Uriah Gravois

Building Destruction from Waves and Surge on the Bolivar Peninsula during Hurricane Ike

The Bolivar Peninsula in Texas was severely impacted by Hurricane Ike with strong winds, large waves, widespread inundation, and severe damage. This paper examines the wave and surge climate on Bolivar during the storm and the consequent survival and destruction of buildings. Emphasis is placed on differences between buildings that survived (with varying degrees of damage) and buildings that were completely destroyed. Building elevations are found to be the primary indicator of survival for areas with large waves. Here, buildings that were sufficiently elevated above waves and surge suffered relatively little structural damage, while houses at lower elevations were impacted by large waves and generally completely destroyed. In many areas, the transition from destruction to survival was over a very small elevation range of around 0.5 m. In areas where waves were smaller, survival was possible at much lower elevations. Higher houses that were not inundated still survived, but well-built houses at lower elevations could also survive as the waves were not large enough to cause structural damage. However, the transition height where waves became damaging could not be determined from this study.

Boat-Wake Statistics at Jensen Beach, Florida

Ship/boat wakes are identified in pressure and flow velocity records as chirp signals, which are also known as sweep signals in sonar and radar applications. A chirp is a signal in which the frequency increases or decreases with time. Wakes are analyzed using time-frequency techniques [windowed Fourier transform (WFT), wavelet transform (WT), and instantaneous frequency]. This approach allows for detecting boat wakes and studying their statistics, even in the presence of a relatively strong broad-banded wind-wave background. Time-frequency methods also open a new direction for the statistical description of wakes, which are applicable to the characterization of the wake climate (e.g., for sites with intense boat traffic). The usefulness of the time-frequency analysis on observations collected in 2010 at Jensen Beach, Florida will be demonstrated.

Observations of meteotsunami on the Louisiana shelf: a lone soliton with a soliton pack

The paper reports unique high-resolution observations of meteotsunami by a large array of oceanographic instruments deployed on the Atchafalaya Shelf (Louisiana, USA) in 2008 with the primary aim to study wave dissipation in muddy environments. The meteotsunami event on March 7, 2008, was caused by the passage of a cold front which was monitored by the NOAA NEXRAD radar. The observations of water surface elevations on the shelf show a highly detailed textbook picture of an undular bore (solibore) in the process of its disintegration into a train of solitons. The picture has a striking feature never reported before not only for the meteotsunamis but in other contexts of disintegration of a long-wave perturbation into a sequence of solitons as well—the persistent presence of a single soliton, well ahead of the solibore. Data analysis and simulations based on the celebrated variable-coefficient KdV (vKdV) equation first proposed by Ostrovsky and Pelinovsky (Izv Atmos Ocean Phys 11:37–41, 1975) explain the physics of this phenomenon and suggest that the formation of the lone soliton ahead of the solibore is very likely to be the result of the specific interplay of natural meteotsunami forcing and nearshore bathymetry. The analysis strongly suggests that the patterns of coexisting lone solitons and packets of cnoidal waves should be quite common for meteotsunamis. They were not observed before only because of the scarcity of high-resolution observations. The results highlight the effectiveness of the vKdV equation in providing understanding of the fundamental mechanisms of the complex natural phenomenon that would otherwise require computationally very expensive numerical models.

A Framework for Modelling Shoreline Response to Clustered Storm Events: A Case Study from Southeast Australia

ABSTRACT Nichol, S.L.; McPherson, A., Davies, G., Jiang, W., Howard, F., Baldock, T., Callaghan, D., and Gravois, U., 2016. A framework for modelling shoreline response to clustered storm events: A case study from southeast Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1197 - 1201. Coconut Creek (Florida), ISSN 0749-0208. An overview of a framework for modelling shoreline response to clustered storm events is presented for a case study area on the high energy coast of southeast Australia. We adopt the coastal sediment compartment as the functional management and modelling unit and use sub-surface information (ground-penetrating radar) to assess sediment thickness in the upper beach and foredune. Results for an actively eroding beach face at Old Bar Beach (New South Wales) indicate that sand cover is highly variable at the critical beach-dune interface, ranging from less than 1 m where bedrock occurs in shallow sub-crop to greater than 4 m across a former tidal inlet. The temporal distribution of storm events is examined through statistical modelling. For the duration of the data, modeled wave parameters are in good agreement with wave buoy observations. Event clustering does not appear to be stronger than is expected from events that occur randomly in time. Together, these data provide site-specific information necessary to inform shoreline response modeling to storms by establishing the requisite conditions describing the geomorphic setting and nearshore process regime.

A Wave, Water Level, and Structural Monitoring Plan for Dauphin Island, Alabama

The results of damage assessments following recent hurricane events suggest that predictions of wave transformation across barrier islands during overtopping events are unreliable and, even worse, inaccurate. In many cases, inaccurate model predictions of wave heights in high hazard areas are translating into improper standards for “lowest structural member” elevations on residential and commercial structures. The substantive result of which is increased cost of construction, whether initial or replacement costs. The purpose of this research is to improve guidance on building elevations in high hazard flood plain areas where wave action is the primary structural damage mechanism. A number of novel, autonomous wave gauges will be temporarily mounted to fixed structures on Dauphin Island, Alabama, in advance of an overtopping event during future hurricane seasons. Measured wave heights and water levels will provide an opportunity to characterize wave transformation across the barrier island. When combined with surveyed building elevations and a detailed inventory of structural and foundation characteristics, the measured waves and water levels will provide an opportunity to identify critical building elevations that delineate survival and destruction, as well as determine the adequacy of structural connections and foundations.

Wave-current interaction in the Florida Current in a coupled atmosphere-ocean-wave model

The interaction of waves and currents are investigated in the Florida Current region in two events in early April 2005 using a state-of-the-art coupled atmosphere-ocean forecast model that includes assimilation of observations. During the first event, strong northerly winds force swell southward opposing the Florida Current. Current-wave interaction results in larger significant wave heights than found without currents. The second event has south-easterly winds with a significant component along the current direction. In that case, significant wave heights are smaller for the simulation that includes wave-current interaction than without that feed-back. Wave heights at buoy locations near the coast is generally in good agreement with the models results, which implies that inclusion of wave-current interaction may not be important near the shore. The simulation includes events where the maximum winds reach 20 m/s and significant wave heights exceed 2 m.