On the Transporting Materials of the River Watarase

The River Watarase flows out from the western part of the Nikko Volcanoes, and runs southward through Ashio mountainland and empties into the River Tone in Kwanto Plain. Recently this river flooded frequently and the river floor of its lower course has been elevated. by deposits. The writers studied on the transporting materials of this river, specifically referenced to the upper course in Ashio mountainland from the geomorphological and potamological point, of view as a fundamental survey for civil engineering. In this paper, the transporting materials of Watarase River are stated briefly. 1. Suspended materials are supplied in large quantities from the settlingponds of Ashio Cupper Mine and its Refinery situated on the upper stream of this river. These materials are transported and deposited in the lower course and in the flood control lake, Akamanuma. 2. Solution is leached out in a great deal from Akagi volcano region because this volcano erupted in quaternary and its rocks are fish. Consequently the amount of solution of the tributaries from this region is far more than that of the tributaries from palaeozoic slate and granite regions in this mountainland. In Akagi region, as the volcanic ash and detritus are less cohesive and many landslips happen, so the.boulders and gravels of andesite are heaped on this river bed near Omama Town at the entrance to this mountainland. Therefore the fluvial gravel deposits of quartz porphyry and liparite from the headwater of the River Watarase are less than those of the anndesite. The elevation of river floor is mainly due to the detritus from Akagi Volcano. 3. The palaeozoic slate is apt to become small gavels, but granite is apt to become large boulders and not to become gravels. Granite. boulders are disintegrated abruptly into small pieces when they are transported in the river. 4. About 10meters gravel bed in thickness is seemed to be deposited in the flood plain without any depression in the river which has the same physiographical features as the River Watarase. On such thickness of river gravel bed, we consider it to be renewed by several floods, and accordingly the river terraces which have such gravel beds are not to be called alluvial terraces in such rivers. 5. The bed loads of this river are on the increase lately and about 500, 000 q. m. of sands and gravels are transported during a year.