Impacts of Barrier-Island Breaching On Mainland Flooding During Storm Events

Barrier islands help protect the mainland from flooding during storms by affecting the storm surge. However, the protective capability is reduced when barrier islands breach and a direct hydrodynamic connection between the water bodies on both sides of the barrier island is established. Breaching of barrier islands during large storm events is complicated, involving sediment transport and nonlinear processes that connect water and sediment transport, dune height, and island width, among other factors. Because of the many factors involved in the breaching process it is difficult to predict where and when a breach will form. In order to assess how barrier-island breaching impacts flooding on the mainland, we use a statistical approach to analyze the sensitivity of mainland storm-surge runup to barrier island breaching by randomizing the location, time, and extent of a breach event. The shape of the breach is approximated with a gaussian distribution imposed on the barrier island that deepens over time. Breach formation is time dependent after a triggering event during a simulated storm using GeoClaw. The triggering event can be either a specific time during the simulation or a user specified ocean surge near the breach location, and breach growth is limited in its rate of change by a time controlled ratio for when it achieves equilibrium. Varying the timing, extent, and locations of the barrier island breaches during a storm event will provide insight into how the mainland coastline responds to breaches during storms. This insight is invaluable in preparing shoreline communities to be aware of the differing ways the regions can change during storms, depending on how the barrier islands behave. Additionally, we can offer statistical insights into where a breach would impact the mainland coastline more drastically in an effort to provide data for planning and warning purposes.