西安高陵渭河漫滩沉积剖面发育,能较好地指示渭河洪水变化。沉积物以粗粉砂、细粉砂、极细砂及粘粒为主。粒度较粗层位指示较强的水动力条件和短暂的湿润气候或一定地区的暴雨增加,粒度较细的层位则代表较弱的水动力条件和短暂的湿润程度略低的气候,而在各洪水沉积层之间无洪水发生的阶段则是正常的气候阶段或偏干的气候阶段。高陵渭河近120年来的河漫滩沉积剖面可分为16层,代表了16个大的洪水阶段。高陵渭河近120年来的河漫滩沉积粒度成分比更早期的河漫滩沉积粒度偏细,反映出近120年来渭河洪水深度与规模在变小,这主要是气候变干造成的。

According to the grain size analysis to 210 samples of floodplain deposition of the Weihe River in Gaoling and the age material recorded in history books,we had studied the flood change of the Weihe River in recent about 120 years in Gaoling,Xi′an.The materials indicate that the flood-plain deposit develops well and the change of the grain size is obvious,which can indicate the flood change of the Weihe River clearly and with high-resolution.The flood-plain sediment is mainly composed of the coarse silt,fine silt,very fine silt and clay,and the grain size is comparatively small in general.The layer that the contents of fine sand and the very fine sand are high is the one that the grain size is big,and the layer that the contents of silt and clay are high is the one that the grain size is small.The layer that the grain size is big indicates the strong hydrodynamic condition and the transient moist climate or the rainstorm increase in certain area,the layer that the grain size is small indicates the weak hydrodynamic condition and the transient less moist climate,and the climate of the periods when no flood occurred were the normal or dryer.The flood-plain deposit of the Weihe River in recent 120 years in Gaoling can be divided into 16 layers,which represent 16 big flood stages.In the 1st,3rd,5th,7th,9th,11th,13th and 15th layers the grain size is comparatively small and in the 2nd,4th,6th,8th,10th,12th,14th and 16th layer the grain size is comparatively big,which is clearly shown not only in the accumulative content of the grain size but in the distribution range of such grani size parameters as Md,Mz,σ,Sk and Kg and the characteristic values,and reflects the flood scale in the 2nd,4th,6th,8th,10th,12th,14th and 16th stages is bigger than that in the 1st,3rd,5th,7th,9th,11th,13th and 15th stages.After eliminating the influence of the landform heightened by deposition on the grain size,we can make sure that the order of the depth and scale of 16 flood stages from big to small is the 16th,14th,4th,2nd,6th,1st,5th,8th,3rd,10th,12th,7th,9th,11th,13th and 15th.When the 1st,2nd,4th,6th,14th and 16th layers formed the height that the flood level passed over the flood plain was bigger than 2 m.When the 3rd,5th,7th,8th,9th,10th,11th,12th,13th and 15th layers formed the height that the flood level passed over the was smaller than 2 m.The grain size of the flood plain deposit of the Weihe River in recent about 120 years in Gaoling is smaller than that in early stages,which inflects the depth and scale of the flood of the Wei River in recent 120 years are changing small.This is caused mainly by the drying climate.