Environment Ministry to rejig projections of disaster debris

The Environment Ministry will review the way it estimates the amount of debris generated by major quakes and tsunami to improve the accuracy of its calculations, ministry officials said Saturday.

The ministry will establish up a panel of experts in late September to discuss the matter and will decide on a new method by the end of next March, the officials said.

Currently, the ministry multiplies the number of buildings it projects would be destroyed by disasters — such as quakes, tsunami and soil liquefaction — by their average weight, using data on the devastation caused in Kobe and nearby areas by the 1995 Great Hanshin Earthquake.

The Cabinet Office uses this technique to forecast the level of damage that will be caused by the next massive quake to strike Tokyo as well as the next major movement of the Nankai Trough, which stretches ominously down Japan’s Pacific coast.

The amount of debris generated by the March 2011 quake and tsunami that laid waste to large parts of the northeast coast turned out to be less than projected under the current method because part of the rubble was swept away to sea.

On the other hand, the disposal costs initially exceeded the predicted levels because some of the debris was transported for incineration to municipalities outside the disaster areas.

The new method will enable the Environment Ministry to estimate how much debris would be washed out to sea by tsunami. In addition, it will take into account the type of materials involved, such as wood and metal, according to the officials.

The new calculations will also incorporate computer simulations to estimate the spread of tsunami debris in the sea, the officials added.

The ministry hopes such projections will allow local governments to more accurately forecast the costs of disposing of disaster debris and the amount of space necessary for its temporary storage, thereby facilitating the process, they said.

The 9.0-magnitude Great East Japan Earthquake and tsunami left 16.08 million tons of debris strewn across the three worst-hit prefectures, Iwate, Miyagi and Fukushima. This figure excludes rubble in heavily contaminated areas around the stricken Fukushima No. 1 nuclear plant.

Under the ministry’s current method, the next major Nankai Trough temblor is estimated to generate a maximum of 250 million tons of debris, and the next big quake to hit Tokyo up to 96 million tons.