Mitsuru Komatsu

On the value of lithofacies data for improving groundwater flow model accuracy in a three‐dimensional laboratory‐scale synthetic aquifer

Improvement of the prediction accuracy of groundwater flow models has been receiving substantial attention from many researchers through the development of enhanced characterizations of the structure of subsurface lithofacies and of the distribution of hydraulic conductivity. In this study, we investigated how incorporating increasing amounts of lithofacies data into the construction of a conceptual model of aquifer heterogeneity helps to reduce prediction error and uncertainty in groundwater flow models. An approach based on both laboratory experiments and numerical simulations was tested using data from an intermediate-scale synthetic heterogeneous aquifer. The heterogeneous aquifer consisted of five lithofacies, corresponding to five test sands. Three pumping tests were conducted and provided experimental data to perform groundwater flow model calibration and validation. The pumping tests were also simulated numerically in order to provide a series of error-free synthetic hydraulic data sets. On the basis of Markov chains models of transition probabilities, a total of 901 random realizations of the heterogeneous distribution of lithofacies were created using varying amounts of conditioning lithofacies data sampled along randomly placed hypothetical boreholes. For each realization and for two other simplified lithofacies models, parameter estimation was performed to estimate the hydraulic conductivity of the lithofacies using the experimental and synthetic hydraulic data from the three pumping tests. The results generally showed that the use of more lithofacies data in the construction of the lithofacies realizations led to an improvement in groundwater flow model prediction accuracy. When using the error-free synthetic hydraulic data, the calibration-prediction error and uncertainty decreased drastically when the mean borehole spacing was on the order of twice the horizontal correlation length or less. When the experimental hydraulic data were used, this drastic improvement in the calibration-prediction error was somewhat obscured and, in some cases, exhibited a local minimum. This local minimum, although beyond practical limits, corresponded to an optimal number of boreholes. Finally, the effect of incorporating more lithofacies data for the construction of lithofacies realizations was found to have a similar impact on the quality of model calibration and on the quality of predictive simulations conducted using the calibrated model.

Fabrication of a hydrophilic property impedance sensor to stably monitor soil water content for slope failure prognostics

To minimize the damage caused by slope failure, knowledge of the increase in water content in mountain soil is important. Our group has been studying miniaturized impedance sensor for multipoint measurements in the soil. To improve contact characteristics between sensor surface and free water in soil, SiOx film of hydrophilic property covered on our conventional sensor chip. For contact property test, the sensor chip measured impedance of model soils. The proposed sensor achieved to stable contact the free water in the soil. Moreover, the chip operated for long period of time in mountain slope. The sensor could measure nearly theoretical outputs which responded to rainfalls. We succeeded to fabricate the stably soil monitor sensor with hydrophilic film SiOx.

Construction of a Sensor Network to Forecast Landslide Disasters Sensor Terminal Development and On-Site Experiments

We believe it is extremely important to quickly communicate information — on matters such as the extent of the damage and the safety of affected persons — when a large-scale earthquake or other disaster occurs. However, if electric power is lost, communication will be impossible with existing information networks. For this reason, we have built an Ad-Hoc network in Shiojiri City enabling communication even if electric power is lost due to a large-scale disaster. Using this Ad-Hoc network, we are building a sensor network to forecast landslide disasters. Among the various sensors installed to the sensor terminals, this paper reports in particular on observation results with EC sensors.

Fabrication of a low leakage current type impedance sensor to monitor soil water content for slope failure prognostics

A low-leakage-current type impedance sensor chip with shield structures has been fabricated. The low limit detection of soil-water-content measurement was improved compared with that of the other semiconductor type sensors. The shield structures were fabricated under the impedance sensor areas. To measure weak signal current eliminated the leakage current, we proposed a new operation circuit to separate the leakage current. Our sensor achieved to measure low water content 10 % or less.

Characterization of soil permeability in prambanan temple yard based on development of in situ test

Prambanan Temple is a cultural site which has been declared as world cultural heritage that is required to be conserved. Due to heavy equipment activities during maintenance period after Yogyakarta earthquake in May, 2006, soil in temple yard become dense, and ponding occurred after rainfall. A poodle layer and a drainage system has ever built to avoid such a problem, but the pond still didn’t stop appearing after rain. Permeability parameter needs to be characterized to find exact method of solution. This experiment used Constant Discharge method which suitable for permeability test of sandy soil. The procedure were carried out from unsaturated until saturated soil condition. Volumetric water content were being monitored by using soil moisture probe. The results were value of permeability coefficient from unsaturated until saturated condition. The value of permeability coefficient and soil type characterization was mapping based on geographic reference using software Arcview GIS 3.3. Developed instruments were quite efficient and easy to be implemented on determining field soil permeability coefficient of sandy soil. Using constant discharge model, the value of unsaturated soil permeability can be obtained without establishing the matrix suction. The result of soil permeability characterization mapping can be used to determine the alternative solution of the ponding problem.

Realization of a Safe and Secure Society using ICT in Shiojiri-City, Nagano Prefecture, Japan

For some time, we have been working toward the “Realization of a Safe and Secure Society using ICT in Shiojiri-City, Nagano Prefecture.” This is a project comprised of two phases: information gathering, and dissemination of information. For information gathering, we are developing systems to confirm the whereabouts of children and the elderly, who are vulnerable in disasters, and systems to gather information on the situation in mountainous regions, rivers etc. For dissemination of information, we are developing systems using broadcast technology for disseminating information to residents, such as disaster information and evacuation warnings derived from the gathered information. This presentation will describe the project goals, the background of the project thus far, and an overview of the developed system. The current situation and plans for the future will also be discussed.