渭河眉县段高河漫滩沉积与洪水变化研究

A study on flood series recorded by sediments in high alluvial flat along the Meixian reach of Weihe River

根据粒度指标和历史文献记录,研究了渭河洪水的变化。眉县河漫滩沉积剖面共分为16个沉积层,指示至少发生了16次大小不同的洪水。剖面最上层为2005年大洪水沉积,其它15层是约近120年的洪水沉积层。在考虑了沉积厚度引起的地形增高对粒度成分的影响之后,可以确定这16个阶段洪水深度和规模由大到小的变化顺序为：第15阶段〉第12阶段〉第13阶段〉第16阶段〉第14阶段〉第9阶段〉第10阶段〉第11阶段〉第4阶段〉第1阶段〉第2阶段〉第6阶段〉第5阶段〉第7阶段〉第8阶段〉第3阶段。其中第12,15,13,16,14,9,10,11,4,1阶段为大洪水,第2,3,5,6,7,8阶段为常遇洪水。渭河大洪水的形成主要是由于年降雨量的增加,其次是由于短时间的暴雨造成的。历史文献资料的统计和软件计算表明,眉县渭河洪水发生具有11年和2~7年的周期,分别与太阳活动的11年周期和热带海洋地区的ENSO周期相对应。近400年来,渭河地区洪水的频次变化与太阳黑子数以及我国东部地区的温度变化在几十年尺度上呈近似反相关关系,在太阳黑子数多的时期,我国东部地区温度较高,关中渭河地区洪水发生频次较少。

Flood changes of Weihe River was studied on the basis of grain size analysis and historical records.The profile of the alluvial flat in Meixian reach of Weihe River can be divided into 16 layers,which suggests that 16 floods have happened.The uppermost layer of the profile represents the flood occurring in 2005 A.D.,whereas the other 15 layers indicate other 15 floods occurring in recent 120 years.Considering the influence of terrain elevation increment by alluvial on the composition of grain size,it is concluded that the order of flood scale is： 15th 12th 13th 16th 14th 9th 10th 11th 4th 1st 2nd 6th 5th 7th 8th 3rd.The 15th,12th,13th,16th,14th,9th,10th,11th,4th,1st ones were rare flood,whereas the 2nd,3rd,5th,6th,7th,8th ones were frequent floods.The formation of severe floods is mostly attributed to annual precipitation＇s increase,and secondly to concentrated rainstorms precipitation in a short time.It is indicated by statistics of historical literatures and calculations of professional softwares that there are periods about 11 years and 2-7 years for flood occurrence,which correspond with solar activities and ENSO.The time series of the flood in Weihe River Basin seem to have an inverse correlation with series of sunspots and temperature series of east region in China in decades ： an increase of the number of sunspots often correspond with an increase in the temperature,but an decrease of floods in Weihe River Basin.