| The Yellow River,as the mother river of the Chinese nation is one of the rivers that are most difficult to regulate in the world.The fundamental problem of the lower Yellow River(LYR)is that the water is less while the sediment is too much,which leads to the riverbed sedimentation.The choice of regulation measures lies in the understanding of the regularity of flow-sediment movement and sedimentation.For this reason,based on the measured data of flow and sediment in the lower Yellow River from 1960 to 2010,a year is divided into three periods which include floods and non-flood period in flood season and dry season,and the LYR is divided into four reaches.The refined study on the regularity of flow-sediment movement and sedimentation of different periods in the LYR is conducted which reveals the intrinsic relationship between sediment transport rate at the four stations(Huayuankou,Gaocun,Aishan and Lijin)and the flow-sediment conditions at their nearest upper station,and establishes the relationship between the sedimentation amount in the LYR and the flow-sediment factors.Thus the evolution trend of sedimentation in the LYR in the future is stimulated and is compared with the mathematical model calculation results.The relationships established above can provide a rapid and reasonable prediction technology for the sedimentation influence in the LYR which caused by the water conservancy project construction and the operation of hydraulic engineering in the upper and middle reaches.That has significant practical application value.The main innovations of this paper are as follows:(1)The research on the regularity of flow-sediment movement and sedimentation in the LYR has been refined in time and spatial dimensions.There are a large number of research results on the regularity of flow-sediment movement in the LYR.However,in the time dimension,most of them only pay attention to floods,or the flood season,or the whole year,and pay less attention to the dry season.In the spatial dimension,most of them divide the LYR into Henan reach and Shandong reach.There are few studies which divide the process into floods,non-flood period in flood season,dry season and divide the LYR into wandering reach,transitional reach and meandering reach simultaneously.In fact,the regularities of flow-sediment movement in the flood season and the dry season are significantly different,and the regularities of flow-sediment movement in wandering reach and in transitional reach are also obviously different.If the flow-sediment process and the river reaches are considered in general,it is bound to conceal the regularity of flow-sediment movement and sedimentation in different periods and different river reaches.Thus,in this paper,a year is divided into three periods which include floods and non-flood period in flood season and dry season in order to reflect the differences of the flow-sediment movement in different periods,and the LYR is divided into four reaches which include Xiaolangdi-Huayuankou reach,Huayuankou-Gaocun reach,Gaocun-Aishan reach and Aishan-Lijin reach in order to show the differences in the flow-sediment movement in different river reaches.(2)It reveals the regularity of flow-sediment movement along the LYR in different periods,and establishes the relationship between sediment transport rate and incoming flow-sediment conditions in different river reaches.Using the measured data of flow-sediment and 304 floods data from 5 hydrological stations in Xiaolangdi,Huayuankou,Gaocun,Aishan and Lijin from 1960 to 2010,the relationship between the sediment transport rate at the lower station and the flow rate,sediment concentration and sediment transport rate of the upper station during different seasons is studied.The results show:The relationship between the sediment transport rate at the lower station and the sediment transport rate at the upper station is significantly better than that with the flow and sediment concentration in the three periods.Further,the flow-sediment process is graded according to the sediment coming coefficient(S/Q)at Xiaolangdi station,it is found that the relationship between the sediment transport rate at the lower station and the sediment transport rate at the upper station becomes better,and the majority correlation coefficient reaches 0.95 or more.According to this correlation,when the flow-sand conditions of the Xiaolangdi Station are known,the sediment transport rate of each of the Huayuankou,Gaocun,Aishan and Lijin 4 stations can be quickly calculated one by one,then the sedimentation of each river reach can be obtained.(3)It reveals the regularity of sedimentation of the LYR,and establishes the relationship between the sedimentation amount and water-sediment condition at Xiaolangdi station.The relationship between the sedimentation amount in the LYR and water-sediment condition(the average flow,the average sediment concentration,the average sediment coming coefficient)at Xiaolangdi station during floods,the non-flood period in flood season and the dry season,then the critical threshold of flow-sediment at Xiaolangdi Station when the equilibrium of the LYR in these 3 periods:the average sediment concentration is 45.13kg/m3 at Xiaolangdi station during floods.The sediment load is 177x106t,or the average sediment concentration is 24.25kg/m3,or the sediment coming coefficient is 0.024kg/s/m6 at Xiaolangdi station during the non-flood period in flood season.The sediment load is 182x106t,or the average sediment concentration is 12.6kg/m3,or the sediment coming coefficient is 0.014 kg/s/m6 at Xiaolangdi station during the dry season.(4)The sedimentation amount and the distribution along the LYR are calculated by the relationship of sediment transport rate,which is in good agreement with the measured values.According to the relationship among sediment transport rate,sedimentation amount and flow-sand factors in three different periods and four river reaches established in this paper,the sedimentation process of the LYR from 1960 to 2010 is re-calculated,and then the distribution of sedimentation in the four river reaches are presented during the flood season,the dry season and whole year.The results show that the cumulative amount and the process of sedimentation,or the distribution along the four river reaches,both of them are in good agreement with the measured value.The correlation coefficient between the calculated value and the measured value is above 0.83,and the method for calculating the sedimentation in the LYR established in this paper has high precision.(5)The process of sedimentation in the LYR in the future 50 years under different flow-sediment conditions is simulated.With the three flow-sand series currently used in the study of the sedimentation trend of the LYR in the future,which is the annual average amount of sand is 300x106t,600x106t and 800x106t,and the refined flow-sand relationship established in this paper and a well-developed mathematical model were used to calculatethe cumulative sedimentation process of the LYR in the next 50 years.The results show that the sedimentation processes and amount of the three scenarios calculated by the two methods are highly consistent(the correlation coefficients are 0.92,0.98,and 0.99),and the reliability of the forecast results is increased,which is important for the management of LYR in the future. |
PDF Full Text Request