A novel approach to measuring pore fluid sediment concentrations of debris flows in a volcanic torrent

Pore fluid in a debris flow is not fully understood, despite its contribution to the fluidity of the debris flow. To observe sediment concentrations of the pore fluids in debris flows, we established a novel monitoring system in a volcanic catchment, in southern Japan. An observation culvert, 1.0 m in width, 1.5 m in height and 2.0 m in length, was placed along the stream bank. An intake covered by a grating was equipped on the side of the culvert so that only pore fluid of debris flows was led inside. Measurements of dielectric permittivities were conducted within the culvert and used for the calculation of sediment concentrations of the fluid. The sediment concentrations of the pore fluid were successfully measured for natural debris flows. The preliminary observation revealed that the volumetric sediment concentration of pore fluid varied from approximately 5 to 69 %, which were slightly smaller or similar to those of the entire debris flows. Successive occurrences of debris flow caused decreases in the sediment concentration of the pore fluids with each surge

A simplified numerical model for evaluating sediment control by open-type sabo dams in the Joganji River basin

The present study proposes a method to estimate sediment runoff by introducing a dam function of the relationship between inflow sediment and sediment runoff through a slit dam. The model can process rainfall runoff, sediment yield and runoff of a mountainous basin, and the model is applied to the upper reaches of the Joganji River basin, which is known for its huge amount of sediment runoff and intense bed variation because of the sediment yield caused by the earthquake in 1858. The performance of the calculations of sediment control of the slit dam is evaluated by the model. The result indicates that sediment deposition is significantly changed by sediment runoff. The proposed method can be expected to evaluate sediment transport with sabo dams on a basin scale

ドジョウ ハッスイセイ オ シメス シャメン ニ オケル ヒョウメンリュウ ト ウスイ シントウ カテイ ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(農学)甲第13119号農博第1624号新制||農||941(附属図書館)学位論文||H19||N4245(農学部図書室)UT51-2007-H392京都大学大学院農学研究科森林科学専攻(主査)教授 水山 高久, 教授 三野 徹, 教授 谷 誠学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDA

Downslope soil detachment–transport on steep slopes via rain splash

This study developed a one-dimensional model of downslope rain splash transport based on field experiments and previous studies. The developed model considers soil detachment processes, ground cover, probability densities, and the effect of overland run-off in preventing detachment. Field monitoring was conducted to observe precipitation run-off, ground cover, and sediment production on steep hillslopes. Field-observed data were used to develop the splash detachment rate equation, probability densities for splash transport, and the maximum splash transport distance. Observed and estimated splash transport showed overall agreement, with some differences for small storm events or events with relatively low intensity, probably caused by variation of overland run-off depth and connectivity as well as differences in soil surface cohesion at various degrees of wetness. Our model can provide insights on the interactions among rainfall intensity, soil surface condition, soil wetness, and splash transport on forested hillslopes

Application of time domain reflectometry to high suspended sediment concentration measurements: Laboratory validation and preliminary field observations in a steep mountain stream

The dielectric constant around a sensor was measured with a time domain reflectometry (TDR) system and used to calculate the volumetric sediment concentration (SC) of stream water and deposition on a streambed. The measurements of various SCs in laboratory experiments demonstrated that the TDR system proposed in this study had an accuracy of 0.01 m³ m⁻³ for practical uses, and that the measured concentrations were not sensitive to particle size. The vertical SC distributions were measured at heights of 17–37 cm in a steep mountain stream. The resulting SCs at the various heights increased by 0.01–0.07 m³ m⁻³ at the time of peak stream discharge during an extreme storm with a return period of approximately 12 years. After extreme precipitation, the SC of the lowest probe increased rapidly from approximately 0 to 0.4 m³ m⁻³. This was followed by rapid increases in the SCs at the other heights, indicating deposition around each probe. The TDR measurement system, with its straightforward calibration procedure, effectively measured deposition and a high-concentration layer above the deposited layer even during the storm event

Application of Rainfall–Runoff Model to Study Flash Floods in Volcanic Mountain Catchments

The Second International Symposium on Flash Floods in Wadi Systems: 25-27 October 2016. Technische Universität Berlin, Campus El Gouna, Egypt

Reassessing chain tilt in the lamellar crystals of polyethylene

Abstract Semicrystalline polymers are extensively used in various forms, including fibres, films, and bottles. They exhibit remarkable properties, e.g., mechanical and thermal, that are governed by hierarchical structures comprising 10–20-nm-thick lamellar crystals. In 1957, Keller deduced that long polyethylene (PE) chains fold to form thin single lamellar crystals, with the molecular chains perpendicular to the flat faces of the crystals (the chain-folding model). Chains inclining to the perpendicular orientation in single crystals have since been reported, along with their effects on the physical properties of PE. For bulk specimens, the chain tilt angle (φ) has been investigated only for model samples with well-annealed internal structures. However, for briefly annealed specimens, the φ values of lamellae and their origins are controversial owing to the disordered lamellar morphology and orientation. Herein, we report the direct determination of molecular-chain orientations in the lamellar crystals of high-density PE using a state-of-the-art electron-diffraction-based imaging technique with nanometre-scale positional resolution and provide compelling evidence for the existence of lamellar crystals with different inner-chain orientations. Clarifying the nanoscale variation in lamellar crystals in PE can allow precise tuning of properties and expedite resource-saving material design

Effect of ground cover on splash and sheetwash erosion over a steep forested hillslope: a plot-scale study

The contributions and relationships of erosion by splash and overland flow over a steep slope in a Japanese beech forest in plots with different percentages of ground cover were examined. Three erosion plots (2 m wide × 5 m long) with average understory coverage of 1%, 45%, and 94% were installed. Sediment transported by rain splash and by overland flow was sampled separately. For the plots with sparse, moderate, and high understory coverage, the average proportions of splash soil to total soil erosion during the monitoring period were 16%, 32%, and 18%, respectively. A significant correlation between the amount of splash soil and precipitation was found in the plots with 1% and 45% understory coverage, whereas no statistical relationship was identified for the plot with high understory coverage. At the sparse ground cover plot showing the largest sediment movement, the contribution of splash transport decreased with increasing precipitation. The amount of sheetwash erosion was significantly correlated with the amount of splash soil under the condition of sparse ground cover. This relationship was more pronounced during high precipitation events and the rainy season. Splash contribution to the sediment transport was in the range of 0.8%–76.7%, 2.8%–81% and 2.1%–60.8% for plot with high, moderate and low ground cover, respectively. The sparse ground cover showed the largest variation of splash and sheetwash contribution in soil erosion. This variability was due to variation in ground cover and soil surface wetness condition which led to a variation of detachment and non-linear relationship of sheetwash splash

A novel approach to measuring pore fluid sediment concentrations of debris flows in a volcanic torrent

Pore fluid in a debris flow is not fully understood, despite its contribution to the fluidity of the debris flow. To observe sediment concentrations of the pore fluids in debris flows, we established a novel monitoring system in a volcanic catchment, in southern Japan. An observation culvert, 1.0 m in width, 1.5 m in height and 2.0 m in length, was placed along the stream bank. An intake covered by a grating was equipped on the side of the culvert so that only pore fluid of debris flows was led inside. Measurements of dielectric permittivities were conducted within the culvert and used for the calculation of sediment concentrations of the fluid. The sediment concentrations of the pore fluid were successfully measured for natural debris flows. The preliminary observation revealed that the volumetric sediment concentration of pore fluid varied from approximately 5 to 69 %, which were slightly smaller or similar to those of the entire debris flows. Successive occurrences of debris flow caused decreases in the sediment concentration of the pore fluids with each surge