用风洞实验方法计算土壤风蚀量的时距问题

通过对延津县沙质壤土原状土进行风蚀风洞模拟实验，探讨了土壤风蚀量计算中的时距问题。结果表明，前人使用“风蚀模数”概念来计算土壤风蚀量会导致较大误差，原因在于同一风蚀事件中单位时间内的风蚀量随吹蚀时间的延续而递减，在风洞实验计算风蚀量时使用“累积风蚀量”概念将会有更精确的结果。     

AN EXPERIMENTAL STUDY OF INFILTRATION AND EROSION UNDER SLOPE GRADIENTS AND VEGETAL COVERS

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Turbulent entrainment at an inversion

Three separate conditions controlling the structure of the inversion are discussed. The rate of change of boundary layer temperature and the vertical gradient of potential temperature in the overlying air set the maximum limit to possible rise rates. In transient conditions, the rise of the inversion layer is sometimes dominated by turbulent transport and erosion, however this cannot continue indefinitely. The horizontal advection above the inversion can also change the relative temperature increase at the inversion, and so may partly determine inversion history.In this paper the theory of the plume-connective boundary layer has been extended to allow the plumes to erode material from the overlying stable air, and so permit study of how the boundary layer could deepen by eroding upward into the capping inversion. Only clear-air processes without condensation are included in the model described here.When the mechanism of convection is examined, it is demonstrated that, because of energetic considerations, the rate of erosion, by buoyancy generated turbulence of the overlying air down across the inversion, will not usually determine the rate of rise of the inversion, except briefly. Other effects often dominate in determining the average erosion rate. Furthermore, because of the limitations set by the buoyancy of the entrained air, sharp inversions, exceeding about 1°C, cannot be formed without the action of latent heat from evaporating droplets. An intermediate buffer layer forms in the inversion zone whenever the erosion rate is high enough to produce a temperature increase above the boundary layer, sufficient to inhibit direct entrainment.     

Transporting capacity of overland flow on plane and on irregular beds

In this paper the transporting capacity of thin flows, in the laminar and transitional flow regime, is studied. Experiments were carried out on irregular as well as on plane beds, using two totally different set-ups. The results of these two types of experiment were convergent. In both cases, sediment concentration was clearly related to grain shear velocity and unit stream power, expressed as the product of mean velocity and slope (Yang, 1973). The data agreed with those of Kramer and Meyer (1969). For a sandy bed, the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface. For laminar and transitional flows, both the unit stream power and the shear velocity are related in the same way to slope and unit discharge. The unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow. However, before a sediment transport equation for thin flows can be developed, more information is needed about the influence of the flow regime and grain size and density.     

陕西凤太矿田层控铅锌矿床古剥蚀面与古构造对成矿的控制作用

野外和室内研究表明,凤太矿田古道盆古道岭组岩层沉积结束后,曾出露水面,致使该组顶部出现不规则古剥蚀面和喀斯特地貌,为相继沉淀的矿石提供了堆积的场所。随后,由于北东向同沉积构造的反复活动,将该区分割成一系列的凹槽,同沉积构造的活动驱动深部流体上升,形成海底喷流铅锌矿床。     

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.