Some rainfall-related thresholds for erosion and sediment yield in the upper Yangtze River basin   总被引：1，自引：0，他引：1  

Jiongxin Xu 《Environmental Geology》2009,56(6):1183-1192

This study examines rainfall thresholds for erosion and sediment yield in the upper Yangtze River basin. Sediment reduction effects of soil conservation measures depend on the magnitudes of rainstorm. When the latter is less than a critical threshold, sediment reduction effects of soil conservation measures are positive; when this magnitude is exceeded, the effect is negative. An analysis based on data from the Jialingjiang River shows that the sediment reduction by soil conservation measures increased with annual precipitation to a peak, and then decreased to a negative value. The annual precipitation at the peak and zero values of sediment reduction are 970 and 1,180 mm, respectively, which can be regarded as two thresholds. Annual precipitation at the zero-value of sediment reduction has a return period of 25 years. In general, the design standard of soil conservation works in China is related with rainstorms with return periods of 10–20 years. When the magnitude of rainstorm exceeds this, the soil conservation works may be partly or totally destroyed by rainstorms, and the previously trapped sediment may be released, resulting in a sharp increase in sediment yield. It was also found in the lower Jinshajiang River that when annual precipitation exceeds 1,050 mm or high-flow season precipitation exceeds 850 mm, the annual sediment yield increased sharply. These can also be regarded as key rainfall thresholds for erosion and sediment yields. When precipitation is less than the two thresholds, dominant erosion types are sheet, rill and gully erosions. When precipitation crosses the two thresholds, debris flows may occur more frequently. As a result, the previously stored loose sediment is released and sediment yield increases sharply.  相似文献   

Soil and plant composition in the Noun river catchment basin,Western Cameroon: a contribution to the development of a biogeochemical baseline   总被引：1，自引：0，他引：1  

Clémentine Njofang  Jörg Matschullat  Akoa Amougou  Jean Pierre Tchouankoué  Hermann Heilmeier 《Environmental Geology》2009,56(7):1427-1436

Soils and selected edible plants of the Noun river catchment basin of western Cameroon were sampled to investigate the distribution of trace elements, based on the preliminary idea of unusual anomalies. Analytical techniques for trace elements included ICP-AES, GF-AAS, and ICP-MS. Further soil analyses comprised the mineralogy and contents of the biogenic elements carbon, nitrogen and sulphur (CNS). The trace element concentrations in the soils reflect those of the lithogeochemical background of the pluto-volcanic rocks of the region. This is consistent with the results from the mineralogical analyses and physicochemical parameters such as pH, taken in the field, which also do not suggest any geochemical anomaly. Most trace elements analyzed in the plants showed concentrations that reflect those of the soils (Al, Fe, Ti, and Rb). However, some trace elements were enriched in the plants as compared to the soils, such as Zn, Cu, Cd, Mo (excluding yam), Ni (peanut), Ba (peanut), Sr (peanut, bean), and B. Trace elements such as As, Cr, V, and Se were not bioavailable for all the analyzed plants. Besides, trace elements such as Cu, Zn, Mo, Fe, Al, Ni, B, Ti, Rb, Cs, and Ba were in the range of phytotoxicity and reached or exceeded human food tolerance level (Cu). The plants with seeds showed a higher absorption of trace elements compared to plants with tubercles.  相似文献   

Characterization of insolubilized humic acid and its sorption behaviors     

Hui Chen  Ronny Berndtsson  Mingguang Ma  Kun Zhu 《Environmental Geology》2009,57(8):1847-1853

Insolubilized humic acid (IHA) was prepared in the laboratory by heating approach. Through the comparison between the endothermic peaks, optimal heating temperature was determined to be 330°C. The modified IHA then was characterized by TG-DTA, SEM, FTIR, element analysis, and nitrogen adsorption–desorption isotherms. The removal efficiency of p-nitrophenol from the aqueous solution by adsorption onto solid IHA surfaces was shown to be a function of pH, reaction temperature, and p-nitrophenol concentration. Adsorption equilibrium data satisfactorily fitted the Langmuir adsorption isotherm. Under a certain concentration range, the removal rate of p-nitrophenol at pH 3.5 could reach 24, 29, and 35 mg/g at a temperature of 25, 35, and 45±0.1°C. The results suggest that IHA could play a role as a potential efficient absorbent to remove organic contaminants, e.g., utilized to purify water contaminated by organic compounds.  相似文献   

Rigid Foundations Resting on an Elastic Layered Soil     

Leonidas T. Stavridis 《Geotechnical and Geological Engineering》2009,27(3):407-417

A rigid foundation of arbitrary shape resting on a stratified half space (soil), with specific geometrical and elastic properties for its horizontal layers, is examined under the action of a vertical load placed anywhere on the foundation area. On the basis of a purely analytical treatment of the deformability of the soil surface, i.e. without using a finite element discretization of the layered soil mass, a general method is developed in order to determine the contact soil pressures and the resulting settlements through an easily implemented numerical procedure. The possible presence of “inactive” foundation parts not being in contact with the soil surface is taken into account. Parametric studies are performed showing the influence of the variability of the soil layers, as well as of the vertical load location, on the contact pressures developed. In this context, for the cases of a rectangular and a circular foundation the area borders for the location of a vertical load are determined, either for the development of compressive soil pressures all over the footing (core), or for allowing the existence of some inactive part without contact with the soil (zero contact pressure), not exceeding the half of the total foundation surface (limit core).  相似文献   

Pseudo-Static Analysis of Soil Nailed Excavations     

Gosavi Meenal  Swami Saran  Satyendra Mittal 《Geotechnical and Geological Engineering》2009,27(4):571-583

In this paper, a pseudo-static analysis has been presented to investigate the stability of soil nailed vertical/nearly vertical excavations. The failure surface is assumed as the arc of log-spiral passing through the toe of the excavation and intersecting the ground at right angle. The horizontal and vertical seismic forces are taken in terms of horizontal and vertical seismic coefficients. The internal failure mode of the nailed cut is considered either by pull-out or rupture or excessive bending whichever is critical. Expression for the factor of safety is derived using moment equilibrium method. Results have been arranged in tabular form considering ranges of the design parameters usually occur in practice. A typical table for the design of nailed excavation with driven nails is presented in the paper. Analytical results have been compared with the findings of model tests and reasonably good agreement has been observed.  相似文献   

From radon hazard to risk prediction-based on geological maps,soil gas and indoor measurements in Germany   总被引：3，自引：0，他引：3  

J. Kemski  R. Klingel  A. Siehl  M. Valdivia-Manchego 《Environmental Geology》2009,56(7):1269-1279

Mapped geological units can be regarded as proxies standing for a complex series of subsoil geochemical and physical properties including the assigned radon activity concentration in soil gas, which is taken as best estimator of the regional geogenic radon potential. Areal distribution of measuring sites for soil gas in Germany is adapted to spatial variation of geology. A grid-based and distance-weighted interpolation procedure is applied, following geologically defined neighbourhood relations of measuring sites and accounting for isolated outcrops of known geology but without measurements. To investigate the statistical relationship between indoor radon, house type and building ground specifications, measurements of the indoor radon concentration have been carried out in more than 10,000 dwellings in different regions of Germany. Multiple regression analyses of variance reveal that besides region-specific geological properties and building characteristics, various house type and living style variables significantly contribute to the explained variance for ground floor radon concentrations. These parameters are also dominant in controlling the radon transfer relation from soil gas to indoor air. Risk prediction maps for radon in houses indicating the probability to exceed certain indoor threshold values can be useful especially for regions with no or only a few measurements of indoor radon.  相似文献   

The influence of shallow landslides on sediment supply: A flume-based investigation using sandy soil   总被引：1，自引：0，他引：1  

G. Acharya  T.A. Cochrane  T. Davies  E. Bowman   《Engineering Geology》2009,109(3-4):161-169

The impact of rainfall-induced shallow landslides on hillslope sediment discharge is not well understood. This paper reports experimental measurements of sediment discharge after water-induced shallow landslides are triggered on sandy soil in a flume under simulated rainfall. The principal aim of the research was to investigate how varying soil depth affects the location and occurrence of shallow slope failures, as well as how it affects sediment yields downslope. Four experiments were conducted using the same sandy soil and a 30° and 10° compound slope configuration under average rainfall intensity of 50 mm h^− 1 for up to 390 min. Soil depths were set to 200, 300, 400 and 500 mm. Engineering and geotechnical properties of the soil were examined. Sediment discharge and runoff were collected from the flume outlet at 15 minute intervals. Changes in the soil slope profiles after landslides and soil physical properties resulted from soil armouring, under continuous rainfall were also recorded. Results showed that sediment yields at the flume outlet, before landslides occurred, were very low and limited to the finer soil particles as would be expected for a sandy soil. However subsequent variations in sediment discharge were strongly related to failure events and their proximity to the outlet. Sediment yield was also affected by the original soil depth; the greater the depth, the higher the sediment yields. Post-failure reductions in sediment discharge were observed and attributed to post-failure slope stabilization under continuing rainfall and extensive soil armouring near the flume outlet. The results provide a clear linkage between landslides and sediment discharge due to hydrological processes occurring in the hillslope. This knowledge is being used to develop a model to predict sediment discharges from hillslopes following shallow landslide events.  相似文献   

EFFECT OF DIGITAL ELEVATION MODEL RESOLUTION ON EMPIRICAL ESTIMATION OF SOIL LOSS AND SEDIMENT TRANSPORT WITH GIS     

SimonWU JonathanLI GordonHUANG G.M.ZENG 《国际泥沙研究》2004,19(1):28-36

The horizontal accuracy of topographic data represented by digital elevation model (DEM) resolution brings about uncertainties in landscape process modeling with raster GIS. This paper presents a study on the effect of topographic variability on cell-based empirical estimation of soil loss and sediment transport. An original DEM of 10m resolution for a case watershed was re-sampled to three realizations of higher grid sizes for a comparative examination. Equations based on the USLE are applied to the watershed to calculate soil loss from each cell and total sediment transport to streams. The study found that the calculated total soil loss from the watershed decreases with the increasing DEM resolution with a linear correlation as spatial variability is reduced by cell aggregation. The USLE topographic factors (LS) extracted from applied DEMs represent spatial variability, and determine the estimations as shown in the modeling results. The commonly used USGS 30m DEM appears to be able to reflect essential spatial variability and suitable for the empirical estimation. The appropriateness of a DEM resolution is dependent upon specific landscape characteristics, applied model and its parameterization. This work attempts to provide a general framework for the research in the DEM-based empirical modeling.  相似文献   

用于非均匀地表通量估计的一种积分算子   总被引：3，自引：2，他引：1  

王纪军  刘晶淼  丁裕国 《高原气象》2004,23(5):605-611

在文献[1]的基础上,将Giorgi(1996)提出的通量计算方案进一步推广为非对称分布的简化形式,求得非均匀地表区域平均通量。以土壤水分饱和度为例,求解出土壤水分通量区域值的数学解析解形式,用随机仿真数据和实测资料对该方案进行数值模拟试验,验证其适用性。  相似文献   

Risk assessment of heavy metals in topsoil along the banks of theYangtze River in Huangshi,China          下载免费PDF全文

LIN Dan  JIN Meng-gui  LI Xiu-juan 《地下水科学与工程》2017,5(2):162-172

High concentrations of heavy metal in farmland threatens food production and human health. Our study assesses soil quality and the distribution of Cd, Cr, Cu, Zn, Pb and Ni, to identify possible sources of heavy metals along the banks of the Yangtze River in Huangshi. Heavy metal concentrations of 22 topsoil samples were measured using the inductively coupled plasma mass spectrometry instrument and data was analyzed by multivariate statistic approaches. Heavy metal contamination risk assessment was performed using a combination of the Nemerow multi-factor index method, the Hakanson potential ecological risk index method and the Muller index of geo-accumulation method. These methods determined similar results indicating that cadmium (Cd) poses a health risk to residents at the study site while Cr, Cu, Zn, Pb and Ni do not. The Nemerow multi-factor index method demonstrated that 18 samples were heavily polluted, three moderately polluted and one lightly polluted. The Muller index of geo-accumulation method found ten samples were moderately to strongly polluted by Cd, five were moderately polluted, six were lightly to moderately polluted and one was lightly polluted. The Hakanson potential ecological risk index method proved six samples were strongly polluted, seven were moderately polluted and nine were lightly polluted. Since our sampling sites were all in agricultural lands, we recommend the potential ecological risk index method as the most effective given it not only considers the range of pollutants contributing to soil pollution but factors in heavy metals toxicity. We are apt that the source of the high concentrations of Cd found in topsoil is derived from alluvial sediments upstream of the Yangtze River with a high percentage of residual speciation and a low percentage of exchangeable speciation distribution of Cd. This in turns indicates that a high concentration of Cd in soil had little impact on the natural environment. However, 31.9% of the iron-manganese oxides bound speciation indicating that such levels of Cd in soil would be potentially hazardous to the crops, particularly if exposed to a reductive condition.  相似文献