MACROPORE FLOW AND MASS WASTING OF GULLIES IN THE LOESS PLATEAU, CHINA     

G. V. WILSON Mingxiang XU Yunming CHEN Guobin LIU M. J. M. ROEMKENS 《国际泥沙研究》2005,20(3):249-258

Due to the extensive gullying from historically excessive erosion in the loess plateau of China, much of this region is being converted to native grass and shrub vegetation. Tunnel scour and mass wasting are important gully erosion processes resulting from preferential flow through macropores （ pores 〉 1 mm diameter）. The objective of this study is to assess the changes with time in macropore flow characteristics of soils on the Loess Plateau following conversion to grass vegetation and the associated degree of mass wasting of gully faces. Ridge areas that had been revegetated for 1 year, 6 years, and 〉 15 years following tilling, and for 6 years following contour-ditching and the adjacent gully faces were characterized for their macropore and soil matrix properties on a 50 cm by 50 cm area. The total number of macropores increased from 11.6/m^2 to 39.6/m2 from 1 to 6 years and to 51.6/m2 after 15 years of revegetation following tillage. The macroporosity increased from 0.0008 m^3/m^3 to 0.0018 m^3/m^3 from 1 to 6 years of revegetation following tillage but the lowest macroporosity （0.0005 m3/m3） was 6 years of revegetation following contour-ditching. The contourditched area had the lowest infiltration rate （95 m/d） through the soil matrix （areas without macropores） with the tilled areas having similar infiltration rates regardless of the number of years of revegetation （averaged 146 m/d）. Due to tunnel scour erosion of macropores during infiltration into the area revegetated for 1 year, pore diameters enlarged by more than 200% resulting in this condition having the highest individual macropore infiltration rates （7967 m/d）. Macropores in all other areas were stable with no tunnel scour erosion of macropores. The total capacity for infiltration through macropores increased significantly with time following revegetation. The number of macropores on the gully faces was triple （92.8/m2） and the macroporosity quadruple （0.004 m3/m3） that of the ridge surfaces. The upper gully faces exhibited 1.1 slumps m^-1 for a total soil loss of 48622 kg per ha.  相似文献   

Modeling scale-dependent runoff generation in a small semi-arid watershed accounting for rainfall intensity and water depth     

《Advances in water resources》2014

Observed scale effects of runoff on hillslopes and small watersheds derive from complex interactions of time-varying rainfall rates with runoff, infiltration and macro- and microtopographic structures. A little studied aspect of scale effects is the concept of water depth-dependent infiltration. For semi-arid rangeland it has been demonstrated that mounds underneath shrubs have a high infiltrability and lower lying compacted or stony inter-shrub areas have a lower infiltrability. It is hypothesized that runoff accumulation further downslope leads to increased water depth, inundating high infiltrability areas, which increases the area-averaged infiltration rate. A model was developed that combines the concepts of water depth-dependent infiltration, partial contributing area under variable rainfall intensity, and the Green–Ampt theory for point-scale infiltration. The model was applied to rainfall simulation data and natural rainfall–runoff data from a small sub-watershed (0.4 ha) of the Walnut Gulch Experimental Watershed in the semi-arid US Southwest. Its performance to reproduce observed hydrographs was compared to that of a conventional Green–Ampt model assuming complete inundation sheet flow, with runon infiltration, which is infiltration of runoff onto pervious downstream areas. Parameters were derived from rainfall simulations and from watershed-scale calibration directly from the rainfall–runoff events. The performance of the water depth-dependent model was better than that of the conventional model on the scale of a rainfall simulator plot, but on the scale of a small watershed the performance of both model types was similar. We believe that the proposed model contributes to a less scale-dependent way of modeling runoff and erosion on the hillslope-scale.  相似文献   

A new modeling approach for simulating microtopography-dominated,discontinuous overland flow on infiltrating surfaces     

《Advances in water resources》2015

Realistic modeling of discontinuous overland flow on irregular topographic surfaces has been proven to be a challenge. This study is aimed to develop a new modeling framework to simulate the discontinuous puddle-to-puddle (P2P) overland flow dynamics for infiltrating surfaces with various microtopographic characteristics. In the P2P model, puddles were integrated in a well-delineated, cascaded drainage system to facilitate explicit simulation of their dynamic behaviors and interactions. Overland flow and infiltration were respectively simulated by using the diffusion wave model and a modified Green–Ampt model for the DEM-derived flow drainage network that consisted of a series of puddle-based units (PBUs). The P2P model was tested by using a series of data from laboratory overland flow experiments for various microtopography, soil, and rainfall conditions. The modeling results indicated that the hierarchical relationships and microtopographic properties of puddles significantly affected their connectivity, filling–spilling dynamics, and the associated threshold flow. Surface microtopography and rainfall characteristics also exhibited strong influences on the spatio-temporal distributions of infiltration rates, runoff fluxes, and unsaturated flow. The model tests demonstrated its applicability in simulating microtopography-dominated overland flow on infiltrating surfaces.  相似文献   

包气带气压计算及其影响入渗的模拟     

沈铁元 《沙漠与绿洲气象(新疆气象)》2012,6(2):8-12

降雨入渗过程中土壤内空气压力的变化影响到土壤的入渗能力,当包气带气压大于地球表面大气压后会对入渗水流起到顶托的作用。本文根据包气带气压变化的观测结果理论分析了包气带气体运动的一般规律,并以此为依据假设气体外逸函数,然后推导了土壤包气带中气压变化的计算公式,并模拟分析了考虑包气带气压前后对入渗过程的影响：均匀降雨条件下考虑包气带气压后开始积水时间提前,入渗率平均减小27%,有时减小程度可达32%;渗透总量在初期相同,但到压缩外逸阶段后开始出现差别,时间越长,差距越大,包气带气压的减渗作用愈显著,24小时时入渗总量平均减小约20% 。  相似文献   

An experimental study of the water transfer through confined compacted GMZ bentonite   总被引：6，自引：0，他引：6  

W.M. Ye  Y.J. Cui  L.X. Qian  B. Chen 《Engineering Geology》2009,108(3-4):169-176

GMZ bentonite has been considered as a possible material for engineered barrier in the Chinese program of nuclear waste disposal at great depth. In the present work, the hydraulic conductivity of this bentonite was determined by simultaneous profile method. A specific infiltration cell equipped with five resistive relative humidity probes was designed for this purpose. The water retention properties were studied under both confined and unconfined conditions; the results show that at high suctions (> 4 MPa) the water retention capacity is independent of the confining condition, and by contrast, at low suctions (< 4 MPa) the confined condition resulted in significant low water retention. Furthermore, the microstructure was investigated at mercury intrusion porosimetry (MIP) and Environmental Scanning Electron Microscope (ESEM) in different states: on oven-dried powder, bentonite slurry, as-compacted and wetted samples. It has been observed that the soil powder is constituted of aggregates of various sizes; these aggregates are destroyed by full saturation at a water content equal to the liquid limit; compaction at the initial water content of 11–12% and a dry density of 1.7–1.75 Mg/m³ led to a microstructure characterized by a dense assembly of relatively well preserved aggregates; saturation of the compacted sample under constant volume condition defined a non-homogeneous microstructure with the presence of well preserved aggregates. This non-homogeneous microstructure would be due to the non uniform distribution of the generated swelling pressure within the soil sample upon wetting. The hydraulic conductivity determined has been found decreasing first and then increasing with suction decrease from the initial value of about 80 MPa to zero; the decrease can be attributed to the large pore clogging due to soft gel creation by exfoliation process, as observed at ESEM.  相似文献   

Correlation of unsaturated soil and dielectric property for monitoring of subsurface characteristics: development of unsaturated dielectric mixing models and its application     

Man-Il Kim  Byung-Gon Chae  Gyo-Cheol Jeong 《Environmental Geology》2009,57(1):49-58

The behavior due to rainfall infiltrating the ground plays a role in landslides, groundwater recharge and various other ground responses. Most of these geotechnical behaviors have a correlation between soil pore space and soil volumetric water content in the unsaturated and saturated soil porous media. Therefore, the soil porosity associated with soil pores and the distribution of volumetric water content are significantly important hydrological characteristics. In the case of shallow slope failure such as landslide, the infiltration activity due to the connectivity of soil pore spaces in a porous media is induced. Slope failure may be attributed to the effect of a wetting front with the slope due to liquid infiltration, which changes the volumetric water content, soil matric suction and shear strength of the slope. This study was performed with an unsaturated injection test using a frequency domain reflectometry (FDR) dielectric device which measures the dielectric constant of unsaturated soil and the study then proposed the unsaturated dielectric mixing models to calculate soil porosity and effective porosity of unsaturated soils. From the experimental results the ratio of effective porosity to porosity of soils are measured in a range of 70–85%. These experimental results show a decrease of about 5–10% for unsaturated soil compared to the ratio of effective porosity to porosity of saturated soil. The infiltration passages of tracer material are restricted within the pore connectivity in the unsaturated soil which is caused by dead-pores in the soil. Using the FDR device and the unsaturated dielectric mixing models, we can consider the acquisition of physical properties to detect the infiltration activity, the response of the dielectric constant along with the injected tracer and hydrological parameters for the unsaturated soil porous media.  相似文献   

Textural development in sulfide-matrix ore breccias in the Voisey's Bay Ni-Cu-Co deposit,Labrador, Canada     

《Ore Geology Reviews》2017

Magmatic Ni-Cu sulfide ores at Voisey’s Bay contain complex assemblages of extremely heterogeneous rocks. These range from polymict breccias, with rock fragments in sulfide-rich and/or sulfide-poor matrices, to heterogeneous “vari-textured” gabbros with rapid short range variations in grain size and content of hydrous phases. Rock fragment populations in the breccias include endogenous olivine gabbros (cumulate and non-cumulate) and cumulate peridotites along with extensively depleted plagioclase-hercynite gneisses interpreted as restites from extensive partial melting of country rock quartzo-feldspathic paragneisses. Using a combination of desk-top microbeam XRF mapping at cm scale and 3D X-ray tomography, we show that both sulfide-poor and sulfide-rich breccias comprise heterolithic assemblages of clasts within a matrix of olivine gabbro. This matrix is characterised by an interconnected 3D framework of plagioclase crystals, highly variable in grain size at mm to cm scale, with interstitial olivine and poikilitic clinopyroxene, and is texturally indistinguishable from clast-free olivine gabbro. Sulfide forms interconnected networks at cm to dm scale and possibly larger. Much of the plagioclase developed by outgrowth from the margins of paragneiss xenoliths when the porosity was occupied by silicate melt. The observed range of textures is explained by a model of percolation of molten sulfide through variably crystalline inter-clast matrix, displacing the silicate melt to leave the refractory plagioclase-olivine or in some cases plagioclase-only component, now entirely within a sulfide matrix. The process is analogous to that believed to have formed interspinifex ore in komatiite-hosted deposits. Biotite rims on plagioclase enclosed in sulfide are interpreted as the result of reaction between plagioclase, olivine and a hydrous component derived from the sulfide melt itself, with a possible component of migrating residual silicate melt wicking along sulfide-silicate contacts. This sulfide infiltration model offers an alternative to the current model for upward emplacement of a slurry of silicate melt, sulfide melt and breccia fragments as a late stage injection into the dyke-sill complex. The preserved range of textures is interpreted as being due to gravity-driven percolation of sulfide liquid through a pre-existing partially molten intrusion breccia. In this model, the breccia serves as a physical trap site, accumulating downward migrating sulfide liquid. However, the invariable close mutual association of sulfide and rock fragments at Voisey’s Bay implies a common derivation.  相似文献   

Estimating the effects of spatial variability of infiltration on the output of a distributed runoff and soil erosion model using Monte Carlo methods     

A. P. J. De Roo  L. Hazelhoff  G. B. M. Heuvelink 《水文研究》1992,6(2):127-143

Monte Carlo procedures were used to evaluate the effects of spatial variations in the values of the infiltration parameter on the results of the ANSWERS distributed runoff and erosion model. Simulation results obtained were compared with measured values. Field infiltration measurements indicated spatial correlation at much smaller distances than the size of an element. Therefore, at first only the error of the mean had to be taken into consideration for block infiltration rates. Consequently, not only single hydrographs were produced, but also error bands. Secondly, nine other hypothetical spatial correlation structures were also evaluated using Monte Carlo methods. in particular at low nugget variances, increasing spatial correlation of infiltration resulted in increasing coefficients of variation in model outputs. In general, rainstorms with low rainfall intensities were more difficult to simulate accurately than extreme events with high rainfall intensities. This is explained by the greater influence of the infiltration uncertainties at low rainfall intensities.  相似文献   

冀东高级变质作用中流体演化   总被引：8，自引：2，他引：8  

刘树文 《岩石学报》1996,12(1):48-58

冀东太古宙麻粒岩相变质岩石的结构、矿物组合和反应关系反映了其变质作用经历了峰前、峰期、峰后和退化变质四个阶段。通过平衡热学计算和流体包裹体研究获得了各变质阶段Ｐ－Ｔ条件和流体性质。峰前阶段的变质条件为６５０－７３５℃，０．５－０．７ＧＰａ，平衡变质流体中水的摩尔分数是０．４９－０．９５。峰期阶段为８１２－８６０℃，０．８－１．２ＧＰ，ＸＨ２ｏ从０．４９－０．９５下降到０．３２－０．４９，捕获的流体  相似文献   

Analysis of water movement in paddy rice fields (I) experimental studies   总被引：2，自引：0，他引：2  

Shih-Kai Chen  Chen Wuing Liu   《Journal of Hydrology》2002,260(1-4):206-215

For the purpose of increasing the amount of ground water recharge, we investigated the hydraulic characteristics of water infiltration in a flooded paddy rice field in Ten-Chung, Chung-Hwa county, Taiwan. Experimental results based on mini-tensiometers and double ring infiltrometer measurements indicated that the least permeable layer occurred at the interface of the puddled topsoil and non-puddled subsoil. The average thickness of this layer was about 7.5 cm and saturated hydraulic conductivity ranged from 0.034 to 0.083 cm/day. Vertical infiltration flow was saturated within the plow sole layer and became unsaturated in the subsoil below the plow sole layer. The hydraulic conductivity of the subsoil, 20–30 times greater than that of the plow sole layer, revealed that the subsoil was more permeable than the plow sole layer. In situ measurements also demonstrated that breakage of the plow sole layer increased infiltration rate by a factor of 3.7. Increasing ponded water depth from 6 to 16 cm increased infiltration 1.5 fold. It is suggested that using the fallow paddy rice fields without puddling is a feasible way to enhance groundwater recharge, but for cultivated paddy rice fields, breaking the plow sole needs further study in terms of its recoverability and because of the potential contamination of the shallow aquifer by agrochemicals. The experimental data can be applied in numerical simulation models to quantify detailed water movement mechanisms and accurately estimate the amount of ground water recharge in paddy rice fields.  相似文献