Browsing by Author "Kennedy, Andrew"

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    Hurricane Michael in the Area of Mexico Beach, Florida
    Kennedy, Andrew; Copp, Andrew; Florence, Matthew; Gradel, Anderson; Gurley, Kurtis; Janssen, Matt; Kaihatu, James; Krafft, Douglas; Lynett, Patrick; Owensby, Margaret; Pinelli, Jean-Paul; Prevatt, David O.; Rogers, Spencer; Roueche, David; Silver, Zachariah (2020-09-01)
    Category 5 Hurricane Michael made landfall near Mexico Beach, Florida on October 9, 2018, with measured high water marks (HWMs) reaching 7.2 m NAVD88. The town itself received great damage, with many areas destroyed down to the foundations. In this study, we document the storm and its effects on the greater Mexico Beach area: hazard, structural damage, and their relationships. Wave and surge damage was nearly total for low-lying properties, but damage decreased greatly with increasing elevation. Major wave and surge damage was noted in Federal Emergency Management Agency (FEMA) X zones, which are out of the 100-year floodplain, and it is suggested that the 100-year storm is a deficient measure for categorizing flood risk. This work is made available under the terms of the Creative Commons Attribution 4.0 International license, https://creativecommons.org/licenses/by/4.0/
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    Scour Development and Possible Effects of Momentary Liquefaction in Inundated Coastal Areas During Hurricane Michael
    Florence, Matthew; Stark, Nina; Kennedy, Andrew (ASCE, 2022-03)
    Scour holes around slender piles were measured in areas inundated during Hurricane Michael and were compared with scour hole depths estimated from existing scour prediction equations. Despite testing a wide range of feasible input parameters, some measured scour depths could not be predicted by five common scour prediction equations (one wave only, three current only, one wave and current equation). Current only equations yielded the best prediction rate despite the site being in a wave-dominated environment. The scour depths that were not accurately predicted by the equations tended to be underpredictions despite the range of input values. A range of factors were considered that might have caused these differences. Momentary liquefaction was investigated as one possible explanation to some of the discrepancies between observed and predicted scour depths using laboratory tests and field measurements. The results suggested that momentary liquefaction of the top layer of sediment is possible for wave heights of approximately 0.83 m in 1.3 m of water depth, indicating that momentary liquefaction of sediments was possible during Hurricane Michael with 2 m waves in 3.5 m of water and therefore presents one possible explanation for the observed mismatch between the scour predictions and observations.
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    Systematic Review Shows That Work Done by Storm Waves Can Be Misinterpreted as Tsunami-Related Because Commonly Used Hydrodynamic Equations Are Flawed
    Cox, Ronadh; Ardhuin, Fabrice; Dias, Frederic; Autret, Ronan; Beisiegel, Nicole; Earlie, Claire S.; Herterich, James G.; Kennedy, Andrew; Paris, Raphael; Raby, Alison; Schmitt, Pal; Weiss, Robert (2020-02-05)
    Coastal boulder deposits (CBD), transported by waves at elevations above sea level and substantial distances inland, are markers for marine incursions. Whether they are tsunami or storm deposits can be difficult to determine, but this is of critical importance because of the role that CBD play in coastal hazard analysis. Equations from seminal work by Nott (1997), here referred to as the Nott Approach, are commonly employed to calculate nominal wave heights from boulder masses as a means to discriminate between emplacement mechanisms. Systematic review shows that this approach is based on assumptions that are not securely founded and that direct relationships cannot be established between boulder measurements and wave heights. A test using an unprecedented dataset of boulders moved by storm waves (with associated sea-state data) shows a lack of agreement between calculations and actual wave heights. The equations return unrealistically large heights, many of which greatly exceed sea states occurring during the boulder-moving storms. This underscores the finding that Nott-Approach wave-height calculations are unreliable. The result is general, because although the field data come from one region (the Aran Islands, Ireland), they represent a wide range of boulder masses and topographic settings and present a valid test of hydrodynamic equations. This analysis demonstrates that Nott Approach equations are incapable of distinguishing storm waves from tsunami transport and that wave heights hindcast from boulder masses are not meaningful. Current hydrodynamic understanding does not permit reliable computation of wave height from boulder measurements. A combination of field, numerical, and experimental approaches is required to quantify relationships between wave power and mass transport onshore. Many CBD interpreted as tsunami deposits based on Nott-Approach analysis may in fact have been emplaced during storms and should therefore be re-evaluated. This is especially important for CBD that have been incorporated into long-term coastal risk assessments, which are compromised if the CBD are misinterpreted. CBD dynamics can be better determined from a combination of detailed field measurements, modeling, and experiments. A clearer understanding of emplacement mechanisms will result in more reliable hazard analysis.