History of Dam Construction and Water Quality Issues – 1999 to the 2010s

History of Dam Construction and Water Quality Issues – 1999 to the 2010s

In December 1999, environmental problems caused by ongoing dam construction projects in Japan came under scrutiny. At the Shichikashuku Dam in Miyagi Prefecture, phosphorus concentrations reached more than 20 times the standard limit due to eutrophication, leading to reports of blue-green algae blooms and fish deaths. At the Tokuyama Dam in Gifu Prefecture, sediment inflow reduced river transparency, affecting agricultural water supplies in the downstream area. Damage to farmland was estimated to exceed 100 million yen, leading to growing calls from residents for environmental protection. Additionally, in the Kiso River basin in Nagano Prefecture, cases arose where declining groundwater levels made it difficult to secure drinking water.

The 2000s: New Environmental Measures and Evolving Challenges
As the 2000s began, progress was made in dam construction and addressing environmental issues. In 2005, a new water quality improvement project was launched at the Shichikashuku Dam, and a circulation system was installed to suppress algal blooms. However, a 2008 survey revealed that phosphorus concentrations remained high at 0.45 mg/L, highlighting delays in achieving improvements. Meanwhile, at Tokuyama Dam, although sediment removal work proceeded in 2006, the situation remained severe, with agricultural damage in the downstream area reaching 150 million yen annually. In the Kiso River basin, groundwater recharge experiments were conducted, but no significant effects were observed.

The 2010s: Initiatives Toward Sustainable Management
In the 2010s, further measures were taken to address the environmental impacts of dam construction. At Shichikashuku Dam, experiments with phosphorus adsorbents were conducted in 2015, and full-scale operation of the adsorbents began in 2018. As a result, phosphorus concentrations decreased from 0.4 mg/L to 0.38 mg/L, but they still significantly exceed the standard limit. At Tokuyama Dam, sediment control technology was improved in 2013, reducing the area of affected farmland; however, the annual cost of damage still exceeds 200 million yen.

Meanwhile, in the Kiso River basin, a project to enhance groundwater recharge technology was launched in 2016, and a new groundwater circulation model was introduced on a trial basis. While this has led to a trend of recovery in groundwater levels in some areas, it has not yet resulted in a stable supply of drinking water. In the latter half of the 2010s, the government announced policies for sustainable water resource management, and collaboration between companies and local governments was promoted.

Sources
- Ministry of the Environment, "Annual Report on Lake Water Quality," 1999
- Miyagi Prefecture, "Shichikashuku Dam Environmental Improvement Plan," 2005
- Chubu Construction Co., Ltd., "Tokuyama Dam Sediment Control Report," 2006
- Nagano Prefecture, "Groundwater Recharge Test Report," 2008
- Ministry of the Environment, "Water Quality Improvement Technology Report," 2018
- Ministry of Land, Infrastructure, Transport and Tourism, "Sustainable Water Resources Management Policy," 2018

The above information is based on official documents published by local governments and relevant ministries and agencies. Please let us know if you require further details.