C-3: Mechanism of Viscous Debris Flow and
Countermeasures against Debris-Flow Hazards
Photo 1. Setting up of the video observation
system at the slope of Da'aozi gully.
Photo 2. Survey work of channel deposits after
the passage of an artificial debris flow.
Studies on the mechanism of viscous type debris flow and on countermeasures against its hazards are the objectives of this joint research with the Chengdu Institute of Mountain Disasters and Environment, Academia Sinica, Debris flows of viscous type are found generally in China especially at the geologic settings of highly fractured slate, mudstone, limestone and metamorphic rock in tectonically active regions, and frequently bring about significant hazards under a condition of heavy rainstorm, while hazards due to debris flow of stony type are dominant in Japan.
Observation of debris flows using video systems( see Photos ) and various surveys of slopes in the watershed of Jiangjia gully, Yunnan Province-a small tributary in the upstream of Chang Jiang(the Yangzi River)- till 1995 clarified many special processes and characteristics of debris flows of viscous type and related phenomena. Main results are as follows: 1) Smaller intensity of rainfall is also effective for debris flow occurrence, and much longer time lag of debris flow occurrence should be expected from the onset of heavy rain fan. 2) Each event of viscous debris flow usually consists of more than one hundred intermittent surges and several continuous surges. Each surge has very high mobility, although it has very high concentration of solid particle. The most significant discovery was the fact that it has no plug in its flow, 3) Alluvial fan is susceptible to hazards due to flooding of viscous debris flow over a large area because the flow usually forms very flat and vast deposits of debris-flow lobe.
Five Japanese research members visited the Dongchuan Debris Flow Observatory in August, 1995 and executed the observation work of debris flow including some field experiments of artificial debris flows. Two Chinese researchers, Prof. Wu Jishan( Director of CIMDE ) and Prof. Kang Zhicheng( Director of Dongchuan Debris Flow Observatory ) visited many sites of Sabo works in Japan last November and held several discussions with Japanese researchers about countermeasures against debris flow hazards.
Five Japanese research members( Director Takahashi, Dr. Sawada and Dr. Suwa of DPRI, Prof. Mizuyama of Kyoto Univ. and Dr. Arai of Meijyo Univ.) are planning to visit the Dongchuan Debris Flow Observatory from July 27 to August 15 this year to execute the observation of debris flow and the surveys further, and to hold a symposium on "Mechanism of Viscous Debris Flow and Countermeasures against it" with many Chinese researchers of debris flow also from Chengdu and Beijing.
