2024 CSDMS meeting-067

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Modeling the coupled evolution of barrier landscapes and communities

Brad Murray, (he/him),Duke Univ. Durham , United States. abmurray@duke.edu

Laura Moore, University of North Carolina at Chapel Hill Chapel Hill North Carolina, United States. laura.moore@unc.edu

Benton Franklin, University of North Carolina at Chapel Hill Chapel Hill North Carolina, United States. wbenton@email.unc.edu

ian Reeves, Woods Hole Oceanographic Institution Falmouth Massachusetts, United States. ian.reeves@whoi.edu

Katherine Anarde, North Carolina State University Raleigh North Carolina, United States. kanarde@ncsu.edu

On low-lying coastlines, sand (and/or gravel) washed landward of a beach during storms creates barrier landscapes. This ‘overwashed’ sand also tends to maintain barrier elevation in the face of rising sea level, and barrier width in the face of an eroding shoreline. However, from the point of view of coastal communities, the storm processes that deposit the sand, as well as the sand itself, presents hazards that need to be mitigated, or even disasters that need to be recovered from. The strategies typically chosen to mitigate storm hazards and recover from storm impacts typically involve attempts to prevent overwash processes (e.g. by building and maintaining large dunes) or to undo the effects of overwash processes (e.g. bulldozing overwashed sand off roads and using it to rebuild dunes). Although these mitigation and recovery strategies seem necessary in the short term, they can reduce coastal resiliency in the long term, by tending to make a barrier lower (relative to rising sea level) and narrower (in the case of an eroding shoreline). A lower and narrower barrier is more vulnerable to sunny day flooding and severe storm impacts.

The newly developed CoAStal Community-lAnDscape Evolution (CASCADE) model couples physical processes (storm erosion and sediment redistribution, dune growth, sea-level rise, shoreface and shoreline change, and gradients in alongshore sediment flux) and the effects of management strategies (e.g. overwash removal and dune maintenance, highway relocation, and beach nourishment). Using this model, we examine the outcomes, over decades, of the coupling between natural dynamics and commonly employed management strategies. Modeled outcomes depend on sea-level-rise rate, storm sequences, and initial barrier topography, and they range from developed barrier systems that can be sustained for over a century before becoming uninhabitable (effectively drowned), to scenarios in which highways and/or communities need to be abandoned within decades. Subsequent barrier recovery depends on the final state of the developed system before abandonment, as well as stochasticity in the timing of storms. When different management strategies are employed at different locations alongshore, their effects are coupled via the redistribution of sediment along a curved coastline.

We are also using CASCADE in a participatory modeling collaboration involving managers and planners with the Cape Hatteras National Seashore and the North Carolina Department of Transportation, as well as community representatives. Together, we will examine the range of outcomes, under different climate scenarios, of the strategies being considered for managing a critically threatened transportation corridor along a barrier within the National Seashore.