Severe Erosion (severe + erosion)

Distribution by Scientific Domains

Selected Abstracts

Design of an estimator of the kinematics of AC contactors

Jordi-Roger Riba Ruiz
Abstract This paper develops an estimator of the kinematics of the movable parts of any AC powered contactor. This estimator uses easily measurable electrical variables such as the voltage across the coil terminals and the current flowing through the main coil of the contactor. Hence, a low cost microcontroller would be able to implement a control algorithm in order to reduce the undesirable phenomenon of contact bounce, which causes severe erosion of the contacts and dramatically reduces the electrical life and reliability of the contacts. To develop such an estimator is essential to have at our disposal a robust model of the contactor. Therefore, a rigorous parametric model that allows us to predict the dynamic response of the AC contactor is proposed. It solves the mechanic and electromagnetic coupled differential equations that govern the dynamics of the contactor by applying a Runge,Kutta-based solver. Several approaches have been described in the technical literature. Most of them are based on high cost computational finite elements method or on simplified parametric models. The parametric model presented here takes into account the fringing flux and deals with shading rings interaction from a general point of view, thus avoiding simplified assumptions. Copyright 2008 John Wiley & Sons, Ltd. [source]

Quantitative evaluation of strategies for erosion control on a railway embankment batter

Y. Gyasi-Agyei
Abstract Strategies for erosion control on a railway embankment batter (side slope) are quantitatively evaluated in this paper. The strategies were centred on control (,do nothing' treatment), grass seeding, gypsum application, jute mat (an erosion control blanket) placement and planting hedgerows of Monto vetiver grass. Rainfall and runoff were monitored at 1 min intervals on 10 m wide embankment batter plots during 1998 and 1999. Total bedload and suspended sediment eroded from the plots were also measured but only for a group of storm events within sampling intervals. It has been demonstrated that vetiver grass is not cost-effective in controlling erosion on railway batters within Central Queensland region. Seeding alone could cause 60% reduction in the erosion rate compared with the control treatment. Applying gypsum to the calcium-deficient soil before seeding yielded an additional 25% reduction in the erosion rate. This is the result, primarily, of 100% grass cover establishment within seven months of sowing. Therefore, for railway embankment batter erosion control, the emphasis needs to be on rapid establishment of 100% grass cover. For rapid establishment of grass cover, irrigation is necessary during the initial stages of growth as the rainfall is unpredictable and the potential evaporation exceeds rainfall in the study region. The risk of seeds and fertilizers being washed out by short-duration and high-intensity rainfall events during the establishment phase may be reduced by the use of erosion control blankets on sections of the batters. Accidental burning of grasses on some plots caused serious erosion problems, resulting in very slow recovery of grass growth. It is therefore recommended that controlled burning of grasses on railway batters should be avoided to protect batters from being exposed to severe erosion. Copyright 2001 John Wiley & Sons, Ltd. [source]

Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang-nga Province, southwestern Thailand

ISLAND ARC, Issue 3 2010
Shigehiro Fujino
Abstract Measurements of thickness and grain size along flow-parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer-wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low-relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland. [source]

Water use (and abuse) and its effects on the crater-lakes of Valle de Santiago, Mexico

Javier Alcocer
Abstract Most Mexicans live in the arid and semiarid regions that represent two-thirds of the Mexican territory, where water is scarce. Natural, as well as human, causes are favouring the degradation of Mexican lakes. There is a clear need to develop and implement sustainable water-use programmes at a catchment scale. However, the accelerated degradation rate of the Mexican lakes means that there will not be enough time to perform whole-basin evaluations to establish sustainable water-use programmes before the lakes dry up. The case of the Valle de Santiago crater-lakes clearly illustrates the declining trend that Mexican inland aquatic resources follow. Vegetation clearance, overgrazing, abatement of phreatic waters and salinization have induced severe erosion and overall desertification (land degradation) in the basin for what, it seems, a long time (i.e. prehispanic times). In this way, human activities could be provoking at least the following negative consequences: a hotter and drier local climate, water scarcity, dust storms and soil salinization. The aquatic (surface and groundwater) resources of the Valle de Santiago basin have been seriously threatened. Two of the four crater-lakes have already dried up and phreatic mantle abatement reaches up to 2.5 m per year. In spite of these facts, no sustainable water-use programme has been established yet. The future scenery of this Mexican basin looks alarmingly like many other basins in the central and northern Mexican territories. [source]

Debunking the myth of overgrazing and soil erosion

K. Rowntree
Abstract What is overgrazing? Does it cause soil erosion? The recent debate from the ecological literature is reviewed as background to the debate on overgrazing and soil erosion. This debate stresses the need to view dryland grazing systems as dynamic ecosystems driven more by rainfall events than by livestock numbers. The case for soil erosion is then examined. Two case studies from communal rangelands in the Eastern Cape, South Africa, have cast doubts on the conventional wisdom that overgrazing leads to soil erosion. The first, a study of historical land-use change and erosion in a communal area, showed that the most intense erosion, taking the form of steeply dissected badlands, was associated with cultivated land that had been abandoned and reverted to grazing from the 1960s onwards. Such severe erosion was generally absent from land that had been under grazing since the 1930s. The second study demonstrated that erosion rates from communal grazing lands (,overgrazed') were only slightly higher than those from land under ,optimal' grazing, that is grazing at a level considered not to exceed the carrying capacity of the land. These results support the ecologist's contention that communal grazing systems do not necessarily degrade the range condition relative to management systems based on a notional carrying capacity. Copyright 2004 John Wiley & Sons, Ltd. [source]

Environmental change and adaptation in degraded agro-ecosystems: the case of highland Madagascar

AREA, Issue 3 2010
Jon Unruh
While the view that the poorer agricultural populations in developing countries will be at the forefront of negative consequences due to environmental change is widely accepted, this perspective must become considerably more nuanced in order to recognise and take advantage of emerging opportunities for realistic adaptation. This paper presents a case from Madagascar that suggests adaptation opportunities involve more than looking for alternatives to what are presently perceived to be negative socio-ecologic processes. In Madagascar the severe erosion occurring on the deforested central plateau actually appears to create, over time, opportunities for increased food security and environmental management compared with uneroded portions of the same landscape. The paper proposes that while concern and action are needed to attend to the problems that the poor of the developing world will face due to impacts from environmental change, the repercussions of such change on agricultural systems also need to be looked at in ways that involve recognising the local and aggregate potential opportunities that they may present in certain systems, in order to realise the prospects for adaptation. [source]