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Setsuo HAYASHI
1997 Volume 50 Issue 3 Pages
1-3
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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Michiya IRASAWA, Shiro TAKEMORI, Asao YOO, Jiro ENDO
1997 Volume 50 Issue 3 Pages
4-11
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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Debris flows, landslides and landslips are recognized as severe disasters. The warning system is very important for protecting human lives from these disasters. In the current warning system, the warning is issued if the predicted total effective rainfall and effective precipitation intensity exceed certain criterion determined from past occurrences of such disasters. The historical maximum rainfall up to one or two hours is used as the predicted rainfall. In this system, unnecessary evacuations may tend to occur depending on the location or the predetermined criterion. The short term rainfall forecasting (nowcast) has not been used.
In contrast, introducing the nowcast to the warning system, we have developed a method to calculate the probability distribution of near future rainfall by radar. For example, it can be used for deriving upper confidence limit value of rainfall in arbitrary confidence level and the value will be substituted for the historical maximum rainfall in the warning system. We have estimated the effectiveness of the warning system using the method that predicts probability distribution of rainfall.
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Hirokazu KITAMURA
1997 Volume 50 Issue 3 Pages
12-20
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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The supply of oxygen into water by reaeration and subsequent transfer process is one of the most significant self-purification processes in natural streams. Thus, the purpose of this paper is to investigate the transfer process of dissolved oxygen by turbulent diffusion in a natural stream.
Velocity during 300 seconds with 1 second interval at the maximum-velocity point was measured and analyzed based on the Taylor's turbulent-diffusion theory modified by the assumption that Lagrange's velocity in natural streams depends on the velocity of flow direction in each section.
The results are summarized as follows: 1) the strongest correlation is observed between velocity and the strength of turbulence, 2) the turbulent diffusion process is accelerated by subsurface flows which consist of the periodical long wave and the short wave of auto-correlation function, and 3) a clear and accurate linear relationship exists between turbulent diffusivity and mixing rate depending on the length of residence time.
Auto-correlation function of subsurface flows and residence time are strongly influenced by discharge and topographical conditions such as water depth, river width and head. The turbulent diffusion process is, therefore, thought to be, the multiple effects of these factors in natural streams. Consequently, conservation and effective use of the self-purification process in natural streams is possible when erosion control techniques incorporate these aforementioned factors skillfully into minor bed fishway and so on.
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Masaharu FUJITA, Takahisa MIZUYAMA, Takeyuki IIDA
1997 Volume 50 Issue 3 Pages
21-27
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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In this paper, a few problems and points of sediment erosion control works with groundsels are discussed by means of numerical simulation of a long-term bed variation and a short-term bed variation under no sediment supply. On a long-term basis, groundsels have to reduce remarkably erosion depth as well as erosion volume at an equilibrium bed condition. So, the effect of groundsels on erosion depth was investigated with the simulation of the bed variation of a river for a time-series of water discharge with a duration of 100 years. The result has pointed out that a series of groundsels can reduce the erosion volume, but not the erosion depth because the river bed with non uniform materials is not much eroded even without the groundsels due to the development of armor coat. An increase in groundsels can not always, therefore, improve efficiency on reducing erosion depth. On a short-term basis, a role of groundsels is to protect river beds from too much erosion by a heavy flood. The simulation of bed variation for a hydrograph with a design discharge has shown that the erosion depth could be thoroughly reduced if a series of groundsels is placed only in the most upstream section with three times length of the erosion region predicted in the case of no groundsel.
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Takahiko FUJIMOTO, Katsuo SASAHARA, Keiichi MONMA
1997 Volume 50 Issue 3 Pages
28-34
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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On the Shirasu slope, most parts of slope failures caused by rainstorms have often occurred near knick lines. On the slope with some knick lines, tha failures sometimes occur at several elevations.
On the Shirasu plateau, there exist the paleovalley which characterized by no waters. Paleovalley has some knick points and these knick points continue downstream to the knick lines on the Shirasu slope. Paying attention to the topographical features such as a knick point, we examined the possibility of forecasting the slope failure sites.
We regarded a headward of valley as the circle which inscribed around the ridge lines on the topographical map, and we get the average inclination within the circle and the radius. Measured by this method on varied scales of valley, collapsed and not collapsed slopes could be discriminated by the approximate formula “i=2.39r
-0.50” (i; average inclination, r; radius). Under the same method above we also defined the efficient hight “He=h
2/2r” (h; relative height, r; radius) as a meaningful values of topography, and calculated “He” of every slope. Using these formulas of the research on the case of Kagoshima disaster in 1993, we clarified that most collapsed slopes have efficient height above 11.4 (m).
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Yukiyoshi TERAMOTO, Takashi JITOUSONO, Etsuro SHIMOKAWA, Nobuo ANYOJI
1997 Volume 50 Issue 3 Pages
35-39
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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Nobutomo OSANAI, Yutaka KOIZUMI, Yoshiharu ISHIKAWA
1997 Volume 50 Issue 3 Pages
40-44
Published: September 15, 1997
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Hideaki MARUI, Nobutomo OSANAI
1997 Volume 50 Issue 3 Pages
45-51
Published: September 15, 1997
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Shunroku NAKAMURA
1997 Volume 50 Issue 3 Pages
52-57
Published: September 15, 1997
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Takeshi OKABE
1997 Volume 50 Issue 3 Pages
58-65
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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Hiroshi SHINOHARA, Takashi SAIMOTO
1997 Volume 50 Issue 3 Pages
66-69
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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Yoshiharu ISHIKAWA, Takashi YAMADA, Okichika KUROKAWA
1997 Volume 50 Issue 3 Pages
70-73
Published: September 15, 1997
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Kazuhiko HOSHINO, Takeyasu OHONAKA, Koichiro YAMADA
1997 Volume 50 Issue 3 Pages
74-76
Published: September 15, 1997
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Keiji TAKESHITA, Akira SHIMIZU
1997 Volume 50 Issue 3 Pages
77-80
Published: September 15, 1997
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Noriyuki MINAMI, Takashi YAMADA, Hideaki MIZUNO, Shouzo KOGA
1997 Volume 50 Issue 3 Pages
81-82
Published: September 15, 1997
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Yoko TOMITA, Naoki YAMAGUCHI
1997 Volume 50 Issue 3 Pages
83-84
Published: September 15, 1997
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[in Japanese]
1997 Volume 50 Issue 3 Pages
84
Published: September 15, 1997
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Kenlo NISHIDA
1997 Volume 50 Issue 3 Pages
85
Published: September 15, 1997
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Kenji SAWAI
1997 Volume 50 Issue 3 Pages
86
Published: September 15, 1997
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[in Japanese]
1997 Volume 50 Issue 3 Pages
87-88
Published: September 15, 1997
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1997 Volume 50 Issue 3 Pages
96
Published: September 15, 1997
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1997 Volume 50 Issue 3 Pages
A1-A2
Published: September 15, 1997
Released on J-STAGE: April 30, 2010
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