琼江两次洪水过程的水文气象分析

Hydrometeorological Analysis of Two Flood Events in Qiongjiang River Basin

对2012年7月3-5日和2013年6月30日至7月1日四川盆地东南部四川省和重庆市交界处的琼江流域两次洪水过程的水文气象条件进行了分析。利用数字高程模型DEM提取了琼江流域的河网分布和河道距离出口的分布,结合标准化时间距离方法客观地反映了降水(尤其是强降水)的时空分布情况。SWAN输出的组合反射率因子拼图表明两次琼江流域的强降水均由多段强降水雨带导致,对流系统多在右岸支流源头新生,移向与河流流向一致,在于流产生洪水的叠加效应。由于"6.30"过程中强回波几乎覆盖整个琼江流域长达约16 h,导致严重的洪水叠加效应,洪水漫过原有河道形成大面积滞洪区,洪水行至下游河段回归河槽时,加之河道收窄,造成下游水文站洪峰时间滞后。

Analyses and descriptions of the hydrometeorological conditions that contributed to two flood events in the Qiongjiang River Basin from 3 to 5 July 2012( '7.4') and from 30 June to 1 July 2013( '6.30') are presented.The digital elevation model(DEM) is used to extract the distribution network of Qiongjiang River and its distance to the outlet,and the standard time distance objectively reflects the temporal and spatial distribution of precipitation(especially severe precipitation).Composite reflectivity mosaic from SWAN suggests that the heavy precipitation is caused by multiple extreme rainfall bands in both of the flood events,and the convective systems mainly initiates in the headstreams of the right tributaries moving northeastward slowly down the tributaries and producing flood overlap in Qiongjiang River stem.Since basin-wide severe radar echo persists over the Qiongjiang River Basin for about 16 h,serious flood overlap is significant in the '6.30' case,resulting in the flood overflowing in the bank and forming a large area of flood detention basin.When the flood gets to downstream and returns to the river channel,the runway gets narrowed,so the flood peak time at the Taian Hydrological Station is late.