Study on the Annual Variations and Intra-Annual Distributions of Incoming Water and Sediment in Lower Yellow River
In order to explore the new regime of water and sediment in the Lower Yellow River in recent 20 years,based on the measured da-ta from 1997 to 2020 at Huayuankou Station,and compared with the water and sediment data at Tongguan Station in the same period,the an-nual fluctuation characteristics of incoming water and sediment in the Lower Yellow River were systematically analyzed from five aspects of trend,variability,periodicity,annual distribution and water-sediment collocation.The results show that the overall trend of runoff and sedi-ment load at the two stations from 1997 to 2020 is a notable increase and a significant decrease respectively.The amount of water and sedi-ment in Tongguan mutates around 2018 and 2004 respectively.Meanwhile,the amount of water and sediment in Huayuankou mutates signifi-cantly in 2017 and 2001-2002 respectively.The main cycles of water and sediment at Tongguan Station are 14 and 13 years respectively,with an average cycle of about 9.5 years.The main cycles of water and sediment at Huayuankou Station,on the other hand,are 13 and 12 years respectively,with an average cycle of about 8 years.Based on the above analysis,the study period of 1997-2020 can be divided into five phases.The intra-annual distribution inhomogeneity of the flow at the two stations during the five phases is similar,both experienced an alternating process of decreasing-increasing,while the intra-annual distribution of the sediment concentration differs in the phases.At Tong-guan Station,the incoming sediment coefficient ξ decreases while the water-sediment coefficient K increases with each stage.On the other hand,at Huayuankou Station,the incoming sediment coefficient ξ decreases in the first four stages and rebounds in the V stage,while the water-sediment coefficient K remains small in the first two stages and increases from Ⅱ to Ⅳ stages before decreasing in the Ⅴ stage.Under the combined effect of the changes in the natural incoming water and sediment process and the artificial water and sediment regulation,the water-sediment process has been characterized by obvious stage changes,and overall,the water-sediment conditions have been improved rela-tively in the past 20 years.
water and sediment regimetrendwater-sediment collocationwandering river reachLower Yellow River
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