Seymour, R J

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UC San DiegoOceanography Program PublicationsTitleWave Observations in the Storm of 17-18 January 1988Permalinkhttps://escholarship.org/uc/item/1pb196f4JournalShore & Beach, 57(4)AuthorSeymour, R JPublication Date1989-10-01Data AvailabilityThe data associated with this publication are available upon request. Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaWave Observations in the Storm of 17-18 January, 1988 BY RICIIARD J. SEYMOUR Scripps Institution of Oceanography, UCSD La Jolla, CA 92093 INTRODUCTION WAVE DATA OUTHERN CALIFORNIA, BECAUSE of the com- plexity of its maritimc borderlands, its rclative sus- ceptibility to wave attack from major storms any- where in the Pacific Basin, the economic significance of its developed shoreline and offshore petroleum production fa- cilities, and the wisdom and foresight of a few government sponsors, is blessed with perhaps the greatest concentration of wave measurement devices of any comparable area in the world. Therefore, although the Great Storm of January '88 was small in area, it was still possible to obscrvc some of the structure in its wave fields as it developed andmoved ashore. This paper will report on the observations and will consider some aspects of their characteristics. WAVE MEASUREMENT STATIONS In all, 21 stations between San Francisco and the border with Mexico reported the storm. Five of these were buoys operated by NOAA as part of their data gathering in support of weather forecasts andothcr scrviccs. Theremaining 16 are opcrated by Scripps as part of the Coastal Data Information Program (CDIP) and sponsored jointly by the Coastal Engi- neering Research Center of the U.S. Army Engineers and by the California Department of Boating and Waterways6. Although the CDIP data gathering network was unaffected by the storm, thePacific Telephone lines on which it depends went out close to the peak of the storm, resulting in a data gap of several hours. A utility power outage at Impcrial Bcach kept that station down throughout the storm. Thelocations of the 21 active measurement sites are shown in Figure 1. Of the CDIP stations, eight of these (Mission Bay en- trance, Scripps Pier, Del Mar, Oceanside, San Clemente, Sunset Beach, Marinaand Santa Cruz) are nearshore stations (average depth about 30 ft) and are sheltered in various degrees by the offshore islands or headlands. The Mission Bay Buoy, although in deeper water, is similarly sheltered. This limits the usefulness of these stations for this study. The remaining 7 stations, either in deep water or on open coast- lines, have been selected for their generality in characteriz- ing the storm (although the Santa Cruz Canyon buoy, in deep water, is sheltered by the Channel islands). The deep water NOAA buoys (CatalinaRidge is partially sheltered), plus the 7 selected CDIP stations provide the mosl general data on the storm. Figure 2 shows the growth and decay of the significant wave height measured at the three stations in the vicinity of the Channel Islands. The gap in the CDIP data caused by the loss of telephone service is clearly evident. The highest measurement at Begg Rock (33.4 ft) was the maximum measurcd by any of the stations during the storm and the energy at this point was peaked at a period of about 15 s. Because of the similarity in the rise and decay between the Begg Rock buoy (essentially open ocean exposure) and the nearby and partially shadowed NOAA Catalina Ridge site, the peaking of NOAA buoy an hour or so after the start of the data gap, and the rapid riserate of the Begg Rock significant height all suggest that the actual peak weight may have been significantly higher than recordcd here - pcrhaps as great as 36-38 ft, with the peak period near 17 s. If so, this would imply a one-in-one-thousand wave height of about 75 ft! This assumption is based upon a theoretical distribution of wave heights for a storm in which conditions change very slowly. It would not necessarily be the best model for this rapidly changing event. Figure 3 shows the build up and decay of wave heights near Point Conception. The maximum significant height Figure 1. Wave measurement stations that reported during the storm of 17-18 January, 1988. SHORE AND BEACH HOUIZS AFTER MIDUIGIIT 1G JANU.4RY I Figure 2. Wave heights near the Channel Islands during the storm. 7 5 10 15 20 25 30 35 40 H O U R S  AFTER MIDNIGHT 16 JANUARY Figure 3. Wave heights in the vicinity of Point Conception during the storm. Figure 4. Wave heights in Central California, between Monterey Bay and San Francisco, during the storm. 30 7 5  - 4 +. - 8 20- 3: W > 2 P 5 5- 2 ti: z 0 II) 10 5 d C a t a l ~ n a  Ridge ,Santa M a r l a  5 3 u -  3 W C2 2 5 -  Z 3 2 0 H a r v e s t  X Sdri F r a n c ~ s c o  D ~ a b l o  C a n y o n ,  15- I 34 0 35 0 36 0 37 0 NORTH 1,ATITIJnE - NOAA SANTA CRUZ + NOAA SAN FRAACISCO - * NOAA hlOUTEREY - - FARALLON ISLAND NORTH MONTEREY - I 0 5 10 15 20 25 30 35 40 - Figure5. Maximum growth rates of significant wave height, averaged over 3 hour periods, from a number of open coast sites. H O L R S  AFTFR MIDNIGHT 16 JANUARY OCTOBER 1989 measured in this region was 30.4 ft at a peak period of about 17 s. In Figure 4, the heights from the 6 reporting stations in Table 1 the ~ o n t e i e ~ / ~ a n  Fr cisco area are shown. ~ h k  maximum Winter Maximum Maximum height here was the same-30.4 ft- but was peakedat only Season Velocity Squared Acceleration 15 %The intensity of the winds and, very probably, the (ft2/sZ) existence before the storm of long period swell (about 17 s) (ft/s2) of considerable height (about 10 ft), caused a very rapid increase in the significant wave height. Figure 5 shows the maximum rise rates (3 hour averages) for several open coasl sites withBegg Rock measuring about 5 ft/hr. This compares with a maximum growth rate of about 1 ft/hr at this same site during the 27 January, 1983 storm when the significant height reached 24 ftl. It should be noted that the pcak wave generation zone was far removed in space and time from the Begg Rockmeasurement site in 1983, but wasprobably very close in 1988. A better comparison can be made with rise rates for the 1 March storm, the largest in 1983. Earle et a13 shows, in the generation area about 1500 miles offshore, an average rise rate of 4.6 ftlhr in the 3 hours prior to the peak significant height of 39 feet. The growth of the '88 storm as a function of latitude is shown schematically in Figure 6. STORM RANK tion (proportional to the inertial force) were about twice as great in the '88 storm as the worst observedduring the'82-'83 season. CONCLUSIONS It is clcar from thesc wave observations that this was an exceptional event, far exceeding any ocean storm in recorded history in this area. As pointed out by Strange et a1 in this issue, the presence of pre-existing swell resulted in wave periods of much greater length and much larger significant heights than can be predicted by any wave generation model that starts, as the present models all do, from an assumption It is of interest to try to rank this storm in the long term of a flat ocean. This may be the most important single wave climate of southern California. The record of storm observation about the Storm of '88 if it leads to successful wave observations along this coast is less than 100 years in research on wave generation with pre-existing swell. length, so that very little can be said about return periods. Howcvcr, it is possiblc to make some conjectures based upon what is known. Seymour et a15 reportcd on the major storms in the period 1900-1983 in this region. Figurc 7 shows a distribution of extreme significant wave heights taken from that study, as reported in Walker et a18. Moffatt & Nicho14 calculated another return period estimate for various wave heights applicable to the southern California area and this has been plotted in Figure 8. The January, 1988 storm has been shown on both dismbution lines. The return period implied by each of thesedistributions is much greater than 200 years, perhaps as much as 406500 years. Because projections beyondabout 200 years would be totally unwar- ranted, based upon the length of the data record, a recurrence interval of not less than 100-200 years for a storm of this magnitude appears reasonable. Two recent studies of the January '88 storm further illustrate the intcnsity of this event. Seymour et a? describes the extremc damage to the Point Loma kelp forests, much greater than the combined effects of thc six major storms of 1983 (the largest previous recorded). Dayton et a12 dcals with damage to geological structures at great depths (up to 100 ft) offshore of San Diego that also greatly exceeded that in the 1983 season. Table 1, taken from the latter study, suggests the likely reason for this increased destructiveness. It shows that, at a nominal depth of about 60 feet near the entrance to Mission Bay, both the maximum velocity-squared (proportional to the drag force) and the maximum accelera- Figure 6. The growth of the storm along the coast. The vertical dimension is relative significant wave height, plotted against Pacific Standard Time on 17 January, 1988, and north latitude. SHORE AND BEACH Figure 7. Return period estimation function tor major 7. storms of various significant wave heights from Walker et a/., 1984 The January 1988 storm is indicated with an asterisk. 8. 35 30 - i u -& 25- 0 W z e 2 4v 5 20- Z 0, ti] 15 10 REFERENCES - + - - / / / 5 10 50 100 200 Coastal Data Information Program (CDIP), 1983. Monthly Report, January, 1983. Scripps Institution of Oceanography, La Jolla, CA. Dayton, P.K., R.J. Seymour, P.E. Parnell and M.J. Tegner, 1989. Unusual Marine Erosion in San Diego County from a Single Storm. Estwrine, Coastal and SheEfScience, Vo1.28, (in press.) Earle, M.D., K.A. Bush and G.D. Hamilton, 1984. "High- height Long-period Ocean Waves Generated by a Severe Storm in the no fie as^ Pacific Ocean during February 1983". J. of Physical Oceanography, Vo1.14, No.8: pp 1286-1299. Moffatt & Nichol, Engineers, 1988. SanDiego Region Historic Wave and Sea Level Data Report. U.S. Army Engineers District, Los Angeles, CA. Seymour, R.J., R.R. Strange, HI, D.R. Cayan and R.A. Nathan, 1984. "Influence of El Ninos on California's Wave Climate". Proc. 19th Intl. Con5 on Coastal Engrg, Houston, TX, ASCE Vol. I: pp 577-592. Seymour, K.J., M.H. Sessions and D. Castel, 1985. "Automated Remote Recording and Analysis of Coastal Data". J. Waterway, Port, Coastal and Ocean Engrg, Proc. ASCE, Vol. 111, No. 2: pp 388-400. Seymour, R.J., M.J. Tegner, P.K. Dayton and P.E. Parnell, 1989. "Storm Wave Induced Mortality of Giant Kelp, Macrocyctis pyrifera, in Southern California". Estuarine, Coastal and ShelfScience, Vol. 28, No. 3: pp 277-292. Walker, J.R., R.A. Nathan, R.J. Seymour and R.R. Strange, 111, 1984. "Coastal Design Criteria in Southern California". Proc. 19thInll. Conf. onCoasra1 Engrg, Houston,TX, ASCE Vol. III: pp 2827-2841. RECCRRENCE INTERVAL (yr) Figure 8. Return interval estimates, similar to Figure 7, from Mottatt & Nichol, 1988. OCTOBER 1989 

Wave Observations in the Storm of 17-18 January 1988

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Wave Observations in the Storm of 17-18 January 1988

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