Nearshore morphology and lithology: Links to framework geology and shoreline change.

摘要

Despite evidence of the geologic and morphologic complexity of inner shelves worldwide, there is a paucity of observations from the nearshore, inhibiting direct comparison of these factors to coastal change. Using geophysical instruments to characterize the geology of the nearshore, this research focuses on the relationships between nearshore stratigraphy, sediment heterogeneity, shoreface morphology and shoreline behavior. While generally not considered in engineering models of shoreline evolution, these factors influence nearshore processes. Overall, the findings presented highlight the importance of nearshore geology, both at the seafloor and underlying it, in contributing to modem sediment transport processes affecting beaches. Shallow, sub-seafloor geology limits the availability of nearshore sediment available for exchange with the shoreline and is correlated to shoreline change occurring over time scales related to coastal sediment resource management (decades). Shore-oblique sandbars are related to higher volumetric variability in the nearshore and on the beach, whereas traditional shore-parallel sandbars are not. Shorelines adjacent to shore-oblique bars respond to hurricanes and nor'easters differently than other regions of shoreline, helping to explain some spatial variability in patterns of shoreline erosion and accretion. Finally, the geologic framework underlying the seafloor is a source of mixed sediments to the modern coastal system. This contribution has implications for the formation and preservation of specific inner shelf morphologies associated with varied sediments. These results further our knowledge of the geologic variability inherent to sandy coastlines and challenge coastal scientists and engineers to represent this natural variability in predictive models of shoreline change to better predict coastal response to rising sea level and storms.