Mt. Fuji & Sabo Project

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Achievements

Sabo facilities in the Osawa alluvial fan have caught many times of debris flow, so that damages to downstream area by debris flows have been prevented.
Recently, debris flowings were caught in November 2000 and December 2004. Osawa sand pocket facilities captured both sediments, so there were no damage to the lower reaches.

List of captured flows such as debris flow with the Sabo facilities

Debris flow occurrence date Weather factor River name Continuous rainfall
（mm）		 Day rainfall
（mm）		 Maximum amount of rainfall (mm / h)

Deposited sediment volume
(1000m3)

 Type of Outflow
November 28, 1991 bad temper Osawa River 226 166 39 182 debris flow
December 8, 1992 snow melting Kurinokisawa River 246 231 37 　 yukishiro*
March 30, 1996 snow meilting Kazamatsuri River 138 137 27 18 yukisiro*
June 20, 1997 typhoon Osawa River 321 221 63 195 debris flow
November 26, 1997 bad temper Osawa River 298 283 33 199 debris flow
November 20, 2000 bad temper Osawa River 260 149 37 280 debris flow
December 20, 2004 bad temper Osawa River 162 106 31 110 debris flow
*yukishiro: sediment flow caused by snow avalanches or snow melting.

Yukishiro, December 8, 1992
A yukishiro destroyed Climber’s Security Center located at the sixth station on the Osawa Trail in Yamanashi Prefecture. Flows of melted snow caused another yukishiro in Kurinoki-sawa located in our service area, reaching Kurinoki Dams.
 
平成4年12月8日　雪代　栗ノ木第４えん堤
 

yukishiro, March 30, 1996


Snow slides intruded the Fuji Subaru Line on three different points. Melted snow caused yukishiro in our service area as well. Sediments as much as 18.000m3 were caught at the Kazematsuri Basin.
 
平成8年3月30日　雪代　風祭沈砂地工


Debris flow, November 21, 2000
  Heavy rainfall over 2 days caused the largest debris flow on record, originating in the Osawa failure.
Sediment caught at the Osawa sand pocket mounted up to 280,000m3.


Debris flow, December 5, 2004
Heavy rainfall and melted snow caused debris to flow. Sediment that reached the Osawa sand pocket mounted up to 110,000 m3.
土石流発生前　大沢遊砂地　堆積状況


Efficient Use of Sediment

Flowing out of the Osawa failure, large amounts of sediment are stopped and accumulated at our debris flow countermeasure facilities, such as the sand pocket and basins. This needs to be taken out, as it can flow out again to the under reaches and cause disasters, in case of any additional debris flow out. Thus we remove the sediment from our facilities, so their functions are maintained.

We use a stock yard on the Osawa alluvial fan as a tentative storage place for removed sediments. Stocked sediment consists of various sizes of sand and rocks (some of which are 2 meters long in diameter), making it difficult for us to find private contractors who would take it in for their own use.

In order to attract more contractors to accept the sediment, we started screening and fracturing the sand and rocks in 1998. Consequently, the sediment has been used for a broader range of purposes, including beach improvement materials and road bed materials.

自走式破砕機による粒径処理
 
海岸の養浜材として利用(富士海岸　吉原工区) 道路の路体材として利用(静岡県　富士土木事務所)

Copyright (c) 2006 Mt. Fuji Sabo Office, Chubu Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism. Allrights reserved.