SUMMARY
Landslide
in the humid tropical regions and problem of its warning:
case studies in the provinces of Cao Bằng and Hà Giang, Việt
Lê
Đức An, Uông Đình Khanh, Võ
Thịnh
In the humid tropical mountainous regions of Việt
Up to now, there are many researches concerning problems of landslide
distribution and evolution, and risk assessment for mountainous areas in Bắc
Bộ and Trung Bộ regions. These studies have shown places and areas of
high risk of lanslide, and indicated the causes of these phenomena and proposed
solutions for limiting them. In the past years (2000-2008), in Cao Bằng
and Hà Giang provinces occurred several huge landslides. They often appear on
the slopes of stream valleys of 1st to 3rd order, with a
relative height of 100-300 m and close to the local base level of erosion.
Scale and quantity of landslides depend also on the characteristics of vertical
and horizontal dissection of regions.
On many lines of communication, landslides occurred strongly at the
road sections cutting across slopes formed by metamorphic, terrigenous and volcano-terrigenous rocks crushed by faults and
fissures, with a thick weathering crust of coarse-grained beds interbedded with
clay, especially in high and steep talus.
Aiming to experimentally study for warning on
the time-point of landslide occurrence by using the rainfall intensity, the
authors have analyzed all rainfalls that have caused landslides (information
from newspapers and local reports), as well as all heavy and very-heavy
rainfalls during the period of 2000-2008 (according to data from main rain
stations of the Hà Giang Province). It was found that the total quantity, the
mean daily quantity and the biggest daily quantity of rainwater caused by
storms causing landslides are all clearly higher than that of other normal
heavy rainfalls. It was carried out in more detailed research into the
evolution of rainfall causing landslides in Hà Giang Town (on 3 August, 2007)
by using quantity of rainwater per every 6 hours, and establishement of a chart
expressing the relationship between rainfall, landslides and rain time, to be
able to refer to warning of the risk degree of heavy rainfalls in the region.
The authors preliminarily suggest a warning
research procedure of the time-point of landslide occurrence by using rainfall
intensity that includes three steps, such as statistic study, model study and
warning study. This procedure is a suggestion necessary to continue experiment
and supplement in order to apply in practice.
Người biên tập: TS. Ngô Gia Thắng