Benefit-Cost of River Water Environment and Investments Related to Water Environment in the River Basin

Abstract

Huge investments for water and waste water management and ambient water environment improvement have been conducted for many years in economically developed countries including Japan. The investment for water supply, on-site and centralized municipal waste water treatment systems (WWTSs), river water purification facilities and dissemination of soft measures in households, and benefits from water quality improvement in the Yamato-gawa River Basin, Japan, in 1965–2009 were summarized based on the statistical data and existing literature. The benefits include ambient water quality improvement and employment of local fishery persons. The former was estimated based on the existing literatures. Average and 75% biological oxygen demand (BOD) in the River was less than 5 mg l-1 in 1963, rapidly deteriorated in the 1960s and exceeded 20 mg l-1 in 1970. The national level regulations on ambient water quality and pollutant discharges have been established in 1970. The relationship between accumulated investments and 'difference of estimated BOD based on BOD generation (PG(BOD)) and monitored BOD' (ΔBOD) suggested the critical history of pollutant discharge, water quality, and investments on the measures to improve river water quality: effects of investments were negative and not yet observed in the 1960s and the early 1970s when the total accumulated investment was less than USD 6.0 billion, effects of investments became positive in 1973, the relationship between PG(BOD) and water quality returned to the similar conditions in the 1960s after the late 1990s, and (4) positive combined effects of the measures on the River BOD quality were about 10 mg-BOD l-1 in 2010. The methods are applicable for other river basins in the world to evaluate the effectiveness of water quality improvement measures.