Responses of bed load yields from a forested headwater catchment in the eastern Tanzawa Mountains, Japan

We investigated bed load yields from a headwater catchment (7.0 ha) in the eastern Tanzawa Mountains in Kanagawa Prefecture, Japan from 2009–2014 using measurements from a weir pond in the catchment. Precipitation and stream discharge were continuously monitored at 10-min intervals. The mean (± standard deviation) volume of transported bed load was 0.019 ± 0.040 m3/ha/day (0.023 ± 0.049 t/ha/day by yield) and zero bed load events were observed during the monitoring period. The particle size of the bed load sediment tended to be small compared to that of sediment in the stream bed. Bed load yields in summer–autumn were 5.7-fold those during winter–spring. A significant correlation was detected between bed load yield and peak discharge (p < 0.05). Variations in the availability of sediment induced discontinuous sediment transport during major precipitation events. These intermittent responses of the bed load yield were associated with the available sediment and transport capacity in the stream channel. Our findings help for clarifying sediment flux in a headwater channel based on its potential storage and yields.