黄浦江流域洪灾动态风险演化趋势研究

Variation Analysis of Flood Dynamic Risk in Huangpu River Basin

改革开放以来,黄浦江流域经历了快速的城市化过程,人类活动极大改变了流域的自然环境和洪灾风险特征。利用洪水数值模型开展1979、1990、2000和2009年黄浦江流域5、50和500年一遇洪水情景模拟。在此基础上,参考相关标准,构建基于土地利用的脆弱性分级方法和风险判别矩阵,进而分析了黄浦江流域洪灾动态风险的演化特征。研究结果显示:转型期黄浦江流域洪灾动态风险呈现先缓慢增加后显著降低的演化趋势,在空间上洪灾风险表现为从几乎全流域分布到中上游地区集中分布的趋势,防汛墙的扩建加固以及快速城镇化进程是导致洪灾风险演化的主要因素。

Huangpu River Basin has experienced rapid urbanization since＂reform and opening up＂. Increasing human activities greatly changed the natural environment and flood risk characteristics in this area. This article presented a scenario-based study that investigated the flood dynamic risk in Huangpu River floodplain during the transitional period（1979-2009）. A 1D/2D coupled flood inundation model（Flood Map） was firstly used to simulate the designed flood scenarios with 5 a, 50 a and 500 a return periods in 1979, 1990, 2000 and 2009. The flow hydrographs at the boundary gauging stations（i.e. upstream Mishidu and downstream Wusong） were derived using a simplified algebraic subtraction of the water levels with different return period which have been calculated in our previous studies and the maximum water level during the 9711 flood event where hourly stage hydrograph was available. The flood processes are only represented with 24 h stage hydrographs, including two rising and falling phases. 175 rectangular cross-sections were used as the 1D river channel model. The DEMs of 1979, 1990, 2000 and 2009 were generated based upon the 2005 DEM and land subsidence data of 1980-2009 for the study area. Roughness parameters of river channel and floodplain were represented by varying manning＇s. These provided the boundary conditions and the calibrated parameters for the model simulations. Furthermore, land use maps of the study area in various time points were used for vulnerability analysis and then they were categorized into four classes. On the basis of some relevant national standards and expert judgments, a flood risk matrix, which comprehensively considerate the relationship between flood inundation and vulnerability, was constructed for the analysis of flood dynamic risk variation in Huangpu River Basin during the transitional period. The results shown that over the past 30 years, the flood dynamic risk of Huangpu River Basin slightly increased between 1979 and 1990 due to rapid urbanization and land subsidence in floodplain but significantly reduced afterwards particularly in city center because the floodwall system along Huangpu River has been largely extended and reinforced. As expected, the flood risk obviously increased with the increasing return periods. Spatially, the flood risk appeared in most of riparian regions in 1979 and then it was gradually restricted to mid- and upstream. Finally, uncertainties and limitations were analyzed and some suggestions were presented for future researches.