生产堤溃决后漫滩水流的概化模型试验研究

黄河下游主槽两侧修建的生产堤通常仅能抵御中小洪水,用于保护滩区农田与村庄安全;当遭遇大洪水引发生产堤溃决时,漫滩洪水会严重威胁滩区群众的生命财产安全。当前研究溃堤洪水的传播过程与演进机理多采用数值模拟,而原型观测及模型试验成果十分有限。通过溃堤漫滩洪水的概化模型试验,模拟了生产堤溃决后主槽内的水位变化及不同程度漫滩洪水的传播过程。试验结果表明:(1)溃堤后漫滩水流以涨水波的形式向滩区迅速传播,主槽内水位具有先降低,然后维持稳定,再升高,最后趋于稳定的变化过程,且溃口上、下游水位变化速率不同;滩区水位总体表现为持续升高,最后趋于稳定的趋势。(2)漫滩洪水波的波前到达时间主要与滩区地形及距溃口的距离有关,波前首先以溃口为中心呈近似对称式椭圆形分布,而后转变为非对称分布;溃堤水流在滩区传播过程中伴有水跃发生,水跃发生的位置由距溃口较远处逐渐趋向溃口位置。(3)溃口流量与溃口内外水位差直接相关,呈先减小、然后维持稳定、再减小最后为0的变化特性。研究成果不仅可以提升对溃堤洪水在滩区演进规律的认识,丰富溃堤洪水动力学理论,还可为数学模型验证提供实测资料。

Experimental studies on farm dike-break induced overbank floods using a sketched physical model

Farm dikes constructed along the main channel in the Lower Yellow River can withstand small and median floods, and protect farmland and villages from flooding. Farm dike-break induced overbank floods not only cause water level changes in the main channel, but also lead to severe flood disasters on the floodplain. Numerical simulation is often employed to study dike-break floods, and previous results obtained from prototype and model measurements are very limited. In this study a sketched laboratory model was constructed to investigate the inundation process of farm dike-break induced overbank floods, and characteristics of water level changes along the main channel and over the floodplain were analyzed. Experiment results show that:① after the farm dike burst, the diffusion flood wave rapidly routed over the floodplain, which caused the surface-negative wave in the main channel and the surface-positive wave on the floodplain. Water levels in the main channel decreased first, and then kept stable, and then rose to another stable level, and the rates of water level change were different in the reaches upstream and downstream of the dike breach site. Water levels on the floodplain generally kept rising firstly and finally tended to be stable, with inverted slopes of water surface in local regions; ② arrival times of wavefront routing in overbank floods were mainly associated with the terrain and the distance from the site of dike breach, and the measured wavefront had a distribution of symmetric elliptic shape firstly and then a asymmetric distribution. Hydraulic jumps occurred in the process of dike-break induced overbank floods, and the position of hydraulic jump gradually approached the dike breach site from a farther distance; and ③ the breached discharge was directly related to the difference in water levels on both sides of breach. The breached discharge decreased first, and then remained stable, finally decreased to zero. Experimental results can provide the basis experimental data not only for the research into overbank floods due to farm dike-break, but also for validation of mathematical models.