Hydrometeorological thresholds for landslide initiation and forest operation shutdowns on the north coast of British Columbia

Debris flows and debris avalanches are the most widespread and hazardous types of landslides on the British Columbia north coast. Triggered by heavy rain, they pose risks to forestry workers in sparsely developed regions. The scarcity of long-term quality rain gauges and the lack of weather radar information create significant challenge in predicting the timing of landslides, which could be used to warn and, when necessary, evacuate forestry personnel. Traditional methods to relate rainfall antecedents and rainfall intensity to known landslide dates have proven to be unsatisfactory in this study due to extreme spatial variability of rainfall, enhanced by the orographic effect and the scarcity of rain gauges in a very large area. This has led to an integration of meteorological variables in a landslide advisory system that classifies three types of approaching storms by the 850-mbar wind speed and direction, the occurrence of subtropical moisture flow, and the existence of a warm layer characterized by high thickness values of the 500- to 1,000-mbar pressure levels. The storm classification was combined with a 4-week antecedent rainfall and the 24-h rainfall measured near or in the watershed where logging operations are taking place. This system, once implemented, is thought to reduce loss of life, injury, and economic losses associated with forestry works in the study area.     

Natural hazards vs human impact: an integrated methodological approach in geomorphological risk assessment on the Tursi historical site, Southern Italy

The Tursi–Rabatana historical site is very representative of the cultural heritage of Basilicata, Southern Italy. Morphological evolution of the landscape is characterized by very intense erosive phenomena such as landslides, deep gullies, rills, and piping, which affect the perimeter of urban settlements and threaten the conservation of these sites. Rainfalls and the lithology of the substratum are the main factors to which the landscape evolution is linked, triggering landslide and linear erosion phenomena. Climate analysis carried out during the last century showed an increasing trend in the rainfall intensity over extremely short periods. This condition also induced an increase in the vulnerability level of the slopes. Integrated analysis between territorial data (geology, geomorphology, climate) and historical documents showed that, at least from the last century, the geomorphological hazard has been accentuated by the intense human activity of cave excavation along several fronts under the present urban area. The geophysical investigation also permitted the mapping of shallow caves and tunnels in the subsurface reconstructing the multilevel complex hypogeal system. This work also produced evidence that the human interventions occurring during the historical period have been a determining factor in increasing the hazard level and accelerating the preexisting morphological processes.     

Loading/Unloading response ratio theory applied in predicting deep-seated landslides triggering

Rainfall is the most relevant factor for the triggering of landslides and it is characterized by an extreme variability. Rainfall analysis is the most frequently adopted approach for predicting landslides. But predicting deep-seated landslides by means of rainfall thresholds is sometimes inadequate due to the complexity of such slopes. In this paper, further study of the loading / unloading response ratio theory applied in landslides prediction was carried out. As the aforementioned effect and character of rainfall was concerned, a prediction for the known Xintan landslide was carried out by means of the loading / unloading response ratio method, in which the action of water was regarded as loading/unloading measures. The results show that it is an effective method for landslides prediction, and it has an advantage over conventional rainfall thresholds or time sequences analysis method.     

Probabilistic landslide hazards and risk mapping on Penang Island, Malaysia

This paper deals with landslide hazards and risk analysis of Penang Island, Malaysia using Geographic Information System (GIS) and remote sensing data. Landslide locations in the study area were identified from interpretations of aerial photographs and field surveys. Topographical/geological data and satellite images were collected and processed using GIS and image processing tools. There are ten landslide inducing parameters which are considered for landslide hazard analysis. These parameters are topographic slope, aspect, curvature and distance from drainage, all derived from the topographic database; geology and distance from lineament, derived from the geologic database; landuse from Landsat satellite images; soil from the soil database; precipitation amount, derived from the rainfall database; and the vegetation index value from SPOT satellite images. Landslide susceptibility was analyzed using landslide-occurrence factors employing the probability-frequency ratio model. The results of the analysis were verified using the landslide location data and compared with the probabilistic model. The accuracy observed was 80.03%. The qualitative landslide hazard analysis was carried out using the frequency ratio model through the map overlay analysis in GIS environment. The accuracy of hazard map was 86.41%. Further, risk analysis was done by studying the landslide hazard map and damageable objects at risk. This information could be used to estimate the risk to population, property and existing infrastructure like transportation network.     

Permanent seismic deformation analysis of a landslide

A failed slope may not necessarily require a remedial treatment if it can be shown with confidence that the maximum movement of the slide mass will be within tolerable limits, i.e., not cause loss of life or property. A permanent displacement analysis of a landslide for static and seismic conditions is presented using a continuum mechanics approach. Computed values of displacement for static conditions compare favorably with field measurements and computed values of seismic displacements for a postulated earthquake motion appear reasonable. Also, the seismic displacements using the continuum mechanics approach compare favorably with those obtained using the Newmark sliding block procedure for assessing seismically-induced slope deformations.     

Worth of head data in well-capture zone design: deterministic and stochastic analysis

In this study, we examine the effects of conditioning spatially variable transmissivity fields using head and/or transmissivity measurements on well-capture zones. In order to address the challenge posed by conditioning a flow model with spatially varying parameters, an innovative inverse algorithm, the Representers method, is employed. The method explicitly considers this spatial variability.

A number of uniform measurement grids with different densities are used to condition transmissivity fields using the Representers method. Deterministic and stochastic analysis of well-capture zones are then examined. The deterministic study focuses on comparison between reference well-capture zones and their estimated mean conditioned on head data. It shows that model performance due to head conditioning on well-capture zone estimation is related to pumping rate. At moderate pumping rates transmissivity observations are more crucial to identify effects arising from small-scale variations in pore water velocity. However, with more aggressive pumping these effects are reduced, consequently model performance, through incorporating head observations, markedly improves. In the stochastic study, the effect of conditioning using head and/or transmissivity data on well-capture zone uncertainty is examined. The Representers method is coupled with the Monte Carlo method to propagate uncertainty in transmissivity fields to well-capture zones. For the scenario studied, the results showed that a combination of 48 head and transmissivity data could reduce the area of uncertainty (95% confidence interval) in well-capture zone location by over 50%, compared to a 40% reduction using either head or transmissivity data. This performance was comparable to that obtained through calibrating on three and a half times the number of head observations alone.     

A comparison of landslide rates following helicopter and conventional cable-based clear-cut logging operations in the Southwest Coast Mountains of British Columbia

A comparison of landslide rates following helicopter and conventional, cable-based, clear-cut logging was carried out using results from two independent terrain attribute studies in the Eldred and Lois River watersheds in the Southwest Coast Mountains of British Columbia. Landslides initiating from directly within a road prism were excluded from the study in order to focus the comparison on landslides related primarily to conventional versus helicopter yarding methods. A landslide rate of 0.02 landslides/ha was observed in 162 terrain polygons logged by helicopter 8 years prior to this study. Landslide rates in 38 gullied polygons were 0.06 landslides/ha. No landslides were observed in 124 open-slope polygons. Over a similar 8-year average period, 0.03 landslides/ha were observed in 142 cable-yarded terrain polygons; 0.06 and 0.02 landslides/ha occurred in gullied and open-slope polygons, respectively. t-Tests indicate that total landslide rates are not significantly different following helicopter and conventional logging; however, a dichotomy exists between gullied and open-slope terrain polygons. Landslide rates are not significantly different in gullied terrain but are significantly higher on open-slopes following conventional cable logging. Consequently, landslides appear to have a greater potential to occur in open-slope terrain following conventional logging, but differences in gullied polygons are less likely. Increased post-logging landslide rates in conventionally logged, open slopes are more likely the result of undetected road-related drainage changes than differences between helicopter and conventional yarding-related ground disturbance.     

Landsat 7 pan数据与多光谱数据融合的工程化实现

采用建立流程化模型的方法对Landsat7pan数据与多光谱数据进行融合,并分别用乘积变换、Brovey算法、IHS变换进行了试验。其中,用乘积变换算法做了大量的工程实现。实践表明,采用建立流程化模型的方法直观、简单、快捷,而且在操作上比较灵活,可以根据实际情况进行设计,避免固定流程算法所带来的输入输出格式转换,为大批量数据的快速生产提供一种有效方法。     

Incorporating the effect of ALS-derived DEM uncertainty for quantifying changes due to the landslide in 2011, Mt. Umyeon,Seoul

ABSTRACT

The landslide, which occurred at Umyeon mountain (Mt. Umyeon) in Seoul, Korea in 2011, was a prime example that raised awareness about the landslide in the highly urbanized area. Although many studies have been done on Umyeon landslide, there is a lack of research that detects the area where the landslide occurred and quantifies the elevation changes through remote sensing data. In this regard, this paper aims to detect and assess topographic changes quantitatively over Mt. Umyeon by using digital elevation models (DEMs) derived from airborne laser scanning (ALS) data. Since Mt. Umyeon was hilly and covered with dense trees during summer, traces of the landslide were detected by estimating the spatially distributed uncertainty of ALS-derived DEMs. The probabilistic analysis with Bayes'? theorem considering the spatially distributed DEM of difference (DoD) uncertainty enabled to detect the landslide traces efficiently and was less affected by the influence of ALS errors. The results indicated that ALS-derived DEMs have the potential to detect landslides with their uncertainty estimation, although the ALS data were acquired in hilly and densely vegetated areas. Moreover, quantifying topographic changes due to landslides with high reliability is considered to be beneficial and practically helpful for disaster recovery.     

宝鸡市斗鸡台滑坡区滑坡地震稳定性计算与分析

本文是在斗鸡台滑坡区区域自然条件和地质地貌环境的广泛调查、工程地质勘探和可靠土质岩性力学性能试验［１］的基础上，用简布方法和“二分法”搜索法对滑坡体的整体稳定性和局部稳定性进行了计算评价。