Report No. : GEO Report No. 359

Report Title : Review of the Practice on Slope Surface Drainage Management (2022), 50 p.

Author : R.W.H. Lee & R.H.C. Law

Abstract

The vast majority of the landslides in Hong Kong are triggered by rainfall. Surface drainage commonly provided on man-made slopes aims to prevent surface erosion and reduce infiltration. It plays an important role to avert slope instability. However, inadequate management of surface drainage could hamper its efficiency and often results in uncontrolled surface water flow contributory to landsliding.

This Technical Note provides insights on the importance of slope surface drainage management under the dense urban settings in Hong Kong from the landslide perspective. Selected landslides involving inadequately managed surface drainage are presented to shed light on the key lessons learnt on various drainage aspects. It is noteworthy that inadequate surface drainage maintenance could exacerbate and lead to sizeable landslides even on engineered slopes. A review of landslide records over the years suggests that some landslides might have been averted had there been proper surface drainage maintenance.

With reference to the observations from landslide studies and the published guidance documents, the areas that deserve particular attention in managing the surface drainage on slopes at various stages of a project cycle, from design, construction to maintenance, are highlighted. Examples of good practice and inadequacy are presented for the ease of reference of the practitioners with a view to promoting further enhancement of the practice.

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