Survey of Sediments in Reservoirs (2nd Report)

Abstract

This paper presents the result of the survey on sediments in the Odomari and the Natsuse reservoirs with the tributary drainage basins consisting of plutonic rocks or effusive rocks. According to the survey of the impounded water in the Odomari reservoir, its values of the Secchi-disc readings were from 1.6m to 4.4m, its pH values from 5.7 to 7.2, its temperature values from 6.0°C to 29.9°C, for August in 1954, and in the Natsuse reservoir, its values of the Secchi-disc readings were from 1.5m to 3.0m, its pH values from 4.6 to 5.8, its temperature values from 16.0°C to 23.0°C., for September in 1956.Moreover, the pH and the temperature distributions of the Odamari reservoir show the thermoclines and the metalimnions, whereas such phenomenons are not clearly seen in the Natsuse reservoir.The sediments in both reservoirs consist of silt, sand and gravel. Sand and gravel are deposited in the upstream area, but silt is spread out in the middle and downstream areas of the bottoms.The form of the delta with the_topset, the foreset and the bottomset beds is not clear in the Odomari and in the Natsuse reservoir.In the last chapter, four reservoirs are able to divide into two types on the point of sedimentary processes.