Quantification of Distinguishing Features of Tsunami versus Hurricane Sediment Overwash Events

Monday, 15 December 2014
Stephanie Smallegan, Steven T Keith, Wei Cheng, Robert Weiss and Jennifer L Irish, Virginia Tech, Blacksburg, VA, United States
Hurricanes and tsunamis are known to be highly erosive events, even though their characteristics differ greatly. A hurricane is a storm that typically impacts an area over a number of hours, has an associated storm surge, and generates wind waves with periods on the order of seconds. Tsunamis, however, impact an area over one or two hours and are long waves with periods on the order of tens of minutes. In this study, we use the numerical model XBeach to simulate typical hurricane and tsunami conditions, using an idealized bathymetric profile of a barrier island, to determine differences in the resulting morphology from each event type. For hurricane conditions, the offshore wave heights, periods and peak surge level range from 6m to 14m, 8s to 12s, and 1m to 3m, respectively, and the storm duration is 6 hours. Tsunami conditions are then determined using a 1:100 scale, such that the total energy of the hurricane equals 100 times the energy of the tsunami. By assuming a constant 20-minute wave period for the tsunami and a total duration of 1 hour, the tsunami wave heights are calculated using linear wave theory, resulting in wave heights ranging from 1m to 3.5m. The results show that tsunamis mobilize about 20% more sediment from the dune and deposit it at least 50% farther into the bay area, when compared to a hurricane with 100 times the energy. These results exemplify morphological characteristics of hurricanes and tsunamis and provide important insights into the differences between deposits from both events.