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Kawamura, Makoto; Nishiyama, Nariaki; Komatsu, Tetsuya; Jia, H.*; Kageyama, Soichiro*; Koizumi, Yukiko*; Nakanishi, Toshimichi*
no journal, ,
In geological disposal projects and safety regulations for high-level radioactive waste, one of the challenges in surveying and evaluating technology related to uplift and erosion, which is important in site selection and safety assessment of geological disposal, is that in the distant future, topography mainly due to river undercuts will occur. It is necessary to be able to quantitatively evaluate the changes and effects that these changes have on the underground geological environment. Among the geological environmental conditions, changes in groundwater recharge areas and outflow areas are important when building performance evaluation models because they can change the flow direction of surface water infiltration into the ground or groundwater outflow to the surface. This time, we selected rivers with different basin areas and uplift rates, and divided the basins into which we would like to measure the topographic features of each river. We measured 10 items of topographic features for the divided watersheds, and created data on trends in changes in topographic features. In addition, we calculated the ``runoff index,'' which is defined as an index that expresses the ease or difficulty of surface runoff flow, and estimated and visualized the influence of river undercuts on topography. Regarding the rivers studied, the divided basins with high principal component scores of "basin average erosion height," "topographical complexity," and "basin relief number," which are indicators of topographical steepness among topographical features, were medium to high. There was a tendency to concentrate in the upper reaches. It was shown that the runoff index tends to be high in areas where high-elevation catchments are concentrated. Although this tendency is consistent with general understanding, I think it is significant that we were able to present this area classification quantitatively rather than qualitatively.
Nishiyama, Nariaki; Kawamura, Makoto; Komatsu, Tetsuya; Jia, H.*; Koizumi, Yukiko*; Nakanishi, Toshimichi*; Umeda, Koji*
no journal, ,
One of the key issues in the investigation and assessment technologies related to uplift and denudation, which are important for site selection and safety assessment of geological disposal of HLW, is the need to enable quantitative assessment of changes and their effects on the surface topography and geological environment in the distant future due to river cutting. In the study of performance assessment models that take into account landform development, simulations are based on information on river cross-section geometry, however information on river cross-section geometry has not been well organized. Against this background, the authors have obtained river cross-section data mainly for major rivers in Japan by GIS topographic analysis using the GSI's 10 m DEM (Kawamura et al., 2023). In this study, we expanded the data by increasing the number of target rivers and organized the data. In this presentation, we report the results of the comparison of cross-section profiles for each river, and the results of the grouping of specific height change from downstream to upstream and horizontal distance from riverbed to peak elevation by uplift rate, geology, climatic conditions, and other factors. These results will contribute to the validation of future projections such as landform development simulations and performance assessment models.
Kawamura, Makoto; Jia, H.*; Koizumi, Yukiko*; Nishiyama, Nariaki; Umeda, Koji*
no journal, ,
Using topographical analysis with GIS using 10 m DEM, we created 2 km river crossing lines on each side of the three rivers, Abegawa, Oigawa and Kumanogawa, starting from the estuary and going straight to the course of the river every 3 km. In addition, the geological information of the river transverse line was extracted. When the cross-sectional lines of the three rivers are displayed together, it can be seen that the river bed rises and the undulations increase as it goes upstream. A comparison of the cross-sectional shapes of the three rivers reveals similar trends, with peaks of undulations on both sides of the rivers in the middle to upper reaches located approximately 500-1,500 m from the center of the river. The relative height between bed and peak also tends to be around 200-600 m. The difference in elevation between the peaks on both sides of the river and the river bed increased in the upstream direction, that is, the depth of the valley to the river bed increased in the upstream direction. When the riverbed slope of the river longitudinal created from the riverbed elevation was taken, an inflection points where the slope trend rose from the upstream area was seen in all three rivers regardless of the geology and geological structure. Although the trend of elevation of the riverbed and increase in undulations from the relatively flat landform near the mouth of the river upstream is pseudo, it suggests a temporal process of landform formation due to uplift and denudation from the flat lowland. This will be information that contributes to verification of the validity of future predictions and performance evaluation models that incorporate topographical changes, such as topographical change simulations.
Kawamura, Makoto; Nishiyama, Nariaki; Jia, H.*; Koizumi, Yukiko*; Umeda, Koji*; Nakanishi, Toshimichi*
no journal, ,
The topography around the river is flat with wide plains near the river mouth, but deep valleys are formed upstream. These differences in topography reflect the relationship between the hardness of the ground, the rate of uplift, and the erosive force of rivers that carve the ground. In this presentation, we will use the topography around the Abe River and Oi River in Shizuoka Prefecture as an example, and introduce a research example in which cross-sectional data of rivers from the coast to the upper reaches are analyzed. The examples introduced in this article will provide clues to the process by which Shizuoka Prefecture's alluvial fan-like coastal plains and upstream relief are formed by uplift of the ground and erosion by rivers.