漠阳江入海口海岸线分维及其机制分析

分维数是反映海岸线复杂程度的客观依据。结合国内外海岸线分形研究进展,本文以漠阳江入海口附近海域为研究区,基于Landsat 8 OLI遥感影像对研究区域提取瞬时水边线,并利用潮汐数据进行校正得到海岸线;利用Fractal Fox2.0计算获得该海岸线的分维数为1.071;通过对研究区的分形机制分析,认为漠阳江附近的断裂构造对海岸起宏观控制作用,从而对海岸线的分维值也起了决定作用。根据断裂体系模型计算得到西侧海岸线的理论分维值为1.089,而对数螺线模型计算得到东侧海岸线的分维值为1.171;实际分维值相对理论值偏小,说明海岸带的沉积与侵蚀影响了分维值。此外,根据本区海岸侵蚀原因的分析,对分维机制进行了探究,初步论证的分维值大小可为海岸的冲淤变化研究提供参考。     

苏北废黄河三角洲海岸时空演变遥感分析

基于遥感与地理信息系统技术,使用苏北废黄河三角洲海岸地区1978,1987和2000年的Landsat卫星遥感数据,选取岸线指标与波段,提取岸线信息,生成1978-1987年和1987-2000年海岸土地增减时空变化分布图,建立岸线变化距离及增速衡量指标,定量分析了废黄河三角洲海岸面积变化特征,以及灌河口-中山河口、中山河口-扁担港口和扁担港口-双洋河口以南岸段的时空变化格局与分布特征.研究结果表明,废黄河三角洲海岸的自然侵蚀速率呈减小趋势,但侵蚀作用仍在继续.侵蚀强度以废黄河口地区为中心,向南北两侧逐渐减弱.人工保滩护岸措施在一定程度上影响着自然侵蚀格局.其内部各岸段分别呈现缓蚀、侵蚀和基本侵淤平衡的变化格局.     

Automated threshold selection methods for extreme wave analysis

The study of the extreme values of a variable such as wave height is very important in flood risk assessment and coastal design. Often values above a sufficiently large threshold can be modelled using the Generalized Pareto Distribution, the parameters of which are estimated using maximum likelihood. There are several popular empirical techniques for choosing a suitable threshold, but these require the subjective interpretation of plots by the user.In this paper we present a pragmatic automated, simple and computationally inexpensive threshold selection method based on the distribution of the difference of parameter estimates when the threshold is changed, and apply it to a published rainfall and a new wave height data set. We assess the effect of the uncertainty associated with our threshold selection technique on return level estimation by using the bootstrap procedure. We illustrate the effectiveness of our methodology by a simulation study and compare it with the approach used in the JOINSEA software. In addition, we present an extension that allows the threshold selected to depend on the value of a covariate such as the cosine of wave direction.     

黄河口粉质土沉积物侵蚀性动态变化试验研究

通过一系列室内试验,研究了黄河口粉质类沉积物在循环动荷载作用后侵蚀性的变化.在试验中,采用真空预压固结装置制备重塑土样,采用液压伺服土动三轴试验机实现了不同幅值及不同振次的动荷载作用条件,并通过动三轴静态试验及贯入强度测试,测定了动荷载作用后土样强度的变化.通过水槽冲刷试验测试了不同条件的动荷载作用后,土样抗冲刷能力的变化,并进行了临界剪切应力的计算.试验结果表明:对于黄河口粉质类沉积物,动荷载作用后其强度及抗侵蚀性均降低;沉积物强度指标(不排水剪切强度、残余强度、贯入阻力)、侵蚀性指标(起动流速、临界剪切应力、冲刷率)与动荷载幅值、动荷载振次均呈现出较好的线性相关性.     

RS、GIS一体化研究——以湖北省土壤侵蚀遥感调查为例

遥感信息的提取是信息采集的重要部分 ,地理信息系统 (GIS)是遥感信息与其它信息集成的基础平台。通过遥感(RS)、GIS一体化在土壤侵蚀调查中的研究表明 ,RS、GIS一体化技术具有投资省、周期短、精度高等优点 ,是今后国土资源调查研究所采用方法的发展趋势     

Soil Loss by Wind Erosion for Three Different Textured Soils Treated with Polyacrylamide and Crude Oil, Iraq

ＩＮＴＲＯＤＵＣＴＩＯＮＬａｒｇｅａｒｅａｓｏｆａｒｉｄａｎｄｓｅｍｉａｒｉｄｒｅｇｉｏｎｓｏｆｔｈｅｗｏｒｌｄａｒｅａｆ ｆｅｃｔｅｄｂｙｗｉｎｄｅｒｏｓｉｏｎ .Ａｐｐｒｏｘｉｍａｔｅｌｙ 2 8.4%ｏｆｔｈｉｓａｒｅａａｒｅａｆｆｅｃｔｅｄｂｙｓｅｖｅｒｅａｎｄｖｅｒｙｓｅｖｅｒｅｗｉｎｄｅｒｏｓｉｏｎ (Ｋａｔｅｓｅｔａｌ.,1977) .ＩｎＩｒａｑ ,ｔｈｅａｒｉｄａｎｄｓｅｍｉａｒｉｄｒｅｇｉｏｎｓｒｅｐｒｅｓｅｎｔｎｅａｒｌｙ 75%ｏｆｔｈｅｔｏｔａｌｌａｎｄ .5 0 %ｏｆｔｈｉｓｌａｎｄｉｓｓｕｂｊｅｃ…     

Magnetostratigraphic evidence for deep-sea erosion on the Pacific Plate,south of Mariana Trench,since the middle Pleistocene: potential constraints for Antarctic bottom water circulation

Abstract

The Antarctic Bottom Water (AABW) current plays a crucial role in storing and transporting heat, water, and nutrients around the world. However, it is impossible to monitor AABW in the Plio-Pleistocene by direct measurement. Hence, abyssal erosion was usually chosen as an effective indicator of the presence of the AABW in the Indian and Eastern Pacific Oceans during that period. Here, we report a high-resolution magnetostratigraphy of a gravity core, the JL7KGC-01A from the south of the Mariana Trench, northwest Pacific Ocean. The main results are as follows: (1) polarity data suggest that the sequence recorded the late Gauss chron to the early Brunhes chron, including the Jaramillo, Cobb Mountain, and Olduvai normal subchrons; (2) the sedimentary processes in the study area since 2.9 Ma show three stages of sedimentation: 83 cm/Ma during 2.9–1.2 Ma, 183 cm/Ma during 1.2–0.7 Ma, and no sedimentation since ~0.7 Ma; (3) the area south of the Mariana Trench experienced a significant change in the deposition rate at 1.2 Ma, which could be correlated with the intensified desertification in inland Asia, and experienced a prominent depositional hiatus since the early middle Pleistocene, which likely resulted from the enhanced/expanded AABW. Based on these new polarity data and comparisons with previous studies around the Pacific Ocean, we therefore propose that the AABW experienced a notable change during the early–mid Pleistocene transition.     

沙漠公路风蚀破坏规律的数值模拟研究

通过Fluent软件对沙漠公路的风蚀破坏规律进行数值模拟研究。分析公路不同横断面时风沙流扰动、增速、减速、恢复的过程,确定路基(堑)高度、边坡坡率和路面宽度等公路断面设计参数对风沙流扰动的影响,提出沙漠公路路基(堑)风蚀破坏规律。结果表明：路面宽度的改变对路基沿程风速变化影响较小,各特征点处风速变化小于5%。路基(堑)高度和边坡坡率对风沙流扰动的影响较大。随路基(堑)高度增加,风沙流流场的扰动被增强,路基(堑)风蚀破坏越显著,当边坡坡率为1:1时,路基模型高度250 mm时的迎风路肩风速为模型高度60 mm时的 1.15倍,其背风坡脚风速降低45%;路堑模型高度250 mm时的背风堑顶风速为模型高度60 mm时的1.05倍,迎风堑脚处风速降低高达80%。建议沙漠公路宜采用中低路基(堑),不宜高填深挖。当路基(堑)高度一定,边坡坡率为1:1.75或1:2时,路基(堑)沿程风速变化平缓,沙漠路肩不易被吹蚀破坏;路堑中堑脚位置处不易出现堆积。其结论与室内风蚀风洞试验结果有很好的一致性     

流滑型崩岸河岸侧蚀模式初探

流滑型崩岸是冲积河流河岸常见的一种崩塌形式,其发展速度快、破坏力强;该类崩岸主要取决于水流的直接冲刷,河岸崩退过程中水面与岸顶高差较小.依据此类崩岸的特征,基于水流冲刷分析,在基础层面上初步探讨并建立了流滑型崩岸的河岸侧蚀模式.结合水槽试验与土工离心模拟试验,对该模式进行了分析研究,初步率定了模式中的河岸侧蚀系数,计算...     

基于碎屑锆石特征的雅鲁藏布江山南宽谷风成沙丘物源示踪

雅鲁藏布江河谷（尤其是"一江两河"区域）风沙化较为严重,制约了当地社会经济的可持续发展,追踪河谷风沙来源对当地风沙治理意义重大。本研究聚焦于拉萨贡嘎机场附近的山南宽谷风沙地貌,采集2个河沙、3个风成沙丘和1个坡积物样品,以及引用前人研究的2个河沙样品。基于碎屑锆石U-Pb年龄及微量元素地球化学特征,进行沙源示踪研究,旨在为当地风沙治理提供科学依据。对360颗锆石进行LA-ICP-MS U-Pb定年,获得322个谐和年龄。分析结果表明,河沙、风成沙丘及坡积物样品碎屑锆石U-Pb年龄分布特征高度相似,主要峰值与冈底斯岩浆弧新生代的两期岩浆活动一一对应;非矩阵多维标度统计技术（MDS）分析也证实了样品与冈底斯岩浆弧有良好的亲缘性;地球化学判别图解显示锆石具有亏损轻稀土元素、富集重稀土元素、明显正Ce异常和明显负Eu异常的特征,亦指示其岩浆成因,表明冈底斯岩浆弧为沙丘、河沙与坡积物中碎屑锆石的主要来源。依据不同类型样品碎屑锆石年龄对比以及锆石年龄相似程度对比,结果发现：1）雅鲁藏布江地区风沙地貌主要是由于枯水季河床水位下降,导致河岸和河漫滩出露地表,就地起沙吹扬到山坡上所形成;2）研究区河沙并非主要从上游搬运而来,更多是拉萨河搬运汇入的泥沙。依据沙源分析结果,欲解决河谷风沙化问题,首要应在河岸和河漫滩种植适宜当地气候的耐旱植物固定河床上的泥沙,这是最直接有效的手段。