The Kurosegawa River, a polluted small river, flows through Higashi-Hiroshima, Hiroshima, where the population has increased steadily within the last decade. In order to clarify the impact of urbanization on the quality of the river water, changes in the state of organic pollution were studied in relation to population, construction of sewers and septic tanks in a recent 13-year period (1989-2001). Improvement in water quality (as indicated by BOD) was observed in the central area of the city, possibly as a result of the co11struction of sewers and septic tanks. In contrast, the BOD tended to increase in the lower reaches of the river. The pollutant flow analysis indicated that inflow of pollutant from a sewage treatment plant contributed to a significant proportion of the load. A simulation suggested that, with increasing population and sewage water, the BOD in the lower reaches of the river would be higher in the future because of the increase in the load from the plant. Based on the pollutant flow analysis, some solutions for reducing organic pollution are suggested.

本研究の一部は学園都市づくり交流会議の地域課題研究事業の補助を受けて行われたものである。