Hsiaolin Village Research Articles

Evolution of the large landslide induced by Typhoon Morakot: A case study in the Butangbunasi River, southern Taiwan using the discrete element method

In 2009, Typhoon Morakot delivered high intensity rainfall and triggered many sites of large landslide, which projected areas were larger than 10,000m2 from the satellite image, especially in southern Taiwan. According to DTM analysis, the material volume of the large landslide in Butangbunasi River was more than four times larger than that of the nearly famous landslide disaster in Hsiaolin village. Nevertheless, the different movement of these two large landslides led to different disaster impacts. Based on literatures and field works, the large Hsiaolin landslide was a catastrophic landslide, which had high velocity and less energy loss in the kinematic process. The source area of the large landslide in the Butangbunasi River, on the other hand, was composed of several landslide events, and the kinetic energy dissipated when the landslide materials attained to riverbed in sequence. In this study, we divided the Butangbunasi River large landslide into five slope units, namely A, B, C, D and E landslide events, to recognize the mechanism of the large landslide, and the simulation by using the Particle Flow Code 3D (PFC3D), which is based on the discrete element method, provided the kinematic process of the large landslide in the Butangbunasi River. It is noticed that most of the initial energy dissipated during the movement which the fist happening landslide event counteracted the crash of the follow-up events, and the residual energy gradually declined by the collision interaction of landslide blocks until the end of the large landslide. The result helps to reconstruct the evolution of the large landslide from small-scale landslide events and contributes to predict the affected region of the disaster. It also reveals that even though the impact of the large landslide is reduced by sequent small-scale landslide events, there still remain secondary disasters, such as landslide dam, which show a high potential risk in the river valley and midstream.

Compound Strategy Forward to Compound Disaster Mitigation: Lessons from Hsiaolin Village, Typhoon Morakot 2009

In 2009, the heavy rainfall induced by Typhoon Morakot hit Hsiaolin Village that caused catastrophic flooding, landslides, landslide dam breakages and debris flows. Such a called “compound disaster” is defined as a disaster in which extensive floods or sediment transports occur simultaneously or consecutively at the catchment area during an event. It challenges current warnings, forecasting and responses to sediment disasters. New concepts and procedure thus are needed to cope with such “compound disasters.” Rainfall hydrographs show downpours of long duration, high intensity, high accumulation and large extent. To better delineate these disasters and provide possible coping strategies, we rebuild the temporal order and spatial distribution of the disaster processes involved. The study suggest correlating individual disaster types with rainfall through simulation. This could clarify the causality between what happened in Hsiaolin Village and related disasters. Our results will strengthen disaster prevention in debris flows and shallow landslides using strateghies that could then be applied to warning systems for deep-seated landslide and landslide dams. The derivative issues and the approach to compound disaster prevention are suggested for future tasks.

Dark tourism. The Effects of Motivation and Environmental Attitudes on the Benefits of Experience

This study aims to discuss the experience model for visitors participating in Dark Tourism. The Hsiaolin Village relics, which were destroyed by the 2009 typhoon in Taiwan, are selected as the research subject. A total of 341 visitors to Hsiaolin Village Memorial Park were interviewed through a survey questionnaire. Structural equation models (SEMs) were utilized to verify the causal relationship among the visitors ’Dark Tourism motivation, environmental attitudes, and benefits of experience in Dark Tourism relics. The benefits of experience in Dark Tourism are divided into social benefits, learning benefits, and pressure relief for psychological benefits in this study. The empirical results show that the higher Dark Tourism motivation could enhance the visitors’ environmental attitudes towards Dark relics and further affect the acquired benefits of experience. Moreover, the stronger Dark Tourism motivation could directly influence the psychological benefits of experience such as emotional and pressure relief. The direct effects of learning and social benefits are not as strong where the benefits of experience are affected by the emotional perception of environmental attitudes. In other words, environmental attitudes present partial mediating effects. The research results provide useful reference information for the planning of Dark Tourism relics and the development of tourism activities.

Rapid geometry analysis for earthquake-induced and rainfall-induced landslide dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam’s geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.

Numerical simulation on a tremendous debris flow caused by Typhoon Morakot in the Jiaopu Stream, Taiwan

In August 2009, Typhoon Morakot brought a large amount of rainfall with both high intensity and long duration to a vast area of Taiwan. Unfortunately, this resulted in a catastrophic landslide in Hsiaolin Village, Taiwan. Meanwhile, large amounts of landslides were formed in the Jiaopu Stream watershed near the southeast part of the Hsiaolin Village. The Hsiaolin Village access road (Provincial Highway No. 21 and Bridge No. 8) was completely destroyed by the landslide and consequent debris flow. The major scope of this study is to apply a debris flow model to simulate the disaster caused by the debris flow that occurred in the Jiaopu Stream during Typhoon Morakot. According to the interviews with local residents, this study applied the destruction time of Bridge No. 8 and Chen’s house to verify the numerical debris flow model. By the spatial rainfall distributions information, the numerical simulations of the debris flow are conducted in two stages. In the first stage (before the landslide-dam failure), the elevation of the debris flow and the corresponding potential damages toward residential properties were investigated. In the second stage (after the landslide-dam failure), comparisons of simulation results between the longitudinal and cross profiles of the Jiaopu Stream were performed using topographic maps and satellite imagery. In summary, applications of the adopted numerical debris flow model have shown positive impact on supporting better understanding of the occurrence and movement of debris flow processes.

Using real-time abnormal hydrology observations to identify a river blockage event resulted from a natural dam

This study proposes an automatic identification approach for landslide dam formation using a real-time abnormal hydrology record and artificial neural network (ANN). In Taiwan, natural dams occur frequently and have the potential to cause significant disasters, especially in the presence of fragile geological conditions such as steep mountains, earthquakes, intense typhoon, and storm events. During a river blockage event, obtaining immediate real-time information can be difficult or even impossible due to extreme weather conditions, remote locations, and the mountainous terrain of the area. As a result of these issues, there is a strong need for a practical tool that can not only detect the occurrence of this type of natural dam but also estimate the potential real-time risk of dam failure. In order to develop the appropriate safety response, a rapid preliminary assessment of the failure type must be identified, followed by a thorough investigation into the failure process after the event has occurred. In this study, a new method is developed that applies an ANN model (1) to evaluate, in real time, the occurrence of a natural dam and the storage changes behind that dam; (2) to rapidly assess the natural dam failure type and failure process; and (3) to reconstruct the dam height variation during the dam failure process after the event. The proposed methodology is applied to Chi-Shan River Basin located in Kaohsiung, Taiwan, during Typhoon Morakot in 2009. In 3 days, Typhoon Morakot produced 1,911 mm of precipitation. The typhoon event produced a landslide dam and a debris flow that inundated Hsiaolin Village, causing 398 deaths. The tragic results of this case study demonstrate the need for an applicable, accurate, and efficient method to evaluate dam formation and its failure rate.

Movement of deep-seated rainfall-induced landslide at Hsiaolin Village during Typhoon Morakot

This study analyzes the mechanism of the landslide event at Hsiaolin Village during Typhoon Morakot in 2009. This landslide event resulted in 400 deaths. The extremely high intensity and accumulative rainfall events may cause large-scale and complex landslide disasters. To study and understand a landslide event, a combination of field investigations and numerical models is used. The landslide area is determined by comparing topographic information from before and after the event. Physiographic parameters are determined from field investigations. These parameters are applied to a numerical model to simulate the landslide process. Due to the high intensity of the rainfall event, 1,675 mm during the 80 h before the landslide event, the water content of soil was rapidly increased causing a landslide to occur. According to the survivors, the total duration of the landslide run out was less than 3 min. Simulation results indicated that the total duration was about 150 s. After the landslide occurrence, the landslide mass separated into two parts by a spur at EL 590 in about 30 to 50 s. One part passed the spur in about 30 to 60 s. One part inundated the Hsiaolin Village and the other deposited at a local river channel and formed a landslide dam. The landslide dam had height between 50 and 60 m and length between 800 and 900 m. The simulation result shows that the proposed model can be used to evaluate the potential areas of landslides induced by extremely high intensity rainfall events.

The Landslide Movement Process at Hsiaolin Village During Typhoon Morakot

The Landslide Movement Process at Hsiaolin Village During Typhoon Morakot

The landslide stage of the Hsiaolin catastrophe: Simulation and validation

[1] Typhoon Morakot struck southern Taiwan in the summer of 2009, causing the most severe flooding since the 1950s. In the early morning of August 9, rainfall triggered the Hsiaolin landslide, and the resulting debris avalanche covered the township of Hsiaolin Village, Kaohsiung. Around five hundred people were buried alive. Reconstruction of the runout of the debris avalanche would increase understanding of the large-scale avalanches for future hazard mitigation purposes. Simulation of the debris avalanche runout can provide valuable information for this purpose. A new continuum shallow-water model is applied to flow over general topography. The Coulomb friction law is adopted; the friction coefficient is initially determined by high pressure rotary-shearing tests and subsequently fine-tuned by an iterative procedure to minimize the difference between the simulation and the measurement. The friction coefficients measured by laboratory tests are found to be in reasonable agreement with the best-fit result of the simulation. In addition, Voellmy rheology is applied, but it is found that the role of the fluid viscous drag is insignificant. The simulation result in the village area is further corroborated by near-surface magnetic surveys. These indicate that the northern part of the village is dislocated, while the artifact structures of the southern part are buried near their original locations. By comparing the landslide front and the flow direction of the simulation, we are able to confirm, as also described by survivors, that the landslide swept the northern part of the village into the Cishan River, while the southern part was flooded subsequently by the debris from a dam breach about 20 min after the landslide.

A kinematic model of the Hsiaolin landslide calibrated to the morphology of the landslide deposit

This paper presents results of a case study on the Hsiaolin catastrophic landslide, including its kinematic process and the geometry of deposition. Based on geomorphologic analysis, the landslide initiated in thick, multi-aged colluvium soils at the headwaters of a small stream upslope of Hsiaolin village. A 3D discrete element program, PFC3D was used to model the kinematic process that led to the landslide and destruction of Hsiaolin village. The landslide advanced from debris slide to debris avalanche during the kinematic process. Assuming a friction coefficient of each particle of 0.1, the predicted maximum velocity was about 70 m/s, a velocity which permits the debris to cross Qishanxi stream and deposit on the opposite bank. Based on simulation results, Hsiaolin village was inundated in 60 to 65 s after failure initiation and at 112 s after the event, the debris avalanche came to rest, forming a landslide dam.

The formation and breaching of a short-lived landslide dam at Hsiaolin Village, Taiwan — Part II: Simulation of debris flow with landslide dam breach

Typhoon Morakot (2009) caused serious damage in southern Taiwan due to intensive rainfall with long duration. The issue of greatest concern arising from the disasters brought about by this extreme event was the burying of the entire village of Hsiaolin by a massive debris flow and landslide. Based on seismological and near-surface magnetic data, this tragic scenario arose due to a combination of events, a massive landslide, the formation of a landslide dam, and the consequent debris flow when this dam was breached. The objective of this part of the study is to investigate the spatial and temporal characteristics of the debris flow induced by the landslide breach. The US National Weather Service BREACH model and the Federal Emergency Management Agency approved FLO-2D model are integrated to facilitate the investigation of this catastrophe. A series of simulations including a 2D rainfall-runoff simulation over the Cishan River basin, landslide dam breach routing, and 2D debris flow simulation around the Hsiaolin Village were conducted. Hydraulic calculations were performed to determine the equivalent top elevation of the landslide dam based on inflows computed from the 2D rainfall-runoff simulation in association with the Digital Terrain Model (DTM) and upstream constraint of the backwater inundation areas. The hydrograph of the upstream inflow which induced overtopping failure was provided by a 2D rainfall-runoff simulation using the FLO-2D model calibrated by comparison with the downstream discharge record. The longevity of the landslide dam was less than 1 h, and it took only about 8 minutes to completely breach. The peak discharge rate of this massive landslide dam breach was 70,649 m 3/s. The dam break hydrograph was then used for upstream inflow to drive the FLO-2D debris flow simulation. The average sediment concentration by volume was 0.362. The simulated deposited sediment depth showed a reasonable match to the differences of DTMs before and after the disaster.

Geomorphologic characteristics of catastrophic landslides during typhoon Morakot in the Kaoping Watershed, Taiwan

A high-resolution digital elevation model (DEM) and field investigations are used to analyze the distribution and characteristics of rainfall-induced landslides in the Kaoping watershed of southwest Taiwan during Typhoon Morakot. The heavy rainfall brought by Typhoon Morakot is characterized as high intensity and long duration, with a return period well over 200 years. The landslide distribution correlates well with the heavy rainfall distribution. Heavy rainfall and flood triggered 12,697 landslides, including four giant landslides. The cumulative area of the landslides was 183.1 km 2. The landslide ratio in four sub-watersheds of the Kaoping watershed exceeded 6.5%. Analysis results indicate that the percentage of the downslope landslide areas is approximately 3.2–10.5 times higher than that of upslope landslide areas owing to serious scour of the riverside. The power–law exponent β for rainfall-induced landslide distribution during Typhoon Morakot is lower ( β = 1.3–1.4) than that for earthquake-induced landslide distribution in the comparison of self-organized criticality, because the heavy rainfall induced many new landslides at different scales. The Hsiaolin landslide, one of four giant landslides, was a deep-seated, dip-slope landslide with an area of 2.5 km 2 and a volume of 2.7 × 10 7 m 3. A portion of the sediment slid into the original valley and dammed the Chishan River, while another portion buried Hsiaolin village. Based on the results, the extremely high intensity and long duration of rainfall caused numerous landslides with different scales near the downslope region. We recommend using the detailed topographic changes that occurred during the Hsiaolin landslide to identify and prevent similar deep-seated landslide disasters.

The formation and breach of a short-lived landslide dam at Hsiaolin village, Taiwan — part I: Post-event reconstruction of dam geometry

In this paper, technologies from multiple disciplines are used to reconstruct the shape of the Hsiaolin landslide dam, a short-lived landslide dam (SLD), that was triggered by Typhoon Morakot. Here, the formation, failure mode and breaching process of this SLD are investigated. The results indicate that the overtopping time and the debris budget constrained the dam geometry. The inferred volume of the Hsiaolin landslide dam (15.4 million m 3) is much smaller than the actual landslide volume (25.2 million m 3) even considering the rock-mass dilation and debris entrainment. Meanwhile, a 46% error could be induced if an over-simplified equation (a function of the dam height, length and width) is used to calculate the dam volume. The saddle of the dam crest, which is where overtopping occurred, could be used as a reference to measure the dam height and length. Accordingly, the determined dam dimensions of height (44 m), length (370 m) and width (1500 m) are suggested to be the representative geometrical indices that influenced the stability of the Hsiaolin landslide dam. The flow rate of the dammed river, another variable relevant to dam stability, was determined from a run-off simulation. It is suggested that, instead of the peak flow before the dam formation, the flow rate during the blockage period (2974 m 3/s) should be used as the training data for building a statistical model for stability predictions. Finally, the low hydraulic gradient at the toe of the dam's surface and the high safety factor of the dam slope indicate that the piping and slope instability were irrelevant to the failure of the Hsiaolin short-lived landslide dam. It is postulated that overtopping (about one hour after the blockage) dominated the failure process of this heavy-rainfall-induced landslide dam.

Detection of landslides and submarine slumps using broadband seismic networks

We detected 52 seismic events associated with landslides and submarine slumps on 8 August 2009 when Typhoon Morakot hit Taiwan. These events were neither felt nor reported because their seismic energy was primarily in the long period band (20–50 s). Most of these events were located in mountain areas where the accumulated rainfall was extremely high, though some were found offshore southern Taiwan. Among all events, the fatal landslide earthquake was located at Hsiaolin Village, where 474 people were buried. Inversion modelling of the seismic waveforms generated by the Hsiaolin landslide shows that the seismic source was represented by single force, consistent with downhill sliding. Some offshore seismic events indicate that submarine slumps probably occurred along submarine canyons and steep slopes. Our study shows that broadband seismic monitoring can be used to issue early warnings for mitigating disasters generated by inland and offshore landslides.