1994 Fiscal Year Final Research Report Summary
Study on effective protiction works by stones or gravel against local scour of sand bed
| Project/Area Number |
05650495
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
水工水理学
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| Research Institution | Ehime University |
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Principal Investigator |
SUZUKI Koichi Ehime Univ., Dept.of Civil & Ocean Eng., Dr.Eng., Professor, 工学部, 教授 (70026285)
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| Co-Investigator(Kenkyū-buntansha) |
KURIHARA Takashi Ehime Univ., Dept.of Civil & Ocean Eng., Ms.Eng., Research Associate, 工学部, 助手 (70243805)
WATANABE Masahiro Ehime Univ., Dept.of Civil & Ocean Eng., Dr.Eng., Asociate Professor, 工学部, 助教授 (70036458)
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| Project Period (FY) |
1993 – 1994
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| Keywords | sand-gravel mixture / sorting of sediment / flow resistance / mountain river / stair-like bed form / bed protection by gravel / armor coat / filter effect |
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| Research Abstract |
There are some hydraulic phenomena specific to the river bed with mixture of sand, gravel and stone such as armor coat formation or stair like bed form. Here two phenomena are studied : 1) conditions for effective protection works by stones or gravel against local scour of sand bed, and 2) flow resistance and bed form with transverse limb in mountain rivers. Main results are as folloes ;
1) Protection works by stones or gravel against local scour of sand bed around river structures are effective only if the protected bed sand is not drawn out through the cover layr of stones or gravel which is stable against tractive force by the local flow. Hydraulic conditions for the effective protection works are studied experimentally. Bed sand can not geometrically move through the stones or gravel layr, when the ratio, D/d, of stones or gravel scale D to sand scale d is less than 2. The tractive force on the bed sand is exponentially reduced through the protection layr as a function of the ratio, L/D,of the protection layr thickness L to D.
2) Flow resistance and bed form with trasverse limb are discussed with data observed in a mountain river and obtained by experiments for the bed with sand-gravel mixture or fixed crosspiece roughness. The ratio, lambda/DELTA, of wave length lambda to wave high DELTA of limb bed in mountain rivers is about 10, in which case flow resistance is proved to become maximum by experiments. Flow resistance on the bed with relatively large roughness changes largely according to the flow patterns, and it becomes largestwhen the ratio, h_m/DELTA, of flow depth h_m to the roughness height DELTA is about 1.7 for lambda/DELTA=10
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