CUINR-R-82-047 C. 2

THEPHYSICAL OCEAXOCRAPHY OF HUMBOLDT BAY

Steven L Costa Dept.of Oceanography HumboldtState Uni versity Areata, CA 9SS21 and Dept.of Oceanography andOcean engineering FloridaInstitute of Technology AIelbourne, FL 92901

Preface It is this deficiencyin communicationsthat this sym- posiumaddresses. The fact that the symposium, at least JohnIsaacs had a marvelousgrasp of the problems in part, resultsfrom work JohnIsaacs supported and involvingall aspectsof marinescience. He wasa man encouragedis appropriateand rewarding. who did not ignorethe practicalitiesof life. He wasat onetime a commercialsalmon fisherman in Oregonand ultim.":elybecame one of theforemost oceanographers lntroducti on in moderntimes. This direction to hislife's work was spurredpartly because the scientific community could It isthe purpose of thispaper to brieflyoutline the not answerhis incisive questions about the sea in which majorfeatures of physicaloceanography of Humboldt heworked. That he recognized the problem at which Bay. Particularattention is paidto whatis known thissymposium isultimately aimed is demonstrated by aboutthe bay rather than presenting a compendium of the followingremarks taken from his introductionto "studiesthat should bedone". Hopefully, this may be thefirst volume of theSea Grant report series: ofvalue to those requiring answers orsolutions topar- ticularquestions and problems. Reference is made to "Thereare great and ever-growing funds of manyof the studies and data collection efforts presently scientificand technicalknowledge and un- availableto aid thoserequiring information based on derstandingof humankind and the planet. One thebest avialable data. A consciouseffort is madeto of themost active is theunderstanding of the avoidthe academic "insufficient data" syndrome. sea,of humaninfluence upon it, andof op- portunitiesfor human bettermentfrom its Considerationsof the physical oceanography of an resources. estuarineor lagoonalsystem involve many interactions "Knowledgeand understandingof the whichtend to bequite complex. It isconvenient to ar- oceansencompass the span between the broadly tificiallysegment the discussions intothree main areas; fundamentaland the sharplypractical. This thedriving forces acting on the system, the processes widerange of knowledgeof the seaclearly throughwhich the system responds, and finally the possessesgreat potential for importantguid- responsesof the system to thedriving forces. Each of anceof thedirections of humanactivities. Yet its these,and each of theindividual topics within these tnfluencehas been less than its potential. Most majorgroupings, must be viewed within the framework legislativeand regulatoryactions have been lit- of thephysical setting, geometric characteristics, and tle influencedby what is knownabout the sea geomorphologyof thesystem. andreflect a failureof theresearch scientist, the publicand those in industryand government to The scopeof thispaper is obviouslytoo limitedto communicate. presentevery aspect of the bay and the processesaf- "This failure of communicationbetween the fectingit. Onlythose topics considered of primary im- scientistand the public is not restrictedto portance will be addressedbelow. Other areas of marine science,of cottrse,but it is common in "secondary"importance will bementioned where ap- manyfields. It thusbecomes vital to develop propriatebut a detailedpresentation would not add sub- insight into the complexitiesof this fun- stantiallyto thepurposes of this presentation. damentaland generalproblem of our times,to engagein thoughtfullydesigned experiments, andto encourageand nurture ideas that may Morphology of the 8ay grow into meaningful bridges of com- municationacross the gulf that now cleavesac- The general morphologicalcharacteristics of Hum tion from understanding." boldtBay make it a ratherunique estuarine system. It is best described as a multi-basin coastal lagoon with limitedfreshwater input. The entirebay covers about IN: Proceedings, Humboldt Bay ~s Eureka, Gal i fornia I saacs/Kerstet ter; R/CZ-lt7! 90 squarekilometers at high tide 5 squaremiles! and from the NOS tables, but should be viewed as about 29 squarekilometers at low tide 8 squaremiles!. illustrative only and not exact. Approximately 70 percent of the bay consists of tidal mud flats exposedat low ~ater cut by a complexsystem A number of tide stationshave been occupied in the of channels. Only the EntranceBay portion of the bay bay at varioustimes. Much of this data is quite recent remains constant in surface area over a tidal cycle. 977-1982!. The reference datums and elevations of Table I details the geometricproperties of various por- these stations are shown in Table II. Note that theseare tions of the bay. Thereexists a setof aerialphotographs final datumsas received by the NationalOcean Survey taken in connection with a Sea Grant project at Hum- NOS!rather than the preliminarydatums previously boldt StateUniversity HSU! that graphicallyshow the published for exampleby Shapiro Associates!. The variations in bay area and shoreline at various tidal locationsof thesestations are shownin Figure 3. Ad- stands. ditional tidal data have beenrecorded by investigators at Humboldt State University in connection with Sea Due to the nature of the morphologyof the bay it is Grant and U,S. Army Corpsof Engineersprojects generally divided into several distinct areas. The nomenclature usually ascribed to the basins and chan- nels is presentedin Figure 1. South Bay and Entrance The noted increase in tidal range at locations in the Bay are more-or-lessdirectly connectedby a very short bay are also reflectedin historicaldata. The tide range channel. Arcata Bay communicateswith EntranceBay, appearsto haveincreased through time. This may well by the relatively long North Bay Channel, which bifur- be a reflectionof the effectsof navigationchannel im- catesat the north end. Oneof thesebranches splits once provement in the bay. Deepening these channels more Eureka Channel! around Woodley Island. The decreasesthe frictional resistanceto tidal flows. There bay is separatedfrom the seaby two long sandspits and is also someevidence of responseof meantide level to is connected to the ocean by the twin-jettied Entrance changesin sealevel during the last 70 years. Channelapproximately 1829 meters in length000 feet! and 671 meters wide 200 feet! at the seawardend.

-Waves- Driving Forces The entrance to Humboldt Bay has undergone -Tides- significant modification during the last century as a result of improvements to the harbor for navigation Humboldt Bay is a tidally driven coastal lagoon, thus purposes. Becauseof the high wave energy climate in one of the major considerations here must be a the region, waves are one of the major driving forces af- somewhat detailed summary of the tidal characteristics fecting the entrance and the immediately adjacent in- of the system. This bay is well described as an in- terior portions of the bay. Offshore wave data for the terconnected series of three distict shallow basins. This region are generally limited to that provided by hindcast compartmentalized nature of the bay results in relatively techniques. However, such data sets are still of great complex tidal responses. Simple descriptions of the value in assessing the role of waves in the evolution and tides will not suffice for many purposes and operation of the bay entrance. sophisticated data processing techniques are often required to gain a better understanding of the dynamics The Pacific northwest experiencesthe most severe of the bay. Such detailed treatment will not be dealt wave conditions, on an annual basis, in the continental with in this paper, but potential and necessary ap- United States. For the California coastline there exist plications will be pointed out. two hindcastdata sets. Until a fewyears ago the only data availablefor usewere those developed by National Marine Consultantsfor the Army Corpsof Engineers. This bay is characterized by mixed semi-diurnal tides These statistics were based on a three year hindcast which generally increasein amplitude with distance analysis 956-58! of synoptic weathermaps. More away from the entrance. Phase lags correlated with recently a far more extended data base was constructed distance from the entrance are also observed. Figure 2 for the California Dept. of Navigation and Ocean shows typical tidal elevation curves within the bay. Development by Meteorology International In- Figure 3 illustrates the variations of tidal elevations corporated based on the 'U.S, Navy Fleet Numerical . within the bay. This figure was constructed from recen- Weather Control singular wave analysis. Thesedata are tly obtained tidal data and is not taken from the provided for six deep water stations off the California published tide tables, which are only approximations. coast and are basedon the 24-year period from 1951-74. The corresponding relation with phase e.g. time of high At the presenttime thereis an ongoingdata collection and low water! is not readily available at this writing. effort by the Stateof California and the Army Corpsof Figure 3 shows the differences in phase as obtained Engineers to provide a coastalwave data base. 0CD N CL Ch D OO 0 «C $71 LL. 0 L 0 Z Z O 4l 0 I CD Q. Ch CD «C CU Z L Z W OCI X CD 0 Z K0 X 0 0 0 D

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D the primary values of this study will be the ability to precipitation in the region is strongly seasonaland verify the previous hindcast data sets. Fortunately, one sporadic storm event controlled! even during the wet of the wave stations occupied is directly offshore of season November through March!, the overall effects Humboldt Bay. of stratification are minimal.

Figure 4 presentsannual wave roses constructed from Figure6 showsthe averageannual rainfall at Eureka, the hindcast data for sea and swell. Figure 5 shows the and to illustrate the event oriented nature of the fresh- monthly averages of this data. The predominant swell is water input into the bay, the cumulative rainfall over a seen to b» from the northwest. Thc: predominant direc- particular annual cycle is also shown. Figure 7 shows tions of seas are from the south-southwest and north- the responseof the salinity distribution of the bay as a northwest. Since the jetties at thy entrance to the bay whole for a particularyear. It is immediatelyseen that are oriented toward the nothwest, the longer period there are seasonal changes in the longitudinal swell would be expectedto have the most direct impact distribution of salinity with season. However, the ver- within the entrance and in the interior of Entrance Bay. tical stratificationremains rather insignificant. The bay changesfrom a completely mixed coastal lagoon system The arriving swell is equal to or greater than I meter during the dry seasonto a weak vertically homogeneous .3 feet! in height about 31 percent of the time. stuary in the wet season. Similarly, the seasare 1 meteror higher about 57 per- cent of the time. It is of particular interest that the com- Considering the seasonalnature and limited extent of bined sea swell data not shown in the figures! indicate this input, many of the generalizationsconcerning that the combined wave height is 1 meter or greater classical estuarine behavior will not suffice. On the about 58 percent of the time. High seasand swell often average, Humboldt Bay has the appearance of an un- occur at thc: same time. The coastline experiences in- stratified coastal lagoon. Overall it might appear that cident open ocean swell from winter storms at the same the effects of fresh water input can be ignored. Further time that locally high seasare generated. The statistics consideration, however, shows that at localized places are not such to make the above statements exact, throughout the bay the effects of such input can be ex- however they do appear to be qualitatively correct. tremely important. These localized effects, particularly on processesinvolving sedimentation rates and patterns, Examination of the data on a monthly basis shows nutrient influx, and productivity, can be of importance that the predominant incident swell arrives from a west- to large areas within the bay. One such localized area northwestc;rly direction 80-300 degrees! during Oc- where density stratifications are important will be tober through April. This is also the period of the examined as an example. highest and most frequent occurrence of swell. May through August exhibit frequent occurrencesof local seas from the north. In the months November through -Wind- March the seas arrive from the west-southwest. As will be seen later the direction, intensity, and frequency of The nature of Humboldt Bay also admits wind as a the waves impinging on the entrance to Humboldt Bay major driving force. Approximately 70 percent of the have dramaticaily affected the evolution of Entrance bay consists of very shallow areas, much of which is Bay in recent years. generally exposed at lower low water. The effects of wind blowing across these areas can be significant in a number of ways. The surface currents in the shallower -Density Differences- portions of the bay can be influenced by the wind, despite the overall dominance of the tidal action in the In addition to waves and tides there are other driving bay. There are particular reachesin the bay with a fetch forces to be considered. The most obvious of these is the distance over water which the wind blows! long the density difference in the water column resulting enough to allo~ the formation of locally generated from fresh water inflow. The drainage area of Hum- waves two to three feet high, especiallyduring southerly boldt Bay is only about 805 square kilometers 33 or southwesterly storms. The action of the wind can be square miles!. Point source runoff to the bay is via Elk quite important in redistributing dissolved and suspen- River, Jacoby Creek, FreshwaterEureka Slough, Mc- ded material within the bay.. Unprotected bank erosion, Daniel Slough, Mad River Slough, and other smaller particularly on the remaining sali.niarsh areas is greatly sloughs and creeks. The total annual fresh water input enhancedby the combination of varying water level and to the bay is only on the order of the tidal prism. The wind induced wave action. tidal prism is the amount of water exchanged between the bay and the ocean over a half tidal cycle.! The winds in the vicinity of Humboldt Bay have Therefore, the overall circulation of this bay is seasonal characteristics very much like the wave data dominated by tidally driven flows, modified by the presented above. Figure 8 presents an example of a bathemetry and the wind field over the bay. Since the wind rose for the area. Table III is an example of the Ilt fit III Cl 0 O I 0 a < ,8 a -r- tlt ~Y I

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13 seasonalvariations in wind speedsand alsopresents the at any point in the futurebecomes extremely difficult. maximumwinds that have been observed in thepast. Simplyto predictthe astronomicalcomponent of the tides requires sophisticatedmathematical treatment. Mher Driving Forces- Fortunately,our ability to do this is presentlywell developedand publishedtide tablesare availableworld- Thephenomena mentioned above are consideredby wide. the author to be the most important of the myriad driving forces operatingon this bay. Without doubt, A "tidal epoch"is approximately19 years in length. manyother such forces can be identified and play a role Therefore,accurate predictions of the tidesrequire 19 in the behaviorand responseof the bay. Theseinclude years of past data. Most people familar with Humboldt solar heating, variations in cloud cover, a host of an- Bay have recognized significant deviations from the thropogenicinfluences, and so on. Other individuals, published tide tables. Some of these are due to dependingon their particular interestsmay considerany meteorological effects that cannot be forecast. of theseothers of "primary" importance. The par- However,there is anotherelement in tidal predictionsin ticular forcing functions chosen here do however, the bay which is not generaHyrecognized. The represent the minimum set that must be considered to pubHshedtid» tables are based on a rather short record constructthe physicalframework, within which, the bay of tidal observationsat SouthSpit takenin the early operates. In this sense,they are given the appellation 1900's see Table II! andthen tied into CrescentCity to of "primary". the north. It is not unexpectedthat the presentday tide tables leave something to be desired. The National The influenceof man is, of course,an important and OceanSurvey currently occupiesa tidestation on North often overriding force on this and most other estuarine Spit, and the data collected from this station should systems. The ways in which such influence interacts eventuaHybe available to allow more precise tidal with the natural forces at work add an additional degree predictions in the bay. of complexity to the analysis. Some of the more im- portant affects are considered in a separate section of The prediction of waves is a much more statistical ef- this paper. fort; that is, wecan only determine what will happenon the average.Even this is a difficult process. It is often of more interestto be able to predict how a particular Processes wave climate will affect coastlines and coastal struc- tures. An excellentexample of this is the ability to The process through which the driving forces act to determinethe rate at which waveson the adjacent produce the resultant responsesof the bay are of the beacheswill move sand along those beachesand into the most critical interest to the scientist and engineer. An entrance of the bay. In addition we would like to know understanding of the underlying physics of these underwhat conditionsthe sandwill bypassthe entrance processes allows an understanding of the ultimate and when it will actually enter the entrance channel and behavior of the system. More importantly, such un- degradethe depthavailable for navigation. derstandingallows the prediction of how the bay will respond to changes induced by both natural evolution This is a particularly difficult problem for Humboldt and man's activities. Such predictionsare absolutely Bay. There exist few estimates,and even fewer good required to engage in wise management of the natural ones, as to how much sand is transported along the resources of the bay, particularly in view of the com- beaches. Recent work has indicated that the Humboldt petingand often conflicting interestsof variousseg littoral cell is somewhat different than the classical men ts of the population. situationsthat are well studied e.g. southernCalifor- nia!. The seasonalnature of the waves incident on the coast, the amount of sand introduced by the nearby Unfortunately, a complete description of these rivers, the identifiable sinksand transport pathsof this processes,even if theywere well understood, is well material, and a host of other factors must be con- beyondthe scope of thispaper. A fewexamples of the sidered. importanceof effortsto providean understandingmust suffice here. The processby which fresh water input to an estuary are better understood than the role of waves discussed TheabiVity to predicttides and tidal currentsneeds no above. Again, however, Humbo/dt Ray is somewhat 'ustificationto anyoneat all familiar with the marine unique and does not fit any of the classical schemesof and coastalenvironment. The tidesare generated by t he analysisvery well. We do find that this processcan be gravitationalattraction of thesun and moon and the adequatelydescribed under the correct assumptions characteristicsof their positionswith respectto the Ear- basedon actual observationswithin the bay to a good th. But sincethere are literally scoresof astronomica1 degree. The problems in this area are more of factors,as well as the geographic features of the planet, inadequate observations than those of inadequate to be considered,the predictionof what the tideswill be theory. TABLE IE. MONTHLY AVERAGE AND MAXIMUM WINDS

MEANWIND SPEED PREVAILING 5eIXUM WIND SPEED MPH! DIRECTION MPH I RECTION

JANUaRV 6.9 SE S FEBRUARY 7,2 SE 48 SW IIARCN 7.6 48 SW APR IL 8.0 49 N ttav 7 ~9 40 NW JUNE 7 ' 4 N 39 NNWNW Jucv 6 ' 8 35 N AUGUST 5.8 34 N SEPTEMBER 5.5 44 N 0CTOBER 5,6 NSE N 56 SW NOVEMBER 6.0 43 S DECEMBER 6.4 SE 56 S ANNUAL 6,8 N 56 SW

LENGTk OF RECORD YRS! 54 67 67

FROMU.S. DEPARTMENTOFCOMMERCE, 1977!

INCLUSIVE DATES MILES PER HOUR July I939- DecI942 I - 3,4- l5, l6-3I TOTAL OBSERVATIONS 9002 Hour'Iyoverage surfoce winds MPH!, percentage frequencyof occurrence ofter U.S. Army Corps of Engineers,1956!. FIGURE 8

15 The commentsin the aboveparagraph generally ap- Anchored streamersplaced across the entranceto ply to eachof the other processesthat may bc of South Bay haveindicated that the inflow to this basin ,primaryor secondaryimportance in the bay. Each from EntranceBay beginson the easternside of the estuarine system is unique, generalizations are channelwhile an ebb current still existson the western dangerous,and experience with theindividual system is sideof thechannel. The timing of this flow appearsto invaluable. be a fairly well definedfunction of tidal range. The phenomenonis a resultof the larger massof watereb- Responses bingfrom Arcata Bay but beingimpeded by thelong narrow North Bay Channel. The above situation has current Patterns- been observedand documented,but at this time the quantitativeimportance of the flow patterncan only be Of most direct interest to the non-academiccom- guessed at. munity are the results obtained once the data on the -Longshore Transport- drivingforces is analysedto thepoint wheredescriptive andpredictive output is obtained.Again, the scopeof The transport of sandalong the beachesadjacent to this paperlimits the discussion here to a fewmain topics the entrance to the bay is of critical importance to the of general interest. Concentration will be focused on viabilit. and operationof Humboldt Bay asa port. It is recentdevelopments in the understanding of howHum- this material that forms the outer bar and inner shoal at boldt Bay operatesas a naturalsystem. theentrance. This is alsothe material that findsits way into thenavigation channel and hmits the available dep- Theoverall current pattern has been the subjectof a th. Thus, it is of some interest to determine how the number of investigations. Figure 9 illustrates the material moves along the beaches. general ebb and flood patterns. It is obvious that flood and ebb dominantregions exist throughoutthe bay. In the past it has always been assumed that the net Thesefeatures of the circulationare very iinportant average! annual longshore transport af sand was from whenattempts ar» madeto predict the distribution and north to south at about 380 thousandcubic metersper ultimate fate of dissolvedand suspendedsubstances year 00 thousand cubic yards per year!. The estimates within the bay. of the amount of sand delivered to the northern beaches do not support this assumptian. The evidence,in fact, There have been a number of studies of detailed cir- showsthat the Eel River to the south is the main supply culations at localized placeswithin the bay. At first of sandto the Humboldt beaches. Sincemost of this thought it might seeminconsequential to considerdif- material is delivered during times of very high river ferences i.e. net currents!that are only on the order of discharge,this raisessome important questionsabout centimetersper secwhen the major flows are on the or- damming and diversion of Eel River water that have not derof metersper sec. However,the followingexample been adequatelyaddressed.! It appearsthat the tran- should adequately demonstrate the critical nature of sport of sand in the winter is from south to north, some of these small scale features. driven by the high locally generated seasthat exist at this time Figure12!. A return flow to the south prevailsin Recentinvestigations have reinforced the hypothesis the summerbut at a smallerrate of transport and in a of a net circulation within EntranceBay that is narrower surf zone. The cyclic migrations of the mouth describedin Figure10. Oneof themost stiking features of the Mad River and a similar type of behavior shown of this circulationis the ability of waterexiting North for the mouth of the bay before jetty constructionsup- Bay Channel to work araund the eastern shore of En- port this idea. trance Bay and enter South Bay. This means that ac- tiviesin the northernparts of HumboldtBay can affect During the winter months, with a wide surf zone the water massesof the extremesouthern part of the dominated by steep waves, a portion of the material is bay. trapped in the entranceand bar channelsto the bay. During the milder summerconditions the majority of To further investigatethis phenomenona numberof the material bypassesthe bay entranceby meansof drifter and streamer studies were accomplishedthat movement over the outer bar. The extensive dune fields shawtwo important aspectsof this circulation. Thereis of North Spit appearto be an important sink of beach a fairly well defined location at the southern end of Nor- sand. The relativesizes of North and Southspit appear th Bay Channel that determines which water tnasses to be a consequenceof the seasonalnature of the driving might be expectedto fallow a trajectory that will result forces waves! rather than directly indicative of the in their introduction into South Bay. Water from fur- direction of sediment transpart. The tentative con- ther north than this point is subjectto mixinglaterally clusion from examination of all of the data is that the acrossth» entire channeland only relativepredictions'a. net transport is from south to north and at a rate equal to its fate can be made. Someof thesedrifter pathsare to or greater than that previously assumed for this shown in Figure 11. region. R RENTS ENTS

RENT Y,CA K, i964!. HYPOTHETICAL NET CIRCULATION }N ENTRANCE BAY A FTER EBBE SME YER ET AL, 1980!

FIGURE IO

18 DRIFTER I.D. x RELEASE POINT a&i <. 2 EAST o¹3 Z¹4 <> ¹5 MID o&6 6 ¹7,8,9-WEST

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MHW DRIFTER PATH CHANNEL ~ -- SEPARATION BETWEEN NORTH BAY AND SOUTH BAY WATER MASSES

EBB CURRENT DRIFTER TRAJECTORIES IN EhlTRANCE BAY, HUMBOLDTBAY, CA 3 AUG FROM DIEBEL 8 COSTA, 15 MAY FROM EBBESMEYER,ET AL!

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2G -Wave Patterns in Entrance Bay- cupied in Mad River Slough during the rainy season Figure 1S!. One set of data were coHectedafter ap- The incident oceanwaves impinging on the coast at proximately two weeks of no rain. Another set of data the entrance to the bay, of course, provide energy to the wer» coHectedjust after a period of heavy rain fall. It interior of the bay. This is naturally limited to the En- was found that following an infusion of fresh water this tranceBay region. Figure13 is a diagram,gleaned from arm of the bay sequentially displays the entire range of aerial photographs,of the wave patterns introduced. classicalestuarine types. InitiaHy it behavesas a highly Note that the Entrance Channel acts as something of a stratified salt wedgetype, becomespartiaHy mixed, then filter to the oceanwaves arriving at the coast. The depth verticaHyhomogeneous, and without further input of of the channeland over the bar prohibits wavesof water takeson the coastd lagoonnature of the bay asa more than a certainheight from enteringthe bay. In a whole. similar mannerthis also limits the periodsof the waves that are to be found in EntranceBay. For a ratherwide range of incident ocean waves oiie finds a much more This descriptionis oversimplified, especidly as the compact range of waves. timing and intensity of rainfaH modifies this progression. But it does indicate that the material There is obviously a great deal of information on a welshedfrom the adjoining pasture land is not released diagram such as Figure 13. A few of the more im- into the main body of the bay immediately. The tran- portant points are describedhere. Note that the region sient nature of the slough allows the dissolvedand near Point Humboldt is a dividing line betweenwaves suspendedmatter to be releasedinto the bay over an ex- tending to transport material either south toward King tended period of time. This is demonstratedby the Salmon or north toward Elk River. Most of the wave salinity history of the bay over an annualcycle as recor- energy entering the bay is seen to act to transport ded by other investigators at Humboldt State Univer- materid to the north, and hasprovided the mechanism sity's OceanographyDepartment. Figure 16 iHustrates for building Elk River Spit. However, a significant such a cycle, amount of energyis still availablefor transport to the south. This hasbeen dramaticaHy demonstrated by the Flushing times in the bay as a whole have been recent erosiond events along the King Sa1mon shore variouslyestimated from 7 to 40 tidal cycles, Part of the line. Another point of interest is the reflected com- reason for the wide range in estimatesis due to the com- ponent of wave energy from the eastern shoreline plex nature of the bay and the interests of the various in- toward back acrossthe bayto North Spit. This hascon- vestigators. Displacement calculations have demon- tributed to some serious shoreline erosion at this strated that it is possiblefor a water parcel to travel location which, at first glance,would appearto be well from the bay entranceto the extremenorthern part of sheltered from wave attack. Arcata Bay during a tidal half cycle of sufficient range. Thus it is possiblefor marinewater to travel to any part There is another, until recently unrecognized,wave of the bay on a single tidal cycle, with the converse also driven phenomenain Entrance Bay of considerable being true. Obviously, the dispersion and mixing theoretical and practical interest. There exists a processesare being ignored here for simplicity. There is mechanism by which energy provided by incident ocean some evidence that the bay is compartmentalized into waves with periods in the range of 6 to 20 secondsdrives distinct water massesthat mix relatively slowly. Any a much longer period oscillation within this basin with estimate of flushing times must be viewed with extreme periods of from 1 to 6 minutes. This is a sloshingor caution. seichingof the waterin thebasin with amplitudeson the order of a foot. Such action has been recorded and documented by a group of graduate students from HSU, Figure 14 shows records of this occurrence. The One of the most difficult points to address when figure showsthe frequencyat which oceanwave energy estimating flushing times are the seasonaltransients of as recorded offshore is approaching the coast and the the type discussed above. The author estimates the frequency bands in which the wave energywithin the completeflushing time of Mad River Sloughto be about bay was recorded. Both the filtering action on wave SStidal cycleswhen the stratification cycle mentioned period and the presenceof the longer period seicheis above is considered, Arcata Bay may have a flushing easilyseen from information presentedin the figure. time much lessthan this done, but the long term in- fusion of material from the adjacentsloughs during the -Seasonal Transients- rainy seasonwould makeany such cdculation about the basin as a wholerather meaningless.That is the small Localized effectsof eventoriented fresh water input sloughs would continue to feed dissolved material in- into the bay canbe of importanceas mentioned earlier. troducedby runoff into Arcata Bay on everytidal cycle Under the author's direction, students at HSU have in- long after the basin would have eliminated such vestigated one such area. A number of stations were oc- materialif it had beendirectly input aHat one time.

A PLOT OF THE PRESSURE TRANSDUCER DATA FROM 3/I4/8I

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Record showing seiche in EntranceBay ofter Hathoway and Land- steiner, l982!. FIGURE l4 EA: m~ MHW! m MLLW!

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STATION LOCATIONSIN MAD RIVER SLOUGH AFTER COSTA,I98I!.

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FIGURE l6

25 -Response to Wind- was made narrower than its natural state, the currents tended to scour it to a much greater depth. This is The responseof the bay to wind is as yet essentially graphicallydisplayed in Figure 18. Thesechanges had unstudied, It is possible to predict the characteristics of the effect of focusing wave energy and allowing more wind wave generation within the bay using standard energy into the bay. The extensive breaker flats disap- engineering practices. This requires only the wind direc- peared and in their place the infamous outer bar was tion, intensity, and duration. The effects of wind on formed. Although this bar does absorb some incident circulation and sediment redistribution are as yet un- waveenergy its main effect is to actually focusincident documented. The author believes that this is the next wave energy, particularly the notthwest swell, at the logical step to be addressedin the overall study of the seaward end of the jetties. This has the effect of in- oceanography of the bay. creasing the amount of energy entering the bay.

The recent prototype data collection program by the The complexities and interactions inherent in the ef- Army Corps of Engineers has provided the data to begin fectsof the navigationimprovements on the featuresof such a study. Synoptic current, tide, and wind data at Entrance Bay are readi1y seenby consideration of selec- locations throughout the bay were collected by in- ted examples. The developmentof Elk River Spit did vestigators at Humboldt State University. Once these not brome apparent until the early 1930's. data are reduced and processed it will be possible to Throughout the next ten to fifteen yearsthe spit grew significantly extend our knowledge of the ba; in a num- rapidly. Sincethere was no obviousgrowth of this spit ber of areas. The aspects of wind driven circulation until 40-50 years after the initial navigation im- superimposed on tidally driven flows are of particular provements,this could be taken to indicatethat the two interest. The stations at which data on current speed events are unrelated. However, closer examination of and direction, temperature, salinity, wind speed and historical charts shows that there existed an eastward direction, and tidal elevation will soon be available are channel, up to 30 feet deep in some places, that had to shown in Table IV. be completely fille before material was availableto build the spit. Figure 18 illustratesthe evolution and filling of this channel by following changes in the 18 Effects of Navigation Improvements foot depth contour.

The Entrence Bay portion of Humboldt Bay has been in a state of rapid evolution for many decades. Since Figure 19 illustrates the extent of the changesin the the initial navigation improvements at the entrance to bathymetryof the southernpart of EntranceBay. This the bay in the late 1800's the changes observed in En- figure shows a number of historic profiles at the trance Bay have been dramatic. There is httle doubt locations shown. The erosion of the shoreline in the that the orientation of the jetties and the subsequent Buhne Point region has been an ongoing processfor deepening of the navigation channel have been respon- many years until halted by the constructionof rock sible for both the rate and direction of the evolution of revetmentsalong most of the easternshore of Entrance Entrance Bay. There is no apparent reason to suspect Bay. The recenterosion at King Salmonis simplyan ex- that the recent erosion in the Buhne Point area is not tension of the patterns shown here. closely linked to the overall changes in Entrance Bay in the past. Afterword The premise that the navigational improvements to the Entrance Channel are the causitive factors in the The precedingdiscussions have attempted to give an processeswithin this portion of the bay is based on a overview of the physical oceanogrphyof Humboldt simple observation. Examination of available charts of Bay. What is known about the bay, rather than what is th» location shows that prior to any improvements to yet to be investigated,was stressed.The presentation the bay the entrance channel appears to have been fixed was brief by necessity, and incomplete in many details. in its general location but its orientation was extremely The author aknowledges his bias toward the particular variable. An example is shown in Figure 11. The in- aspectsof the bay of personalinterest.' terior of the bay was well protected from incident waves by extensive breaker flats on the seaward side of the en- It is customary to present a list of referencesused. In trance. There was no mechanism for focusing waves this case the list would be more extensive than the through the channel and into Entrance Bay. The wave presentation. The author acknowledgesall those in- energy that did enter the bay was greatly reduced by the vestigators who have contributed to the body of presenceof these breaker flats. knowledgeabout the bay, but defers a formal list of references. The reader can consult the previously Construction of the jetties fixed the orientatation of publishedbibliographies and literature surveyson the the Entrance Channel. Furthermore, since the channel bay and adjacent regions for more information. Ap-

26 TABLE IK. PROTOTYPEDATA COLLECTIONSTATIONS

STATION R P N LaS~IIDZ LauZIIDE MULTI-METERS

MADRIvER SL0UGH 124 08'56" 40 51'55" C2 MID ARCATABav 124 08'04" 40 49'55" C3 SANDACHANNEL 124 10'41" 40 48'52" C4 WODDLEY-GUNTHERCHANNEL 124 09'39" 40 48'48" C5 NORTHCHANNEL EUREKA 124 11'21" 40 47'48" C6 NORTHCHANNEL - BUCKSPORT 124 12' 0" 40 46'28" C7 IIORTHSPIT COASTGUARD! 124 13'l8" 40 45'29" C8 ENTRANCECHANNEL 124 13'50" 40 45'18" C9 SOUTH SPIT 124 13'24" 40 44'56" C10 ENTRANCEBAY 124 12'54" 40 45'01" C11 SOUTHPORTCHANNEL 124 13'43" 40 44'l4" C12 FIELDS LANDING 124 13'28" 40 43'20" C13 IIOOKTONCHANNEL 124 13'30" 40 42'21"

TIDE GAGES

Tl Se RivER SLDUGH 124 08'56" 40 51 55 T2 EUREKASLOUGH 124 08'31" 40 48'25" T3 SANDACHANNEL LP DOCK! 124 10'45" 40 49'04" T4 IIIORTHCHANNEL - EUREKA 124 ll'll" 40 47'44" T5 ELK RIVER SLOUGH 124 11'44" 40 46'21" T6 FIELDS LANDING 124 13'21" 40 43'25"

ANEHOHETERS Al WEATHERSERYIcE 124 09'46" 40 48'10" A2 COASTGUARD STATION 124 13'00" 40 46'01" A3 PGaE 124 12'39" 40 44'30"

MULTI METERS: SAI INITY. TEHPERATURE.TURBIDITY. CURRENTSPEED AND DIRECTION ~ STATION NOTOCCUPIED ~ B = BUOY STATION~ S = STANDOFFSTATION NAY AID!

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OOO.OO c OQOQO 4 OQOOO D I OO CD ! ~n!OBO Quo< V O 'CD CII 30 propriarecredits are given for eachof thefigures and International Technology, I rd. l9!. Bathymcri ii irrr- tables presented in the text. vey-Humboldt Bay, Eureka, CA, US Arm! 'or!ls Lr! Fngineers S.F. I>ist., Co»tract No. DACWt-!t l- '- 0043.

Johnson, J.W. 1972. Tidal inlets on the Calit'orrri;r, Acknow edgemenrs Oregonand WashingtonCoasts. Hydraulic Enginccriir!. Lab., UC Berkeley, Tech. Rept. No. H EL-24-12. Many peopleand agenciesare responsiblefor con- tributionsto the increasingknowledge of Humboldt Melvin, E.F., and J.E, Pequegnat 1981. Unpublished Bay. An exhaustivelist wouldviolate the space data. HSU Dept. of Oceanography. limitationsof theseproceedings. The risk of unin- tentionalomissions is also forbidding. However,of Meteorology international, lnc. 1977. Deep-water wave particularnote is the San Francisco District, Corps. of statistics of the California coast Station l!. Dcpr. o! Engineerscurrent data collection program, and the past Nav. and Ocean Development, Sacramento, CA, support by NOAA, National Sea Grant College Program, Dept. of Commerce,under Grant 04 8 M01 ~ National Ocean Survey, NOAA, 'fide Tables, 1980. 189and the State Resources Agency, Project RCZ41 High and low water predictions, west coast of North t'..rcugh the Califorttia Sea Grant College. and South America.

National Ocean Survey, NOAA. 1981-82. Preliminary and final tidal datums for Humboldt Bay. Personal Communication, Mr. Ray Smith, Rockville, MD. Referencesfor Figures O' Brien, M.P. 1971,Equilibrium flow areasof inletson Bodin,C. 1982. Longshoreand seasonalvariations in sandy coasts. J. Waterways and Harbor Div. Proc. beachsand, Humboldt Co., CA. Implicationsfor bulk Amer, Soc. Civil Engr, Vol. 95, No. l. longshoretransport direction. MS Thesis,Humboldt State Univ., Arcata, CA. Shapiro and Assoc., lnc. 1980. Humboldt Bay wetlands review and baylands analysis. US Army Corps ol Costa, S.L. 1980. Unpublished data. UC Sea Grant Engineers, SF Dist. Contract No. DACW-07-78-C- CollegeProgram, Project No. RCZ-47. 0082.

Costa,S.L,1981. Circulation in a seasonallytransient Skeesick, D.G. 1963. A study of some physical- estuary. Sixth Int. EstuarineRes. Conf., E.R.F., chemical characteristics of Humboldt Bay. MS Thesis. GlenedenBeach, OR. Abstractin Estuaries4!!. HSU, Arcata, CA.

Costa,S.L.,J.W.Stork, C.E.Diebel, and M.E.Lan- Stork, J.W., S.L. Costa, M. Landsteiner and C. Diebel, dsteiner. 1981. Wastewaterdischarge windows for 1982. Humboldt Bay prototype data collection. Draft HumboldtBay,CA. Final Rept, to Brownand Caldwell Rpt. US Army Corps of Engr. SF Dist. Contract No. ConsultingEngineers, Eugene, OR. DACW4-81-C-0029,

Diebel,C.E.,andS.L. Costa. 1980.Unpublished data, Thompson, R.W. 1971. Recent sediments of Humboldt UC SeaGrant College Program, Project RCZX7. Bay, Eureka, CA. Final Rpt. to Petroleum Research Foundation. PRF No. 789-G2. Divisionof NaturalResources, Dept. of PublicWorks, HumboldtCounty, CA. Aerial photographfiles of US Army Corps of Engr. and War Dept.! Historic Humboldt Bay. maps and charts of Humboldt Bay. HSU Library, Humboldt County Collection. Ebbesmeyer,C.,C.E.Diebel,S.L. Costa, and L. Hin- chey. I980..Tidallypowered exchange between two in- US Army Corps of Engr, 1956. Beacherosion control terconnectedshallow bays. Unpublished manuscript. report. Cooperative study of Humboldt Bay Buh»c Point!, Pacific Coastline of California. Gast,J.A., and D.G.Skee:iCkk.1964. The circulation, water quality, and sedimentationof Humboldt Bay. US Army Corps of Engr. 1976. Humboldt Harbor and M.S. Thesis,Humboldt State College, Arcata, CA. Bay, CA, NavigationImprovement.

Hathaway,K., andM.C. Landsteiner.1982. A studyof US Dept. of Commerce, National Climatic Center. seiching in humboldt Bay, CA. Unpublished Various Years!. Local climatologicaldata - annual Manuscript. summary, Eureka, CA Asheville, N.C.