卡特里娜飓风引起的新奥尔良市溃坝洪水演进过程模拟

Simulation of the evolution process of the dam-break flood in New Orleans caused by hurricane Katrina

卡特里娜飓风于2005年袭击了美国墨西哥湾沿海地区,给路易斯安那、密西西比和亚拉巴马等州带来了巨大灾难,造成经济损失800亿美元。其中位于路易斯安那州的新奥尔良市由于堤坝故障导致庞恰特雷恩湖湖水倒灌,80%的地区发生了洪水,损失尤为严重。为了动态且高效地模拟其溃坝后洪水的演进过程,建立了基于“体积法”与元胞自动机的溃坝洪水演进模型。模型通过设置元胞属性来考虑洪水流向以及不同土地覆盖类型的汇流差异性;提出了一种洪水淹没元胞多级分类的快速搜索算法(MLCFC),采用不同准则处理各类元胞以提高计算效率;利用“体积法”计算不同时刻元胞的水深来间接反映洪水演进的时空特性。以新奥尔良市为例,计算其溃坝发生后2~20 h不同时刻的淹没情况。结果表明,模型模拟的淹没过程符合溃坝洪水的蔓延特性;试验结果与遥感影像中提取的水体重合率为61.18%,能较好地模拟城市地区溃坝时洪水演进的时空特性。

Hurricane Katrina struck the coast of the Gulf of Mexico in 2005,causing huge disasters in Louisiana,Mississippi,and Alabama with economic losses of$80 billion.In New Orleans,Louisiana,80%of the area was flooded due to the backflow of Lake Pontchartrain caused by dam failures.In order to simulate the flood evolution process after the dam break dynamically and efficiently,a dam break flood evolution model is established based on the“bulk method”and cellular automata.The flood flow direction and the difference of the confluence of different land cover types are considered by setting cell attributes.A fast search algorithm for multi-level classification of flood submerged cells(MLCFC)is proposed,which uses different criteria to process various types of cells to improve calculations efficiency.“Bulk method”is used to calculate the depth of the cell at different times to indirectly reflect the temporal and spatial characteristics of the flood evolution.Taking the city of New Orleans as an example,the inundation conditions at different times from 2 h to 20 h after the dam break is calculated.The results show that the inundation process simulated by the model is consistent with the spreading characteristics of the dam-break flood.The coincidence rate of the experimental results and the water body extracted from the remote sensing image is 61.18%,which can well simulate the temporal and spatial characteristics of the flood evolution during the dam-break in urban areas.