Development Of A Coupled Urban Hydrological-Hydrodynamic Model And Its Application

Under the context of global climate change and rapid urbanization,the characteristics of urban rainfall,underlying surface conditions and hazard-affected body have significantly changed,resulting in frequent urban flood disasters and increasing disaster losses,which have aroused widespread concern of the whole society.Numerical simulation of urban flooding is one of the most important technical means for urban stormwater management.The current urban flood model are mainly classified into hydrological methods based model and hydrodynamic methods based model,the former is often unable to simulate the surface inundation process,while the latter does not consider the hydrological mechanism of the urban runoff process.Based on previous studies,the urban hydrological process and hydrodynamic process simulation principles are analyzed,and the coupling mechanism between hydrological and hydrodynamic processes,one and two-dimensional hydrodynamic process are expounded,and the coupled urban hydrological and hydrodynamic model(CUHHM)is developed.Based on CUHHM,the urban stormwater model of the Central City of Beijing(CCB)and the sponge city model of the Lejia Garden Area(LJGA)were established respectively.Furthermore,the urban flood risk were assessed and the hydrological responses of the sponge city measures were evaluated within the simulation results.The main results of this study are as follows:(1)Simulation principles of urban hydrological and hydrodynamic processes are explained separately,and the applicability and limitations of the single two-dimensional hydrodynamic urban flood model were evaluated.City s hydrological response unit(CHRU)was considered as the basic calculating unit of urban hydrological simulation,and a new CHRU division method based on "natural-society" information was proposed,and the simulation methods of urban surface runoff,social runoff.surface convergence and green infrastructure hydrological processes were analyzed.Besides,the basic principles of urban hydrodynamic process simulation were analyzed.the principles of EXTRAN module and solving the two-dimensional shallow water wave equation by TELEMAC-2D were expounded.Additionally,the applicability of TELEMAC-2D and the limitations of two-dimensional hydrodynamics urban stormwater simulation were discussed based on case studies.(2)A coupled urban hydrological hydrodynamic model(CUHHM)was developed.The coupling mechanism between urban hydrological and hydrodynamic processes was classified.Both of the structural coupling mechanism and process coupling mechanism were clarified,and specific coupling mechanisms of CHHUM were determined.The method of spatial coupling between urban hydrological process and hydrodynamic process was proposed,the temporal coupling method and corresponding exchange flow calculation formula of one and two dimensional hydrodynamic processes were determined.On the basis of analyzing key coupling processes,the calculation procedures were analyzed,the design ideas of key programs were clarified,and the calculation program of CHHUM was developed.(3)The approach of "City-Block-Facility" multi-scale urban flood risk elevation was proposed,and multi-scale urban flood risk of City Central of Beijing(CCB)was elevated based on numerical simulation.According to the basic theory of disaster risk elevation,within considering the characteristics of urban flood risk,this study proposed a"City-Block-Facility" multi-scale urban flood risk assessment approach.On the city scale,risk mapping of urban flood of CCB was carried out based on risk assessment indicators and their weighted synthesis;on the block scale,the urban flood risk of CCB was evaluated based on the simulated submerged water depth,under design rainstorm scenarios with six different return periods,results showed that the inundation area were 47.17,59.87,68.11.83.46,100.93 and 110.39 km2 with design rainstorm return period ranging from 2 to 100 year;on the facility scale,the instability risk of pedestrians and vehicles was assessed,based on inundation simulation results of submerged site water flow velocity and water depth and combined with the human and vehicle instability critical velocity formula.(4)The evaluation model of sponge city measures construction for the Lejia Garden area(LJGA)was constructed within CHHUM.The hydrological responses,cost-effectiveness and inundation reduction effects of the sponge city scenarios for the LJGA were evaluated.Possible sponge city measures were estimated based on land type of LJGA and combined into seven sponge city scenarios.and life cycle costs of seven sponge city scenarios were calculated.Cost-benefit analysis method was conducted to evaluate cost-effectiveness of sponge city scenarios.Reduction rates of peak flow total runoflf volume were selected as the flood control benefit indicators,cost-effectiveness evolution of different sponge scenarios under different design storm conditions was evaluated.Additionally,the effects of sponge city measures on reducing urban inundation area were assessed based on the numerical simulation results,results showed that,the reduction rates of inundation area under six rainfall scenarios are 21.4%,14.7%.6.6%.3.9%.1.7%and 1.2%,respectively.