Abstract
Historical variation and present state of water quality as well as flow rate of the Nogawa River, one of the tributaries of the Tama River, which flows in the southwest of Tokyo are examined The population of the river basin has grown 4.0 times in these 35 years and urbanization change of situations around the river has made the Nogawa River a typical urbane polluted river.
Close show observation of the mechanism of the pollution in the Nogawa River, therefore, may give general keys to show how to restore the water environment in populated area. Two main problems could be referred as concluding remarks :
(1) Though the water quality has been slowly recovered by gradual accomplishment of the river basin sewerage system, such a system has reduced the Nogawa's flow rate seriously.
(2) The Nogawa River has bigger BOD flux at the connection with the Tama River in summer season than in winter time. This is caused by the growth and decomposition of benthic algae (about 3 ton BOD/day is produced in the Nogawa River at summer season). To keep off the growth of benthic algae is one of the important subjects to be considered for the restoration of water quality.
