2006 Fiscal Year Final Research Report Summary
Regional analysis of the impact of river basin modifications on neighboring coasts
| Project/Area Number |
17560455
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
水工水理学
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| Research Institution | Kanazawa University |
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Principal Investigator |
YUHI Masatoshi Graduate School of Natural Science and Technology, Associate, Professor, 自然科学研究科, 助教授 (20262553)
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| Co-Investigator(Kenkyū-buntansha) |
YAMADA Fumihiko Kumamoto University, Graduate School of Science and Technology, Associate Professor, 自然科学研究科, 助教授 (60264280)
UMEDA Shinya Graduate School ofNatural Science and Technology, Lecturer, 自然科学研究科, 講師 (30313688)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Coastal Erosion / Regional Analysis / Sediment Budget / Sediment Discharge / Longshore Bar |
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| Research Abstract |
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.
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