HR: 0800h
AN: H41C-0319    [Abstracts]
TI: Surprising Long Range Effects of Local Shoreline Stabilization in a Large-Scale Coastline Model
AU: * Slott, J
EM: jordan.slott@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Center for Nonlinear and Complex Systems, Center on Global Change, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27708 United States
AU: Murray, B
EM: abmurray@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Center for Nonlinear and Complex Systems, Center on Global Change, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27708 United States
AU: Valvo, L
EM: lisa.valvo@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Center for Nonlinear and Complex Systems, Center on Global Change, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27708 United States
AU: Ashton, A
EM: andrew.ashton@duke.edu
AF: Division of Earth and Ocean Sciences, Nicholas School of the Environment and Earth Sciences, Center for Nonlinear and Complex Systems, Center on Global Change, Duke University, 103 Old Chemistry Box 90229, Durham, NC 27708 United States
AB: As coastlines continue to retreat and threaten communities, roads, and other infrastructure, humans increasingly employ shoreline stabilization techniques to maintain the shoreline in its current position. Examples of shoreline stabilization techniques include beach nourishment and seawall construction. During beach nourishment, sand is typically dredged from locations offshore and placed on the beach. Seawalls or revetments, on the other hand, are hardened concrete structures which prevent the shoreline from retreating further yet do not add sand to the nearshore system. Coastal engineers and scientists have only addressed the local and relatively short-term effects of shoreline stabilization. Can beach nourishment or seawalls affect coastline behavior tens or hundreds of kilometers away in the longer term? We adapted a recently developed model of large-scale, long-term shoreline change to address such questions. On predominately sandy shorelines, waves breaking at oblique angles to the shoreline orientation drives the alongshore transport of sediment. Though traditionally believed to smooth out shoreline features, Ashton, et. al. (2001) have shown that alongshore-driven sediment transport can cause more complex shoreline evolution. Their model showed the spontaneous formation of large-scale features such as capes and cuspate forelands (e.g. the shape of the coastline of the Carolinas) using simple sediment transport relationships. This model accounts for non-local shoreline interactions, such as wave "shadowing." In this work, we have further developed the large-scale shoreline model to include the effects that shoreline stabilization techniques have on shoreline position and sediment supply. In one set of experiments, we chose an initial shoreline with cape-like features separated by approximately 100 kilometers, roughly similar to that of the coast off the Carolinas. In each individual experiment, we nourished a different 10 kilometer section of coastline. In each case, we compared the coastline that evolved after 50, 100, and 200 years with the coastline in a control run which received no nourishment. We found several surprising results. The difference in shoreline position attributable to the nourishment project is as much as 1 kilometer regionally (up to 10's of kilometers away in the alongshore direction after 200 years). Changes on the order of 10's of meters were seen as far away as hundreds of kilometers. Nourishment directly altered the geometry of the adjacent cape. Shadowing propagated the changes over long distances, changing the local wave climate felt by distant capes, and thereby altering their position. The distant changes in shoreline position attributable to the nourishment were concentrated entirely near the capes rather than in the cuspate bays. These experiments suggest that the long-term effects of a single, local beach nourishment project can be much more widespread than might be expected.
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
DE: 1803 Anthropogenic effects
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting