Source identification of suspended sediment from grain-size distributions: I. Application of nonparametric statistical tests

Suspended sediment flux (SSF) supplied from sediment generated by logging and deposited on hillslopes, and that from unpaved road surface, were obtained in the Hiyamizusawa Brook basin, Hokkaido Japan. The ratio between SSF from deposited sediment fines (DSF) and that from suspended sediment in the road surface flow (SSR), i.e. the ratio DSF:SSR, was estimated from grain-size distributions of the river-suspended sediment based on nonparametric statistical tests. The grains supplied from DSF were sorted while they were being transported to the river; thus the ratio between the weight percentages of two subdistributions representing the grain-size distribution of DSF (i.e., the ratioSd1Sd2) was considered to estimate the grain-size distribution of grains supplied from DSF into the river. The compounded grain-size distribution with variousSd1:Sd2 ratios was again combined with the grain-size distribution of SSR at the various DSF:SSR ratios, and the twice: compounded distribution, which was most similar to the grain-size distribution of river-suspended sediment was found. Each of the DSF:SSR ratios of the most similar distribution was all within 10% of the each actual ratio.