北京山区泥石流专业监测技术要求及实践

泥石流是北京山区主要突发地质灾害之一,虽然发育规模以中小型居多,但危险性很大,开展专业监测十分必要。科学选取监测对象、合理选择监测方法、监测设备类型和可靠的安装位置,明确监测技术要求,是泥石流监测预警的关键。根据北京市突发地质灾害监测预警系统(二期工程)建设的工作实践,在北京山区泥石流特征分析的基础上,总结得出泥石流监测对象选择、监测方法及设备、监测点位确定方法及技术要求等,并以小梁后沟印子峪泥石流专业监测实践为例,验证了上述原则、方法和技术的合理性。研究成果可为泥石流监测预警的前期选点工作提供思路方法和借鉴参考。     

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.     

The knowledge rules of debris flow event: A case study for investigation Chen Yu Lan River, Taiwan

Debris flow, one of the most active hydrological processes, brings about a great loss of life and properties in the Chen Yu Lan River area, Nan-Tou County, Taiwan. The goal of this study is to manage and monitor the debris flows in a vast area. Thus, the strategy is to collect hydraulical and in-situ data easily and quickly through our spatial information system. Then, a novel Data Mining technique will be developed to find a rule-based knowledge system of debris flow. The entire study can be divided into two parts. In the first part, using spatial information the debris flow image is extracted from the outbreak area. The system provides precise positional information pertaining to the debris flow events. Attributes such as effective watershed area, Normalized Difference Vegetation Index (NDVI), and slope are automatically obtained from the system. In the second part of this study, K-mean theory is used to classify the observed hydraulical and in-situ data into different categories. Then, the ‘Effective Rough Set’ method is successfully used to analyze the factors influencing the debris flow phenomenon and delivers rational knowledge rules. The contribution of this study is presented that NDVI, slope and effective watershed area are the major factors influencing debris flow in the study area. The knowledge rules can provide better understanding on the elevation of high potential debris catchments.     

Experimental evidences and numerical modelling of debris flow initiated by channel runoff

Debris flow initiation by channel bed mobilization is a common process in high mountainous areas. Initiation is more likely to occur at the outlet of small, steeply sloping basins where concentrated overland flow feeds an ephemeral channel incised in slope deposits. Such geological conditions are typical of the Dolomite region (Italian Alps), which is characterized by widespread debris flow activity triggered by severe summer thunderstorms. Real-time data and field observations for one of these catchments (Acquabona catchment, Belluno, Italian Alps) were used to characterize the hydrological response of the initiation area to rainfalls of varying intensity and duration. The observed behaviour was then reproduced by means of a simple hydrological model, based on the kinematic wave assumption, to simulate the generation of channel runoff. The model is capable of predicting the observed hydrological response for a wide range of rainfall impulses, thus providing a physical basis for the understanding of the debris flow triggering threshold.     

A study of methods to estimate debris flow velocity

Debris flow velocities are commonly back-calculated from superelevation events which require subjective estimates of radii of curvature of bends in the debris flow channel or predicted using flow equations that require the selection of appropriate rheological models and material property inputs. This research investigated difficulties associated with the use of these conventional velocity estimation methods. Radii of curvature estimates were found to vary with the extent of the channel investigated and with the scale of the media used, and back-calculated velocities varied among different investigated locations along a channel. Distinct populations of Bingham properties were found to exist between those measured by laboratory tests and those back-calculated from field data; thus, laboratory-obtained values would not be representative of field-scale debris flow behavior. To avoid these difficulties with conventional methods, a new preliminary velocity estimation method is presented that statistically relates flow velocity to the channel slope and the flow depth. This method presents ranges of reasonable velocity predictions based on 30 previously measured velocities.     

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。     

Relationships between debris flows and earth surface factors in Southwest China

Southwest China, including the Provinces of Yunnan, Guizhou, Sichuan and Chongqing, is a region with serious debris flow hazards, where 7,561 debris flow sites have been identified. Based on the data from these sites, the distribution regularity of debris flows was analyzed. Earth surface factors that may influence the formation of debris flows were analyzed from the viewpoints of energy and material conditions. Four major earth surface factors were selected: relative relief, stratigraphy, fault density and land-use conditions. With the support of GIS, the research region was divided into 125,177 grid cells and for each cell data for the four factors were collected. Based on this information, the distribution of quantity and the occurrence probability of debris flows and the role of each factor were statistically analyzed. The results should be helpful for the assessment of debris flow hazards and debris flow forecasting in the research region.     

Experimental study on rheologic behaviour of debris flow material

In order to describe the flow behaviour of debris flows often rheologic models are used. This study introduces two novel facilities to determine rheologic parameters of different models for debris flow material mixtures containing grain sizes larger than to be measured in standard viscometers. The diameter of the vertically rotating flume (VRF) is 2.5 m, the rectangular cross section has a width of 0.45 m, and the maximum rotational speed is around 30 revolutions per minute, corresponding to a mean speed of the examined mixture of ∼4 m/s. From the measured flow parameters total boundary shear stress and corresponding shear rate of the flowing mixture are derived. The ball measuring system (BMS) consists of a sphere that is dragged at specific speeds across a sample of 0.5 l volume with the help of a small sphere holder. Accordingly torques due to drag exerted on the sphere and its holder as well as corresponding speeds are measured and transformed into values of shear stress and shear rate based on the method of Metzner and Otto. Material taken from fresh debris flow deposits in Eastern Switzerland have been investigated with both facilities. We present results from experiments involving mixtures with different sediment concentrations and with grain sizes up to 5 mm. Although estimated from completely different approaches the rheologic parameters of the independent measurements are generally in reasonable agreement.     

2001 debris flow and debris flood in Nam Ko area, Phetchabun province, central Thailand

The factors of the debris flow and debris flood (debris flow-flood) occurrence on 11 August 2001 on the active Nam Ko alluvial fan in Phetchabun province, central Thailand, were studied. Evidences of past activity registered in the alluvial fan, and the debris flow-flood event were reconstructed. The disastrous debris flow-flood event was not the work of the unusual high amount of rainfalls alone, as previously theorized, but is a work of combined factors from the terrain characteristics with specific land covers to the time delay for accumulation of debris and sediments. This combination of factors could lead to a debris flow-flood after a high amount of precipitation. The process could also be worse if a landslide formed a natural dam, then the dam was destroyed under the weight of impounded water. After such a disastrous event, it would take time for more plant debris and sediments in the sub-catchment area to accumulate before the next debris flow-flood.     

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.     

缺资料地区泥石流预警雨量阈值研究

合理的雨量阈值指标是保障泥石流预警报准确性的关键,对于研究泥石流形成机制、分析预测未来活动特点以及指导防治工程设计等方面均具有重要意义。由于国内山区大多数泥石流沟均无降雨和灾害资料,目前国内外通行的实证法和频率计算法不能满足其泥石流预警报的需要。通过分析泥石流预警区的降雨条件、水文特征及下垫面条件,提出了基于水力类泥石流起动机制来计算泥石流预警雨量阈值的方法。主要根据流域地形及松散固体物质等特征,计算该流域泥石流起动的临界水深,并结合流域产汇流机制、特征降雨量随海拔变化规律、暴雨雨型特征,进而计算该流域泥石流预警雨量阈值。研究成果在四川省凉山州宁南县城后山史家沟流域进行了应用和验证,结果表明该方法具有合理性和可行性。该方法解决了缺资料地区泥石流预警报的难题,为山区泥石流预警报提供了一种新的思路。     

降雨诱发坡面型泥石流形成机理

基于野外调查和室内测试分析,依据岩土体破坏准则理论,结合典型坡面型泥石流进行剖析,从坡面型泥石流形成的影响因素、运动学特征、动力条件、形成与演化过程等方面,探讨了降雨诱发坡面型泥石流的形成机理。研究结果表明:坡面流以平移式滑动方式破坏为主,通常发生于残坡积土层厚度小(≤2.0 m)的陡坡地带(坡度≥40°),降雨是坡面型泥石流的主要触发因素,雨水入渗促使斜坡残坡积岩土体饱和软化,当土体含水率超过28%~30%,粘聚力、内摩擦角与含水率关系曲线都出现了明显的拐点,即饱和度超过75%时,其粘聚力和内摩擦角都发生急剧降低,斜坡土体由稳定状态向破坏状态演化。遇持续降雨(或暴雨)作用,此种残坡积土局部发生失稳下滑——流土,进而在动水压力作用下发生下泻造浆形成坡面泥石流。     

Practical research on quantitative calculation of debris flow magnitude and disaster intensity

Wind scale or earthquake magnitude is easier to remember and to be understood by the community. Although many systems of classifying debris flows are presently available, it is necessary to propose an index as simple as wind scale or earthquake magnitude for measuring debris flows. Based on the principles used in wind scale and earthquake magnitude calculation, this paper presents the concepts of debris flow magnitude and disaster intensity as well as a new numerical calculation method. Debris flow magnitude is a quantitative index describing the scale of a debris flow. The disaster intensity of a debris flow is a quantitative index describing the severity of the damage to society caused by a debris flow. With their explicit definitions and simple concepts, both indices are considered to be important both practically and theoretically.     

基于黏土颗粒含量的泥石流容重计算

泥石流灾害的防治通常采用“稳、拦、排”的基本模式,但对于不具备排导条件的泥石流治理方法,仍在探索之中。本文以阿勒泰布尔津县科克逊泥石流为例,对排导受限条件下的泥石流防治模式进行了探索性的分析研究,提出了“上游拦挡物源、中游稳固沟道和消能、下游综合排导”泥石流治理新模式。该模式在稳定和拦截泥石流物源的基础上,充分利用下游地形地质条件,在下游沟口地形开阔处修建拦水堤坝,坝前设置渗水区,拦截和储存水体,借助该区地层良好的渗透性,使临时储存的水体快速下渗转化为地下水进行排泄,从而有效达到治理泥石流灾害的目的。本文以新疆布尔津科克逊泥石流为例,系统分析了研究区地形地貌、水文、工程地质条件、下游堆积区地质结构等,优化了工程布局和结构设计,通过现场工程应用验证了新模式的可行性和有效性,并根据不同地质条件、气候特征、社会经济情况等提出了相应的适应性调整措施,提高泥石流防治的长期有效性,成果可为排导困难区域的泥石流防治提供借鉴。     

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.     

滑坡转化泥石流启动的人工降雨试验研究

滑坡直接转化而成的泥石流通常比滑坡本身运移距离更远,波及范围更广,危害也更严重,但目前相关转化机制及其影响因素的研究较少。2020年10月20日位于白龙江左岸、甘肃省舟曲县的虎家崖暴发小型泥石流,侵入省道313,威胁毗邻村庄。通过现场调查、室内岩土试验、遥感解译和降雨资料分析,本文对虎家崖泥石流形成的地质环境条件、运移及堆积特征等进行了调查,研究了浅层滑坡失稳并直接转化为泥石流的主要特征、过程、影响因素及其形成机理,探讨其未来发展趋势。研究表明：(1)虎家崖上游狭长沟道堆积体受到长达19 d、累计98.5 mm的持续性降雨的激发而发生慢速滑坡,区域强震造成的坡体结构损伤对滑坡发育也有贡献。(2)滑坡后段与滑坡前缘的剪出部分在运动过程中直接转化为泥石流,但中段滑坡体则维持剪切滑动。(3)转化过程受滑坡前缘剪出土体饱水程度、沟道坡度与落差以及地表径流等因素的影响。(4)虎家崖狭长沟道后缘可能因毗邻泄流坡滑坡活动牵引而破坏,同时上游沟道残余滑坡体与灰岩崩塌体、出口右侧残余滑坡体可能受降雨、地震等激发而失稳,再次转化为泥石流,威胁沟道下方虎家崖村和省道S313。

     

Size of a debris flow deposition: model experiment approach

 The prediction of the dangerous extent of a debris flow deposition is of vital importance, but difficult to achieve. Precise prediction of the depositional boundary of a debris flow event is impossible, but the size of a debris flow deposition could provide some estimates of the area, length, width, and thickness of a debris flow deposition. Based on in situ depositional experiments performed on a debris flow creek just after debris flows, a rule of thumb expressed by a group of equations containing the multiple-variate nonlinear functions is proposed in this paper. The interrelationships between the size and the causation also are discussed, and some empirical formulae to calculate the causative parameters for different regions are presented. Received: 24 April 1995 · Accepted: 21 June 1995     

Application of back-propagation networks in debris flow prediction

Debris flows have caused serious loss of human lives and a lot of damage to properties in Taiwan over the past decades. Moreover, debris flows have brought massive mud causing water pollution in reservoirs and resulted in water shortage for daily life locally and affected agricultural irrigation and industrial usages seriously. A number of methods for prediction of debris flows have been studied. However, the successful prediction ratio of debris flows cannot always maintain a stable and reliable level. The objective of this study is to present a stable and reliable analytical model for occurrence predictions of debris flows. This study proposes an Artificial Neural Networks (ANN) model that was constructed by seven significant factors using back-propagation (BP) algorithm. These seven factors include (1) length of creek, (2) average slope, (3) effective watershed area, (4) shape coefficient, (5) median size of soil grain, (6) effective cumulative rainfall, and (7) effective rainfall intensity. A total of 178 potential cases of debris flows collected in eastern Taiwan were fed into the ANN model for training and testing. The average ratio of successful prediction reaching 93.82% demonstrates that the presented ANN model with seven significant factors can provide a stable and reliable result for the prediction of debris flows in hazard mitigation and guarding systems.     

Erosion and morphology of a debris flow caused by a glacial lake outburst flood,Western Norway

This article documents a 240,000-m³ debris flow resulting from a glacial lake outburst flood in Fjærland, Western Norway, May 8, 2004. The event started when a glacial lake breached a moraine ridge. The ensuing debris flow was able to erode material along its path, increasing in volume from about 25,000 to 240,000 m³ before depositing about 3 km from its starting point. Field investigations, pre- and post-flow aerial photographs as well as airborne laser scanning (LIDAR) were used to describe and investigate the flow. The most striking and unusual feature of this case study is the very pronounced erosion and bulking. We have made a detailed study of this aspect. Erosion and entrainment is quantified and the final volume of the debris flow is determined. We also present geometrical and sedimentological features of the final deposit. Based on the Fjærland data, we suggest that a self-sustaining mechanism might partly explain the extreme growth of debris flows traversing soft terrain.     

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。