CHANGES IN WATER QUALITIES OF RIVERS IN THE KANTÔ DISTRICT

Abstract

A summary of field studies since 1959 on how and to what extent the rivers around TokyR in the KantR District were contaminated by the urbanization of the district is given.
1. The neutralization project of the Agazuma River by using calcium, which was made possible both economically and technically, has changed inorganic acid water of the Agazuma River, a branch of the Tone, the quality of which was a matter of concern for many years, to neutral or alkali. As a result of the project, the water quality system of the lower stream of the Tone, from the junction with the Agazuma River, has been changing since 1964 from what it used to be.
2. A method of classification of pollution degree is established by using a combination of COD, BOD₅ and ABS contents so as to indicate the water quality influenced by urban waste water. According to the pollution distribution map for tested stations of the Tone and Arakawa water systems constructed by using the above classification, three groups are distinguished such as (a) water is polluted due to the enlargement of built-up areas, (b) water is influenced by middle class cities and (c) there is no pollution by human activities.
3. The quality of river water influenced by human activities changes greatly, particularly, by season (due to seasonal changes in the flow volume and, generally speaking, winter is the most polluted season) and by hour (influenced by the discharged amount of waste water). As to the Nakagawa of which water is used for irrigation to a great extent, some of its water systems are found more polluted during the non-irrigation period because less water flows into them during that period while in other water systems pollution is relatively reduced during that period because the water is not used for irrigation. In the future study, it is necessary to obtain accumulated value of flow volume by pollution degree.
4. The result of observations heretofore conducted tells us that the most polluted water system among the four systems of the Nakagawa is the Moto-Arakawa. Though its pollution degree was No. 3 in 1962, it became No. 1 in 1967 as shown in Fig. 2. due to the increase in organic contents and salts in the water on account of the development of the area Even with the least polluted Edogawa River, the water is getting more and more polluted as it flows down stream because of the in-flow of contaminated water from tributaries joining it from the left bank. The pollution of the stream lower than Matsudo City is worth to be mentioned. Since 1960 there has been a close relationship between the annual change in the water quality and the increase in population, particularly in Matsudo City. The relationship is shown by an exponential curve.
5. The author tried a regional classification on the basis of relationship of water qualities. The area can be divided into: (a) where agriculture is still maintained, (b) where agricultural areas are kept in the suburbs but changeable to the non-agricultural regions, and (c) where it is little worth while to keep it as an agricultural region. (See Fig. 8)