漫滩洪水中不同房屋分布的阻力特性研究

Investigation into resistance characteristics of building distributions in overbank floods

漫滩洪水是威胁滩区居民生命财产安全的一种主要自然灾害,村庄等微地貌直接影响洪水演进过程,故采用概化物理模型和数值模拟的方法研究滩区房屋分布的阻力特性。以黄河下游兰考东明滩区地形为参考,修建概化滩区的物理模型,研究主槽4种不同进口流量下,房屋呈4种不同排列方式及4种迎流角度条件下,房屋试验区水流的变化情况。试验结果显示随主槽进口的流量增大,房屋试验区四周的水深呈非线性增加;房屋试验区房屋呈不同排列方式时,模型试验区形成的局部阻力不同。然后采用数学模型计算典型工况的洪水演进过程,水位的计算值与实测值符合较好,模型具有较好的计算精度。最后采用加大糙率法计算溃堤水流演进过程,发现以曼宁系数取0.05、0.08、0.12和0.16分别代表房屋以3×3、4×4、5×5及交错排列情况下的综合阻力时,计算得到水深、水跃位置与模型试验结果基本一致。研究结果将为房屋合理布局,减少漫滩洪水淹没损失提供参考依据,亦可用于检验水动力学模型的计算精度。

Dike-break flooding is a main natural disaster that could cause losses in life and property on river floodplain, and studying its routing characteristics is crucial to protection of such areas. However, complex types of the underlying surface of a river floodplain produce different flow resistances. In this study, a generalized physical model and numerical simulations are used to examine the influence of buildings distributions on flood routing over the Lankao-Dongming floodplain area of the lower Yellow, focusing on the flows over an area of buildings arranged in four different patterns under four main channel discharges and four incoming flow angles. The experimental results show that flow depth over this area is increased with the increase in the inflow discharge of the main channel and its flow resistance varies with different building arrangements. Then, we use a two dimensional hydrodynamic model to calculate the flood inundating process, and obtain calculated flow depths in good agreement with the measurements. For the building area, different Manning coefficients are calculated for the simulations to improve its resistance modeling by comparing to the corresponding measured depths. Results show that at Manning coefficients of 0.05, 0.08, 0.12 and 0.16, the calculated depths are in good agreement with the measured values under building patterns of 3×3, 4×4 and 5×5 arrays and a staggered array respectively;and that the location of the simulated hydraulic jump are nearly the same as experimentally measured. This study helps the planning of building arrangement on river floodplain to reduce dike-break flooding, and it is also useful for verifying the accuracy of hydrodynamic models.