Environmental degradation | EPFL Graph Search

Environmental degradation is the deterioration of the environment through depletion of resources such as quality of air, water and soil; the destruction of ecosystems; habitat destruction; the extinction of wildlife; and pollution. It is defined as any change or disturbance to the environment perceived to be deleterious or undesirable. Environmental concerns can be defined as the negative effects of any human activity on the environment. The biological as well as the physical features of the environment are included. Some of the primary environmental challenges that are causing great worry are air pollution, water pollution, natural environment pollution, rubbish pollution, and so on. Environmental degradation is one of the ten threats officially cautioned by the High-level Panel on Threats, Challenges and Change of the United Nations. The United Nations International Strategy for Disaster Reduction defines environmental degradation as "the reduction of the capacity of the environm

Fonctionnement hydrique de différents types de placages sableux dans le sahel burkinabè

Dial Niang

The study was performed in the Sahelian part of Burkina Faso. The country is subject to difficult climatic conditions, a strong demographic growth and a continuous decrease in soil fertility. The resulting degradation affects the processes which govern ecological systems and leads, on the long run, to a modification of the ecosystems. This is particularly the case of the eolian formations, the only ecological units susceptible of being useful in the area, since they present good infiltration capacity and support the main part of the vegetation. Field measurements (rainfall, runoff, saturated hydraulic conductivity, bulk density, hydraulic conductivity function, soil water content and pressure head) have been done to asses the impacts of the environmental degradation on the hydrodynamic behavior of these formations. Within this context, an experimental device made of seven measurement sites has been installed in three contrasting zones. The results show significant differences in the hydrodynamic behavior of the soils, according to their surface properties. On one hand, the sites located on an erosion crust as well as on a drying crust in transition towards an erosion crust, are characterized by a low infiltration capacity which favors runoff. The quantity of infiltrated water is very low when compared to total precipitation. Water is stored near the soil surface (in the first 30 cm) favoring evaporation in the days following rainfall events. Thus, little water is available for plants. The resulting water stress causes a weak density, or even complete absence of plants which have difficulties to colonize such surfaces. Surface runoff is favored with runoff coefficients ranging from 50 to 80 %. On the other hand, the sites situated on drying crusts are characterized by good hydraulic conductivity and infiltration capacity. The storage of water in the root zone is more important. Water flows deeper into the soil and, occasionally, drains at the reference depth of 50 cm. The runoff coefficients were found to be lower than in the other sites (30 to 40 %). This differentiated behavior is one of the main factors affecting the formation of different landscapes in the area through the existence of a relationship between soil surface properties, the type of landscape and the ratio runoff/infiltration. The sites located on an erosion crust and those in transition towards an erosion crust behave like impluviums, while those situated on drying crusts are more favorable to infiltration. Observation of the evolution of the hydraulic properties of the soil surface shows a progressive alteration that frequently leads to strongly degraded mediums unfavorable to plants. Control and rehabilitation methods considered in the study, namely "restoration" and "mise en défens" have only partial and time-limited effects; they do not make it possible to stop durably degradation or to favor rehabilitation. Among the other measures assessed on the INERA plots, only the restitution to the soil of the beforehand mown plants causes an improvement of the soil surface properties; the restitution causes the formation of an important macroporal system favoring water infiltration and circulation in the soil. The effects of those different measures occur mainly in the first years after their introduction and concern especially vegetation regeneration, soil protection against degradation factors, improvement of hydrodynamic soil properties, reduction of runoff and erosion. They make it possible to slow down soil degradation, but not to stop it definitively. Within this context, proposals of further studies focussed on other measures to control and rehabilitate degraded areas have been suggested, taking into account the specificity of the sahelian zone, the endogenous knowledge of the agro-pastors, as well as socio-economic and ecological conditions.

EPFL2006

Thermodynamic and kinetic degradation reactions of organic substances in groundwater modelled with PHREEQC

Johann Jakob Holch

Aim of this diploma thesis is to approach to kinetic modelling of subsurface hydrochemistry with the program code phreeqc. The reaction considered is the degradation of organic mass and its concomitant reactions. Phreeqc is a program for thermodynamical based equilibrium calculations of geo- and hydrochemistry. Although the degradation of organic matter, and the associated reduction reactions due to the oxidation of organic matter, can be modelled with phreeqc, it does not account for kinetically controlled reactions, whose characteristic feature is the dependency of time. This study focuses on the state of the art of environmental modelling, the thermodynamical based calculation of the degradation of organic matter and on two mathematical approaches to model bacterial degradation of a contaminant, the Monod equation and the Michaelis-Menten approach. Sensitivity analyses of the respective models runs were done. As a result one can see, that the redox chemistry of a natural water depends strongly on the abundance of oxygen and nitrate and, as a matter of course, on the abundance of organic matter. Considering bacterial activity within the degradation process, two basic mathematical formulations have been stated. The Monod equation and the Michaelis-Menten formulation were implemented in a BASIC interpreter in PHREEQC. The sensitivity analyses show, that that a accurate determination of the parameters in laboratory or field is essential. The coupling of kinetically controlled reactions and thermodynamical based equilibrium calculations might lead to auspicious hydrochemical modelling capabilities.

2008

Comportement du ballast sous l'action du bourrage et du trafic ferroviaire

Chiara Paderno

The geometry of the railway track is degraded under traffic load, and must be maintained periodically. This degradation is due to the arrangement of ballast particles under loads and vibrations, which results into irreversible plastic settlements. Tamping is a procedure of maintenance, used to restore the correct geometrical position of the ballasted tracks. However, the penetration of the vibrating tines into the ballast causes an increase in the fine particles content by rupture of the edges of the grains and leads to a progressive degradation of the ballast and thus to a loss of its mechanical properties. The main consequence is that the interval between two tamping operations decreases, along with the long-term effectiveness of the process. This vicious circle can be broken only by ballast renewal. Ballast and geometry maintenance represent 40 to 50% of the total railway maintenance budget during lifetime. The goal of this research is a better understanding of ballast degradation and the development of a tool to evaluate the effectiveness of the track tamping, according to the ballast condition and the infrastructure stiffness. This knowledge will make it possible to decrease the destroying effects of tamping over ballast and, consequently, increase the durability of track geometry and ballast. A full-scale laboratory study has been done on ballasts and infrastructures of different qualities. The dynamic loading of freight trains is simulated with a big hydraulic actuator, while the deformations of the track and his infrastructure are continuously measured. The accelerated loading corresponds to a period of 20 years of traffic operation on a high loaded line. Empirical settlement laws are written, based on the traffic results. Tamping process is performed with a special machine, which was built by purpose. The parameters to regulate tamping process can be controlled. The whole process and the equipment are completely instrumented, in order to control and measure several parameters in real time. The evolution of the ballast behaviour is analysed with the measurement of the bearing modulus. Plate load tests are performed under specially equipped sleepers, after each traffic cycle and tamping. The parameters of a new tamping are tested. The short and long-term effects on ballast are analysed and discussed. A two-dimensional finite element model has been applied to simulate the response of the ballast layer under traffic loading, and the development of settlements. Ballast at different degradation levels is studied. The influence of the subgrade stiffness is also taken in account. The elastoplastic Hujeux behaviour law is applied, in order to study the cyclic plasticity. Results are presented and the critical zones, which show the most plastic behaviour, are identified. A phenomenological model is also developed to analyse separately the effects of traffic loading and track tamping on ballast behaviour and degradation. This analysis is based on a backcalculation approach, and is performed on a 3-D finite elements model of the track. The Young modulus of the ballast and the infrastructure layers in situ is calculated by iteration. Along with the traffic simulation, the evolution of the ballast elastic modulus is measured. A comparison between two sections with different infrastructures is done.

EPFL2010