Abstract
In this paper the features of grain size distributions are shown on the Senzu, the Kuze, the Nateuse and the Odomari reservoirs described in the 1st and 2nd Reports.
The Wentworth's grade scale of grain size and the Shepard's nomenclature based on the sand-silt-clay ratios being used, the sediments are found to range in the sandy-silty-clayey materials from upstream to downstream in reservoirs. The Krum-bein's Phi scale of grain size and the Inman's descriptive parameters being used, the Phi median diameter has the wide range of 1.0-8.5 with the tendency to increase from upstream to downstream in reservoirs, but the sorting has little variation range which centers 1.50 in the Phi deviation measure in the Senzu and Kuze reservoirs, or the complicated distribution with the range from very well sorted to poorly sorted degree in the Nat suse and Odomari reservoirs. In the Senzu reservoir, Sand is deposited in the topset bed, Silty Sand and Sandy Silt in the foreset bed, and Siilt n the bottomset bed of the delta.
It is found, that silty and clayey sediments corresponding to suspension load described by Harrison spread over the whole bottom, whereas sandy sediments corresponding to traction load are deposited from the river mouth to the dam in reservoirs.
