COLLABORATIVE RESEARCH: Coasts in Motion: Quantifying the patterns of coastal change using LIDAR

摘要本研究主要是收集和分析海岸线变化的新观测资料。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，每次调查间隔六个月。这些调查，加上1997年、1998年、1999年和2000年对同一段海岸线的调查，将能够分析18个时间间隔内海岸线变化的模式，时间间隔从6个月到8年不等。以前应用于单一年度间隔变化的分析技术（Tebbens等人，2002年）量化统计数据，包括：1）作为沿岸长度尺度函数的海岸线变化量; 2）侵蚀和加积毗连区沿岸长度的分布; 3）在一个时间间隔内发生的侵蚀和加积幅度的分布。在先前的分析中，海岸线模式的统计数据在测量的不同海岸线段之间存在差异。这些海岸线段具有不同的方向，因此具有不同的有效波浪气候。在许多时间间隔内重复分析将测试统计数据和从一个海岸线段到另一个海岸线段的变化是否稳健。 拟议的工作还将测试一个假设和潜在的模型，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表明了这样一种假设，即这些变化主要是由与平滑海岸线的细微偏差相关的沿岸运输中的细微梯度驱动的。最近的研究表明，当波浪以大于约45 °的相对角度从深水接近海岸时，海岸线扰动增长，导致沿海岸的非均匀海岸线变化，其在任何尺度下都存在扰动（Ashton等人，2001年）。从深水角度接近海岸正常的波浪往往平滑的海岸线。在一段较长的时间内，变化的模式将至少部分地由粗糙化和平滑化影响之间的相互作用引起，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等人，2001; Ashton等人，2003 a; Ashton等人，2003年b）预测了观测到的趋势与海岸线方向（区域波浪气候）在以前的分析（Tebbens等人，2002年）的统计数据之一。 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调查结果，如果其他模型的预测与观测结果一致，则该模型能够概括观测和分析的有用性;该模型将提供一种方法，扩展到任何可以估计波浪气候的海岸线，概率预测，包括在一段时间内预计的最大侵蚀和加积幅度，以及沿岸侵蚀和加积区的范围。沿着这些预测可以给海岸管理者带来实际的好处，成功的模型试验将代表着对海岸线变化过程的基本理解的进步，这些过程对数百米到数十公里的尺度上的海岸线变化非常重要。随着海平面加速上升，下个世纪海岸线预计将发生变化，而这些模型将能够阐明这一变化的范围，这有赖于对基本认识的这种改进。 此外，本科生和研究生将参加研究和成果介绍。

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.