中文摘要：

2013年10月受＂菲特＂台风的影响,浙江余姚境内的姚江流域发生了特大洪水。通过系统采集不同河段高、低河漫滩及泛滥平原的沉积物样品,开展粒度分析和磁性测量,探讨了该地区特大洪水事件在沉积物粒度及磁性参数方面的表征特征。研究表明,沉积物粒度组成以粉沙为主（平均58.72%）,黏土次之（23.27%）,沙最少（18.01%）,主体成分为黏土-沙质粉沙;从低河漫滩、高河漫滩到泛滥平原,沉积物粒度具有变细趋势,但差别不大;频率曲线表现为较宽的单峰,略显正偏;概率累积曲线较为平缓且均为两段式。入城段与城区干流段沉积物中磁性参数χ、SIRM呈现高度的相关性,表明磁性矿物主要由亚铁磁性矿物组成,较高的χ（ARM）表明沉积物中含有较多的稳定单畴亚铁磁性矿物。区域横向对比结果表明,余姚洪水沉积物在粒度结构上可与同时期形成的嘉兴地区的洪水沉积物作比较,也与良渚古城附近、杭州平原广泛发育的＂黄粉土＂相近,而与杭州湾高潮滩沉积物明显不同。

英文摘要：

Deposits of an extrordinary flood that took place in October 2013 in the lower Yaojiang River were systematically collected.Then grain size analysis and magnetic measurement were conducted to study the characteristics of grain size and magnetic properties in relation to the flood dynamics.The results showed that the flood sediments were composed mainly of silts（58.72%）,clay（about 23.27%） and fine sand（18.01%）,or could be named as clay-sandy silt.The grain size of the deposits respectively from low flat,high flat and flood plain showed a gentle finer trend or with little difference.The frequency curve of grain-size had twin peaks or multimodal peak,and positive bias.The probability cumulative curves were relatively flat and all of them had two-stage.Magnetic parameters showed that the magnetic minerals in the flood sediment were mainly composed of ferri magnetic minerals.The high values of χARMin the sediments from the two branch streams（Lanshu and Houqing） in the downtown and the lower stream out of the town indicated a relative higher concentration of ferri magnetic minerals,reflecting the sediments getting finer or more local materials.Through correlation of the grain-size composition with some other fine deposits formed in different sedimentary environment,it indicated that the deposits was much similar to that from Jiaxing（another flood deposit formed in the same time）,and also similar to the ＂yellow silt＂ collected from the area of the ancient Liangzhu city near Hangzhou,but different quite a lot from the intertidal sediments from Hangzhou Bay.