| Many researches have been conducted on riverway shift of historical period of Weihe River in China, and some progress has been made in understanding of water level changes of the Weihe River. However, no study has ever been published about flood intensity variability, evolvement of water environment and water contamination of historical period of the Weihe River so far. Therefore, it is important to study those problems starting studying on hydrodynamic force and the aspect of water environment. Based on the detailed investigation and systemic design, 331 samples were collected in high floodplain of Xianyang XY profile, Gao Ling GL profile, and Xi'an Caotan CT profile. And granulometric composition, content of trace elements, calcium carbonate and magnetic susceptibility of samples were determined. Based on analyzing these indexes and historic literature, some conclusions have been summarized as follows:1. The delamination of 300 years' flood deposition of Weihe River is obvious and can be regarded as an indication of flood occurrence and change of precipitation.2. The CT profile is formed by the ancient flood deposit, 16 sediment phases indicating 16 flood depositions differently, and its thickness is 4.5m. The XY and GL profiles also indicated 16 flood depositions stages, including the cataclysm of 2003 which the topside indicated and the other 15 flood depositions formed during the ancient flood. According to the historical material, the waterway of the Weihe River changed 300 years ago at Caotan, migrated to the north. The last record of waterway shift of the Weihe River was in 1881, therefore the 16 flood depositions which showed in the GL and XY profiles is the sediments of the recent 120 years, while the CT profile indicated flood depositions of the past 300~120 years.3. There is a obvious variety rhythm of granularity along with the depth in the XY, GL and CT profiles. The granularity in the 1st,3rd, 5th, 7th, 9th, 11th, 13th and 15th sections was thinner than the 2nd, 4th, 6th, 8th, 10th, 12th, 14th and 16th sections of the XY and GL profiles. After eliminating the influence of the landform heighten caused by the deposition thickness on granulometric composition, the order of flood depth and theflood scale of these 16 flood phases was: 12th >15th >6th >9th >16th >lst>5th >14th >7* >llth>3th>13th>8th>10th>4th>2nd>.The 12th , 15th , 6\ 9th. 16th and 1stwere the catastrophic flood phases and the 5 *, 14 th, 7 th, 11th, 3*. 13 *> 8*. 10 th, 4 * and 2 nd were the big flood stages. The order of flood depth and the flood scale of these 16 flood phases which indicated by the CT profile was: 9th>lst >13th > 2nd> 4th 15 th>3rd>12th>16th>14th>8th>5th>6th>llth>10th>7th.The9th ,lM3* >2ndand 4Nverethe catastrophic flood stages .while thel5th , 3r<\ 12th, 16th , 14*. S\ 5\ 6 th, 11th, 10 th and 7 th were the big flood stages.4. The granularity of the CT profile was thicker than that of the XY and GL profiles at the same height and section, which indicated the hydrodynamic force was strong, the stream was great, the velocity of flow was rapid and climate was humid.5. There is a strong relativity between the content of the heavy metal elements and the granularity of the depositions in the research profiles. The higher contents of the heavy metal elements corresponded to the thinner granulometric composition, while the lower content of the heavy metal corresponded to the thicker granulometric composition. The contents of the heavy metal elements changed obviously and decreased along with the profile depth, reflected the influence of humanity activity on the Weihe River water environment.6. CaCO3 in the sections mainly came from transportation detritus of river and the low content of CaCC>3 reflected the granularity of the flood deposit was small, and the hydrodynamic force is weak, while the high content of CaCO3 reflected the granularity of the flood deposit was big, and the hydrodynamic force was strong. After analyzing the content of CaCC>3 in the profile ,it is shown that the the content of CaCO3 in ls\ 3rd, 5\ 7th> 9th> 11th, 13 th and 15 th was smaller than that in 2nd, 4th, 6th, 8th, 10th> 12 th ^ 14 th and 16 th. After eliminating the influence of the landform heighten caused by the deposition thickness on the content of CaCO3, it was shown that the hydrodynamic force of the 1st , 6th* 9th, 12*^ island 16th flood was strong and they were catastrophic flood, while the hydrodynamic force of the 2nd> 3r(\ 4 *> s"1,?"1, 8 * n 10 * <. 11 * and 13 ft was weak and they were big flood. This was consistent with the characteristic of the flood scale and climatic change which was indicated by the granulometric composition.7. Magnetic susceptibility of samples in the floodplain of the Weihe River also indicated environmental variation sensitively. The deposit of thick granularity and highmagnetic susceptibility formed in the relatively warm and wet environment indicated higher flood level;Otherwise, the deposit of thin granularity and low magnetic susceptibility formed in the relatively cold and dry environment indicated lower flood level. The change of magnetic susceptibility in the XY and GL profiles was obviously and had the change rhythm, which reflected the different water level of the Weihe River and indicated the climate change during the flood time.
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