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The study area of Cala Gonone in NE Sardinia (Italy) consists of a wide terraced re-entrance/valley crowned inland by carbonate hills and, near the coast bounded laterally and partly floored by thin basaltic lava lying over carbonate bedrock. In this re-entrance, several inland alluvial fans (500 m length by 700 m wide) have developed, and a local ~ 30 m high, about 10 m wide (thick), 400 m long scarp body-remnant of semi-consolidated alluvial fan deposits is exposed along the coast. The fans experience depositional events mostly developed during the late Pleistocene. They although nowadays dormant may be reactivated by major rainstorms during strong climate changes. In these last few decades, the touristic village of Cala Gonone has been rapidly expanding over the mid to lower parts of two coalescing alluvial fans (Stadium and Gustui) and along the coastal marine scarp edge (Palmasera alluvial fan system). The village thus may become exposed to natural hazards if extreme climatic conditions may re-occur. Moreover, rock falls and the instability of the costal scarp due to wave erosion may add addition hazards for habitations built near the scarp crest and visitors to the frontal replenished beach. As commonly occurring elsewhere since antiquity, the risk perception of such events is low because of the centennial, millennial of longer recurrence. Such perception does not negate the hazards but a long event recurrence may be accepted as a reasonable risk for the human's activity. Nevertheless, serious consideration should be given to potential problems and plan and build for amelioration and defense. The evidence of what environmentally did and could still happen in the Cala Gonone and similar other area is in part clearly imprinted on the landscape: geology, geomorphology, and relative details in the stratigraphy and sedimentology of the deposits. [ABSTRACT FROM AUTHOR]

Landslides are a serious concern in the Western and Eastern Ghats of India. They impede the social and economic development of the region. Landslides can manifest in various forms like translational slides, rock falls, debris flow, etc. Each type of landslide has a set of characteristic conditioning factors and are required to be modelled separately. This study attempts to develop an integrated model to assess different types of landslides in a region. A stretch of hill road severely affected by different of types of landslides along the Kodaikkanal–Palani traffic corridor is selected for the study. The model developed is capable of assessing the susceptibility of the region to translational slides, rock falls and debris flow. Analytical Network Process, a heuristic model that can accommodate the interdependency of the conditioning factors is used to model landslide susceptibility. The results of the study show that the model performs satisfactorily. Control measures are also suggested for mitigating landslides in the region. [ABSTRACT FROM AUTHOR]

The ability to forecast debris flows is important because of their frequent occurrence and potential for large-scale damage in the Wenchuan Earthquake-hit area. Accurate understanding of the characteristics of rainfall responsible for triggering debris flows is necessary for an effective early warning procedure. This study examined the general characteristics and spatiotemporal variation of rainfall events that responsible for debris flows. Analysis was performed on rainfall data extracted during 2008-2013. The results revealed that the rainfall thresholds for debris flows varied annually and showed tendency toward higher conditions required. The coefficient of variation of relevant rainfall events indicated that the characteristics of the rainstorms changed. In addition, the coefficient of deviation revealed the spatial variation of rainfall in subregions, which was attributed to differences of the local climatic conditions that control debris flow occurrence. The primary controlling rainfall indices for triggering debris flows were filtered, and the most suitable models for establishing rainfall thresholds were selected. Ultimately, the rainfall thresholds were obtained for each subregion within the study area. [ABSTRACT FROM AUTHOR]

The temporal and spatial evolution of pore-fluid pressure exerts strong control on debris flow motion because it can counteract normal stresses at grain contacts, reduce friction, and enhance bulk flow mobility. In Iverson’s two-phase debris flow model, the depth-averaged pore pressure equation, which takes into account the effect of shear-induced dilatancy, was combined with a previous model to describe the simultaneous evolution of flow velocity and depth, solid mass, and pore-fluid pressure. In this work, a high-resolution scheme based on the finite volume method was used to solve the system of equations. Several numerical tests were performed to verify the ability of the presented model and the accuracy of the proposed numerical method. Numerical results were compared with experimental data obtained in a laboratory, and the effectiveness of the proposed numerical method for solving practical problems has been proven. Numerical results indicated that increases of the pore-fluid pressure could enhance the motion of debris flow and expand the spread area. Furthermore, results showed that the debris shear-induced dilatancy could affect the evolution of pore-fluid pressure, thus further influencing the motion of debris flow. [ABSTRACT FROM AUTHOR]

The Ms 8.0 Wenchuan earthquake greatly altered the threshold for rainfall-triggered debris flows in the affected areas. It is of both scientific and practical significance to determine the rainfall thresholds. This study examines one of the regions most prone to debris flows to analyze the characteristics of rainfall that caused debris flows, and to explore local rainfall thresholds. We applied the relation between rainfall intensity and duration, peak intensity and event amount, and other single factor approaches. Comparison of effectiveness and accuracy indicates that the event rainfall is the most sensitive factor for forecasting. Analysis of the annual rainfall thresholds showed that the rainfall conditions required for debris flows have increased on the continent during the past 6 years. Besides the rainfall fluctuations over the past few years, material changes were the primary reason for threshold variability. Recovery of vegetation plays an important role in reducing potential loose material that supplies volume for debris flows. Natural solidification, decrease of the potential erosion depth, and surface coarsening make it more difficult to initiate a debris flow, and ultimately increased rainfall conditions required. The change in rainfall thresholds can be predicted and verified for the entire earthquake-affected region. [ABSTRACT FROM AUTHOR]

Assessing susceptibility to debris flows is of great importance for hazard prevention and mitigation. Kangding County, a region with a high occurrence of destructive geological events, was selected as the study area, to evaluate the area’s susceptibility to debris flows using the weights-of-evidence method based on ArcGIS. First, the determination method of training points was revised. The unit cells covered by the debris flow catchments were set as the training points, rather than using one point to represent the debris flow catchment. Then, the landforms, lithology, faults, earthquakes, and river systems were selected as evidential themes for the analysis. The optimum buffer zones cutoff distance of the faults and rivers was determined by the maximum studentized value of the contrast. Finally, the map of the susceptibility to debris flow in Kangding County was obtained by combining the evidential themes. The susceptibility was categorized as low, moderate, and high susceptibility. The low-susceptibility zones cover an area of 6253 km2, accounting for 53.93 % of the county area. The moderate-susceptibility zones cover an area of 3323 km2, accounting for 28.67 % of the county area. The high-susceptibility zones cover an area of 2018 km2, accounting for 17.40 % of the county area. The moderate-susceptibility zones surround the high-susceptibility zones. The assessment results agree well with field data, demonstrating that the revised method is more suitable for debris flow assessment than the previous method. The assessment results can be used as guidelines for policy makers regarding prevention and mitigation of debris flow hazards. [ABSTRACT FROM AUTHOR]

Worldwide concern for continuing loss of montane forest cover in the tropics usually focuses on adverse ecological consequences. Less recognized, but equally important to inhabitants of these affected regions, is an increasing susceptibility to rainfall-induced debris flows and their associated impacts. The same high rainfall rates that sustain tropical forest cover can often serve as the triggering mechanism for debris flows. The natural rate of debris flow occurrence on steep slopes subject to episodic, intense rainfall is dependent on the stabilizing effect of tropical forests. Either loss or significant reduction in forest cover can weaken this natural defense. Information from postdisaster observations and research on the November 1988 storm event in southern Thailand provides a case study illustrating the potential impacts of increased debris flow susceptibility resulting from conversion of forest cover to rubber tree crops. Development resulting in the loss of tropical forest cover may be accompanied by local increase in population, property development, and infrastructure. Consequently, the potentially disastrous consequences of increased debris flow occurrence are amplified by the greater vulnerability of local populations. Preserving the tropical forest cover is an obvious and often difficult means of retaining this natural protection. Effective policy should capitalize on the values of tropical forests as part of the strategy for retaining adequate forest cover. Policy should also seek to avoid creating pressures that foster forest removal or their conversion to other types of land cover in steep terrain. Areas where tropical forests were converted to other cover types can be restored to secondary forests to avoid a permanent state of increased debris flow susceptibility. Restoration of secondary tropical forests can successfully re-establish the forest characteristics that limit debris flow occurrence. Experience in Central America and the Caribbean demonstrates that successful restoration is possible but requires a significant commitment of both time and resources. In addition to the cost and technical difficulties involved, the increased susceptibility to debris flow occurrence persists through many years until successful restoration is achieved. Both retention of existing tropical forests and restoration of forest cover where loss has occurred are often justified by the reduced risk of debris flow impacts to vulnerable populations and infrastructure. [ABSTRACT FROM AUTHOR]