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The Current State and Future Developments for the Inclusion of Waves in Coastal Flooding Forecasting in Newfoundland and Labrador

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The Current State and Future Developments for the Inclusion of Waves in Coastal Flooding Forecasting in Newfoundland and Labrador The Current State and Future Developments for the inclusion of Waves in Coastal flooding forecasting in Newfoundland and Labrador 14th International Workshop on wave Hindcasting & forecasting and 2nd international Storm Surge Symposium, Key West, Florida Devon Ross Telford Marine and Coastal Lab for Meteorology, Environment Canada Motivation • During 1978, AES in the Atlantic Region assumed the responsibility for alerting the public whenever coastal sea levels appeared likely to be significantly higher (0.6 m for example) than normal, and this practice has continued for areas without flood stage information. • However, numerous cases of coastal flooding have occurred that, if the forecaster had relied solely on storm surge models, would have been missed. • The inclusion of waves and the impact of wave set-up in conjunction with the storm surge model has improved the forecasting of coastal flooding. • This presentation will outline the guidance and techniques currently used by operational forecasters at the Newfoundland and Labrador Weather Office. A Rogue Wave Event at Middle Cove Beach, Newfoundland Devon Ross Telford Newfoundland and Labrador Weather Office, Gander, Newfoundland Introduction Analysis Conclusions Methods On the afternoon of Sunday, August 31, 2008, large shoaling On Thursday, August 28, 2008 a quasi-stationary low south of the Denmark Cross Section of Middle Cove Beach With the knowledge of this synoptic event and the use of the waves that were described by observers as ‘rogue’ occurred at Strait had its central pressure rapidly deepen from 1000 to 970 mb over the next 10 nomogram perhaps similar situations may be accurately 30 hrs (Fig 4 and 5). By the morning of Friday, August 29, 2008 (Fig 5 and 6) Middle Cove Beach, Newfoundland. These waves washing the storm began to slowly weaken only filling by 17 mb over the next 24 hrs. Upon examining the 5 forecasted and appropriate action may be taken to inform the over beach-goers and effectively pulling four of them out into 0 public. For a forecasted northeasterly swell over the northern bathymetry surrounding 100 -100 -300 -500 -700 -900 m = 0.058 (1:18) the cove where they were rescued by bystanders. The raw Middle Cove Beach three -5 half of the East Coast a forecaster could determine the coastal m = 0.015 (1:67) hazard at Middle Cove Beach using this nomogram (Fig 13). wave data obtained for this study shows that rogue waves were distinct slopes are observed. -10 present in the wave field. However, even in the absence of Figure 11. Cross section of Proposed Middle Cove Beach warning Criteria bathymetry and -15 these waves the significant wave height and peak period of the 9 -20 [m] LLMWL 0 is where Elevation/Depth, topography from Middle 8.5 wave field was the important contributor to the event. Through LLMWL (0m) Cove beach from the -25 8 this study an operational nomogram was developed to give m = 0.042 (1:24) 0.3 m 7.5 parking lot into the cove -30 Horrizontal Distance [m] msl (0.6m) proposed warning thresholds for similar events based on 7 along the same line as 0.9 m significant swell height, peak period and tide height. With the 6.5 figure 2. The wave set-up for waves breaking over each 1.2 m knowledge of this synoptic event and with the use of the 6 section can be solved in terms of near shore slope, significant wave HHMWL (1.6 m) nomogram perhaps similar situations may be accurately 5.5 height and peak period. 5 forecasted and appropriate action may be taken to inform the −0.254 4.5 0.031 H s − = Significant Height Wave [m] public. Figure 4. 2008-08-28 Figure 5. 2008-08-29 Figure 6. 2008-08-30 Wave _ set up 1.15* H s .575m 2 4 1.56 *T 12Z 12Z 12Z 3.5 On the evening of Thursday, August 28, 2008, 3 QuikScat images observed a wind field with a fetch approximately 120 nm wide 2.5 Site Survey Wave height observations from both the Terra Nova and SeaRose buoys 2 across the Denmark Strait and 300 nm long with an average wind speed of ~30 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 kts from the northeast. The winds over the fetch strengthened to upwards of 60 did show individual waves that where twice the size of the significant Peak Period [s] Middle Cove Beach is located ~10 km north of the city of St. kts by the following evening-pass on Friday, August 29, 2008 (Fig 7). By the wave height during the event. However, even in the absence of these Figure 13 John’s, Newfoundland and faces northeast. Its rugged and morning of Saturday, August 30 2008 (Fig 8), the winds had begun to subside waves one would expect the set-up from the significant waves to be a and the effective fetch had grown to 550 nm in length. This study also raises additional questions that may be worth scenic U–shaped bay is surrounded by a steep cliff making it threat in this situationShoaling (Fig Wave 12) Heights. for Middle Cove Beach Derived from buoy data from the SeaRose further investigation. What is the frequency for a similar event to popular among tourists and residence alike. The beach is 10 tide [m] occur at Middle Cove Beach? Are there other popular beaches composed of gravel and sand with the largest clast sizes 9 in Newfoundland that are at risk and what would their warning tide + Hs Set-up [m] distributed half way up the beach creating a berm dividing 8 criteria be? parking lot elevation plus the difference the foreshore from the backshore and denoting the high tide 7 between MSL and MLLWL [m] mark. The parking lot is found at the south end of the beach 6 at an elevation of 7.3 m above the mean sea level, which for 5 this site is 60 cm above the lowest low mean water level. Literature cited 4 Coastal Engineering Research Center Engineering Waterways Experiment. 1984. Shore Protection Manual. Height above LLMWL [m] LLMWL above Height 3 Parking Lot COMET. (2005). Wave Life Cycle I: Generation, Retrieved June 15, 2009 from http://www.meted.ucar.edu/marine/mod2_wlc_gen Web Figure 7 Figure 8 2 COMET. (2006). Shallow-Water Waves. Retrieved June 15, 2009 from http://www.meted.ucar.edu/marine/SWW/ Web 1 By the evening of Friday, August 29, 2008, the fetch had Herbich, John B. 1999. Handbook of Coastal Engineering, High Tide created a sea state with a significant wave height of ~13.5 m and a peak period of 0 McGraw-Hill. Ne w York, NY 08-31-2008 2008-31-2008 32008-31-2008 62008-31-2008 92008-31-2008 122008-31-2008 155008-31-2008 185008-31-2008 215009-01-2008 5009-01-2008 35009-01-2008 65009-01-2008 95009-01-2008 125009-01-2008 155009-01-2008 185009-01-2008 2150 ~16 seconds in the generation area (Fig 9). These waves left the generation region Holthuijsen, Leo H. 2007. Waves in Oceanic and Coastal Waters. Cambridge University Press. as swell and travelled southwestward. Located ~1200 nm to the southwest, the Hsu, Shih-Ang. 1988. Coastal Meteorology. Academic Press. northern Avalon Peninsula of Newfoundland and the Northern Grand Banks first Time UTC Figure 1. Middle Cove Beach, looking Mercer, Doug. 2008. Breugem and Holthuijsen Nomogram for Deep Water Waves. started to observe the bulk of the wave energy late in the afternoon local time on North from the a hill on the East side of the Figure 12. A time series of perturbed sea level using the near shore NWS. (2005). Rogue Waves, Retrieved June 15, 2009 Sunday, August 31, 2008. The swell’s significant wave height peaked to ~3.5 m @ http://www.opc.ncep.noaa.gov/perfectstorm/mpc_ps_rogue.shtml Web Cross Section From A to B slope, the tide gage in St. John’s Harbour and the peak periods and beach 16 sec after midnight (Fig 10). World Meteorological Organization, 1998. Distance [m] Guide to Wave Analysis and Forecasting (second edition). W MO-No. 702. 0 1000 2000 3000 4000 5000 significant wave heights observed at the SeaRose located ~340 km 0 to the East-Southeast of Middle Cove Beach. Young, I. R. 1999. Wind generated ocean wave. Elsevier. 20 40 Using the height of the parking lot, 7.9 m above the lowest low mean water level, as a proposed warning criterion for 60 height of the wave set-up to reach, an equation for significant wave 80 Depth, where 0 is LLMWL [m] LLMWL is 0 where Depth, height as a function of near shore slope and peak period is derived. 100 1 0.746 120 − −0.254 Wave _ set up 2 Acknowledgments HS = 0.031 (1.56 * T ) Figure 3. Cross section of 1.15*.575m I would like to thank Reg Fitzgerald, Jeremy Whittle and Larry Breen, for their help and co-operation with Figure 2. bathymetry attaining the buoy data from the Northern Grand Banks. Doug Mercer and Bridget Thomas for all their of Middle Cove water depth from Middle help and direction during this study. Goldie Porter and Peter Browne for their help attaining the Cove Beach to a point 5.25 km By subtracting the tide height from the parking lot height this equation topography charts. Charles O’Reilly with his help with the tide information. As well as members of the Beach NLWO and ASPC for their insight. to the Northeast Figure Figure 10 can then be solved for differing levels of tide height and plotted as a 9 nomogram (Fig 13).
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