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

基于40多年的调查记录，研究了日本Tedori河流域至石川海岸综合流域的长期和大尺度形态变化。为了评估流域人为变化的影响，对沿海和河床演变的当代数据进行了汇编和比较。重点讨论了采沙和筑坝对沉积亏损的影响，从而加速了海岸侵蚀。河口附近的形态响应表明，河流输沙量的减少对沙洲周期性迁移等不同时间尺度的形态动力学行为具有深远的影响。综合流域现有记录的整理表明，持续的采沙、防洪和陆源水库泥沙淤积导致海岸泥沙收支严重失衡，导致研究区21.5 km2的海岸泥沙体积在侵蚀最加速时减少了约5×105 m3/年。在此基础上，提出了一种量化不同时间尺度下共存形态变化的有效方法。该方法基于经验正交函数（EOF）技术，并结合时间移动平均预处理操作。该方法已应用于日本Tedori河口附近跨岸海底剖面的长期变化。结果表明，在EOF分析之前进行适当的移动平均运算可以实现有效的模态分解。侵蚀机制的长期转变和沙洲迁移的周期性特征都被清楚地捕捉到了。

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.