Debris Flow Hazard Assessment Research Articles

Prediction of spatially explicit rainfall intensity–duration thresholds for post-fire debris-flow generation in the western United States

Early warning of post-fire debris-flow occurrence during intense rainfall has traditionally relied upon a library of regionally specific empirical rainfall intensity–duration thresholds. Development of this library and the calculation of rainfall intensity-duration thresholds often require several years of monitoring local rainfall and hydrologic response to rainstorms, a time-consuming approach where results are often only applicable to the specific region where data were collected. Here, we present a new, fully predictive approach that utilizes rainfall, hydrologic response, and readily available geospatial data to predict rainfall intensity–duration thresholds for debris-flow generation in recently burned locations in the western United States. Unlike the traditional approach to defining regional thresholds from historical data, the proposed methodology permits the direct calculation of rainfall intensity–duration thresholds for areas where no such data exist. The thresholds calculated by this method are demonstrated to provide predictions that are of similar accuracy, and in some cases outperform, previously published regional intensity–duration thresholds. The method also provides improved predictions of debris-flow likelihood, which can be incorporated into existing approaches for post-fire debris-flow hazard assessment. Our results also provide guidance for the operational expansion of post-fire debris-flow early warning systems in areas where empirically defined regional rainfall intensity–duration thresholds do not currently exist.

A GIS-Based Framework for Real-Time Debris-Flow Hazard Assessment for Expressways in Korea

Debris flows caused by heavy rainfall in mountain areas near expressways lead to severe social and economic losses and sometimes result in casualties. Therefore, the development of a real-time system for debris-flow hazard assessment is necessary to provide preliminary information for rapid decision making about evacuations or restoration measures, as well as to prevent secondary disasters caused by debris flows. Recently, various map-based approaches have been proposed using multi-attribute criteria and assessment methods for debris-flow susceptibilities. For the macrozonation of debris-flow hazard at a national scale, a simplified method such as the Korea Expressway Corporation (KEC) debris-flow hazard assessment method can be applied for systematic analysis based on geographic information systems (GIS) and monitoring networks. In this study, a GIS-based framework of real-time debris-flow hazard assessment for expressway sections is proposed based on the KEC debris-flow hazard assessment method. First, the KEC-based method was standardized in a systematic fashion using ArcGIS, enabling the objective and quantitative acquisition of various attribute datasets. The quantification of rainfall criteria also was considered. A safety management system for debris-flow hazard was developed based on the GIS platform. Finally, the method was applied and verified on three expressway sections in Korea. The grading standard for each individual influencing attribute was subsequently modified to more accurately assess the debris-flow hazards.

도심지 도로의 인적취약성 지표를 고려한 토석류 위험도 평가 연구

도심지 도로의 인적취약성 지표를 고려한 토석류 위험도 평가 연구

Large-scale assessment of avalanche and debris flow hazards in the Sakhalin region, Russian Federation

We explore the challenges of avalanche and debris flow hazard assessment for urban areas exposed in the Sakhalin region. Avalanches are a threat to more than 60 settlements in the region and debris flows to more than 30. Data are provided for avalanche and debris flow events that occurred in the Sakhalin region between 1928 and 2015. In this paper, the method for the design of hazard maps for snow avalanches and debris flows is described, providing the starting point for any planning constraints in general settlement planning schemes. These maps further allow conducting an assessment of avalanche and debris flow risk within a short time period for a larger territory and at minimum cost.

DEBRIS FLOW RISK ASSESSMENT AT HUOERGUTU HYDROPOWER DAM SITE USING GREY CORRELATION METHOD AND EXTENSION THEORY

Hazard assessment of debris flow is a hot research topic of the disaster science. It is an important task of disaster forecast, prevention and reduction. This paper takes the debris flow gullies atthe dam site in Huoergutu hydropower along Xinjiang Kaidu River as the research area. Based on the studying of the geological environment, it selects eight aspects as evaluation factors. They include debris flow scale, outbreak of the frequency. The weight coefficient of contestant factors is obtained using thegray correlation degree. The risk assessment of debris flow gulliesis evaluated through the qualitative and analogical methods. The results are compared with the results of site-specific debris flowharazd assessment by LIU Xilin. The risk degrees of the Qingshui gully and Xuelian gully using the extension theory are greater than the results of site-specific debris flow harazd assessment, which iscoincided with the filed investigation. Therefore, the grey correlation and extension theory based method for debris flow gullies at the dam site is reasonable and reliable. The method provides reasonable and scientific basis for risk assessment, planning and controlling of debris flows at the dam site.

Dynamic process-based risk assessment of debris flow on a local scale

After the Wenchuan earthquake in China, debris flows have been more frequent. Multiple debris flows commonly occur in earthquake-affected areas during heavy rainfall, often causing losses of lives and property. We analyzed the dynamic movement of debris flows and proposed a quantitative method of debris flow hazard assessment, based on kinetic energy. Validated using field study of an actual debris flow disaster, these analyzes help determine the type, quantity, distribution, economic worth, and susceptibility of elements at risk. We established a method to determine vulnerability of elements at risk and we propose a systematic and quantitative method for local risk analysis of debris flows. We applied the proposed method to a debris flow in Qipan gully, which caused serious damages for Duwen Highway and Qipan settlements of Sichuan Province in 2013. With the support of a debris-flow movement numerical simulation, remote sensing, and GIS techniques, the proposed method analyzed disaster effects and divided the hazardous areas into three risk zones. Calculated risk zones coincided with the actual distribution and severity of damage of the event, suggesting that the risk assessment generated by the proposed method is consistent with results from the actual disaster.

A Strategic Approach to Debris Flow Risk Reduction on the Road Network

Rainfall-induced debris flows frequently cause disruption to the Scottish road network. A regional assessment of debris flow hazard and risk allows risk reduction actions to be targeted effectively. To this end a strategic approach to landslide risk reduction, which incorporates a classification scheme for landslide management and mitigation has been developed, in order to provide a common lexicon (or group of words) that can be used to describe goals, outcomes, approaches and processes related to risk reduction, and to allow a clear focus on those goals, outcomes and approaches. The focus is thus first on the desired outcome from risk reduction: whether the exposure, or vulnerability, of the at-risk infrastructure and people (and their associated socio-economic activities, which may be impacted over significant areas) is to be targeted for reduction or whether the hazard itself is to be reduced (either directly or by affecting the physical elements at risk). This paper describes the strategic approach in the context of perhaps Scotland's most active debris flow site, the Rest and be Thankful on the A83 strategic road.

Debris-Flow Hazard Assessment and Methods Applied in Engineering Practice

Debris-Flow Hazard Assessment and Methods Applied in Engineering Practice

Advances in debris-flow hazard assessment in mountainous area

Advances in debris-flow hazard assessment in mountainous area

An FAHP-based Quantitative Method for Risk Assessment of Debris-flow Hazards Using Different Fuzzy Numbers

An FAHP-based Quantitative Method for Risk Assessment of Debris-flow Hazards Using Different Fuzzy Numbers

Probabilistic rainfall thresholds for triggering debris flows in a human-modified landscape

In the Carrara Marble Basin (CMB; Apuan Alps, Italy) quarrying has accumulated widespread and thick quarry waste, lying on steep slopes and invading valley bottoms. The Apuan Alps are one of the rainiest areas in Italy and rainstorms often cause landslides and debris flows. The stability conditions of quarry waste are difficult to assess, owing to its textural, geotechnical and hydrogeological variability. Therefore, empirical rainfall thresholds may be effective in forecasting the possible occurrence of debris flows in the CMB. Three types of thresholds were defined for three rain gauges of the CMB and for the whole area: rainfall intensity–rainfall duration (ID), cumulated event rainfall–rainfall duration (ED), and cumulated event rainfall normalized by the mean annual precipitation–rainfall intensity (EMAPI).The rainfall events recorded from 1950 to 2005 was analyzed and compared with the occurrence of debris flows involving the quarry waste. They were classified in events that triggered one or more debris flows and events that did not trigger debris flows. This dataset was fitted using the logistic regression method that allows us to define a set of thresholds, corresponding to different probabilities of failure (from 10% to 90%) and therefore to different warning levels. The performance of the logistic regression in defining probabilistic thresholds was evaluated by means of contingency tables, skill scores and receiver operating characteristic (ROC) analysis. These analyses indicate that the predictive capability of the three types of threshold is acceptable for each rain gauge and for the whole CMB. The best compromise between the number of correct debris flow predictions and the number of wrong predictions is obtained for the 40% probability thresholds. The results obtained can be tested in an experimental debris flows forecasting system based on rainfall thresholds, and could have implications for the debris flow hazard and risk assessment in the CMB.

Hazard Assessment of Debris Flows in the Reservoir Region of Wudongde Hydropower Station in China

The outbreak of debris flows in a reservoir region can affect the stability of hydropower stations and threaten the lives of the people living downstream of dams. Therefore, determining the hazard degree of debris flows in a reservoir region is of great importance. SPOT5 remote sensing images and digital elevation models are introduced to determine the characteristics of debris-flow catchments. The information is acquired through comprehensive manual investigation and satellite image interpretation. Ten factors that influence debris flow are extracted for the hazard assessment. The weight of these factors is determined using the analytic hierarchy process method. As a multi-criterion decision analysis method, fuzzy synthetic evaluation is applied for hazard assessment.

Effects of debris flow composition on runout, depositional mechanisms, and deposit morphology in laboratory experiments

AbstractPredicting debris flow runout is of major importance for hazard mitigation. Apart from topography and volume, runout distance and area depends on debris flow composition and rheology, but how is poorly understood. We experimentally investigated effects of composition on debris flow runout, depositional mechanisms, and deposit geometry. The small‐scale experimental debris flows were largely similar to natural debris flows in terms of flow behavior, deposit morphology, grain size sorting, channel width‐depth ratio, and runout. Deposit geometry (lobe thickness and width) in our experimental debris flows is largely determined by composition, while the effects of initial conditions of topography (i.e., outflow plain slope and channel slope and width) and volume are negligible. We find a clear optimum in the relations of runout with coarse‐material fraction and clay fraction. Increasing coarse‐material concentration leads to larger runout. However, excess coarse material results in a large accumulation of coarse debris at the flow front and enhances diffusivity, increasing frontal friction and decreasing runout. Increasing clay content initially enhances runout, but too much clay leads to very viscous flows, reducing runout. Runout increases with channel slope and width, outflow plain slope, debris flow volume, and water fraction. These results imply that debris flow runout depends at least as much on composition as on topography. This study improves understanding of the effects of debris flow composition on runout and may aid future debris flow hazard assessments.

Predicting locations of post-fire debris-flow erosion in the San Gabriel Mountains of southern California

Timely hazard assessments are needed to assess post-fire debris flows that may impact communities located within and adjacent to recently burned areas. Implementing existing models for debris-flow probability and magnitude can be time-consuming because the geographic extent for applying the models is manually defined. In this study, a model is presented for predicting locations of post-fire debris-flow erosion. This model is further calibrated to identify the geographic extent for applying post-fire hazard assessment models. Aerial photographs were used to map locations of post-fire debris-flow erosion and deposition in the San Gabriel Mountains. Terrain, burn severity, and soil characteristics expected to influence debris-flow erosion and deposition were calculated for each mapped location using 10-m resolution DEMs, GIS data for burn severity, and soil surveys. Multiple logistic regression was used to develop a model that predicts the probability of erosion as a function of channel slope, planform curvature, and the length of the longest upstream flow path. The model was validated using an independent database of mapped locations of debris-flow erosion and deposition and found to make accurate and precise predictions. The model was further calibrated by identifying the average percentage of the drainage network classified as erosion for mapped locations where debris flows transitioned from eroding to depositing material. The calibrated model provides critical information for consistent and timely application of post-fire debris-flow hazard assessment models and the ability to identify locations of post-fire debris-flow erosion.

A Multi-Scale Fuzzy Spatial Analysis Framework for Large Data Based on IT2 FS

The geographical world is an intricate system that comprises the interaction of the Earth's atmosphere, hydrosphere, biosphere, lithosphere, and pedosphere. Existing technologies and systems can only store, represent, and analyze crisp or type-I fuzzy spatial data and obtain spatial knowledge on several discrete scales. However, these technologies are limited to multi-scale and high-order vagueness spatial data representation and analysis, particularly regarding the representation and acquisition of multi-scale knowledge. In this paper, the uncertainty in geographic information systems (GISs) and existing problems in classical spatial analysis methods are summarized. Innovative concepts, such as the scale aggregation model and scale polymorphism, are proposed. A multi-scale fuzzy spatial analysis framework based on an interval type-II fuzzy set is introduced, and critical points are highlighted, such as an interval type-II fuzzy geographical object model (the boundary model and metric methods for geometric properties), direction relations, topological relations, and overlap methods. An actual case based on a multi-scale regional debris-flow hazard assessment is used to confirm the validity of the theory proposed in this paper.

Wenchuan Potential Sudden Debris Flow Hazard Assessment based on Watershed Divide

Wenchuan Potential Sudden Debris Flow Hazard Assessment based on Watershed Divide

Debris flow hazard assessment using set pair analysis models: Take Beichuan county as an example

Assessment of debris flow hazards is important for developing measures to mitigate the loss of life and property and to minimize environmental damage. Two modified uncertainty models, Set Pair Analysis (SPA) and modified Set Pair Analysis (mSPA), were suggested to assess the regional debris flow hazard. A case study was conducted in seven towns of the Beichuan county, Sichuan Province, China, to test and compare the application of these two models in debris flow hazard assessment. The results showed that mSPA only can fit for value-variables, but not for non value-variable assessment indexes, Furthermore, as for a given assessment index xi, mSPA only considers two cases, namely, when grade value increases with xi and when grade value decreases with xi. Thus, mSPA can not be used for debris flow hazard assessment but SPA is credible for the assessment because there are no limitations when using SPA model to assess the debris flow hazard. Therefore, in this study SPA is proposed for assessing debris flow hazard.

Debris-flow hazard assessment based on stepwise discriminant analysis and extension theory

The Wudongde dam is located in the mountainous region of southwestern China. Debris flows form a serious threat to the safety of this site and appropriate hazard assessments need to be carried out. However, the results of such assessments may be erroneous, especially when certain influencing factors are not properly considered. In this study, a stepwise discriminant analysis is used to investigate which factors influence debris-flow occurrence. A total of 27 debris flows, identified through field investigation, are analysed and this resulted in the selection of 17 influence factors. By employing a stepwise discriminant analysis it is possible to reduce these to just five major influencing factors, thus simplifying the calculation of debris-flow hazard assessment. Extension theory has been used to further identify the role of the influencing factors in debris-flow hazard assessment. Thus, reasonable and objective results of hazard degree assessment are expected. Once the criteria for debris-flow hazard assessment are established, the hazard degree of each debris flow is determined. Of the 27 debris flows analysed in this study, four are categorized as ‘extremely hazardous’, 10 as ‘very hazardous’, 10 as ‘moderately hazardous’, and three as ‘slightly hazardous’. The results are consistent with current expert knowledge of these debris flows, thereby providing an indication that the methods used in this study adequately replicate the expert assessments.

Debris-flow hazard assessment and validation following the Medano Fire, Great Sand Dunes National Park and Preserve, Colorado

A debris-flow hazard assessment was conducted for the Medano Creek drainage basin, at Great Sand Dunes National Park and Preserve, following the 2,400 ha Medano Fire in 2010. Debris-flow probability and volume predictions were made using empirical regression models. Model parameters include burn severity, rainfall intensity, topographic characteristics, and soil properties. Model results provided park resource managers with information on potential sub-basin-specific hazards to park visitors, roads, and campsites. Monitoring of the first significant rainfall events following the fire and the resulting debris-flow responses provided means for model validation. Of the three probability models utilized, two predicted high probability of debris-flow occurrence for all sub-basins that produced debris flows, with numerous false positives, while the third failed to predict high probability in any of the sub-basins. The volume model predicted volumes within approximately one order of magnitude higher than those measured.

Derivation of critical rainfall thresholds for shallow landslides as a tool for debris flow early warning systems

Abstract. Real-time assessment of debris-flow hazard is fundamental for developing warning systems that can mitigate risk. A convenient method to assess the possible occurrence of a debris flow is to compare measured and forecasted rainfalls to critical rainfall threshold (CRT) curves. Empirical derivation of the CRT from the analysis of past events' rainfall characteristics is not possible when the database of observed debris flows is poor or when the environment changes with time. For debris flows and mud flows triggered by shallow landslides or debris avalanches, the above limitations may be overcome through the methodology presented. In this work the CRT curves are derived from mathematical and numerical simulations, based on the infinite-slope stability model in which slope instability is governed by the increase in groundwater pressure due to rainfall. The effect of rainfall infiltration on landside occurrence is modelled through a reduced form of the Richards equation. The range of rainfall durations for which the method can be correctly employed is investigated and an equation is derived for the lower limit of the range. A large number of calculations are performed combining different values of rainfall characteristics (intensity and duration of event rainfall and intensity of antecedent rainfall). For each combination of rainfall characteristics, the percentage of the basin that is unstable is computed. The obtained database is opportunely elaborated to derive CRT curves. The methodology is implemented and tested in a small basin of the Amalfi Coast (South Italy). The comparison among the obtained CRT curves and the observed rainfall amounts, in a playback period, gives a good agreement. Simulations are performed with different degree of detail in the soil parameters characterization. The comparison shows that the lack of knowledge about the spatial variability of the parameters may greatly affect the results. This problem is partially mitigated by the use of a Monte Carlo approach.