汶川地震后北川县城防洪计算

Quantifying Flood Control Capacity of Beichuan City After the Wenchuan Earthquake,China

"5·12"汶川地震形成了大量颗粒松散物质,导致河道大幅淤积、抬升等剧烈地貌变化,从而在相当长时间内改变原有的河道行洪特征,诱发次生洪水灾害。论文对唐家山至北川县城一线的通口河河道进行洪水数值模拟,定量分析该河段由于河床地貌突变所导致的汛期洪水威胁增强效应及其对北川县城地震遗址防洪能力的影响。计算表明:由于唐家山堰塞湖泄洪和魏家沟泥石流的影响,该河段沿程大幅淤积抬升,现状行洪能力大大低于震前20年一遇洪水的水平,远低于国家地震遗址保护要求的防洪标准;计算的水位和冲深对河道糙率较为敏感,但是由于河床地貌和床沙组成剧烈变化,糙率变化需要进一步研究。

A quantitative analysis of the increased flood hazard in the Wenchuan Earthquake-hit region was carried out.Flood routing was performed for the reach of Tongkou River from Tangjiashan Quake Dam to Beichuan City and the change of flood defense capacity of Beichuan City was examined.It was shown that since the river bed was seriously raised by the Tangjiashan Quake Lake drainage and subsequent Weijiagou Debris Flow,the present flood defense capacity near Beichuan City had become much lower than that before the earthquake（i.e.,the capacity against a 20-year flood） and far away from the requirement of protecting a national commemoration earthquake site.Meanwhile,the predicted water level and erosion depth were sensitive to the manning roughness coefficient for flood routing.It would be desired in future to explore the manning roughness coefficient changing with river geomorphology and bed material composition.