Study On The Process And Numerical Simulation Of River Ice Transport In The Upper Reaches Of The Main Stream Of Heilongjiang River During The Break-up Period

The upper reaches of the Heilongjiang River are located in the middle and high latitudes above53°N.Sometimes,due to the influence of temperature or river topography,the upper reaches of the river open earlier than the lower reaches,forming an "inverted river",and the ice from the upper reaches acts on the unsealed ice,making the water surface rapidly congested and easily causing ice jam,ice dam,and other flooding disasters.In order to improve the flood prevention ability along the Heilongjiang River,we combined the meteorological data from 1958 to 2022,and conducted a study on the change of ice phenology in the main stream of Heilongjiang River,including the freezing degree days,the starting and ending dates of negative temperature accumulation,the number of days of negative temperature accumulation calculation,and the trend of maximum ice thickness.In order to investigate the changes of river ice velocity along the river and the transport process during the river opening period,we analyzed the distribution of river ice velocity in the main stream of Heilongjiang River and the changes of river ice velocity under different river characteristics by throwing miniature ice buoy locators for drift ice tracking test,and combined with MIKE21 hydrodynamic model to simulate the river ice process in typical river sections,and combined with actual data to analyze the influence mechanism of river ice hydrodynamic change process.The specific research contents are as follows:1.From 1958 to 2022,the multi-year monthly average temperature of the Mohe continued to increase.Throughout the ice period,the monthly average temperature warming ranged from 0.42 to0.75°C per decade,the multi-year monthly average wind speed showed a yearly decrease,and the monthly average wind speed decrease rate during the icing period did not differ much.From 1954 to 2022 in Huma,the multi-year monthly average temperature continued to increase.Throughout the icing period,the monthly average temperature increases between 0.25 and 0.72°C per decade,and the monthly average wind speed also shows a gradual decrease,and the decrease of the monthly average wind speed is close to each other.The yearly increase in winter temperatures leads to a decrease in the number of freezing degree days and affects the river ice process.2.From 1958 to 2022,the starting date of negative cumulus temperature calculation in the Mohe region was delayed by 0.52 d per decade,the ending date of negative cumulus temperature calculation was advanced by 0.81 d per decade,the linear decreasing trend of negative cumulus temperature calculation days was 1.29 d per decade from 1957 to 2022,and the multi-year average of negative cumulus temperature was 3417.03 d·℃;from 1954 to 2022;the negative cumulus temperature calculation in Huma region was delayed by 0.61 d per decade,the ending date of negative cumulus temperature calculation was advanced by 1.27 d per decade,and the linear decreasing trend of negative cumulus temperature calculation days was decreased by 2.27 d per decade from 1954 to 2022.The linear decreasing trend of the number of days of negative cumulative temperature calculation between 1954 and 2022 is 2.62 d per decade,and the multi-year average of negative cumulative temperature is 2860.04 d·℃.The maximum ice thickness of each region is calculated,When α is 1.7,the maximum ice thickness is 108.35 cm and the average ice thickness is99.29 cm in the Mohe region from 1957 to 2022;the maximum ice thickness is 102.42 cm and the average ice thickness is 90.80 cm in the Huma region from 1954 to 2022.When α is 2.4,the maximum ice thickness is 152.96 cm and the average ice thickness is 140.18 cm in the Mohe region from 1957 to 2022;the maximum ice thickness is 144.60 cm and the average ice thickness is 128.19 cm in the Huma region from 1954 to 2022.Maximum ice thickness has a negative correlation with year,showing a decreasing trend from year to year.3.The velocity of drift ice during the opening period can be accurately obtained by throwing miniature ice buoy locators.2019 observations of the mainstream of the Heilongjiang River show that the velocity of drift ice during the opening period is distributed between 0.79 and 3.56 m/s at69-692 km from the source of the mainstream of the Heilongjiang River,with an average velocity of 1.65 m/s.The velocity of drift ice decreases as the river width increases.The average velocity is about 3.00 m/s when the river width is about 180 m.When the river width increases to about 600 m,the average velocity decreases to about 1.42 m/s,with a decrease of about 52.7%.4.The flow velocity decreased significantly when the ice flowed through the curved river section and the branching river section.Among the curved river sections,the flow velocity of the "First Bay of Heilongjiang River" from the upstream to the first bend of the river downstream decreases the most,from 2.30 m/s to a minimum of 0.10 m/s,and the ice velocity decreases by95.65%,and the average flow velocity through this section is 0.82 m/s.In the branching river,there are also river bends,sudden channel shrinkage,tributary convergence,and river core islands,which have a great influence on the passage of river ice,In the branching river channel,there are also river bends,sudden shrinkage of the river channel,tributary convergence and the influence of the river island,which also has a great impact on the passage of river ice.The maximum velocity reduction of the river ice in the Pioneer Island section of the Beihong Village is about 88.00%,from the highest of 2.5 m/s to the lowest of 0.3 m/s.The average velocity of the river ice in this section is 0.98 m/s.The maximum velocity reduction is 47.39% in the Ussuri Shoal section,from the highest 2.87 m/s to 1.51 m/s,with an average velocity of 2.07 m/s.It can be seen that river characteristics reduce the strength of the effect of flow ice velocity in the following order: the curved river section is greater than the branching river section(river center island)is greater than the straight river section.The curved river section is more prone to ice jamming and ice damming.5.Based on the measured data of the river channel,a hydrodynamic model of the river channel under different channel characteristics in the upper reaches of the Heilongjiang River was established to analyze the changes of water surface elevation,flow velocity and flow field along the river channel during the opening period.The water surface elevation in the shallow section of the Ussuri River did not show any water surface congestion during the opening period,and the flow velocity was evenly distributed without any sudden increase or decrease,and the flow velocity in the center of the river was fast and the flow velocity on both sides was slow,and the direction of flow velocity in the river section was almost parallel;the water level rose on the concave bank side of the whole river section in the "First Bay of the Heilongjiang River",but the water level increased from the upstream to the first bend and the last bend in the downstream.The initial water surface elevation of the river in the Xing’an Town section decreases with the ratio of the river and is evenly distributed,but the water level at the branch of the river appears to be high,the flow velocity of the main branch of the river is fast,and the flow velocity of the center of the river is fast and slow on both sides of the bank,and the flow velocity of the branch of the river is complicated and The overall flow velocity is low.