The formation of an anabranching planform in a sandy floodplain by increased flows and sediment load          下载免费PDF全文

Marcin Słowik 《地球表面变化过程与地形》2018,43(3):623-638

Anabranching rivers evolve in various geomorphic settings and various river planforms are present within these multi‐channel systems. In some cases, anabranches develop meandering patterns. Such river courses existed in Europe prior to intensive hydro‐technical works carried out during the last 250 years. Proglacial stream valleys, inherited from the last glaciation, provided a suitable environment for the development of anabranching rivers (wide valleys floors with abundant sand deposits). The main objective of the present study is to reconstruct the formation of an anabranching river planform characterized by meandering anabranches. Based on geophysical and geological data obtained from field research and a reconstruction of palaeodischarges, a model of the evolution of an anabranching river formed in a sandy floodplain is proposed. It is demonstrated that such a river system evolves from a meandering to an anabranching planform in periods of high flows that contribute to the formation of crevasse splays. The splay channels evolve then into new meandering flow paths that form ‘second‐order’ crevasses, avulsions and cutoffs. The efficiency of the flow is maintained by the formation of cutoffs and avulsions preventing the development of high sinuosity channels, and redirecting the flow to newly formed channels during maximum flow events. A comparison with other anabranching systems revealed that increased discharges and sediment loads are capable of forming anabranching planforms both in dryland and temperate climate zones. The sediment type available for transport, often inherited from older sedimentary environments, is an important variable determining whether the channel planform is anabranching, with actively migrating channels, or anastomosing, with stable, straight or sinuous branches. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Google Earth Engine平台支持下的赣南柑橘果园遥感提取研究   总被引：1，自引：0，他引：1  

徐晗泽宇  刘冲  王军邦  齐述华 《地球信息科学学报》2018,20(3):396-404

赣南地区是中国柑橘主产区,柑橘种植产业经数十年发展已具较大规模。本文利用Google Earth Engine平台,使用2140景Landsat影像进行像元级融合,重构目标年份季节最小云量影像集,构建多维分类特征集,利用随机森林分类算法,实现了1990、1995、2000、2005、2010和2016年赣南柑橘果园的分布制图。结果表明：利用Google Earth Engine平台可实现大量遥感影像数据的高效处理;最小云量影像合成方法能够有效解决多云多雨地区高质量光学影像获取困难的问题;以最小云量影像合成构建的数据集,使用随机森林分类算法能够有效提取赣南柑橘果园,分类平均总体精度和Kappa系数分别为93.15%和0.90,分类效果良好;赣南柑橘果园面积由1990年9.77 km²扩大为2016年2200.34 km²,2005年以后呈大规模扩张趋势,果园分布由零星分布,逐步形成连片化的聚集分布特点,柑橘果园用地的主要来源为林地、灌丛和耕地。  相似文献   

Using advanced soft computing techniques for regional shoreline geoid model estimation and evaluation     

Mosbeh R. Kaloop  Mostafa Rabah  Ahmed Zaki 《Marine Georesources & Geotechnology》2018,36(6):688-697

This study aims at evaluating the global geoid model for a regional shoreline fitting using advanced soft computing techniques and global navigation satellite system/leveling measurements. Artificial neural networks, fuzzy logic, and least square support vector machine models are developed and used to fit the global geoid model for the north coastal Egyptian line. In addition, a novel estimation geoid model is designed and evaluated based on the latest global geoid models. The results of the three estimation models show that they can be used to correct the shoreline geoid model, in terms of root mean square error that ranges from 1.7 to 8.5?cm. Moreover, it is found that the least square vector machine model is a competitive approach with certain advantage in solving complex problems represented by missing data.  相似文献   

Analysis of nonstationarity in low flow in the Loess Plateau of China          下载免费PDF全文

Kun‐xia Yu  Lars Gottschalk  Xiang Zhang  Peng Li  Zhanbin Li  Lihua Xiong  Qian Sun 《水文研究》2018,32(12):1844-1857

An approach for nonstationary low‐flow frequency analysis is developed and demonstrated on a dataset from the rivers on the Loess Plateau of China. Nonstationary low‐flow frequency analysis has drawn significant attention in recent years by establishing relationships between low‐flow series and explanatory variables series, but few studies have tested whether the time‐varying moments of low flow can be fully described by the time‐varying moments of the explanatory variables. In this research, the low‐flow distributions are analytically derived from the 2 basic explanatory variables—the recession duration and the recession coefficient—with the assumption that the recession duration and recession coefficient variables follow exponential and gamma distributions, respectively; the derived low‐flow distributions are applied to test whether the time‐varying moments of explanatory variables can explain the nonstationarities found in the low‐flow variable. The effects of ecosystem construction measures, that is, check dam, terrace, forest, and grassland, on the recession duration and recession coefficient are further discussed. Daily flow series from 11 hydrological stations from the Loess Plateau are used and processed with a moving average technique. Low‐flow data are extracted following the pit under threshold approach. Six of the 11 low‐flow series show significant nonstationarities at the 5% significance level, and the trend curves of the moments of low flow are in close agreement with the curves estimated from the derived distribution with time‐dependent moments of the recession duration and time‐constant moments of the recession coefficient. It is indicated that the nonstationarity in the low‐flow distribution results from the nonstationarity in the recession duration in all 6 cases, and the increase in the recession duration is resulted from large‐scale ecosystem constructions rather than climate change. The large‐scale ecosystem constructions are found to have more influence on the decrease in streamflow than on the increase in watershed storage, thus resulting in the reduction of low flow. A high return period for the initial fixed design value decreases dramatically with an increasing recession duration.  相似文献   

基于圆柱多段拟合的隧道中轴线提取方法研究     

荆海峰  李广云  王力  杨文锋 《大地测量与地球动力学》2018,38(2):211-215

提出基于圆柱多段拟合的隧道中轴线提取方法。首先对隧道点云数据进行预处理，并将点云按隧道走向分成不同区段；然后对各区段依据轴线与表面点云法线垂直关系，提取精度较低的中轴线；最后对各区段利用圆柱多段拟合，提取精度较高的中轴线。实验表明，隧道中轴线的提取在一定的采样区间具有较高的稳定性，对直线和弯曲的圆形隧道有良好的适用性，算法可靠，精度较高。  相似文献   

关于地震科学实验场的一些思考——地下云图     

陈颙  徐逸鹤  蔡辉腾  李稳 《中国地震》2018,34(2):165-171

由中国地震局和美国国家科学基金委、地质调查局合作建立的地震预报研究实验场为中国早期地震工作的发展起到了良好的推动作用。由于种种客观原因,地震预报实验场的多数预想目标未能达成,发展受到了阻碍。最近几年,实验场重新受到重视,并更名为"地震科学实验场"。结合目前地震学发展的前沿和防震减灾事业的实际需求,本文提出增加"地下云图"作为实验场的新方向。利用高重复性、环境友好、安全性高的气枪震源,持续激发地震信号,实现对地下介质速度变化的连续监测;结合背景噪声成像获得的高分辨率3维地壳结构,构建4维(三维空间+一维时间)地下结构成像。"地下云图"可以反映地下速度和应力变化,为全国范围的地震监测预测提供新的业务手段,推动地震预测从经验预测到物理预测的转换。  相似文献   

青海地区地震序列参数的早期特征研究     

余娜  张晓清  袁伏全 《中国地震》2018,34(4):695-703

采用时间序列的"传染型余震序列"(ETAS)模型系统估算了青海地区地震序列参数,并对地震序列的震后早期特征进行分析。采用"自然边界法"选取了2009年以来青海地区9个地震序列,利用"震级-序号"法确定了每个地震序列的完整性震级M_c,并对每个地震序列进行估算。研究表明,截止震级选取对地震序列参数的影响很大,在应用中需谨慎。α值和p值的稳定时间与序列的主震震级间没有明显的关系,主震震级较大的地震序列,序列参数的稳定时间可能较短;主震震级较小的地震序列,序列参数的稳定时间也可能较长。同一个地震序列,α值和p值的稳定时间与不同截止震级间也没有明显的对应关系。最后给出了研究区域地震序列参数的最长稳定时间和最短稳定时间。  相似文献   

地震台智能电源Android平台控制系统     

石磊  刘静  李凤  尹宏伟 《地震地磁观测与研究》2018,39(3):218-222

针对无人值守地震台因供电故障造成的观测数据质量问题，现阶段GPRS在地震台站的应用大多以手机短信呈现，无良好的可视化操作界面，设计开发一种底层基于STM32单片机，以GPRS为数据传输方式，Android手机APP为监控界面的智能电源控制系统。通过在河北省地震局石家庄中心台下属的深州郭家庄地震台进行应用，证明该电源控制系统能够保证观测设备的稳定运行，并为设备维护提供了保障和依据。  相似文献   

2017年6月3日阿拉善左旗5.0级地震震源深度测定   总被引：1，自引：1，他引：0  

郝美仙  宋晓燕  徐岩  翟浩 《地震地磁观测与研究》2018,39(2):18-24

2017年6月3日18时11分内蒙古阿拉善左旗（37.99° N，103.56° E）发生5.0级地震，利用近震深度震相sPL测定法、CAP波形反演法、sPn与Pn震相走时差法，进行震源深度精确测定。研究结果表明，3种方法测得的该地震震源深度基本一致，分布范围为8.5—11 km，表明该地震发生在上地壳。  相似文献   

西安地震台极远震震相记录特征     

冯红武  王建昌  颜文华 《地震地磁观测与研究》2018,39(6):120-129

以西安地震台记录的2001-2018年13次6级以上极远震为研究对象，依据AK135走时表进行震相分析，总结归纳典型极远震震相记录特征，以期提高震相分析水平和测震分析工作质量，为其他地震台站极远震分析工作提供借鉴。  相似文献