Author: D. L. Hutchison
Publisher:
ISBN:
Category : Soil erosion
Languages : en
Pages : 95

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 331

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Author: R. N. Croad
Publisher:
ISBN:
Category : Clay soils
Languages : en
Pages : 366

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A theoretical model of erosion was developed in which it is proposed that the entrainment of fragments of clay is caused by the negative pressure fluctuations which are associated with the turbulent 'burst' cycle (the origin of turbulence in the flow). An analogy is drawn between the erosion process and processes which occur in chemical reactions. An application of the erosion model to the sheet erosion problem is also considered.

Author: Johan C. Winterwerp
Publisher: Elsevier
ISBN: 0080473733
Category : Science
Languages : en
Pages : 577

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This book is an introduction to the physical processes of cohesive sediment in the marine environment. It focuses on highly dynamic systems, such as estuaries and coastal seas. Processes on the continental shelf are also discussed and attention is given to the effects of chemistry, biology and gas.The process descriptions are based on hydrodynamic and soil mechanic principles, which integrate at the soil-water interface. This approach is substantiated through a classification scheme of sediment occurrences in which distinction is made between cohesive and granular material. Emphasis is also placed on the important interactions between turbulent flow and cohesive sediment suspensions, and on the impact of flow-induced forces on the stability of the seabed. An overview of literature on cohesive sediment dynamics is presented and a number of new developments are highlighted, in particular in relation to floc formation, settling and sedimentation, consolidation, bed failure and liquefaction and erosion of the bed. Moreover, it presents a summary on methods and techniques to measure the various sediment properties necessary to quantify the various parameters in the physical-mathematical model descriptions. A number of examples and case studies have been included.

Author: Hicham Salem
Publisher:
ISBN:
Category :
Languages : en
Pages :

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A set of solutions to the cohesive soil erosion problem were developed through this study. A first device, the Erosionometer, was developed to perform a quick and reliable test to determine the critical shear stress of soils. The Erosionometer is based on physical shearing of the soil surface and has been calibrated through comparison with piston flume measurements of critical shear stress for entrainment of various fluvial bed sediments. This device is portable, easy to deploy in the field and in the laboratory and allows engineers and researchers to cover a sizeable terrain by performing many tests in a short timeframe, with immediate results. A modification to the Erosionometer was made to allow for subjecting the soil sample to a pressure differential while testing for critical shear stress. The added functionality is intended for investigating the effect of pressure gradient on the erodibility of cohesive soils by allowing for the erosion test to be conducted under a high pressure head while the other face of the sample (away from the flow) is maintained at zero head. Testing demonstrated that a positive pressure gradient on the eroding side (high pressure on flow side) can significantly increase the critical shear stress of cohesive soils, which is in line with other research available in the literature. The results show a simple linear relation between pressure differential and critical shear stress. Practical implications of these results are discussed. A second device, the Erosion Rate Meter, or ERM, was developed to test cohesive soil samples to determine the rate of erosion under various levels of bed shear stress. This device, while being portable and fast to setup and run, is a very realistic simulation of the flow-bed interaction and allows for a direct measurement of bed shear stress on the soil sample and a precise measurement of the erosion rate. An obvious outcome of using the ERM is the easy development of erosion rate vs. bed shear stress relationships or models to characterize the different soils for design projects or further research. Of the 16 tested cohesive soils, all but two demonstrated a linear relation between erosion rate and bed shear stress. The testing systems and methods developed in this research provide a comprehensive solution to the erodibility of cohesive soils from investigation to design. Significant improvements are achieved over existing systems in the speed, reliability, accuracy, and cost of estimating the erodibility of cohesive soils.

Author: Yaping Shao
Publisher: Springer Science & Business Media
ISBN: 1402088957
Category : Science
Languages : en
Pages : 459

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Wind erosion occurs in many arid, semiarid and agricultural areas of the world. It is an environmental process in?uenced by geological and climatic variations as well as human activities. In general, wind erosion leads to land degradation in agricultural areas and has a negative impact on air quality. Dustemissiongeneratedbywinderosionisthelargestsourceofaerosolswhich directly or indirectly in?uence the atmospheric radiation balance and hence global climatic variations. Strong wind-erosion events, such as severe dust storms, may threaten human lives and cause substantial economic damage. The physics of wind erosion is complex, as it involves atmospheric, soil and land-surface processes. The research on wind erosion is multidisciplinary, covering meteorology, ?uid dynamics, soil physics, colloidal science, surface soil hydrology, ecology, etc. Several excellent books have already been written about the topic, for instance, by Bagnold (1941, The Physics of Blown Sand and Desert Dunes), Greeley and Iversen (1985, Wind as a Geological P- cess on Earth, Mars, Venus and Titan), Pye (1987, Aeolian Dust and Dust Deposits), Pye and Tsoar (1990, Aeolian Sand and Sand Dunes). However, considerable progress has been made in wind-erosion research in recent years and there is a need to systematically document this progress in a new book.

Author: Irving S. Dunn
Publisher:
ISBN:
Category : Erosion
Languages : en
Pages : 212

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Author: Peter Brian Hairsine
Publisher:
ISBN:
Category : Soil erosion
Languages : en
Pages : 574

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Book Description
Abstract: A new model of the erosion by water of cohesive soils is developed using physical principles. The theoretical framework which is developed recognises the changing nature of the eroding surface of a soil. Raindrop impact and overland flow are considered to act upon a soil surface so removing soil from the cohesive original (or parent) soil. Once this soil enters the overland flow, either as aggregates or primary particles, it is considered to return to the soil bed, from which it may be re-removed. The development of a deposited layer makes it necessary to distinguish between processes removing sediment from the original soil and those processes removing the deposited layer. This layer, being formed by the relatively gentle action of deposition during the current erosion event, is presumed cohesionless. The physical properties of the original soil and the deposited layer are considered to be very different.--The development of two experimental apparatus, a rainfall/runoff simulator and a settling tube for the measurement of aggregate settling velocities, is first described. Experimental investigations, using these apparatus, and field observations to inform the description of the erosion and deposition processes, are then presented. The processes by which rainfall impact removes sediment from the original soil and the deposited layer are termed rainfall detachment and rainfall re-detachment respectively. Initially, descriptions of these processes in the presence of deposition, are combined in a model describing net rainfall detachment when removal of sediment from the flow bed by overland flow is not occurring. The developriient of the deposited layer is considered both quantitatively and qualitatively. The solution of the equation describing mass conservation is then given for the equilibrium situation when the mass of the deposited layer, and therefore the sediment concentration, is constant with respect to time.-- The processes by which overland flow removes sediment from the original soil and the deposited layer are termed entrainment and re-entrainment. The work done by the process of entrainment is considered to be done wholly against the cohesive strength of the original soil. In contrast to the process of entrainment, the work done in re-entraining sediment from the deposited layer is considered only to be done against gravity. The resulting description of these processes is then combined with the previous descriptions of rainfall detachment, rainfall re-detachment and deposition and with the equation describing the conservation of mass of sediment within any arbitary number of size (or settling velocity) classes. A plane geometry model Is developed in which the surface water flow is considered to be uniformily distributed across a plane slope on which all processes act. When the mass of the deposited layer is steady, two possible forms of equilibrium are shown to exist. When the coverage of the original soil by deposited layer is partial, the sediment concentration is limited by the removal of the cohesive original soil by entrainment and rainfall detachment, in the presence of deposition. This situation is termed 'source limiting' and is shown to provide a lower limit to sediment concentration. When the coverage of the deposited layer is complete so that entrainment and rainfall detachment of the original soil are considered not to occur, then the ability of the erosive agents to re-entrain and re-detach sediment in the presence of deposition limits sediment concentration. This situation, termed 'transport limiting', is shown to provide a practical upper limit to sediment concentration.--This plane geometry flow model is followed by a revised model in which all processes are considered to occur but the flow of water on a plane surface is modified by the formation of rills. In this 'detailed geometry model' the spatial distribution of the erosive agents is shown to have a marked influence on the resulting processes and sediment concentrations. A potential description of the sediment transport across a change in land slope is also developed.-- Finally, a discussion of this new modelling approach is presented in which the conceptual developments of this thesis are considered and future developments are suggested. This discussion also includes a comparison of the outcomes of this new work with similar erosion models.

Author: Dirk Berghager
Publisher:
ISBN:
Category :
Languages : en
Pages : 63

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Author: J.-L. Briaud
Publisher:
ISBN: 9780309480758
Category : Soil erosion
Languages : en
Pages : 327

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TRB's National Cooperative Highway Research Program (NCHRP) has released NCHRP Research Report 915: Relationship Between Erodibility and Properties of Soils, which provides reliable and simple equations quantifying the erodibility of soils based on soil properties. The report presents a detailed analysis of the issue. In addition, the project that developed the report also produced a searchable spreadsheet that uses statistical techniques to relate geotechnical properties to soil erodibility. The spreadsheet, NCHRP Erosion, includes a searchable database that includes compiled erosion data from the literature review and a plethora of erosion tests. It contains equations which may be used to estimate the erosion resistance of soil and determine whether erosion tests are needed.