HR: 0800h
AN: H51C-0387    [Abstracts]
TI: Shoreline Response to Climate Change and Human Manipulations in a Model of Large-Scale Coastal Change
AU: * Slott, J M
EM: jordan.slott@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27707 United States
AU: Murray, A B
EM: abmurray@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27707 United States
AU: Valvo, L
EM: lisa.valvo@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27707 United States
AU: Ashton, A
EM: andrew.ashton@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27707 United States
AB: Gradients in wave-driven alongshore sediment transport cause long-term change in the shape of sandy coastlines. Recent modeling work (Ashton, et. al. 2001) suggests coastlines can attain shapes that are in quasi-equilibrium with a regional wave climate (the distribution of wave influences as a function of wave-approach angles). Mid-latitude winter storms and tropical cyclones, for example, dominate the wave climate off of the Southeast coast of the United States. The resulting wave distribution likely determines the basic shape of the Carolina Capes, which extends along 400 kilometers of coastline. Global warming-related changes in storm (and therefore wave) patterns will likely cause this coastline pattern to adjust. In preliminary computer simulations, Murray, et. al. (in review) demonstrate coastline evolution accelerating by a factor of two to three times for a 5% increase in storminess and four to five times for a 10% increase in storminess after 200 years. Accelerated coastal change will undoubtedly place greater demand on shoreline stabilization techniques. Beach nourishment and seawalls ameliorate the effects shoreline erosion and migration have on homes and roads built on or near the beach. Beach nourishment rebuilds the beach using sand typically dredged from off-shore. Seawalls are hardened structures which prevent the shore from eroding farther landward. Scientific research on shoreline stabilization has focused on the local and short-term effects of these manipulations. In contrast, we study the longer-term (decades to centuries) and the larger scale (10's to 100's of kilometers) consequences of shoreline stabilization, coupling our experiments to scenarios of greatly-accelerated coastal migration induced by changes in global climate. Our modeling approach builds upon one-line coastal engineering models. It incorporates wave shadowing; protruding coastal features may shadow other parts of the coast from waves. Using the model, Ashton, et. al. (2001) show that large-scale coastal features (e.g. capes and cuspate spits) may self-organize as smaller coastal features grow and merge by interacting over large distances through wave shadowing. Our current work extends this model by including the effects of beach nourishment and seawalls. These simulations start with a cape-like shoreline, resembling the Carolina coastline, which we generated using the one-line model driven by the statistical average of 20 years of hindcast wave data measured off Cape Lookout, NC (WIS Station 509). In our experiments, we explored the effects of shoreline stabilization under four different wave climate scenarios: (a) unchanged, (b) increased winter storms, (c) increased tropical storms, and (d) decreased storminess. For each of these four scenarios, we ran three simulations: a control run with no shoreline stabilization, a run with a 10 km beach nourishment project, and a run with a 10 km seawall. We identified the effects of shoreline stabilization by comparing each of the latter two simulations to the control run. In each experiment, shoreline stabilization had a large effect on shoreline position--on the order of a few kilometers--within tens of kilometers of the stabilization area. We also saw sizable effects on adjacent capes nearly 100 kilometers away. Analysis of the simulations indicate that these distant impacts occurred because shoreline stabilization altered the extent to which the stabilized cape shadowed other parts of the coast. We thank the National Science Foundation and the Duke Center on Global Change for supporting our work.
DE: 1630 Impacts of global change (1225)
DE: 1847 Modeling
DE: 4217 Coastal processes
SC: Hydrology [H]
MN: Fall Meeting 2005