TITLE:
Characteristics and Causes of Disastrous Debris Flows on July 4, 2013, in Shimian County, Sichuan, China
AUTHORS:
Yonggang Ge, Fenghuan Su
KEYWORDS:
Disastrous Debris Flows, Characteristics, Hazards, Causes, Shimian County
JOURNAL NAME:
International Journal of Geosciences,
Vol.7 No.4,
April
25,
2016
ABSTRACT:
Debris flow is an abrupt
phenomenon of earth surface movement and typical disaster in mountainous areas
with steep terrace, quantity of loose soil and abundant surface runoff. Intense
rainfall and rainstorm easily triggered debris flows and generated huge losses.
The disastrous debris flows, on July 4, 2013 at the gullies of Hou, Heilinzi
and Xiongjia in Shimian County, Sichuan Province, resulted in 18 casualties and
endangering Shimian city with a population of 50,000. These debris flows were
characterized by low viscosity with only 0.9% - 1.4% clay soil of less than
0.05mm, density of 1.77 - 1.84 t/m3, velocity of 4.4 - 13.5m/s and
discharge of 827 - 1248 m3/s, respectively, and also delivered
sediment of 16.8 × 104m3, 12.7 - 13.5 × 104 m3, 20.5 × 104m3 out of the outlet, respectively. These
three events all generated a hazard chain, which involved in flash flood,
channelized debris flow, dammed lake and outburst flood. The threshold conditions
of debris flow blocking Nanya River and forming this hazard chain are that the
unit width peak discharge and the deposition volume in river channel are more
than 37.0 m3/s and 4500 m3, respectively. These debris
flows were initiated by intense rainfall with the antecedent rainfall of over
52 mm and triggering rainstorm of over 36 mm/h. And, the property losses and
casualties mainly originated from impacting and scouring, burying and blocking,
highway destructing and river channel rising. The irrational location of
constructions and the destruction of under-standard prevention constructions
were responsible for loss worsening. It was strongly recommended for mitigating
that hazards reassessment, integrated control, emergency plan and integrated
risk management were made at mountainous urban areas, especially in high-hazard
areas.