西安高陵马坊滩渭河洪水变化研究

根据高陵渭河马坊滩河漫滩沉积剖面中的沉积层测量和147个样品的粒度分析和历史记载的年代资料,研究了西安高陵渭河距今14001100年间洪水和降雨量变化。高陵渭河古洪水沉积分层清楚,能敏感反映洪水的变化和短期降水量的变化,也能弥补历史文献记载的不足。粒度成分和粒度参数资料指示,高陵马坊滩厚约3.5m的河漫滩沉积剖面至少包括了9个颗粒成分不同的沉积层,代表了9个大洪水阶段;其中厚度大、粒度粗的第2、4、6、8层形成时的洪水规模比厚度小、粒度细的第1、3、5、7、9层形成时要明显大。这9个大洪水阶段均比2003年洪水大,第2、4、6、8阶段应为特大洪水阶段。根据沉积学原理和洪水沉积物粒度成分差异,可确定这9个阶段洪水规模由大到小的顺序是:第2阶段>第6阶段>第4阶段>第8阶段>第3阶段>第1阶段>第5阶段>第9阶段>第7阶段。这9个阶段的洪水发生时河漫滩上的洪水深度均大于2m,当时洪水深度、洪水动力和规模均比现代洪水大,大洪水发生的原因应当是当年降水量的明显增加造成的。 

Study on Flood Changes of Weihe River at Mafangtan in Gaoling

On the basis of the field investigation, grain size analyses for 147 samples from Mafang sections in valley flat in Gaoling and the historical record age material, flood and precipitation change between 1400 and 1100 years were studied. Ancient flood deposit layers of Weihe River in Gaoling is clear and can sensitively reflect the flood change and the short-term rainfall change, and also can make up the insufficiency of the historical literature record. The grain composition and the grain size parameter show that there are at least 9 sedimentary layers of different grain composition in the section with 3.5 m thick in valley flat at Mafangtan in Gaoling, which indicates 9 great flood stages. Among them, 2nd, 4th, 6th and 8th layer is bigger in thick and grain diameter than 1st, 3rd, 5th, 7th and 9th, and the flood scale was greater when the former 4 layers deposited than when the later 5 layers deposited. The scale of the 9 flood stages is greater than that in 2003, and 2nd, 4th, 6th, and 8th flood stage are catastrophic flood stages. According to the sedimentary principle and difference of grain diameter of the 9 flood stages, the magnitude order of the 9 flood stages is 2nd>6th>4th>8th>3rd>1st>5th>9th>7th. The water depth on the valley flat during the 9 flood stages was above 2m, the flood depth, flood energy and flood magnitude are greater at that time than at present, and the origin of the 9 flood stages is the precipitation increased obviously at that time.