潮汐河口动床洪水的数值模拟

Numerical simulation of flood on movable bed of a tidal estuary

潮汐河口洪水水位受流域来水和海域潮汐双重作用,动力机制复杂,在特大洪水作用下,河口床面边界还将发生显著变形,造成水面相应明显升降,以致用定床模型预报洪水位误差很大。本文以钱塘江河口为例,采用Delft3D数学模型对潮汐河口洪水水位进行二维数值模拟试验。在定床和动床模型均取得良好验证的基础上,进一步预报洪水过程,发现定床模型可产生近1m的计算误差;而动床模型则能比较精确地计算整个洪水过程的水位,最大误差不超过0.08m。因而预测冲淤幅度较大的潮汐河口的洪水水位最好采用动床数学模型。论文还就洪水位的空间分布探讨弯道水面横比降随洪水流量的变化。

The dynamical mechanism of water level in tidal estuaries is complicated owing to the cooperation of flood runoff and tidal current. Under extreme flood the considerable change of bed boundary would also cause the obvious rise and fall of water level correspondingly so that the prediction of the flood water level, based on a fixed bed model, would be inaccurate. Delft3D numeral model is adopted to simulate the water level of flood in tidal estuaries. The water level during flood is simulated respectively by two models, the fixed bed and the movable bed, which are well verified. The comparsion of the water level computed with the measured data indicates that error nearly lm occurs when the fixed bed model is used, whereas the error is less than 0.08m when the movable bed model is adopted. The latter has much higher precision and thus the 2D movable bed model should be adopted to predict the flood water level in tidal estuaries with the rapid varied bed. Moreover, the spatial varieties of the lateral hydraulic slope in the estuarine bends during flood are discussed.