Pioneer Surveyors, Sailors, Scientists . The Coast Survey on the Southern California Coast

150 YEARS OF TIDES ON

THE WESTERN COAST

THE LONGEST SERIES OF TIDAL OBSERVATIONS IN THE AMERICAS

CAPTAIN ALBERT E. THEBERGE, JR. , NOAA (RET.)

NOAA Central Library

U.S. DEPARTMENT OF COMMERCE

Donald L. Evans, Secretary

National Oceanic and Atmospheric Administration

Vice Admiral Conrad C. Lautenbacher, Jr., U.S. Navy (Ret.)

Undersecretary of Commerce for Oceans and Atmosphere and NOAA Administrator

National Ocean Service

Dr. Richard W. Spinrad, Assistant Administrator for NOAA Oceans and Coasts

Center for Operational Oceanographic Products and Services

Michael Szabados, Director

Abstract

The same year as the acquisition of California by the United States Government, the United States Coast

Survey had been authorized to begin surveying the coast of Oregon Territory from the northern border

of Alta California to the Puget Sound area of Washington Territory. Discovery of gold in 1848 and the

subsequent gold rush added urgency to the requirement to chart our western coast including California.

Small crews of Coast Surveyors headed west, either around Cape Horn or to Chagres, Panama, thence

overland to Panama City, and then by ship to California. Accurate astronomic latitudes and longitudes

of prominent points and landmarks on the Coast were first determined, magnetic declinations at these

points observed, thence topographic surveys of critical areas including suggested locations for

lighthouses were conducted, and finally reconnaissance hydrographic surveys based primarily on

astronomic positioning and dead reckoning were run. Once this critical first work was accomplished,

local triangulation schemes tied into the established astronomic positions were observed, and then

topographic and offshore hydrographic surveys controlled by the triangulation were conducted. After

years of work, an arc of triangulation parallel to the coast tied together all of the local triangulation

networks and a coherent set of charts of our western seaboard based on a common geodetic datum were

produced. In the early years, a final step prior to conducting hydrographic surveys was the installation

of a tide staff in the local area of a survey so as to be able to determine the stage of tide during the time

of survey work and relate the observed soundings to an arbitrary zero point. This arbitrary zero point

could be the mean tide level, mean high water, mean low water, or, as in the case of the western shores

of North America, mean lower low water. As technology improved with the development of self-

recording instruments and a network of permanent gauges was installed, many serendipitous

geophysical and oceanographic discoveries were made over and above the primary mission of providing

safe passage for mariners. Remarkably, the self-recording gauge installed at Fort Point at the entrance to

the Golden Gate and its successors have subsequently survived storms, earthquakes, the potential for

human error and intervention, and produced the longest running series of tidal observations in the

Americas. Since the early surveys, the study of tides has matured and accurate long-term tide

predictions have been developed and coupled with real time water-level and meteorological

observations to guide the shipping of America into its ports.

150 Years of Tides

Construction of an early visual Tide Elevation Recorder at Alcatraz Island

The Colonial Period

For two hundred years Spanish mariners had

been skirting the coast of California on the return

leg of the Mexico-to-Manila trade route but had

always stayed well offshore from the rock-bound

coast of California. However by the late 1700’s

other colonial powers had begun casting lustful

eyes upon the western coast of North America. In

response, in 1769 the Spanish sent out an overland

expedition to establish a series of missions along

the coast of Alta California both to convert the

native Americans and to consolidate their claim to

this territory . Led by Don

Gaspar de Portola, the

expedition was

searching for the

harbor described by

earlier explorers at

Monterey. Not

recognizing the bay

or any harbor when

passing through the

area (in fact there is

not much of a natural

harbor at Monterey),

the expedition

continued to the

north, crossed over

the coast ranges and

camped near present-

day Palo Alto in late

October, 1769. Portola

sent out a group of scouts to

investigate the surrounding area. On November 3,

1769, Sergeant Jose Francisco Maria de Ortega

returned to camp after a three day-excursion to

report that he had discovered a great estuary and

ridden up its east side for quite a distance before

turning back.

Ironically, this great estuary, since named San

Francisco Bay, had been discovered by a sergeant in

the Spanish colonial army. However, it was another

five years before the entrance to the bay would be

viewed from the site of the present city of San

Francisco and another year before a first European

ship would sail through its entrance. This first ship,

the San Carlos which was commanded by Frigate-

Lieutenant don Juan Manuel de Ayala, entered the

bay on August 5

, 1775. Carrying full sail with a

stiff WNW wind blowing from astern, his little ship

strained to stem the current of an ebb-tide flowing

out of the narrow entrance. Ayala estimated the

current at 6 knots (perhaps an exaggeration but

three knot currents are common), the first inkling of

the nature of the tides and tidal currents in San

Francisco Bay. Over the next

month and a half, an initial

survey of San Francisco Bay

was produced. Although

few observations of range

of tide were made, there

were numerous comments

concerning tidal currents.

The following year

Captain Juan Bautista de

Anza led an expedition to

the San Francisco

Peninsula for the purpose

of choosing the site of a

mission and a fort. The

site chosen for the fort, or

presidio, was just to the

east of a point that he

named Cantil Blanco. The

site for a mission was also

selected and a first mass celebrated

by Fathers Palou and Cambron on June 29, 1776,

marking the founding of both the mission and the

city of San Francisco. The birth of the city pre-

dates the birth of our Nation by 5 days.

The Spanish charts of this era were inaccurate

and it was not until the winter of 1826-27 that the

English surveyor Captain Frederick Beechey

arrived in San Francisco and produced the first

accurate chart of the bay. It was he who designated

the prominent point, earlier named Cantil Blanco,

on the south side of the entrance Fort Point.

Entrance to the Golden Gate

Over the next twenty years United States

interest in this area grew. Exploring expeditions

came overland; American maritime traders headed

around Cape Horn and traded for cattle hides and

sea otter furs. Some stayed to increase the

American presence in the region. Ironically, the

gateway to the San Francisco Bay was baptized

Chrysopylae, or “Golden Gate” by overland

explorer John Charles Fremont in 1846 because he

felt the wide entrance to the Bay would be

advantageous for commerce. “To this gate I gave

the name of Chrysopylae, or GOLDEN GATE; for

the same reasons that the harbor of Byzantium

(Constantinople afterwards) was called Chrysoceras

or GOLDEN HORN.” This same year Commodore

Robert F. Stockton took possession of Upper

California for the United States on July 7 and in

1848 the Treaty of Guadalupe-Hidalgo was signed

ceding California and much of the American

Southwest to the United States.

Prior to signing of this treaty, a world-

changing event occurred on January 24, 1848, at

Sutter’s Mill in northern California. James

Marshall discovered gold. With the announcement

by President James Polk on December 5, 1848, to

Congress that, "Recent discoveries render it

probable that these mines are more extensive and

valuable than was anticipated," the rush was on.

The Golden Gate became the port of entry for

thousands of miners headed to the gold fields and,

virtually overnight, San Francisco became a

metropolis. Clipper ship captains headed to

California with children’s school atlases or copies

of old maps produced by Spanish explorers, George

Vancouver, Charles Wilkes of the United States

Exploring Expedition, or those of a few other

mariners and surveyors who had given the coast a

cursory reconnaissance years before. The best of

these charts were generally

inaccurate with prominent

points being in error by as

much as fifteen miles and

virtually no depths

recorded outside of major

harbors. Although the

channel islands were

known, the orientation and

location of virtually all of

the islands were either

significantly in error or not

even shown on the various

explorers’ charts.

Early Coast

Survey Work on

the Western

Coast

Because of immigration to the Oregon

country, the Coast Survey had been making plans to

survey the coast of Oregon Territory as early as

1846. In 1848, Congress authorized this work and

the Coast Survey sent its first crews to the West

Coast in 1849. Unfortunately, the gold rush was on;

labor, transportation, and costs of supplies

Early surveying along the Pacific Coast

skyrocketed with an accompanying stoppage of

field operations. One crew, under Assistant James

Williams, was sent for the land operations and

another, under Lieutenant William P. McArthur,

USN, for the offshore hydrographic surveying

operations. The Coast Survey Schooner EWING

arrived in San Francisco after fighting its way

around Cape Horn after a seven-month trip on

August 1, 1849. The EWING was a topsail

schooner 91 feet in length. For a variety of reasons

including desertions and a mutiny, the EWING also

was stymied

in 1849 and

retired with

the land

crew to the

Hawaiian

Islands for

the winter of

1849-50 to

obtain new

crew

members

and to

resupply at

cheaper

rates.

Because

of the above

frustrations, Alexander Dallas Bache, Superinten-

dent of the Coast Survey, decided that a crew of

young energetic men with “reputation to make” and

a desire to overcome all hardships should be sent to

the West Coast in 1850. This group of four men

was led by George Davidson, who would become

the leader of the West Coast scientific community

over the next half century. James Lawson, A. M.

Harrison, and John Rockwell comprised the remain-

der. Davidson, Lawson, and Rockwell sailed from

the East Coast on May 5 on the steamer PHILA-

DELPHIA for Panama. They landed at Chagres,

hired native Indians for traveling by canoe to the

head of the Chagres River, and then joined a mule

train to go the rest of the way to the city of Panama.

On May 30 they embarked on the Pacific Mail

Steamship TENNESSEE and arrived in San

Francisco on June 20. After a few weeks spent

establishing a base of operations, they proceeded to

Point Conception, landing at El Coxo in mid-July.

In Lawson’s words, “Pt. Conception is one of

the most notable points on the California coast, and

its accurate position was particularly desirable, as it

marked, in fact is the key to, the Northern entrance

to the Santa Barbara Channel.” Harrison, the chief

topographer of this group, joined them during the

Point Conception work. By the end of September

an accurate latitude and longitude of Point

Conception had been obtained by precise

astronomic means, its magnetic declination

determined, a site for a lighthouse selected, and a

topographic survey of the area about the selected

location conducted. The labor involved with this

was quite difficult involving the carrying of large

heavy instruments from El Coxo to Point

Conception and a 300-pound instrument stand.

Relative to the wages of the times, each of the

young Coast Surveyors was paid $30.00 per month.

A cook they hired in San Francisco was paid

$125.00 per month, making more than this whole

group of skilled engineers. Lawson suggested the

weather was better than the storied “Italian skies”

for this sojourn at Point Conception but noted the

continual offshore fog hid the Channel Islands from

view for the first six weeks of their stay. Finally,

early in October the work was finished and the crew

hired a pack train and headed into Santa Barbara to

await transportation to San Francisco. They “did

the town” while there and met the famous otter

hunters George Nidever and Isaac Sparks. They

had earlier made friends with Don Luis Carillo, son

of Don Anastasio Carillo, the owner of the Point

Conception area. They stayed at Don Anastasio’s

home while awaiting transportation and had many

conversations with Don Luis. He felt they were

near to transgressing the truth when they described

the multi-story buildings of the East Coast and the

railways, but “morally certain they lied” when they

described the wonders of the telegraph.

Little was accomplished in southern

California the following year as the Coast Survey

ALEXANDER DALLAS BACHE

The second Director of the Coast Survey

concentrated its efforts to the north of San

Francisco. Although a source of supplies, southern

California was still considered a relative backwater

at this time. However, an astronomic position,

magnetic declination, and site for a lighthouse were

determined at San Diego and a triangulation scheme

and topography carried southward to the Mexican

border from San Diego. The EWING proceeded

north in a first reconnaissance survey from San

Francisco to the Columbia River entrance and

conducted a few surveys at the river entrance as

well.

In 1852, the Coast Survey Steamer ACTIVE,

under the command of Navy Lieutenant James

Alden (one of approximately 800 Navy officers

who served with the Coast Survey in the Nineteenth

Century), made a first reconnaissance hydrographic

survey from San Francisco to San Diego. On this

trip George Davidson was put ashore with his

equipment and acquired astronomic positions at San

Luis Obispo, Santa Barbara, Prisoner's Harbor on

Santa Cruz Island, San Pedro, Santa Catalina Island,

San Clemente Island, San Nicolas Island, and

Cuyler's Harbor on San Miguel Island. This

marked the first time that these islands had been

adequately located. By the end of 1852, most of the

major headlands and points of interest for mariners

between the California-Mexico border and Cape

Flattery, Oregon Territory, had been

accurately determined by George

Davidson and his assistant John Rockwell.

Rudimentary charts of many of the

observed harbors and islands of Southern

California were produced by the end of

1852.

During these first three years of

Coast Survey operations on the western

coast, a relatively accurate general outline

of the coast was sketched in and many

dangerous errors corrected, the geographic

positions of the major headlands and

landmarks determined, magnetic

declinations at strategic points observed,

and locations for lighthouses

recommended. The detail work of

connecting the various independent astronomically

determined locations by triangulation (much more

rigid positioning than attainable through astronomic

means), conducting topographic mapping of the

shoreline and offshore hydrographic surveying that

would be controlled by the triangulation network

was ready to begin. However, little had been done

with observing tides other than the establishment of

a few tide staffs to measure tides during

hydrographic survey operations such that water

depths could be reduced to a local plane of

reference. To obtain readings, either a sailor

attached to the survey party or a local citizen was

hired to read the water level on the tide staff either

every hour or some fraction of an hour never less

than every 15 minutes.

Of the four young men who came west in

1850, George Davidson (1825-1911) and James

Lawson (1828 – 1893) would remain on the West

Coast for most of the remainder of their lives.

Davidson made his home in San Francisco and was

by far the most well-known of the group as he was

considered California’s most prominent scientist for

many years and had many geographic features

named after him including Mount Davidson in San

Francisco and Davidson Seamount to the southwest

of Monterey. Lawson made his home in Olympia,

Washington. A.M. Harrison and John Rockwell

Section of U.S. Coast Survey Chart engraved in 1859

returned to the East Coast.

Rockwell died an early

death in 1857 and Harrison

passed away in 1881.

The Tides

There are few

backdrops as dramatic as the

Golden Gate to observe the

nature of our clockwork

universe. Twice daily the

tides rush into the bay on the

floods and twice out on the

ebbs. Ships plan sailing

times and arrival times on

these daily risings and

fallings. The commercial

and naval wharves,

seawalls, the great bridges of

the Bay Area, underwater

communications cables,

pipelines, and other engineering works all have

been designed and built taking the tides into

consideration. Fishing trips are planned to coincide

with stages of the tide, recreational beachcombing

and tidepooling are planned to coincide with

favorable stages of the tide, surfers plan trips to

favorite breaks based on tide predictions, and even

those who come to the shore for love, friendship

and renewal can be affected by the action of the

tides. How do we predict the stages of the tides for

ship operations, engineering purposes, commercial

and recreational fishing, or other recreational and

personal activities?

There is a grand symphony that has been

played out for billions of years – an orchestration of

moon, sun, earth, and ocean. There are physical

consequences to the Earth and Moon revolving

about a common center of gravity, the Earth-Moon

system revolving about the sun, the varying

distances between Earth and Moon and Earth and

Sun, and the progression of continually changing

declination of the moon and sun relative to the

earth. All of these motions and interactions are

manifested by predictable, but changing,

gravitational forces acting upon the atmosphere, the

oceans, and the solid earth itself. The most visible

result of these forces, particularly for those who live

along our coastlines, is the continual changing of

the level of the sea as the tide rushes in and out.

Although humankind has observed these

phenomena for thousands of years, it was not until

relatively recently that we took to studying,

attempting to understand, and predicting the tides.

Coming from areas adjacent to the Mediterranean

Sea, both Alexander the Great in 325 B.C. and

Julius Caesar in 55 BC almost met disaster because

of tidal phenomena. Alexander’s fleet almost met

its end on the Indus River as the result of tides and

a similar occurrence caused Caesar to retreat from

the shores of England after suffering damage to his

fleet after anchoring in tidal waters. There is a

continuing but unfounded rumor that in 322 BC

Aristotle committed suicide because he was unable

to determine the cause of the tides.

Golden Gate view from the San Francisco tide gauge

Portable tide gauge installation with tide staff

Some progress was made in understanding the

tides in the classical era and even through the Dark

Ages. The relationship between phases of the moon

and tidal range was noted by many observers and

even crude tide tables were produced for a few

areas. However, it was not until 1687 that Sir Isaac

Newton developed the concept of tides being

caused as a result of predictable but varying

gravitational forces resulting from the changing

relative positions of sun and moon relative to the

Earth. But, recognizing the cause of tides and being

able to predict them are two different things. The

configuration of oceanic basins and local conditions

such as water depth, configuration and slope of

bottom, and meteorological effects all combined to

confound attempts to understand the nature of tides.

This situation was exacerbated by inadequate

technology to observe tides under a variety of

conditions, lack of accurate solar and lunar tables,

lack of accurate time-keeping instruments, and lack

of any scientific infrastructure to coordinate

observations from geographically dispersed

locations.

This remained the

situation until the early to

mid-Nineteenth Century.

By this time more

accurate sun and moon

tables had been

developed, better time-

keeping mechanisms to

coordinate observations

had been invented, and

perhaps, most

importantly, dedicated

scientists and cadres of

engineers in organizations

such as the United States

Coast Survey had begun

turning their energy to

solving the problems of

tide observations and tide

predictions. Until the

mid-Nineteenth Century

the only method for

observing the tide was to place a vertical staff in the

water graduated in some unit of linear measure (feet

in the United States Coast Survey) and station an

observer close enough to the tide staff such that he

could read the stand of the tide on the staff every

hour or some increment of an hour and record these

values.

Although challenging in confined harbors

with easy access to piers and other structures, on

open coasts the observation of tides was difficult if

not impossible. In the case of tide staffs installed in

harbors, a slight variation over fixed-staff

observations was the introduction of a floating staff

encased in a stilling well that would move vertically

with the tides. The top of this moving staff would

be equipped with rollers that slid up and down in

guides attached to a fixed staff graduated in feet and

decimal parts of feet. The observer would read the

value that was adjacent to the very top of the

moving staff. This arrangement of fixed and

moving staff often was enclosed in a small tide

house not unlike those in use in many locations

along the United States coastline today. The

advantage of this arrangement was that

the observer was not exposed to the

elements and that it was possible, on

average, to make much more accurate

observations than was possible from a

remotely viewed fixed staff. The tide

staff method, whether fixed or floating,

was subject to human error,

carelessness, and to some degree

subjectivity. Although there were a

few professional tide observers in the

Coast Survey, notably Gustavus

Wurdemann who was repeatedly

praised in annual reports for his

accuracy and devotion to duty, in most

cases the observations were entrusted

to members of the hydrographic party

or local citizens who did not always

meet the same high standards as

Wurdemann.

The problem of varying quality of

observations was noted in the first

attempt to obtain accurate tide observations on the

western coast of the United States. Two

coordinated sets of observations were planned from

staffs at Rincon Point (famous now for being close

to Pac Bell Park and the site of Barry Bonds’

homerun marathon) and Sausalito. These

observations were conducted for a little less than a

month in late January through early February of

both 1852 and 1853. The Rincon Point

observations, under the direction of Lieutenant

James Alden, commanding officer of the Coast

Survey Steamer ACTIVE, were praised for their

accuracy and attention to detail. Conversely, it was

suggested that the Sausalito observations “were not

made with the same care which appears to

characterize” the Rincon Point observations.

As a result of the short series of Rincon Point

observations, Alexander Dallas Bache,

Superintendent of the Coast Survey and great-

grandson of Benjamin Franklin, was able to draw

many conclusions of importance to the navigation

of San Francisco Bay. The first of these was that

there was a large diurnal inequality between the

successive high and low waters of each lunar day

(24 hours and 50 minutes for moon to complete a

revolution about the Earth). What this meant to

navigators was that an obstruction having three and

a half feet of water over it at a first low tide of the

day could be awash at the time of the second low

tide of the day. This had great significance both for

the immediate needs of assuring safe passage of

commerce but also relative to choosing a plane of

reference for soundings for charting purposes.

Ultimately, mean lower low water was chosen as

the plane of reference for Coast Survey charts on

the West Coast and Alaska as opposed to mean low

water as used on the East Coast and Gulf Coast. As

hydrographic surveys were performed for creating

updated nautical charts of the region, the data from

the tide gauges were used to correct the soundings

for stage of tide and refer them to a common datum.

Other information obtained from this short series of

observations were rules for determining times of

high and low water relative to the declination of the

moon, average range of tides between highest high

water and lowest low water, and probable greatest

range of tides in the Bay.

Although these first tide observations

provided the mariner with a rough means to

determine the times of high and low water in the

Bay, it was understood that only a small inroad had

been made in understanding the Pacific tides.

Fortunately a new technology had been recently

developed. The great instrument-maker Joseph

Saxton invented a self-registering tide gauge in

1851 which ran twenty-four hours per day with

minimal human care. This gauge was not the first

self-recording tide gauge but was considered to be a

marked improvement over existing instruments. It

consisted of a float attached by wire to a gearing

mechanism. The gearing mechanism drove the

location of a pencil relative to a rotating drum

covered with a paper tide record sheet. The whole

system was time synchronized such that the pencil

tracings of the risings and fallings of the tide in a

sinusoidal curve could later be scaled for heights

and times of various stages of the tides. This new

system effected a revolution in both the quantity

and quality of tide records acquired by the Coast

Survey. Shortly after the introduction of and

possibly as a result of this new technology, a new

tidal division was established in the Washington,

D.C., headquarters of the Coast Survey under Count

Louis F. de Pourtales, a Swiss immigrant like

Ferdinand Hassler (1770-1843), the founder of the

Coast Survey. An interesting aspect of this new

division was that Alexander Dallas Bache hired

Mary Thomas as a tides computer, the second

woman science professional in the Federal

Government. The first was Maria Mitchell, the

great astronomer, who had been hired by Bache to

do observations for the Coast Survey in the mid-

1840’s and then hired by the Nautical Almanac

Office. Not only was the Coast Survey the pioneer

surveying organization on our coastlines, but it was

the pioneer agency in hiring talented women

scientists and mathematicians to work side-by-side

with their male counterparts.

In 1853 Superintendent Bache sent a

dedicated tides party under Army Lieutenant

William P. Trowbridge to the West Coast with three

of the new self-registering tide gauges. These

gauges were to be installed at San Francisco and

San Diego in California and at

Astoria, Oregon. Trowbridge

accompanied by Army enlisted

man Andrew Cassidy and a few

other observers (apparently all

Army enlisted men), who were

chosen for their intelligence

and devotion to duty, traveled

to California via steamship to

Panama, proceeded over the

nearly complete Panama

Railroad to Panama City, and

continued to San Francisco by

Panama steamer, arriving in

July 1853. They established a

self-registering gauge in the

North Beach area of San

Francisco and then proceeded

to San Diego where Cassidy was left in charge of

the newly installed gauge. From there Trowbridge

proceeded to Astoria.

Although a self-registering gauge was

established in San Francisco in 1853, it was decided

to move the gauge to Fort Point on the grounds of

the Presidio in July 1854 as portions of San

Francisco were in turmoil because of land squatters

causing civil unrest. Amazingly, since that time

this gauge and its successors have produced the

longest running unbroken series of tidal

observations in the Americas. It is probable that

there is no other geophysical phenomena in the

Western Hemisphere that has a longer continuous

record.

Although the San Francisco record is the

longest continuous tidal record, it is noted that self-

registering tide gauges were established at four

other permanent locations at that time – Governor’s

Island, New York; Old Point Comfort, Virginia;

San Diego, California; and Astoria, Oregon.

Because of storm, disaster, carelessness, or any of a

myriad of other possible causes, the only gauge able

Self-registering tide gauge "Saxton"

Presidio tide station

to survive with an unbroken record of observations

was the San Francisco gauge. For one hundred and

fifty years observations from this gauge have

assisted the mariners of the world entering and

sailing from the ports of the Bay Area as well as

having helped in the planning and construction of

all the waterfront facilities of this great port.

Serendipitous Science

Observation of tides for commercial and naval

shipping interests was and remains the primary

purpose of the San Francisco tide gauge. However,

this particular gauge has a record of adding to our

knowledge of the oceans and its relationship to the

Earth in general that is without peer. Within six

months of the installation of the gauge at Fort Point,

a great earthquake occurred on December 23, 1854,

near the central coast of Japan raising a series of

great tsunamis along portions of the Japanese coast.

The tsunamis traveled across the Pacific Ocean and

were recorded as attenuated waves on the self-

registering tide gauges along the western coast.

These waves were superimposed upon the regular

tidal record as a series of sinusoidal squiggles. The

first person to recognize the significance of these

squiggles was Lieutenant Trowbridge who wrote to

Superintendent Bache in early 1855, “There is

every reason to presume that the effect was caused

by a sub-marine earthquake.” This was an amazing

insight given that recording seismographs were still

twenty-five years in the future and that no

earthquake had ever been remotely sensed by any

means up to this time.

Trowbridge’s insight was validated when

word of a major earthquake occurring on the coast

of Japan on December 23 reached Superintendent

Bache. Armed with knowledge of the time of the

earthquake, its location, times of arrival of the

tsunami waves at both San Francisco and San Diego

(from the tide gauge records), and times between

crests of the various waves, Superintendent Bache

was able to estimate the average depth of the

Pacific Ocean. Bache was familiar with the latest

basic research published by Sir George Biddell Airy

and his treatise on Waves and Tides in the

Encyclopaedia Metropolitana in 1849. Airy had

mathematically developed theoretical expressions

that govern the motion of waves in canals of

uniform depth and compiled tables for expressing

the relationships between wave length, wave period,

wave velocity and depth of water. Bache

interpolated the Airy table values using his distance

estimates and the tide gauge measurements for the

theoretical tsunami wave travel lines between

Shimoda, Japan and both San Diego and San

Francisco. Using two separate estimates for the

times of the disturbance due to the tsunami on the

tide gauge curve at San Francisco, Bache estimated

the average depth of the Pacific between Shimoda

and San Francisco to be 13,380 feet and 15,000

feet. For the line between Shimoda and San Diego,

the average depth was estimated to be 12,600 feet.

Considering that these were estimates of the

average depth of the Pacific Ocean using indirect

measurement and theoretical relationships of

waves for canals of uniform depth, these numbers

agree remarkably well with modern published

values based upon modern measurement

technology. Modern day estimates for the average

depth for the depth profile from Shimoda to San

Francisco are 15,504 feet and 15,221 feet from

Shimoda to San Diego. Bache published his

estimates at a time when deep sea sounding

technology was in its infancy, inaccurate

soundings ranging between 30,000 to 50,000 feet

were fairly common, and there was great

uncertainty concerning the true average depth of the

oceans.

Over the next 150 years the San Francisco tide

gauge recorded many of the great tsunamigenic

events of the Pacific Ocean. It even recorded

tsunami waves from the great Krakatau explosion

of August 26, 1883, a few hours after the event and

the Coast and Geodetic Survey published notice of

an extraordinary event prior to any notice of the

details or location of the disaster were known. The

gauge has also survived many major events in its

vicinity including the Hayward earthquake of 1868

which did major damage to the East Bay and to land

fill areas in San Francisco, the great earthquake of

1906, and the 1989 Loma Prieta earthquake.

It may seem strange, but elevations

throughout the United States and North America

have been determined relative to mean sea level as

determined at Coast and Geodetic Survey tide

stations. Attempts to determine elevations of points

inland from coastal tide stations began as early as

1857 when a line of levels was run up the Hudson

River between tidal bench marks in New York City

and Albany, New York. Bench marks, usually

distinct monuments in the form of concrete

cylinders with brass monuments on top that are set

in the ground, or in the early years of tidal

observations marks etched on permanent rock

surfaces, are established at all tide stations in order

to assure that there has been no change of position

of a tide staff between the water surface and the

land surface. After a series of tidal observations

have been made, local mean sea level can be

determined at a gauge location and the elevation

above sea level of the bench marks in the general

area can be determined. It was not until 1904 that

the first trans-continental line of levels connecting

the tide gauge at Seattle, Washington with the one

at Sandy Hook, New Jersey was completed. Over

the next twenty years there were a number of

additional connections made between Atlantic and

Pacific gauges. In 1929 the Sea Level Datum of

1929 was introduced by the Coast and Geodetic

Survey which incorporated data from twenty-one

tide stations in the United States and five in Canada.

This datum was the basis of elevation determination

for all government mapping and for the planning

and design of all major engineering projects in the

United States. Prior to this time there was no

standard means of determining elevations in the

United States and the establishment of this datum

began with the tidal observations of the Coast

Survey. Since 1929 there have been two major

readjustments of the vertical geodetic datum

(see

footnote).

An issue related to the determination of

mean sea level as an elevation datum is the concept

of changing sea level. The San Francisco tide

gauge is the longest continuous record of sea level

change in existence in the western hemisphere.

Whether sea level is increasing, decreasing, or

remaining static is of major importance to people

living in coastal regions. The determination of

changing sea level is a difficult issue. Because of

tectonic forces, subsidence caused by withdrawal of

subsurface fluids or mineral material from coastal

areas, isostatic adjustment or rebound of land areas

previously covered by glaciers, or a combination of

these effects, coastal lands can be rising relative to

the sea, sinking relative to the sea, or remaining

static. However, after taking into account these

perturbing forces, most of the last century has

shown a steady rise in sea level as determined by

tidal records augmented over the last decade by

satellite altimetry. Tidal records show rise rates of

approximately 2 mm per year over the last century

while satellite altimetry is showing even higher

rates of rising sea levels (Note: the satellite

altimetry record is only 10 years long, so several

This Sea Level Datum of 1929 was re-named as National Geodetic

Vertical Datum of 1929 (NGVD29) and superseded by North American

Vertical Datum of 1988 (NAVD88) so that geodetic datums could be

de-coupled from mean sea level observations at tide gauges. There is

no consistent vertical relationship between NGVD29, NAVD88 and

mean sea level around the coast. The long-term tide gauge records show

us that trends in relative mean sea level are highly variable around the

coast due to varying rates of vertical land movement and using them

together as baseline geodetic datum un-ravels over time. Modern tide

gauges, precisely tied to the new geodetic networks and GPS reference

frames, are helping to distinguish regional sea level trends from global

sea level rise due to climate change and from vertical land movement.

Variations in Annual Mean Sea Level at San Francisco: 1856 - 2002

more years of record are required to establish a

trend). These rates of sea level rise have many

ramifications for human occupation of coastal

areas. If sea level continues rising at present rates,

engineering works will have to be rebuilt or

modified; less area

will be available for

human habitation;

wetland habitats will

be drowned and lost;

low-lying islands will

be inundated; and

many areas immune

today from storm

surges caused by

coastal storms will in

the future be subject

to the walls of water

that accompany major

wind events

Extreme high water events during periods of

El Nino are clearly seen in the San Francisco

historical tide record. El Nino events generally

occur every 3 to 7 years in the Pacific Basin and

are caused by the interaction between unusually

warm sea surface currents and high sea levels

generated in the tropical Pacific drifting eastward

and colliding with lower temperatures in the

Eastern Pacific. According to historical records, the

most severe El Nino events have occurred in the

Century, and most recently during the period

1997-1998.

As shown in the plot above, the effect of the

1983 El Nino is clearly pronounced and is the event

of record in the monthly and annual mean sea

levels. By analyzing the Interannual to Decadal

variations in sea level, especially from a long

baseline record like San Francisco, it=s now possible

to better understand the El Nino Southern

Oscillation phenomenon and help predict future

events.

Sea level records from the San Francisco

gauge are indispensable for conducting climate

change research, investigations of global warming

and predicting El Nino events and the impacts of

sea level change on coastal communities. Analysis

of localized sea level trends also provide insight and

better understanding of regional tectonic changes

and accompanying seismic activity. San

Francisco's 150 years of sea level record adds a

wealth of

information to the

knowledge of

global climate

change and

relative rates of

sea level rise. In

fact, the San

Francisco record

indicates that the

positive sea level

trend (1.41

mm/year) has not

always been

uniform over time

and experienced a downward trend between 1875

and 1913. This sea level anomaly has also been

noted in the historical records of comparable long

term sea level records world wide.

Establishing the Record

To obtain a continuous record of the tides in

San Francisco since 1854 has been a monument to

human perseverance and ingenuity coupled with

improvements in the technology of water level

measurement. The self- registering tide gauge,

established at Fort Point in June 1854, was

accompanied by the establishment of bench marks,

which are permanently fixed vertical reference

points; in this case, the bench mark was a cross cut

in the face of a large stone near the wharf where the

gauge was installed. Leveling surveys were

conducted on a yearly basis between the bench

mark and tide gauge to insure that stability of the

gauge was maintained. Tide observers made daily

visits to the gauge to make tide staff readings and

check gauge time. Problems with wharf settlement

were soon discovered, but were corrected by

stabilizing the area around the wharf with rock and

stone fill. In 1877, the wharf came under disrepair

and was abandoned. A new gauge site was chosen

across the Golden Gate at Sausalito. Meticulous

care was taken to preserve the Fort Point data series

through the simultaneous operation of the Fort

Point gauge and Sausalito gauge coupled with the

transfer of tide staff elevations by a water crossing

technique. This involved limiting the refraction

effect during survey leveling operations by

simultaneously observing targets at bench mark

sites at Fort Point and on the north shore at Lime

Point, a little more than a mile distant across the

Golden Gate, and then transferring elevations

through repeated leveling and eventually to bench

marks at the new Sausalito gauge on Government

Wharf at the Fort Baker military reservation. In

1881, the Sausalito wharf began to deteriorate and

the gauge was moved to a more stable site; then

in1897, it was finally decided to move the gauge

back across the San Francisco Bay to the Presidio

area, which was just east of the original Fort Point

site and in the approximate vicinity of the present

day gauge.

This era in the history of the San Francisco

tide gauge was also marked by the association of

two major Bay Area authors with the work of

NOAA ancestor agencies. It is little-known, but

both John Muir and Jack London were associated

with the Coast and Geodetic Survey and the United

States Fisheries Commission respectively. Muir

worked through the Sierra Nevada and the Great

Basin as a guide and artist for the Coast Survey

during reconnaissance work for the 39

Parallel

Survey which was the first great survey line

connecting the Atlantic and Pacific coasts of the

United States. This work was done with Coast

Survey Assistant Augustus Rodgers, brother of the

naval hero Rear Admiral John Rodgers. Muir’s

only published work on this part of his wilderness

life was “Snowstorm on Mount Shasta” although

diaries of his Great Basin experiences are still in

existence. Jack London worked for and against the

Fisheries Commission in his youth as both a

fisheries enforcement agent and oyster pirate on

San Francisco Bay and as a deck hand on a sealing

schooner in the Bering Sea. His San Francisco Bay

experience is recounted in “The Raid on the Oyster

Pirates,” a delightful tale in which London, on the

right side of the law, captures a group of oyster

pirates by stealing their boats and using the rising

tide to force their surrender and arrest them. “The

Sea Wolf”, the dark tale of seal poacher Wolf

Larsen, draws on his sealing schooner experiences.

Standard Tide Gauge

The Harris-Fischer Tide prediction machine or "Old Brass-Brains."

Tide gauge technology evolved little from

1854 until the early 1960’s. The processing of tidal

records also changed little and was very labor

intensive during these years as it required manual

scaling of tidal heights and time from the pen-

recorded sinusoidal record. The scaled

observations were entered into record books for

further processing. Tide predictions were computed

manually in the early years of the Coast Survey

Tidal Division. However, in 1867 a new method of

computing tides, termed the harmonic method, was

introduced by Sir William Thomson of Great

Britain. This method, although showing promise of

greater accuracy in tide predictions, was impractical

because it was extremely labor intensive. Thomson

solved this by inventing a tide prediction machine

that summed ten constituents of the harmonic

analysis equations in 1876. The values of the

constituents were obtained manually from the

observed high and low waters. William Ferrel of

the Coast and Geodetic Survey designed a second

computing instrument of this type in 1880 which

was operational by 1884. Reducing harmonic

analysis to a series of gears, pulleys, and levers, the

Ferrel machine computed times and heights of tidal

maxima and minima using nineteen constituents.

The harmonic method of tide prediction has been

used by NOAA since that time. A second tide

prediction machine was built by the Coast and

Geodetic Survey and became operational in 1912.

This machine, formally known as the Harris-Fischer

Tide Prediction Machine, or “Old Brass-Brains” as

it came to be affectionately termed, summed 37

constituents and was used until the advent of digital

computers in the early 1960’s. This machine has a

long and honorable history and was used not only to

compute domestic tide predictions, but during the

Second World War computed tide predictions for

world-wide for use by our naval and amphibious

forces. Obtaining the values of the harmonic

constituents for input into the tide prediction

machine was also accomplished manually up to the

time of computers using a series of forms and

stencils on the tabulated hourly heights of the tide

gauge record.

In Jan-

uary 1976, a

digital paper

punch recorder

termed an

analog to

digital

recorder

(ADR)

replaced the

venerable

pencil and

drum

recording

mechanism.

This

instrument

recorded the

height of the

tide at set time

intervals, usually every six minutes, by punching

holes indicating the observed times and float height

on an aluminum-backed paper tape. As the paper

punch tapes could be machine-read, this system

sped up the processing of tide records but the gauge

itself still relied on a float/wire water level sensor

and gearing mechanism on the recorder that

synchronized time and rate of advance of the paper

record. A tide observer was also required to

maintain the gauges on correct time and to make

daily tide staff readings.

This instrument had a life-span of

approximately one human generation as beginning

in 1985, the National Ocean Service embarked on a

major upgrade of what had become termed the

National Water Level Observation Network. The

network of old float/wire systems was replaced by

the Next Generation Water Level Measurement

System (NGWLMS) which consisted of an air

acoustic water level sensor coupled with an

electronic data acquisition system. These systems

have numerous advantages including the direct

leveling of the water level sensor to local

benchmarks (tide observers and tide staffs are no

longer required), electronic data storage, a backup

The ADR Gauge,

a mechanical “punch” recorder.

pressure water level sensor with its own data

logger, and ancillary sensor capability such as water

and air temperature, wind speed and direction and

barometric pressure. The acoustic sensor capability

allowed much more accurate water level readings

but what really set this system apart from the earlier

systems was the ability to transmit data to a central

facility via telephone line or via NOAA’s

Geostationary Operational Environmental Satellite

(GOES) data collection system for near real-time

data analysis, processing, and distribution. By

comparison, prior to introduction of this system,

tidal data rolls were removed monthly from the

ADR gauges and mailed to the National Ocean

Service for processing. The NGWLMS system

replaced the ADR gauge at San Francisco in

January 1996.The modern day ports in San

Francisco Bay region continue to play a vital role in

the nation’s economy. Approximately 95% of

foreign trade in and out of the U.S. is by ship and

every U.S. citizen, not just those living along the

coast, relies upon the nation’s ports for energy

delivery, exports, transportation, and cost effective

consumer goods. The new water level

measurement gauges have also been integrated into

the NOAA Physical Oceanographic Real-Time

System (PORTS), that has been introduced into

many major United States harbors including San

Francisco Bay. This system measures real-time

water levels, currents, and meteorological

phenomena such as winds and visibility and makes

these data immediately available to the local user

for operational decision-making.

These decisions include when to load or off-

load more cargo, when the best time to make

transits, when there is enough clearance to go under

a bridge, or when to sail or not to sail with or

against the currents and tides. This information is

critically important considering that there is an

average of 261 deep-draft vessels entering San

Francisco Bay each month and that there are

approximately 85,000 registered pleasure boats

using approximately 100 yacht clubs in the Bay

system.

Summary

A U.S. Coast Survey tide gauge was installed

at San Francisco on June 30, 1854 and will soon

have produced the continuous recording of water

level for 150 years. The tide station, now operated

by NOAA, is part of a network of 175 long-term

tidal and Great Lakes water level stations that have

been established throughout the continental United

States, Alaska, Hawaii, Pacific Island territories,

Puerto Rico and the Virgin Islands.

The historical record from the tide station at

San Francisco transcends the maritime history of

the San Francisco Bay, from the days when clipper

ships relied upon tide predictions provided by the

station to navigate the dynamic waters of the

Golden Gate, to the modern day mariner that

obtains real-time water levels so that the huge ship

and crane barge operators can tell if they have

enough depth in the channels and enough clearance

under the bridges.

The record from the station continues to be

used to update national nautical chart and shoreline

reference datums. The data record itself contains

the signatures of important maritime events that

have affected human populations and the California

culture over time, from the traces of Pacific Ocean

Tsunamis, to high tides from storm surges, to high

sea levels due to El Nino, and to the long term

The Next Generation Water Level Measurement System

record of sea level rise since the turn of the century.

It is one of the longest continuous records of sea

level in the world and has been used by the

scientific community in research for estimating

global sea level rise.

Today, the San Francisco tide gauge plays a

central role in the San Francisco Bay Physical

Oceanographic Real-Time System (PORTS) which

supports safe, cost efficient navigation and provides

shipping interests with accurate real-time tide,

current and meteorological data and is an important

component of the NOAA Tsunami Warning

System. It continues to provide information critical

to maintaining and improving economic prosperity

for California and for maintaining and monitoring

port activities important for Homeland Security.

And finally, the data from the gauge are used to

provide water level and reference datum

information needed for the increasing number

habitat and marsh restoration programs in the bay

region.

Crane barge with just enough bridge clearance during transit