Discharge in break-up period in the Inner Mongolia reach of the Yellow River
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Abstract:
Ice and water regime changed drastically due to frozen thaws in the break-up period in Inner Mongolia reach of the Yellow River,so it is difficult to forecast the flood and the accuracy is low.There are relatively few researches on ice flood forecasting methods,and most of the existing research methods focus on the flooding process under open flow condition.Due to the limitation of the measured data during the ice period,the research on ice floods is far from enough.The Muskingum method and its derivation method are suitable for the discharge routing under open flow conditions,but how to reflect the characteristics of discharge routing in ice flood season needs to be studied.Given the characteristics of the channel with unbalanced storage in the upstream and downstream channels,there is still no better solution in the derivative method of the Muskingum method. Based on the prototype observation of Inner Mongolia reach of the Yellow River and the measured discharge data during the ice period,the transformation process of ice and water during the freezing and thawing periods is analyzed,and the ice flood type is identified by the ice flood characteristics to predict the downstream discharge in advance.The discharge process of Inner Mongolia reach during the break-up period is calculated.The modified Muskingum method is used to calculate the flood routing by analogy with the river channel with tributaries.Considering the propagation time of discharge,channel-storage increment during the freezing period is added into the calculation to calculate the ice peak discharge during the break-up period. Compared with the flood in flood season,the ice flood occurred during the break-up period,the flood peak spread to the downstream not only did not flatten but also had a sudden change in the short term.When the temperature changes violently during the break-up period,the channel-storage increment is released in a short time.Channel-storage increment during the freezing period is considered,which can solve the problem of the increase of the channel storage in the prediction of discharge during the break-up period.Root mean square error,average absolute percentage error is used as the evaluation indexes of the prediction results.Compared with the measured discharge,root mean square error and average absolute percentage error of the calculated discharge reach the ideal accuracy,and the average absolute percentage error is less than 10.29%.The ice flood during the break-up period is mainly composed of ice dam flood and ice melting flood.According to the transformation process of ice and water and the characteristics of ice flood,it is found that the sudden change of discharge in ice flood season is mainly caused by ice dam flood.When ice dam flood occurs,the ice peak discharge increases along the way,with fast-rising rate,large amplitude,and large peak value.When ice melting flood occurs,the water potential is stable,and the discharge difference between upstream and downstream is small,and the ice peak discharge is small. During the break-up period,the increasing ice peak discharge from the upstream to the downstream can easily cause flood disasters along the river.The application of the modified Muskingum method can predict the sudden change of the downstream discharge,which has a good prediction effect on the discharge routing in ice flood season during the break-up period and greatly reduces the influence of ice regime and other uncertain factors on the prediction of ice flood process.The research results can provide a reference for the discharge forecast during the break-up period and the work of preventing and reducing disasters.In future,the influence of temperature and other factors on the discharge routing in ice flood season can be considered,and the relationship between temperature,channel-storage increment,and discharge can be further studied.
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