The section of the Tone River upstream of its confluence with the Watarase River was traditionally called the Kamitone River. On the right bank of this Kamitone River a dyke running between the river and elevated ground, is called the Chujo Dyke. The area upstream of this dyke, where a number of settlements were located, provided a large retardingbasin, wtich served to protect the portion of the Saitama Plain downstream of the dyke, and since before the beginning of the modern era, there has been a long-standing dispute concerning the presence of this dyke between those living upstream and downstream of the dyke. How to assess the retarding effect of the basin above the Chujo Dyke is a major problem in modern flood control planning on the Tone River. The present paper provides a number of observations concerning this problem in the light of the river improvement plans drawn up during the Meiji Era (1869-1912) and the flood control plans of 1939 and 1949.
