The Water Environment Change Of Weihe River In Gaoling County Of Xi'an Area During Last 120a

As the largest branch of Yellow river, Weihe River is also the longest river in Guanzhong Plain. Many studies have focused on water environment of Weihe River, most of which viewed on physiognomy from large area and the channel change of Weihe River during history. It is seldom to reveal the change law of water environment during history through viewed from floodplain deposits.We collected three profiles in the south floodplain near the riverbed and analyzed the samples by grading analysis, total organic carbon analysis, CaCO₃ content analysis and heavy metals Hg analysis. We try to discuss the change law of Weihe River during last 120a and give the developing trend of water environment. We used field survey, laboratory analysis and historical documents to study the three profiles. The character of grain size, particle size distribution and the change of grain parameter have been studied by grading analysis. The change of TOC, CaCO₃ content and Hg content has also been determined. Based on study, the water environment change law has been discussed. The main conclusions are following:1. The materials obtained from two profiles in Weihe floodplain in Gaoling Xi'an show that the sediment developed well and grain size changed greatly, which indicated the flood change of Weihe River clearly. The change of grain size was mainly caused by the fluvial power, which was related with the climate change in Weihe River watersheds. So the change of grain size would indicate the climate change indirectly. The coarser sedimentary layers reflect the strong fluvial power and the warm-wet climate; on the contrary, the finer sedimentary layers reflect the weak fluvial power and the lower warm-wet climate. The climate of the periods during the sedimentary layers was dry, during which no heavy floods occurred. So we can rebuild hydrolohical and climate environment according to the flood sedimentary layers.2. The first layer was the latest flood sediment, i.e. the sediment of the heavy flood in 2003. The other 15 layers below it were sediment of historic flood. It is 1881 that is the latest record of Weihe River north moving. So the sediment of SC and LB profiles in Gaoling floodplain should reflect the Weihe River change during last 120a.3. The most thickness of SC profile is 3.9m. Based on analysis the finest layer on the top profile below the sediment of flood in 2003, it reflects the flood deep is no less...