How "Fresh" Is the Water in Japan's Major Rivers?

The River Bureau of the Ministry of Land, Infrastructure and Transport of Japan has devised a new index of the purity of river water, and on November 7 announced the results of calculations for selected points along 15 major rivers nationwide.

The freshness index is calculated based on a formula (1 minus the amount of water used upstream, divided by the total water flow in the river, multiplied by 100 to get a percentage). The figure for the amount of water used includes wastewater from households, sewage treatment plants, factories, and the livestock industry. Agricultural wastewater is excluded from the calculation, because the degree of impact on rivers is unclear at present.

A higher freshness index rating indicates that less water is being used upstream. Generally speaking, the higher the rating, the lower the risk of accidents related to water quality, though the rating does not reflect efforts upstream to improve water quality. MLIT considers the index to be an effective indicator from the viewpoint of risk control of river water.

The freshness of the Agano River in Hokuriku was calculated to be 99.1 percent and the Toyohira River in Hokkaido 98.7 percent, while the Tama River in the Kanto region is 27.1percent and the Yodo River in the Kinki region is 58.7 percent. These examples show the tendency for the index to be lower in rivers in metropolitan areas.



Posted: 2004/01/17 06:13:39 PM
Japanese version