NOAA Technical Report NOS CO-OPS 035

HISTORICAL GOLDEN GATE TIDAL SERIES

Silver Spring, Maryland

October, 2002

noaa National Oceanic and Atmospheric Administration

U.S. DEPARTMENT OF COMMERCE

National Ocean Service

Center for Operational Oceanographic Products and Services

Products and Services Division
Center for Operational Oceanographic Products and Services

National Ocean Service

National Oceanic and Atmospheric Administration

U.S. Department of Commerce

The National Ocean Service (NOS) Center for Operational Oceanographic Products

and Services (CO-OPS) collects and distributes observations and predictions of water

levels and currents to ensure safe, efficient and environmentally sound maritime

commerce. The Center provides the set of water level and coastal current products

required to support NOS' Strategic Plan mission requirements, and to assist in

providing operational oceanographic data/products required by NOAA's other

Strategic Plan themes. For example, CO-OPS provides data and products required

by the National Weather Service to meet its flood and tsunami warning

responsibilities. The Center manages the National Water Level Observation

Network (NWLON), and a national network of Physical Oceanographic Real-Time

Systems (PORTS®) in major U.S. harbors. The Center: establishes standards for the

collection and processing of water level and current data; collects and documents

user requirements which serve as the foundation for all resulting program activities;

designs new and/or improved oceanographic observing systems; designs software to

improve CO-OPS' data processing capabilities; maintains and operates

oceanographic observing systems; performs operational data analysis/quality control;

and produces/disseminates oceanographic products.
NOAA Technical Report NOS CO-OPS 035

HISTORICAL GOLDEN GATE TIDAL SERIES

Raymond A. Smith

October 2002

noaa National Oceanic and Atmospheric Administration

U.S. DEPARTMENT OF COMMERCE National Oceanic and Atmospheric Administration

Don Evans, Secretary Conrad C. Lautenbacher, Jr. Under Secretary for Oceans

 and Atmosphere and NOAA Administrator

National Ocean Service

Margaret A. Davidson, Acting Assistant Administrator

for Ocean Services and Coastal Zone Management

 

Center for Operational Oceanographic Products and Services

Michael Szabados, Director
ii
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TABLE OF CONTENTS

 Page

I. INTRODUCTION .................................................... 1

II. HISTORY OF TIDE STATIONS AT THE GOLDEN GATE . . . . . . . . . . . . . . . . . . . 1

A. Fort Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

 B. Sausalito ......................................................... 1

 C. Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

III. BENCH MARK AND LEVELING HISTORY AT THE GOLDEN GATE ........ 3

A. Fort Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

B. Sausalito ......................................................... 3

C. Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

D. Relating the Tide Staff Zeros for the Three Locations to a Common Zero . . . . . . 4

IV. TIDAL DATUMS FOR THE GOLDEN GATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

 A. Fort Point/Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

B. Sausalito ......................................................... 8

 

V. ADJUSTMENTS TO SAUSALITO 1877-1897 TIDAL HEIGHTS .............. 9

 

VI. DATUM RECOVERY AT SAUSALITO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

VII. GEODETIC RELATIONSHIPS TO TIDAL DATUMS AT THE GOLDEN GATE . 13

 A. National Geodetic Vertical Datum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

 B. North American Vertical Datum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

VIII. SPECIAL DATUMS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

IX. VARIATIONS IN MEAN SEA LEVEL AT THE GOLDEN GATE . . . . . . . . . . . . . 17

 A. Seasonal Variations in Sea Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

 B. Interannual-to-Decadal Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

C. Long-TermVariations in Annual Mean Sea Level . . . . . . . . . . . . . . . . . . . . . . . . . 19

 D. Sea Level Trends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

 

 

X. EXTREME HIGH AND LOW WATER LEVELS AT THE GOLDEN GATE . . . . . 23

 A. Observed Highest Water Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

 B. Observed Lowest Water Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

 C. One Hundred Year Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
iv

 D. The Great January 1862 Floods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

 E. Return Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

XI. FREQUENCY AND DURATION OF INUNDATION . . . . . . . . . . . . . . . . . . . . . . . . 31

 

XII. COMPARISON OF OBSERVED AND PREDICTED HIGH AND LOW WATER

 LEVELS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

 

XIII. CONCLUDING REMARKS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

 ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

APPENDIX A. History of Tide Gauges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

APPENDIX B. Leveling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

APPENDIX C. Comparative Readings and Adjustments to Tidal Heights at Fort Point 

Between 1855 and 1859 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1

APPENDIX D. Water Level Crossings of the Golden Gate . . . . . . . . . . . . . . . . . . . . . . . . D-1

 
v

LIST OF FIGURES

 Page

1. Location of Golden Gate Tide Stations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Summary of the relationships between tide staffs at the Presidio and Sausalito . . . 5

3. Tidal Datum Elevations at the Golden Gate for 7 Different Tidal Epochs 

Between 1855 and 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

4. Seasonal Variations in Sea Level for Select Years in the Golden Gate Tidal Series 17

5A. Seasonal Variations in Sea Level During Several El Nino Events 

Between 1939 and 1983 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5B. Seasonal Variations in Sea Level During Several El Nino Events 

Between 1990 and 1998 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

6. Annual Mean Sea Level, 19-Year Moving Average of Sea Level and Sea Level

Trend for the Golden Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

7. Observed Annual Highest Water Levels at the Golden Gate 

 Between 1855 and 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

8A. Observed Highest Water Level, Predicted and Storm Surge for 

January 27, 1983 at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

8B. Observed Highest Water Level, Predicted and Storm Surge for

December 3, 1983 at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

9. Observed Annual Lowest Water Levels at the Golden Gate . . . . . . . . . . . . . . . . . . 25

10A. Observed Lowest Water Level, Predicted, and Storm Surge for 

December 26, 1932 at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

10B. Observed Lowest Water Level, Predicted, and Storm Surge for 

December 17, 1933 at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

11. Observed, Predicted and Storm Surge for January 22 - 24, 1862 at Fort Point . . . . 28

12A. Frequency of Inundation for High Waters at the Presidio Between 1922 and 1984 31

12B. Duration of Inundation for High Waters at the Presidio Between 1922 and 1984 . . 32

12C. Frequency of Inundation for Low Waters at the Presidio Between 1922 - 1984 . . . 32

12D. Duration of Inundation for Low Waters at the Presidio Between 1922 and 1984 . . 33

13A. Frequency Distribution of Differences for High Water Heights at the Presidio . . . 35

13B. Frequency Distribution of Differences for Low Water Heights at the Presidio . . . . 36

A-1. Self-Registering Tide Gauge Installed at Fort Point in 1854 . . . . . . . . . . . . . . . . . . A-4

A-2. ADR and Bubbler Tide Gauge Systems in Operation at the Presidio in the 1970s . A-5

A-3. NGWLMS Installed at the Presidio in the Late 1980s . . . . . . . . . . . . . . . . . . . . . . . A-7

C-1. Monthly Means of MLLW Elevations at Fort Point Corrected for Wharf Sinking 

Between 1855 and 1859 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-4
vi

 LIST OF TABLES

 Page

1. Bench Mark and Leveling History at Fort Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Bench Mark and Leveling History at Sausalito .............................. 4

3. Primary Bench Marks at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4. Tidal Datums and Associated Tidal Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5. Tidal Datums for Fort Point and the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

6. Tidal Datums for Sausalito .............................................. 8

7. Tidal Datum Elevations at Sausalito Adjusted to Reflect Tidal Datum Elevations at 

the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

8 . Tidal Datum Recovery at Sausalito . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

9. Geodetic Relationships to Tidal Datums at the Golden Gate . . . . . . . . . . . . . . . . . . . . 13

10. Relationships Between Tidal Datums (1960-1978 Tidal Epoch), NGVD and 

NAVD at the Presidio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

11. Tidal Datums (1960 - 1978 Tidal Epoch) Related to Special Datums at the Presidio 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

12 Sea Level TrendsComputed for the Golden Gate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

13. Highest Observed Water Levels in 100-Year Periods for the Golden Gate, 

Adjusted for Sea Level Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

14. Return Periods for San Francisco (1920 - 1970) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
vii

Executive Summary

 

This report is a comprehensive summary of the tide data and tidal datums for the

Golden Gate tidal series covering the period from 1854 to 2000. The Golden Gate

tidal series is the longest uninterrupted tidal series in the United States and one of the

longest tidal series in the world. The Golden Gate is the entrance to the San

Francisco Bay Estuary, one of the largest and most important commercial and

industrial estuarine areas in the United States. The Golden Gate tidal series serves

an important reference for tidal studies conducted within the San Francisco Bay

Estuary. 

The primary objective of this report is to document the establishment of the common

datum relationship between the three long data sets at Fort Point, Sausalito and

Presidio locations. Tidal measurements have been recorded in the Golden Gate area

since the mid-1800s at Fort Point (1854-1877), Sausalito (1877-1897) and the

Presidio (1897- Present). Once the datum relationships were established, the data

sets were referenced to one common datum in order to establish the 146 year long

data series for the National Ocean Service tidal program. Tidal analyses were

performed and tidal datums were computed on the basis of long-term data sets

leading to increased reliability of chart datums, and marine boundary determination

with San Francisco as the reference station. Comprehensive studies of sea level

changes and trends relative to land were possible. Long-term extreme high water

levels are an important factor in studies of the influence of storms on the water

levels. Return periods were determined with a higher degree of accuracy. Frequency

and duration of inundation procedures were developed in which the data set at San

Francisco provided ample long-term data. The scientific, engineering and academic

communities have found this information useful to support resolution of many

developmental and environmental issues related to the Golden Gate region. 

* The National Ocean Service was previously named the Survey of the Coast (1807 - 1837), then the Coast Survey (1837

- 1878), followed by the Coast and Geodetic Survey (1878 - 1970). It was called the National Ocean Survey from 1970

until 1982 when it was renamed the National Ocean Service.
viii
1

I. INTRODUCTION

Long tidal series in the Golden Gate area of California have been observed at four different

locations. These include Fort Point (1854-1877), Sausalito (1877-1897) and Presidio (two

locations1897- present). This report describes the procedures used to relate the tidal heights from

the three locations to a common reference zero for the entire time period 1854-present. This has

enabled one continuous time series to be constructed. From this time series, analyses of seasonal

and long term variations in sea level and of the observed extremes in high and low water levels are

possible. Preliminary results of this effort were reported by Smith (1980).

II. HISTORY OF TIDE STATIONS AT THE GOLDEN GATE

A history of tide gauges that have been used at the Golden Gate are described in Appendix A and

locations of the tide stations are shown in Figure 1. San Francisco had the only harbor north of San

Diego in the 1850s which was safe to enter all seasons of the year, therefore it proved essential to

the Coast Survey to have a tide station in this locality. 

A. Fort Point

A self-registering tide gauge was installed at Fort Point on June 30, 1854 at the end of a 500 foot

long wharf projecting out from the Golden Gate southern shore. The tide gauge was located

approximately 2100 feet east of Fort Point. The wharf on which the gauge and staff rested decayed

to the point that it was necessary to abandon the site on November 27,1877. 

B. Sausalito

The Sausalito station was established on February 27, 1877. Operation of the Sausalito tide station

overlapped that of the Fort Point station for about 9 months. The tide gauge and staff were moved

to a new wharf, adjacent to the old location, on October 12, 1881. The wharf at the old location had

decayed to the point it was unsafe to continue tide operations. Data collection at Sausalito was

discontinued on September 1, 1897 because a decision was made by the Coast and Geodetic Survey

to move operations back across the Golden Gate to the Presidio.

C. Presidio

New facilities were established at a tide station at the Presidio on July 15, 1897. This was about one

mile east of the Fort Point fortress. The Presidio and Sausalito stations operated simultaneously for

less than 2 months. On July 26,1927, the tide gauge and staff were moved east of the 1897-1927

location to the Fort Point Coast Guard wharf at Crissy Field, where tide observations continue to be

recorded at this location. 
2

 Figure 1. Location of Golden Gate Tide Stations
3

III. BENCH MARK AND LEVELING HISTORY AT THE GOLDEN GATE

In the early days of the Coast Survey in the 19th century, standard brass disks were not yet in use.

Bench marks were often chiseled marks on concrete abutments or other structures that were believed

to be relatively stable. The result of levels runs between bench marks and tide staffs in place at the

various Golden Gate locations are summarized in Tables 1-3. Leveling techniques are detailed in

Appendix B.

A. Fort Point

On June 30, 1854 a bench mark (BM), designated BM I(2), was established at Fort Point. It was a

cross cut in the face of a large stone at the shore end of the wharf. In 1872 the Coast Survey

established two additional bench marks, designated BM II(3) and BM III(5), to provide a more

stable reference network at Fort Point. The history of the leveling to these bench marks is shown

in Table 1. 

Table 1. Bench Mark and Leveling History at Fort Point

Date of Leveling BM I (2) BM II (3) BM III (5)

Elevations (feet) Related to Zero of Staff in Place

June 30, 1854 14.445

January 2, 1858 16.84

April 2, 1858 14.44*

June 21, 1859 15.22*

May 6, 1872 14.523* 19.685 57.111

May 25, 1872 14.513 19.680 57.063

May 1877 14.495 19.665 57.128

November 28, 1877 19.659

*New Staff

Historic levels show that the wharf and staff settled 2.40 feet between June 30, 1854 and January

2, 1858. A new staff was installed on April 2, 1858 closer to the shore on the same wharf. The 1859

levels indicate a staff settlement of 0.78 feet between April 1858 and June 1859. The wharf and

staff were stabilized in 1859 by repairs to the wharf and the use of rock and stone fill in the area

around the wharf. The water level heights between 1854 and 1859 were corrected to a common

reference to take into account this movement. Appendix C, Figure C-1, shows a plot of the

corrected versus uncorrected data and information on the wharf and staff movement.

 

B. Sausalito

Bench marks were established near the Sausalito tide station in 1877 prior to the water level

crossing of the Golden Gate, including bench mark 2 (copper bolt) and bench mark 3 (granite block).
4

Bench mark 2 is recoverable today and has been virtually undisturbed for over 100 years. Bench

mark elevations and the mean elevation difference from the level results are presented in Table 2.

Table 2. Bench Mark and Leveling History at Sausalito 

Event BM 2

(Copper Bolt)

BM 3

(Granite)

May 25, 1877 (1877 Staff) 12.614 ft. 46.093 ft.

October 12, 1881 (1881 Staff)

(1886-1896 Levels, Mean of

24 level runs) 

12.829 ft. 46.282 ft.

Difference 0.215 ft. 0.189 ft.

Mean Difference 0.202 ft.

C. Presidio

The zero of the fixed staff to which the automatic tide gauge record at the Presidio wharf was

referred was designated as Bench Mark 11. Tidal heights were referred to this tide staff zero from

July 1897 to July 1905. Bench Mark 11 was 14.494 feet (mean of level results between 1897 and

1905) below BM 15 (Granite BM) which was designed as the primary bench mark (PBM) at the

Presidio. The PBM is the principal mark of a group of tidal bench marks to which the tide staff and

tidal datums are referred. New PBM’s are established over time to replace PBM’s that have become

unstable or are destroyed. The other bench marks to replace BM 15 in time as the PBM are shown

in Table 3.

Table 3. Primary Bench Marks at the Presidio

PBM Above 1897 Tide Staff

Zero (Elevation in Feet)

Years as PBM

 15 (1897) 14.49 1897-1912

166 (1912) 17.05 1912-1927

173 (1927) 15.80 1927-1936

180 (1936) 19.01 1936-1995

 

D. Relating the Tide Staff Zeros for the Three Locations to a Common Zero

The level crossing of the Golden Gate between Fort Point and Sausalito in 1877 and the water

crossing of the Golden Gate in 1906-07, after the "Great San Francisco Earthquake of 1906", were

instrumental in relating the water level heights for the three locations to a common datum. The

procedures used in the level crossings are described in Appendix B and the level runs are shown in

Appendix D. The relationships between the zeros of the respective staffs at the three locations are
5

0.20 foot

0.25 foot

0.01 foot

1877 Tide Staff 0

1881 Tide Staff 0

1897 Tide Staff 0

1877 Tide Staff 0

Sausalito

Sausalito

Presidio

Fort Point

0.46 foot

Figure 2. Summary of the relationships of the tide staffs at the Presidio and Sausalito.

summarized as follows:

1. Sausalito 1877 tide staff zero is 0.46 feet higher than the Fort Point 1877 staff zero

2. Sausalito 1877 tide staff zero is 0.20 feet higher than the Sausalito 1881 tide staff zero

3. Sausalito 1881 tide staff zero is 0.25 feet higher than the Presidio 1897 tide staff zero

4. Presidio 1897 tide staff zero is therefore 0.01 feet higher than the Fort Point 1877 tide

staff zero 

 

Figure 2 illustrates the above relationships in a "stick diagram" format.
6
7

IV. TIDAL DATUMS COMPUTED FOR THE GOLDEN GATE

A datum is a base elevation used as a reference from which to reckon heights or depths. It is called

a tidal datum when defined in terms of a certain phase of the tide. The seven tidal datums and

associated tidal parameters routinely computed by NOS are listed in Table 4 (See National Ocean

Service (2000) for definitions).

Table 4. Tidal Datums and Associated Tidal Parameters

Tidal Datums Tidal Parameters

Mean Seal Level (MSL) Diurnal High Water Inequality (DHQ)

Mean Tide Level (MTL) Diurnal Low Water Inequality (DLQ)

Diurnal Tide Level (DTL) Mean Range of Tide (Mn)

Mean Higher High Water (MHHW) Diurnal Mean Range of Tide (Gt)

Mean High Water (MHW)

Mean Low Water (MLW)

Mean Lower Low Water (MLLW)

By the middle of the 20th century NOS adopted the concept of a National Tidal Datum Epoch

(NTDE). A tidal epoch is a specific 19-year period accepted as the official time segment over which

tide observations are taken and averaged to obtain mean values for tidal datums (Marmer, 1951).

Establishment of an epoch was necessary to take into account the slowly varying changes in the tides

due to the 18.6 year variation in the path of the moon called the regression of the moon’s nodes. A

tidal epoch is sometimes referred to as the Metonic cycle, which is defined as the period in which

the new and full moon would recur on the same day of the year. Changes over time in the specific

official 19-year period adopted are necessary because of observed periodic and apparent secular

trends in sea level. The 19-year period is also used to "smooth out" the long-period meteorological,

hydrologic, and oceanographic fluctuations. NOS has adopted the 1924-1942 (in 1953), 1941-1959

( in 1964) and 1960-1978 (in 1980) tidal epochs. Sea level changes are monitored and

approximately every 25 years NOS determines whether sea level has changed at a sufficient number

of its National Water Level Observation Network (NWLON) stations (long term continuously

operating tide stations) in the United States coastal areas to warrant an update to a more recent tidal

epoch. A new epoch update is presently underway in NOS.

A. Fort Point/Presidio

All the tidal datums for Fort Point and Presidio are referred to the station datum (the 1897 tide staff

zero at Presidio) as shown in Table 5.
8

Table 5. Tidal Datums and Tidal Parameters for Fort Point and Presidio

Tidal Datums

Elevation (Feet) above 1897

Tide Staff Zero at Presidio

 Fort

 Point

Presidio

Tidal Epoch

Datum 1855

-1873

1898

-1916

1924

-1942

1941

-1959

1960

-1978

1980

-1998

MHHW 10.97 11.15 11.31 11.46 11.60 11.12

MHW 10.40 10.57 10.72 10.86 11.00 11.22

MTL 8.50 8.60 8.73 8.86 8.95 9.17

MSL 8.44 8.54 8.67 8.80 8.90 9.11

MLW 6.62 6.64 6.74 6.87 6.90 7.13

MLLW 5.43 5.49 5.61 5.75 5.77 6.00

Tidal Parameters

Mn 3.78 3.93 3.98 3.99 4.10 4.09

DHQ 0.57 0.58 0.59 0.60 0.60 0.61

DLQ 1.19 1.15 1.13 1.12 1.13 1.13

Gt 5.54 5.66 5.70 5.75 5.83 5.83

B. Sausalito

Tidal datums (1878 - 1896), referred to the station datum (the 1881 tide staff zero) at Sausalito, are

summarized in Table 6.

Table 6. Tidal Datums and Tidal Parameters for Sausalito 

Tidal Datum 

(1878-1896)

Elevation 

(Feet)

Tidal

 Parameters

Elevation

(feet)

MHHW 10.79

MHW 10.22 Mn 3.57

MTL 8.43 DHQ 0.57

MSL 8.39 DLQ 1.13

MLW 6.65 Gt 5.27

MLLW 5.52
9

Range of tide (1878-96) for Sausalito 3.57

Range (Mn) Ratio 0.94

V. ADJUSTMENTS TO SAUSALITO 1877 - 1897 TIDE HEIGHTS

The difference in the mean level of the sea surface across the Golden Gate between San Francisco

and Sausalito was thought to be small enough that adjustments were not made to the MSL elevations

at Sausalito when the datum elevations were transferred to the Presidio. The concept of a minimal

sea surface slope across the Golden Gate between Fort Point and Sausalito was supported by the

computed difference of MSL (1960 - 1978) - NGVD of 0.02 feet between the two locations. 

The mean range of tide at Sausalito had an average range ratio (mean range of tide at Sausalito

divided by the mean range of tide at Fort Point) of 0.94, therefore adjustments to the mean range of

tide at Sausalito were needed. The range ratio was computed from an average of the ranges from

the results of simultaneous comparisons between Fort Point and Sausalito. The mean high water and

mean low water datum elevations also needed adjustments. The diurnal high water (DHQ = MHHW

- MHW) and diurnal low water (DLQ = MLW - MLLW) inequalities were not required to be

adjusted in the transfer. The following procedures were used to make adjustments to the tidal

datum elevations for Sausalito to obtain values for these parameters for Fort Point/Presidio:

 1.

 = = 3.80 Ft 

 

2. MTL and MSL are computed by transferring values to the 1897 tide staff at the Presidio.

 Station datum at Sausalito is defined as the 1881 tide staff zero which 0.25 foot above the

Presidio station datum (1897 tide staff zero).

MTL + 0.25 = 8.43 + 0.25 = 8.68 Ft

 MSL + 0.25 = 8.39 + 0.25 = 8.64 Ft

3. MLW = MTL - 1/2 Mn = 8.68 - 1/2(3.80) = 6.78 Ft

4. MHW = MLW + Mn = 6.78 + 3.80 = 10.58 Ft

5. MHHW = MHW + DHQ = 10.58 + 0.57 = 11.15 Ft

6. MLLW = MLW - DLQ = 6.78 - 1.13 = 5.65 Ft

All these adjusted values have been combined to reflect the tidal datum elevations reduced to mean

values (1878 -1896) at Presidio, referred to the 1897 tide staff zero (Table 7).
10

Figure 3. Tidal Datum Elevations at the Golden Gate For 7 Different 

Tidal Epochs Between 1855 and 1896

4

5

6

7

8

9

10

11

12

13

MHHW

Elevation in Feet Above Station Datum

MHW

MTL

MSL

MLW

MLLW

1855 - 1873 1878 - 1896 1898 -1916 1924 - 1942 1941 - 1959 1960 - 1978 1980 - 1998

Table 7. Tidal Datum Elevations at Sausalito Adjusted to Reflect Datum Elevations at Presidio

Tidal Datum Elevation (Ft)

Tidal Datums (ft) Tidal Parameters (ft)

MHHW 11.15 Mn 3.80

MHW 10.58 DHQ 0.57

MTL 8.68 DLQ 1.13

MSL 8.64 Gt 5.50

MLW 6.78

MLLW 5.65

The tidal datums, reduced to mean values for the 7 tidal epochs previous discussed (Table 5 and

Table 7) are summarized in Figure 3.
11

VI. DATUM RECOVERY AT SAUSALITO

A datum recovery is made at a tide station to determine how accurate the datum computed from one

data set compares with the datum computed from a different period of time. It also assesses how

accurate the datum at a location can be transferred from one period in time to another. The

difference may also give an indication of how much the datum has changed over time due to manmade/or natural causes. If the recovery of the datum over time between different hydrographic

surveys in the area are possible, then a history of the changes in sounding datum between

hydrographic surveys can be determined which may provide information on bathymetric or other

changes in the area.

Tidal datum recovery at Sausalito has been computed over a 100 year period with the use of the tidal

series 1878 - 1896 and 1977 - 1979. Bench mark 2 1877 is a common bench mark to both tidal series

in the analysis. The preliminary steps in the datum recovery are shown in Table 8.

Table 8. Tidal Datum Recovery at Sausalito

MTL

(on staff 0)

BM 2

Elevation

MTL 

( on 1881

Staff 0)

Series 

8.43 ft. 12.83 ft. 8.43 ft. First reduction 1878-1896 

5.99 ft. 10.11 ft. 8.71 ft. 24 months 1977-1979 datums

reduced to mean value to 1960-1978

tidal epoch 

The information in Table 8 is used to determine the datum recovery at Sausalito using the following

steps: 

a. The difference in the elevation of the common bench mark on the respective staffs for the

two series is computed. From Table 8, the difference is 12.83 - 10.11 = 2.72 feet.

b. To refer the MTL elevation on the 1977 tide staff to the 1881 tide staff zero , 2.72 feet is

added to 5.99 so that the corrected MTL (1878 - 1896) = 8.71 feet.

c. The datum recovery must take into account the change in relative mean sea level over time.

This is estimated from Table5. The difference in mean sea level at the Presidio between the

1898-1916 and 1960-78 tidal epochs is 8.90-8.54 = 0.36 feet or a rate 0.0058 ft./yr

(0.36ft./62 years).

d. The MTL of 8.43 feet in Table 8 needs to be adjusted as follows to reflect the sea level

change between epochs 1878-1896 and 1960-78 (82 years). This difference is 0.48 ft.

(0.0058 x 82 years).

MTL (1878-1896) of 8.43 + 0.48 = 8.91 feet. (Corrected to MTL (1960-78)

e. The computed datum recovery for MTL is therefore 8.91 - 8.71 = 0.20 feet.
12

This datum recovery 0.20 foot is quite good given that the two tidal series are separated by such a

long period of time. This indicates is that there has probably been little movement of BM 2 at

Sausalito and the comparison of the results of 19 year datums at Sausalito from 1878 - 1896 compare

well with those based on 1977 - 1979 Sausalito data, reduced to mean values (1960 - 1978) through

a simultaneous comparison with the Presidio.

There are difficulties in obtaining a precise datum recovery (0.10 foot or better) at tide stations when

a station is re-occupied again years later. The factors that affect the datum recovery include:

common bench mark(s) available for both series, the bench marks may have been destroyed, settled

or disturbed; and the quality of the tide data for one of the tidal series at the location may be

questionable. The tidal datums for both series should be reduced to mean values (same tidal epoch)

through simultaneous comparison with the same reference station in computing the tidal datums. 
13

VII. GEODETIC RELATIONSHIPS TO TIDAL DATUMS AT THE GOLDEN GATE

The tidal datum of MSL has frequently been incorrectly referred to as a geodetic datum. MSL is a

tidal datum determined over a 19-year National Tidal Datum Epoch. It pertains to local mean sea

level and should not be confused with the fixed datums of North American Vertical Datum of 1988

(NAVD 88) or National Geodetic Vertical Datum of 1929 (NGVD 29). NGVD 29 and NAVD 88

are fixed geodetic datums whose elevation relationships to local MSL and other tidal datums are not

expected to be consistent from one location to another.

A. National Geodetic Vertical Datum

NGVD 29 is a fixed datum that was adopted as a national standard geodetic reference for heights

but is now considered superseded. NGVD 29 is sometimes referred to as Sea Level Datum of 1929

or as Mean Sea Level on some early issues of Geological Survey Topographic Quads. NGVD 29

was originally derived from a general adjustment of the first-order leveling networks of the U.S. and

Canada after holding mean sea level observed at 26 long term tide stations as fixed. Numerous local

and wide-spread adjustments have been made since establishment in1929. Bench mark elevations

relative to NGVD 29 are available from the National Geodetic Survey (NGS) data base via the

World Wide Web at http://www.ngs.noaa.gov/.

The relationships between NGVD and the local tidal datums for the Golden Gate tidal series for the

three different adopted tidal epochs by NOS are listed in Table 9.

Table 9. Geodetic Relationships to Tidal Datums at the Golden Gate

Tidal Epoch (Elevation in Feet)

Relationship 1924 - 1942 1941 - 1959 1960 - 1978

MHHW- NGVD 2.71 2.85 2.99

MHW - NGVD 2.12 2.25 2.39

MTL - NGVD 0.12 0.25 0.34

MSL - NGVD 0.06 0.19 0.29

MLW - NGVD -1.87 -1.74 -1.71

MLLW - NGVD -3.00 -2.86 -2.84

 

B. North American Vertical Datum (NAVD 88)

NAVD 88 is a fixed datum derived from a simultaneous, least squares, minimum constraint

adjustment of Canadian/Mexican/United States leveling observations. Local mean sea level

observed at Father Point/Rimouski, Canada was held fixed as the single initial constraint. NAVD

88 replaces NGVD 29 as the national standard geodetic reference for heights. Bench mark

elevations relative to NAVD 88 are available from NGS through the World Wide Web at

http://www.ngs.noaa.gov/. Explanations of the datum update can be found at this web site.
14

Table 10 shows how NAVD 88 derived heights compare to NGVD 29 computed heights in an

example using San Francisco where the difference between NGVD 29 and NAVD 88 is 2.72 feet.

 

Table 10. Relationships to Tidal Datum(1960-1978 Tidal Epoch) 

NGVD and NAVD at the Presidio 

 Datum 

 

MHHW MHW MTL MSL NGVD MLW NAVD MLLW 

Elevation

(Ft) 

5.83 5.23 3.18 3.13 2.84 1.13 0.12 0.00
15

VIII. SPECIAL DATUMS

There are several local vertical datums adopted historically at San Francisco that appear on

engineering drawings and other documents. For instance, the U.S. Army Corps of Engineers, state,

county and local jurisdictions sometimes adopted a local datum as a reference to relate to elevations

of structures in the locality. Local datums for San Francisco are listed below with a background on

how the values were generated. Table 11 provides a tabular summary of the datum relationships.

 

1. San Francisco lower low water datum or Standard Lower Low Water. 

This elevation is based on miscellaneous tide observations recorded before 1907 as adopted by the

U.S. Army Corps of Engineers. It has a value of 5.55 feet above the 1897 tide staff zero at Presidio.

 

2. Standard Mean Sea Level at San Francisco

 

Because of the continual variations in sea level recorded at the Presidio, the mean sea level elevation

changed as additional sea level measurements were incorporated into the accepted value of mean

sea level. It was cumbersome for scientists and engineers to frequently update datums prior use of

computers, therefore it was decided to adopted a "standard mean sea level datum" at Presidio of

8.52 feet referred to the 1897 tide staff zero. This datum elevation was determined from the mean

of the hourly heights at observed at Presidio over the continuous period from 1898 to 1913. This

datum was held fixed and was not updated.

3. Several other tidal datums have been computed and used historically by other countries, but are

not used by NOS.

a. Mean High Water Spring (MHWS)

b. Mean Low Water Spring (MLWS)

c. Mean High Water Neap (MHWN)

d. Mean Low Water Neap (MLWN)

Two ways that these tidal datums may be computed are: 

a. Mean of the high or low waters around the time of spring tide or neap tide each month over

a specific 19-year period. There are 4 high waters and 4 low waters used each month for both

the spring tide and the neap tide. Spring tide occurs around the time of new and full moon

and neap tide occurs around the time of the first and third quadrature of the moon each

month. 

It is sometimes subjective which days and tides to select.

b. The approach that can be used to compute approximate values for these tidal datums

involves calculations using amplitudes of selected harmonic constituents from harmonic

analysis for the location. The following is an example using the tidal parameters at Presidio

for the 1960 -1978 tidal epoch and a 365 day harmonic analysis for 1994.
16

The harmonic analyses results provide ratios of the mean ranges of tide: 

1. Sg/Mn = Spring Range of Tide/Mean Range of tide = 1.182

2. Np/Mn = Neap Range of Tide/Mean Range of tide = 0.792

From the accepted datums for the Presidio:

3. Mn = 4.10 ft. and MTL = 8.95ft. (1960-78 tidal epoch) 

Thus:

4. Sg = 4.10 x 1.182 = 4.84 ft.

5. Np= 4.10 x 0.792 = 3.25 ft.

6. MHWS = MTL+1/2 Sg = 11.37 ft.

7. MHWN= MTL+1/2 Np = 10.58 ft.

8. MLWS = MTL-1/2/ Sg = 7.32 ft.

9. MLWN = MTL-1/2 Np = 6.53 ft.

Table 11. Presidio Tidal Datums (1960-1978 Tidal Epoch) Related to Special Datums 

Tidal Datum Elevation (Ft) Above 1897 Tide Staff Zero

MHHW 11.60

MHWS 11.37

MHW 11.00

MHWN 10.58

MTL 8.95

MSL 8.90

STD MSL 8.52

MLWN 7.32

MLW 6.90

MLWS 6.53

MLLW 5.77

STD LLW 5.55
17

IX. VARIATIONS IN MEAN SEA LEVEL AT THE GOLDEN GATE

The previous sections of this report describe how the tidal observations at the Golden Gate have

been referenced to a common datum, the 1897 tide staff zero at the Presidio, resulting in a 146-year

continuous record of MSL as well as other tidal datums and tidal parameters. MSL is frequently

thought of as an equipotential surface, however it is known that MSL at any given location will

deviate from that surface due to the effects of wind, barometric pressure, circulation patterns, and

river flow. For tidal work, MSL is computed by averaging all hourly water level over specific time

periods. NOS routinely computes monthly MSL, annual MSL, and the accepted tidal datum of

MSL. The accepted datum of MSL is computed using 19-years of data over the accepted National

Tidal Datum Epoch period. The long sea level series at the Golden Gate may provide important

clues to climate and global change investigations. Sea level records are the longest and highest

quality records of any oceanographic parameter and the primary evidence suggesting apparent rise

in sea level comes from records of tide gauges such as San Francisco. In addition to reflecting

changes in sea level, measurements of water level at a tide gauge may reflect changes due to the land

movement in the region where the tide gauge is located. The following sections present analyses

of the variations in mean sea level for the Golden Gate over various time scales. Previous

examination of water level variations along the California coast was carried out by Smith and Leffler

(1980).

A. Seasonal Variations in Sea Level

The seasonal variations in sea level over the months of the year differ from year to year due to

meteorological and oceanographic influences. Generally sea level is lowest in the spring months

and highest in the winter months at the Golden Gate. Seasonal MSL variations are shown in Figure

4 for the four different years separated by 40 years between 1860 and 1980 at the Golden Gate.

Figure 4. Seasonal Variations in Sea Level for Select Years in the Golden Gate Tidal Series

7

7.5

8

8.5

9

9.5

10

Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec

1980

1940

1900

1860

Elevations in Feet Above Station Datum

Month

. 

Figure 4. Seasonal Variations in Sea Level for Select Years in the Golden Gate tidal Series.
18

Figure 5A. Seasonal Variations in Sea Level During Several El Nino Events 

Between 1939 and 1983

8

8.5

9

9.5

10

10.5

Mar

May

Jul

Sept

Nov

Jan

Mar

May

Jul

Sept

Nov

Jan

Mar

May

Jul

Sept

Nov

1981 - 1983________

1939 - 1941

Elevation in Feet Above Station Datum

Month

1956 - 1958______

Figure 5A. Seasonal Variations in Sea Level During Several El Nini Events 

Between 1939 and 1983

B. Interannual to Decadal Variations in Sea Level

El Nino events occur in the Pacific Ocean approximately every 3 to 7 years, and cause much higher

than expected water levels at locations in the eastern Pacific Ocean. Each event has a life time of

at least 15 months. Elevated water levels have been recorded at the Golden Gate during these event

years. The most severe El Nino events in the 20th century occurred in the time periods 1939 - 1941,

1956 - 1958, 1981 - 1983 and 1991 - 1993. The monthly sea level variations for these years are

shown in Figures 5a and b. Duncan et al (1998) provide detailed descriptions at the data for west

coast stations for the 1997-1998 El Nino.

Interannual sea level variations play an important role in understanding climate phenomena such as

the El Nino South Oscillation. These events reflect climatic interaction between the ocean and the

atmosphere. The long term sea level records such as those at the Golden Gate, provide not only data

for the study of sea level rise, but since climatic events such as El Nino vary in size and global

influence from decade to decade, these data sets provide the baseline from which to measure future

events. 

.
19

 Figure 5B. Variations in monthly MSL during several El Nino events between 1990 and 1999 

C. Long-term Variations in Annual Mean Sea Level

The annual means of sea level for the Golden Gate tidal series are available for each year from 1855

through 1998 (Figure 6). The notable upward spikes in the curve have been identified as years when

El Nino events were in progress in the Pacific Ocean. El Nino is the name given to a general

warming of the surface waters of the tropical Pacific Ocean that happens at irregular interval of

years. It is a meteorological and oceanographic phenomenon. It is characterized by warmer surface

water temperatures and higher water levels in the Eastern tropical Pacific Ocean with a lowering of

the surface water temperatures and water levels in the Western Pacific. More is discussed later with

seasonal-to-interannual-to-decadal variations in sea level. The notable downward spikes have not

been addressed but may be associated with years of near drought conditions in the region. The

annual mean sea level curve shows a rise in sea level relative to land. The amount of rise relative

to land over the 140 years, is estimated to be at least 0.7 feet.

The sea level data have been filtered further to eliminate annual variations in the record with a 19-

year moving average starting with 1855-1873 and ending with 1976-1998. Each 19-year value has

been plotted at the mid-year of the 19-year period in Figure 6. The moving average curve provides

a better visual sense of the long term variations than just the annual means themselves because of

their high degree of variability.
20

Figure 6. Annual Mean Sea Level, 19 Year Moving Avererge Sea Level

 and Sea Level Trend for the Golden Gate

8

8.2

8.4

8.6

8.8

9

9.2

9.4

9.6

9.8

Elevation in Feet above Station datum

Annual MSL

Sea Level Trend

19 Year Moving Average of Sea Level

_____

__________

 

1855 1999

__________________________________________________________________________________ Sausalito Presidio

1877 1897

Fort Point l l

Figure 6. Annual Mean Sea Level, 19 Year Moving Average Sea Level and Sea Level Trend 

for the Golden Gate

E. Sea Level Trend

Computation of the sea level trend utilizes the regression analysis of a straight line fit. The sea level

trend has been computed for 7 different tidal epochs (19 years) between 1855 and 1998 and the

entire series, 1855 - 1998. The results are shown in Table 12. The sea level trend over the period

1855 - 1994 appears in Figure 6. Sea level trends for the national network have been compiled by

Zervas (2001).

Table 12. Sea Level Trends Computed For the Golden Gate 

Period of Record Sea Level Trend (Feet/year)

1855-1873 +0.006

1875-1893 -0.004

1895-1913 -0.002

1915-1933 +0.002

1935-1953 +0.004

1955-1973 +0.008

1976-1998 +0.011

1855-1998 +0.005
21

The rates of relative sea level rise is not uniform as the data clearly do not follow a straight line fit.

There is, in fact, a downward trend between 1875 and 1913 at the Golden Gate which the annual sea

level curve (Figure 6) indicates. This long period variation in the historical record also appears in

other comparable long term sea level records around the world.
22
23

Figure 7. Observed Annual Highest Water Level at Golden Gate Between 1855 and 1999

X. EXTREME HIGH AND LOW WATER LEVELS AT THE GOLDEN GATE

Tabulations and summaries of observed highest water levels values at the Golden Gate are important

products for NOAA, USGS, USACE, FEMA, EPA and state and local agencies because of the

concern for impacts of coastal flooding the Bay area. Extreme low water levels have not received

as much attention as the highest water levels in the Bay area, but these data are important as they

relate to drought periods and salt water intrusion into the fresh water areas of the San Francisco Bay

Estuary. 

The California Department of Water Resources and U.S. Bureau of Reclamation(CADWR, 1970)

summarizes the seasonal weather patterns in the bay region that partially drive the variations of the

water levels. It is generally dry in summer due to the migrating high pressure systems that deflect

storm patterns to the north. In the winter, the high pressures decrease in intensity and move

southward and the intrusion of moisture-laden air is no longer blocked. The winter will frequently

arrive as a series of storms that move in from the southeast and provide gale winds, heavy rains and

large changes in atmospheric pressure. 

 

A. Observed Highest Water Levels 

Extreme high water levels result from the combined influence of meteorological and astronomical

phenomena. Meteorological phenomena include local barometric pressure and winds, as well as

large scale disturbances such as El Nino episodes affecting the San Francisco Bay region. Figure 7

shows the observed annual highest observed water levels between 1855 and 1999. The highest

observed water level at the Golden Gate occurred on January 27, 1983 and December 3, 1983

(Figures 8A and 8B). The January 27, 1983 storm was wide spread over the West Coast while the

December 3, 1983 storm was highly localized in the San Francisco Bay area.
24

Figure 8A. Observed Highest Water, Predicted and Storm Surge January 27, 1983 

at the Presidio

Figure 8B. Observed Highest Water Level, Predicted and Storm Surge for December 3, 1983

at the Presidio
25

Figure 9. Observed Annual Lowest Water Levels at the Golden Gate

Between 1860 and 1999

The annual highest water levels for the Golden Gate have elevations between 6.7 and 8.9 feet above

MLLW (1960 -1978). The storm surge associated with particular high water levels is of interest.

For this report storm surge is defined as the difference between the observed and predicted water

levels, both referenced to MLLW. For example, the storm surge for the January 27, 1983 storm

event (observed - predicted) is just over 2.0 feet, and for the December 3, 1983 it is over 3.0 feet.

The highest water level does necessarily imply the greatest storm surge value because the highest

water level is the combination of storm surge with the astronomical tide. 

B. Observed Lowest Water Levels 

Extreme low water levels in the San Francisco Bay region are caused primarily by the combination

of extreme tides to due particular earth-moon-sun alignments and the effects of large scale weather

patterns. The lowest water level of record at the Golden Gate occurred on both December 26, 1932

and December 17, 1933. The time series of the hourly heights for both events are shown in Figures

10A and 10B. There are small differences of tenths of a foot in the annual lowest water levels from

year to year with the range of annual lowest water levels being between 2.7 below to 1.0 feet below

MLLW (1960-78). A value of 5.77 feet can be subtracted from the values of the annual lowest water

levels shown in Figure 9 to refer the elevations to MLLW (1960 - 1978). 
26

Figure 10A. Observed Lowest Water Level, Predicted and Storm Surge for 

December 17, 1933 at the Presidio

Figure 10B. Observed Lowest Water Level, Predicted and Storm Surge for December 26,

1932 at the Presidio
27

C. One Hundred Year Flood Level 

The observed annual highest water levels of record between 1854 and 1994 at the Golden Gate have

been tabulated and summarized . These observed values are not adjusted for the sea level change

over the 140 year period and a separate analysis must be performed in order to use the information

for some applications. Table 13 is a summarization of 100 year increments with the highest

observed water level of record in that period identified.

Table 13. Highest Observed Water level in 100-Year Periods for the Golden Gate

100 Year

Period

Date of Highest

Water Level in 100

Year-Period

Highest 

Observed

(Feet)

1855-1954 December 20, 1940 13.8

1865-1964 December 20, 1940 13.8

1875-1974 January 16, 1973

January 18, 1973

14.1

14.1

1885-1984 January 27, 1983 

December 3, 1983

14.6

14.6

1895-1994 January 27, 1983

December 3, 1983

14.6 

14.6 

D. The Great January 1862 Floods

A good example of wide spread extreme flooding in the San Francisco Bay Estuary occurred in

January 1862. Rains were heavy between November 1861 and January 1862 in the Delta region of

Estuary such that Sacramento was under water along with most of the Central Valley. Reports from

journals of the time state that for at least ten days "water flowed through the Golden Gate in a steady

torrent, blocking tide reversal." Such a flood today would probably cause billions of dollars in

damage in the region. The Golden Gate tide records between November 1861 and January 1862

have been reviewed for what influence such floods had on the water levels at that location. The rains

were heaviest during January 1862. Figure 11 shows that water levels at the Golden Gate between

January 22nd and 24th were influenced by the events. The observed low waters between January

22 and 24, 1862 were higher than normal (the predicted low waters). From the January 23 evening

high water to the evening low water there was only a 0.3 foot change in the water level at the Golden

Gate. Such occurrences are anomalous at the Golden Gate.
28

Figure 11. Observed, Predicted and Storm Surge for January 22 - 24, 1862 at Fort Point

-2

-1

0

1

2

3

4

5

6

7

Observed

Predicted

Observed - Predicted 22-Jan 23-Jan 24-Jan

(Storm Surge)

Elevation in Feet Above MLLW (1855 - 1873)

Return Period

Earle (1979) defines return periods time intervals between the occurrence of extreme water levels.

The return period, or recurrence interval, for a given elevation is the time interval between

occurrences of an elevation greater than or equal to the given elevation. Heights of and intervals

between storm surges, which add to the astronomical tide, occur in a random manner so that return

periods are useful for extreme measured water elevations greater than normally occurring

astronomical tides. The values can be obtained from a statistical analysis of extreme measured

elevations greater than normally occurring astronomical tides. 

Return period results are useful for design elevations for sea walls, levees and other structures along

coastal and waterways where extreme high water levels frequent such shores. Universities, coastal

engineer firms, U.S. Corps of Engineers and the Federal Emergency Management Administration

(FEMA) are among those that have a need for such information where flooding is a concern.

Table 14 provides return periods for San Francisco from a 50 year period between 1920 and 1970

where there is a long history of extreme high water levels and concerns of flooding in the San

Francisco Bay region. The 100 year estimate is lower than the maximum observed value (8.8 ft.)

since the 1920– 1970 time period of the analysis.

 
29

Table 14. Return Periods for San Francisco (1920-1970)*

(50 Years of Record with Least Square Correlation Coefficient of 0.984)

Return Periods

(Years)

Elevation

Above MLLW

Feet

Upper 90%

Confidence

Limits

Elevation

Above

MHHW

Feet

5 

10 

25 

50 

100 

7.8

8.0

8.1

8.3

8.4

7.9

8.1

8.3

8.4

8.6

2.0

2.2

2.3

2.5

2.6

* The values were computed by from tabulated monthly highest water level elevations at

San Francisco over the period 1920 - 1970 for select return periods using NOS tide data

(Earle 1979).
30
31

Figure 12A. Frequency of Inundation for High Waters at the Presidio

 Between 1922 and 1984

0

20

40

60

80

100

120

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.6

CUMULATIVE FREQUENCY(%)

Elevation in Feet Above Station Datum

XI. FREQUENCY AND DURATION OF INUNDATION 

Frequency and duration of inundation is a statistical analysis of historic records of water level

values. The hourly heights are selected around the period of high water or low water as input to the

analysis. The analysis includes the following:

 

1. Elevations above the station datum in feet at specified increments (e.g. tenths of a foot) over

the range of water levels at a station.

2. Frequency of inundation is the number of times the water level has equaled of exceeded

each incremental elevation for a period of the analysis.

3. Percent frequency of inundation is the number of inundations in step 2 above expressed as

a percentage of the total number of inundations occurring in the period of the analysis.

4. Duration of inundation is the total hours at which the water level remained at or exceeded

each incremental height for the period of the analysis.

5. Percent duration of inundation is the number of hours in step 4 expressed as a percentage

of the total number of hours in the period of the analysis.

Figures 12A-12D includes plots of the cumulative duration vs. incremental heights and cumulative

frequency (%) vs. incremental heights for both the high waters and low waters. The San Francisco

data set for the years 1922-1984 have been used in the statistical analysis. The results of such a

study are utilized frequently in engineering design of structures to control flooding in an area or

biological studies related to frequency and duration of water levels at various heights to growth of

particular species in tidal marsh areas.

12A. Frequency of Inundation for High Waters at the Presidio 

Between 1922 and 1984
32

Figure 12B Duration of Inundation for High Water at the Presidio 

Between 1922 and 1984

0

10

20

30

40

50

60

9 9.5 10 10.5 11 11.5 12.5 13 13.5 14.5

CUMULATIVE DURATION (%)

Elevation in Feet Above Station Datum 

12 14.0

Figure 12B. Duration of Inundation for High Water at the Presidio

Between 1922 and 1984

Figure 12C Frequency of Inundation for Low Waters at the Presidio

 Between 1922 and 1984

0

10

20

30

40

50

60

2 2.4 2.9 3.4 3.9 4.4 4.9 5.4 5.9 6.4 6.9

Cumulative Frequency(%)

Elevation in Feet Above Station Datum

Figure 12C. Frequency of Inundation for low Waters at the Presidio

Between 1922 and 1984
33

Figure 12D. Duration of Inundation for Low Waters at the Presidio

 Between 1922 and 1984

0

2

4

6

8

10

12

14

16

18

Accumulative Duration (%)

2 2.4 2.9 3.4 3.9 4.4 4.9 5.4 5.9 6.4 6.9

Elevation in Feet Above Station 

Datum

Figure 12D. Duration of Inundation for low Waters at the Presidio

Between 1922 and 1984
34
35

Figure 13A. Frequency Distribution of Differences for High Water Heights at the Presidio

XII. COMPARISON OF OBSERVED AND PREDICTED HIGH AND LOW WATERS

NOS tide predictions are based on the pre-knowledge of the motions of the earth-moon-sun system.

Differences between predicted and observed tides are typically due to the effects of weather on the

observed water levels. Table 8 of the NOS Tide Tables for the West Coast provides summary

statistics of the accuracy of tide predictions for several west coast stations. For San Francisco, for

instance, at the 90% distribution level, the times of the predicted high and low waters are within 0.3

hours and 0.4 hours respectively. The heights of the predicted high and low waters are within 0.4

foot and 0.6 foot respectively. Although there are variations in these observed - predicted

differences occurring from year to year, a year of observed and predicted high waters and low waters

has been chosen using the year 1981 at San Francisco to further analyze these differences. A

frequency distribution of differences between observed and predicted water level heights, referred

to MLLW, have been generated from the 1981 data set and the results are presented in Figures 13A

and 13B. 
36

Figure 13B. Frequency Distribution of Differences for Low Water Heights at the Presidio
37

XIII. CONCLUDING REMARKS FOR THE GOLDEN GATE TIDAL SERIES

With the connection of the three historical data sets at Fort Point, Sausalito and Presidio to one long

continuous tidal series it has been possible to tap a wealth of information previously unavailable.

Sea level variations over a long continuous data set referred to a common datum for 140 period at

one location can now be studied. Tidal datums have been reduced to mean values for any number

of tidal epochs between 1855-1873 and 1976-1994. Datum recovery at Sausalito was completed,

providing important assessment for one of the Golden Gate tide stations from two different tidal

series separated by 100 years. Relative sea level rise determinations and land movements are now

accurately measured through the long series at the Golden Gate. 

ACKNOWLEDGMENTS

The tide data sets in this report represent the cumulative effort of the National Ocean Service; those

who installed and maintained the tide gauges for recording tide measurements and those who

analyzed the data, documented the results and summarized them in an accessible manner. Special

recognition should to go to those who have made the long tidal series and related historical tide

information possible for the Golden Gate tidal series over the many decades since 1854. I thank the

members of the CO-OPS review committee for their patience, outstanding effort in the edits and

recommendations they have made in this detailed report to help improve the appearance of this

report and maintain the high standards of National Ocean Service publications. 
38
39

REFERENCES

Brick, William and Mathison, Alan, San Francisco Bay Tidal Stage vs. Frequency Study, U.S. Army

Corps of Engineers, San Francisco District, San Francisco, California 1984

CADWR, 1970. Sacramento-San Joaquin River Low Tides in April-May 1970, California

Department of Water resources and U..S. Bureau of Reclamation Report, May 1970.

Conomos, T.S., Editor, San Francisco Bay The Urbanized Estuary, Pacific Division American

Association for the Advancement of Science, San Francisco, California 1979

Duncan,S., S.K. Gill, and K.A. Tronvig, 1998. Proceedings of the Ocean Community Conference

“98, The Marine Technology Society Annual Conference, Baltimore, MD, November 1998.

Earle, Marshall D., Storm Surge Conditions for the California Coast and Continental Shelf, Marine

Environments Corporation, Rockville, Maryland, 1979

Marmer, H.A., 1951. Tidal Datum Planes, Special Publication 135, GPO, Washington D.C. 1951

National Geodetic Survey, 1996. The New Adjustment of the North American Vertical Datum. A

Collection of papers Describing the Planning and Implementation of the Adjustment of the North

American Vertical Datum of 1988, Compiled by the Spatial Reference System Division, National

Geodetic Survey, November 1996 at www.ngs.noaa.gov.

National Ocean Service, 2000. Tide and Current Glossary, NOAA, National Ocean Service, Silver

Spring, MD, January 2000.

Smith, R. A., 1980. Golden Gate Tidal Measurements 1854-1978, Journal of the Waterways Port

Coast and Ocean Division, American Society of Civil Engineers, Vol 106 NO WW3, August 1980

Smith, R. A. and R.J. Leffler 1980. Water Level Variations for the California Coast, Journal of the

Waterways Port Coastal and Ocean Division, American Society of Civil Engineers, Vol 106 NO

WW# August 1980.

U.S. Coast and Geodetic Survey, Superintendent Reports of the Survey to Congress 1844-1927

Washington, D.C.

Zervas, C. 2001. Sea Level Variations of the United States 1854-1999, NOAA Technical Report

NOS CO-OPS 36, NOAA/NOAS/Center for Operational Oceanographic Products and Services,

Silver Spring, MD, July 20.
40
A-1

APPENDIX A

HISTORY OF TIDE GAUGES
A-2

Many types of tide gauges were proposed and constructed in the 19th century. The first selfregistering tide gauge was used in 1831 by Henry Palmer of England. The earliest tide gauges in use

are described below:

A. Parts of a Tide Gauge

The essential parts of a tide gauge are composed of a stilling well to dampen wave action; a time

piece and some way of recording the height, either in a continuous manner or at discrete intervals

of time.

B. Workings of a Tide Gauge

The motion of the float as it rises and falls with the tide is communicated along the recording portion

of the gauge by means of a flexible cord which passes over a grooved wheel (float wheel). The

motion is transferred, but on a reduced scale, through some mechanism depending upon the

particular kind of gauge, to a pencil which traces a curve upon a moving sheet of paper. The paper

is driven or carried along by means of a cylinder connected with a well-regulated clock. The pencil

is free to move in a direction perpendicular to the line of the motion of the paper.

C. First Coast Survey Tide Gauge 

Joseph Saxton, of the Office of United States Weights and Measures, constructed the first selfregistering tide gauge in the United States used by the Coast Survey. There were two principal

movements provided for in Saxton's gauge. The first being a uniform movement, proportional to

time, of the record sheet under the pencil, and the second being a transverse movement of the pencil,

strictly proportional to its rise and fall of the float. To give a uniform motion to the sheet of paper,

a clock-work was used. The moving parts of the old-fashioned eight-day clock, with the striking

parts taken out, were employed for this purpose. The clock-work gives a uniform motion of rotation

to the cylindrical roller that revolves 360 degrees once in twelve hours. The second principal

movement in the gauge originates in the vertical movement of the float, and extends to the recording

pencil. The float was an air-tight cylinder or canister-shaped copper box, which was first thoroughly

painted for protection. A small ballasting weight was attached to the center of its bottom. On its top

was an eye, in which was fastened the end of a wire leading up through the float box. This box was

a water-tight wooden case, large enough to permit a free play of the float, and terminating at the

bottom in a funnel, with an orifice at its apex, through which the water could pass as rapidly as

necessary, but not so as freely as to make the float oscillate sensibly with the surface waves. Figure

A-1 is a diagram of the type of tide gauge installed at Fort Point in 1854. Additional workings of the

tide gauge may be obtained from the 1853 and 1876 Superintendent Report of the Coast Survey.

D. Other Tide Gauges Used by NOS

After the tide staff or tide pole, that required an observer to physically be there and record changes

in the water level, and the first self-registering tide gauge there have been many innovations in tide

gauge technology. These include:

 
A-3

Figure A-1. First Self-Registering Tide Gauge Installed at Fort Point in 1854 
A-4

1. Standard Tide Gauge

The standard automatic tide gauge first appeared in the marine environment in the 1890s with many

improvements over the years until it was replaced with a completely new gauge, the analod digital

recorder, in the 1960s. By the 1970s, all standard tide gauges operations ceased to be used by NOS.

The product of its recordings was a marigram trace of the tide curve. The workings of the standard

tide gauge may be found in NOS Publication 30-1 Manual of Tide Observations. 

2. Gas-Purging Pressure Tide Gauge (Bubbler Gauge)

This tide gauge has made it possible to obtain satisfactory records in areas where the installation of

the structure-supported tide gauge was impractical. The compact size and relative ease of

installation and operation has lead to its use for reconnaissance surveys for tidal datum purposes.

This tide gauge was pioneered at Woods Hole Oceanographic Institution by Alfred Redfield. It was

first used by NOS in the 1960s for use at subordinate stations which is a tide station from which a

relatively short series of observations is reduced by comparison with simultaneous observations

from a tide station with a relatively long series of observations. The bubbler has been used as a backup tide gauge at control stations starting in the 1970s for use in filling breaks in ADR data records.

The workings of the gauge may be found in the NOS publication, "User's Guide for Gas-Purged

Pressure Recording (Bubbler) Tide Gauge."

3. Analog Digital Recorder (ADR)

This tide gauge was first used in the 1960s and finally replaced the standard tide gauge completely

in the 1970s. It is a float actuated tide gauge that records the heights at regular intervals replaced

(6 minutes) on a digital punch tape. The internal workings of the gauge can be found in NOS

publication, "Special Publication 30-1 Manual of Tide Observations." Figure A-2 is a diagram of

the tide gauge setup for the Standard/ADR and bubbler.

 Figure A-2. ADR and Bubbler Gauges Systems in Operation at the Presidio starting in the 1970s

 
A-5

4. Next Generation Water Level Measurement System (NGWLMS)

The Next Generation Water Level Measurement System began to be implemented into operations

in the National Water level Observation Network (NWLON) in the late 1980's and ending with

complete implementation at Great Lakes stations in 2000. At most locations, the NGWLMS was

operated simultaneously present ADR tide gauge system during a transition period, after which the

ADR was removed. 

The NGWLMS uses state-of-the-art technology that includes self-calibrating downward-looking

acoustic water level sensors, back-up pressure sensors, micro-processor based data acquisition and

storage, telemetry to the GOES satellite with a telephone as back-up and the capability of automated

collection of up to 11 ancillary measurements (meteorological data, for instance). 

The NGWLMS acoustic sensor does not have the physical contact of a device with the water

surface, such as the float with the ADR, and the NGWLMS does require a full mechanical filter

known as the stilling well. A large source of systematic error and uncertainty in the older float

operated systems that used stilling wells is being eliminated or reduced using the NGWLMS. The

stilling well is replaced by a more open protective well, much less subject to nonlinear filtering

effects and biofouling, less conducive to density gradient buildups, and more indicative of the

outside environment. The rapid sampling (1 - second pulses) possible with the acoustic sensor of the

NGWLMS allows the well to be open to the dynamics of the ocean. High frequency waves are

removed by digital filtering (by the microprocessor that is part of the water level measurement

system), rather than analog filtering through an orifice in the ADR system. 

A significant improvement with the NGWLMS is that leveling from the bench marks can be done

directly to the sensor itself (the head of the transducer at the end of the sound tube). The sensor can

also be replaced and re-calibrated. The elimination of the tide observer with the replacement of the

ADR with the NGWLMS does away with the systematic errors of observations read from a staff and

adjustments to the ADR gauge itself. The NGWLMS does not require simultaneous observations

from a tide staff and tide gauge to compute the average monthly difference between the tide staff

and marigram zero in the process of referring the water level heights to the station datum. The

possibility of timer drift is also eliminated with the replacement of the ADR with the NGWLMS.

 

 
A-6

Figure A-3. NGWLMS Installed at the Presidio in the Late 1980s at the Presidio
B-1

APPENDIX B

LEVELING TECHNIQUES
B-2

A. Methods of Leveling

The method of leveling adopted was known as "leveling from the middle" or more properly defined,

that of equidistant backsights and foresights. The manner of taking the sights was to bring the target

of the rod nearly into the horizon of the telescope, and to measure with the micrometer the vertical

angle between the horizon and the target by repeated pointings, so as to eliminate errors of level and

collimation. The target reading on the rod was then reduced to the horizon by computation. With

this method, two systems had been in use:

1. Simultaneous Double Leveling in One Direction

By this method the difference in height between two bench marks was determined by

observing from the same station and with the same instrument, backsights on two different

rods, set up at unequal distances from the instrument, and foresights on the same two rods,

carried forward and placed at the same relative distance previously occupied.

2. Leveling in Opposite Directions

This procedure consisted of running a line between two bench marks in one direction, and

releveling it according to the same method in the opposite direction.

3. Comparison of the Two Systems

 a. System 1 offers the advantage of a considerable savings in time over system 2, and

affords a perfect check against errors of observations from station to station, since the

difference in height between two rods, obtained in a foresight should be equal to the

difference in the following backsights.

 b. System 2, on the other hand, offered the advantage of making the determination in

opposite directions under different conditions, and exhibiting with greater certainty the

existence of any cumulative error.

B. Water Crossing

When a line of levels was to be carried across a wide body of water, and, where, from the lowness

of the banks, the line of sight would pass very near the water, the instrument was elevated so as to

be above the vitiating influence of irregular refraction. If possible, two instruments would be

mounted on opposite sides of the waterway, and simultaneous observations would be made on

targets mounted near the respective instruments.

The elevation of each target above a bench mark on its side of the waterway must be carefully

determined and each target and instrument should be as nearby as possible in the horizon of the

other.

The observations were made in the usual manner, if the distance across the waterway is not

otherwise known with sufficient accuracy. The known value of micrometer would serve to

determine it sufficiently for the purpose of reduction, by measuring across the waterway the length

of rod or other known length in terms of the micrometer.

If only one instrument was available, observations made in one direction would be repeated as soon

as possible in the other direction and several times alternately in opposite directions. With

observations in opposite directions, effects of refraction were minimized. Present leveling
B-3

procedures are available in many NOS manuals such as the Manual of Tide Observations Special

Publication 30-1 and NOAA publication "User's Guide for the Installation of Bench Marks and

Leveling Requirements for Water Level Stations."

C-1

Appendix C

 Comparative Readings and Adjustments to

 Tidal Heights at Fort Point Between 1855 and 1859
C-2

A. Comparative Readings

Comparative readings (Table A) were made by tide observers hired to take readings of the water

level from the tide gauge and tide staff simultaneously. Both readings were written on the marigram.

The monthly means of the differences between the staff and gauge reading were computed and

applied to the tidal heights tabulated from the marigram to refer the tidal heights to tide staff zero.

Readings in the 1850s at Fort Point were made 3 times a day and daily averages computed.

Attempts were made to hold comparative reading results relatively consistent over long periods of

time. 

Table A. Comparative Readings Between 1854 and 1862 at Fort Point

Period of Time Average Staff - Marigram Difference*(ft)

1854 June 30 - 1856 June 2 + 1.50

1856 June 2 - 1857 June 16 + 1.80

1857 June 17 - October 20 + 3.00

1857 October 21 - 1858 February

16

 + 3.55

1858 April 5 - November 30* + 2.75

1858 December 1 - 1859 January

19

+ 2.10

1859 January 20 - July 31 + 2.00

1859 August 1 - November 24 + 0.90

1859 December 1 - 1860 June 18 + 1.80 

1860 June 18 - 20 + 0.30

1860 June 21 - 1861 December 9 1.85 

1861 December 10 - 31 + 2.05 

1862 January 1 - June 12 + 2.00

1862 June 13 - 1868 December 31 + 2.10

*The change in the staff minus marigram differences between 1854 and 1959 are attributed to: 

1. The wharf and staff settling at Fort Point.

2. New staff on April 2, 1858 with 2.4 feet movement of staff between June 30, 1854 and

April 2, 1858 and 0.78 foot settlement between April 2, 1858 and June 21, 1859.
C-3

Figure C-1. Monthly Means of MLLW Elevations at Fort Point corrected for the Wharf sinking

Between 1855 and 1859

B. Adjustments to Fort Point Elevation

Table B. Adjustments to Fort Point Tidal Series Between 1855 and 1859 to 

Account for Wharf Sinking

Period of Record Adjustments (Feet)

June 1, 1855 - Jan 31, 1857 - 0.7

Feb 1, 1857 - Feb 28, 1857 - 0.8

March 1, 1857 - March 31, 1857 - 1.0

April 1, 1857 - April 30, 1857 - 1.5 

May 1, 1857 - May 31, 1857 - 1.8

June 1 , 1857 - Jan 31, 1858 - 2.2

Feb 1, 1858 - Feb 28, 1858 -2.5

March 1, 1858 - March 31, 1858 - 3.0

January 1859 - 0.1

February 1859 - 0.2

March 1859 - 0.3

April 1859 - 0.4

May 1859 - 0.5

June 1859 - 0.6

July 1859 - 0.7

There is a history of leveling between 1855 and 1859 that shows the amount of movement of the

staff/wharf. This leveling history appears in Table 1. Table A in Appendix C is a summarization of

the average staff - marigram differences between 1854 and 1859. These two NOS historical record

files along with the tide data from records for 1860 - 1874 - 1859 were used to develop the

adjustment that appears in Table B above. In this way a reduction of the data from 1854 through

1859 was adjusted to a uniform level with the reliable data series 1860 through 1874. The period

1854 - 1859 was then added to the tidal series 1860 through the present, referred to a common datum

zero. Figure C - 1 shows the uncorrected and corrected values of MLLW elevations at Fort Point

between 1854 and 1859.
C-4

It is believed that the pier settled because it was resting on a peat foundation. The shore in the region

was comprised of marsh and peat bogs which were common in the area. According to NOS

historical files of the description of the locality, “The peat structure near the Fort Point pier was

covered in 1859 by gravel and pebbles to give the appearance of greater stability.” The question that

comes to mind also is how piers were constructed in the 1850s. Letters from the National Archives

state that the Fort Point wharf was “constructed on piers of a crib filled with stone.” On one of these

piers the self-registering gauge was placed. In Webster’s unabridged dictionary a crib is described

as the following: “ In the engineering sense, a crib is a frame of logs or beams to be filled with

stones, rubble or the like and sunk as a foundation or retaining wall in the building of docks, piers,

dams, etc.” This is consistent with literature describing the construction of docks and piers in the

text, “The Construction of Harbors’ by Thomas Stevenson and published by the U.S. Coast and

Geodetic Survey in 1886.

Marine organisms contributed to the decay of the timbers forming the cribs. This resulted in the

shifting of the timbers as they weakened from the decay. In time, the stones within the confines of

the timbers also started to shift. The Fort Point wharf being in a high wave and current energy area

also contributed in the wharf sinking.
D-1

Appendix D

Water Leveling Crossings of the Golden Gate

.
D-2

A water leveling crossing was made across the Golden Gate in 1877 from Fort Point to Sausalito to

establish a relationship between the 1877 tide staff zero at Fort Point with the 1877 tide staff zero

at Sausalito. Another crossing was made in 1906 - 1907 after the “1906 San Francisco Earthquake”

to determine if there had been any vertical movement on either side of the Golden gate and vicinity.

The level runs are show in Tables A and B for these crossings.

A. Level Crossing of the Golden Gate in 1877

Table A. Level Crossing of the Golden Gate in 1877

Level Between Marks Differences in

Elevations

Elevation Above 

Tide Staff Zero (Feet)

Fort Point Staff 20.000 

A-I -5.506 14.494

I - II 5.170 19.664

II-III 37.460 57.124

II- IV 1.807 21.471

IV-Target 1 5.153 26.624

Target 1-Target 2 0.586 27.210

Target 2 - V -1.266 25.944

V - VI -4.546 21.398

VI - VII 70.465 91.863

VII - VIII 26.296 118.159

VIII -IX -39.803 78.356

IX- Stone at Sausalito -31.797 46.559

Stone- X stake -20.461 26.098

X - 22 Ft Mark -3.634 22.464 

 

 22.464 - 20.000 = 0.464 feet difference in zero of the two staffs in 1877

B. Spirit Level Between the Tide Staff Zero at Fort Point with the Tide Staff Zero at Sausalito

in 1877

On most of the spirit levels there were two rods, the Boston rod and the Davidson tod, used together.

The two rods were read on the same bench mark by each instruction. As these two readings were

taken without a resetting of the instrument, each reading was given a weight of 2/3 of the weight of

the independent measure in the computation.

The section of the line from Fort Point to bench mark IV on the extreme north shore of Fort Point

was re-leveled about eight times. The several results of differences in level between the bench mark

were tabulated with weights in accordance with the remarks above.

C. Level Crossing of the Golden Gate in 1906 - 1907 Between the Presidio and Sausalito
D-3

Table B. Level Crossing of the Golden Gate from Sausalito to San Francisco in 1906 - 1907

after the 1906 San Francisco Earthquake

Bench

Mark

Elevation Above MSL

In Feet

Elevation Above Presidio

Tide Staff Zero

2 4.4255 Sausalito 13.0774

4 1.0712 9.7231

3 37.9438 46.5957

5 31.0521 39.7040

6 31.0554 39.7073

7 87.0166 95.6685

8 121.9171 130.5690

9 108.5557 117.2075

10 102.5792 111.2311

11 15.3983 Lime Point 24.0502

12 15.1371 23.7890

13 9.4501 18.1020

14 9.8281 18.4800

15 17.6384 26.2903

16 25.4842 34.1361

17 28.5252 37.1771

64 28.2083 Near Fort 36.8602

65 140.4718 149.1237

66 161.1135 169.7654

9 199.2532 207.9051

6 12.7477 21.4000

62 9.0334 17.6853

4 22.0357 30.6876

63 82.4801 91.3120

5 48.4048 57.0567

67 7.7178 16.3697

68 8.2654 16.9173

69 8.6138 17.2657

70 9.3451 17.9970

71 16.5685 25.2204

72 11.2208 19.8727

15 8.8602 17.5121

Staff - 8.6519 Presidio 00.0000
D-4