钱塘江河口洪水特性

Flood characteristics at Qiantang River Estuary

钱塘江河口是强潮河口,流域来水过大、下游潮位过高,沿江即可能造成非常高水位.半个世纪以来,上游兴修水库,流域洪水已得到部分控制.河口地区大规模围涂,河道趋于稳定.同时,沿江对洪水、潮汐的响应特性有一定程度变化.上游水库拦蓄了一些小洪水,汛前河道容积因此减小;大规模围涂缩窄了河道,加强潮波反射,影响波及杭州湾湾口;河道过水断面减小,杭州20世纪90年代的平均高潮位比80年代高近50cm,70年代开始,年最高水位超过警戒水位的次数几乎每10年增加1倍.

The Qiantang River Estuary is a strong tide estuary. The large volume of incoming water from the river basin and the high tidal level on the lower Qiantang River might result in high water level along the river. For about half a century, the construction of reservoirs on the upper Qiantang River has brought floods in the river basin partly under control, and the large scale reclamation at the river estuary has improved the stability of the river channel. However, the characteristics of response to flood and tide along the river have changed in a certain degree: reservoirs on the upstream have stopped some weak floods, resulting in the decrease of the river capacity before the flood season; large scale reclamation has narrowed the river channel and strengthened its reflection of tidal waves, the impact spreading to the mouth of the Hangzhou Bay; the overflow section of the river channel has decreased, the mean high tide level at Hangzhou City in 1990s being nearly 50cm higher than that in 1980s, and the number of times that the highest water level exceeds the warning water level having doubled once in ten years since 1970.