The Engineering Geological Characteristics and Triggered Mechanism of Debris Flow in the Chishan River and Laonong River of Kaohsiung
Date Issued
2014
Date
2014
Author(s)
Hung, Yi-Wen
Abstract
This study is aimed to investigate the rainfall, sedimentological and morphological characteristics of debris flow occurred in the catchments of the Chishan river and Laonong river during 2009 Typhoon Morakot, and the links between engineering geological characteristics and triggered mechanism of debris flows. The study methods include field geomorphological investigations, satellite images, geomaterial testing and rainfall analysis of three debris flows occurred in the Lushan Formation, Nanchuan Formation and Kueichulin Formation.
According to the interpretations of the satellite images and field investigations, landslides located near the river and expanded to hilltop in the source area of debris flows in the Lushan Formation and Nanchuan Formation become the main source of geomaterial when the debris enter the channel and cause the debris flow. The rock discontinuities is well-developed in the transportation area of debris flow in the Kueichulin Formation, formed various types of failure models, such as dip slope and wedge failure, which provide a large volume of deposited materials. The deposited materials, river sediments, deposited materials left by the former debris flow and the geomaterial which eroded on the both sides of valley while the debris flow occurred, have become the main geomaterial source of the debris flow. About 51.0 % of the landslides located near the river and expanded to hilltop and about 32.4 % of the landslides located near the river. Consequently, more deposits were transported into the river during the typhoon and become the triggering factor of debris flow occurrence.
According to the morphology analysis, the big area of catchment, long length of river, and low elevation may be corresponding to the high sediments transport ability; therefore, the portion of geomaterial which comes from river sediments in debris flow would be higher. Furthermore, the higher the drainage density and hypsometric integral, the higher the landslide ratio will be; therefore, the portion of geomaterial which comes from landslides would be higher.
The experimental results show that the low strength of rock and high number of discontinuity per cubic meter may induce the high geomaterial recharge rate. While during storm events, failure is easy to occur on slope, bringing the geomaterial alone to the channel, and become the main source of the debris flow.
The result of rainfall analysis demonstrated that when the regional rainfall intensity surpass 50 mm/hr or the cumulative rainfall exceed 1100 mm, debris flow may be induced.
Subjects
土石流
旗山溪
荖濃溪
工程地質
發生機制
Type
thesis
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