Browsing by Author "Dong, Jia-Jyun"

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A systematic approach for the assessment of flooding hazard and risk associated with a landslide dam
(2013-01-01)
Yang, Sheng-Hsueh
;
Pan, Yii-Wen
;
Dong, Jia-Jyun
;
Yeh, Keh-Chia
;
Liao, Jyh-Jong
Inundation caused by landslide dams may occur in the upstream and downstream of the dams. A proper flooding hazard assessment is required for reaction planning and decision-making to mitigate possible flooding hazards caused by landslide dams. Both quick and detailed procedures can be used to evaluate inundation hazards, depending on the available time and information. This paper presents a systematic approach for the assessment of inundation hazards and risks caused by landslide dam formation and breaches. The approach includes the evaluation of dam-breach probability, assessment of upstream inundation hazard, assessment of downstream inundation hazard, and the classification of flooding risk. The proposed assessment of upstream inundation estimates the potential region of inundation and predicts the overtopping time. The risk level of downstream flooding is evaluated using a joint consideration of the breach probability of a landslide dam and the level of flooding hazard, which is classified using a flooding hazard index that indicates the risk of potential inundation. This paper proposes both quick and detailed procedures for the assessments of inundation in both the upstream and downstream of a landslide dam. An example of a landslide dam case study in southern Taiwan was used to demonstrate the applicability of the systematic approach.
Deriving landslide dam geometry from remote sensing images for the rapid assessment of critical parameters related to dam-breach hazards
(2014-02-01)
Dong, Jia-Jyun
;
Lai, Po-Jung
;
Chang, Chung-Pai
;
Yang, Sheng-Hsueh
;
Yeh, Keh-Chia
Dam-breaches that cause outburst floods may induce downstream hazards. Because landslide dams can breach soon after they are formed, it is critical to assess the stability quickly to enable prompt action. However, dam geometry, an essential component of hazard evaluation, is not available in most cases. Our research proposes a procedure that utilizes post-landslide orthorectified remote sensing images and the pre-landslide Digital Terrain Model in the Geographic Information System to estimate the geometry of a particular dam. The procedure includes the following three modules: (1) the selection of the reference points on the dam and lake boundaries, (2) the interpolation of the dam-crest elevation, and (3) the estimation of dam-geometry parameters (i.e., the height, length, and width), the catchment area, the volumes of barrier lake and landslides dam. This procedure is demonstrated through a case study of the Namasha Landslide Dam in Taiwan. It was shown the dam-surface elevation estimated from the proposed procedure can approximate the elevation derived from profile leveling after the formation of the landslide dam. Thus, it is feasible to assess the critical parameters required for the landslide dam hazard assessment rapidly once the ortho-photo data are available. The proposed procedure is useful for quick and efficient decision making regarding hazard mitigation.
Discriminant analysis of the geomorphic characteristics and stability of landslide dams
(2009-09-15)
Dong, Jia-Jyun
;
Tung, Yu-Hsiang
;
Chen, Chien-Chih
;
Liao, Jyh-Jong
;
Pan, Yii-Wen
Landslides can cause the formation of dams, but these dams often fail soon after lake formation. Thus, rapidly evaluating the stability of a landslide dam is crucial for effective hazard mitigation. This study utilizes discriminant analysis based on a Japanese dataset consisting of 43 well documented landslide dams to determine the significant variables, including log-transformed peak flow (or catchment area), and log-transformed dam height, width and length in hierarchical order, which affect the stability of a landslide dam. The high overall prediction power (88.4% of the 43 training cases are correctly classified) and the high cross-validation accuracy (86%) demonstrate the robustness of the proposed discriminant models PHWL (with variables including log-transformed peak flow, and log-transformed dam height, width and length) and AHWL (with variables including log-transformed catchment area, and log-transformed dam height, width and length). Compared to a previously proposed "DBI" index-based graphic approach, the discriminant model AHV - which uses the log-transformed catchment area, dam height, and dam volume as relevant variables - shows better ability to evaluate the stability of landslide dams. Although these discriminant models are established using a Japanese dataset only, the present multivariate statistical approach can be applied for an expanded dataset without any difficulty when more completely documented worldwide landslide-dam data are available. (C) 2009 Elsevier B.V. All rights reserved.
Effects of seismic anisotropy and geological characteristics on the kinematics of the neighboring Jiufengershan and Hungtsaiping landslides during Chi-Chi earthquake
(2009-03-10)
Dong, Jia-Jyun
;
Lee, Wang-Ru
;
Lin, Ming-Lang
;
Huang, An-Bin
;
Lee, Yen-Liang
The Chi-Chi earthquake (Mw=7.6) of September 21, 1999 triggered many landslides in central Taiwan. Two of these landslides, Hungtsaiping (HTP) and Jiufengershan (JFES) were situated as close as 2 km from each other but had significant differences in their kinematics. JFES landslide was a catastrophic rockslide-avalanche and the HTP landslide was relatively slow-moving. The authors conducted a study to explore the reasons for such differences. Factors such as the characteristics of strong ground motion, sliding direction of landslide, and friction angle of the sliding surface were considered in the study. An analysis of 12 strong-motion records collected in the study area showed that the distribution of horizontal pseudostatic coefficients, earthquake energy ratio and permanent sliding-block displacements (Newmark displacement) were anisotropic with their predominant direction mostly in the E/W-ESE/WNW trending. This direction is perpendicular to the axis of the main geological structures of the studied area. The computed Newmark displacement in the sliding direction of the JFES landslide is larger (44%) than that of the HTP landslide with sliding surface inclination of 21 degrees and friction angle of 28 degrees We can conclude that the seismic anisotropy and the corresponding sliding direction are important contributing factors to the kinematics of studied landslides. The back-calculated friction angle of the sliding surface that corresponds to a critical Newmark displacement for the JFES landslide is about 3.5 degrees higher than that of HTP landslide. The material (colluvium) on the sliding surface in HTP should be less velocity-dependent than that of the JFES landslide (rock) according to the back calculations. The importance of seismic anisotropy, sliding direction, and mechanical properties of sliding surface on the kinematics of deep-seated landslides is demonstrated. (c) 2007 Elsevier B.V. All rights reserved.
Logistic regression model for predicting the failure probability of a landslide dam
(2011-01-10)
Dong, Jia-Jyun
;
Tung, Yu-Hsiang
;
Chen, Chien-Chih
;
Liao, Jyh-Jong
;
Pan, Yii-Wen
Landslides may obstruct river flow and result in landslide dams; they occur in many regions of the world. The formation and disappearance of natural lakes involve a complex earth-surface process. According to the lessons learned from many historical cases, landslide dams usually break down rapidly soon after the formation of the lake. Regarding hazard mitigation, prompt evaluation of the stability of the landslide dam is crucial. Based on a Japanese dataset, this study utilized the logistic regression method and the jack-knife technique to identify the important geomorphic variables, including peak flow (or catchment area), dam height, width and length in sequence, affecting the stability of landslide dams. The resulting high overall prediction power demonstrates the robustness of the proposed logistic regression models. Accordingly, the failure probability of a landslide dam can also be evaluated based on this approach. Ten landslide dams (formed after the 1999 Chi-Chi Earthquake, the 2008 Wenchuan Earthquake and 2009 Typhoon Morakot) with complete dam geometry records were adopted as examples of evaluating the failure probability. The stable Tsao-Ling landslide dam, which was induced by the Chi-Chi earthquake, has a failure probability of 27.68% using a model incorporating the catchment area and dam geometry. On the contrary, the Tangjiashan landslide dam, which was artificially breached soon after its formation during the Wenchuan earthquake, has a failure probability as high as 99.54%. Typhoon Morakot induced the Siaolin landslide dam, which was breached within one hour after its formation and has a failure probability of 71.09%. Notably, the failure probability of the earthquake induced cases is reduced if the catchment area in the prediction model is replaced by the peak flow of the dammed stream for these cases. In contrast, the predicted failure probability of the heavy rainfall-induced case increases if the high flow rate of the dammed stream is incorporated into the prediction model. Consequently, it is suggested that the prediction model using the peak flow as causative factor should be used to evaluate the stability of a landslide dam if the peak flow is available. Together with an estimation of the impact of an outburst flood from a landslide-dammed lake, the failure probability of the landslide dam predicted by the proposed logistic regression model could be useful for evaluating the related risk. (C) 2010 Elsevier B.V. All rights reserved.