Special Issue "Natural Disasters Occurrence, Reduction, and Restoration in Mountain Regions"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydrology".

Deadline for manuscript submissions: closed (30 September 2022) | Viewed by 13473

Special Issue Editor

Prof. Dr. Su-Chin Chen
E-Mail Website
Guest Editor
Department of Soil and Water Conservation, National Chung Hsing University, Taichung City 40227, Taiwan
Interests: sediment transport; soil erosion and scour; dam breach; landslides; vegetation restoration; eco-hydrology; disaster mitigation
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Mountain regions are critical because of their diverse geological conditions, dynamic changes, and the multiple natural hazards that often occur. Mountains are high-risk environments that can experience a variety of natural hazards, since initiated hazards often trigger secondary, cascading hazards, having a significant impact not only on the area of occurrence but often also on up- and downstream regions. High economic losses and human casualties are caused by geophysical- (rockfalls, earthquakes, and volcanic activities), hydrological- (floods, avalanches, and dammed-lake outbursts), and sediment-related hazards (landslides, driftwood, debris/mud flows, and surface erosion). Under the impacts of global warming and climate change the spatiotemporal patterns of rainfall and other weather events have become more unevenly distributed, often with a more extreme magnitude and/or intensity of events. The complexity of mountain regions in addition to the continued changes in the climate and land use have made it more challenging to predict mountainous hazards and their impacts on communities. Based on the countless efforts made worldwide on natural hazards in mountain regions, tight international collaboration is strongly required to answer questions related to the causes of disasters, the monitoring of hazardous phenomena, predicting disasters, and the effective reduction of hazardous consequences.

Related Conference:

INTERPRAEVENT International Symposium 2022 has teamed up with this Special Issue. The oral presenters are encouraged to submit manuscripts to this SI; if accepted, the papers will be published in Water and collected in the INTERPRAEVENT proceedings.

For more information about the INTERPRAEVENT Symposium, visit the conference website: https://interpraevent2022.nchu.edu.tw/

Prof. Dr. Su-Chin Chen
Guest Editor

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Keywords

  • disasters caused by dammed-lake outbursts and driftwood, debris/mud flows
  • disasters caused by landslides and rockslides
  • disasters caused by seasonal floods and surface erosions
  • the relationships between natural hazards and climate change
  • strategy from natural disasters to restoration
  • stream ecosystem services and nature-based solutions
  • disaster-resilient community and rural regeneration

Published Papers (18 papers)

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Research

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Article
The Mobility of Landslides in Pumice: Insights from a Flume Experiment
Water 2022, 14(19), 3083; https://doi.org/10.3390/w14193083 (registering DOI) - 30 Sep 2022
Abstract
Risk of landslide hazards strongly depends on how far landslide sediment travels, known as landslide mobility. Previous studies mentioned enhanced mobility of earthquake-induced landslides in volcanic deposits compared to those from other geologic/soil settings. A flume apparatus constructed at a 1:300 scale was [...] Read more.
Risk of landslide hazards strongly depends on how far landslide sediment travels, known as landslide mobility. Previous studies mentioned enhanced mobility of earthquake-induced landslides in volcanic deposits compared to those from other geologic/soil settings. A flume apparatus constructed at a 1:300 scale was used to examine the mobility of landslides with pumice. Four pumice samples were collected from landslides induced by the 2018 Eastern Iburi earthquake, Hokkaido, Japan. Laboratory tests confirmed the unique low specific gravity of the pumice (1.29–1.33), indicating numerous voids within pumice particles. These voids allowed pumice to absorb a substantial amount of water (95–143%), about 9–15 times higher than other coarse-grained soils. Our flume experiments using various saturation levels (0–1) confirmed the influence of this inner-particle water absorption on pumice mobility. Because a low value of specific gravity indicates a low strength of soil, grain crushing may occur on the pumice layer, causing water from the internal voids to discharge and fluidize the transported landslide mass. Our findings indicate that such earthquake-induced landslides can be as mobile as those induced by rainfall, depending on the initial water content of the pumice layers. These conditions might be associated with water accumulation from previous rainfall events and the water-holding capability on pumice layers. Full article
Article
Three-Dimensional Engineering Geological Model and Its Applications for a Landslide Site: Combination of Grid- and Vector-Based Methods
Water 2022, 14(19), 2941; https://doi.org/10.3390/w14192941 - 20 Sep 2022
Viewed by 313
Abstract
A three-dimensional engineering geological model (EGM), which provides an approximation of the geological conditions, is a key element in any engineering project. The slope at Huafan University, Mt. Dalun, in the Western Foothills of northern Taiwan, is a dip slope that has been [...] Read more.
A three-dimensional engineering geological model (EGM), which provides an approximation of the geological conditions, is a key element in any engineering project. The slope at Huafan University, Mt. Dalun, in the Western Foothills of northern Taiwan, is a dip slope that has been assumed to be unstable. The bedrock is mainly composed of intercalated sandstone and shale, where the thickness of the sandstone varies from thin to massive, interbedded with shale from the Miocene age. By interpolating the thickness of the colluvium derived from borehole data and analyzing the contours of the interpolation surface result, we find that the landslide material accumulates at the slope foot, towards the southwest in the direction of movement. Due to tectonic control—in particular, considering the two local faults that pass through the study area—the strata’s orientation significantly changes over the studied slope. As a basis for the 3D EGM, polynomial surface fitting is applied for detailed analysis of the sub-surface geological structure, as well as to compute the regressive orientation of the bedding plane derived from the borehole data. Based on the calculated regression plane passing through the elevations of the geological interface (key bed), the results indicate that the regression plane’s direction is consistent with the outcrop measurements. Moreover, several cross-sectional profiles are considered to visualize and clarify the 3D EGM. Finally, surface and sub-surface monitoring data are compared with the result, in order to refine the 3D EGM. The proposed geological model is expected to contribute to the comprehensive understanding of gravitational slope deformation, and may serve as a guideline to minimize potential disasters. Full article
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Article
Using Landslide Statistical Index Technique for Landslide Susceptibility Mapping: Case Study: Ban Khoang Commune, Lao Cai Province, Vietnam
Water 2022, 14(18), 2814; https://doi.org/10.3390/w14182814 - 09 Sep 2022
Viewed by 374
Abstract
Ban Khoang is a mountainous commune in Sa Pa district located in the central part of Lao Cai province, Vietnam. Landslides occur frequently in this area and seriously affect the local living conditions. To help the local authority in developing a landslide disaster [...] Read more.
Ban Khoang is a mountainous commune in Sa Pa district located in the central part of Lao Cai province, Vietnam. Landslides occur frequently in this area and seriously affect the local living conditions. To help the local authority in developing a landslide disaster action plan, the statistical index method for landslide susceptibility mapping is applied. As the result, the landslide susceptibility zonation (LSZ) map was created. The LSZ map indicates that areas of low, moderate, high and very high landslide susceptibility zones are, respectively, 20.3 km2, 12.4 km2, 15.4 km2, and 5.2 km2; most of the observed landslide areas that are well predicted belong to high or very high landslide susceptibility classes. In detail, 80% observed landslide areas and 78.57% number of observed landslides were well predicted, and the area (AUC) under the receiver operating characteristic (ROC) curve obtained 80.3%. Hence, the high and very high landslide susceptibility classes in the LSZ map can be considered highly believable, and the LSZ map will be reliable to use in the practice. Full article
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Article
Analysis of Socio-Economic Factors That Influence Loss of Life in Sediment-Related Disasters
Water 2022, 14(15), 2408; https://doi.org/10.3390/w14152408 - 03 Aug 2022
Viewed by 519
Abstract
Non-structural measures, including relocation from a hazard zone, land development regulations, and evacuation, are important sediment-related countermeasures. Such measures depend on the behaviour of residents and are affected by socio-economic conditions. In Japan, the declining birth rate and ageing population are expected to [...] Read more.
Non-structural measures, including relocation from a hazard zone, land development regulations, and evacuation, are important sediment-related countermeasures. Such measures depend on the behaviour of residents and are affected by socio-economic conditions. In Japan, the declining birth rate and ageing population are expected to result in rapid changes in socio-economic conditions; accordingly, there is a need to evaluate the impact of such changes. However, there is no established methodology for the establishment of non-structural measures that considers the socio-economic conditions of all areas. Therefore, this study analysed the regional characteristics of disaster-affected areas with high numbers of casualties to elucidate the impact of socio-economic conditions. The results imply that severe losses occurred under various topographical and socio-economic conditions, such as in urban areas with high population densities and in mountainous areas with increasing depopulation. More data are needed, especially regarding socio-economic conditions. Importantly, the community-based analytical method used in this study enables a comparative analysis of disasters in different regions at different times. Full article
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Article
An Approach for Preliminary Landslide Scarp Assessment with Genetic Algorithm (GA)
Water 2022, 14(15), 2400; https://doi.org/10.3390/w14152400 - 02 Aug 2022
Viewed by 495
Abstract
For the investigation of landslide mass movement scenarios through numerical simulation, a well-defined released mass and a precise initial source area are required as prerequisites. In the present study, we present a genetic algorithm-based approach for preliminarily assessing the landslide scarp when the [...] Read more.
For the investigation of landslide mass movement scenarios through numerical simulation, a well-defined released mass and a precise initial source area are required as prerequisites. In the present study, we present a genetic algorithm-based approach for preliminarily assessing the landslide scarp when the local field data are limited, using an ellipse-referenced idealized curved surface (ER-ICS)—a smooth surface constructed with respect to an ellipse. According to a specified depth at the center, there are two distinct curvatures along the major and minor axes, respectively. To search for the most appropriate ICS, the reference ellipse is translated, rotated, and/or side-tilted to achieve the optimal orientation for meeting the best fitness to the assigned condition (delineated area or failure depths). The GA approach may significantly enhance the efficiency, by reducing the number of candidate ICSs and notably relaxing the searching ranges. The proposed GA-ER-ICS method is examined and shown to be feasible, by mimicking the source area of a historical landslide event and through application to a landslide-prone site. In addition to evaluating the fitness of the ICS-covered area with respect to the source scarp, the impacts of various ICSs on the flow paths are investigated as well. Full article
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Article
Streamflow Measurement Using Mean Surface Velocity
Water 2022, 14(15), 2370; https://doi.org/10.3390/w14152370 - 31 Jul 2022
Viewed by 470
Abstract
This study developed an efficient discharge measurement method that can be applied to estimate the streamflow of natural streams and artificial channels. The conventional methods that apply current meters to measure discharge are costly, time-consuming, and labor-intensive. Owing to a shortage of observers [...] Read more.
This study developed an efficient discharge measurement method that can be applied to estimate the streamflow of natural streams and artificial channels. The conventional methods that apply current meters to measure discharge are costly, time-consuming, and labor-intensive. Owing to a shortage of observers in streamflow measurement and for the safety of hydrologists and with advances in measurement techniques, many have strongly suggested the use of non-contact methods when determining streamflow. The non-contact methods that use floats or surface velocity radar to determine the streamflow are becoming more and more popular especially during periods of high water. However, it is not easy to estimate the surface velocity coefficient of each vertical directly for determining the mean velocity in each subsection. As the relationship between the mean surface velocity and mean velocity of a stream cross-section is constant, an efficient and accurate non-contact method of streamflow measurement could be further developed. Thus, streamflow can be estimated by the constant, the mean surface velocity, and cross-sectional area of a stream. The mean velocity of a cross-section, used for parameter calibration, is usually obtained from the discharge made based on the velocity-area principle and cross-sectional area. The surface velocity was measured at the vertical that is then used to estimate mean velocity of a subsection. Once the parameter is determined, streamflow can be obtained from the surface velocity. This approach was further applied to a natural stream and an artificial channel. Measurements were made to verify the reliability and accuracy of the proposed approach. The results show that the relationship between mean channel velocity and mean surface velocity is very stable in both a natural stream and an artificial channel because the streamflow differences, given by the proposed and the conventional method, are relatively insignificant. As a result, mean surface velocity can be used to determine the streamflow quickly and provides for a reliable and accurate measurement of streamflow. Full article
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Article
The Role of Citrus Groves in Rainfall-Triggered Landslide Hazards in Uwajima, Japan
Water 2022, 14(13), 2113; https://doi.org/10.3390/w14132113 - 01 Jul 2022
Viewed by 706
Abstract
Landslides often cause deaths and severe economic losses. In general, forests play an important role in reducing landslide probability because of the stabilizing effect of the tree roots. Although fruit groves consist of trees, which are similar to forests, practical land management, such [...] Read more.
Landslides often cause deaths and severe economic losses. In general, forests play an important role in reducing landslide probability because of the stabilizing effect of the tree roots. Although fruit groves consist of trees, which are similar to forests, practical land management, such as the frequent trampling of fields by laborers and compression of the terrain, may cause such land to become prone to landslides compared with forests. Fruit groves are widely distributed in hilly regions, but few studies have examined their role in landslide initiation. This study aims at filling this gap evaluating the predisposing and triggering conditions for rainfall-triggering landslides in part of Uwajima City, Japan. A large number of landslides occurred due to a heavy rainfall event in July 2018, where citrus groves occupied about 50% of the study area. In this study, we combined geodata with a regression model to assess the landslide hazard of fruit groves in hilly regions. We developed maps for five conditioning factors: slope gradient, slope aspect, normalized difference vegetation index (NDVI), land use, and geology. Based on these five maps and a landslide inventory map, we found that the landslide area density in citrus groves was larger than in forests for the categories of slope gradient, slope aspect, NDVI, and geology. Ten logistic regression models along with different rainfall indices (i.e., 1-h, 3-h, 12-h, 24-h maximum rainfall and total rainfall) and different land use (forests or citrus groves) in addition to the other four conditioning factors were produced. The result revealed that “citrus grove” was a significant factor with a positive coefficient for all models, whereas “forest” was a negative coefficient. These results suggest that citrus groves have a higher probability of landslide initiation than forests in this study area. Similar studies targeting different sites with various types of fruit groves and several rainfall events are crucial to generalize the analysis of landslide hazard in fruit groves. Full article
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Article
Quantitative Land-Use and Landslide Assessment: A Case Study in Rize, Türkiye
Water 2022, 14(11), 1811; https://doi.org/10.3390/w14111811 - 04 Jun 2022
Viewed by 781
Abstract
Currently, many studies have reported that many landslides occur in tea or rubber plantation areas. In these areas, it is important to make a landslide susceptibility map and to take necessary measures to mitigate landslide damage. However, since historical landslide distribution data and [...] Read more.
Currently, many studies have reported that many landslides occur in tea or rubber plantation areas. In these areas, it is important to make a landslide susceptibility map and to take necessary measures to mitigate landslide damage. However, since historical landslide distribution data and land use data are not available, quantitative landslide assessment measurements have not been made in many countries. Therefore, in this study, landslide distribution maps and land use maps are created with worldwide available satellite imagery and Google Earth imagery, and the relationship between landslides and land use is analyzed in Rize, Türkiye. The results show that landslides are 1.75 to 5 times more likely to occur in tea gardens than in forests. It was also found that land use has the highest contribution to landslides among the landslide conditioning factors. The landslide assessment, using a simple landslide detection method and land use classification method with worldwide available data, enabled us to quantitatively reveal the characteristics of landslides. The results of this study reveal that quantitative landslide assessments can be applied in any location, where relatively high resolution satellite imagery and Google Earth imagery, or its alternatives, are available. Full article
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Article
Transition Indices of Sediment-Transport Modes on a Debris Flow Resulting from Changing Streambed Gradients
Water 2022, 14(11), 1810; https://doi.org/10.3390/w14111810 - 04 Jun 2022
Viewed by 705
Abstract
We conducted experiments using an experimental flume with two variable streambed gradients in the upstream and downstream parts with various debris flows, composition sizes, and supply flow rates. We investigated the transition processes of sediment transport modes along the longitudinal distances from the [...] Read more.
We conducted experiments using an experimental flume with two variable streambed gradients in the upstream and downstream parts with various debris flows, composition sizes, and supply flow rates. We investigated the transition processes of sediment transport modes along the longitudinal distances from the gradient change point using the transition mode indices, ICs¯x, Ih¯x, and IU¯x; these indices were calculated based on measurements of sediment transport concentrations, flow depths, and gravel migration velocities in the debris flow’s front in the downstream part. Using these indices, we postulated that after the debris flow passed the gradient change point, the transition of the sediment transport modes progressed by changing the measured parameters to those in the steady-state condition on the gradient of the downstream parts. In addition, these indices suggested that the gravel migration velocities in the flow front interior changed most rapidly after passing the gradient change point, and that flow depths tended to change most slowly. Finally, the indices suggested that as the debris flow material became finer and the supplied flow rates became larger, the longitudinal transition sections tended to be longer because the momentum needed to transport the material was less than the total debris flow momentum. Full article
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Article
Disaster-Resilient Communities on Flood Plains and Their Agricultural Regeneration: A Case Study in Meinong Plain, Taiwan
Water 2022, 14(11), 1736; https://doi.org/10.3390/w14111736 - 28 May 2022
Viewed by 601
Abstract
Taiwan’s near-mountain alluvial plain is a high-risk area with frequent disasters, and residents have become more tolerant of the compound disasters that occur with overall environmental changes associated with the development of urbanization in recent years. This paper presents a case study of [...] Read more.
Taiwan’s near-mountain alluvial plain is a high-risk area with frequent disasters, and residents have become more tolerant of the compound disasters that occur with overall environmental changes associated with the development of urbanization in recent years. This paper presents a case study of a near-mountainous alluvial plain in Southern Taiwan. The Hakka ethnic group is the main community in the study area and also the main research object. This case study illustrates the disaster resilience of the community to natural and artificial disasters. This study adopted two research approaches, namely historical geography and political economic geography, as well as community resilience theory. Research methods including case study, secondary literature analysis, fieldwork, and interviews were used. Through text analysis, it was found that (1) the community’s awareness of disaster avoidance was rooted in the experience of reclamation in the early 17th century; (2) communities have experienced artificial disasters caused by political and economic intervention, which have been transformed into disaster awareness and community resilience; (3) cumulative artificial disasters have a greater impact on communities than unpredictable natural disasters; and (4) the energy of community resilience and agricultural regeneration is based on the duality of disasters. Full article
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Article
The Robust Study of Deep Learning Recursive Neural Network for Predicting of Turbidity of Water
Water 2022, 14(5), 761; https://doi.org/10.3390/w14050761 - 28 Feb 2022
Cited by 1 | Viewed by 941
Abstract
Water treatment is an important process, as it improves water quality and makes it better for any end use, whether it be drinking, industrial use, irrigation, water recreation, or any other kind of use. Turbidity is one of the fundamental measurements of the [...] Read more.
Water treatment is an important process, as it improves water quality and makes it better for any end use, whether it be drinking, industrial use, irrigation, water recreation, or any other kind of use. Turbidity is one of the fundamental measurements of the clarity of water in water treatment. Specifically, this component is an optical feature of the amount of light on scatter particles when light is shined on a water sample. It is crucial in water reservoirs to provide clean water, which is difficult to manage and predict. Hence, this study focuses on the use of robust deep learning models to analyze time-series data in order to predict the water quality of turbidity in a reservoir area. Deep learning models may become an alternative solution in predicting water quality because of their accuracy. This study is divided into two parts: (a) the first part uses the optical bands of blue (B), green (G), red (R), and infrared (IR) to build a regression function to monitor turbidity in water, and (b) the second part uses a hybrid model to analyze time-series turbidity data with the recursive neural network (RNN2) model. The selected models’ accuracies are compared based on the accuracy using the input data, forecasting level, and training time. The analysis shows that these models have their strengths and limitations under different analyzed conditions. Generally, RNN2 shows the performance regarding the root-mean-square error (RMSE) evaluation metric. The most significant finding is that the RNN2 model is suitable for the accurate prediction of water quality. The RMSE is used to facilitate a comparison of the accuracy of the sampling data. In the training model, the training data have an RMSE of 20.89, and the testing data have an RMSE of 30.11. The predicted R-squared values in the RNN2 model are 0.993 (training data) and 0.941 (testing data). Full article
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Article
Performance Assessment of Event-Based Ensemble Landslide Susceptibility Models in Shihmen Watershed, Taiwan
Water 2022, 14(5), 717; https://doi.org/10.3390/w14050717 - 24 Feb 2022
Viewed by 539
Abstract
While multi-year and event-based landslide inventories are both commonly used in landslide susceptibility analysis, most areas lack multi-year landslide inventories, and the analysis results obtained from the use of event-based landslide inventories are very sensitive to the choice of event. Based on 24 [...] Read more.
While multi-year and event-based landslide inventories are both commonly used in landslide susceptibility analysis, most areas lack multi-year landslide inventories, and the analysis results obtained from the use of event-based landslide inventories are very sensitive to the choice of event. Based on 24 event-based landslide inventories for the Shihmen watershed from 1996 to 2015, this study established five event-based single landslide susceptibility models employing logistic regression, random forest, support vector machine, kernel logistic regression, and gradient boosting decision tree methods. The ensemble methods, involving calculating the mean of the susceptibility indexes (PM), median of the susceptibility indexes (PME), weighted mean of the susceptibility indexes (PMW), and committee average of binary susceptibility values (CA) of the five single models were then used to establish four event-based ensemble landslide susceptibility models. After establishing nine landslide susceptibility models, using each inventory from the 24 event-based landslide inventories or a multi-year landslide inventory, we identified the differences in landslide susceptibility maps attributable to the different landslide inventories and modeling methods, and used the area under the receiver operating characteristic curve to assess the accuracy of the models. The results indicated that an ensemble model based on a multi-year inventory can obtain excellent predictive accuracy. The predictive accuracy of multi-year landslide susceptibility models is found to be superior to that of event-based models. In addition, the higher predictive accuracy of ensemble landslide susceptibility models than that of single models implied that these ensemble methods were robust for enhancing the model’s predictive performance in the study area. When employing event-based landslide inventories in modeling, PM ensemble models offer the best predictive ability, according to the Kruskal–Wallis test results. Areas with a high mean susceptibility index and low standard deviation, identified using the 24 PM ensemble models based on different event-based landslide inventories, constitute places where landslide mitigation measures should be prioritized. Full article
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Article
Evaluating the Landslide Stability and Vegetation Recovery: Case Studies in the Tsengwen Reservoir Watershed in Taiwan
Water 2021, 13(24), 3479; https://doi.org/10.3390/w13243479 - 07 Dec 2021
Cited by 1 | Viewed by 949
Abstract
The sediment yield from numerous landslides triggered in Taiwan’s mountainous regions by 2009 Typhoon Morakot have had substantial long-term impacts on the evolution of rivers. This study evaluated the long-term evolution of landslides induced by 2001 Typhoon Nari and 2009 Typhoon Morakot in [...] Read more.
The sediment yield from numerous landslides triggered in Taiwan’s mountainous regions by 2009 Typhoon Morakot have had substantial long-term impacts on the evolution of rivers. This study evaluated the long-term evolution of landslides induced by 2001 Typhoon Nari and 2009 Typhoon Morakot in the Tsengwen Reservoir Watershed by using multiannual landslide inventories and rainfall records for the 2001–2017 period. The landslide activity, vegetation recovery time, and the landslide spatiotemporal hotspot analyses were used in the study. Severe landslides most commonly occurred on 35–45° slopes at elevations of 1400–2000 m located within 500 m of the rivers. The average vegetation recovery time was 2.29 years, and landslides with vegetation recovery times exceeding 10 years were most frequently retrogressive landslide, riverbank landslides in sinuous reaches, and the core area of large landslides. The annual landslide area decline ratios after 2009 Typhoon Morakot in Southern Taiwan was 4.75% to 7.45%, and the time of landslide recovery in the Tsengwen reservoir watershed was predicted to be 28.48 years. Oscillating hotspots and coldspots occupied 95.8% of spatiotemporal patterns in the watershed area. The results indicate that landslides moved from hillslopes to rivers in the 2001–2017 period because the enormous amount of sediment deposited in rivers resulted in the change of river geomorphology and the riverbank landslides. Full article
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Article
The Effect of Temporal Characteristics on Developing a Practical Rainfall-Induced Landslide Potential Evaluation Model Using Random Forest Method
Water 2021, 13(23), 3348; https://doi.org/10.3390/w13233348 - 25 Nov 2021
Viewed by 616
Abstract
With the unique rainfall patterns of typhoons, plum rains, and short-term heavy rainfalls, the frequent landslide and debris flow disasters have caused severe loss to people in Taiwan. In the studies of landslide susceptibility, the information of factors used for analysis was usually [...] Read more.
With the unique rainfall patterns of typhoons, plum rains, and short-term heavy rainfalls, the frequent landslide and debris flow disasters have caused severe loss to people in Taiwan. In the studies of landslide susceptibility, the information of factors used for analysis was usually annual-based content, and it was assumed that the same elements from different years were independent between each year. However, the occurrence of landslides was usually not simply due to the changes within a year. Instead, landslides were triggered because the factors that affected the potential of landslides reached critical conditions after a cumulative change with time. Therefore, this study had well evaluated the influence of temporal characteristics and the ratios of antecedent landslide areas in the past five years in the landslide potential evaluation model. The analysis was conducted through the random forest (RF) algorithm. Additional rainfall events of 2017 were used to test the proposed model’s performance to understand its practicality. The analysis results show that in the study area, the RF model had considerably acceptable performance. The results have also demonstrated that the antecedent landslide ratios in the past five years were essential to describe the significance of cumulative change with time when conducting potential landslide evaluation. Full article
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Article
Visual Harmony of Engineering Structures in a Mountain Stream
Water 2021, 13(23), 3324; https://doi.org/10.3390/w13233324 - 23 Nov 2021
Viewed by 793
Abstract
This study uses the cognitive factor of “visual harmony” to assess the visual quality of stream engineering in a mountainous region. Images of engineering structures such as revetments and submerged dams in the mountain streams of Taiwan were collected. Three image groups with [...] Read more.
This study uses the cognitive factor of “visual harmony” to assess the visual quality of stream engineering in a mountainous region. Images of engineering structures such as revetments and submerged dams in the mountain streams of Taiwan were collected. Three image groups with different structures invaded by vegetation were used for a questionnaire survey, which yielded 154 valid samples. We used statistical analysis to develop a model of visual harmony H with respect to the percentage of visible greenery GR, that is, the perceived curve of vegetation change. A comparison of our data with the literature determined the upper and lower bound curves of the relationship between H and GR. We found that the physical elements of “softscape” and “hardscape”—namely, percentage of visible water WR, visible structure IR, and visible natural material on the structure NR—affected this relationship. Results show that H is equivalent to visual preference P, and both can be improved by better green visibility (increasing GR and GR < 50%), avoiding low water visibility (WR < 10%), or increasing the amount of visible natural material (NR > 0.9). High visibility of the structures (IR > 0.3) may decrease H and P. We ultimately propose a visual harmony or preference model concerning a combined physical indicator that comprises GR, WR, IR and NR. Results of this study could be helpful to improve or access the aesthetics of stream engineering design. Full article
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Article
Extreme Droughts Change in the Mekong River Basin: A Multidisciplinary Analysis Based on Satellite Data
Water 2021, 13(19), 2682; https://doi.org/10.3390/w13192682 - 28 Sep 2021
Viewed by 738
Abstract
This study evaluates droughts in the Mekong River Basin (MKB) based on a multidisciplinary method, mainly using the Standardized Precipitation Index (SPI) and Mann–Kendall (MK) test. Precipitation data corresponding to the seasonality of the regional climate were retrieved from Integrated Multi-satellitE Retrievals for [...] Read more.
This study evaluates droughts in the Mekong River Basin (MKB) based on a multidisciplinary method, mainly using the Standardized Precipitation Index (SPI) and Mann–Kendall (MK) test. Precipitation data corresponding to the seasonality of the regional climate were retrieved from Integrated Multi-satellitE Retrievals for Global Precipitation Measurement from 2001 to 2020, at a monthly temporal scale and 0.1 degree spatial resolution. Drought events and their average interval, duration, and severity were determined based on Run theory. Our results revealed the most extreme drought period was in January 2014, at the time the lowest precipitation occurred. Spatial extreme drought results indicated that Zone 2 in the upstream MKB has the highest frequency of drought, with 44 events observed during 19 years, and experiences the most severe droughts, whereas Zone 24 in the downstream MKB has the most prolonged drought duration of seven months. The periods and locations of extreme drought were identified using the SPI, corresponding to historic droughts of the MKB. Furthermore, the MK test shows an increasing trend of droughts in the lower MKB and the cluster analysis identified six clusters of times series. Overall, our study provides essential findings for international and national water resource stakeholders in identifying trends of extreme drought in the MKB. Full article
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Article
Evaluation of Rainfall-Triggered Debris Flows under the Impact of Extreme Events: A Chenyulan Watershed Case Study, Taiwan
Water 2021, 13(16), 2201; https://doi.org/10.3390/w13162201 - 12 Aug 2021
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Abstract
This study examined the conditions that lead to debris flows, and their association with the rainfall return period (T) and the probability of debris flow occurrence (P) in the Chenyulan watershed, central Taiwan. Several extreme events have occurred in the Chenyulan watershed in [...] Read more.
This study examined the conditions that lead to debris flows, and their association with the rainfall return period (T) and the probability of debris flow occurrence (P) in the Chenyulan watershed, central Taiwan. Several extreme events have occurred in the Chenyulan watershed in the past, including the Chi-Chi earthquake and extreme rainfall events. The T for three rainfall indexes (i.e., the maximum hourly rainfall depth (Im), the maximum 24-h rainfall amount (Rd), and RI (RI = Im× Rd)) were analyzed, and the T associated with the triggering of debris flows is presented. The P–T relationship can be determined using three indexes, Im, Rd, and RI; how it is affected and unaffected by extreme events was developed. Models for evaluating P using the three rainfall indexes were proposed and used to evaluate P between 2009 and 2020 (i.e., after the extreme rainfall event of Typhoon Morakot in 2009). The results of this study showed that the P‒T relationship, using the RI or Rd index, was reasonable for predicting the probability of debris flow occurrence. Full article
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Recent and Historical Background and Current Challenges for Sediment Disaster Measures against Climate Change in Japan
Water 2022, 14(15), 2285; https://doi.org/10.3390/w14152285 - 22 Jul 2022
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Abstract
Japan is a country with one of the highest incidences of sediment disasters, which will become more severe and more frequent as a result of climate change. This paper reviews the recent occurrence of sediment disasters caused by heavy rainfall affected by climate [...] Read more.
Japan is a country with one of the highest incidences of sediment disasters, which will become more severe and more frequent as a result of climate change. This paper reviews the recent occurrence of sediment disasters caused by heavy rainfall affected by climate change in recent years, challenges in adaptation measures, and recent policies targeting such sediment disasters in Japan. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has been conducting non-structural and structural measures based on legislation. Recently, climate change has resulted in more severe and frequent disasters along with damage caused by sediment movement phenomena that are not covered by the present system for warning and evacuation. Efforts to establish assessment methods concerning the risk of these phenomena are shown as examples of current challenges of climate change. Full article
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