Citation

Feng WK, Huang RQ, Lin ZJ. Disaster Adv. 2013; 6(5): 31-40.

Copyright

(Copyright © 2013, Shankar Gargh)

DOI

unavailable

PMID

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Abstract

On 6 July 2011, a disastrous flood and debris flow was triggered by a heavy rainfall in Yanfang gully, Qingyu Town, Tongjiang County, Southwestern China. The debris flow burst following three-hour rainstorm with a maximum intensity of 62.6 mm per hour and an average intensity of 41.73 mm per hour. The gully has two branches divided in the place with elevation of 640m. The upper branch is in V-shape on the whole, with large gully gradient and steep slope. The branch, as the main source zone and catchment zone, has good hydrodynamic condition and large catchment area. The lower branch, gentle and broad, takes on a U-shape on the whole. The branch is the main zone of debris transport and deposit. The source material is mainly derived from transportable gully floor alluvial-pluvial deposits, colluvium and landslide deposits. The volume of the source material is 16.77x10(4)m(3) and that of the dynamic volume is 5.17x10(4)m(3). The gas well site is just situated in the gully-branch-division area, in the mouth of debris initiation area in the upper gully reach. In the gas well site construction, channel deflection in the gully lowered flood-discharge capacity. That, together with improperly designed overflow bridge, unreasonable site selection and well site lower elevation, resulted in serious gas well site destruction on 6 July disaster. Incision and lateral erosion of the disastrous flood and debris flow produced intense bottom tearing scouring in the gully which caused the slope deposits on the two sides of gully bed to undergo obvious disturbance deformation. That greatly increased debris flow risk happening again in rainy seasons. Thereafter, it can be concluded that debris flow will burst frequently in Yanfang gully in the future.