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1.
Many investigators have attempted to define the threshold of landslide failure, that is, the level of the selected climatic variable above which a rainfall-induced landslide occurs. Intensity–duration (I–d) relationships are the most common type of empirical thresholds proposed in the literature for predicting landslide occurrence induced by rainfall. Recent studies propose the use of the kinetic power per unit volume of rainfall (J m−2 mm−1) to quantify the threshold of landslides induced by rainfall. In this paper, the relationship between rainfall duration and kinetic power corresponding to landslides triggered by rain was used to propose a new approach to define the threshold for predicting landslide occurrence. In particular, for the first time, a kinetic power per unit volume of rainfall–duration relationship is proposed for defining the minimum threshold needed for landslide failure. This new method can be applied using commonly used relationship for estimating the kinetic power per unit volume of rainfall and a new equation based on the measured raindrop size distribution. The applicability of this last method was tested using the data of rainfall intensity, duration and median volume diameter for 51 landslides in Taiwan. For the 51 landslides, the comparison between the measured pairs' kinetic power–duration and all selected relationships demonstrated that the equation based on the measured raindrop size distribution is the best method to define the landslide occurrence threshold, as it is both a process-oriented approach and is characterized by the best statistical performance. This last method has also the advantage to allow the forecasting of landslide hazard before the end of the rainfall event, since the rainfall kinetic power threshold value can be exceeded for a time interval less than the event duration.  相似文献   

2.
Landslide dams are a common phenomenon. They form when a landslide reaches the bottom of a river valley causing a blockage. The first effect of such a dam is the infilling of a lake that inundates the areas upstream, while the possibility of a sudden dam collapse, with a rapid release of the impounded waters, poses a higher flood risk to the downstream areas. The results of the main inventories carried out to date on landslide dams, have been examined to determine criteria for forecasting landslide dam evolution with particular emphasis on the assessment of dam stability. Not all landslides result in the blockage of a river channel. This only occurs with ones that can move a large amount of material with moderate or high‐velocities. In most cases, these landslides are triggered by rainfall events or high magnitude earthquakes. A relationship also exists between the volume of the displaced material and the landslide dam stability. Several authors have proposed that landslide dam behaviour can be forecast by defining various geomorphological indexes, that result from the combination of variables identifying both the dam and the dammed river channel. Further developments of this geomorphological approach are presented in this paper by the definition of a dimensionless blockage index. Starting with an analysis of 84 episodes selected worldwide, it proved to be a useful tool for making accurate predictions concerning the fate of a landslide dam. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

3.
汶川Ms8.0级地震驱动的构造抬升作用和滑坡、泥石流剥蚀作用如何影响龙门山的地貌生长是目前争论的焦点。本文运用GIS技术,定量计算了湔江流域的坡度、地形起伏度、面积—高程积分等地貌参数,根据这些参数的计算结果,对湔江流域的构造地貌特征进行了量化分析;以汶川Ms8.0级地震重灾区湔江海子河右岸流域的滑坡、泥石流为例,并且利用野外实测资料、卫星照片及数字高程资料等,对于汶川地震驱动的构造抬升与滑坡、泥石流的表面侵蚀过程进行研究,获得以下初步认识:(1)湔江流域的映秀—北川断层以北地区地貌处于"壮年期",坡度、地形起伏度大;(2)汶川Ms8.0级地震后该地区发生了严重的同震滑坡及震后滑坡、泥石流灾害,海子河右岸流域的同震抬升量为5 339×104m3,同震滑坡量为3 852×104m3,同震抬升量大于同震滑坡量,地貌出现生长现象;(3)地震产生的泥石流量应略大于1 000×104m3,同震滑坡物质的30%转化为了泥石流量,因其海子沟右岸陡峻的坡度,绝大部分的泥石流冲入海子河,成为河道沉积物;(4)以目前湔江海子河流水搬运能力,在能够完全搬运出同震滑坡物质的前提下,同震滑坡物质搬运出龙门山至少需要283.2 a,表明在一个地震周期内,龙门山的同震滑坡物质可以搬运出龙门山;(5)准周期性相当震级地震引起的构造抬升及其均衡反弹作用也是龙门山的形成有重要作用的因素之一。  相似文献   

4.
A complete landslide inventory and attribute database is the importantly fundamental for the study of the earthquake-induced landslide. Substantial landslides were triggered by the MW7.9 Wenchuan earthquake on May 12th, 2008. Google Earth images of pre- and post-earthquakes show that 52 194 co-seismic landslides were recognized and mapped, with a total landslides area of 1 021 km2.Based on the statistics,we assigned all landslide parameters and established the co-seismic landslides database, which includes area, length, and width of landslides, elevation of the scarp top and foot edge, and the top and bottom elevations of each located slope. Finally, the spatial distribution and the above attribute parameters of landslides were analyzed. The results show that the spatial distribution of the co-seismic landslides is extremely uneven. The landslides that mainly occur in a rectangular area (a width of 30 km of the hanging wall of the Yingxiu-Beichuan fault and a length of 120 km between Yingxiu and Beichuan) are obviously controlled by surface rupture, terrain, and peak ground acceleration. Meanwhile, a large number of small landslides (individual landslide area less than 10 000 m2)contribute less to the total landslides area. The number of landslides larger than 10 000 m2 accounts for 38.7% of the total number of co-seismic landslides, while the area of those landslides account for 88% of the total landslides area. The 52 194 co-seismic landslides are caused by bedrock collapse that usually consists of three parts:source area, transport area, and accumulation area. However, based on the area-volume power-law relationship, the resulting regional landslide volume may be much larger than the true landslide volume if the landslide volume is calculated using the influenced area from each landslide.  相似文献   

5.
Quantifying the removal of co‐seismic landslide material after a large‐magnitude earthquake is central to our understanding of geomorphic recovery from seismic events and the topographic evolution of tectonically active mountain ranges. In order to gain more insight into the fluvial erosion response to co‐seismic landslides, we focus on the sediment fluxes of rivers flowing through the rupture zone of the 2008 Mw 7.9 Wenchuan earthquake in the Longmen Shan of the eastern Tibetan Plateau. Over the post‐seismic period of 2008–2013, we annually collected river sediment samples (0.25–1 mm) at 19 locations and measured the concentration of cosmogenic 10Be in quartz. When compared with published pre‐earthquake data, the 10Be concentrations declined dramatically after the earthquake at all sampling sites, but with significant spatial differences in the amplitude of this decrease, and were starting to increase toward pre‐earthquake level in several basins over the 5‐year survey. Our analysis shows that the amplitude of 10Be decrease is controlled by the amount of landslides directly connected to the river network. Calculations based on 10Be mixing budgets indicate that the sediment flux of the 0.25–1 mm size fraction increased up to sixfold following the Wenchuan earthquake. Our results also suggest that fluvial erosion became supply limited shortly after the earthquake, and predict that it could take a few years to several decades for fluvial sediment fluxes to go back to pre‐earthquake characteristics, depending on catchment properties. We also estimate that it will take at least decades and possibly up to thousands of years to remove the co‐seismic landslide materials from the catchments in the Longmen Shan. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

6.
Here, we propose that an earthquake can trigger the failure of a landslide mass while simultaneously triggering liquefaction of runout‐path materials before the arrival of the landslide mass, thus greatly increasing the size and mobility of an overriding landslide. During the 2008 Wenchuan earthquake, about 60 000 landslides were triggered, directly resulting in about 20 000 casualties. While these landslides mainly originated from steep slopes, some landslides with high mobility formed in colluvial valley deposits. Among these, the most catastrophic was the Xiejiadian landslide in Pengzhou city, which traveled hundreds of meters before coming to rest. Through field investigation and laboratory testing, we conclude that this landslide primarily formed from colluvial deposits in the valley and secondarily from failure of slopes in granitic rock located uphill. Much of the granitic slope failure was deposited in the upper part of the travel path (near the slide head); the remainder was dispersed throughout the main landslide deposit. Superposition of deposits at the landslide toe indicates that landslide debris derived from colluvial soil was deposited first. The deposits at the landslide toe displayed flow characteristics, such as fine materials comprising basal layers and large boulders covering the deposit surface. We hypothesize that the main part of the landslide resulted from seismogenic liquefaction of valley colluvium, rather than from liquefaction potentially caused by undrained loading from the granitic slope failures impacting the colluvium. To examine the likelihood that seismogenic liquefaction occurred, we took samples from different areas of the landslide deposit and performed undrained cyclic shear tests on them in the laboratory. The results showed that the sandy soils that comprise most of the deposit are highly liquefiable under seismic loading. Therefore, we conclude that liquefaction of the colluvium in the valley during the earthquake was the main reason for this rapid (~46 m/s) long‐runout (1·7 km) landslide. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

7.
Landslide inventories and their statistical properties   总被引：1，自引：0，他引：1  
Landslides are generally associated with a trigger, such as an earthquake, a rapid snowmelt or a large storm. The landslide event can include a single landslide or many thousands. The frequency–area (or volume) distribution of a landslide event quanti?es the number of landslides that occur at different sizes. We examine three well‐documented landslide events, from Italy, Guatemala and the USA, each with a different triggering mechanism, and ?nd that the landslide areas for all three are well approximated by the same three‐parameter inverse‐gamma distribution. For small landslide areas this distribution has an exponential ‘roll‐over’ and for medium and large landslide areas decays as a power‐law with exponent ‐2·40. One implication of this landslide distribution is that the mean area of landslides in the distribution is independent of the size of the event. We also introduce a landslide‐event magnitude scale mL = log(NLT), with NLT the total number of landslides associated with a trigger. If a landslide‐event inventory is incomplete (i.e. smaller landslides are not included), the partial inventory can be compared with our landslide probability distribution, and the corresponding landslide‐event magnitude inferred. This technique can be applied to inventories of historical landslides, inferring the total number of landslides that occurred over geologic time, and how many of these have been erased by erosion, vegetation, and human activity. We have also considered three rockfall‐dominated inventories, and ?nd that the frequency–size distributions differ substantially from those associated with other landslide types. We suggest that our proposed frequency–size distribution for landslides (excluding rockfalls) will be useful in quantifying the severity of landslide events and the contribution of landslides to erosion. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

8.
Natural damming of upland river systems, such as landslide or lava damming, occurs worldwide. Many dams fail shortly after their creation, while other dams are long‐lived and therefore have a long‐term impact on fluvial and landscape evolution. This long‐term impact is still poorly understood and landscape evolution modelling (LEM) can increase our understanding of different aspects of this response. Our objective was to simulate fluvial response to damming, by monitoring sediment redistribution and river profile evolution for a range of geomorphic settings. We used LEM LAPSUS, which calculates runoff erosion and deposition and can deal with non‐spurious sinks, such as dam‐impounded areas. Because fluvial dynamics under detachment‐limited and transport‐limited conditions are different, we mimicked these conditions using low and high erodibility settings, respectively. To compare the relative impact of different dam types, we evaluated five scenarios for each landscape condition: one scenario without a dam and four scenarios with dams of increasing erodibility. Results showed that dam‐related sediment storage persisted at least until 15 000 years for all dam scenarios. Incision and knickpoint retreat occurred faster in the detachment‐limited landscape than in the transport‐limited landscape. Furthermore, in the transport‐limited landscape, knickpoint persistence decreased with increasing dam erodibility. Stream capture occurred only in the transport‐limited landscape due to a persisting floodplain behind the dam and headward erosion of adjacent channels. Changes in sediment yield variation due to stream captures did occur but cannot be distinguished from other changes in variation of sediment yield. Comparison of the model results with field examples indicates that the model reproduces several key phenomena of damming response in both transport‐limited and detachment‐limited landscapes. We conclude that a damming event which occurred 15 000 years ago can influence present‐day sediment yield, profile evolution and stream patterns. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
An inventory of 846 mass movements, mainly landslides, in two alpine regions of southwest New Zealand was created to explore the geomorphic impacts of slope‐failure processes on river channels and valley floors. In total, 213 (i.e. 27 per cent) of the slope failures descended to valley floors, affecting the geomorphology of trunk channels (catchment area AC > 10 km2) and valley floors in recurring patterns. A nominal classification system is introduced for characterizing (a) the physical contact nature between landslides and river channels, and (b) the resulting geomorphic consequences for drainage. Although landslide area A is useful for estimating the length of channel directly impacted by debris, it does not necessarily predict the direction of fluvial response or type of impact. Dominant persistent geomorphic imprints of bedrock landslides include channel occlusions and landslide dams in South Westland and Fiordland, respectively. Differences in size distribution and geomorphic effects on river systems between the two study regions are attributed to bedrock geology, tectonics and sediment flux. Although South Westland rivers are more frequently affected by landslides, disrupting long‐term effects such as blockage are more persistent in Fiordland. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
Summary statistics derived from the frequency–area distribution (FAD) of inventories of triggered landslides allows for direct comparison of landslides triggered by one event (e.g. earthquake, rainstorm) with another. Such comparisons are vital to understand links between the landslide‐event and the environmental characteristics of the area affected. This could lead to methods for rapid estimation of landslide‐event magnitude, which in turn could lead to estimates of the total triggered landslide area. Previous studies proposed that the FAD of landslides follows an inverse power‐law, which provides the basis to model the size distribution of landslides and to estimate landslide‐event magnitude (mLS), which quantifies the severity of the event. In this study, we use a much larger collection of earthquake‐induced landslide (EQIL) inventories (n=45) than previous studies to show that size distributions are much more variable than previously assumed. We present an updated model and propose a method for estimating mLS and its uncertainty that better fits the observations and is more reproducible, robust, and consistent than existing methods. We validate our model by computing mLS for all of the inventories in our dataset and comparing that with the total landslide areas of the inventories. We show that our method is able to estimate the total landslide area of the events in this larger inventory dataset more successfully than the existing methods. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

11.
Sediments produced by landslides are crucial in the sediment yield of a catchment, debris flow forecasting, and related hazard assessment. On a regional scale, however, it is difficult and time consuming to measure the volumes of such sediment. This paper uses a LiDAR‐derived digital terrain model (DTM) taken in 2005 and 2010 (at 2 m resolution) to accurately obtain landslide‐induced sediment volumes that resulted from a single catastrophic typhoon event in a heavily forested mountainous area of Taiwan. The landslides induced by Typhoon Morakot are mapped by comparison of 25 cm resolution aerial photographs taken before and after the typhoon in an 83.6 km2 study area. Each landslide volume is calculated by subtraction of the 2005 DTM from the 2010 DTM, and the scaling relationship between landslide area and its volume are further regressed. The relationship between volume and area are also determined for all the disturbed areas (VL = 0.452AL1.242) and for the crown areas of the landslides (VL = 2.510AL1.206). The uncertainty in estimated volume caused by use of the LiDAR DTMs is discussed, and the error in absolute volume estimation for landslides with an area >105 m2 is within 20%. The volume–area relationship obtained in this study is also validated in 11 small to medium‐sized catchments located outside the study area, and there is good agreement between the calculation from DTMs and the regression formula. By comparison of debris volumes estimated in this study with previous work, it is found that a wider volume variation exists that is directly proportional to the landslide area, especially under a higher scaling exponent. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

12.
In this study, a detailed database of landslides triggered by the 25 April 2015 Gorkha (Nepal)MW7.8 earthquake is constructed based on visual interpretation of pre- and post-earthquake high-resolution satellite images and field reconnaissance. Results show the earthquake triggered at least 47 200 landslides, which have a NWW direction spatial distribution, similar with the location and strike of the seismogenic fault. The landslides are of a total area about 110km2 and an oval distribution area about 35 700km2. On the basis of a scale relationship between landslide area (A)and volume (V), V=1.314 7×A1.208 5, the total volume of the coseismic landslides is estimated to be about 9.64×108m3. In the oval landslide distribution area, the landslide number density, area density, and volume density were calculated and the results are 1.32km-2, 0.31%, and 0.027m, respectively. This study provides a detailed and objective inventory of landslides triggered by the Gorkha earthquake, which provides very important and essential basic data for study of mechanics of coseismic landslides, spatial pattern, distribution law, and hazard assessment. In addition, the landslide database related to an individual earthquake also provides an important earthquake case in a subduction zone for studying landslides related to multiple earthquakes from a global perspective.  相似文献   

13.
At present, with the wide application of the Newmark method, various Newmark empirical formulas with different ground motion parameters have been fitted by many researchers based on global strong-motion records. However, the existing study about the Wenchuan earthquake does not quantitatively evaluate the applicability of different Newmark models based on the actual landslides distribution. The aim of this paper is to present a comparison between observed landslides from the 2008 Wenchuan earthquake and predicted landslides using Newmark displacement method based on different ground motion parameters. The factor-of-safety map and critical acceleration(ac)map in the study area are obtained by using the terrain data and geological data. The distribution of Arias intensity(Ia)and PGA in the study area is obtained by using the attenuation formulas of Arias intensity(Ia)and PGA, which is regressed by Wenchuan ground motion records. Based on the distribution of Arias intensity(Ia)and PGA parameters, we obtained the predicted locations of landslide using Newmark regression equations which are generated using global strong-motion records. The results shows that the assessment results can better reflect the macroscopic distribution characteristics of co-seismic landslides, most predicted landslide cells are distributed on the two sides of the Beichuan-Yingxiu Fault, especially the Pengguan complex rock mass in the hanging wall. The abilities to predict landslide occurrence of the two Newmark simplified models are different. On the whole, the evaluated result of simplified model based on parameter Ia is better than that based on PGA parameter. The GFC values obtained by the Newmark model of Ia and PGA parameters are 65.7% and 34.9%respectively. The evaluated result based on Ia can better reflect the macro distribution of coseismic landslides. The Ls_Pred value based on the Newmark model of parameter Ia is 26.5%, and the Ls_Pred value based on the Newmark model of PGA parameter is 10.3%. However the total area of predicted landslides accounts for 2.4% of the study area, which indicates that the predicted landslide cells are greater than the observed landslide cells. This reminds us that depending on the current input of shear strength and ground-motion parameters, we can only conduct landslide hazard assessment in macro areas, the ability to predict landslide can be improved using more accurate topographic data and input parameters.  相似文献   

14.
In this work, a transient rainfall infiltration and grid‐based regional slope‐stability model (TRIGRS) was implemented in a case study of Yan'an City, Northwest China. In this area, widespread shallow landslides were triggered by the 12 July 2013 exceptional rainstorm event. A high‐resolution DEM, soil parameters from in‐situ and laboratory measurements, water table depths, the maximum depth of precipitation infiltration and rain‐gauge‐corrected precipitation of the event, were used as inputs in the TRIGRS model. Shallow landslides triggered on the same day were used to evaluate the modeling results. The summarized results are as follows: (i) The characteristics and distribution of thirty‐five shallow landslides triggered by the 12 July 2013 rainfall event were identified in the study area and all were classified as shallow landslides with the maximum depth, area and volume less than 3 m, 200 m2 and 1000 m3, respectively, (ii) Four intermediate factor of safety (FS) maps were generated using the TRIGRS model to represent the scenarios 6, 12, 18 and 24 hours after the storm event. The area with FS < 1 increased with the rainfall duration. The percentage of the area with FS < 1 was 0.2%, 3.3%, 3.8% and 5.1% for the four stages, respectively. Twenty‐four hours after the rainstorm, TRIGRS predicted that 1255 grid cells failed, which is consistent with the field data. (iii) TRIGRS generated more satisfactory results at a given precipitation threshold than SINMAP, which is ideal for landslide hazard zoning for land‐use planning at the regional scale. Comparison results showed that TRIGRS is more useful for landslide prediction for a certain precipitation threshold, also in the regional scale. (iv) Analysis of the responses of loess slope prone to slope failure after different precipitation scenarios revealed that loess slopes are particularly sensitive to extended periods of heavy precipitation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

15.
An MW6.6 earthquake occurred in eastern Hokkaido, Japan on September 6th, 2018. Based on the pre-earthquake image from Google Earth and the post-earthquake image from high resolution (3 m) planet satellite, we manually interpret 9 293 coseismic landslides and select 7 influencing factors of seismic landslide, such as elevation, slope, slope direction, road distance, flow distance, peak ground acceleration (PGA) and lithology. Then, 9 293 landslide points are randomly divided into training samples and validation samples with a proportion of 7:3. In detail, the training sample has 6 505 landslide points and the validation sample has 2 788 landslide points. The hazard risk assessment of seismic landslide is conducted by using the information value method and the study area is further divided into five risk grades, including very low risk area, low risk area, moderate risk area high risk area and very high risk area. The results show that there are 7 576 landslides in high risk area and very high risk area, accounting for 81.52% of the total landslide number, and the landslide area is 22.93 km2, accounting for 74.35% of the total area. The hazard zoning is in high accordance with the actual situation. The evaluation results are tested by using the curve of cumulative percentage of hazardous area and cumulative percentage of landslides number. The results show that the success rate of the information value method is 78.50% and the prediction rate is 78.43%. The evaluation results are satisfactory, indicating that the hazard risk assessment results based on information value method may provide scientific reference for landslide hazard risk assessment as well as the disaster prevention and mitigation in the study area.  相似文献   

16.
The peak ground acceleration (PGA), the volume of a sliding mass V, the height of a mountain H L and the slope angle θ of a mountain are four important parameters affecting the horizontal run-out distance of a landslide L. Correlations among them are studied statistically based on field investigations from 67 landslides triggered by the ground shaking and other factors during the Wenchuan earthquake, and then a prediction model for horizontal run-out distance L is developed in this study. This model gives due consideration to the implications of the above four parameters on the horizontal run-out distance L and the validity of the model is verified by the Donghekou and Magong Woqian landslides. At the same time, the advantages of the model are shown by comparing it with two other common prediction methods. The major findings drawn from the analyses and comparisons are: (1) an exponential relationship exists between L and log V, L and log H L, L and log PGA separately, but a negative exponential relationship exists between L and log tanθ, which agrees with the statistical results; and (2) according to the analysis results of the relative relationship between the height of a mountain (H) and the place where the landslides occur, the probabilities at distances of 2H/3-H, H/3-2H/3, and 0-H/3 are 70.8%, 15.4%, and 13.8%, respectively, revealing that most landslides occurred at a distance of H/2-H. This prediction model can provide an effective technical support for the prevention and mitigation of landslide hazards.  相似文献   

17.
2008年MW7.9汶川地震导致龙门山断裂发生强烈地壳变形,同时引发的巨量同震滑坡加速了该地区的地表剥蚀和河流侵蚀.然而,目前尚缺少系统的数据定量研究滑坡物质的运移以及河流侵蚀速率随时间的演化规律,这些对理解龙门山前缘物质的再分配以及强震对活动造山带地形塑造的作用至关重要.为此,本研究在汶川地震后的6年间,对震区沱江上游3条支流湔江、石亭江、绵远河流域进行了多期次的定点现代河沙采样.通过系统测量河沙中的石英10Be浓度,并与震前已发表的数据进行对比,发现如下基本特点：（1）震后河沙10Be浓度均有明显降低,表明同震滑坡物质对河沙的稀释作用;（2）震后河流对河沙的运移量增加为震前的1.3~18.5倍,因此震后龙门山地区侵蚀速率短期显著增加;（3）初步估计得到汶川地震产生的滑坡物质被完全运移出造山带所需要的时间至少为100~4000年,接近龙门山地区强震复发周期;（4）震间和同震产生的构造变形和地表剥蚀在空间上具有互补性.考虑到地表剥蚀引起的地壳均衡反弹效应,认为类似汶川地震的强震有利于龙门山的隆升.认识震前、震时和震后的地壳变形及侵蚀过程有助于更好地理解单次强震事件对高原边界龙门山地形演化的作用.  相似文献   

18.
利用同震GPS观测数据,采用多面函数法,以数据分片拟合方式对2008年5月12日汶川MS8.0大震同震面应变进行计算,评定了计算结果的精度,并分析与强震有关的面应变变化特征。结果表明:在计算同震应变变化时,分片拟合较整体拟合得到的应变结果精度更高;同震应变结果对龙门山断裂能量释放特征及地表破坏分布有一定的反映。  相似文献   

19.
Long‐term effects of different forest management practices on landslide initiation and volume were analysed using a physically based slope stability model. The watershed‐based model calculates the effects of multiple harvesting entries on slope stability by accounting for the cumulative impacts of a prior vegetation removal on a more recent removal related to vegetation root strength and tree surcharge. Four sequential clearcuts and partial cuts with variable rotation lengths were simulated with or without leave areas and with or without understorey vegetation in a subwatershed of Carnation Creek, Vancouver Island, British Columbia. The combined in?nite slope and distributed hydrologic models used to calculate safety factor revealed that most of the simulated landslides were clustered within a 5 to 17 year period after initial harvesting in cases where suf?cient time (c. 50 years) lapsed prior to the next harvesting cycle. Partial cutting produced fewer landslides and reduced landslide volume by 1·4‐ to 1·6‐fold compared to clearcutting. Approximately the same total landslide volume was produced when 100 per cent of the site was initially clearcut compared to harvesting 20 per cent of the area in successive 10 year intervals; a similar ?nding was obtained for partial cutting. Vegetation leave areas were effective in reducing landsliding by 2‐ to 3‐fold. Retaining vigorous understorey vegetation also reduced landslide volume by 3·8‐ to 4·8‐fold. The combined management strategies of partial cutting, increasing rotation length, provision of leave areas, and retention of viable understorey vegetation offer the best alternative for minimizing landslide occurrence in managed forests. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

20.
Landsliding induced by earthquakes and rainstorms in montane regions is not only a sculptor for shaping the landscape, but also a driver for delivering sediments and above‐ground biomass downstream. However, the terrain attributes of earthquake‐ and rainstorm‐induced landslides are less discussed comprehensively in Taiwan. As part of an island‐wide inventory, we here compare and contrast the landslide terrain attributes resulting from two catastrophic events: the Chi‐Chi earthquake (M w = 7.6, September 1999) and typhoon Morakot (rainfall >2500 mm, August 2009). Results show that the earthquake‐induced landslides are relatively small, round‐shaped and prone to occur primarily in middle and toe of slopes. In contrast, the rainstorm‐induced landslides are larger, horseshoe‐shaped and preferentially occurring in slope toes. Also, earthquake‐induced landslides, particularly large landslides, are usually found at steeper gradients, whereas rainstorm‐induced landslides aggregate at gradients between 25° and 40°. Lithologic control plays a secondary role in landsliding. From an island‐wide perspective, high landslide density locates in the region of earthquake intensity ≥ VI or one‐day rainfall ≥600 mm day?1. Through the landslide patterns and their terrain attributes, our retrospective approach sheds light on accessing the historical and remote events for close geophysical investigations. Finally, we should bear in mind that the landslide location, size, and terrain attributes varying with triggers may affect the landscape evaluation or biogeochemical processes in landslide‐dominated regions. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

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