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摘要
Rational estimation of debris flow velocity is one of the key issues in debris hazard mitigation. Among the various procedures, back-calculation of debris flow velocity is one of the most frequently used approaches. Back-calculation includes determination of super-elevations and channel properties, and velocities are calculated using the forced vortex equation. Super-elevation and bend radius are biasing parameters in the back-calculation scheme. Therefore, an iterative approach based on simplified assumptions is developed to avoid the direct and subjective determination of bend radius. Besides, as only the highest mud prints are visible after the disaster, this misreads the actual super-elevation. To seek better ways to fix this anomaly, a series of three-dimensional numerical curved flume tests using smoothed particle hydrodynamics are carried out. Estimated velocities from highest flow marks underestimate the actual velocities near the source, while they converge on the actual velocities as the distance to source increases. A best-fit line is then proposed to adjust the mud-marks-derived velocities to the real velocities. The assumption taken during development of the iterative approach for determining bend radii is also justified from the numerical simulations. The law of similarity allows application of these findings to real debris flow disasters. Thus, two real debris flow disasters in Japan are examined for validation of the developed procedure and adjusted velocities are proven to be consistent with verbal evidences and previous analyses.
- 出版日期2018-7
