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四万十川における治水とスジアオノリの生育環境の創出を両立させる新たな河道改修方法の検討

岡田 将治^*, 松岡 直明^**, 中平 歩^***

^* 高知工業高等専門学校ソーシャルデザイン工学科 〒783-8508 高知県南国市物部乙200-1
^** 高知県幡多土木事務所 〒787-0010 高知県四万十市古津賀4-16
^*** いであ(株)大阪支社 〒559-0034 大阪府大阪市住之江区南港北1-24-22

Study On Extraction Of Enviromental Conditions Suitable For Spawning Eggs Of Sweet Fish And Prediction Of Its Change After Flood In The Shimanto River

Shoji OKADA^*, Naoaki MATSUOKA^**, Ayumi NAKAHIRA^***

^* Department of Social Design Engineering, National Institute of Technology, Kochi College
^** Kochi Prefecture, Hata Civil Engineering Office
^*** IDEA Consultants, Inc., Osaka Branch Office

Abstract

Recently, the lack of discharge capacity due to sediment deposition and reduction of crop yields of natural Enteromorpha prolifera become problems in the downstream area of the Shimanto River. After the riverbed was dredged to be suitable for the growth of the Enteromopha prolifera in the section where discharge capacity was insufficient, new vegetation area was observed. To examine the dredging method, we constructed a riverbed variation analysis model that reproduces the flow and the sediment dynamics during the flooding. Moreover, it was confirmed that river bed fluctuation did not occur in the entire river channel at the average annual maximum discharge of 6000m3/s, and no sediment deposition occurred at the dredged area. By using the riverbed variation analysis model constructed in this research, we could propose effective dredge method of sandbar which can secure the discharge capacity and enable creation of Enteromorpha prolifera growing environment.

Key Words: Enteromorpha prolifera, Sandbar excavation，Growth ground creation