Daizo Tsutsumi

Effect of Hydrotropism on Root System Development in Soybean (Glycine max): Growth Experiments and a Model Simulation

To observe root system development, soybean plants (Glycine max) were grown in root boxes that were set horizontally to reduce the effect of gravity. Along with the root system development, the two-dimensional distribution of soil water content in the root boxes was measured continuously by the time domain reflectometry (TDR) method. Root system development and its morphological architecture were strongly affected by the positions of the water supply. It is suggested that root hydrotropism plays the dominant role in root system development. In addition to root hydrotropism, the importance of root compensatory growth is suggested. A combined model of root system development and soil water flow considering root hydrotropism and compensatory growth was used to simulate root system development and soil water flow. The morphological architecture of root systems and the distribution of soil water content obtained in the experiment were successfully explained by the model simulation. These results confirmed that root hydrotropism and compensatory growth are dominant factors in root system development under a reduced effect of gravity. The validity of the model was confirmed, and its applications for various purposes were suggested.

Three-Dimensional Modeling of Hydrotropism Effects on Plant Root Architecture along a Hillslope

A three-dimensional model of root system development and soil water flow is described and applied to actual conditions along a hillslope. In the model, gravitropism, hydrotropism, and circumnutation were employed as the main factors controlling root elongation. Root systems of 2-yr-old pine trees ( Pinus massoniana Lamb.) on natural slopes in southern China were excavated and examined, and their development was simulated through the use of continuously monitored temperature and rainfall data. In the simulated root systems, angles between first-order lateral root segments and the vertical direction on the upslope portion of a tree were larger than those on the downslope portion of the tree; hence, root systems exhibited asymmetric architectures. This asymmetry was more obvious for root systems developed on the downslope side of the hillslope. Because root systems simulated without the effect of hydrotropism did not develop asymmetric architectures, the direction of soil water flux and the effect of hydrotropism appear to be the main factors contributing to the observed architectural asymmetry, typical of root systems along hillslopes. Calculations with the proposed root system model were helpful in elucidating and understanding the predominant processes affecting root system development on hillslopes.

Development of new sensor systems for continuous bedload monitoring using a submerged load-cell system (SLS): Development of new sensor systems for continuous bedload monitoring

It is important to evaluate bedload discharge and temporal changes of the bed surface, and bed deformation can be estimated during floods if the bedload discharge is properly evaluated in an arbitrary cross-section. With the exception of grain size and its distribution within the bedload, bedload discharge has been measured using both direct and indirect methods. Bedload slot is a direct method but cannot be used to measure bedload during a flood because of volume limitations. Indirect methods require correlation between the signals and sediment volume measured using another method. In the present study, a small, automatically recording bedload sensor with an iron plate and a pair of load cells is developed in order to evaluate not only large particles but also sand particles as bedload. Bedload mass is calculated by integrating with respect to both the velocity of sediment particles and the averaged particle weight as measured by a pair of load cells, and, as an example, the velocity is estimated by the cross-correlation function of weights measured by load cells. The applicability of the proposed sensor is discussed based on the results of flume tests in the laboratory (2014) and the observation flume of the Hodaka Sedimentation Observatory of Kyoto University in Japan (2015). The system was installed in the observation flume in November of 2012, and flume data were obtained using natural sediment particles. In particular, it was difficult to estimate the velocity of averaged bedload particles, and it was better to apply a cross-correlation function in the laboratory tests. However, it appears that the previous estimation can estimate these velocities in the observation flume using a connecting tube and submerged load-cell systems. Copyright

Gravel-Bed Rivers: Processes and Disasters

With contributions from key researchers across the globe, and edited by internationally recognized leading academics, Gravel-bed Rivers: Processes and Disasters presents the definitive review of current knowledge of gravel-bed rivers. Continuing an established and successful series of scholarly reports, this book consists of the papers presented at the 8th International Gravel-bed Rivers Workshop. Focusing on all the recent progress that has been made in the field, subjects covered include flow, physical modeling, sediment transport theory, techniques and instrumentation, morphodynamics and ecological topics, with special attention given to aspects of disasters relevant to sediment supply and integrated river management. This up-to-date compendium is essential reading for geomorphologists, river engineers and ecologists, river managers, fluvial sedimentologists and advanced students in these fields.

Transport measurement with a horizontal and a vertical pipe microphone in a mountain stream: taking account of particle saltation: Bedload measurement with a horizontal and a vertical pipe microphone

The pipe microphone has been shown to be an effective means for monitoring bedload transport in mountain streams. It is commonly installed perpendicular to the flow direction on a stable river bed, such as that of a check dam. Acoustic pulses caused by bedload collisions with the pipe are detected by a microphone. However, bedload particles saltating over the pipe remain undetected. To overcome this disadvantage, we installed a horizontal as well as a vertical pipe microphone in the Ashi-arai-dani supercritical channel located in the Hodaka mountain range, Japan. The vertical pipe was installed on the wall of the channel and the horizontal pipe was installed on the channel bed. The acoustic response of the horizontal pipe is expected to be larger than that of the vertical pipe, because the bedload concentration decreases with increasing height above the bed. However, at high amplifications, the peak pulse value from the vertical pipe is higher than that from the horizontal pipe. We explain this observation as follows: under high bedload discharge conditions, the pulses of the horizontal pipe are saturated but those of the vertical pipe are not. We proposed a ratio (Rhv) between the pulses detected by these sensors, and applied this ratio for calibrating the contemporaneous pulses detected by a microphone located immediately upstream of a bedload slot sampler. Indeed the Rhv-corrected pulses correlated well with the bedload discharge calculated from the sampler, supporting our explanation. We conclude that bedload monitoring using concomitant vertical and horizontal pipe microphones can be used to calibrate centrally located pipe microphones when the bedload concentration is approximately homogeneous laterally across the width of the channel cross-section, and thereby represent bedload discharges more accurately than with only a single pipe microphone. Copyright

Development and installation of bedload monitoring systems with submerged load cells

Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain river. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of: (1) an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, (2) two submerged load cells 0.7 m apart, (3) a pressure sensor and, (4) an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute (DPRI) of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells. Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data.

STUDY ON BEDLOAD MEASUREMENT BY PLATE-TYPE VIBRATION SENSOR

Measuring the bedload transport rate is utmost interest to understand and quantify all sediment transport related phenomena. Three existing bedload measuring systems are 1) the hydrophone, 2) the geophone, and 3) the plate microphone as their modified system. All systems estimate transport rate based on sediment impact, whereas each has respective disadvantages. In this paper, as the other improved system, plate-type vibration sensor is discussed. Calibration experiment is conducted and the system is compared with the other plate hydrophone. In the experiments, impact data is perceived as both vibration pressure and vibration pulse, and analyzed the same as plate microphone. Although it has been clarified that fine sediments lower than 10 mm are not detectable with plate hydrophone, plate-type vibration sensor detected vibration pulses of them clearly. Moreover, detection rate can be linked to the sediment bulk density and the gravel jump length.

DETECTION OF UNDERGROUND WATER PATHWAYS BY UNDERGROUND HYDROSONIC METHOD

In this study, a new method to detect the underground water path positions was developed. Water path position was estimated by the sound of ground water flow. As a first step, water flow through a single water pathway installed within an isotropic model soil layer was examined by this method. From the measured sound pressure, position of sound source was estimated. Results indicated that the estimated position of sound source corresponded to location of the installed actual water pathway. As a next step, this method was also applied both to natural hillslopes and road cut slopes. Water springs from lower part of every slope were observed, and the relationship between estimated water pathway within the slopes and the position of these springs were examined. Results indicated that the estimated water pathways were corresponded to springs position with accuracy of 0.5 m or less. From these results, it is obvious that we can detect underground water pathways with high accuracy using this new method.