Yuhi, M., Dang, M.H., Umeda, S., 2013. Comparison of accelerated erosion in riverbed and downstream coast by EOF analysis.
This study investigates the long-term variations of sediment volume in an integrated watershed composed of the Tedori River and the Ishikawa Coast, Japan, where both the riverbed and the coast have experienced rapid and serious erosion due to the combined effects of natural and anthropogenic factors. Contemporary data for coastal and riverbed evolution were compiled and compared, and the decadal variations of the seabed and riverbed elevation were examined using a set of field surveys collected over several decades. These topographic data have been analyzed using empirical orthogonal functions (EOFs) to determine the coastal responses to the reduction of sediment supply related to the antecedent riverbed erosion. It was shown that the characteristics of volumetric variation could be captured well by the temporal coefficient of the first mode of EOFs. The study area was divided into several sub-regions, and the variations of sediment volume were examined on decadal scales. The correlation between the variations has been discussed in relation to the anthropogenic modification such as the material mining in the river basin and the construction of coastal structures. On the regional scale, the correlation between the river and coastal evolution showed that the anthropogenic modifications in the fluvial basin have led to an accelerated imbalance of the coastal sediment budget, while the modified river regulations and construction of coastal structures have recently mitigated the river and coastal erosion. Several years of time lag were recognized between the riverbed and the coastal erosion.