From 7 to 9 September 2023, Hong Kong experienced a record-breaking torrential rain, resulting in over 200 reports of landslides. The Geotechnical Engineering Office of the Civil Engineering and Development Department has conducted systematic investigations on major landslides to determine the likely causes of the failure and identify the necessary follow-up actions.

Some of the landslide cases near roadsides led to the collapse of sole accesses to communities, bringing inconvenience to the residents. The investigation revealed that these landslides were mainly due to uncontrolled surface water, stemming from blockage of the catchpit and cross-road drain by trapped debris due to heavy rain, flowing along the road and overtopping the slopes at topographical low points.

The investigation findings highlight the importance of adequate and effective surface and subsurface drainage with proper detailing and precautionary measures, such as trash grilles or debris screens at inlets of drains and roadside upstand walls at topographical low points.

A dear lesson was learnt about how inconvenient it could be for residents when there are landslides on sole accesses. Consequently, about 500 man-made slopes with relatively high potential impact on society (for example, those adjacent to sole accesses to community or important livelihood facilities) have been further identified for special inspection, on top of regular inspection and maintenance, before wet seasons. This minimises the risks of incidents on these slopes.

This article is contributed by the Development Bureau of the HKSAR Government.