抄録
The Yahagi River which flows through the eastern part of Aichi Prefecture has a length of 117km, and two big cities, Toyota and Okazaki. There are many gravel and silica sand pits in this river basin (Fig. 1). In recent years, water pollution of the river has worsened. A series of investigations of water quality of the river was carried out during the period from December 1971 to November 1972, and the findings were as follows.
As shown in Table 1 and Fig. 2, the water quality of the Yahagi River is characterized by higher concentration of suspended solids.
Outflows of suspended solids and COD are approximately constant without reference to the change of river discharge under about 90m3/sec. Outflows of other components increase as the discharge of river rises (Fig. 4).
A comparison between the water quality at the end of and before the New Year holidays shows that the former has a lower concentration of suspended solids (Fig. 5).
It may be said that the largest factor contributing to water pollution is waste water containing a large quantity of clay discharged from the gravel and silica sand pits.
