A Model for Simulating Barrier Island Geomorphologic Responses to Future Storm and Sea-Level Rise Impacts

Dai, H.; Ye, M., and Niedoroda, A. W., 0000. A model for simulating barrier island geomorphologic responses to future storm and sea-level rise impacts. Journal of Coastal Research, 00(0), 000–000. Coconut Creek (Florida), ISSN 0749-0208. This paper presents the Barrier Island Profile (BIP) model, a new computer code developed to simulate barrier island morphological evolution over periods ranging between years and decades under the impacts of accelerated sea-level rise and long-term changes in the storm climate. The BIP model is a multiline model that represents the time-averaged dynamics of major barrier island features from front beach to backshore. Unique contributions of BIP to coastal modeling include a dynamic linking of interacting barrier island features and consideration of both future sea-level rise and storm climate impacts. The BIP model has the built-in capability of conducting Monte Carlo (MC) simulations to quantify predictive uncertainty caused by uncertainty in sea-level rise scenarios and storm parameters. For a series of barrier island cross-sections derived from the characteristics of Santa Rosa Island, Florida, BIP was used to evaluate their responses to random storm events and five potential accelerated rates of sea-level rise projected over a century. The MC simulations using BIP provide multiple realizations of possible barrier island morphologic responses and their statistics, such as mean and variance. The modeling results demonstrate that BIP is capable of simulating realistic patterns of barrier island profile evolution over the span of a century using relatively simple representations of timeand spaceaveraged processes with consideration of uncertainty of future climate impacts. ADDITIONAL INDEX WORDS: Beach sand dunes, storm erosion, sediment transport, overwash, Monte Carlo, uncertainty analysis, SLOSH, Santa Rosa Island. INTRODUCTION In response to impacts of future storms and sea-level rise, coastal planners and engineers are making accommodations in their management plans for protection of coastal infrastructure and natural resources. Barrier islands are important for coastal protection and restoration, and they have been well studied. However, little attention has been given to the balance of processes and sand transport fluxes that combine to shape the composite morphology. The principal morphological elements include the beach prism, the frontal and secondary dunes, the overwash channels, the island platform, and the back-island shoreline. Understanding the balance of these time-averaged processes and representing them in a quantitative framework is especially of value when this can be used to forecast decadaland century-scale evolution of a barrier island system as a whole. The morphology of barrier islands will be dramatically affected by the future climate, including storms and sea-level rise. Accurately predicting the morphological evolution of barrier islands is necessary for coastal management, and mathematical modeling is a vital tool for such predictions. This paper presents a barrier island profile (BIP) model with consideration of future uncertainty for simulating barrier island morphological evolution with multiple features such as beach, dunes, island platform, and backshore under both long-term and short-term climate impacts including uncertain sea-level rise and storms. A number of recent studies of changes in barrier island morphology as it has reacted to, and recovered from, the devastation wrought by major hurricanes have provided insight into the major factors to consider in developing a conceptual model of the linkages between morphological features and the processes that shape them. Morton (2002) has identified the principal factors influencing storm impacts as being the characteristics of the storm or storm sequence, the location of barrier island features relative to the storm track and point of landfall, the sequencing of storms over time, and the height and duration of storm surge flooding, along with the antecedent topography and framework geology. Several studies describe differences in storm impact and poststorm recovery along individual barrier island systems, providing insight into the interaction between morphological features. It has long been accepted that storm overwash, which transports sand from the beach prism through the dunes to be deposited on the island platform and along the island backshore, is key to sustaining barrier islands, especially in the presence of sea-level rise (Godfrey and Godfrey, 1976). Houser and Hamilton (2009) and Timmons et al. (2010), among others, have noted a relationship between the stability of the island backshore and the width of the island. Wider barrier islands limit or prevent overwash from being carried completely across the island to the backshore beach. If the barrier island is transgressive, this leads to erosion of the backshore and a tendency for the island width to decrease over time. Timmons et al. (2010) describe how this leads to a DOI: 10.2112/JCOASTRES-D-14-00094.1 received 12 May 2014; accepted in revision 16 October 2014; corrected proofs received 25 November 2014; published pre-print online 31 December 2014. *Corresponding author: [email protected] Coastal Education and Research Foundation, Inc. 2014 Journal of Coastal Research 00 0 000–000 Coconut Creek, Florida Month 0000