A rainfall intensity-duration threshold for landslides in a humid-tropical environment, Puerto Rico
The leading cause of landslides in Puerto Rico is intense and/or prolonged rainfall. A rainfall threshold for rainfall-triggered landsliding is delimited by 256 storms that occurred between 1959 and 1991 in the central mountains. A comparison
of the Puerto Rico threshold with rainfall data from other humid-tropical regions suggests that the threshold developed for Puerto Rico may be applicable to other similar environments throughout the world.
A new statistical model for threshold friction velocity of sand particle motion
Aeolian features ; Aeolian transport ; Forecast ; Friction velocity ; Model ; Random process ; Sand ; Threshold ; Wind erosion
A theoretical formulation of threshold friction velocity of sand particles is established by considering the equilibrium of moment forces acting on an irregular particle following Bagnold's scheme. Owing to the statistical nature
of the microstructure of soil surface, of the particle shape and of positions in the bed, the threshold friction velocity is random. Based on the probability theory of multi-dimension random variable, the probability of the threshold friction velocity, its mean value
and standard deviation are calculated. The mean value and standard deviation are fitted as functions of sand particle's diameter. A formula of wet threshold friction velocity is also given.
The disruption of Grassy Creek : implications concerning catastrophic events and thresholds
Catastrophe ; Channel geometry ; Concept ; Dam ; Fitting ; Illinois ; Longitudinal section ; Mass movement ; Stream ; Threshold ; United States of America
Two catastrophic events, occurring simultaneously in the valley of Little Grassy Creek, allow for an examination of the threshold concept in geomorphology. Movement of debris associated with failure and sliding of valley-side material, caused
damming and avulsion of Little Cassy Creek. Slope and river disruptions were linked because the effect of one event (slope failure) was the cause of the second event (fluvial avulsion). Criteria needed to employ thresholds to explain geomorphic events
are suggested, and a definition of thresholds as time-dependent phenomena is presented as a means of reducing confusion over the use of the threshold concept.
of maximum temperatures above a selected threshold. The relationships are extrapolated and used to estimate the frequency in the new climatic conditions projected by general circulation models.
Threshold conditions for incipient rilling in Rill erosion. Processes and significance.
This paper aims to add more information about critical threshold conditions for incipient rilling with special attention to clay-rich soils. Four types of soil are tested, under simulated rain, with their textures ranging from sandy loam to clay.
Thresholds of particle entrainment in a poorly sorted sandy gravel-bed river
Barcelona ; Carrying capacity ; Fluvial hydrology ; Grain size distribution ; Methodology ; Sediment load ; Sediment transport ; Spain ; Stream ; Threshold
This paper presents an analysis of a new data set on threshold conditions for bed material entrainment in the poorly sorted sandy gravel-bed of the Arbúcies River (NE Spain), an interesting example of a perennial to ephemeral transitional
Geomorphic thresholds: the concept and its applications
Geomorphic thresholds were defined initially as the condition at which there is a significant landform change without a change of external controls such as base level, climate and land use. Landforms evolve to a condition of incipient instability
and extrinsic geomorphic thresholds. The threshold concept has practical significance. If the threshold conditions can be recognized, not only will different explanations for some landforms emerge but also the ability to identify incipiently unstable landforms
and to predict their change will be of value to land managers and engineers. For example, the development of gullies and fan-head trenches can be explained by the depositional steepening of valley floors and fan-heads to threshold slope. As a consequence, as yet
ungullied but potentially unstable areas can be recognized. In addition, channel pattern variations and the conversion of meandering channels to braided ones, and of braided channels to single-thalweg sinuous ones can occur naturally at pattern thresholds
. Such changes can also be accomplished artificially, when it is recognized that a channel is near a pattern threshold. Sediment yield variations will be related to these periods of instability. Recognition of this will aid in the explanation of some hydrologic
Based on data from the Loess Plateau of China, some non-linear relationships between forest cover, mean annual rainfall erosivity and annual precipitation have been found. A threshold has been identified. Furthermore, 2 thresholds are identified
in the relationship between rainall erosivity and annual precipitation. Based on these relationships, the non-linear relationship between erosion intensity and annual precipitation is explained. The implication of these thresholds for erosion control on the Loess
Thresholds for channel initiation at road drain outlets
Australia ; Forest ; Gully erosion ; New South Wales ; Precipitation ; Regression analysis ; Road ; Slope gradient ; Soil erosion ; Threshold ; Watershed
In this study the validity and usefulness of channel initiation thresholds for road runoff management has been evaluated using field data from 3 catchments in south-east Australia. Logistic regression using road area and slope gradient shows
that both variables contribute significantly to channel initiation in the Albert and Tyers River catchments, while for the Sandy Creek catchment only slope gradient is significant at the 0.05 level. The slope-area thresholds are still considered useful
and vertical profile variations and to define wave thresholds for important morphological changes. Results show that the active zone of the profile lies between 5 m above and 10.4 m below mean sea level. Based on the pattern of vertical variability, the AA
. divided the profile into 4 cross-shore sectors and calculated thresholds for significant wave height generating important morphological changes in each sector.
A method for establishing the critical threshold for aeolian transport in the field
Aeolian features ; Aeolian transport ; Arid area ; Dune ; Methodology ; Texas ; Threshold ; United States of America ; Wind erosion ; Wind speed
A mathematical expression that relates saltation activity and relative wind strength was reformulated so that threshold may be calculated from measurements of saltation activity and the mean and standard deviation of wind speed. To test the new
. It was found that during periods of active aeolian activity, threshold values could be calculated every 5 minutes.
Drainage basin sensitivity to tectonic and climatic forcing : implications of a stochastic model for the role of entrainment and erosion thresholds
Earth surface processes ; Erosion ; Erosion rate ; Model ; Precipitation ; Runoff ; Sediment transport ; Stochastic model ; Threshold ; Watershed
The A. describes a stochastic model for modelling long-term sediment transport and erosion rates that (a) incorporates an erosion threshold, and (b) captures the integrated effects of a spectrum of runoff events. Solutions are derived
and numerically tested for 3 erosion/transport formulas : The Howard-Kerby shear-stress incision model, the Bridge-Domininic sediment transport model, and a generic shear-stress sediment transport model. Results imply that non-linearity resulting from threshold
China ; City size ; Methodology ; Population size ; Rank-size distribution ; Sampling ; Threshold ; Town ; Urban population ; Urban system
This study tests three existing threshold methods (number threshold, size threshold, and urban pop-ulation percentage threshold) using China’s city system as a case study. In addition, it proposes a new method based upon the percentage threshold
of the total number of cities. The results show that Pareto exponent is sensitive to sample size and the truncation point. Furthermore, this method yields a consistent set of results over a wide range of thresholds. Finally, when using this new method
diagram and a lower boundary was clearly noticeable : it was interpreted as a threshold representing the rainfall conditions associated to landsliding which is consistent with literature thresholds. The influence of predisposing factors (such as lithology
and land use) and rainfall characteristics was investigated as well and statistical analysis revealed to be the most effective way to define a more advanced early warning system based on a set of multiple thresholds. Four thresholds corresponding to four