长江中游荆江河段典型断面崩岸预警方法及应用

Study on early-warning method of bank collapse at typical sections of Jingjiang Reach of Middle Yangtze River and its application

受三峡水库蓄水拦沙的影响,进入长江中游荆江河段的泥沙量剧减,河床持续冲刷下切,崩岸现象频发,不仅影响河势稳定,而且还增大了防洪压力。首先从水沙条件和河床边界条件方面选取10个崩岸影响因子,对其量化处理;其次基于实测数据,采用随机森林模型计算崩岸发生的可能性,并对模型进行率定和验证;最后基于DS证据理论融合崩岸可能性、临江居民区面积和堤外滩体宽度3个预警指标,划分典型断面的崩岸预警等级。研究结果表明:随机森林模型可较好地对崩岸现象进行预测,模型测试集准确率为75%;划分的预警等级与长江水利委员会水文局发布的预警信息总体相符,其中青安二圣洲荆60L断面和北门口荆98R断面预警等级较高,在2018~2020年均为Ⅰ级或Ⅱ级预警。此外还分析了各崩岸影响因子的重要性,其中护岸工程对崩岸的影响最大(重要度为16.6%),河岸坡度对崩岸的影响次之(14.4%),流量的重要度为10.2%。

Affected by the operation of the Three Gorges Reservoir,sediment amount entering the Jingjiang reach of middle Yangtze River was sharply decreased,resulting in intensive river bed incision and bank erosion,which would not only affect the channel stability,but also increase the flood control pressure.In this paper,firstly 10 bank collapse influencing factors were selected from the aspects of water-sediment conditions and riverbed boundary conditions,and quantified.Secondly,based on the measured data,the random forest model was used to calculate the possibility of bank collapse,and the model was calibrated and verified.Finally,based on the DS evidence theory,three early-warning indicators(bank erosion possibility,nearby residential area and the width of floodplain)were combined to divide the early-warning level of bank collapse of typical sections.The results showed that:①the random forest model could well reflect the correlation between the influencing factors of bank collapse and its occurrence possibility,with a high accuracy of 75%being obtained during the model test.②The obtained early-warning levels agreed with the published results of Changjiang Water Resource Commission,and especailly at the right banks of sections of Jing 60L and Jing 98R,the calculated warning levels of bank collapse was relatively high,with grade I or grade II from 2018 to 2020.Furthermore,analysis on the contributions of different influencing factors to bank collapse in the Jingjiang reach indicated that bank revetment had the greatest contribution of 16.6%,followed by the bank slope of 14.4%,whereas the contribution of discharge is 10.2%.