Study On Flood Coincidence And Backwater Effect In Nen River And The Second Songhua River

Flood disaster is one of the major natural disasters in Songhua river basin.Affected by factors such as river bottom terrain and upstream inflow,the phenomenon that the floods of Nen river and the Second Songhua river(referred to as Ersong river)have frequently encountered in history,resulting in the occurrence of large floods and backwater effect in the intersection area,which has greatly increased the flood control risks and the pressure of flood control work in Songhua river basin,especially in the intersection area of the two rivers and the main stream of the downstream Songhua river(referred to as Songgan).Therefore,it is necessary to carry out analysis and research on the flood encounters and flood jacking in Nen river and Ersong rivers,so as to understand the flood encounters and flood evolution laws in the intersection estuary area,and to provide support for effectively reducing flood impact and scientifically controlling flood season.This paper takes Nen river and Ersong rivers in Songhua river basin as the main research objects,focusing on the analysis and research of flood encounters and backwater effect of the two rivers.The main research contents are as follows:(1)Firstly,the trend and consistency analysis methods of time series are used to analyze the trend and consistency of long-series measured hydrological data of Jiangqiao hydrologic station of Nen river and Fuyu hydrologic station of Ersong river.Then,the P-Ⅲ distribution is used to carry out parameter fitting calculation on the flood sequences of the two rivers that meet the consistency requirement,and the fitting results are used for flood frequency analysis and calculation.(2)Statistics and Copula methods were used to analyze the flood problems of Nen river and Ersong river respectively.On the one hand,based on the measured data of Jiangqiao station and Fuyu station,the flood peak encounter and flood process encounter of the two rivers are statistically analyzed.On the other hand,based on Copula method,the risk of flood peaks in the two rivers is mainly analyzed.Von Mises distribution function and P-Ⅲ distribution are respectively used as marginal probability density function of peak occurrence time and peak discharge of the two rivers and parameter fitting is carried out.Select the appropriate Copula joint distribution function to construct the flood magnitude and peak time joint probability distribution of joint distribution function,Nen river and Ersong river respectively.Finally,based on the joint probability distribution function,the exposure risk of the two rivers in flood season is calculated,and the exposure risk of the two rivers in different flood levels is further calculated.(3)The MIKE11 one-dimensional hydrodynamic flood routing model is constructed to simulate and calculate the river channel flood routing in Jiangqiao hydrologic station of Nen river,Fuyu hydrologic station of Ersong river and Harbin hydrologic station Songgan.Based on the simulation results,the regularity of Nen River under different flood combinations is qualitatively analyzed,and the distance and backwater height influenced by Ersong River jacking are quantified.