Report No. : GEO Report No. 361

Report Title : Debris Mobility of Failures within Topographic Depression Catchments (2022), 52 p.

Author : F.L.C. Lo, J.S.H. Kwan, F.W.Y. Ko & H.Y. Ho

Abstract

A study has been carried out to examine the debris mobility of failures in topographic depression catchments (TDF). In the study, 46 historical mobile TDF were identified and back analysed using computer program 2d-DMM. The methodology adopted in identifying the TDF, the assumptions made in the back analyses and results of the study are documented in this Report. Recommendations pertinent to debris mobility assessments of TDF are also included.

This study revealed that mobility analyses using Voellmy parameters φ_a = 18^o and ξ = 1000 m/s² produce suitably conservative estimates of runout distances of most of the mobile TDF, and that debris velocities match reasonably well with those of a historical TDF in Kau Lung Hang Shan. It is recommended that the rheological parameters should be adopted for forward prediction purposes. However, where historical landslides in the TD catchments of concerned have resulted in more mobile debris runout than that assessed using the above recommended rheological parameters, the appropriate rheological parameters to be adopted in analytical design of TDF mitigation measures should be assessed on a case-by-case basis.

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