略论二级悬河

悬河是指河床明显高出河流堤防背河侧地面的河流(或河段),又称地上河,它具有水位常年高于背河侧地面、河势多变、防洪工程自行降低标准、堤防决口后灾害严重、一旦堤防决口可能造成改道等特点。二级悬河是指河槽平均河底高程高于滩地平均河底高程的河流(或河段),黄河下游20世纪70年代初开始形成二级悬河。平原堆积性河流,河床不断淤积抬高,存在滩面横比降;悬河,具有平原堆积性河流的特点,且河床明显高于河流堤防背河侧地面;二级悬河由悬河淤积而成,除具有堆积性河道、悬河的特点外,就断面形态而言,还应同时具有滩面横比降陡、滩唇高程远高于堤防临河侧附近滩面高程、河槽平均河底高程高于滩地平均河底高程的特点。

Brief discussion on the secondany perched river

The perched river means that its river bed is higher than the ground elevation outside banks,and the secondary perched river is a river with the mean elevation of the main channel higher than that of floodplains.Usually the perched river has such characteristics as that the water level is higher than ground elevation outside river banks,the flood disaster is more severe,and the river course may change in the case of dike breach.Besides these characteristics,the secondary perched river exhibits its own characters including that the main channel is higher than floodplains,the floodplains is higher than ground level outside river banks,floodplains have lateral slope,ect.After a brief introduction about the current condition of the perched river in the Lower Yellow River,this paper gives a sketchy discussion on the formation reasons,the evolution processes,and the characteristics of the secondary perched river in the Lower Yellow River.