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

The same year as the acquSurvey had been authorizeof Alta California to the Psubsequent gold rush addeSmall crews of Coast Survoverland to Panama City, of prominent points and lpoints observed, thence lighthouses were conducastronomic positioning anlocal triangulation schemtopographic and offshore hyears of work, an arc of tnetworks and a coherent sproduced. In the early yeof a tide staff in the local of survey work and relate could be the mean tide levof North America, mean recording instruments angeophysical and oceanograsafe passage for mariners. the Golden Gate and its shuman error and intervenAmericas. Since the epredictions have been dobservations to guide the s

150 Years of T

d
1

The Colonial Period

For two hundred years Spanish mariners had

been skirting the coast of California on the returnleg of the Mexico-to-Manila trade route but hadalways stayed well offshore from the rock-boundcoast of California. However by the late 1700’sother colonial powers had begun casting lustfuleyes upon the western coast of North America. Inresponse, in 1769 the Spanish sent out an overlandexpedition to establish a series of missions alongthe coast of Alta California both to convert thenative Americans and to consolidate their claim tothis territory . Led by DonGaspar de Portola, theexpedition wassearching for theharbor described byearlier explorers atMonterey. Notrecognizing the bayor any harbor whenpassing through thearea (in fact there isnot much of a naturalharbor at Monterey),the expeditioncontinued to thenorth, crossed overthe coast ranges andcamped near presentday Palo Alto in lateOctober, 1769. Portolasent out a group of scouts toinvestigate the surrounding area. On November 3,1769, Sergeant Jose Francisco Maria de Ortegareturned to camp after a three day-excursion toreport that he had discovered a great estuary andridden up its east side for quite a distance beforeturning back. 

Ironically, this great estuary, since named San

Francisco Bay, had been discovered by a sergeant inthe Spanish colonial army. However, it was anotherfive years before the entrance to the bay would beviewed from the site of the present city of San

Francisco and another year before a first Europeanship would sail through its entrance. This first ship,the San Carlos which was commanded by FrigateLieutenant don Juan Manuel de Ayala, entered thebay on August 5th, 1775. Carrying full sail with astiff WNW wind blowing from astern, his little shipstrained to stem the current of an ebb-tide flowingout of the narrow entrance. Ayala estimated thecurrent at 6 knots (perhaps an exaggeration butthree knot currents are common), the first inkling ofthe 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 rangeof tide were made, therewere numerous commentsconcerning tidal currents.

The following year

Captain Juan Bautista deAnza led an expedition tothe San FranciscoPeninsula for the purposeof choosing the site of amission and a fort. Thesite chosen for the fort, orpresidio, 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 thecity of San Francisco. The birth of the city predates 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 theEnglish surveyor Captain Frederick Beecheyarrived in San Francisco and produced the firstaccurate chart of the bay. It was he who designatedthe prominent point, earlier named Cantil Blanco,on the south side of the entrance Fort Point.

Entrance to the Golden Gate

Over the next twenty 

interest in this area grew. Ecame overland; American maaround Cape Horn and traded sea otter furs. Some staAmerican presence in the regateway to the San FranciscChrysopylae, or “Golden explorer John Charles Fremonfelt the wide entrance to advantageous for commerce. the name of Chrysopylae, or the same reasons that the h(Constantinople afterwards) wor GOLDEN HORN.” This sRobert F. Stockton took pCalifornia for the United Sta1848 the Treaty of Guadalupceding California and mucSouthwest to the United States

Prior to signing of t

changing event occurred on Sutter’s Mill in northern 

Early 
3

skyrocketed with an accompanying stoppage offield operations. One crew, under Assistant JamesWilliams, was sent for the land operations andanother, under Lieutenant William P. McArthur,USN, for the offshore hydrographic surveyingoperations. The Coast Survey Schooner EWINGarrived in San Francisco after fighting its wayaround Cape Horn after a seven-month trip onAugust 1, 1849. The EWING was a topsailschooner 91 feet in length. For a variety of reasonsincluding desertions and a mutiny, the EWING also

was stymiedin 1849 andretired withthe landcrew to theHawaiianIslands forthe winter of1849-50 toobtain newcrewmembersand toresupply atcheaperrates. 

Because

of the above

frustrations, Alexander Dallas Bache, Superintendent of the Coast Survey, decided that a crew ofyoung energetic men with “reputation to make” anda desire to overcome all hardships should be sent tothe West Coast in 1850. This group of four menwas led by George Davidson, who would becomethe leader of the West Coast scientific communityover the next half century. James Lawson, A. M.Harrison, and John Rockwell comprised the remainder. Davidson, Lawson, and Rockwell sailed fromthe East Coast on May 5 on the steamer PHILADELPHIA for Panama. They landed at Chagres,hired native Indians for traveling by canoe to thehead of the Chagres River, and then joined a muletrain 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 SanFrancisco on June 20. After a few weeks spentestablishing a base of operations, they proceeded toPoint 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, andits accurate position was particularly desirable, as itmarked, in fact is the key to, the Northern entranceto the Santa Barbara Channel.” Harrison, the chieftopographer of this group, joined them during thePoint Conception work. By the end of Septemberan accurate latitude and longitude of PointConception had been obtained by preciseastronomic means, its magnetic declinationdetermined, a site for a lighthouse selected, and atopographic survey of the area about the selectedlocation conducted. The labor involved with thiswas quite difficult involving the carrying of largeheavy instruments from El Coxo to PointConception 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 wholegroup of skilled engineers. Lawson suggested theweather was better than the storied “Italian skies”for this sojourn at Point Conception but noted thecontinual offshore fog hid the Channel Islands fromview for the first six weeks of their stay. Finally,early in October the work was finished and the crewhired a pack train and headed into Santa Barbara toawait transportation to San Francisco. They “didthe town” while there and met the famous otterhunters George Nidever and Isaac Sparks. Theyhad earlier made friends with Don Luis Carillo, sonof Don Anastasio Carillo, the owner of the PointConception area. They stayed at Don Anastasio’shome while awaiting transportation and had manyconversations with Don Luis. He felt they werenear to transgressing the truth when they describedthe multi-story buildings of the East Coast and therailways, but “morally certain they lied” when theydescribed 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 Francisco. Although a source California was still considered at this time. However, an magnetic declination, and site determined at San Diego and a and topography carried southborder from San Diego. Thnorth in a first reconnaissanFrancisco to the Columbia conducted a few surveys at well. 

In 1852, the Coast Surv

under the command of NaAlden (one of approximatelwho served with the Coast SuCentury), made a first reconnsurvey from San Francisco to trip George Davidson was equipment and acquired astronLuis Obispo, Santa Barbara, Santa Cruz Island, San Pedro, San Clemente Island, San Cuyler's Harbor on San Mmarked the first time that thadequately located. By the enmajor headlands and points obetween the California-MexiFlattery, Oregon Territory, accurately determined bDavidson and his assistant JohRudimentary charts of maobserved harbors and islands California were produced by 1852. 

During these first thr

Coast Survey operations on coast, a relatively accurate geof the coast was sketched idangerous errors corrected, thpositions of the major healandmarks determined, declinations at strategic poinand locations for lirecommended. The detai
5

returned to the East Coast.Rockwell died an earlydeath in 1857 and Harrisonpassed away in 1881. 

The Tides

There are few

backdrops as dramatic as theGolden Gate to observe thenature of our clockworkuniverse. Twice daily thetides rush into the bay on thefloods and twice out on theebbs. Ships plan sailingtimes and arrival times onthese daily risings andfallings. The commercialand naval wharves,seawalls, the great bridges ofthe Bay Area, underwatercommunications cables,pipelines, and other engineering works all havebeen designed and built taking the tides intoconsideration. Fishing trips are planned to coincidewith stages of the tide, recreational beachcombingand tidepooling are planned to coincide withfavorable stages of the tide, surfers plan trips tofavorite breaks based on tide predictions, and eventhose who come to the shore for love, friendshipand renewal can be affected by the action of thetides. How do we predict the stages of the tides forship operations, engineering purposes, commercialand recreational fishing, or other recreational andpersonal activities? 

There is a grand symphony that has been

played out for billions of years – an orchestration ofmoon, sun, earth, and ocean. There are physicalconsequences to the Earth and Moon revolvingabout a common center of gravity, the Earth-Moonsystem revolving about the sun, the varyingdistances between Earth and Moon and Earth andSun, and the progression of continually changingdeclination of the moon and sun relative to theearth. All of these motions and interactions are

manifested by predictable, but changing,gravitational forces acting upon the atmosphere, theoceans, and the solid earth itself. The most visibleresult of these forces, particularly for those who livealong our coastlines, is the continual changing ofthe level of the sea as the tide rushes in and out. 

Although humankind has observed these

phenomena for thousands of years, it was not untilrelatively recently that we took to studying,attempting to understand, and predicting the tides.Coming from areas adjacent to the MediterraneanSea, both Alexander the Great in 325 B.C. andJulius Caesar in 55 BC almost met disaster becauseof tidal phenomena. Alexander’s fleet almost metits end on the Indus River as the result of tides anda similar occurrence caused Caesar to retreat fromthe shores of England after suffering damage to hisfleet after anchoring in tidal waters. There is acontinuing but unfounded rumor that in 322 BCAristotle committed suicide because he was unableto determine the cause of the tides.

Golden Gate view from the San Francisco tide gauge

Some progress was mad

tides in the classical era and eAges. The relationship betweand tidal range was noted by even crude tide tables were areas. However, it was not unNewton developed the concaused as a result of pregravitational forces resulting relative positions of sun and Earth. But, recognizing the caable to predict them are two configuration of oceanic basinsuch as water depth, configbottom, and meteorological econfound attempts to understaThis situation was exacerbtechnology to observe tides conditions, lack of accurate slack of accurate time-keeping of any scientific infrastruobservations from geogrlocations.

This remained the

situation until the early tomid-Nineteenth Century.By this time moreaccurate sun and moontables had beendeveloped, better timekeeping mechanisms tocoordinate observationshad been invented, andperhaps, mostimportantly, dedicatedscientists and cadres ofengineers in organizationssuch as the United StatesCoast Survey had begunturning their energy tosolving the problems oftide observations and tidepredictions. Until themid-Nineteenth Centurythe only method for
7

attempt to obtain accurate tide observations on thewestern coast of the United States. Twocoordinated sets of observations were planned fromstaffs at Rincon Point (famous now for being closeto Pac Bell Park and the site of Barry Bonds’homerun marathon) and Sausalito. Theseobservations were conducted for a little less than amonth in late January through early February ofboth 1852 and 1853. The Rincon Pointobservations, under the direction of LieutenantJames Alden, commanding officer of the CoastSurvey Steamer ACTIVE, were praised for theiraccuracy and attention to detail. Conversely, it wassuggested that the Sausalito observations “were notmade with the same care which appears tocharacterize” the Rincon Point observations.

As a result of the short series of Rincon Point

observations, Alexander Dallas Bache,Superintendent of the Coast Survey and greatgrandson of Benjamin Franklin, was able to drawmany conclusions of importance to the navigationof San Francisco Bay. The first of these was thatthere was a large diurnal inequality between thesuccessive high and low waters of each lunar day(24 hours and 50 minutes for moon to complete arevolution about the Earth). What this meant tonavigators was that an obstruction having three anda half feet of water over it at a first low tide of theday could be awash at the time of the second lowtide of the day. This had great significance both forthe immediate needs of assuring safe passage ofcommerce but also relative to choosing a plane ofreference for soundings for charting purposes.Ultimately, mean lower low water was chosen asthe plane of reference for Coast Survey charts onthe West Coast and Alaska as opposed to mean lowwater as used on the East Coast and Gulf Coast. Ashydrographic surveys were performed for creatingupdated nautical charts of the region, the data fromthe tide gauges were used to correct the soundingsfor stage of tide and refer them to a common datum.Other information obtained from this short series ofobservations were rules for determining times ofhigh and low water relative to the declination of themoon, average range of tides between highest high

water and lowest low water, and probable greatestrange of tides in the Bay. 

Although these first tide observations

provided the mariner with a rough means todetermine the times of high and low water in theBay, it was understood that only a small inroad hadbeen made in understanding the Pacific tides.Fortunately a new technology had been recentlydeveloped. The great instrument-maker JosephSaxton invented a self-registering tide gauge in1851 which ran twenty-four hours per day withminimal human care. This gauge was not the firstself-recording tide gauge but was considered to be amarked improvement over existing instruments. Itconsisted of a float attached by wire to a gearingmechanism. The gearing mechanism drove thelocation of a pencil relative to a rotating drumcovered with a paper tide record sheet. The wholesystem was time synchronized such that the penciltracings of the risings and fallings of the tide in asinusoidal curve could later be scaled for heightsand times of various stages of the tides. This newsystem effected a revolution in both the quantityand quality of tide records acquired by the CoastSurvey. Shortly after the introduction of andpossibly as a result of this new technology, a newtidal division was established in the Washington,D.C., headquarters of the Coast Survey under CountLouis F. de Pourtales, a Swiss immigrant likeFerdinand Hassler (1770-1843), the founder of theCoast Survey. An interesting aspect of this newdivision was that Alexander Dallas Bache hiredMary Thomas as a tides computer, the secondwoman science professional in the FederalGovernment. The first was Maria Mitchell, thegreat astronomer, who had been hired by Bache todo observations for the Coast Survey in the mid1840’s and then hired by the Nautical AlmanacOffice. Not only was the Coast Survey the pioneersurveying organization on our coastlines, but it wasthe pioneer agency in hiring talented womenscientists and mathematicians to work side-by-sidewith their male counterparts. 

In 1853 Superintendent Bache sent a

dedicated tides party under Army Lieutenant

William P. Trowbridge to the of the new self-registering gauges were to be installed San Diego in California and Astoria, Oregon. Trowbridgaccompanied by Army enlisteman Andrew Cassidy and a feother observers (apparently aArmy enlisted men), who wechosen for their intelligenand devotion to duty, traveleto California via steamship Panama, proceeded over thnearly complete PanamRailroad to Panama City, ancontinued to San Francisco bPanama steamer, arriving July 1853. They established self-registering gauge in thNorth Beach area of SaFrancisco and then proceede

Self-registering tide gaug
9

to survive with an unbroken record of observationswas the San Francisco gauge. For one hundred andfifty years observations from this gauge haveassisted the mariners of the world entering andsailing from the ports of the Bay Area as well ashaving helped in the planning and construction ofall the waterfront facilities of this great port. Serendipitous Science 

Observation of tides for commercial and naval

shipping interests was and remains the primarypurpose of the San Francisco tide gauge. However,this particular gauge has a record of adding to ourknowledge of the oceans and its relationship to theEarth in general that is without peer. Within sixmonths 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 ofgreat tsunamis along portions of the Japanese coast.The tsunamis traveled across the Pacific Ocean andwere recorded as attenuated waves on the selfregistering tide gauges along the western coast.These waves were superimposed upon the regulartidal record as a series of sinusoidal squiggles. Thefirst person to recognize the significance of thesesquiggles was Lieutenant Trowbridge who wrote toSuperintendent Bache in early 1855, “There isevery reason to presume that the effect was causedby a sub-marine earthquake.” This was an amazinginsight given that recording seismographs were stilltwenty-five years in the future and that no

earthquake had ever been remotely sensed by anymeans up to this time.

Trowbridge’s insight was validated when

word of a major earthquake occurring on the coastof Japan on December 23 reached SuperintendentBache. Armed with knowledge of the time of theearthquake, its location, times of arrival of thetsunami waves at both San Francisco and San Diego(from the tide gauge records), and times betweencrests of the various waves, Superintendent Bachewas able to estimate the average depth of thePacific Ocean. Bache was familiar with the latestbasic research published by Sir George Biddell Airyand his treatise on Waves and Tides in theEncyclopaedia Metropolitana in 1849. Airy hadmathematically developed theoretical expressionsthat govern the motion of waves in canals ofuniform depth and compiled tables for expressingthe relationships between wave length, wave period,wave velocity and depth of water. Bacheinterpolated the Airy table values using his distanceestimates and the tide gauge measurements for thetheoretical tsunami wave travel lines betweenShimoda, Japan and both San Diego and SanFrancisco. Using two separate estimates for thetimes of the disturbance due to the tsunami on thetide gauge curve at San Francisco, Bache estimatedthe average depth of the Pacific between Shimodaand San Francisco to be 13,380 feet and 15,000feet. For the line between Shimoda and San Diego,the average depth was estimated to be 12,600 feet. Considering that these were estimates of theaverage depth of the Pacific Ocean using indirect

measurement and theoretical relationships ofwaves for canals of uniform depth, these numbersagree remarkably well with modern publishedvalues based upon modern measurementtechnology. Modern day estimates for the averagedepth for the depth profile from Shimoda to SanFrancisco are 15,504 feet and 15,221 feet fromShimoda to San Diego. Bache published hisestimates at a time when deep sea soundingtechnology was in its infancy, inaccuratesoundings ranging between 30,000 to 50,000 feetwere fairly common, and there was great

uncertainty concerning the truoceans.

Over the next 150 years 

gauge recorded many of thevents of the Pacific Oceantsunami waves from the greaof August 26, 1883, a few houthe Coast and Geodetic Survean extraordinary event prior details or location of the disasgauge has also survived manvicinity including the Haywarwhich did major damage to thfill areas in San Francisco, th1906, and the 1989 Loma Prie

It may seem stran

throughout the United States have been determined relative determined at Coast and Gstations. Attempts to determininland from coastal tide stati1857 when a line of levels wRiver between tidal bench maand Albany, New York. Bdistinct monuments in the cylinders with brass monumein the ground, or in the observations marks etched surfaces, are established at all to assure that there has been of a tide staff between the wland surface. After a series have been made, local meadetermined at a gauge locatiabove sea level of the bench area can be determined. It wthe first trans-continental line the tide gauge at Seattle, Waat Sandy Hook, New Jersey wthe next twenty years there additional connections made Pacific gauges. In 1929 the 1929 was introduced by the Survey which incorporated dtide stations in the United Stat
11

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 manyramifications for human occupation of coastalareas. If sea level continues rising at present rates,engineering works will have to be rebuilt ormodified; less areawill be available forhuman habitation;wetland habitats willbe drowned and lost;low-lying islands willbe inundated; andmany areas immunetoday from stormsurges caused bycoastal storms will inthe future be subjectto the walls of waterthat accompany majorwind events 

Extreme high water events during periods of

El Nino are clearly seen in the San Franciscohistorical tide record. El Nino events generallyoccur every 3 to 7 years in the Pacific Basin andare caused by the interaction between unusuallywarm sea surface currents and high sea levelsgenerated in the tropical Pacific drifting eastwardand colliding with lower temperatures in theEastern Pacific. According to historical records, themost severe El Nino events have occurred in the20th 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 eventof record in the monthly and annual mean sealevels. By analyzing the Interannual to Decadalvariations in sea level, especially from a longbaseline record like San Francisco, it=s now possible

to better understand the El Nino SouthernOscillation phenomenon and help predict futureevents. 

Sea level records from the San Francisco

gauge are indispensable for conducting climatechange research, investigations of global warmingand predicting El Nino events and the impacts of

sea level change on coastal communities. Analysisof localized sea level trends also provide insight andbetter understanding of regional tectonic changesand accompanying seismic activity. SanFrancisco's 150 years of sea level record adds a

wealth ofinformation to theknowledge ofglobal climatechange andrelative rates ofsea level rise. Infact, the SanFrancisco recordindicates that thepositive sea leveltrend (1.41mm/year) has notalways beenuniform over time

and experienced a downward trend between 1875and 1913. This sea level anomaly has also beennoted in the historical records of comparable longterm sea level records world wide.

Establishing the RecordTo obtain a continuous record of the tides in

San Francisco since 1854 has been a monument tohuman perseverance and ingenuity coupled withimprovements in the technology of water levelmeasurement. The self- registering tide gauge,established at Fort Point in June 1854, wasaccompanied by the establishment of bench marks,which are permanently fixed vertical referencepoints; in this case, the bench mark was a cross cutin the face of a large stone near the wharf where thegauge was installed. Leveling surveys wereconducted on a yearly basis between the benchmark and tide gauge to insure that stability of thegauge was maintained. Tide observers made dailyvisits to the gauge to make tide staff readings andcheck gauge time. Problems with wharf settlement

were soon discovered, but were corrected bystabilizing the area around the wharf with rock and

stone fill. In 1877, the wharf and was abandoned. A new gacross the Golden Gate at Scare was taken to preserve the through the simultaneous oPoint gauge and Sausalito gatransfer of tide staff elevationtechnique. This involved limeffect during survey levesimultaneously observing tasites at Fort Point and on the Point, a little more than a mGolden Gate, and then trthrough repeated leveling and marks at the new Sausalito gWharf at the Fort Baker mili1881, the Sausalito wharf begthe gauge was moved to a min1897, it was finally decideback across the San Franciscarea, which was just east of tsite and in the approximate vday gauge.

This era in the history 

tide gauge was also marked two major Bay Area authoNOAA ancestor agencies. It both John Muir and Jack Lowith the Coast and Geodetic SStates Fisheries Commission 

Standard Tide G
13

Tide gauge technology evolved little from

1854 until the early 1960’s. The processing of tidalrecords also changed little and was very laborintensive during these years as it required manualscaling of tidal heights and time from the penrecorded sinusoidal record. The scaledobservations were entered into record books forfurther processing. Tide predictions were computedmanually in the early years of the Coast SurveyTidal Division. However, in 1867 a new method ofcomputing tides, termed the harmonic method, wasintroduced by Sir William Thomson of GreatBritain. This method, although showing promise ofgreater accuracy in tide predictions, was impracticalbecause it was extremely labor intensive. Thomsonsolved this by inventing a tide prediction machinethat summed ten constituents of the harmonicanalysis equations in 1876. The values of theconstituents were obtained manually from theobserved high and low waters. William Ferrel ofthe Coast and Geodetic Survey designed a secondcomputing instrument of this type in 1880 whichwas operational by 1884. Reducing harmonicanalysis to a series of gears, pulleys, and levers, theFerrel machine computed times and heights of tidalmaxima and minima using nineteen constituents.The harmonic method of tide prediction has beenused by NOAA since that time. A second tideprediction machine was built by the Coast andGeodetic Survey and became operational in 1912.This machine, formally known as the Harris-FischerTide Prediction Machine, or “Old Brass-Brains” asit came to be affectionately termed, summed 37constituents and was used until the advent of digitalcomputers in the early 1960’s. This machine has along and honorable history and was used not only tocompute domestic tide predictions, but during theSecond World War computed tide predictions forworld-wide for use by our naval and amphibiousforces. Obtaining the values of the harmonicconstituents for input into the tide predictionmachine was also accomplished manually up to thetime of computers using a series of forms andstencils on the tabulated hourly heights of the tidegauge record.

In January 1976, a

digital paperpunch recordertermed ananalog todigitalrecorder(ADR)replaced thevenerablepencil anddrumrecordingmechanism.Thisinstrumentrecorded theheight of thetide at set time

intervals, usually every six minutes, by punchingholes indicating the observed times and float heighton an aluminum-backed paper tape. As the paperpunch tapes could be machine-read, this systemsped up the processing of tide records but the gaugeitself still relied on a float/wire water level sensorand gearing mechanism on the recorder thatsynchronized time and rate of advance of the paperrecord. A tide observer was also required tomaintain the gauges on correct time and to makedaily tide staff readings. 

This instrument had a life-span of

approximately one human generation as beginningin 1985, the National Ocean Service embarked on amajor upgrade of what had become termed theNational Water Level Observation Network. Thenetwork of old float/wire systems was replaced bythe Next Generation Water Level MeasurementSystem (NGWLMS) which consisted of an airacoustic water level sensor coupled with anelectronic data acquisition system. These systemshave numerous advantages including the directleveling of the water level sensor to localbenchmarks (tide observers and tide staffs are nolonger required), electronic data storage, a backup

The ADR Gauge, 

a mechanical “punch” recorder.

pressure water level sensor logger, and ancillary sensor caand air temperature, wind spbarometric pressure. The acoallowed much more accurate but what really set this system systems was the ability to tranfacility via telephone line Geostationary Operational En(GOES) data collection systedata analysis, processing, acomparison, prior to introdutidal data rolls were removeADR gauges and mailed to Service for processing. Threplaced the ADR gauge aJanuary 1996.The modern Francisco Bay region continue the nation’s economy. Apforeign trade in and out of thevery U.S. citizen, not just tcoast, relies upon the natiodelivery, exports, transportaticonsumer goods. The measurement gauges have alsthe NOAA Physical OceanSystem (PORTS), that has many major United States hFrancisco Bay. This system 

The Next Generation Water Leve
15

record of sea level rise since the turn of the century.It is one of the longest continuous records of sealevel in the world and has been used by thescientific community in research for estimatingglobal sea level rise. 

Today, the San Francisco tide gauge plays a

central role in the San Francisco Bay PhysicalOceanographic Real-Time System (PORTS) whichsupports safe, cost efficient navigation and providesshipping interests with accurate real-time tide,current and meteorological data and is an importantcomponent of the NOAA Tsunami WarningSystem. It continues to provide information criticalto maintaining and improving economic prosperityfor California and for maintaining and monitoringport activities important for Homeland Security.And finally, the data from the gauge are used toprovide water level and reference datuminformation needed for the increasing numberhabitat and marsh restoration programs in the bayregion.

Crane barge with just enough bridge clearance during transit