Sediment critical shear stress and geotechnical properties along the modern Yellow River Delta,China     

Xiao-Lei Liu  Jie-Wen Zheng  Hong Zhang  Shao-Tong Zhang  Bao-Hua Liu  Hong-Xian Shan 《Marine Georesources & Geotechnology》2018,36(8):875-882

A geological engineering study was undertaken to determine the spatial distribution of sediment critical shear stress in the modern Yellow River Delta and to determine the influence of sediment erodibility on sediment erosion and microtopography formation. The critical shear stress was tested using a cohesive sediment meter for sediments along lines running perpendicular to the coast in different sedimentary lobes of the delta, where the geotechnical properties of sediments were also determined. The results demonstrate that significant differences in critical shear stress exist among high, middle, and low tidal flats, which are influenced by biodisturbation in the different sedimentary lobes. Regional characteristics of the modern Yellow River Delta show that critical shear stress levels are the lowest in the northern area (0.11–0.4?Pa), are the highest in the eastern area (2.8–4.55?Pa), and are significantly heterogeneous in the northeastern area. The critical shear stress is found to be more nonuniform and levels of antierosion strength are relatively lower than values found for other estuarine deltas around the world.  相似文献   

珠江三角洲传统村落生态侵蚀时空演变特征     

黄铎  孙莹  张世君  魏成 《地球信息科学学报》2018,20(3):340-350

传统村落的保护随着中国第四批保护名录的公布逐渐成为全社会的共识。传统村落是人类与自然环境长期相互作用与有机融合的产物,其周边农田、山林、水塘等自然生态环境使着传统村落生产及生活活动得以延续。1978年改革开放后,快速城市化的背景下,不同背景下的城乡建设使得传统村落周边生态自然环境不断遭受到侵蚀威胁,为其整体保护带来极大的挑战。为开展快速城市化背景下传统村落生态环境的影响研究,本文首先界定了传统村落生态侵蚀的概念,应用侵蚀动力学理论对自我生态侵蚀、外来生态侵蚀、突发性生态侵蚀与生态侵蚀修复4种生态侵蚀方式提出生态侵蚀演变的4种模型,同时以珠江三角洲中国传统村落为研究案例,从时间和空间上对珠江三角洲地区传统村落生态侵蚀情况进行分析,探讨其生态侵蚀演变规律,揭示快速城市化背景下传统村落生态侵蚀的时空演变特征,总结了“城镇建设外侵模式、村落建设扩张模式、道路交通占领模式、综合发展模式”4种传统村落生态侵蚀的用地演化模式,丰富和深化传统村落生态视角的研究,为传统村落的保护和相关规划提供了重要参考。  相似文献   

大别山北缘合肥盆地中,新生代构造演化   总被引：26，自引：3，他引：23  

薛爱民  袁学诚 《高校地质学报》1999,5(2):157-163

合肥盆地中、新生代经历了多次沉降和降升变化,侏罗系沉积作用分布于整个盆地,中、晚侏罗世盆地内地层遭受广泛剥蚀。白垩纪沉积物局限于盆地东部,最大剥蚀区在盆地东南部。下第三系沉积集中于断裂带控制的断陷盆地中,剥蚀主要在盆地东部和南部。根据南北向平衡剖面分析,早侏罗世盆地为南北挤压,晚侏罗世盆地拉张松驰形成东西向断层;白垩纪受东西向挤压,早第三纪为南北向拉张。东西向平衡剖面分析表明：在盆地内存在一条规模巨大的南北向巨型隆起,隆起形成干早白垩世早期延续到晚白垩世晚期。盆地经历了早侏罗世前挤压推覆,侏罗－白垩纪松驰下陷,白垩纪盆地西部及中部隆升,晚白垩世－早第三纪盆地受南北向拉张作用。形成北断南超的箕状断陷盆地;晚第三纪挤压降升。  相似文献   

MODELING OF INTERRILL EROSION IN THE LOESS PLATEAU OF CHINA     

《国际泥沙研究》1999,(2)

IINTRODUCTIONTheinterrillerosiononafieldplotisaffectedbythekineticenergyoftherainfall,wind,topographyfactors,propertiesofsoilandthecanopy.Theinterrillerosionoccursasthefirstdropimpactsthehillslopes.Theinterrillerosionoccursinallkindsofrainfallandtheamountofthesplasherosion,whichisthemainpartofinterrillerosion,canaccountforagreatpanofthetotalerosionamountinaheavystorm(Baner1990,Glymph1957,QianandWan1986,Zhou1981).Therefore,itisveryimportanttorevealthemechanismtoestimatetheamountofinterri…  相似文献   

Sensitivity Analysis on GIS Procedures for the Estimate of Soil Erosion Risk   总被引：1，自引：0，他引：1  

Mendicino  Giuseppe 《Natural Hazards》1999,20(2-3):231-253

Land degradation by water erosion is one of the majorissues in the field of environmental planning. Soilerosion and sediment transport are spatiallydistributed processes, and their evaluation can beeasily realised by means of the use of GeographicInformation Systems. The greater availability ofdigital and geo-lithological data managed and storedinside GIS has implied the development of techniquesand procedures aimed at the definition of the spatialprediction of erosion and deposition rates across acatchment. In this paper using terrain data measuredon an experimental basin in southern Italy, asensitivity analysis on different GIS-basedmethodologies for the estimate of a Length-Slope factorhas been developed with the aim of determining whichof these is more reliable for spatial erosion riskassessment. Specifically, by using the unit stream powertheory, different estimates are shown, depending on thescheme adopted to represent the hydrological andtopographic three-dimensional effects inside theLength-Slope factor. The performances of theprocedures analysed have been evaluated through theinformation content of the corresponding spatialdistributions, estimated as an entropy measure. Theresults obtained have shown that among the approachesutilised to describe the routing of the surface runoffalong the hillslope profiles, the two-dimensionalscheme appeared to be more realistic both on divergingand converging surfaces. Such a scheme, during thecomputational phases also aimed at distinguishing the areasof the basin experiencing net erosion from those areasexperiencing net deposition, resulted, being inaccordance with on-site investigations.  相似文献   

Velocities of shallow overland flow on semiarid hillslopes          下载免费PDF全文

Viktor Polyakov  Mark A. Nearing  Jeffry Stone 《地球表面变化过程与地形》2018,43(12):2578-2583

A series of 188 rainfall plot simulations was conducted on grass, shrub, oak savanna, and juniper sites in Arizona and Nevada. A total of 897 flow velocity measurements were obtained on 3.6% to 39.6% slopes with values ranging from 0.007 m s^‐1 to 0.115 m s^‐1. The experimental data showed that shallow flow velocity on rangelands was related to discharge and ground litter cover and was largely independent of slope gradient or soil characteristics. A power model was proposed to express this relationship. These findings support the slope–velocity equilibrium hypothesis. Namely, eroding soil surfaces evolve such that steeper areas develop greater hydraulic roughness. As a result overland flow velocity becomes independent of the slope gradient over time. Our findings have implications for soil erosion modeling suggesting that hydraulic friction is a dynamic, slope and discharge dependent property. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

From incipient island arc to doubly‐vergent orogen: A review of geodynamic models and sedimentary basin‐fills of southern Central America          下载免费PDF全文

Christian Brandes  Jutta Winsemann 《Island Arc》2018,27(5)

Southern Central America is a Late Mesozoic/Cenozoic island arc that evolved in response to the subduction of the Farallón Plate beneath the Caribbean Plate in the Late Cretaceous and, from the Oligocene, the Cocos and Nazca Plates. Southern Central America is one of the best studied convergent margins in the world. The aim of this paper is to review the sedimentary and structural evolution of arc‐related sedimentary basins in southern Central America, and to show how the arc developed from a pre‐extensional intra‐oceanic island arc into a doubly‐vergent, subduction orogen. The Cenozoic sedimentary history of southern Central America is placed into the plate tectonic context of existing Caribbean Plate models. From regional basin analysis, the evolution of the southern Central American island arc is subdivided into three phases: (i) non‐extensional stage during the Campanian; (ii) extensional phase during the Maastrichtian‐Oligocene with rapid basin subsidence and deposition of arc‐related, clastic sediments; and (iii) doubly‐vergent, compressional arc phase along the 280 km long southern Costa Rican arc segment related to either oblique subduction of the Nazca plate, west‐to‐east passage of the Nazca–Cocos–Caribbean triple junction, or the subduction of rough oceanic crust of the Cocos Plate. The Pleistocene subduction of the Cocos Ridge contributed to the contraction but was not the primary driver. The architecture of the arc‐related sedimentary basin‐fills has been controlled by four factors: (i) subsidence caused by tectonic mechanisms, linked to the angle and morphology of the incoming plate, as shown by the fact that subduction of aseismic ridges and slab segments with rough crust were important drivers for subduction erosion, controlling the shape of forearc and trench‐slope basins, the lifespan of sedimentary basins, and the subsidence and uplift patterns; (ii) subsidence caused by slab rollback and resulting trench retreat; (iii) eustatic sea‐level changes; and (iv) sediment dispersal systems.  相似文献   

Quantifying relations between surface runoff and aridity after wildfire          下载免费PDF全文

René E. Van der Sant  Petter Nyman  Philip J. Noske  Christoph Langhans  Patrick N.J. Lane  Gary J. Sheridan 《地球表面变化过程与地形》2018,43(10):2033-2044

Post‐wildfire runoff and erosion are major concerns in fire‐prone landscapes around the world, but these hydro‐geomorphic responses have been found to be highly variable and difficult to predict. Some variations have been observed to be associated with landscape aridity, which in turn can influence soil hydraulic properties. However, to date there has been no attempt to systematically evaluate the apparent relations between aridity and post‐wildfire runoff. In this study, five sites in a wildfire burnt area were instrumented with rainfall‐runoff plots across an aridity index (AI) gradient. Surface runoff and effective rainfall were measured over 10 months to allow investigation of short‐ (peak runoff) and longer‐term (runoff ratio) runoff characteristics over the recovery period. The results show a systematic and strong relation between aridity and post‐wildfire runoff. The average runoff ratio at the driest AI site (33.6%) was two orders of magnitude higher than at the wettest AI site (0.3%). Peak runoff also increased with AI, with up to a thousand‐fold difference observed during one event between the driest and wettest sites. The relation between AI, peak 15‐min runoff (Q₁₅) and peak 15‐min rainfall intensity (I₁₅) (both in mm h^‐1) could be quantified by the equation: Q₁₅ = 0.1086I₁₅ × AI ^2.691 (0.65<AI<1.80, 0<I₁₅<45) (adjusted r² = 0.84). The runoff ratios remained higher at drier AI sites (AI 1.24 and 1.80) throughout the monitoring period, suggesting higher AI also lengthens the window of disturbance after wildfire. The strong quantifiable link which this study has determined between AI and post‐wildfire surface runoff could greatly improve our capacity to predict the magnitude and location of hydro‐geomorphic processes such as flash floods and debris flows following wildfire, and may help explain aridity‐related patterns of soil properties in complex upland landscapes. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Simulating a century of soil erosion for agricultural catchment management          下载免费PDF全文

Hugh G. Smith  Andrés Peñuela  Heather Sangster  Haykel Sellami  John Boyle  Richard Chiverrell  Daniel Schillereff  Mark Riley 《地球表面变化过程与地形》2018,43(10):2089-2105

Agricultural land management requires strategies to reduce impacts on soil and water resources while maintaining food production. Models that capture the effects of agricultural and conservation practices on soil erosion and sediment delivery can help to address this challenge. Historic records of climatic variability and agricultural change over the last century also offer valuable information for establishing extended baselines against which to evaluate management scenarios. Here, we present an approach that combines centennial‐scale reconstructions of climate and agricultural land cover with modelling across four lake catchments in the UK where radiometric dating provides a record of lake sedimentation. We compare simulations using MMF‐TWI, a catchment‐scale model developed for humid agricultural landscapes that incorporates representation of seasonal variability in vegetation cover, soil water balance, runoff and sediment contributing areas. MMF‐TWI produced mean annual sediment exports within 9–20% of sediment core‐based records without calibration and using guide parameter values to represent vegetation cover. Simulations of land management scenarios compare upland afforestation and lowland field‐scale conservation measures to reconstructed historic baselines. Oak woodland versus conifer afforestation showed similar reductions in mean annual surface runoff (8–16%) compared to current moorland vegetation but a larger reduction in sediment exports (26–46 versus 4–30%). Riparian woodland buffers reduced upland sediment yields by 15–41%, depending on understorey cover levels, but had only minor effect on surface runoff. Planting of winter cover crops in the lowland arable catchment halved historic sediment exports. Permanent grass margins applied to sets of arable fields across 15% or more of the catchment led to further significant reduction in exports. Our findings show the potential for reducing sediment delivery at the catchment scale with land management interventions. We also demonstrate how MMF‐TWI can support hydrologically‐informed decision making to better target conservation measures in humid agricultural environments. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Assessment of long‐term Holocene soil erosion rates in Polish loess areas using sedimentary archives from closed depressions          下载免费PDF全文

Renata Kołodyńska‐Gawrysiak  Jean Poesen  Leszek Gawrysiak 《地球表面变化过程与地形》2018,43(5):978-1000

Soil erosion is a particularly important problem in the loess areas of Central Europe. Numerous studies of past and present soil erosion based on colluvial sediments have so far been conducted. The main problem is the fact that colluvia usually do not represent the complete sedimentation record. Closed depressions (CDs) collect all colluvial sediments from their catchment, therefore, constitute sediment stores enabling the calculation of soil erosion rates. Colluvial sediments and fossil soils, infilling four CDs in the Polish loess belt, were OSL and C‐14 dated. Human settlements near the studied CDs were analyzed. Phases of soil erosion and colluviation from the Neolithic (5400–2900 bc ), from the Middle Bronze Age to the Early Iron Age (1600–0 bc ), and from the Early Middle Ages to Modern Times (500 AD until today) were documented within the CDs studied. Phases of low soil erosion rate and pedogenesis occurred from the Late Vistulian to the Early Neolithic and from the Iron Age to Early Middle Ages. This study reveals that these phases are not synchronous with the soil erosion phases in Central Europe, as the latter mainly occurred in the Bronze Age, Roman Period and Middle Ages. The obtained soil erosion rates were compared with erosion rates in different areas of Central Europe. This study indicates that in loess regions with long‐term agricultural land use, mean erosion rates (i.e. 3.7–5.9 t ha^‐1 yr^‐1) from the Middle Ages to Modern Times were ten times higher than during the entire prehistoric period (0.39–0.67 t ha^‐1 yr^‐1). The mean soil erosion rates for forested CDs was 0.24–0.74 t ha^‐1 yr^‐1. Soil erosion phases are most probably caused by human activities (i.e. land use change) but the early Holocene erosion phase (7.96 +/‐ 0.67 kyr) could have been induced by a climatic fluctuation (e.g. a 8.2 kyr Bond event). Copyright © 2018 John Wiley & Sons, Ltd.  相似文献