摘要:
根据泾阳泾河高漫滩JYa沉积剖面的野外观察，128个样品的粒度、元素与化合物含量实验分析, 以及历史文献对该区洪水的记载，研究了泾阳泾河高漫滩剖面沉积特征与洪水变化。结果表明,泾阳泾河高河漫滩沉积物发育良好,以粗粉砂、极细砂为主,各组分在整个剖面上变化明显,分辨率高,能够清晰地指示各次的洪水以及降水量的变化。JYa剖面分为18个沉积阶段，指示了18次大小不同的洪水和18个降水较多的年份。JYa剖面18个洪水沉积阶段的规模由大到小的变化顺序为：第14层>12层>13层>8层>5层>1层>2层>4层>9层>3层>7层>6层>11层>10层>18层>15层>16层>17层。JYa剖面最上部第1层形成时的河床洪水深度约为4.56 m，流量为4 010 m3/s。第14、12、13、8、5层形成时的河床洪水深度大于4.56 m，流量大于4 010 m3/s。其余各层形成时的河床洪水深度应等于或小于4.56 m，流量等于或小于4 010 m3/s。第14层推断为1841年的特大洪水沉积层，代表了高河漫滩沉积过程中洪水动力与洪水规模最大一次特大洪水事件，当时张家山水文站洪峰流量为18 700 m3/s。沉积物粒度细，元素Mn、Cu和化合物Al2O3、Fe2O3、K2O含量高，元素Ba含量低，指示沉积时洪水强度小，洪水位低，降雨量少。沉积物粒度粗，元素Mn、Cu和化合物Al2O3、Fe2O3、K2O含量低，元素Ba含量高，指示沉积时洪水强度大，洪水位高，降雨量多。在这18次洪水中，同一次洪水沉积层内形成了两个以上薄层的元素和化合物含量、粒度成分的微小变化，指示多数期次的洪水发生时期可能有两个以上洪峰出现。泾阳泾河高漫滩第14、12、13、8、5、1层洪水沉积反映了泾河全流域性的年降水增加或较大范围年降水量增加，且年降水量至少达到800多毫米。
Abstract:
According to the field observation, the grain size, the element and compound analysis of 128 samples, and historical flood records of this area, we studied flood variation indicated by sediments in floodplain of the Jing River in Jingyang reach during deposit of floodplain. The result shows that the sediments which developed well on floodplain of the Jing River in Jingyang reach are mainly of coarse silt and very fine sand. Each component changes obviously in the entire profile, which can clearly reflect the variations of flood and precipitation with high resolving power. The profile is divided into 18 sediment stages, indicating 18 floods of different scales and 18 years with much precipitation. The order of depth and scale of floods of JYa from big to small is 14th, 12th, 13th, 8th, 5th, 1st, 2nd, 4th, 9th, 3rd, 7th, 6th, 11th, 10th, 18th, 15th, 16th, 17th. The flood depth of 1st is about 4.56 m, of which discharge is 4 010 m3/s. The flood depth of 14th, 12th, 13th, 8th, 5th are more than 4.56 m, of which discharge are more than 4 010 m3/s. The other flood depth are equal to or less than 4.56 m, of which discharge are equal to or less than 4 010 m3/s. The 14th flood sediment is the most thick layer of JYa, which should be the extreme flood sediment in 1841, and on the behalf of the largest flood dynamic and scale of the extreme flood event during deposit of floodplain. When the flood peak flow was 18 700 m3/s in Zhangjiashan hydrological station. The fine grain size is, the high contents of Mn,Cu,Al2O3,Fe2O3,K2O are, and the low content of Ba is, which indicates small flood intensity, low flood level and less precipitation at deposition. In contrast, The coarse grain size is, the low contents of Mn,Cu,Al2O3,Fe2O3,K2O are, and the high content of Ba is, which indicates big flood intensity, high flood level and more precipitation at deposition. The small changes of two or more elements, compounds and grain size in the thin layer was formed in the same sedimentary layer in this 18 floods indicates two or more flood peaks often appeard in the period of most floods. The sediments of 14th, 12th, 13th, 8th, 5th, 1st in floodplain of the Jing River in Jingyang reach reflect annual precipitation increase in the whole basin or largescale, and annual rainfall is more than 800 mm.
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