0000 

BG1832 30.33000 -87.29222 -0.0925 -0.0923 0.0002 

BG3613 30.33000 -87.29250 -0.0925 -0.0923 0.0002 

BG4569 30.33416 -87.14083 -0.0543 -0.0586 -0.0043 

BG4576 30.33444 -87.13416 -0.0638 -0.0668 -0.0030 

BG4568 30.33472 -87.14305 -0.0630 -0.0567 0.0063 

BG4568 30.33472 -87.14305 -0.0503 -0.0567 -0.0064 

BG4575 30.33472 -87.13361 -0.0668 -0.0668 0.0000 

BG4567 30.33611 -87.14444 -0.0505 -0.0515 -0.0010 

BG4566 30.33638 -87.14361 -0.0513 -0.0518 -0.0005 

BG1815 30.34472 -87.26888 -0.0886 -0.0886 0.0000 

BG1814 30.34527 -87.27027 -0.0885 -0.0889 -0.0004 

BG1809 30.34638 -87.27944 -0.0909 -0.0909 0.0000 

BG3633 30.34888 -87.41277 -0.1032 -0.0977 0.0055 

BG3634 30.34916 -87.41388 -0.1031 -0.0891 0.0140 

BG3635 30.34916 -87.41444 -0.1031 -0.0866 0.0165 

BG3636 30.34916 -87.41500 -0.0821 -0.0832 -0.0011 

BG1823 30.36916 -87.27666 -0.0965 -0.0947 0.0018 
61

Table G.3 (Continued). 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BG3667 30.36944 -87.27666 -0.0935 -0.0947 -0.0012 

BG4544 30.37083 -87.32027 -0.0965 -0.0964 0.0001 

BG4543 30.37166 -87.32083 -0.0965 -0.0965 0.0000 

BG3666 30.37361 -87.27500 -0.0935 -0.0937 -0.0002 

BG3665 30.38194 -87.27694 -0.0968 -0.0962 0.0006 

BG1692 30.38222 -87.27805 -0.0964 -0.0964 0.0000 

BG3685 30.38638 -86.86222 -0.0617 -0.0752 -0.0135 

BG3685 30.38638 -86.86222 -0.0842 -0.0752 0.0090 

BG1892 30.38666 -86.99222 -0.0721 -0.0726 -0.0005 

BG3686 30.38777 -86.86277 -0.0618 -0.0731 -0.0113 

BG3686 30.38777 -86.86277 -0.0843 -0.0731 0.0112 

BG3410 30.39500 -87.42361 -0.1139 -0.1142 -0.0003 

BG3422 30.39527 -86.51388 -0.1227 -0.1229 -0.0002 

BG3659 30.39527 -86.51388 -0.1257 -0.1229 0.0028 

BG3660 30.39527 -86.51388 -0.1197 -0.1229 -0.0032 

BG3580 30.39861 -86.22861 -0.1145 -0.1174 -0.0029 

BG3581 30.39944 -86.22861 -0.1204 -0.1164 0.0040 

BG3582 30.40055 -86.22861 -0.1204 -0.1154 0.0050 

BG3583 30.40055 -86.22861 -0.1204 -0.1154 0.0050 

BG3653 30.40111 -87.25194 -0.1002 -0.1005 -0.0003 

BG3670 30.40361 -87.21333 -0.1100 -0.1072 0.0028 

BG3590 30.40833 -86.73305 -0.0973 -0.0971 0.0002 

BG3586 30.40916 -86.70027 -0.0956 -0.0958 -0.0002 

BG3589 30.40916 -86.73222 -0.0971 -0.0981 -0.0010 

BG3588 30.40972 -86.73250 -0.0971 -0.0985 -0.0014 

BG3615 30.41805 -87.35527 -0.1266 -0.1195 0.0071 

BG3616 30.41861 -87.35361 -0.1260 -0.1259 0.0001 

BG2209 30.42972 -86.13583 -0.1263 -0.1273 -0.0010 

BG4613 30.43000 -86.13611 -0.1263 -0.1269 -0.0006 

BG4621 30.43055 -86.63333 -0.0572 -0.0403 0.0169 

BG2205 30.43083 -86.13555 -0.1323 -0.1272 0.0051 

BG4620 30.43138 -86.63333 -0.0392 -0.0450 -0.0058 

BG4615 30.43194 -86.13500 -0.1263 -0.1283 -0.0020 

BG3403 30.43527 -86.58416 -0.1174 -0.1174 0.0000 

BG3402 30.43694 -86.58444 -0.1175 -0.1176 -0.0001 

BG4595 30.45972 -87.40944 -0.1287 -0.1272 0.0015 

BG4596 30.45972 -87.40888 -0.1257 -0.1271 -0.0014 

BG4597 30.45972 -87.40805 -0.1257 -0.1268 -0.0011 

BG3680 30.46027 -87.09583 -0.0940 -0.0964 -0.0024 

BG3681 30.46055 -87.09666 -0.0970 -0.0966 0.0004 

BG4594 30.46055 -87.40972 -0.1257 -0.1274 -0.0017 

BG4593 30.46111 -87.40972 -0.1288 -0.1276 0.0012 

BG3662 30.46527 -86.13972 -0.0903 -0.0903 0.0000 

BG3663 30.46583 -86.13888 -0.0903 -0.0904 -0.0001 

BG2194 30.48500 -86.24444 -0.1120 -0.1106 0.0014 

BG0214 30.48694 -86.25222 -0.1005 -0.1056 -0.0051 

BG2181 30.48694 -86.25194 -0.1125 -0.1058 0.0067 

BG3584 30.48694 -86.25083 -0.1004 -0.1070 -0.0066 

BG2179 30.48750 -86.25194 -0.1155 -0.1059 0.0096 

BG4608 30.48888 -86.20583 -0.0999 -0.1011 -0.0012 

BG4607 30.48972 -86.20555 -0.1029 -0.1036 -0.0007 

BG4606 30.49055 -86.20555 -0.1069 -0.1053 0.0016 

BG4600 30.49583 -86.23861 -0.0975 -0.0977 -0.0002 

BG4598 30.49638 -86.23805 -0.0975 -0.0973 0.0002 
62

Table G.3. (Continued). 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BG4599 30.49638 -86.23861 -0.0975 -0.0973 0.0002 

BG4601 30.49638 -86.23972 -0.0975 -0.0973 0.0002 

BG4602 30.49666 -86.24000 -0.0945 -0.0971 -0.0026 

BG1509 30.50138 -86.49083 -0.1460 -0.1462 -0.0002 

BG4635 30.50361 -86.49388 -0.1494 -0.1490 0.0004 

BG4634 30.50416 -86.49277 -0.1494 -0.1494 0.0000 

BG4535 30.54583 -87.10388 -0.0951 -0.0964 -0.0013 

BG4536 30.54583 -87.10444 -0.0981 -0.0979 0.0002 

BG4537 30.54583 -87.10583 -0.0981 -0.0981 0.0000 

BG4538 30.54944 -87.10583 -0.1011 -0.1005 0.0006 

BG4539 30.54972 -87.10611 -0.0981 -0.1005 -0.0024 

BG3605 30.58055 -87.18000 -0.1050 -0.1045 0.0005 

BG3606 30.58055 -87.17972 -0.1050 -0.1046 0.0004 

BG4533 30.58055 -87.01500 -0.0979 -0.0979 0.0000 

BG4534 30.58083 -87.01444 -0.0978 -0.0979 -0.0001 

BG3607 30.58138 -87.17944 -0.1049 -0.1030 0.0019 

BG3608 30.58138 -87.17972 -0.1019 -0.1030 -0.0011 

BG3609 30.58250 -87.17888 -0.1020 -0.1013 0.0007 

BG0231 30.62138 -87.03277 -0.0977 -0.0979 -0.0002 

BG0232 30.62277 -87.03555 -0.1007 -0.1006 0.0001 

8729974 30.30000 -87.44833 -0.1070 -0.1070 0.0000 

8729962 30.39333 -87.42500 -0.1170 -0.1160 0.0010 

8729943 30.45833 -87.40833 -0.1270 -0.1269 0.0001 

8729938 30.35000 -87.41500 -0.1020 -0.1021 -0.0001 

8729909 30.32667 -87.35667 -0.1010 -0.1010 0.0000 

8729905 30.41833 -87.35667 -0.1150 -0.1160 -0.0010 

8729889 30.37000 -87.31833 -0.0960 -0.0961 -0.0001 

8729882 30.33000 -87.29167 -0.0920 -0.0923 -0.0003 

8729871 30.37500 -87.27667 -0.0930 -0.0931 -0.0001 

8729868 30.34500 -87.27333 -0.0910 -0.0910 0.0000 

8729849 30.40167 -87.25167 -0.1020 -0.1014 0.0006 

8729840 30.40333 -87.21167 -0.0900 -0.0963 -0.0063 

8729824 30.58167 -87.18000 -0.1010 -0.1022 -0.0012 

8729808 30.33667 -87.14667 -0.0530 -0.0530 0.0000 

8729806 30.33667 -87.14000 -0.0670 -0.0665 0.0005 

8729793 30.54500 -87.10333 -0.0980 -0.0962 0.0018 

8729791 30.45500 -87.10000 -0.0940 -0.0940 0.0000 

8729757 30.62667 -87.03667 -0.0950 -0.0965 -0.0015 

8729753 30.63667 -87.02833 -0.1090 -0.1087 0.0003 

8729747 30.58167 -87.01500 -0.0960 -0.0965 -0.0005 

8729736 30.38667 -86.99167 -0.0730 -0.0726 0.0004 

8729679 30.38500 -86.86333 -0.0880 -0.0876 0.0004 

8729613 30.40833 -86.73167 -0.1040 -0.1014 0.0026 

8729598 30.40667 -86.70000 -0.0960 -0.0960 0.0000 

8729567 30.42833 -86.63167 -0.0180 -0.0279 -0.0099 

8729538 30.43500 -86.58667 -0.1190 -0.1188 0.0002 

8729511 30.39500 -86.51333 -0.1230 -0.1228 0.0002 

8729501 30.50333 -86.49333 -0.1480 -0.1486 -0.0006 

8729387 30.48667 -86.25333 -0.1100 -0.1057 0.0043 

8729381 30.49667 -86.24000 -0.0990 -0.0971 0.0019 

8729376 30.40000 -86.22833 -0.1150 -0.1155 -0.0005 

8729364 30.48833 -86.20500 -0.1050 -0.1039 0.0011 

8729333 30.46833 -86.13833 -0.0920 -0.0921 -0.0001 

8729332 30.42833 -86.13667 -0.1370 -0.1340 0.0030 
63

Table G.4. Comparison of observed and computed values of NAVD88-to-MSL and their 

differences for the St. Joseph Bay sub-region. 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

AS0930 29.68944 -85.36277 -0.1126 -0.1109 0.0017 

AS0304 29.81722 -85.31222 0.0053 0.0000 -0.0053 

AS0956 29.87250 -85.39194 0.0289 0.0251 -0.0038 

AS0955 29.87305 -85.39138 0.0293 0.0262 -0.0031 

AS0953 29.87416 -85.39055 0.0270 0.0201 -0.0069 

AS0954 29.87416 -85.39138 0.0241 0.0279 0.0038 

8728958 29.87333 -85.39000 0.0070 0.0094 0.0024 

8728949 29.69000 -85.36333 -0.1140 -0.1126 0.0014 

8728942 29.66833 -85.36000 0.0060 0.0061 0.0001 

8728912 29.81500 -85.31333 0.0010 0.0000 -0.0010 

Table G.5. Comparison of observed and computed values of NAVD88-to-MSL and their 

differences for the St. Andrews Bay sub-region. 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BE1732 30.03083 -85.46472 -0.0514 -0.0442 0.0072 

BE1733 30.03083 -85.46444 -0.0394 -0.0397 -0.0003 

BE3817 30.03944 -85.39388 -0.0568 -0.0567 0.0001 

BE3815 30.03972 -85.39305 -0.0567 -0.0567 0.0000 

BE3816 30.03972 -85.39388 -0.0564 -0.0565 -0.0001 

BE3018 30.09222 -85.64750 -0.0343 -0.0343 0.0000 

BE3019 30.09222 -85.64805 -0.0345 -0.0345 0.0000 

BE3020 30.09222 -85.64805 -0.0345 -0.0345 0.0000 

BE1354 30.09277 -85.68500 -0.0632 -0.0607 0.0025 

BE3011 30.09750 -85.61250 -0.0406 -0.0406 0.0000 

BE3012 30.09861 -85.61250 -0.0414 -0.0411 0.0003 

BE3013 30.09916 -85.61305 -0.0435 -0.0434 0.0001 

BE3015 30.10166 -85.61111 -0.0380 -0.0382 -0.0002 

AI3216 30.12388 -85.73333 -0.0229 -0.0229 0.0000 

AI3217 30.12388 -85.73472 -0.0279 -0.0271 0.0008 

AI3215 30.12500 -85.73055 -0.0202 -0.0202 0.0000 

AI3218 30.12500 -85.73166 -0.0229 -0.0230 -0.0001 

BE2976 30.12583 -85.61000 -0.0314 -0.0314 0.0000 

BE2990 30.13027 -85.74305 -0.0451 -0.0388 0.0063 

BE2991 30.13027 -85.74305 -0.0301 -0.0388 -0.0087 

BE2988 30.13194 -85.73055 -0.0243 -0.0243 0.0000 

BE1720 30.13333 -85.50638 -0.0388 -0.0388 0.0000 

BE2956 30.13638 -85.57111 -0.0405 -0.0406 -0.0001 

BE2957 30.13638 -85.57027 -0.0405 -0.0405 0.0000 

BE2958 30.13638 -85.57027 -0.0405 -0.0405 0.0000 

BE2959 30.13638 -85.57027 -0.0405 -0.0405 0.0000 

BE1719 30.13805 -85.51611 -0.0418 -0.0417 0.0001 

BE0760 30.14750 -85.65888 -0.0443 -0.0442 0.0001 

BE0758 30.15138 -85.66000 -0.0414 -0.0414 0.0000 

BE3029 30.15194 -85.66444 -0.0315 -0.0343 -0.0028 

BE3030 30.15194 -85.66444 -0.0375 -0.0343 0.0032 

BE0757 30.15333 -85.65972 -0.0444 -0.0442 0.0002 
64

Table G.5. (Continued). 

PID or SID Latitude 

(deg) 

Longitude 

(deg) 

Observed 

(m) 

TSS Derived 

Value (m) 

Difference 

(m) 

BE2994 30.15888 -85.76166 -0.0381 -0.0381 0.0000 

AI3221 30.17000 -85.75555 -0.0465 -0.0465 0.0000 

AI3222 30.17000 -85.75638 -0.0470 -0.0468 0.0002 

BE2969 30.24472 -85.60583 -0.0462 -0.0531 -0.0069 

BE2970 30.24472 -85.60583 -0.0552 -0.0531 0.0021 

BE2971 30.24472 -85.60583 -0.0522 -0.0531 -0.0009 

BE2972 30.24472 -85.60583 -0.0552 -0.0531 0.0021 

BE1713 30.25277 -85.64805 -0.0413 -0.0412 0.0001 

BE0655 30.25444 -85.64805 -0.0415 -0.0416 -0.0001 

BE0657 30.25444 -85.64972 -0.0442 -0.0413 0.0029 

BE0656 30.25472 -85.64944 -0.0413 -0.0415 -0.0002 

BE0658 30.25500 -85.65000 -0.0409 -0.0410 -0.0001 

BE2963 30.27944 -85.64555 -0.0253 -0.0263 -0.0010 

BE2965 30.27944 -85.64555 -0.0283 -0.0263 0.0020 

BE2964 30.27944 -85.64555 -0.0253 -0.0263 -0.0010 

BE2961 30.28277 -85.64583 -0.0304 -0.0293 0.0011 

BE2962 30.28277 -85.64583 -0.0274 -0.0293 -0.0019 

BE1323 30.29305 -85.85833 -0.0532 -0.0542 -0.0010 

BE1324 30.29333 -85.85833 -0.0594 -0.0546 0.0048 

BE1325 30.29361 -85.85833 -0.0537 -0.0543 -0.0006 

BE1322 30.29388 -85.85833 -0.0535 -0.0535 0.0000 

BE0633 30.29500 -85.85694 -0.0527 -0.0527 0.0000 

8729197 30.29333 -85.85833 -0.0540 -0.0546 -0.0006 

8729155 30.15833 -85.76833 -0.0380 -0.0380 0.0000 

8729152 30.17000 -85.75500 -0.0510 -0.0495 0.0015 

8729149 30.13000 -85.74333 -0.0430 -0.0415 0.0015 

8729141 30.13333 -85.73167 -0.0240 -0.0241 -0.0001 

8729136 30.12500 -85.72167 -0.0260 -0.0260 0.0000 

8729108 30.15167 -85.66667 -0.0330 -0.0331 -0.0001 

8729107 30.15167 -85.66000 -0.0420 -0.0418 0.0002 

8729105 30.09167 -85.64833 -0.0340 -0.0341 -0.0001 

8729102 30.25500 -85.64833 -0.0470 -0.0456 0.0014 

8729101 30.28333 -85.64667 -0.0300 -0.0299 0.0001 

8729085 30.09833 -85.61333 -0.0410 -0.0414 -0.0004 

8729084 30.12667 -85.61167 -0.0290 -0.0290 0.0000 

8729071 30.24500 -85.60500 -0.0540 -0.0537 0.0003 

8729063 30.13667 -85.57167 -0.0410 -0.0410 0.0000 

8729039 30.13667 -85.51667 -0.0410 -0.0410 0.0000 

8729015 30.03000 -85.46500 -0.0390 -0.0384 0.0006 

8728973 30.03833 -85.39333 -0.0570 -0.0570 0.0000