Drainage works are one of the measures for preventing seepage in river embankments. The objective of this study was to apply aDTS (active Distributed Temperature Sensing) as a monitoring tool to determine whether or not the functionality of the drainage works is maintained in good condition over a long period of time. This method combines a continuous measurement of temperature change distribution along optical fibers and an active heating of optical fiber cables. Specifically, heated optical fiber cables are laid in the longitudinal direction of the embankment between the drainage works and the embankment to measure the temperature changes in the ground along the fibers to measure the apparent heat conduction characteristics and estimate the conditions inside the embankment from these changes. As a fundamental study, we first studied filter materials to be used in the levee model experiments based on horizontal one-dimensional experiments, and organized the relationship between bulk thermal conductivity and pore velocity. Next, the change in apparent thermal conductivity in response to detection of the clogging of the filter material was determined from small levee model experiments, and the applicability of aDTS was verified in large levee model experiments. The results suggested the feasibility of using aDTS to detect clogging of the filter material in the drainage works.

Many cases of damage due to seepage at embankments and weirs are considered to be caused by piping phenomena that occur at strata boundaries and other areas with large permeability gaps. It is important in river structure management and geotechnical engineering to understand how the triggering water channel develops and leads to piping. In this paper, the mechanism of water channel development in the piping phenomenon was investigated by conducting seepage experiments on a sheet pile and a multi-layered embankment using the refractive index matching method. The visualization of the ground interior, which has been difficult to visualize so far, was performed with high accuracy, and the behavior of particles in the ground was traced to show the fluid behavior inside the water channel from the slight deformation of the ground during the piping phenomenon.

From July 7 to 10, 2023, the activity of a stationary front intensified, prompting the issuance of the emergency warning for heavy rains in Fukuoka and Oita prefectures. In some observation points in northern Kyushu, the recorded rainfall reached the highest levels in history. As a result, the water levels of the Kose River, a primary tributary of the Chikugo River, rose significantly, causing flooding and inundation damage in surrounding areas due to overtopping and overflow. The authors conducted a comprehensive field survey around the affected river levees near the Kose River starting on July 16, 2023, approximately nine days after the disaster. The survey methods included meticulous on-site inspections and detailed aerial photography using UAVs. From the field survey, although the maximum river water level was observed, the damage to the levee was limited. This result suggests that rising water levels on the landside may affect the levee.

In this study, I examined effective investigation and analysis methods for evaluating groundwater quality formation processes using existing data on springs and groundwater in Japan. The characteristics of the formation process of water quality were investigated using HCO3－, SiO2, and temperature data of springs and groundwater as indices, and were compared with the measured values by analysis using the geochemical reaction analysis code (PHREEQC). The results indicate that the dissolution of plagioclase and carbonate minerals is mainly responsible for the formation of water quality in the case of granitic rocks, while the dissolution of plagioclase and silica minerals may be responsible for the formation of water quality in the case of volcanic rocks. In areas where the geology is sedimentary rock, the groundwater composition is intermediate between granite and volcanic rock, suggesting that a variety of geological types as water sources may influence the formation of water quality. In the limestone, Mesozoic, metamorphic and serpentinite areas, the dissolution of plagioclase is low, indicating that the dissolution of carbonate minerals and brucite are related to the dissolution of plagioclase. The relationship between SiO2 and water temperature in spring water and groundwater indicates that there are cases in which plagioclase and other minerals dissolve with an increase in water temperature during the groundwater flow process, and cases in which the dissolution of plagioclase and other minerals occurs with almost no change in water temperature.