Vulnerability assessment of rainfall-induced debris flows in Taiwan

A GIS-based decision support system, which incorporates local topographic and rainfall effects on debris flow vulnerability is developed. Rainfall at a scale compatible with the digital elevation model resolution is obtained using a neural network with a wind-induced topographic effect and rainfall derived from satellite rain estimates and an adaptive inverse distance weight method (WTNN). The technique is tested using data collected during the passage of typhoon Tori-Ji on July 2001 over central Taiwan. Numerous debris flows triggered by the typhoon were used as control for the study. Our results show that the WTNN technique outperforms other interpolation techniques including adaptive inversed distance weight (AIDW), simple kriging (SK), co-kriging, and multiple linear regression using gauge, and topographic parameters. Multiple remotely-sensed, fuzzy-based debris-flow susceptibility parameters are used to describe the characteristics of watersheds. Non-linear, multi-variant regressions using the WTNN derived rainfall and topography factors are derived using self-organizing maps (SOM) for the debris flow vulnerability assessment. An index of vulnerability representing the degrees of hazard is implemented in a GIS-based decision support system by which a decision maker can assess debris flow vulnerability.     

Impacts of September 21, 1999 Chi-Chi earthquake on the characteristics of gully-type debris flows in central Taiwan

Debris flows are more frequent in central Taiwan, because of its mountainous geography. For example, many debris flows were induced by Typhoon Herb in 1996. The Chi-Chi earthquake with a magnitude of 7.3, which took place in 1999 in central Taiwan, induced many landslides in this region. Some landslides turned into debris flows when Typhoon Toraji struck Taiwan in 2001. This study investigates the characteristics of the gullies where debris flows have occurred for a comparison. Aerial photos of these regions dated in 1997 (before the earthquake) and 2001 (after the earthquake) are used to identify the occurrence of gully-type debris flows. A Geographic Information System (GIS) is applied to acquire hydrological and geomorphic characteristics: stream gradient, stream length, catchment gradient, catchment area, form factor, and geology unit of these gullies. These characteristics in different study regions are presented in a statistical approach. The study of how strong ground motion affects the debris flows occurrence is conducted. The characteristics of the debris flow gullies triggered by typhoons before and after the Chi-Chi earthquake are quantitatively compared. The analysis results show that a significant transformation in the characteristics was induced by the Chi-Chi earthquake. In general, the transformation points out a lower hydrological and geomorphic threshold to trigger debris flows after the Chi-Chi earthquake. The susceptibility of rock units to strong ground motion is also examined. The analysis of debris flow density and accumulated rainfall in regions of different ground motion also reveal that the rainfall threshold decreases after the Chi-Chi earthquake.     

Characteristics analysis for the flash flood-induced debris flows

Typhoon Haitang caused landfall on Taiwan during 15–21 July, 2005 and brought 2,279 mm of maximum cumulative rain with a maximum intensity of 176 mm/h. The torrential rain was mainly distributed from the central mountain range to southern Taiwan and triggered 222 slopeland-related hazards. Among the hazard events, there were 17 debris flows, 157 cases of traffic cut-off, three large-magnitude deep-seated landslides, and 10 villages isolated in the off-track mountainous areas. The debris flows initiated in southern Taiwan were associated with torrential rain, short channel length (<2 km), and small basin area (<3 km²), and were speculated to be induced by flash flood. These flash flood-induced debris flows have a higher rainfall intensity-duration threshold for initiation than in other areas. The deep-seated landslides, isolated villages due to traffic cut-off in off-track mountain areas, and recurrent hazards in areas affected by the M_L 7.6 Chi-Chi earthquake in 1999 are characteristics of slopeland hazards in Taiwan in recent years. One of the most urgently needed mitigation strategies in response to slopeland hazards is the plan for enhancing self-rescue disaster resistance in off-track mountainous villages in Taiwan.     

沟岸侧蚀对泥石流形成和运动过程的影响

沟岸被侧蚀掉的松散物质会通过动量交换将能量传递给龙头,从而影响泥石流的形成和运动过程。前人建立了许多模型来研究泥石流的侵蚀过程对泥石流形成和运动过程的影响,但是模型中大多以底蚀作用为前提条件。通过侧蚀模型和底蚀模型两种水槽实验的对比,针对泥石流的形成和运动过程展开研究。实验发现侧蚀作用更有利于泥石流的形成和运动,泥石流的龙头高度和速度都有波动特征,但侧蚀作用使得这种波动特征更加明显。侧蚀作用使得泥石流的龙身速度更快于龙头速度,龙身颗粒源源不断地堆积于龙头,使得龙头有较大的高度和附加坡降,因此,侧蚀条件下龙头的速度更快。     

基于熵权-正态云模型的泥石流灾害易发性评价

近年来,由于极端天气事件频发和工程建设活动加剧,泥石流灾害对人类的威胁愈加严峻。因此,在综合分析泥石流灾害发育特征及形成机理的基础上,进行泥石流灾害易发性评价对防灾减灾工程活动具有指导意义。选取沟谷岸坡坡度、沟床纵坡比降、植被覆盖率、单位面积固体物源储量、汇水面积、雨季降雨量建立评价指标体系,采用熵权法确定评价指标权重,将泥石流灾害易发性分为高易发、中易发、低易发和不易发四级,建立基于正态云模型的泥石流灾害易发性评价方法,并以西秦岭地区5条泥石流沟为例验证了该评价模型的合理性。进一步将该模型用于陕西吴堡井沟泥石流灾害易发性评价,结果表明井沟泥石流具有中易发性,评价结果与实际相符。     

基于CiteSpace的近三十年中国泥石流灾害风险研究综合分析

本文以吉林省永吉县为研究区,结合历史资料与现场实际情况,研究了基于地理信息相似度的负样本采样策略在泥石流易发性评价中的应用,并探索了不同取值范围下选取的负样本对最终易发性评价结果的影响。本次研究选取了高程、坡度、坡向、平面曲率、剖面曲率、年平均降水量、归一化植被指数、地形湿度指数、断层密度、道路密度、水系密度、人口密度、土地利用类型、岩土体类型等14个因子,依离散型与连续型两种分类采用不同方法计算单因子相似度,综合获得全区地理信息相似度后按其不同阈值进行负样本采样,并以支持向量机模型为基础模型,采用受试者工作特征曲线、正样本准确率和预报效率曲线3种评价方法进行了评价。结果显示：当负样本的地理信息相似度值逐渐增大时,模型精度和正样本准确率逐步降低,预报效率先增后降,易发程度由高估向低估变化;在地理信息相似度取值范围0~0.5内选取的负样本兼顾了模型准确性与土地利用价值,并具有最高的预测效率,是一种优秀的负样本取样策略。本次研究结果与实际较为相近,基于地理信息相似度的负样本采样策略有效提升了负样本质量,提高了预测效率,合理平衡了易发区划分与土地利用的矛盾,可为研究区防灾政策的制订、区域防灾的土地规划提供依据,也为区域泥石流易发性评价提供了一种新的思路。     

Empirical modelling of the May 1998 small debris flows in Sarno (Italy) using LAHARZ

The catastrophic events that occurred in May 1998 in the area of Sarno (Southern Italy) highlight the destructive potential of debris flows, even when they are of relatively low magnitude. More than 130 people were killed and severe property damage took place when volcaniclastic debris flows triggered by heavy rainfall inundated various towns located in piedmont areas. This work investigates the suitability of LAHARZ, a GIS-assisted method for the automatic delineation of lahar inundation areas, for reproducing the May 1998 flows at Sarno. It was found that recalibration of the empirical relationship employed by LAHARZ is required in order to realistically hind-cast the inundation areas of considered events. The potential for further improvements in prediction outputs for this type of geomorphic setting is discussed, taking into account the observed lower mobility of these small volcaniclastic debris flows as compared to lahars of similar size.     

Fire-related hyperconcentrated and debris flows on Storm King Mountain, Glenwood Springs, Colorado, USA

 The South Canyon Fire of July 1994 burned 800 ha of vegetation on Storm King Mountain near Glenwood Springs, Colorado, USA. On the night of 1 September 1994, in response to torrential rains, debris flows inundated seven areas along a 5-km length of Interstate Highway 70. Mapping from aerial photographs, along with field observations and measurements, shows that the September rainstorm eroded unconsolidated, burned surficial soil from the hillsides, flushed dry-ravel deposits from the tributary channels, and transported loose, large material from the main channels. The hyperconcentrated flows and debris flows inundated 14 ha of Interstate Highway 70 with 70 000 m³ of material. Although the burned area was seeded in November 1994, the potential for continuing debris-flow activity remains. Incision and entrainment of channel alluvium, as well as erosion of loose material from the hillslopes could result in future debris- and hyperconcentrated-flow activity. Received: 15 October 1996 / Accepted: 25 June 1997     

基于HBP本构模型的泥石流动力过程SPH数值模拟

泥石流断面内流速垂向分布是研究其流量、冲击力和沟床侵蚀过程的关键。然而,受限于测量装置布设条件,泥石流现场实测及水槽试验中常用的分层流速仪等设备仅能采集断面内少量样本点的流速数据,导致基于实测结果拟合回归的线性分布模型难以准确描述泥石流速度分布规律。对此,本文依托大比例尺泥石流水槽试验开展研究,利用所构建的基于HBP本构的光滑粒子流体动力学(SPH)数值模型反演泥石流三维动力过程,通过分层统计算法对大量粒子速度数据进行分析处理,获得了断面内速度垂向分布规律,并据此提出了基于对数函数的泥石流流速垂向非线性分布模型。为验证所提出模型的准确性,利用其他多组水槽试验数据进行了对比分析,结果表明,本文提出的对数分布模型比传统线性分布模型能够更准确地拟合速度剖面,并在模型参数敏感性方面具有更强鲁棒性。     

Passage of debris flows and turbidity currents through a topographic constriction: seafloor erosion and deflection of flow pathways

Some of the Earth's largest submarine debris flows are found on the NW African margin. These debris flows are highly efficient, spreading hundreds of cubic kilometres of sediment over a wide area of the continental rise where slopes angles are often <1°. However, the processes by which these debris flows achieve such long run‐outs, affecting tens of thousands of square kilometres of seafloor, are poorly understood. The Saharan debris flow has a run‐out of ≈700 km, making it one of the longest debris flows on Earth. For its distal 450 km, it is underlain by a relatively thin and highly sheared basal volcaniclastic layer, which may have provided the low‐friction conditions that enabled its extraordinarily long run‐out. Between El Hierro Island and the Hijas Seamount on the continental rise, an ≈25‐ to 40‐km‐wide topographic gap is present, through which the Saharan debris flow and turbidites from the continental margin and flanks of the Canary Islands passed. Recently, the first deep‐towed sonar images have been obtained, showing dramatic erosional and depositional processes operating within this topographic `gap' or `constriction'. These images show evidence for the passage of the Saharan debris flow and highly erosive turbidity currents, including the largest comet marks reported from the deep ocean. Sonar data and a seismic reflection profile obtained 70 km to the east, upslope of the topographic `gap', indicate that seafloor sediments to a depth of ≈30 m have been eroded by the Saharan debris flow to form the basal volcaniclastic layer. Within the topographic `gap', the Saharan debris flow appears to have been deflected by a low (≈20 m) topographic ridge, whereas turbidity currents predating the debris flow appear to have overtopped the ridge. This evidence suggests that, as turbidity currents passed into the topographic constriction, they experienced flow acceleration and, as a result, became highly erosive. Such observations have implications for the mechanics of long run‐out debris flows and turbidity currents elsewhere in the deep sea, in particular how such large‐scale flows erode the substrate and interact with seafloor topography.     

四川泸定县冷碛镇黑沟泥石流发育特征与危害初探

泸定冷碛镇黑沟流域内发育土层滑坡及土体蠕动变形体20处,为黑沟泥石流的主要松散物源;土层滑坡和土体蠕动变形体规模小,滑速慢,滑体结构松散,滑入溪沟易被洪流卷走,不会形成滑坡堰塞湖和溃决型泥石流。近60年来黑沟发生的最大一次泥石流,经计算泥石流流速为3.47m/s,峰值流量为122.79 m³/s,为大型泥石流,对沟谷两侧财产造成了巨大危害。     

GIS-based hazard mapping and zonation of debris flows in Xiaojiang Basin,southwestern China

Debris flow sites were identified at 140 locations in the Xiaojiang Basin in Yunnan province, southwestern China. Their spatial distribution and catchment characteristics are described in detail on the basis of previous research, air photo interpretation, field investigation and mapping using Geographical Information Systems (GIS). Using a statistical approach, a quantitative model of hazards assessment and zonation was developed through synthesis analysis of basin areas, gradients, and the relative reliefs of these debris flow sites. In terms of debris flow hazard assessment, areas within the Xiaojiang Basin can be classified as severe, heavy and light hazard regions.     

矿山泥石流沟谷形态的分形分维

以2个区域的矿山泥石流为背景,利用分形理论分析了矿山泥石流沟谷形态特征,并与4个区域的自然泥石流沟谷形态进行比较研究。沟谷形态的分形维数具有相同的地学意义:维数越小,该要素对沟道及泥石流的发育和形成的影响越大。沟道比降、汇水面积和沟道长度3个沟谷形态要素中,汇水面积影响最为显著;但矿山泥石流沟谷具有汇水面积少、沟谷尺度小,沟谷比降陡的特点;在此基础上提出了自然—矿山型泥石流的概念。     

物源条件对震后泥石流发展影响的初步分析

强震过后一定时期内,泥石流的活跃性增强,即数量增多、规模增大、频率增加。而随着松散物质储量的减少,泥石流的活跃性会随之衰减。为了具体考察物源条件对震后泥石流活动的影响,使用震后泥石流逐年平均输沙量作为刻画泥石流活跃性的指标,在云南蒋家沟和西藏古乡沟泥石流数据的基础上,定量地分析了震后泥石流活跃性的变化过程。分析表明存在降雨控制型和物源控制型两种泥石流流域。前者的泥石流在震后很长一段时间内都不衰减,其发生主要取决于降雨条件。后者最大规模的泥石流发生于地震过后的短时间内,尔后泥石流活动随时间显著减弱。泥石流规模和频率的关系与暴雨不一致。当物源控制型流域的无量纲化活跃性指标值降为0.12左右时,可以认为泥石流进入了稳定或者衰弱期,不会再有大规模的泥石流事件发生。数据拟合结果表明,整个泥石流活跃性的衰减过程可以用幂函数来描述。其衰减指数与剩余物质储量和总物质储量之比存在密切的关系。这为定量预测震后泥石流发展趋势提供了一个初步的模型。     

神经网络在泥石流活跃程度评判中的应用

泥石流活跃程度的评判结果对保护当地人民生命财产安全和经济建设的发展及地质灾害的防治工程布置有着很大的影响。然而以往的评判方法多以定性评判为主。由于每个人的知识水平、工作经验及评判问题的思维方式的差异，从而使评判结果或多或少存在一定的误差。论文旨在寻求一种新的方法来实现对泥石流活跃程度的定量分析，以便尽可能的减少人为误差。人工神经网络是一种具有学习、记忆、计算、仿真等功能的网络结构。BP网络是目前工程上运用最为广泛的一种误差反传的人工神经网络。它可以模拟任意复杂的非线形映射关系。应用神经网络对泥石流活跃程度进行定量分析评判，可以在一定程度上减少定性评判中的人为因素影响，提高评判的准确性。论文简要介绍了BP神经网络的基本原理、训练过程，以及如何利用MATLAB软件中的神经网络工具箱来创建、训练和应用评判泥石流活跃程度BP网络。在BP网络模型建立时采用了对研究区泥石流活跃程度影响最主要的8个参数作为输入层，并选取了研究区的20个样本对网络进行训练。最后用训练好的网络对研究区的10条支沟分别进行计算。计算结果与实际情况相符，说明利用BP神经网络来评判泥石流活跃程度具有很好的实用价值。     

The sequence of events around the epicentre of the 1929 Grand Banks earthquake: initiation of debris flows and turbidity current inferred from sidescan sonar

Continental slope sediment failures around the epicentre of the 1929 'Grand Banks' earthquake have been imaged with the SAR (Système Acoustique Remorqué) high-resolution, deep-towed sidescan sonar and sub-bottom profiler. The data are augmented by seismic reflection profiles, cores and observations from submersibles. Failure occurs only in water depths greater than about 650 m. Rotational, retrogressive slumps, on a variety of scales, appear to have been initiated on local steep areas of seabed above shallow (5–25 m) regional shear planes covering a large area of the failure zone. The slumps pass downslope into debris flows, which include blocky lemniscate bodies and intervening channels. Clear evidence of current erosion is found only in steep-sided valleys: we infer that debris flows passed through hydraulic jumps on these steep slopes and were transformed into turbidity currents which then evolved ignitively. Delayed retrogressive failure and transformation of debris flows into turbidity currents through hydraulic jumps provide a mechanism to produce a turbidity current with sustained flow over many hours.     

A neural network approach for attenuation relationships: An application using strong ground motion data from Turkey

This paper presents an application of neural network approach for the prediction of peak ground acceleration (PGA) using the strong motion data from Turkey, as a soft computing technique to remove uncertainties in attenuation equations. A training algorithm based on the Fletcher–Reeves conjugate gradient back-propagation was developed and employed for three sample sets of strong ground motion. The input variables in the constructed artificial neural network (ANN) model were the magnitude, the source-to-site distance and the site conditions, and the output was the PGA. The generalization capability of ANN algorithms was tested with the same training data. To demonstrate the authenticity of this approach, the network predictions were compared with the ones from regressions for the corresponding attenuation equations. The results indicated that the fitting between the predicted PGA values by the networks and the observed ones yielded high correlation coefficients (R²). In addition, comparisons of the correlations by the ANN and the regression method showed that the ANN approach performed better than the regression. Even though the developed ANN models suffered from optimal configuration about the generalization capability, they can be conservatively used to well understand the influence of input parameters for the PGA predictions.     

四川壤塘县石吾陇沟泥石流启动条件与堵河程度分析

阿坝州壤塘县宗科乡石吾陇沟于2014年历经20年一遇强降雨,暴发了较大规模泥石流,泥石流峰值流量35.38m^3/s,冲出约6000m^3固体物堆积于沟口,造成沟口宗科河堵塞约三分之二。本文在对石吾陇沟的发育特征进行分析和对运动特征参数进行计算的基础上,对吾陇沟在不同频率泥石流规模下的堵河特征进行研究。首先利用已有经验公式对石吾陇沟在不同频率下堵河程度进行判断,其次结合流体动力学软件CFX对石吾陇沟堵河情况进行模拟分析。经验公式和数值模拟结果均表明,20年一遇泥石流会造成主河严重堵塞,与2014年实际情况基本一致;50年一遇泥石流会造成主河堵断。此研究结果可为石吾陇沟泥石流治理提供依据。     

Use of an artificial neural network for analysis of the susceptibility to landslides at Boun,Korea

The purpose of this study was to develop landslide susceptibility analysis techniques using artificial neural networks and to apply the resulting techniques to the study area of Boun in Korea. Landslide locations were identified in the study area from interpretation of aerial photographs and field survey data. A spatial database of the topography, soil type, timber cover, geology, and land cover was constructed and the landslide-related factors were extracted from the spatial database. Using these factors, the susceptibility to landslides was analyzed by artificial neural network methods. The results of the landslide susceptibility maps were compared and verified using known landslide locations at another area, Yongin, in Korea. A Geographic Information System (GIS) was used to analyze efficiently the vast amount of data and an artificial neural network turned out to be an effective tool to analyze the landslide susceptibility.     

竖向地震动对斜坡场地非线性地震反应的影响

国内外规范中推荐或强制规定竖向地震动取为剪切反应谱的1/2～2/3,但该规定如何改进使其更合理已成为一重要课题。首先,对其研究现状简单总结,给出了可处理辐射阻尼、地震动相位特性、计算高效的二维波动显式有限元等效线性化程序ELPSV编制的必要性,然后进行了分析。初步研究表明,竖向地震动强度对周期在0.3 s以下的地表剪切反应谱有一定的影响,而高于0.3 s部分影响轻微。竖向地震动强度对斜坡场地的竖向地震反应及地表竖向反应谱影响显著,按规范的取值将偏于不安全。受地形条件影响,坡顶剪切地震反应会比坡脚反应要大,而竖向地震反应并不明显。土层边界面的地震反应要比周围反应要低,交界面效应明显。软斜坡场地地震反应特性除场地竖向地震反应自下而上先增加后减小的规律外,其他情形与硬斜坡场地的规律基本一致。该结果定量反映了竖向地震动的影响程度,为斜坡场地上考虑竖向地震动的建（构）筑结构的抗震设计提供了有益的基础。