| Autor: |
Åberg, A.1,2 (AUTHOR) amanda.aaberg@wsl.ch, Aaron, J.1,2 (AUTHOR) jordan.aaron@eaps.ethz.ch, McArdell, B. W.1 (AUTHOR), Kirchner, J.1,3,4 (AUTHOR), de Haas, T.5 (AUTHOR), Hirschberg, J.1,2 (AUTHOR) |
| Předmět: |
|
| Zdroj: |
Journal of Geophysical Research. Earth Surface. Nov2024, Vol. 129 Issue 11, p1-18. 18p. |
| Abstrakt: |
Estimating flow velocities is key to assessing hazards associated with debris flows. One approach to post‐event velocity estimation is the superelevation method, which uses debris‐flow mudlines to measure the cross‐channel surface inclination, or superelevation, produced by centripetal forces acting on the flow in a bend. Flow velocities are then calculated using a subjective parameterization of the forced vortex equation modified to include a debris‐flow specific correction factor. Subjective parameterization of this equation leads to substantial variability and uncertainty in the resulting flow velocities. We present an analysis of the reliability of the superelevation method using a large UAV‐based data set of 14 debris flows with front velocities of ∼0.8–6.5 m s−1 and cross‐channel surface inclinations of ∼0.6–8.5°, as well as a validation for a single debris flow measured using high‐resolution, high‐frequency 3D lidar data fused to video imagery. The validation event indicates that when the flow surface inclination can be measured directly, the forced vortex equation produces excellent results without needing a correction factor for Froude numbers ranging from 0.7 to 1.5. This finding indicates that the main challenge with the superelevation method lies in obtaining accurate measurements of superelevation from the mudlines, and that a correction factor may serve to compensate for measurement difficulties rather than variable flow properties. For very small and highly subcritical flows, the superelevation method may generate a large overestimation of flow velocities. Plain Language Summary: Debris flows are hazardous, surging flows containing a mixture of water, sediment and other debris. Efforts to mitigate debris‐flow hazards depend on accurate estimates of flow velocity, which are difficult to obtain in the field. The superelevation method uses mudlines left by a debris flow in a bend, where it has been affected by centripetal acceleration, to estimate the cross‐channel surface tilt and uses this to achieve a post‐event estimate of flow velocity. We used an unusually large field‐based data set consisting of pre‐ and post‐event orthophotos and digital elevation models from 14 debris flows along with highly detailed laser scanning measurements of one debris flow to evaluate the accuracy and uncertainties of this method. We find that the equation used in the superelevation method produces excellent velocity estimates when the surface tilt can be directly measured, but that the post‐event mudlines are often not representative of the maximum surface tilt and therefore likely result in an underestimate of the peak flow velocity. Practitioners may need to use a correction factor to account for this underestimation when using the superelevation method for hazard mitigation. Key Points: 3D lidar scans (10 Hz) provide new insights into the superelevation method for post‐event debris‐flow velocity estimationResults indicate that the traditional superelevation method overestimates the front velocity and underestimates the peak flow velocityExcellent results generated with a known surface tilt indicate that the challenge lies in obtaining representative post hoc measurements [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
| Externí odkaz: |
|
Plný text