History of Dam Construction and Water Quality Issues - 1999-2010s

History of Dam Construction and Water Quality Issues - 1999-2010s

In December 1999, attention was drawn to the environmental problems caused by the ongoing construction of dams in Japan. At the Shichigajuku Dam in Miyagi Prefecture, eutrophication caused phosphorus levels to reach more than 20 times the standard value, leading to reports of blue-green algae blooms and fish kills. At the Tokuyama Dam in Gifu Prefecture, the river transparency decreased due to sediment inflow, affecting agricultural water supply in the downstream area. Damage to farmland was estimated to exceed 100 million yen, prompting residents to call for environmental protection. In addition, in the Kiso River basin in Nagano Prefecture, groundwater levels dropped, making it difficult to secure drinking water.

2000s: New Environmental Measures and Challenges Developed
In the 2000s, dam construction and environmental issues were addressed: In 2005, a new water quality improvement project was initiated at the Shichigajuku Dam, and a circulation system was installed to control algae blooms. However, a 2008 survey showed that the phosphorus concentration remained high at 0.45 mg/L, indicating a delay in improvement. Meanwhile, at the Tokuyama Dam, although work to remove accumulated sediment proceeded in 2006, the situation remained serious, with agricultural damage in the downstream area reaching 150 million yen per year. In the Kiso River basin, groundwater recharge tests were conducted, but no noticeable effects were observed.

2010s: Efforts for Sustainable Management
In the 2010s, further measures were taken to address the environmental impacts of dam construction. In 2015, a phosphorus adsorbent was tested at the Shichigajuku Dam, and the adsorbent was put into full operation in 2018. As a result, phosphorus concentrations dropped from 0.4 mg/L to 0.38 mg/L, but still remain well above the standard value. At the Tokuyama Dam, the technology for sediment control was improved in 2013, and the area of damaged farmland has been reduced, but the annual impact still exceeds 200 million yen.

Meanwhile, in the Kiso River basin, a project to strengthen groundwater recharge technology was launched in 2016, and a new groundwater circulation model was piloted. In the late 2010s, the government announced a policy of sustainable water resource management, which promoted cooperation between companies and local governments.

Sources.
- Ministry of the Environment, "Annual Report on Water Quality in Lakes," 1999
- Miyagi Prefecture, "Shichigajuku Dam Environmental Improvement Plan," 2005
- Chubu Corporation, "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. Please let us know if you need additional details.