An upland soil erosion model derived from the basic principles

Starting from the basic erosion principles, an upland soil erosion model to predict soil loss by overland flow from individual storms on forested hillslopes can be derived in the form where Q_s is total soil loss for a storm event, n is roughness coefficient, x is down slope distance, K_f is soil erodibility factor, S is slope, α is slope exponent and Q is runoff. Values of n and α are to be determined for different environments and are 0·58 and 2·1 for a mixed pine forest ecosystem. A significant correlation (r = 0·933, n = 96) fits between the observed and predicted values using this expression, and the model fitting is good.     

A model of the redistribution of disaggregated soil particles by rainsplash

A model of the dispersion of splash droplets from a single raindrop impact on a sloping soil surface is combined with a theory of the entrainment of mineral particles from a disaggregated mixture in splash droplets to obtain a model of the dispersion of such particles by a raindrop impact. Stochastic modelling techniques extend this further to a model of the spatial redistribution of soil on a plot after a period of rainfall. Since the model is probabilistic and physically based it enables the incorporation of further advances in the understanding of splash erosion at all stages and can simulate the effect of the stochastic nature of rainfall and soil properties on the process. Several different situations are simulated. These include the movement of marked soil particles from point sources and the spatial patterns of erosion on a sloping plot. The model can also simulate the differential erosion of different soil particle size fractions.     

Salt marsh cliff stability in the oosterschelde

Salt marsh cliff erosion in the Oosterschelde, due to basal scour and small-scale failure, was monitored during a two-year period using reference stakes. The composite marsh cliffs have a cantilever profile. Their stability is evaluated from beam failure analysis. A model is proposed, in which the cantilever weight is taken as the motive force; the major resistive force is the tensile strength. By substituting height, undermining width and soil mechanical properties of the cliff in the model, one can identify the cliffs that are likely to fail. Salt marsh cliffs, which combine a large tensile strength due to roots at the top of the profile with a large compressive stress at the cliff base due to the sandy texture of the subsoil, display the highest resistance to beam failure. The critical cliff dimensions, observed in the field, correspond with the values calculated from the proposed model of beam failure.     

Bank erodibility of shallow sandbed streams

Cross-sections were surveyed at straight reaches of 16 sandbed streams in the midwestern U.S. Two stratigraphic horizons are found in the banks at each site, an upper cohesive unit usually composed of silt and clay, and a lower unit composed of sand. Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by toppling forward into the channel. During failure, the soil is primarily in tension rather than compression or shear. Analysis of this failure mechanism leads to a field method for measuring the tensile strength of riverbanks. Measured values of the tensile strength are not correlated with the channel geometry. Thus, the erodibility of the cohesive bank sediments does not influence the geometry of the rivers studied.     

Recent environmental changes inferred from the sediments of small lakes in Yellowstone's northern range (Engstromet al., 1991)

Sedimentation rate data of Engstromet al. (1991) were analyzed in relation to the elevation of the eight ponds studied. The ... asynchroneity of the stratigraphic changes among the lakes ... that they noted was transformed into a pattern of time-transgressive change of sedimentation rate with elevation. Sediment units representing increasing (and decreasing) sedimentation rate and accelerating (and decelerating) sediment accumulation were correlated from pond to pond, suggesting that the sediment-producing condition somehow moved upslope over time at a rate of 3.4 to >5 m yr^–1. Climatic data appear not to explain this monotonic pattern, but dendrochronological data and elk population numbers suggest that ungulate foraging patterns might. Engstromet al. (1991) concluded that ...the lake-sediment records in the northern range do not convincingly show systematic direct or indirect effects of ungulate grazing during the history of the Park. Reinterpretation of these sediment data suggests that detailed reanalysis might lead to a different conclusion.     

坡面细沟侵蚀产沙时空分布规律试验研究

利用放水冲刷试验结合稀土元素(REE)示踪技术对坡面侵蚀产沙特征及其时空变化进行了研究。结果表明:在径流冲刷下,坡面侵蚀产沙可分为三个不同的阶段并对应不同的产沙特征。其空间变化表现为,在6°、9°情况下,坡面不同坡段的相对侵蚀量沿下坡方向呈现出先减小后增大的趋势;在12°小流量情况下,坡面各坡段的相对侵蚀量与坡度较小的情况相似,当流量较大时,坡面各不同坡段的相对侵蚀量随坡长的增大而减小。但坡面最下端坡段的相对侵蚀量总是随着冲刷历时的延长而减小,其余各坡段的相对侵蚀量则呈现出缓慢的波动式上升。     

Damage to Rocks and Cementitious Materials from Solid Impact

Summary The erosion of four rock types and two cementitious materials by solid particle impact is investigated. The experimental set-up used to perform the erosion tests is briefly described. The materials are eroded predominantly by intergranular and intercrystalline fracture. For the cementitious materials, the interface between cement matrix and aggregate is of decisive importance. The power exponents for the particle velocity are estimated and found to vary between 2.59 and 3.65. A statistical fracture model is derived to discuss deviations in the particle velocity power exponent. It is further shown that the experimental results of this study confirm the erosion model of Finnie and Oh (1966); an exception is schist which shows features of plastic deformation and radial cracking during the Hertzian indentation test.     

A Breadth Averaged Numerical Model for Suspended Sediment Transport in Hooghly Estuary,East Coast of India

Sedimentation is of vital concern in the conservation, development and utilization ofour soil and water resources. The suspended sediment in estuarine waters is hazardousto navigation in estuaries, which have important ports and harbours. A breadth-averagednumerical model to study circulation and sediment transport is presented in this paper.The model is applied to Hooghly estuary, along the east coast of India. The model is fullynon-linear and uses a semi-explicit finite difference scheme to solve mass, momentum andadvection diffusion equation for suspended sediments in a vertical plane. The erosion anddeposition have been computed by empirically developed source and sink terms in thesuspended sediment equation.     

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured ¹⁰Be concentrations has been modelled using a χ² inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.     

A process‐based conversion model for caesium‐137 derived erosion rates on agricultural land: an integrated spatial approach

There is increasing recognition that ¹³⁷Cs data remain one of the few sources of spatially distributed information concerning soil erosion. However, many of the conversion models that have been used to convert ¹³⁷Cs data into soil redistribution rates failed to account for some of the key factors affecting the redistribution of ¹³⁷Cs in agricultural landscapes. The conversion model presented in this paper aims to overcome some of the limitations associated with existing models and therefore to provide more realistic estimates of soil erosion rates on agricultural land. The conversion model aims at coupling soil redistribution processes directly with ¹³⁷Cs redistribution. Emphasis is placed on the spatial representation of soil redistribution processes and the adequate simulation of tillage processes. The benefits of the presented model arise from the two‐dimensional spatial integration of mass balance models with soil erosion models. No a priori assumptions about the intensity of any soil redistribution process are necessary and the level of agreement between observed and simulated ¹³⁷Cs inventories enables us to evaluate the performance of the model. The spatial implementation and the use of fuzzy parameter sets also allow us to assess the uncertainties associated with soil erosion estimates. It was shown that an adequate simulation of tillage processes is necessary and that simplified tillage models may lead to erroneous estimates of soil redistribution. The model was successfully applied to a study site in the Belgian Loam Belt and the results indicated that tillage is the dominant process. Furthermore, the uncertainties associated with the estimation of water erosion rates were much higher than those associated with tillage, especially for depositional areas. Copyright © 2003 John Wiley & Sons, Ltd.