Research On Flood Disaster System Adaptive Simulation And Risk Assessment In Mountainous City Of The Southeast Coast,China

In recent years,the ecosystem of watershed and urban as well as water cycle was destructed by rapid urbanization process,which caused many casualties and economic losses.The frequency of extreme events has increased over the world,which aggravated the flood risk of cities in China,especially in mountainous city of the southeast coast,China.The storm water management idea such as "sponge city"provided new solutions for reducing urban flood risk,whereas effective theory and method support were still lacked in mountainous city of the southeast coast,China.This research introduced the complex adaptive system theory and built flood disaster analysis framework of mountainous city,which take study on the change mechanism of water cycle,interaction model of disaster-formative environments and factors by multi-scenarios systemic analysis.Based on the RS/GIS spatial data operation technics and cellular automata analysis method,this research constructed hydrological model integrating scenarios analysis simulated the process of flood disaster from watershed and city levels,built the damage mechanism of disaster-affected bodies and conducted flood risk assessment.Based on the complex adaptive system theory,the flood disaster system of mountainous city was divided into disaster-formative environments and factors,disaster-affected bodies sub-system.The flood disaster system could be interacted with watershed and urban environment,the disaster-formative environments was constructed through substance exchange,mutual adaption and external transformation of human activities between watershed eco-system and urban system.As adaptive agent of flood disaster,disaster-affected bodies reduced the probability of being damaged by flood control and disaster reduction measures.On the other hand,rational land use planning was adopted to enhance the city’s ability to resist disasters.This process could be explained by four characteristics(accumulation,nonlinear,flow,diversity)and three typical mechanisms(identification,internal model,block).Take the upper reach of Tingjiang river of Changting county in Fujian province as study area.Based on the feature analysis of flood disaster system components,using modified distributed SCS model contains runoff generation and concentration module,parameters of the model were selected and determined according to the comprehensive analysis of model evaluation indexes.The flood peak discharge,flood volume and time to peak were assessed to investigate the outcomes of the different forest reconstruction scenarios.Simulation results showed that the transformation of coniferous forest to broad-leaved forest had a little reduction effect on flood peak discharge and flood volume.Added with bamboo forest based on the previous scenario,the reduction rate of flood volume and flood peak discharge were increased to some extent.The results indicated that bamboo forest reconstruction was an effective solution for flood reduction in the upper reach of Tingjiang river.Based on the low impact development(LID)measures,waterlogging simulation was launched in Tingzhou urban area of Changting county.The runoff generation module of SCS model and inundation module based on cellular automata were constructed to simulated the submerged area and depth under different scenarios.Furthermore,appropriate LID measures were selected according to natural features and land use types in Tingzhou urban area.Results showed that LID measures could decrease the depth and area of waterlogging,the reduction effect was declined when the return period of storm become higher.The reduction effect was greatly reduced by the influence of upstream flood and urban heavy rainfall,LID measures should cope with other solutions to prevent city from waterlogging in this case.The exposure of major disaster-affected bodies such as architecture and population were analyzed according to the waterlogging simulation results under different scenarios,the vulnerability of disaster-affected bodies were measured by property losses and population characteristics.Then,the flood risk was assessed based on the above analysis.Assessment results showed that the relationship between flood disaster intensity and vulnerability of disaster-affected bodies was typically nonlinear.Different damage mechanism of disaster-affected bodies indicated that building structure,cost of landuse types and population characteristics also leading to diverse vulnerability besides flood disaster intensity.The relationship between flood disaster intensity and vulnerability of disaster-affected bodies identify the flood risk.Urban system could raise the adaption to flood disaster by adjustment of land use plan,application of LID and other measures based on the results of flood risk assessment.The adaption process of flood disaster system in mountainous city was spatially simulated in watershed and urban levels.The simulated results confirmed the complexity of flood disaster system.The adaption process of flood disaster system in mountainous city was complex.Different types combination may lead to diverse reduction effect,the reduction rate of flood peak discharge and flood volume was nonlinear because of proportion of vegetation in the underlying surface,as well as the precipitation and runoff cope with LID measures and impervious surface area.The theory framework and simulation module of this research could provide effective support for reduce the flood risk of mountainous city and storm water management.