Ephemeral rollover points and clinothem evolution in the modern Po Delta based on repeated bathymetric surveys     

Fabio Trincardi  Alessandro Amorosi  Alessandro Bosman  Annamaria Correggiari  Fantina Madricardo  Claudio Pellegrini 《Basin Research》2020,32(2):402-418

Reconstructions of ancient delta systems rely typically on a two-dimensional (2D) view of prograding clinothems but may miss their three-dimensional (3D) stratigraphic complexity which can, instead, be best documented on modern delta systems by integrating high-resolution geophysical data, historical cartography, core data and geomorphological reconstructions offshore. We quantitatively compare three precisely positioned, high-resolution multi-beam bathymetry maps in the delta front and pro delta sectors (0.3 to 10 m water depth) of Po di Pila, the most active of the modern Po Delta five branches. By investigating the detailed morphology of the prograding modern Po Delta, we shed new light on the mechanisms that control the topset to foreset transition in clinothems and show the temporal and spatial complexity of a delta and its pro delta slope, under the impact of oceanographic processes. This study documents the ephemeral nature of the rollover point at the transition between sandy topset (fluvial, delta plain to mouth-bar) and muddy seaward-dipping foreset deposits advancing, in this case, in >20 m of water depth. Three multibeam surveys, acquired between 2013 and 2016, document the complexity in space and time of the topset and foreset regions and their related morphology, a diagnostic feature that could not be appreciated using solely 2D, even very high-resolution, seismic profiles. In addition, the comparison of bathymetric surveys gathered with one-year lapses shows the migration of subaqueous sand dunes on the clinothem topset, the formation of ephemeral cut-and-fill features at the rollover point (few m below mean sea level), the presence of collapse depressions derived by sagging of sediments and fluid expulsion (possibly induced by storm waves) on the foreset, and splays of sand likely reflecting gravity flows on the lower foreset. Though the modern Po Delta is anthropogenic in many respects, its subaqueous clinothem can be studied as a scale model for ancient clinothems that are less resolved geometrically and far less constrained chronologically.  相似文献   

Evaluating soil water routing approaches in watershed-scale,ecohydrologic modelling     

Garett Pignotti  Indrajeet Chaubey  Keith Cherkauer  Mark Williams  Melba Crawford 《水文研究》2021,35(3):e14034

Soil water dynamics are central in linking and regulating natural cycles in ecohydrology, however, mathematical representation of soil water processes in models is challenging given the complexity of these interactions. To assess the impacts of soil water simulation approaches on various model outputs, the Soil and Water Assessment Tool was modified to accommodate an alternative soil water percolation method and tested at two geographically and climatically distinct, instrumented watersheds in the United States. Soil water was evaluated at the site scale via measured observations, and hydrologic and biophysical outputs were analysed at the watershed scale. Results demonstrated an improved Kling–Gupta Efficiency of up to 0.3 and a reduction in percent bias from 5 to 25% at the site scale, when soil water percolation was changed from a threshold, bucket-based approach to an alternative approach based on variable hydraulic conductivity. The primary difference between the approaches was attributed to the ability to simulate soil water content above field capacity for successive days; however, regardless of the approach, a lack of site-specific characterization of soil properties by the soils database at the site scale was found to severely limit the analysis. Differences in approach led to a regime shift in percolation from a few, high magnitude events to frequent, low magnitude events. At the watershed scale, the variable hydraulic conductivity-based approach reduced average annual percolation by 20–50 mm, directly impacting the water balance and subsequently biophysical predictions. For instance, annual denitrification increased by 14–24 kg/ha for the new approach. Overall, the study demonstrates the need for continued efforts to enhance soil water model representation for improving biophysical process simulations.  相似文献   

乌兰布和沙漠典型植物群落土壤风蚀可蚀性研究   总被引：1，自引：0，他引：1       下载免费PDF全文

王佳庭  于明含  杨海龙  吴其淦  刘泰含 《干旱区地理》2020,43(6):1543-1550

为探明植被恢复对乌兰布和沙漠土壤风蚀可蚀性的影响，以乌兰布和沙漠内不同沙地固 定阶段的 8 种典型植物群落及群落内表土作为研究对象，对土壤物理因子（可蚀性颗粒含量、土壤 含水量、有机质含量）、土壤结皮因子、植被因子 3 类土壤风蚀可蚀性因子指标进行监测，分析土壤 风蚀可蚀性因子在不同植物群落类型间、沙地固定阶段间的差异。结果表明：（1）在乌兰布和沙漠 典型植物群落中，沙蓬、沙生针茅、盐爪爪等草本植物群落的土壤风蚀可蚀性最强，白刺、梭梭、沙 冬青等灌木植物群落土壤风蚀可蚀性弱于草本植物群落，说明灌木林能显著降低土壤风蚀作用。 （2）随着沙地的不断固定，土壤结构不断发育，土壤可蚀性不断降低，土壤风蚀可蚀性强弱表现为 固定沙地<半固定沙地<流动沙地。（3）土壤可蚀性颗粒含量、土壤有机质含量、土壤含水量、土壤结 皮、植被因子与植被类型及沙地固定阶段具有显著相关关系。因此，在沙区生态建设工程中，为了 减少土壤风蚀量，不仅要考虑物种的选择，还要促进人工生态系统的演替和恢复，从而有效降低土 壤风蚀可蚀性。研究结果可为乌兰布和沙区植被生态系统服务功能的科学评价、防沙治沙工程的 建设与管理提供一定参考。  相似文献   

Modelling the poroelastoplastic behaviour of soils subjected to internal erosion by suffusion     

Quentin Rousseau  Giulio Sciarra  Rachel Gelet  Didier Marot 《国际地质力学数值与分析法杂志》2020,44(1):117-136

Granular soils subjected to seepage flow may suffer suffusion, ie, a selective internal erosion. Extending the classical approach of poromechanics, we deduce a new form of the Clausius-Duhem inequality accounting for dissipation due to suffusion, and we deduce restrictions on the constitutive laws of the soil. We suggest (a) a possible coupling between the seepage forces and the suffusion kinetics and (b) an extension of an existing elastoplastic model for the skeleton mechanical behaviour. Numerical integrations of the elastoplastic model are carried out under drained axisymmetric triaxial and oedometric conditions. As a result, we prove that the extended model is able to qualitatively reproduce the suffusion induced strains and the strength reduction experimentally observed. Predictions on the oedometric behaviour of suffusive soils are also provided.  相似文献   

陕北地区退耕还林还草工程土壤保护效应的时空特征   总被引：1，自引：1，他引：0  

刘文超  刘纪远  匡文慧 《地理学报(英文版)》2020,30(3):401-422

This paper looks at the Green for Grain Project in northern Shaanxi Province.Based on remote sensing monitoring data,this study analyzes the locations of arable land in northern Shaanxi in the years 2000,2010 and 2013 as well as spatio-temporal changes over that period,and then incorporates data on the distribution of terraced fields to improve the input parameters of a RUSLE model and simulate and generate raster data on soil erosion for northern Shaanxi at different stages with a accuracy verification.Finally,combined with the dataset of farmland change,compared and analyzed the characteristics of soil erosion change in the converted farmland to forest(grassland)and the unconverted farmland in northern Shaanxi,so as to determine the project’s impact on soil erosion over time across the region.The results show that between 2000 and 2010,the soil erosion modulus of repurposed farmland in northern Shaanxi decreased 22.7 t/ha,equivalent to 47.08%of the soil erosion modulus of repurposed farmland in 2000.In the same period,the soil erosion modulus of non-repurposed farmland fell 10.99 t/ha,equivalent to 28.6%of the soil erosion modulus of non-repurposed farmland in 2000.The soil erosion modulus for all types of land in northern Shaanxi decreased by an average of 14.51 t/ha between 2000 and 2010,equivalent to 41.87%of the soil erosion modulus for the entire region in 2000.This suggests that the Green for Grain Project effectively reduced the soil erosion modulus,thus helping to protect the soil.In particular,arable land that was turned into forest and grassland reduced erosion most noticeably and contributed most to soil conservation.Nevertheless,in the period 2010 to 2013,which was a period of consolidation of the Green for Grain Project,the soil erosion modulus and change in volume of soil erosion in northern Shaanxi were significantly lower than in the previous decade.  相似文献   

自然和自然贡献情景模型研究综述     

岳天祥  范泽孟  史文娇  赵娜 《地球信息科学学报》2020,22(4):743-750

本文回顾了自然和自然贡献情景模型发展的背景、历史和内容,概括总结了自然和自然贡献情景模型的发展进程以及联合国生物多样性与生态系统服务政府间科学—政策平台(IPBES)情景模型的概念框架,讨论了自然和自然贡献情景模型存在的问题和发展方向。为了在全球层面解决现有综合集成模型存在的问题,根据地球表层建模基本定理和生态环境曲面建模基本定理,提出了具有中国原创特点的自然与自然贡献情景模型概念框架。  相似文献   

Stochastic modelling of groundwater flow and solute transport in aquifers     

T.-C. Jim Yeh 《水文研究》1992,6(4):369-395

This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended.  相似文献   

Irpinia, Italy, 1980 earthquake: waveform modelling of strong motion data     

P. Suhadolc  G. F. Panza  F. Vaccari 《Geophysical Journal International》1990,101(3):631-647

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Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau     

Maarten A. Prins  Hongbo Zheng  Kay Beets  Simon Troelstra  Patrick Bacon  Ilse Kamerling  Wouter Wester  Martin Konert  Xiangtong Huang  Wang Ke  Jef Vandenberghe 《第四纪科学杂志》2009,24(1):75-84

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Application of micropolar plasticity to post failure analysis in geomechanics     

Majid T. Manzari 《国际地质力学数值与分析法杂志》2004,28(10):1011-1032

A micropolar elastoplastic model for soils is formulated and a series of finite element analyses are employed to demonstrate the use of a micropolar continuum in overcoming the numerical difficulties encountered in application of finite element method in standard Cauchy–Boltzmann continuum. Three examples of failure analysis involving a deep excavation, shallow foundation, and a retaining wall are presented. In all these cases, it is observed that the length scale introduced in the polar continuum regularizes the incremental boundary value problem and allows the numerical simulation to be continued until a clear collapse mechanism is achieved. The issue of grain size effect is also discussed. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献