Spatio-distribution analysis of sediment transport rate through drainage nets

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Sediment transport rate, which is defined as an average annual sediment yield per unit area, was surveyed from 59 creek basins in the Saru River and Sorachi River watersheds, Hokkaido. Transport rate primarily changes wirth geology. Rates for basins both in active volcanoes and Neocene sedimentary rocks range from 1000 to 3400 m^3km^<-1>yr^<-1>, averaging about 2000 m^3km^<-1>yr^<-1>, and rates in Cretaceous sedimentary rocks range from 40 to 900 m^3km^<-1>yr^<-1>, averaging about 350 m^3km^<-1>yr^<-1>. Basins in serpentinite and plutonic rocks have average rate of about 250 and 100 m^3km^<-1>yr^<-1>, respectively. This shows that the intensity of upland erosion varies with bedrock types. In addition, as basin area increases, both transport and rate and its range decrease. The former reflects the effect of temporary sediment storage within a basin, especially along downstream channels, while the latter means that transport rate of smaller basin depends more greatly on activity of sediment production in each basin.The relationships between transport rate and some channel-morphological factors associated with transport and stroage processes were analyzed in uniform geology, using rates from Cretaceous sedimentary rocks. Rates of basins with narrow channel width considerably vary, while rates of wide channel-width basins converge into smller value. This shows that channel width is an indicator of sediment stroage capacity, because channel width is confirmed to be uncorrelative with basin area. Further in wide channel-width basins, as channel slope becomes steeper, transport rate increases. This means that transport rate is attributed to channel slope under sediment-rich conditions.