Formation of sedimentary structures in flume experiments under upper-flow-regime conditions

Research Project

Project/Area Number	08640565
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	Geology
Research Institution	Department of Geoiogy, Faculty of Education, Iwate University.
Principal Investigator	YAGISHITA Koji Iwate University, Department of Geology, Faculty of Education Professor, 教育学部, 教授 (90239731)
Co-Investigator(Kenkyū-buntansha)	ASHI Jyuichiro University of Tokyo, Graduate School, Institute of Geoscience Assistant Professo, 大学院・理学研究科, 助手 (40251409)
Project Period (FY)	1996 – 1997
Project Status	Completed (Fiscal Year 1997)
Budget Amount *help	¥1,500,000 (Direct Cost: ¥1,500,000) Fiscal Year 1997: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1996: ¥1,100,000 (Direct Cost: ¥1,100,000)
Keywords	plane beds / flume experiments / upper-flow-regime / imbrication / detrital grains / Froude Number / ripples / low-relief bedform / formational process / critical flow. / 掃流力 / 無次元掃流力 / 粒子配列 / 堆積構造 / リップル
Research Abstract	In an attempt to produce plane beds under upper-flow-regime conditions, we have conducted a number of runs (experiments) using a hydraulic flume of 15 cm wide and 700 cm long, at the Ocean Research Institute, University of Tokyo. We have succeeeded in producing two types of plane beds : 1) laminae formed and buried by the migration of low-relief asymmetric ripples under near- or sub-critical flow (Froude Number Fr=0.94 ; type 1), and 2) laminae formed without causing any low-relief bedform but under super-critical flow (Fr=1.98 ; type 2). After making these two types of plane beds, imbrication of detrital grains along each plane bed was investigated. The sediments of sand-sized quartz grains (mean diameter 0.72 mm) show a high angle of imbrication (up to 30ﾟ) in type 2, whereas very low angle of imbrication (close to 0ﾟ) in type 1. Differences of imbrication angle between the two types of plane bed may be useful to infer the individual formational process of plane beds that are observed in the field.