Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Association of Groundwater Hydrology  

DOI： 10.5917/jagh.64.189

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

For slug-injection tracer tests, tracer concentrations below the detection limit of the measurement instrument can cause truncation of the observed data. This study investigated the truncation effect on the estimation error of parameters based on analytical solutions and the results of laboratory-scale experiments. Spatial moment analysis was performed to estimate the measured total mass and transport parameters, including the pore velocity and the longitudinal and transverse dispersivities. Increasing the travel distance and detection limit caused the measured mass and dispersivities to be underestimated regardless of the dimensionality because hydrodynamic dispersion occurs with increasing travel distance, which smoothens the concentration front. The one- and two-dimensional cases showed that the truncation effect on the measured mass and longitudinal dispersivity depended on dimensionality. In contrast, the pore velocity showed no such dependence; the center of mass did not change as the unmeasured portion due to truncation was increased because the plume, which exhibited a Gaussian distribution, was truncated symmetrically. In the experiment, the measured mass and dispersivities likewise depended on the travel distance and detection limit, but there were large differences in the detection limit at which the dimensionless parameter reached a value of zero between the experimental results and analytical solution. This is because the initial plume in the experiment was of a finite size. Thus, experimental design factors such as the scale, device, and dimensionality should be considered to minimize the estimation error of transport parameters, excluding the pore velocity.

DOI： 10.1007/s12665-022-10309-9

Web of Science

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JSHWR, JAGH, JAHS, JSPH  

The objective of this paper is to evaluate effects of stratified porous formation on solute dispersion using two-dimensional laboratory tracer tests. An image analysis technique was used to analyze the solute dispersion processes and quantify the dispersivity and behaviors of forward and backward tails of solute plumes. Longitudinal dispersivity estimates for the stratified porous media increased with travel distance and are in reasonable agreement with previous work. Moreover, in all of the stratified cases the transverse dispersivity exhibited a similar trend which decayed with travel distance. The summary of dispersivities estimated from this study and previous studies suggests that if both degree of heterogeneity and scale for stratified and randomly heterogeneous porous media are similar, the longitudinal dispersivity is larger in stratified media than in randomly heterogeneous media. In order to quantify behaviors of forward and backward tails, we defined the travel distances x(05) and x(95) corresponding to the 5th and 95th percentiles, respectively, of the cumulative concentrations in the longitudinal direction, and found that the distance between x(05) and x(95) spread out linearly in the stratified cases.

DOI： 10.3178/hrl.14.123

Web of Science

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Authorship：Lead author   Language：Japanese   Publisher：Japan Society of Civil Engineers  

The objective of this study is to investigate the effect of upscaling on spatial distribution characteristic of hydraulic conductivity and solute dispersion for a stratified porous model. A geostatistical analysis allowed quantification of spatial characteristic for the upscaled models. As a result, the smoothing of spatial distribution due to upscaling reduced the heterogeneity, whereas the spatial correlation scale was preserved. In order to identify the relationship between the degrees of solute dispersion and upscaling, a combined experimental and numerical investigation is conducted. The data from the experiment are utilized to validate a numerical model that is then used to estimate the strength of the dispersion processes (i.e., longitudinal and transverse macrodispersivities) in the upscaled models. It is shown that upscaling does not affect the transverse macrodispersivity, while the longitudinal macrodispersivity is underestimated due to the decrease of heterogeneity during the upscaling process. Moreover, the result suggested that the mass transfer between layers be altered by increase in the layer thickness due to upscaling, leading to the plume spreading in the longitudinal direction.

DOI： 10.2208/jscejam.76.2_i_45

CiNii Research

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-19H03074/

Authorship：Lead author   Language：Japanese   Publisher：Japan Society of Civil Engineers  

Intermediate-scale laboratory solute transport experiments were conducted in physically heterogeneous and homogeneous porous formations to investigate the impacts of upscaling of hydraulic conductivity on the behavior of solute macrodispersion. Solute transport in porous media based on geostatistics was visualized and solute macrodispersion parameters were quantified by using dye tracer imaging technique. The results showed the longitudinal and transverse macrodispersivity estimates decrease with the increase of the degree of upscaling due to a lower heterogeneity corresponding to the upscaling. The macrodispersivity estimates were almost constant in heterogeneous porous formations having the cell size of less than 6 cm, which is the correlation length of non-upscaled porous formation, whereas for large cell sizes macrodispersivity estimates depended strongly on the length of the cell. As the degree of upscaling increased, the horizontal distance between forward and backward edges of the solute plume decreased.

DOI： 10.2208/jscejam.75.2_i_93

DOI： 10.3178/hrl.14.123_references_DOI_O7RCnBN634htyKgzU7WXlxmcpX9

CiNii Research

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Other Link： https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-19H03074/

Language：English   Publishing type：Research paper (scientific journal)   Publisher：GEOMATE INT SOC  

Solute transport in groundwater is significantly influenced by the heterogeneity associated with spatial distribution of the hydraulic conductivity. Understanding solute transport behavior in heterogeneous flow fields is fundamental to develop appropriate models in aquifer management. In this study, laboratory-scale two-dimensional tracer experiments were carried out in a 1 m length, 1 m height and 0.03 m thickness sandbox to quantify solute macrodispersion phenomena in heterogeneous porous formation. Dye tracer of Brilliant Blue FCF mixed with NaCl was applied as a pulse type source and subsequent transport behavior of dye was recorded with digital camera. In addition to the spatial moment approach, temporal moment approach was also applied to estimate the longitudinal macrodispersivity by means of NaCl concentrations at an observation point in the flow field. The experimental results indicated that longitudinal and transverse macrodispersivity were larger than those in homogeneous formation. Moreover, it was revealed that both macrodispersivities in longitudinal and lateral directions have a non-dependency of the regional flow rates. Laboratory study was extended by the comparison with other studies, indicating adequate results in a suitable quantification range.

Web of Science

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Language：English   Publisher：Japan Rainwater Catchment Systems Association  

In this study, intermediate scale dye tracer experiments were conducted in a 1m length, 1m height and 0.03m thickness sandbox to quantify macrodispersion phenomena in stratified porous formations and to elucidate the effect of the layering on the degree of macrodispersion. Spatial and temporal moment approaches based on a snapshot of tracer distribution and NaCl concentration at a point, respectively, were applied to identify the macrodispersivities in longitudinal and lateral directions. The experimental results indicated that the longitudinal macrodispersivity depends on the travel distance of solute and the degree of heterogeneity in stratified formations with two or four layers, while the transverse macrodispersivity decreases with the increase of travel distance and depends on the magnitude of the initial solute distribution. A difference between longitudinal macrodispersivity estimates using spatio-temporal moments was also clarified.

DOI： 10.7132/jrcsa.22_1_15

DOI： 10.3178/hrl.14.123_references_DOI_UhYjfEnZ4prDmSS3xw1C8KicMTP

CiNii Research

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Other Link： https://www.jstage.jst.go.jp/article/jrcsa/22/1/22_22_1_15/_pdf

Language：Japanese   Publisher：Japan Society of Civil Engineers  

This paper presents a stochastic methodology using random walk particle tracking to estimate solute capture zones in a pumping well. Realizations of heterogeneous aquifer are represented as randomly correlated hydraulic conductivity and partition coefficient fields. By superposition of all solute capture zones, probability distributions are obtained that describe the probability of a certain grid space from which a solute particle will reach the well and the corresponding travel time. Proposed methodology demonstrated that a larger pumping rate and less heterogeneity of hydraulic conductivity lead to the decrease of the uncertainty factor, which is defined by the ratio of the area having the probability of non-zero and less than 1 to the area having the probability of 1. Chemical heterogeneity related to the retardation factor distribution has little influence on the both spatial distributions of solute capture zone and travel time.

DOI： 10.2208/jscejhe.71.i_229

CiNii Books

CiNii Research

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Other Link： http://id.ndl.go.jp/bib/026330469

Language：Japanese   Publisher：Japan Society of Civil Engineers  

Intermediate-scale laboratory solute transport experiments were conducted in heterogeneous porous formations comprised by 144 sand cells. Visualization of dye solute was applied to transitional estimates in longitudinal and transverse macrodispersivities caused by the presence of heterogeneities. Results showed that a distinct transition of the longitudinal macrodispersivity was confirmed due to the local heterogeneity while a continuous decrease in transverse dispersivity was shown despite of the initial source location. Quantification methodologies were proposed to achieve the ensemble estimation of five distinct transitions of macrodispersivities and the local heterogeneity quantification based on solute pathways, leading to appropriate outcomes relevant to not only the variation and distribution of estimates but the degree of the longitudinal macrodispersivity.

DOI： 10.2208/jscejam.71.i_691

CiNii Research

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Other Link： https://www.jstage.jst.go.jp/article/jscejam/71/2/71_I_691/_pdf

Authorship：Lead author  

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Authorship：Lead author   Language：Japanese  

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Language：English   Publishing type：Research paper, summary (international conference)  

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Language：English   Publishing type：Research paper, summary (international conference)  

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Event date： 2024.2

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2023.11

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Event date： 2023.11

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Event date： 2023.5

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Event date： 2021.11

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Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.8 - 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2021.5

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Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.12

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Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2020.8

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Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2019.11

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Event date： 2019.6

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Event date： 2015.11

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Event date： 2015.10

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2014.8

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Graduate School of Agriculture / Specialized Subjects

Faculty of Agriculture

Faculty of Agriculture

Graduate School of Agriculture