'Forest levees' can pass down important lessons and help recovery
As efforts to dispose of debris generated by the March 11, 2011, Great East Japan Earthquake and tsunami fail to make headway, a proposal to build so-called forest levees has begun to attract widespread attention.
The plan entails gathering and burying debris into the ground to make elevated mounds, where trees would be planted to serve as tsunami breakwaters. For the disasters' victims, rubble from the quake and tsunami are not garbage, but mementos and relics of history. I urge the construction of forest levees, which would not only serve as symbols of our commitment to preventing disasters, but as real tools that protect the lives of future generations.
At a March 13 meeting of Cabinet members involved in disaster waste disposal, Prime Minister Yoshihiko Noda brought up the example of Yokohama's Yamashita Park, which was built upon debris generated from the Great Kanto Earthquake of 1923, and ordered the deliberation of a plan to use the debris left from last year's quake and tsunami to build elevated land and breakwaters.
The creation of forest levees using debris was proposed by Akira Miyawaki, professor emeritus at Yokohama National University and an expert on plant ecology, immediately after the disasters hit on March 11, 2011. According to the plan, hazardous materials would first be removed from the debris, and any wood-based waste would be mixed with concrete and other materials, and buried into soil on the coastline. A mound would be created on top of that, where broad-leaved evergreen trees native to the locale would be planted.
Broad-leaved evergreen trees spread their roots deep inside the soil and entangle themselves into the gaps created by debris, making them more capable of withstanding tsunami. The trees' breakwater capacity can reduce the strength of tsunami that sweep onshore, preventing people and homes from being washed away.
When I accompanied Miyawaki on an inspection tour of Iwate, Miyagi and Fukushima prefectures -- the three prefectures hit hardest by the disaster -- we saw many broad-leaved evergreen trees still standing after massive waves had swept over them.
Learning that there was a "forest levee" precedent in Wakayama Prefecture, I traveled to the prefectural town of Hirogawa. Built after the Ansei-Nankai Earthquake in 1854 by the entrepreneur Goryo Hamaguchi, the Hiromura Levee stands three to five meters high and stretches 636 meters between the fishing port and a residential district. Pine trees approximately 15 meters high line the ocean side of the bank, while Japanese spindles and sweet viburnum line the other side. Children play and residents take walks on the path at the top of the levee. There's a good view of the ocean from between the trees, making it easy to detect any abnormalities in the water.
Rocks washed up by the tsunami that followed the 1854 quake were used for the mound, which victims of the disaster who'd lost their jobs were employed to build. In the 1946 Nankai Earthquake, the town was hit by tsunami 4 to 5 meters high that killed 22 people, but homes in the center of town were protected by the levee and spared damage.
What is most striking is that the levee has been succeeding in passing down the spirit of disaster prevention in the area. Residents pick up trash on the levee and pull weeds. Fifteen people serve as storytelling volunteers that go around telling the history behind the levee and Goryo Hamaguchi. Every November, area firefighters and students from local elementary and junior high schools partake in a "tsunami festival," in which each child brings soil with them to add repairs to the levee. This year's festival will mark its 110th anniversary. It is clear that lessons of the tsunami and a proactive approach to disaster prevention are deeply rooted in the local culture.
Last year's quake generated about 22.46 million tons of debris in the three northeastern prefectures, of which only 8.1 percent has been disposed. The amount of rubble is expected to grow as concrete scraps from the foundations of buildings are torn out of the ground. If we are to resolve the issue of debris disposal as quickly as possible, the forest levee is a promising option.
One obstacle that stands in the way of our building forest levees is a legal one. According to the Environment Ministry, the Waste Disposal Law approves the use of concrete as a building material for breakwaters. The use of wood-based materials for such structures, however, may constitute an infringement of that law because of the risk of wood producing methane gas, which could lead to spontaneous combustion. The ministry has also suggested the possibility that wood-based materials could cause levees to cave in.
But are those real concerns? A sample planting was conducted in Norosan National Forest in the Hiroshima Prefecture city of Kure three years ago, based on Miyawaki's proposed method. Trees were planted in holes about a meter deep in a mixture of soil and a variety of materials that included Japanese cedar logs, but there have been no fires or cave-in.
Miyawaki says that because wood-based materials rot and break down, they turn into nutrients that promote the growth of trees. The Environment Ministry is deliberating the legal issues surrounding the proposal, having received Noda's instructions, and I believe the situation calls for a flexible implementation of the law so that the proposed forest levees can be built.
There are numerous municipal governments in disaster areas trying to put Miyawaki's proposal into practice. If local residents are able to participate in planting, the levees will be made by residents, for residents. As a tool to resolve the current debris disposal problem, prepare for future tsunami, and pass down the lessons of the most recent disaster to future generations, the forest levee plan will undoubtedly be a powerful boost toward the devastated region's reconstruction. (By Satoru Yamamoto, Global Environment Office)
May 20, 2012(Mainichi Japan)