洪水归槽背景下城市洪水风险变化模拟与防洪韧性提升OA

Major river basins in China,including the Yangtze and Pearl River basins,frequently experience floods that recur in the main channel.This phenomenon increases the likelihood of flood peak convergence between main streams and tributaries,raises flood stages and flow velocities under equivalent discharge conditions,and increases the risk of levee failure or overtopping in downstream urban areas.Although some research has been conducted on the impacts of flood returning to the main channel,several limitations remain:① Most studies mainly focus on the backwater effect induced by flood returning to main channel,while high-resolution simulations of post-backwater flood propagation and two-dimensional risk distribution are still lacking;② Levee crest elevations are often determined based on the design of the water levels and safety freeboards,yet practical factors such as existing breaches are seldom incorporated,resulting in idealized findings with limited practical relevance;③ There is a scarcity of systematic strategic analysis and quantitative benefit evaluation pertaining to flood response measures. To fill these gaps,the urban area of Wuzhou was selected as a representative case study.A coupled 1D river channel-2D surface hydrodynamic model was designed to simulate changes in the flood risk before and after intensification of flood returning to the main channel.Furthermore,the effectiveness of mitigation measures such as sealing levee breaches and regulating upstream reservoirs was evaluated.Based on the results,systematic strategies for enhancing flood resilience were proposed,providing a scientific basis for developing urban flood management systems adapted to intensified floods returning to the main channel. The simulation results show that:① After the aggravation of flood returning to main channel,the inundated area in the study region increased significantly,with area expansion of 7.43 km2,22.16 km2,and 16.57 km2 under 20-year,50-year,and 100-year return period flood scenarios,respectively.② The high-risk zone recorded an increase of 15.41 km2,representing a growth rate of 39.80%,which substantially exceeded that of other risk levels.③ Sealing levee breaches minimized inundation areas under all flood frequencies,with a decrease of 7.42 km2,6.48 km2,and 0.33 km2 corresponding to the 20-year,50-year,and 100-year events,respectively.④ Reservoir operation alone reduced the flooded area by 20.94 km2,achieving a reduction rate of 23.30%;When combined with breach sealing,the inundation area was further reduced by 25.91 km2,increasing the mitigation rate to 28.82%. The main findings of the study are as follows:① Under the new hydrological regime characterized by intensified flood returning to main channel,the current flood defense system of the study area exhibits noticeably reduced capacity.② The high-risk zones experience notably greater increases in inundation extent as compared to the other risk levels across all return periods.③ The effectiveness of sealing levee breaches diminishes with increasing flood magnitude,showing significant utility near the design protection standard,whereas reservoir regulation becomes more critical for flood peak control and risk mitigation when floods exceed the structural defense capacity.④ Addressing increased flood risks due to floods returning to the main channel requires integrated strategies that combine structural and non-structural measures,including reservoir operation,flood detention areas,and levee reinforcement,along with emergency plan updating,forecast and warning enhancement,and other non-structural measures,to systematically strengthen urban flood resilience.