Abstract
There are many deltas of various size along the northern coast of Japanese Inland Sea (Setouchi) such as Hiroshima and Iwakuni. To analyse the factors which decide this area, the author (A) calculates the volume of each delta deposit on the key surface in the sea level of Würm ice age, (B) after oberving the factors which determine the volume, (C) analyses the relation between the volume and the area (See table I). The results are as follows:
1 The volume of delta deposit v is mainly determined by each drainage area a which belongs to, and is shown by the next regression line. v=0.000671 a-0, 01295
2 Each quantity calculated by this equation is not co-ordinate to area directly but restrict by the morphological factors of each drowned valley and accumulative efficiency come about great differenciation.
3 There are many morphological factors, i. e. depth to key bed at the end of delta d, length of old burried shore line l, angle of drowned river mouth a, etc, but d is most strong. And so the accumulative efficiency is the highest at Fukuyama and becomes lower both side gradually. These results indicate that be fore the latest submergence Setouchi District is belong to twe drainges with watershed near Shiaku Islands.
4 Delta area expected volume v and depth to key surface d is expressed by next least-quares regression plane, and this multiple correlation coefficient is 0, 93 S=42, 71v-0, 19d+5, 61
