黄河下游凌情特征及变化

黄河下游冰情的基本特点和规律是:冬季有的年份封冻,有的年份不封冻;下游下段河道流凌封冻日期早,融冰、开河日期晚,封冻历时长,冰盖厚冰质坚;上段河道流凌封冻日期晚,融冰、开河日期早,封冻历时短,冰盖薄冰质酥。冰凌洪水特点是流量小,水位高且上涨快;凌峰流量自上而下沿程逐渐增大。近20年来,由于黄河下游河道水量大幅度减少,甚至发生连年断流,冬季气温持续偏高,加上水库调度等因素的共同影响,引起了凌情的相应变化。这些变化主要表现为:封开河日期提前,封河长度缩短、封冻冰量和槽蓄水量减少,冰塞冰坝发生次数减少,不封冻年频率增加等。

Characteristics of ice regime in the lower Yellow River

The characters of ice regime in the lower Yellow River are as follows: the reach is completely freezing in winter for some years, and freezing-free for some others; in the reach, the freeze-up date is earlier, the break-up date later; and the freeze-up period is longer, and the ice-cover is thicker and solider than that of the upstream; the ice flood is characteristics of the small flow, high water level and increase from the upriver channel to downriver channel. In recent 20 years, the ice regime has changed with the discharge decreasing at large scale, the sustaining high temperature and the reservoirs control, so that the dates of the freeze-up and break-up are brought forward; the river length and ice volume of the freeze-up, the channel storage and the times of ice dam and ice jam are shorted; and the frequency of frozen-free years increases.