Search results for "erosion"
showing 10 items of 637 documents
Segmented relationships to model erosion of regression effect in Cox regression
2010
In this article we propose a parsimonious parameterisation to model the so-called erosion of the covariate effect in the Cox model, namely a covariate effect approaching to zero as the follow-up time increases. The proposed parameterisation is based on the segmented relationship where proper constraints are set to accomodate for the erosion. Relevant hypothesis testing is discussed. The approach is illustrated on two historical datasets in the survival analysis literature, and some simulation studies are presented to show how the proposed framework leads to a test for a global effect with good power as compared with alternative procedures. Finally, possible generalisations are also present…
Deducing the USLE mathematical structure by dimensional analysis and self-similarity theory
2010
The Universal Soil Loss Equation (USLE) was originally deduced by a statistical analysis of a large data set of soil loss measurements. The multiplicative structure of the model has been criticised due to the considerable interdependence between the variables. Using the soil erosion representative variables and the reference condition adopted in the USLE, the aim of this paper was to apply dimensional analysis and self-similarity theory to deduce the functional relationship among the selected variables. The analysis yielded a multiplicative equation, similar to the USLE. Therefore, this study suggested that the USLE has a logical structure with respect to the variables used to simulate the …
Soil Erosion as an Environmental Concern ... for Everyone?
2020
Nowadays, the scientific community is aware of the negative environmental impacts of soil erosion on ecosystem services. Soil erosion is one of the most important causes of land degradation because of its immediate influence of the most fertile topsoil parts. It is well-known that questions related to who, what, why, where and when soil erosion causes negative impacts must be considered by stakeholders and policymakers. However, why do the Sustainable Development Goals tell anything about soil erosion? In this keynote, we will try to show the importance to develop tools which can be used to assess soil erosion to obtain convincing results for stakeholders and policymakers. According to this…
Soil Erosion Induced by the Introduction of New Pasture Species in a Faxinal Farm of Southern Brazil
2018
The faxinal management system is an endangered agro-silvopastoral system which forms part of the local traditional management in the Paraná federal state (Brazil). Significant changes in land management since the 1970s caused farmers to look for alternatives to increase the productivity of their farms. The introduction of new pasture species is causing land degradation problems, of which soil erosion is the most important challenge. Therefore, in this study, we assessed the environmental consequences of introducing exotic pasture species, such as Brachiaria decumbens. To achieve this goal, ten erosion plots were installed with exotic and native pastures (Paspalum notatum Flügg&e…
Experiments on Longitudinal and Transverse Bedload Transport in Sine-Generated Meandering Channels
2021
Bedload grains in consecutive meandering bends either move longitudinally or across the channel centerline. This study traces and quantifies the grains’ movement in two laboratorial sine-generated channels, i.e., one with deflection angle θ0 = 30° and the other 110°. The grains originally paved along the channels are uniform in size with D = 1 mm and are dyed in various colors, according to their initial location. The experiments recorded the changes in the flow patterns, bed deformation, and the gain-loss distribution of the colored grains in the pool-bar complexes. We observed the formation of two types of erosion zones during the process of the bed deformation, i.e., Zone 1 in the foresi…
Beaches in Valencian Coast
2018
The main factors that determined the Valencian beaches characteristics are the configuration of relief structures; fluvial sediment supply; low tidal range; the predominance of low energy waves; scarcity of big storms; longshore littoral drift; and human action. There is a significant prevalence of sandy beaches. Nevertheless, both at the northern part of the Gulf of Valencia and in the structural segment, between the Cape Sant Antoni and Alicante city, pebble and gravel beaches are predominant. Most of the Valencian beaches have experienced significant morphological changes during the last decades due to the human interventions -voluntary or involuntary- in the coastal system. The implemen…
Effect of Standard Disk Plough on Soil Translocation in Sloping Sicilian Vineyards
2022
Tillage is the main force of soil redistribution in agricultural land use and has been seen as more critical than water erosion. This study aims to evaluate the effect of tillage with standard disk in vineyards. A representative study area with grapevines was selected, and 39 inter-rows were selected to test the effect of slope and forward speed. In each inter-row, a strip of soil was collected, and mixed with 2 kg of coloured sand used as a tracer, then replaced in the strip, and shallow soil tillage was performed by means of a standard disk plough. Three soil subsamples were collected along the slope every 0.30 m from the coloured strip and the sand tracer was separated from the soil and …
Predicting gully occurrence at watershed scale: Comparing topographic indices and multivariate statistical models
2020
In this study, the ability of five topographic indices to predict the gully trajectories observed in two adjacent watersheds located in Sicily (Italy) was evaluated. Two of these indices, named MSPI and MTWI, as far as we know, have never been employed to this aim. They were obtained by multiplying the stream power index (SPI) and the topographic wetness index (TWI), respectively, by the convergence index (CI). The predictive ability of the topographic indices was measured by using both cut-off independent (AUC: area under the receiver operating characteristic curve) and dependent statistics (Cohen's kappa index κ, sensitivity, specificity). These statistics were calculated also for 100 MAR…
A GIS-based approach for gully erosion susceptibility modelling: a test in Sicily, Italy
2013
The aim of this study is to analyze the susceptibility conditions to gully erosion phenomena in the Magazzolo River basin and to test a method that allows for driving the factors selection. The study area is one of the largest (225 km2) watershed of southern Sicily and it is mostly characterized by gentle slopes carved into clayey and evaporitic sediments, except for the northern sector where carbonatic rocks give rise to steep slopes. In order to obtain a quantitative evaluation of gully erosion susceptibility, statistical relationships between the spatial distributions of gullies affecting the area and a set of twelve environmental variables were analyzed. Stereoscopic analysis of aerial …
Impacts of oak deforestation and rainfed cultivation on soil redistribution processes across hillslopes using 137Cs techniques
2021
Abstract Background As one of the main components of land-use change, deforestation is considered the greatest threat to global environmental diversity with possible irreversible environmental consequences. Specifically, one example could be the impacts of land-use changes from oak forests into agricultural ecosystems, which may have detrimental impacts on soil mobilization across hillslopes. However, to date, scarce studies are assessing these impacts at different slope positions and soil depths, shedding light on key geomorphological processes. Methods In this research, the Caesium-137 (137Cs) technique was applied to evaluate soil redistribution and soil erosion rates due to the effects …