潼关高程下降对渭河下游防洪的影响

Effect of descending Tongguan's elevation on flood defense situation of Weihe River

潼关高程抬升引起渭河下游大量泥沙淤积,给防洪带来一系列问题。本文针对这一问题,通过对渭河下游河道40多年的大断面地形资料进行分析和计算,探讨了潼关高程与渭河下游泥沙冲淤的关系,并分析了典型断面的水位变化。结果表明,潼关高程与渭河下游泥沙冲淤密切相关,潼关高程下降后,渭河会产生溯源冲刷。在大水少沙情况下,近槽滩地也会受到冲刷,但是洪水漫滩后滩地会发生淤积,由于主槽面积增加,过洪能力增强,中小洪水防洪压力减小;但如果发生高含沙漫滩洪水,滩地淤积,漫滩洪水水位反而有所抬高,大洪水威胁依然存在。

The relationship between Tongguan's elevation and the erosion of lower reaches of Weihe River was analyzed according to the data of field measured river cross sections in 40 years. The result indicates that the erosion is closely related with the change of Tongguan's elevation. Retrogressive erosion in the lower reaches of Weihe River developed when Tongguan's elevation descended. Erosion of floodplain occurred in the vicinity of the main channel but sedimentation occurred on the floodplain where far from the main channel, in case of over-bank flood. It may infer that if Tongguan's elevation is descended by 2 m, the gradient of lower reaches of Weihe River will increase because of retrogressive erosion. The cross section of main channel will be enlarged. Hence the flood discharge capacity of the main channel will increase and the flood risk of small-scale or mid-scale flood will be reduced. However, the flood stage will be raised during over-bank flood because of the sedimentation on floodplain resulting in increase of flood threat.