Regional analysis of the impact of river basin modifications on neighboring coasts

基于跨越40多年的广泛时间尺度上的调查记录，研究了从Tedori河流域到日本石川海岸的综合分水岭的长期和大范围的地貌变化。汇编和比较了海岸和河床演变的当代数据，以评估人为改变对河流流域的影响。重点研究了采沙和筑坝对造成海岸侵蚀加速的沉积赤字的影响。河口附近的地貌响应表明，河流输沙量的减少对不同时间尺度下的地貌动力学行为有深刻的影响，包括沙洲的周期性迁移。综合流域现有资料的整理表明，陆相水库的持续采砂、防洪调度和泥沙滞留导致了海岸泥沙收支的严重不平衡：在侵蚀最加速的21.5 km2范围内，海岸泥沙体积减少了约5×105m~3/年，并提出了一种有效的方法来量化不同时间尺度共存的形态变化。该方法基于经验正交函数(EOF)技术和使用时间移动平均的预条件运算相结合。该方法已应用于日本Tedori河口附近跨岸海床剖面的长期变化。结果表明，在EOF分析之前进行适当的滑动平均运算可以实现有效的模式分解。清楚地捕捉到了侵蚀体制的长期过渡和砂坝迁移的周期性特征。

Long-term and large-scale morphological changes in the integrated watershed from the Tedori River basin to the Ishikawa Coast, Japan have been examined based on survey records across a broad time scale spanning over 40 years. Contemporary data for coastal and riverbed evolution was compiled and compared in order to assess implications of anthropogenic modifications of the river basin. Focus is placed on the influence of sand extraction and dam constructions on the sedimentary deficit resulting in accelerated coastal erosion. The morphological response near the river mouth indicates that the reduced sand discharge from the river has profound implications on the morphodynamic behavior under various time scales, including periodical sand bar migration. The collation between existing records of the integrated watershed shows that the persistent sand mining, flood control operation, and retention of sediment in terrestrial reservoirs has led to a serious imbalance of the coastal sediment budget : this has resulted in the decrease of coastal sediment volume at approximately 5×105 m3/year in the study area of 21.5 km2 when the erosion was most accelerated.Furthermjore, an effective method is proposed in order to quantify the co-existing morphological changes of various time scales. The proposed method is based on the EOF (Empirical Orthogonal Function) technique combined with a preconditioning operation using temporal moving-average. The method has been applied to the long-term variations of the cross-shore seabed profile near Tedori River mouth, Japan. The results show that suitable moving-average operation prior to EOF analysis enables effective mode decomposition. Both the long-term transition of eroding regimes and the periodic features of bar migration are clearly captured.