HAMAMATSU, Shizuoka Pref. – People used to ski down the Nakatajima sand dune in Hamamatsu, Shizuoka Prefecture, when it was 20 meters high back in the 1960s, but now it is only about 6 meters high due to erosion from high waves.
What’s left of the once-tan dune is now mainly dark brown.
“That’s where a large pool was created by high waves from a typhoon two years ago,” said 36-year-old Hirotoshi Shimizu, head of an organization that cleans beaches in the area and works to protect the coastline.
“Behind the pine forest is a residential area, and residents didn’t see the water approaching. They could easily have been swept away by a tsunami,” he said.
Sandy beaches stretching more than 100 km from the city of Omaezaki in Shizuoka Prefecture to Cape Irako in Aichi Prefecture have suffered from heavy erosion in recent years.
“One reason is that the volume of sand flowing onto the beaches has decreased because a dam in the upper reaches (of the Tenryu River) is stopping the flow of earth and sand,” reckoned Shinichi Aoki, a professor at Toyohashi University of Technology in Toyohashi, Aichi Prefecture.
The headwaters of the Tenryu River once replenished the shoreline of the Enshunada coast in Shizuoka with earth and sand. But the Sakuma Dam, built in 1956 by Electric Power Development Co., largely halted the alluvial flow.
Fifty years on, the reservoir behind the dam has silted up with about 100 million cu. meters of earth, about one-third of the reservoir’s capacity.
Every year, the dam traps about 2 million cu. meters, about 1.6 times volume of the Tokyo Dome.
The Land, Infrastructure and Transport Ministry is studying whether it is feasible to dredge the reservoir and transfer some of this earth to the lower reaches of the river, and use some of the electricity generated by the dam for flood control. But the plan will take a long time to bring to fruition: the target date is 2023.
The education ministry has awarded Aoki a five-year,1 billion yen grant to research the movement of sand and erosion in the watershed, which could produce ways to ease the problem.
“We have been dependent on local measures so far, such as the installation of blocks to break the surf when sand is lost,” Aoki said. “We’ve actually seen some areas deteriorate into miserable beaches with only artificial structures. If the central and local governments and residents can join forces, a model to regenerate the beaches can be put into place,” Aoki said.
On July 2, Shimizu sponsored a drive to move some of the sand from the bottom of the dam to the beach, with about 60 residents from Omaezaki and Toyohashi taking part.
The residents are also studying the green turtles that come ashore to lay their eggs on the beach. The turtles are facing extinction, and loss of the beach could worsen their plight.
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