[H-CG20] Nuclear Energy and Geoscience

[HCG20-P02] Topographic Information for the development of a model to evaluate the performance assessment of a HLW disposal -Part 2: Runoff index based on catchment area geometry-

*Makoto Kawamura¹, Nariaki Nishiyama¹, Tetsuya Komatsu¹, Hua Jia², Soichiro Kageyama², Yukiko koizumi², Toshimichi Nakanishi³ (1.Japan Atomic Energy Agency, 2.Mitsubishi Materials Techno Corp., 3.Museum of Natural and Environmental History, Shizuoka)

Keywords:Geological Disposal, Digital Elevation Model,, Topographic Change Simulation, Topographic Features, Runoff Index

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.
[Acknowledgment]
This study was funded by the Ministry of Economy, Trade and Industry, Japan as part of its R&D supporting programs (Grant number: JPJ007597), “Establishment of Technology for Comprehensive Evaluation of the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Fiscal Years 2023)”.