西安市东郊渭河河漫滩沉积与洪水变化

Sediment of Floodplain and Flood Change of Weihe River in Eastern Suburb of Xi'an City

[目的]通过揭示历史时期洪水的演变,科学地预测洪水的发生,以求减少洪水灾害造成的损失。[方法]通过分析西安市东郊水流村剖面106个样品的粒度组成,研究了西安市渭河近230a来的洪水事件。[结果]剖面厚度约5m,沉积物主要由粗粉砂、极细砂、中砂和粗砂组成,在各层中变化明显,能够指示古洪水的变化。粒度成分和粒度参数指示,研究剖面中的洪水沉积可分为21层,表明西安市渭河近230a来至少发生了21次洪水事件,各阶段的洪水动力大小为:第18阶段>17阶段>15阶段>16,19阶段>21阶段>4,5阶段>3阶段>1,2阶段>6,7阶段>10阶段>11阶段>8,9阶段>13,14阶段>12阶段>20阶段。在研究剖面发生的21次洪水事件中,除第20次洪水外,其余洪水发生时河漫滩上的洪水深度均大于2m,均为大洪水事件。[结论]洪水沉积层的分布和粒度成分指示,第3,5,7,8次大洪水的发生是由于当年降水量的显著增加造成的,其余次洪水的发生可能是当年降水量增加造成的,也可能是当年降水量没有增加而是由于当年降水量集中造成的。

[Objective] To reveal characteristics of the flood events occurred in historical period, scientifically predict the occurrence of flood and reduce the loss caused by flood disasters. [Methods] According to the analysis of grain size for 106 samples from the floodplain deposition of Shuiliu village in the northern suburbs of Xi＇an City, the flood events of Weihe river in Xi＇an City over the past 230 years was studied. [Results] The section studied was 5 m in thickness and consisted of silt particles, clay sand, middle size sand and coarse sand, which changed distinctly in the stratigraphic section and indicated the flood events very well. Particle size and particle parameters indicated that 21 deposit layers can be determined and at least 21 stages of floods in the section studied in past 230 years. The flood scale of these 21 flood phases were. 18 th〉17 th 〉15 th〉16 th,19 th〉21 th〉4 th, 5 th〉3 rd〉1 st, 2 nd〉6 th, 7 th〉10 th〉11 th〉8 th, 9 th〉13 th, 14 th〉12 th〉20 th. The flood level over the sediment of the floodplain was bigger than 2 m when these 21 flood stages occurred except the 20 th. [Conclusion] The distribution and grain size of flood deposit layers indicated that the occurring reason for the major flood of 3 rd, 5 th, 7 th and 8 th flood was due to the increase in annual mean precipitation, the rest flood events were due to the increase in annual mean precipita- tion or concentrated precipitation in a year.