Landslides and sediment delivery to a drainage system: some observations from Hong Kong

The delivery of sediment from hillslopes to a drainage system has been examined for Hong Kong. Landslides may influence sediment production in small upland drainage basins by the direct delivery of material to the channel, subsequent fluvial action on materials exposed in debris trails and erosion as the failure moves downslope, sometimes to become channelised. Evidence of the direct delivery of sediment by landslides is presented from a small drainage basin. On undeveloped terrain in Hong Kong, in general, less than half of the landslides deliver debris to the channel system. Examples of landslide debris volume exceeding that of source area failure in Hong Kong are presented and this relates to channelisation of debris flows. Revegetation of landslide debris trails may be quite rapid and this restricts the time for fluvial action on the exposed materials. The temporal aspect of sediment delivery has been documented. Rainfall events that are guaranteed to generate large numbers of landslides are relatively rare.