Collaborative Research: Coasts in Motion: Quantifying the patterns of coastal change using LIDAR

摘要提出的研究包括收集和分析新的海岸线变化观测。将对北卡罗来纳州外滩海岸线进行四次新的激光雷达调查，每次间隔六个月。这些调查，结合之前在1997年、1998年、1999年和2000年对同一段海岸线的调查，可以分析18个时间间隔的海岸线变化模式，长度从6个月到8年不等。以前应用于单一年间隔变化的分析技术（Tebbens et al, 2002）量化统计包括：1)岸线变化量作为岸线长度尺度的函数；2)侵蚀加积连片带岸线长度分布；3)侵蚀和吸积在一定时间间隔内的分布。在之前的分析中，不同的海岸线段对海岸线格局的统计是不同的。这些海岸线段有不同的朝向，因此有不同的有效波浪气候。在许多时间间隔内重复分析将检验统计数据和从一个海岸线到另一个海岸线的变化是否可靠。拟议的工作还将测试一个假设和潜在的模型，以确定观察到的海岸线行为的主要原因。描述海岸线变化模式的统计数据作为区域波浪气候的函数而变化的方式，提出了这样一种假设，即这些变化主要是由沿海运输的微妙梯度驱动的，这些梯度与平滑海岸线的微妙偏差有关。最近的研究表明，当波浪从深水以大于约45的相对角度接近海岸时，海岸线的扰动会增加，在扰动存在的任何尺度上都会引起沿岸非均质海岸线的变化（Ashton et al., 2001）。波浪从靠近海岸的深水角来袭，往往使海岸线变得平缓。在一段较长时期内的变化模式至少部分是由粗糙化和平滑化影响之间的相互作用造成的，这将取决于区域波浪气候，包括高和低波浪接近角的相对比例。一个处理沿岸运输的模型（Ashton et al., 2001; Ashton et al., 2003a; Ashton et al., 2003b）在之前的分析（Tebbens et al., 2002）中的一个统计数据中预测了观测到的沿海岸线方向的趋势（区域波浪气候）。更广泛的目标。如果新的数据收集和分析证实了关于不同海岸线段的初步发现，并且如果其他模式预测与观测结果一致，则该模式能够推广观测和分析的有用性；该模型将提供一种方法，将其扩展到任何可以估计波浪气候的海岸线，包括在一段时间间隔内预计的最大侵蚀和增生幅度，以及沿岸侵蚀和增生区的范围。除了这种预测能给海岸管理者带来实际好处外，成功的模型试验还代表着对海岸线变化过程的基本理解取得了进步，这些过程对数百米到数十公里范围内的海岸线变化很重要。当海平面加速上升时，能够阐明下个世纪海岸线变化范围的模型依赖于这些基本认识的改进。此外，本科生和研究生都将参与研究和成果展示。

ABSTRACTThe proposed research involves collecting and analyzing new observations of shoreline change. Four new LIDAR surveys of the North Carolina Outer Banks coastline, each separated by sixmonths, would be conducted. These surveys, combined with previous surveys of the same coastline segments in 1997, 1998, 1999, and 2000, would allow the analysis of patterns of shoreline change over 18 time intervals, ranging in length from six months to eight years. Analysis techniques previously applied to the changes over a single annual interval (Tebbens et al, 2002) quantify statistics including: 1) the amount of shoreline change as a function of alongshore length scale; 2) the distribution of the alongshore-lengths of contiguous zones of erosion and accretion; and 3) the distribution of the magnitudes of erosion and accretion occurring during a time interval. In the previous analysis, the statistics of the patterns of shoreline varied among the different coastline segments measured. These shoreline segments have different orientations, and therefore different effective wave climates. Repeating the analyses over many time intervals will test whether the statistics and the variations from one coastline segment to another are robust. The proposed work would also test a hypothesis and potential model for the main cause of the observed shoreline behaviors. The way the statistics describing the patterns of shoreline change vary as a function of regional wave climate suggests the hypothesis that these changes are driven chiefly by subtle gradients in alongshore transport associated with subtle deviations from a smooth shoreline. Recent work has shown that when waves approach shore from deep water at relative angles greater than approximately 45, shoreline perturbations grow, causing alongshore-heterogeneous shoreline changes on any scale at which perturbations exist (Ashton et al., 2001). Waves approaching from deep-water angles closer to shore-normal tend to smooth out the shoreline. The patterns of change over some extended time period will result at least partly from the interactions between the roughening and smoothing influences, which will depend on the regional wave climate, including the relative proportions of high and low wave-approach angles. A model treating alongshore transport (Ashton et al., 2001; Ashton et al., 2003a; Ashton et al., 2003b) predicts the observed trend with shoreline orientation (regional wave climate) in one of the statistics in the previous analysis (Tebbens et al, 2002). Broader Objectives. If the new data collection and analysis bears out the preliminary findings concerning different coastline segments, and if other model predictions are consistent with the observational results, the model be able to generalize the usefulness of the observations and analyses; the model will provide a way of extending, to any coastline for which a wave climate can be estimated, probabilistic forecasts including expected maximum magnitudes of erosion and accretion over a time interval, and alongshore extents of erosion and accretion zones. Along with the practical benefits such predictions could offer coastal managers, successful model tests would represent an advance in basic understanding of the processes that are important for shoreline changes on scales ranging from hundreds of meters to tens of kilometers. Models that will be able to elucidate the range of coastline changes to be expected in the next century as sea level rise accelerates rely on such improvements in basic understanding. In addition, undergraduate as well as graduate students would participate in the research and the presentation of the results.