中国泥石流灾害强度划分与危险区划探讨

泥石流是山地常见的一种突发性自然灾害现象，进行泥石流灾害强度指标的划分和危险区划是减轻泥石流灾害重要工作之一。本文探讨了中国泥石流的孕育环境和分布规律以及灾害强度的分类分级。根据中国自然环境特征、泥石流形成条件和分布特征等区划原则，将中国泥石流划分为４个一级大区和１５个二级亚区，其大区分别是：Ⅰ．西南印度洋流域极大危险泥石流区；Ⅱ．东南太平洋流域最危险泥石流区；Ⅲ．东北太平洋流域危险泥石流区；Ⅳ．内流和北冰洋流域一般或无危险泥石流区。

Characteristics,Causes and Mitigation of Catastrophic Debris Flow Hazard on 21 July 2011 at the Longda Watershed of Songpan County,China

Debris flow is a common natural hazard in the mountain areas of Western China due to favorable natural conditions, and also exacerbated by mountainous exploitation activities. This paper concentrated on the characteristics, causes and mitigation of a catastrophic mine debris flow hazard at Longda Watershed in Songpan County, Sichuan Province, on 21 July 2011. This debris flow deposited in the front of the No.1 dam, silted the drainage channel for flood and then rushed into tailing sediment reservoir in the main channel and made the No.2 dam breached. The outburst debris flow blocked Fu River, formed dammed lake and generated outburst flood, which delivered heavy metals into the lower reaches of Fu River, polluted the drink water source of the population of over 1 million. The debris flow was characterized with a density of 1.87～2.15 t/m3 and a clay content of less than 1.63%. The peak velocity and flux at Longda Gully was over l0.0～10.9 m/s and 429.o～446.o m3/s, respectively, and the flux was about 700 m3/s in main channel, equaling to the flux of the probability of 1%. About 33o,ooorn3 solid materials was transported by debris flow and deposited in the drainage tunnel （120,000～130,000 m3）, the front of No.1 dam （100,000 m3） and the mouth of the watershed （l00,000～110,000 m3）, respectively. When the peak flux and magnitude of debris flow was more than 462 m3/s and 7,423 m3, respectively, it would block Fu River and produce a hazard chain which was composed of debris flow, dammed lake and outburst flood. Furthermore, the 21 July large-scale debris flow was triggered by rainstorm with an intensity of 21.2 mm/0.5 h and the solid materials of debris flow were provided by landslides, slope deposits, mining wastes and tailing sediments. The property losses were mainly originated from the silting of the drainage tunnel for flash flood but not for debris flow and the irrational location of tailing sediment reservoir. Therefore, the mitigation measures for mine debris flows were presented： （1） The disastrous debris flow watershed should be identified in planning period and prohibited from being taken as the site of mining factories; （2） The mining facilities are constructed at the safe areas or watersheds; （3） Scoria plots, concentrator factory and tailing sediment reservoir are constructed in safe areas where the protection measures be easily made against debris flows; （4） The appropriate system and plan of debris flow mitigation including monitoring, remote monitoring and early-warning and emergency plan is established; （5） The stability of waste dump and tailing sediment reservoir are monitored continuously to prevent mining debris flows.

Comparison of satellite-estimated and model-forecasted rainfall data during a deadly debris-flow event in Zhouqu, Northwest China

The data of several rainfall products, including those estimated from satellite measurements and those forecasted via numerical weather modeling, for a severe debris-flow event in Zhouqu, Northwest China, are compared and analyzed in this paper. The satellite products, including CPC MORPHing technique（CMORPH）, TMPA-RT, and PERSIANN are all near-real-time retrieved with high temporal and spatial resolutions. The numerical weather model used in this paper for precipitation forecasting is WRF. The results show that all three satellite products can basically reproduce the rainfall pattern, distribution, timing, scale, and extreme values of the event, compared with gauge data. Their temporal and spatial correlation coefficients with gauge data are as high as about 0.6, which is statistically significant at 0.01 level. The performance of the forecasted results modeled with different spatial resolutions are not as good as the satellite-estimated results, although their correlation coefficients are still statistically significant at 0.05 level. From the total rainfall and extreme value time series for the domain, it is clear that, from the grid-to-grid perspective, the passive microwave-based CMORPH and TRMM products are more accurate than the infrared-based PERSIANN, while PERSIANN performs very well from the general point of view, especially when considering the whole domain or the whole convective precipitation system. The forecasted data — especially the highest resolution model domain data — are able to represent the total or mean precipitation very well in the research domain, while for extreme values the errors are large. This study suggests that satellite-retrieved and model-forecasted rainfall data are a useful complement to gauge data, especially for areas without gauge stations and areas not covered by weather radars.

The Disastrous 23 July 2009 Debris Flow in Xiangshui Gully, Kangding County, Southwestern China

On 23 July 2009, a catastrophic debris flows were triggered by heavy rainfall in Xiangshui gully, Kangding county, southwestern China. This debris flow originating shortly after a rainstorm with an intensity of 28 mm per hour transported a total volume of more than 480×103 m3 debris, depositing the poorly sorted sediment including boulders up to 2-3 m in diameter both onto an existing debris fans and into the river. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the debris supply conditions, and to estimate debris-flow volume, mean velocity, and discharge. A comparison with adjacent rain-gage records indicates that debris flows in this setting can be produced in response to as little as 17 mm/hour or 3.5 mm/10-minute of rainfall intensity with relatively lower amount of cumulative antecedent rainfall. The field measurement and the interpretation of the Worldview image indicate that abundant landslides occurred on steep slopes within areas underlain by highly weathered granite. Using empirical equations that combine flow depth and channel slope, the mean velocity and discharge of the debris flow were estimated to be 9.2 m/s and 2150 m3/s, respectively. The results contribute to a better understanding of the conditions leading to catastrophic debris flows.

The Impact of Catastrophic Natural Disaster on Land-Use Changes of Qingping Town and the Selection of Suitable Land for Settlement Construction

A Ms 8.0 large earthquake occurred in Sichuan,China on May 12,2008（hereafter called 5.12 Earthquake）,and then a large debris flow happened in the quake-hit Qingping Township of Mianzhu county on August 13,2008（hereafter called 8.13 Debris Flow）.The influence of two disasters on the changes in land use were analyzed by using highresolution aerial photos and satellite remote sensing images taken before and after the 5.12 Earthquake and 8.13 Debris Flow,the selection of suitable construction land were studied by learning experiences and lessons from the selection of resettlement areas and through field surveys and with land use transfer model and analytical model in combination with RS and GIS.The results showed that the influence of the 5.12 Earthquake on ecological environment was far greater than that of the 8.13 Debris Flow;there were more salient conflicts between population and land after the earthquake.Sites for post-disaster reconstruction should not be in disaster-prone areas or in gully-facing areas.Suitable land for settlement construction in I-1~I-5 low-hazard zones is optimal settlement areas for post-disaster reconstruction.

Outlining a stepwise,multi-parameter debris flow monitoring and warning system:an example of application in Aizi Valley,China

In recent years, the increasing frequency of debris flow demands enhanced effectiveness and efficiency of warning systems. Effective warning systems are essential not only from an economic point of view but are also considered as a frontline approach to alleviate hazards. Currently, the key issues are the imbalance between the limited lifespan of equipment, the relatively long period between the recurrences of such hazards, and the wide range of critical rainfall that trigger these disasters. This paper attempts to provide a stepwise multi-parameter debris flow warning system after taking into account the shortcomings observed in other warning systems. The whole system is divided into five stages. Differentwarning levels can be issued based on the critical rainfall thresholds. Monitoring starts when early warning is issued and it continues with debris flow near warning, triggering warning, movement warning and hazard warning stages. For early warning, historical archives of earthquake and drought are used to choose a debris flow-susceptible site for further monitoring. Secondly, weather forecasts provide an alert of possible near warning. Hazardous precipitation, model calculation and debris flow initiation tests, pore pressure sensors and water content sensors are combined to check the critical rainfall and to publically announce a triggering warning. In the final two stages, equipment such as rainfall gauges, flow stage sensors, vibration sensors, low sound sensors and infrasound meters are used to assess movement processes and issue hazardwarnings. In addition to these warnings, communitybased knowledge and information is also obtained and discussed in detail. The proposed stepwise, multiparameter debris flow monitoring and warning system has been applied in Aizi valley China which continuously monitors the debris flow activities.