Debris flows in the Lushan earthquake area: formation characteristics,rainfall conditions,and evolutionary tendency

Debris flows often occur in the mountainous watersheds of earthquake-affected areas, and in the Lushan earthquake area of southwestern China, they have become a significant hazard. In this study, the influencing factors and spatial distribution of debris flows were analyzed through a review of their occurrence history. Debris flows are mainly distributed in the northwestern part of the study area, which hosts the greatest density of active faults. The debris flows are generally formed by the ‘progressive bulking’ effect in channels, and deep incision, lateral erosion, and blockage breaking are common processes that amplify the magnitude of such debris flows. Rainfall thresholds for different types of debris flow were proposed to explain the spatial differences between debris-flow regions, and the temporal variations of those thresholds highlighted how the rainfall conditions required for the occurrence of debris flows have changed. Natural vegetation recovery, reduction in the availability of solid material, and artificial debris-flow control projects play important roles in raising the threshold of the rainfall conditions required for triggering debris flows.

     

震后深切拉槽型泥石流成因模式、暴发特点与防治:以四川九寨沟牙扎沟为例

以四川九寨沟地区牙扎沟泥石流为研究对象,通过数次野外调查及历史资料的统计,详细研究该泥石流的暴发特点、临界雨量及暴发成因,在成因模式分析的基础上提出相应的防治方案。研究结果表明:泥石流具有隐蔽性、突发性、破坏性和输沙能力较强的暴发特点;汶川地震后泥石流暴发的临界雨量仅为2008年“5·12”汶川地震前的一半,2014年至今流域未发生泥石流,临界雨量有逐渐恢复的趋势;短历时强降雨、深切拉槽式物源补给和高陡的地貌条件是泥石流暴发的根本原因;泥石流的成因模式为“降雨渗流、岩土饱水、山洪冲击、沟道深切拉槽、溯源侵蚀、冲刷淘蚀、岸坡侧蚀坍塌、悬移滚动”。这种震后 “拉槽”式泥石流治理应在提高设防标准和优化治理结构形式的同时,以控制集中区物源启动为主、拦挡为辅的防治思路为指导。研究结果可为该地区类似泥石流的防治及预警提供借鉴。     

泥石流源地坡面土体活动随机性规律实验

坡面土体的崩塌活动是泥石流形成的初始过程。为了研究降雨条件下该过程中蕴含的随机性,选择典型泥石流源地坡面进行人工降雨实验,观测坡面径流和坡面土体活动特征。结果表明：坡面径流的产生与坡面土体的供给是2个相对独立的过程;坡面产流过程在时间上具有连续性,空间上具有均匀性,规模上具有稳定性;即使是在恒定的降雨强度条件下,泥石流的源地土体活动也表现为一个离散的土体崩塌序列,具有时间上的间歇性、空间上的聚集性、规模上的随机性,且在时间上服从泊松分布,在规模上服从规模-频率的幂率关系;坡面的水土过程是不完全同步的,泥石流的形成依赖于坡面土体补给的时间、空间和规模分布,这也决定了泥石流阵流的多变和流量的涨落。建立基于土体活动特征的随机性补给模型,结合分布式水文模型,是建立科学的泥石流预报模型的有效方法。     

Rainfall thresholds for debris flow initiation in the Wenchuan earthquake-stricken area,southwestern China

The Wenchuan earthquake-stricken area is frequently hit by heavy rainfall, which often triggers sediment-related disasters, such as shallow landslides, debris flows, and related natural events, sometimes causing tremendous damage to lives, property, infrastructure, and environment. The assessment of the rainfall thresholds for debris flow occurrence is very important in order to improve forecasting and for risk management. In the context of the Wenchuan earthquake-stricken area, however, the rainfall thresholds for triggering debris flows are not well understood. With the aim of defining the critical rainfall thresholds for this area, a detailed analysis of the main rainstorm events was carried out. This paper presents 11 rainfall events that induced debris flows which occurred between 2008 and 2012 after the Wenchuan earthquake. The rainfall thresholds were defined in terms of mean rainfall intensity I, rainfall duration D, and normalized using the mean annual precipitation (MAP). An ID threshold and a normalized I _MAP D threshold graph could be set up for the Wenchuan earthquake-stricken area which forms the lower boundary of the domain with debris flow-triggering rainfall events. The rainfall threshold curves obtained for the study area were compared with the local, regional, and global curves proposed by various authors. The results suggest that debris flow initiation in the study area almost requires a higher amount of rainfall and greater intensity than elsewhere. The comparison of rainfall intensity prior to and after the earthquake clearly indicates that the critical rainfall intensity necessary to trigger debris flows decreased after the earthquake. Rainfall thresholds presented in this paper are generalized, so that they can be used in debris flow warning systems in areas with the same geology as the Wenchuan earthquake-stricken area.     

Rainfall-triggering response patterns of post-seismic debris flows in the Wenchuan earthquake area

Several giant debris flows occurred in southwestern China after the Wenchuan earthquake, causing serious casualties and economic losses. Debris flows were frequently triggered after the earthquake. A relatively accurate prediction of these post-seismic debris flows can help to reduce the consequent damages. Existing debris flow prediction is almost based on the study of the relationship between post-earthquake debris flows and rainfall. The relationship between the occurrence of post-seismic debris flows and characteristic rainfall patterns was studied in this paper. Fourteen rainfall events related to debris flows that occurred in four watersheds in the Wenchuan earthquake area were collected. By analyzing the rainfall data, characteristics of rainfall events that triggered debris flows after the earthquake were obtained. Both the critical maximum rainfall intensity and average rainfall intensity increased with the time. To describe the critical conditions for debris flow initiation, intensity–duration curves were constructed, which shows how the threshold for triggering debris flows increased each year. The time that the critical rainfall intensities of debris flow occurrences return to the value prior to the earthquake could not be estimated due to the absent rainfall data before the earthquake. Rainfall-triggering response patterns could be distinguished for rainfall-induced debris flows. The critical rainfall patterns related to debris flows could be divided on the basis of antecedent rainfall duration and intensity into three categories: (1) a rapid triggering response pattern, (2) an intermediate triggering response pattern, and (3) a slow triggering response pattern. The triggering response patterns are closely related to the initiation mechanisms of post-earthquake debris flows. The main difference in initiation mechanisms and difference in triggering patterns by rainfall is regulated by the infiltration process and determined by a number of parameters, such as hydro-mechanical soil characteristics, the thickness of the soil, and the slope gradient. In case of a rapid triggering response rainfall pattern, the hydraulic conductivity and initial moisture content are the main impact factors. Runoff erosion and rapid loading of solid material is the dominant process. In case of a rainfall pattern with a slow triggering response, the thickness and strength of the soil, high hydraulic conductivity, and rainfall intensity are the impact factors. Probably slope failure is the most dominant process initiating debris flows. In case of an intermediate triggering response pattern, both debris flow initiation mechanisms (runoff erosion and slope failure) can play a role.     

Analysis of the triggering conditions and erosion of a runoff-triggered debris flow in Miyun County,Beijing, China

The occurrence of debris flow from channel-bed failure is occasionally noted in small and steeply sloping watersheds where channelized water flow dominates debris flow initiation. On August 12, 2016, a debris flow from channel-bed failures occurred in the Caozhuangzi Watershed of the Longtan Basin, Miyun, Beijing. Rainfall records over 10-min intervals and field investigations including channel morphology measurements were used to study the triggering conditions and erosion process. The results indicated that the occurrence of this event lagged the peak 10-min rainfall interval and that the cumulative rainfall prior to the occurrence time played an important role in its formation. A mean 10-min rainfall intensity–duration expression in the form of I₁₀?=?5.0?×?D^?0.21, where I₁₀ denotes the mean 10-min rainfall intensity and D is the rainfall duration ranging from 10 to 60 h, was proposed. The debris flows have low proportions of grain size fractions <?0.1 mm and higher fractions of grains 0.1–2 mm in size, indicating that the flow had low viscosity and was coarse-grain dominated. Channel morphology analysis revealed that abrupt changes in topography in the study area, including a steep section, a concave stream bank area, and a partial concave stream section were eroded more extensively than other sites. The maximum sediment erosion volume and erosion depth were not proportional to the variation in stream gradient. Consideration of the degree of erosion in the channel at sites with abrupt morphology changes, the maximum sediment erosion volume, and the erosion depth and volume at the initial channel site and downstream region of forest area together showed that the prime factor controlling erosion was entrained sediment volume. This work, thus, provides a case study regarding the triggering conditions of runoff-triggered debris flows and the topographical changes by debris flow erosion.     

浙东南山丘区泥石流爆发的临界雨量分析

首先对浙东南山区泥石流的形成条件（物源、地形和降水条件）进行了研究。随后研究了本区泥石流的基本特征：在形成方式上,以谷坡或沟源地带的土动力启动方式为主;在侵蚀特征方面,主要有面蚀作用和沟谷侵蚀作用;堆积特征方面,在宏观上当规模较大时可形成堆积扇,规模较小时往往以停积于中下游沟道为主;微观上,主要表现为堆积物质结构杂乱,个别具有期次性。对本区泥石流临界雨量组合进行分析,认为采用基于区域临界雨量组合的泥石流预警预报方法较为合理。利用研究区内4次群发泥石流时的降雨特征值确定了本区泥石流爆发的临界雨量组合,并将其应用于研究区泥石流的临灾预警,分为以下步骤：①收集实时降雨资料;②绘制实时雨量组合曲线;③泥石流灾害预警;④泥石流临界雨量基准的修正。     

An integrated model to assess critical rainfall thresholds for run-out distances of debris flows

A dramatic increase in debris flows occurred in the years after the 2008 Wenchuan earthquake in SW China due to the deposition of loose co-seismic landslide material. This paper proposes a preliminary integrated model, which describes the relationship between rain input and debris flow run-out in order to establish critical rain thresholds for mobilizing enough debris volume to reach the basin outlet. The model integrates in a simple way rainfall, surface runoff, and concentrated erosion of the loose material deposited in channels, propagation, and deposition of flow material. The model could be calibrated on total volumes of debris flow materials deposited at the outlet of the Shuida catchment during two successive rain events which occurred in August 2011. The calibrated model was used to construct critical rainfall intensity-duration graphs defining thresholds for a run-out distance until the outlet of the catchment. Model simulations show that threshold values increase after successive rain events due to a decrease in erodible material. The constructed rainfall intensity-duration threshold graphs for the Shuida catchment based on the current situation appeared to have basically the same exponential value as a threshold graph for debris flow occurrences, constructed for the Wenjia catchment on the basis of 5 observed triggering rain events. This may indicate that the triggering mechanism by intensive run-off erosion in channels in this catchment is the same. The model did not account for a supply of extra loose material by landslips transforming into debris flow or reaching the channels for transportation by run-off. In August 2012, two severe rain events were measured in the Shuida catchment, which did not produce debris flows. This could be confirmed by the threshold diagram constructed by the model.     

Wildfire impacts on the processes that generate debris flows in burned watersheds

Every year, and in many countries worldwide, wildfires cause significant damage and economic losses due to both the direct effects of the fires and the subsequent accelerated runoff, erosion, and debris flow. Wildfires can have profound effects on the hydrologic response of watersheds by changing the infiltration characteristics and erodibility of the soil, which leads to decreased rainfall infiltration, significantly increased overland flow and runoff in channels, and movement of soil. Debris-flow activity is among the most destructive consequences of these changes, often causing extensive damage to human infrastructure. Data from the Mediterranean area and Western United States of America help identify the primary processes that result in debris flows in recently burned areas. Two primary processes for the initiation of fire-related debris flows have been so far identified: (1) runoff-dominated erosion by surface overland flow; and (2) infiltration-triggered failure and mobilization of a discrete landslide mass. The first process is frequently documented immediately post-fire and leads to the generation of debris flows through progressive bulking of storm runoff with sediment eroded from the hillslopes and channels. As sediment is incorporated into water, runoff can convert to debris flow. The conversion to debris flow may be observed at a position within a drainage network that appears to be controlled by threshold values of upslope contributing area and its gradient. At these locations, sufficient eroded material has been incorporated, relative to the volume of contributing surface runoff, to generate debris flows. Debris flows have also been generated from burned basins in response to increased runoff by water cascading over a steep, bedrock cliff, and incorporating material from readily erodible colluvium or channel bed. Post-fire debris flows have also been generated by infiltration-triggered landslide failures which then mobilize into debris flows. However, only 12% of documented cases exhibited this process. When they do occur, the landslide failures range in thickness from a few tens of centimeters to more than 6 m, and generally involve the soil and colluvium-mantled hillslopes. Surficial landslide failures in burned areas most frequently occur in response to prolonged periods of storm rainfall, or prolonged rainfall in combination with rapid snowmelt or rain-on-snow events.     

人工降雨条件下冲沟型泥石流起动试验研究

下垫面以位于贡嘎山东坡的熊家沟为模型,开展了不同降雨强度条件下冲沟型泥石流起动的模拟试验,初步研究了冲沟型泥石流的形成机理和演化特征.试验研究表明:(1)在强降雨条件下,水体入渗速度、不同深度土体含水量变化与降雨强度呈反比例关系,降雨强度越大,越不利于水体入渗,而有利于坡面汇流、冲沟径流和下切侵蚀; (2)在强降雨和径流条件下,土体破坏方式、破坏程度以及泥石流形成机理表现出差异性.相对较小雨强降雨条件下,土体破坏方式以滑坡为主,泥石流形成模式表现为滑坡液化与转化起动,雨强较大降雨条件下,土体破坏方式以侵蚀垮塌为主,泥石流形成模式为洪流席卷垮塌体和沟床揭底; (3)起动试验中泥石流阵性特征明显.在强降雨条件下,雨强与泥石流的规模、黏度之间没有正相关性,雨强越大,泥石流黏度越小,试验中多出现的是高含砂洪流,而相对较小雨强作用下由土体液化转化形成的泥石流黏度较大.试验现象和结果与熊家沟泥石流起动、发生过程具有较高的一致性.     

The formation and development of debris flows in large watersheds after the 2008 Wenchuan Earthquake

The Wenchuan earthquake has caused abundance of loose materials supplies for debris flows. Many debris flows have occurred in watersheds in area beyond 20 km², presenting characteristics differing from those in small watersheds. The debris flows yearly frequency decreases exponentially, and the average debris flow magnitude increases linearly with watershed size. The rainfall thresholds for debris flows in large watersheds were expressed as I?=?14.7 D ^?0.79 (2 h?<?D?<?56 h), which is considerably higher than those in small watersheds as I?=?4.4 D ^?0.70 (2 h?<?D?<?37 h). A case study is conducted in Ergou, 39.4 km² in area, to illustrate the formation and development processes of debris flows in large watersheds. A debris flow develops in a large watershed only when the rainfall was high enough to trigger the wide-spread failures and erosions on slope and realize the confluence in the watershed. The debris flow was supplied by the widely distributed failures dominated by rill erosions (14 in 22 sources in this case). The intermittent supplying increased the size and duration of debris flow. While the landslide dam failures provided most amounts for debris flows (57 % of the total amount), and amplified the discharge suddenly. During these processes, the debris flow velocity and density increased as well. The similar processes were observed in other large watersheds, indicating this case is representative.     

Comparison of recorded rainfall with quantitative precipitation forecast in a rainfall-runoff simulation for the Langat River Basin, Malaysia

Observed rainfall is used for runoff modeling in flood forecasting where possible, however in cases where the response time of the watershed is too short for flood warning activities, a deterministic quantitative precipitation forecast (QPF) can be used. This is based on a limited-area meteorological model and can provide a forecasting horizon in the order of six hours or less. This study applies the results of a previously developed QPF based on a 1D cloud model using hourly NOAA-AVHRR (Advanced Very High Resolution Radiometer) and GMS (Geostationary Meteorological Satellite) datasets. Rainfall intensity values in the range of 3–12 mm/hr were extracted from these datasets based on the relation between cloud top temperature (CTT), cloud reflectance (CTR) and cloud height (CTH) using defined thresholds. The QPF, prepared for the rainstorm event of 27 September to 8 October 2000 was tested for rainfall runoff on the Langat River Basin, Malaysia, using a suitable NAM rainfall-runoff model. The response of the basin both to the rainfall-runoff simulation using the QPF estimate and the recorded observed rainfall is compared here, based on their corresponding discharge hydrographs. The comparison of the QPF and recorded rainfall showed R² = 0.9028 for the entire basin. The runoff hydrograph for the recorded rainfall in the Kajang sub-catchment showed R² = 0.9263 between the observed and the simulated, while that of the QPF rainfall was R² = 0.819. This similarity in runoff suggests there is a high level of accuracy shown in the improved QPF, and that significant improvement of flood forecasting can be achieved through ‘Nowcasting’, thus increasing the response time for flood early warnings.     

Rainfall duration and debris-flow initiated studies for real-time monitoring

A rainfall-induced debris flow warning is implemented employing real-time rain gauge data. The pre-warning for the time of landslide triggering derives the threshold or critical rainfall from historical events involving regional rainfall patterns and geological conditions. In cases of debris flow, the time taken cumulative runoff, to yield abundant water for debris triggering, is an important index that needs monitoring. In gathered historical cases, rainfall time history data from the nearest rain gauge stations to debris-flow sites connected to debris flow are used to define relationships between the rainfall intensity and duration. The effects by which the regional rainfall patterns (antecedent rainfall, duration, intensity, cumulative rainfall) and geological settings combine together to trigger a debris-flow are analyzed for real-time monitoring. The analyses focused on 61 historical hazard events with the timing of debris flow initiation and rainfall duration to burst debris-flow characteristics recorded. A combination of averaged rainfall intensity and duration is a more practical index for debris-flow monitoring than critical or threshold rainfall intensity. Because, the outburst timing of debris flows correlates closely to the peak hourly rainfall and the forecasting of peak hourly rainfall reached in a meteorological event could be a valuable index for real-time debris-flow warning.     

Design and performance of a novel multi-function debris flow mitigation system in Wenjia Gully,Sichuan

The post-earthquake debris flows in the Wenjia Gully led to the exposure of the shortcomings in the design of the original conventional debris flow mitigation system. A predicament for the Wenjia mitigation system is a large amount of loose material (est. 50 × 10⁶ m³) that has been deposited in the gully by the co-seismic landslide, providing abundant source material for debris flows under saturation. A novel design solution for the replacement mitigation system was proposed and constructed, and has exhibited excellent performance and resilience in subsequent debris flows. The design was governed by the three-phase philosophy of controlling water, sediment, and erosion. An Early Warning System (EWS) for debris flow that uses real-time field data was developed; it issues alerts based on the probabilistic and empirical correlations between rainfall and debris flows. This two-fold solution reduces energy of the debris flow by combining different mitigation measures while minimizing the impact through event forecasting and rapid public information sharing. Declines in the number and size of debris flows in the gully, with increased corresponding rainfall thresholds and mean rainfall intensity-duration (I-D) thresholds, indicate the high efficacy of the new mitigation system and a lowered debris flow susceptibility. This paper reports the design of the mitigation system and analyzes the characteristics of rainfall and debris flow events that occurred before and after implementation of the system; it evaluates the effectiveness of one of the most advanced debris flow mitigation systems in China.     

Variability of impact of earthquake on debris-flow triggering conditions: case study of Chen-Yu-Lan watershed,Taiwan

This study investigates the variations in the critical conditions for debris-flow occurrence before and after the Chi-Chi earthquake in the Chen-Yu-Lan watershed, Taiwan. Topographical and rainfall parameters such as the gully gradient, drainage area, rainfall intensity, cumulative rainfall, and rainfall duration in the Chen-Yu-Lan watershed were used to analyze the conditions of debris-flow occurrence over the past 25 years. A recovery equation was proposed on the basis of rainfall parameters and used to determine the variations in the critical line of rainfall that trigger debris flow after the earthquake and to evaluate the recovery period required for the rainfall threshold of debris-flow occurrence after the earthquake to return to that before the earthquake in the watershed. The critical line for the runoff parameter versus gully gradient in the watershed was also presented.     

汶川震区文家沟泥石流成灾机理与特征

文家沟位于绵竹市清平乡,属于5·12汶川Ms8.0级地震极重灾区.地震发生后的3个汛期内,文家沟曾先后发生5次典型泥石流灾害,其中以2010年8月13日泥石流灾害最为严重,规模与灾情巨大,社会影响深远.在对文家沟泥石流跟踪调查的基础上,探讨了泥石流的成灾机理和特征.研究表明:(1)文家沟泥石流是地震和强降雨共同作用的结...     

Rainfall threshold determination for flash flood warning in mountainous catchments with consideration of antecedent soil moisture and rainfall pattern

Flash flood disaster is a prominent issue threatening public safety and social development throughout the world, especially in mountainous regions. Rainfall threshold is a widely accepted alternative to hydrological forecasting for flash flood warning due to the short response time and limited observations of flash flood events. However, determination of rainfall threshold is still very complicated due to multiple impact factors, particular for antecedent soil moisture and rainfall patterns. In this study, hydrological simulation approach (i.e., China Flash Flood-Hydrological Modeling System: CNFF-HMS) was adopted to capture the flash flood processes. Multiple scenarios were further designed with consideration of antecedent soil moisture and rainfall temporal patterns to determine the possible assemble of rainfall thresholds by driving the CNFF-HMS. Moreover, their effects on rainfall thresholds were investigated. Three mountainous catchments (Zhong, Balisi and Yu villages) in southern China were selected for case study. Results showed that the model performance of CNFF-HMS was very satisfactory for flash flood simulations in all these catchments, especially for multimodal flood events. Specifically, the relative errors of runoff and peak flow were within?±?20%, the error of time to peak flow was within?±?2 h and the Nash–Sutcliffe efficiency was greater than 0.90 for over 90% of the flash flood events. The rainfall thresholds varied between 93 and 334 mm at Zhong village, between 77 and 246 mm at Balisi village and between 111 and 420 mm at Yu village. Both antecedent soil moistures and rainfall temporal pattern significantly affected the variations of rainfall threshold. Rainfall threshold decreased by 8–38 and 0–42% as soil saturation increased from 0.20 to 0.50 and from 0.20 to 0.80, respectively. The effect of rainfall threshold was the minimum for the decreasing hyetograph (advanced pattern) and the maximum for the increasing hyetograph (delayed pattern), while it was similar for the design hyetograph and triangular hyetograph (intermediate patterns). Moreover, rainfall thresholds with short time spans were more suitable for early flood warning, especially in small rural catchments with humid climatic characteristics. This study was expected to provide insights into flash flood disaster forecasting and early warning in mountainous regions, and scientific references for the implementation of flash flood disaster prevention in China.     

Debris flow magnitude,frequency, and precipitation threshold in the eastern North Cascades,Washington, USA

We examine the magnitude, frequency, and precipitation threshold of the extreme flood hazard on 37 low-order streams in the lower Stehekin River Valley on the arid eastern slope of the North Cascades. Key morphometric variables identify the magnitude of the hazard by differentiating debris flood from debris flow systems. Thirty-two debris flow systems are fed by basins?<?6 km² and deposited debris cones with slopes?>?10°. Five debris flood systems have larger drainage areas and debris fans with slopes 7–10°. The debris flood systems have Melton ruggedness ratios from 0.42–0.64 compared to 0.78–3.80 for debris flow basins. We record stratigraphy at seven sites where soil surfaces buried by successive debris flows limit the age of events spanning 6000 years. Eighteen radiocarbon ages from the soils are the basis for estimates of a 200 to1500-year range in recurrence interval for larger debris flows and a 450?±?50-year average. Smaller events occur approximately every 100 years. Fifteen debris flows occurred in nine drainage systems in the last 15 years, including multiple flows on three streams. Summer storms in 2010 and 2013 with peak rainfall intensities of 7–9 mm/h sustained for 8–11 h triggered all but one flow; the fall 2015 event on Canyon Creek occurred after 170 mm of rain in 78 h. A direct link between fires and debris flows is unclear because several recent debris flows occurred in basins that did not burn or burned at low intensity, and basins that burned at high intensity did not carry debris flows. All but one of the recent flows and fires occurred on the valley’s southwest-facing wall. We conclude that fires and debris flows are linked by aspect at the landscape scale, where the sunny valley wall has flashy runoff due to sparse vegetation from frequent fires.

     

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。     

泥石流成因机理的非饱和土力学理论研究

泥石流是一种具有较强破坏力的自然山地灾害。对于它的预报研究历来为人们所重视，并建立了很多雨量预报模型。然而，这些雨量预报模型的预报时间很短，往往只能在灾害发生前几十分钟作出预报。论文应用非饱和土强度理论对降雨型泥石漉的成园机理进行了研究，提出降雨型泥石流的形成过程可以划分为2个阶段：第一个阶段与前期实效降雨量有关；第二个阶段与短历时强降雨有关。并对各个阶段降雨作用机理以及固体松散物质的力学性质变化特征进行探讨。为预先判断在降雨条件下，会不会发生泥石流以及所需要的降雨量和雨型提供依据。