排序方式： 共有93条查询结果，搜索用时 15 毫秒
81.
The dramatic decline in the integrity of Australian river systems in recent decades has seen the development of landcare and catchment management groups across the continent as the main facilitators of river rehabilitation works. There is growing concern for the need to develop adaptive management frameworks that assist informed decision making through the integration of social and geomorphological knowledge into catchment planning. In the Mulgrave River Catchment of northeastern Queensland, difficult management decisions have to be made with limited access to knowledge of natural processes and baseline geomorphological data. To date management decisions have been based almost exclusively on oral histories that state that point bars are accreting and the river is becoming shallower due to bank erosion. As a result bank stabilisation and removal of sand from within the channel have been recommended in the absence of any geomorphological assessments. This study compares oral histories of river bank erosion in the Mulgrave River with geomorphic evidence to highlight the need for integrated landscape scenario planning. The results of grain size analysis of bank and bed material from 27 locations, involving 47 samples, suggest that bank erosion cannot be delivering sediments to point bars. Furthermore, qualitative analysis of historic parish maps and aerial photographs shows that there has only been moderate bank erosion at three locations along the Mulgrave River since European settlement. The study demonstrates the important role that geomorphological investigations have for catchment management and the need for management frameworks that integrate geomorphological processes and landholder priorities for sustainable river management. 相似文献
82.
New Zealand provides a useful environment to test the notion that the Anthropocene is a new geological epoch. There are two well‐dated anthropogenic impact ‘events’: Polynesian settlement c. AD 1280, and European colonisation c. AD 1800. Little attention, however, has been given to regional catchment response to these, although it has been assumed that both Polynesian and European farming and land use management practices significantly increased erosion rates across most of New Zealand. This paper addresses the nature and timing of human impacts on river systems using meta‐analysis of a recently compiled nationwide database of radiocarbon‐dated fluvial deposits. This shows highly variable human impacts on erosion and sedimentation in river systems, which are often difficult to separate from naturally driven river activity. Catchment‐scale data with high resolution dating control record clearer evidence of human disturbance. In Northland, anthropogenic alluviation is recorded from c. AD 1300 linked to early Polynesian settlement, enhanced further in the late 19th and 20th centuries by European land clearance, when sedimentation rates exceeded 25 mm year?1. This study demonstrates significant geographical variability in the timing of human impact on river dynamics in New Zealand, despite two synchronous phases of human settlement, and highlights the difficulty of formally designating a simple and single ‘Anthropocene Epoch/Age’. 相似文献
83.
NORM CATTO 《The Canadian geographer》2002,46(1):17-32
Sand‐dominated coastlines backed by transverse foredunes, dome dunes, and parabolic dunes occur at several sites along the coastline of southwest Newfoundland, extending from Sandbanks Provincial Park (Burgeo) to Grand Bay West (Channel‐Port‐aux‐Basques) and north to J.T. Cheeseman Provincial Park. The coastal dunes developed during the mid‐Holocene in response to enhanced sediment availability and flux, coupled with effective sediment retention. Under present environmental conditions, development of aeolian dunes is hindered. Recent changes in the geomorphology of these coastlines provide evidence of the impact of anthropogenic activity. Differing time scales of both weather/climate events and landform response complicate interpretation. Anthropogenic modification, both intentional and accidental, represents a locally dominant geomorphic influence, and these dunes have evolved rapidly in response to anthropogenic pressure coupled with storm events. Changes in the southwest Newfoundland economy have led to increased interest in tourism, and consequent pressure on the sandy coastlines and backing dunes. Increased anthropogenic utilization of the coast for recreational purposes, both by residents and tourists, and limited offshore winter ice and onshore snow cover have resulted in accelerated erosion and degradation of the dunes and coastlines. The influx of sand from the beaches is insufficient to replace that removed through natural and anthropogenic causes. Consequently, the coastal dunes of southwest Newfoundland are essentially relict and will not regenerate following anthropogenic disturbance. On trouve à plusieurs endroits le long des côtes sud‐ouest de Terre‐Neuve, du parc provincial Sandbanks (Burgeo) à Grand Bay Ouest (Channel‐Port‐aux‐Basques) et vers le nord jusqu'au parc provincial J.T. Cheeseman, des littoraux à prédominance de dunes où se sont formées des avant‐dunes transversales, des dunes en forme de dôme et des dunes paraboliques. Les dunes maritimes sont apparues vers le milieu de l'ère holocène en réaction à la disponibilité accrue de sédiments et à leur flux alliés à leur rétention efficace. Ainsi, les conditions environnementales actuelles entravent la formation de dunes éoliennes. Des changements récents à la géomorphologie de ces littoraux fournissent la preuve que l'activité anthropique a des conséquences. Les événements météorologiques et climatiques ainsi que la réaction topographique étant reliés à des échelles de temps différentes, compliquent l'interprétation. Une modification anthropique, qu'elle soit intentionnelle ou accidentelle, constitue une influence géomorphologique locale dominante. Ces dunes ont évolué rapidement en raison de ces pressions anthropiques alliées à des événements pluvio‐hydrologiques. Des changements dans l'économie du sud‐ouest de Terre‐Neuve ont suscité un regain d'intérêt pour le tourisme, ce qui a eu pour effet de créer des pressions sur les littoraux sablonneux et les dunes. L'accroissement de l'utilisation du littoral à des fins récréatives, tant par les résidents que les touristes, et l'accumulation limitée de glace en mer et de neige sur les côtes ont accéléré l'érosion et la détérioration des dunes et des littoraux. L'afflux de sable des plages est insuffisant pour remplacer celui qui disparaît pour des raisons naturelles ou anthropiques. En conséquence, les dunes maritimes du sud‐ouest de Terre‐Neuve sont essentiellement des reliques et ne se régénéreront pas si elles sont perturbées par des causes anthropiques. 相似文献
84.
Kamal 《Journal of Earthquake Engineering》2013,17(3):406-427
This article presents the effects of sediment-damping, impedance-contrast (IC), and size of semi-spherical (SS) basin on the focusing and trapping of the basin-generated surface (BGS) waves and the spatial-variation of average-spectral-amplification (ASA), differential ground motion (DGM), and average-aggravation-factor (AAF). A frequency-dependent focusing of the BGS-wave is inferred. Increase of ASA, DGM, and AAF with increase of size of the SS-basin with a fixed-shape-ratio revealed that the BGS-wave focusing has counter-balanced the sediment-damping effects. It is concluded that the BGS-wave focusing and trapping in the SS-basin is more sensitive to change of IC as compared to the similar change of sediment-damping. 相似文献
85.
The bas-relief carved on the sandstone wall in the central part of the inner gallery of Bayon in the Angkor monuments, Cambodia, has been severely damaged mainly due to calcite crystallization. In order to confirm the mechanism of salt weathering and help determine conservation measures for the bas-relief, measurements of the annual change in the moisture content in the bas-relief were conducted. We found that water supplied from the platform behind the bas-relief is the cause of calcite crystallization. It is therefore indispensable for the conservation of the bas-relief to prevent the water permeating from the inside of the platform behind it. As precipitated calcite from the water block pores near the surface of the sandstone, the surface water absorption test is a useful method to evaluate the degree of the salt weathering. 相似文献
86.
Giacomo Vinci Alessandro Fontana Giorgia Musina Lucia Mancini Carmine Lubritto Lucia Liccioli Federico Bernardini 《Archaeometry》2023,65(2):299-318
Depositional and erosional processes, subsidence and sea-level changes have strongly modified the coastal landscape of northern Adriatic lagoons. Such rapid transformations have induced significant consequences on human settlements and, thus, on the archaeological visibility of the area, still largely unexplored. We present here six metal swords fortuitously retrieved by fishermen over the last decades in front of the barrier islands of Marano Lagoon (north-eastern Italy). Multi-analytical analyses carried out on the artefacts (X-ray radiography and computed micro-tomography, radiocarbon dating and typo-chronology) combined with the study of the coastal paleo-environment (mainly based on historical cartography and remote sensing) allowed the items’ main features to be defined, and highlighted both the historical importance of the area and the significant morphological changes that have occurred there over the last millennium. Data presented indicate that Marano Lagoon was a major hub in the northern Adriatic in the Late Middle Ages, during the crucial period of the Crusades, and in Early Modern times, connecting inland Europe with the Mediterranean Sea. Moreover, the research highlights the onset of coastal erosion that occurred in the last century after a phase of relatively geomorphic stability, possibly deriving from the intensification of human impact and climate change. 相似文献
87.
Aleksander Borejsza Isabel Rodríguez López Charles D. Frederick Mark D. Bateman 《Journal of archaeological science》2008
Several superimposed systems of agricultural terracing are preserved at the archaeological site of La Laguna in central Mexico. Excavations uncovered complex stratigraphic sequences of terrace fills and colluvial deposits. Their chronology was established by radiocarbon, optically stimulated luminescence (OSL), and the presence of diagnostic features and artifacts. The Formative occupations of the site (ca. 600–400 BC and 100 BC–AD 100) resulted in severe erosion and exposure of indurated subsoil horizons. In the Middle to Late Postclassic (AD 1150–1520) stone-walled terraces were built to recover the degraded slopes for cultivation. Renewed reclamation works have been undertaken since the Colonial period, eventually taking the form of sloping-field terraces with berms planted in maguey. The reconstructed sequence of local land use underscores the risks of dating agricultural features by association with sherd scatters, as well as the complexity of the relationships between demographic variables, agricultural intensity and terracing. 相似文献
88.
表面强度是夯土遗址重要的测试指标和加固效果的评价依据。常规的强度测试方法受到取样和运输等因素的制约,不适用于作为夯土遗址如夯土补筑、表面加固等措施的效果评估方法。贯入法是成熟的砂浆强度检测方法,通过改装砂浆贯入仪降低了仪器量程;制作夯土样、室内试验验证了测试的较高精度;标定了夯土样贯入深度测量值与抗压强度的幂函数关系,确定了测强曲线。在夯土遗址现场开展原位测试,分析了布点密度对测试结果精度的影响,并利用测强曲线推算了测试区域的表面抗压强度。本研究提出了一套集“仪器改装-室内标定-现场高密度布点测试”为一体的夯土遗址表面强度评估方法,为土遗址加固效果的评价体系建设提供了参考价值。 相似文献
89.
胡晓伟 《文物保护与考古科学》2013,25(4):54-64
为了对8件西沙华光礁I号沉船遗址出水瓷器进行表面凝结物去除、脱盐清洗和残缺补全等保护处理,采用X射线衍射(XRD),对瓷器表面凝结物进行了成分分析;用三维视频显微镜对瓷器进行脱盐前、后的显微照相对比;对瓷器表面微孔内的物质,用扫描电镜分析(SEM)方法进行成分检测;用电导率仪测量瓷器脱盐过程中电导率变化情况。结果表明,出水瓷器表面凝结物,容易机械去除的样品,其成分主要是镁方解石及文石;不容易机械去除的样品,其成分主要是锰白云石及文石。瓷器微孔内的白色物质为含氯盐分。经两周时间的脱盐清洗,出水瓷器的脱盐电导率值降至较低水平。本工作结果可为西沙海域出水瓷器的后续保护提供资料。 相似文献
90.
河南信阳城阳城遗址M8为高等级战国晚期楚国贵族墓,该墓出土了以漆木器为主的各类文物400余件,其中尤以黑、红两色竹蔑编织而成的髹漆竹席最为精美。为开展彩漆竹席脱水保护提供基础数据,采用激光共聚焦显微镜、拉曼分析仪和傅里叶红外吸收光谱仪(FTIR)及扫描电镜-能谱(SEM-EDS)等现代分析仪器对竹席漆膜的成分及表面形态进行了分析,并在此基础上,结合传统髹漆文献资料探讨了漆膜的制作工艺。结果表明:城阳城彩席中的黑色漆膜为大漆自然显色,红色漆膜是大漆掺加朱砂调制而成;黑色漆膜表面较为平整,漆膜与胎体结合紧密,红色漆膜表面相对粗糙,结构较为疏松;竹席漆膜的厚度在0.02~0.03 mm之间,应是由大漆涂刷至少3~5次制备而成。研究结果可为下一步的彩漆竹席的脱水保护及展示提供基础数据。 相似文献