Experimental studies on debris flow with logs focusing on specific weight difference of log species     

Haruki WATABE  Takahiro ITOH  Kazuhiko KAITSUKA  Shigeki NISHIMURA 《山地科学学报》2013,10(2):315-325

There are many experimental approaches,field investigations and numerical calculations for movements of woods in a clear water and debris flow.However,kinematic conditions for accumulated logs and the interactions between a main flow and logs have not been fully evaluated.Mitigations for woods need taking into account the characteristics of tree species such as conifer and broad-leaf trees and of shapes such as root swells and crown.In the present study,we focus on the differences in specific weight of conifer and broad-leaf trees with some moisture in a sediment-water mixture flow with narrow flow width,and consider that conifer and broad-leaf tree are floating and submerged solid phase,respectively.Flume tests are conducted in steady flow of clear and debris flow over a rigid bed in order to evaluate conifer and broad-leaf tree movement in clear water and debris flow.Experimental data indicates that dimensionless transverse diffusion coefficient can be 0.1 to 0.4 and 0.3 to 0.9 in flow direction.Those diffusive characteristics seem to be independent of Reynolds number and Froude number,but dependent of bed slope,i.e.,gravity,though detailed considerations are needed to discuss about flow characteristics such as spatial eddy structures,momentum transfer induced by interactions of logs and so on.  相似文献   

Sensitivity of Salt-leached Clay Sediments in the Ariake Bay Area,Japan     

Phanny He  Masami Ohtsubo  Takahiro Higashi  Motohei Kanayama 《Marine Georesources & Geotechnology》2013,31(5):429-436

This study aims to determine whether the principle that “divalent cation predominance in the pore water precludes quick clay development” applies to the Ariake Bay sediments. The chemical and geotechnical properties of an Ariake clay sediment are presented, and sensitivity is discussed with a focus on pore-water salinity and cation composition. In recent years, reduction of pore-water salinity has occurred due to permeation of river water through the sediments because of overpumping of groundwater. Sodium remains the dominant pore-water cation in an upper zone, whereas divalent cations are dominant in the deeper zone. Divalent cation domination in the deeper zone is ascribed to Ca release from nearby cement-stabilized sediments and to Mg increase in response to a change in river water quality. The upper zone's sensitivity ranged from 15 to 77, and the remolded strength was mostly <0.5 kPa, such that quick clay was present over much of its depth. In contrast, the deeper zone's sensitivity was <40, and its remolded strength exceeded 0.5 kPa; quick clay was not present despite the <2 g/L salinity. The absence of quick clay is ascribed to the high remolded strength caused by the pore-water divalent to monovalent cation ratio being greater than 0.25.  相似文献   

Modeling interaction of fluid and salt in an aquifer/lagoon system   总被引：1，自引：0，他引：1  

Fujinawa K  Iba T  Fujihara Y  Watanabe T 《Ground water》2009,47(1):35-48

To simulate the dynamic interaction between a saline lagoon and a ground water system, a numerical model for two-dimensional, variable-density, saturated-unsaturated, and coupled flow and solute transport (saltwater intrusion by finite elements and characteristics [SIFEC]) was modified to allow the volume of water and mass of salt in the lagoon to vary with each time step. The modified SIFEC allows the stage of a lagoon to vary in accordance with a functional relation between the stage and water volume of the lagoon, and also allows the salt concentration of the lagoon to vary in accordance with the salt budget of the lagoon including chemical precipitation and dissolution of salt. The updated stage and salt concentration of the lagoon are in turn used as transient boundary conditions for the coupled flow and solute transport model. The utility of the modified model was demonstrated by applying it to the eastern Mediterranean coastal region of Turkey for assessing impacts of climate change on the subsurface environment under scenarios of sea level rise, increased evaporation, and decreased precipitation.  相似文献   

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia   总被引：1，自引：0，他引：1  

Shrestha  Badri Bhakta  Perera  Edangodage Duminda Pradeep  Kudo  Shun  Miyamoto  Mamoru  Yamazaki  Yusuke  Kuribayashi  Daisuke  Sawano  Hisaya  Sayama  Takahiro  Magome  Jun  Hasegawa  Akira  Ushiyama  Tomoki  Iwami  Yoichi  Tokunaga  Yoshio 《Natural Hazards》2019,97(1):157-192

Natural Hazards - This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included...  相似文献   

Crustal structure beneath Aso Caldera,Southwest Japan,as derived from receiver function analysis     

Yuki Abe  Takahiro Ohkura  Takuo Shibutani  Kazuro Hirahara  Mamoru Kato 《Journal of Volcanology and Geothermal Research》2010

Aso Volcano experienced a huge pyroclastic eruption 90 thousand years ago, and formed a large caldera (18 km × 25 km). In order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically, we investigated seismic velocity discontinuities and velocity structure beneath Aso Caldera using receiver functions and a genetic algorithm inversion. We confirm the existence of the Moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath Aso Caldera, from imaging of receiver functions observed only at stations outside the caldera. As a result of a more detailed examination with GA inversion, a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera. S-wave velocity of the layer is estimated to be 2.0–2.4 km/s. We estimate that the low velocity layer contains at most 15% melt or 30% aqueous fluid. The layer exists near the Conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle-eastern part of the caldera. Fluid contained in the layer might be related with huge pyroclastic eruptions of Aso Volcano.  相似文献   

Long-period ground motions from the 2003 Tokachi-oki earthquake     

Takahiro Maeda  Tsutomu Sasatani 《Journal of Seismology》2008,12(2):243-253

We study characteristics of long-period ground motions from the 2003 Tokachi-oki earthquake (Mj 8.0), a large interplate earthquake, based on spatial distribution maps and attenuation relationships for four kinds of peak ground velocity (PGV) value. The first kind (PGV(WB)) is obtained from a maximal value of vector sum of the three-component, wide-band velocity seismograms, and the other three kinds (PGV(BP10), PGV(BP20), and PGV(BP30)) are obtained from a maximal value of vector sum of the three-component, narrow band-pass filtered velocity seismograms (the central periods are 10, 20, and 30 s). The spatial distribution maps for all kinds of PGV value show azimuth dependence; the PGV values in Hokkaido, northern side of the epicenter are larger than those in Tohoku, southwestern side of the epicenter, when compared at a comparable distance. We find that the features result from the radiation pattern of long-period surface waves, that is, the source effect. The attenuation relationships show the following trends: The PGV(WB) values are larger than the sum of the PGV(BP10), PGV(BP20), and PGV(BP30) at distances (D) less than 200 km, while the PGV(WB) values are comparable to the sum of the PGV(BP20) and PGV(BP30) at D > 200 km. This indicates that the PGV(WB) values at D < 200 km are affected by ground motions with periods less than 10 s, while long-period surface waves mainly contribute to the PGV(WB) values at D > 200 km. The basin site effects generate a patchy pattern in the spatial distribution maps and a large scattering in the attenuation relationships for the PGV(WB) and PGV(BP10) values. Finally, we conclude that the PGV(WB) values from the 2003 Tokachi-oki earthquake are controlled by the radiation pattern of long-period S and surface waves and various basin site effects.  相似文献   

Grain size of the surface regolith of asteroid 4 Vesta estimated from its reflectance spectrum in comparison with HED meteorites     

Takahiro Hiroi  Carl M. Pieters  Hiroshi Takeda 《Meteoritics & planetary science》1994,29(3):394-396

Abstract— The grain-size distribution of the regolith of asteroid 4 Vesta has been estimated by comparing its reflectance spectra (0.3–2.6 μm) with those of HED meteorites. The finest grain-size separate (<25 μm) of a particular howardite has a reflectance spectrum most similar to Vesta's. In order to better simulate Vesta's surface mineralogy, reflectance spectra of those finest HED meteorite powders were linearly combined, and Vesta's spectrum was scaled for the best fit between them. Both the albedo and the shape of reflectance spectrum of Vesta were well reproduced by regional mixtures of the finest (<25 μm) powders of HED meteorites. The result suggests the heterogeneity of Vesta's surface and provides an estimate of the visible reflectance of Vesta that is close to its IRAS albedo. Thus, this suggests that fine grains can be generated and retained by relatively small bodies (Vesta is approximately 500 km in diameter).  相似文献   

Influence of various factors on the difference in the liquid limit values determined by Casagrande’s and fall cone method     

Anil Kumar Mishra  Masami Ohtsubo  Loretta Y. Li  Takahiro Higashi 《Environmental Earth Sciences》2012,65(1):21-27

As there are many correlations linking the liquid limit directly or indirectly with various engineering properties of the soil, the accurate determination of the liquid limit is quite essential. Generally, two methods, i.e. Casagrande’s and fall cone are adopted to determine the liquid limit of soil. Research was carried out to study the influence of the properties of bentonite and the presence of the salt solution on the liquid limit values of soil-bentonite mixtures determined by the Casagrande’s and fall cone methods. The results showed that irrespective of the presence of the type of bentonite or salt solution, a higher value of the liquid limit was obtained by the Casagrande’s method as compared to the fall cone method. However, the difference between the two methods decreased with the decrease in the liquid limit, clay fraction, specific surface area and free swelling capacity of the bentonite present in the mixture. Similarly, the difference in the liquid limit values obtained by both these methods is reduced with an increase in the salt concentration.  相似文献   

Historical record of heavy metal pollution deduced by lead isotope ratios in core sediments from the Osaka Bay,Japan     

Takahiro Hosono  Chih-Chieh Su  Kei Okamura  Makoto Taniguchi 《Journal of Geochemical Exploration》2010

Three marine sediment cores from Osaka Bay were analyzed for ²¹⁰Pb geochronology, heavy metal concentrations (Zn, Cu, and Pb) and stable lead isotope ratios (²⁰⁶Pb/²⁰⁷Pb) in order to reconstruct high-resolution heavy metal pollution history from 1900–2006. Anthropogenic metal accumulation in sediments peaked in 1970 in agreement with the high economic growth period in Japan. The comparison of temporal patterns of ²⁰⁶Pb/²⁰⁷Pb ratio with other areas of Japan suggested that the heavy metals, imported from several different countries during the periods of economic growth (1955 to 1973), are the main pollution source for the country. For the period 1970–2006, the sediment data reflect the result of stricter environmental regulations applied after the late 1960s. However, heavy metal concentrations in the surface sediments are still elevated to levels several times higher than the levels at the bottoms of the cores. Additionally, the lead isotope ratio does not show significant change after the 1980s. Secondary heavy metal pollution through the mixing of deeper polluted sediment appears to be the likely reason for the deterioration of present time submarine sediment environments. In conclusion, this study has demonstrated that it is difficult to recover over a period of several years the benthic quality of a bay, once it is heavily polluted.  相似文献   

High-resolution imaging polarimetry of HL Tau and magnetic field structure     

P. W. Lucas  Misato Fukagawa  Motohide Tamura  A. F. Beckford  Yoichi Itoh  Koji Murakawa  Hiroshi Suto  Saeko S. Hayashi  Yumiko Oasa  Takahiro Naoi  Yoshiyuki Doi  Noboru Ebizuka  Norio Kaifu 《Monthly notices of the Royal Astronomical Society》2004,352(4):1347-1364

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