Does morphological adjustment during tsunami inundation increase levels of hazard?
Date
2016
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Previous tsunami inundation mapping for the US East Coast (USEC) have shown that barrier islands would potentially be highly impacted during a possible tsunami. Many of these barrier islands along USEC are home to populated cities like Atlantic City, NJ and Ocean City, MD. Inundation mapping results showed insignificant inundation for many regions on the mainland behind these barriers. However, we know that a tsunami can significantly change coastal morphology, and post-tsunami surveys have confirmed that during tsunami inundation, large amounts of sediment have been eroded from sandy coasts and deposited further onshore. In some cases, sand dunes were completely eroded, and the sediment got deposited either onshore behind the dunes, or offshore during the rundown process. Thus, it seems essential to consider barrier island topographic changes during the inundation mapping process for assessing tsunami hazard. In this thesis, we considered tsunami-induced bathymetric changes to study whether morphological adjustment during tsunami inundation increases levels of hazard. For this purpose, we coupled the FUNWAVE-TVD model with an advection-diffusion depth-averaged sediment transport model and a morphology module to capture bed evolution in tsunami conditions. Then, we used the model to simulated two laboratory experiments. First, bed changes under breaking solitary waves were modeled. Then, we simulated sediment transport of a dam-break wave. Moreover, we simulated tsunami-induced morphological changes inside Crescent City harbor during the 2011 Tohoku-oki tsunami. The results indicated that the model can locate erosion and deposition regions correctly for laboratory and field tests. Finally, we applied our model to study barrier island topographic changes for four different tsunamis: 1) A cone collapse of Cumbre Vieja volcano in the Canary Islands, 2) A tsunami generated by an earthquake in the Puerto Rico subduction zone, 3) Another earthquake-generated tsunami in Azores-Gibraltar convergence zone, and 4) A tsunami caused by a landslide on the USEC shelf break. We studied two different locations on the USEC, Assateague Island as an area without infrastructures, and Ocean City, MD to investigate the effect of complexities such as pavements, buildings, and jetties on tsunami-induced morphological changes. Our results suggest that a tsunami can cause significant bathymetric changes on a barrier island. Due to the erosion on top of the barrier, it is shown that the mainland behind can experience higher levels of tsunami hazard compared to the condition with fixed bathymetry.