DEM-based improved method for river cross-sections modification and evaluation of flood routing accuracy
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Abstract:
River cross-section data is necessary for one-dimensional and one-two-dimensional coupled hydrodynamic flood routing numerical simulations.However,river cross-section field measurement is time-consuming,labor-intensive,and expensive.Under a sudden flood,it is impossible to carry out on-site measurements when modeling the emergency flood evolution.Rapid acquisition of river section data is the key to hydrodynamic flood evolution model modeling. To solve the above-mentioned problems,two methods for river cross-section are proposed.One is to directly extract river cross-sections (called DEM cross-sections) based on the digital elevation model(DEM),and the other is the improved cross-section construction method using parabola.The elevation at the thalweg is corrected by the lowest point elevation correction coefficient k (called constructed cross-sections).Two sets of river section data is obtained by the above two methods as the main input of the hydrodynamic simulation software HECRAS to carry out one-dimensional and one-two-dimensional coupled hydrodynamic numerical simulations,and then simulation results are compared with the flood routing results modeled by the measured river section data to evaluate the effect of rapid acquisition of the two river sections. The research method is applied in the lower reaches of the Miami River in Florida,USA.Two typical floods in 2004,2017 and 2014 are selected to analyze the differences in the simulation results of flood evolution under two different crosssections.The results show that the simulated water level of the measured cross-sections and constructed cross-sections are consistent with the observed water level process,and the simulated maximum inundation range is very close to the results of the model based on the measured cross-sections.In the simulation scheme using the DEM cross-sections,the average error of the simulated water level is up to 3.57 m.The maximum submergence range is calculated using the model based on the DEM cross-sections which is larger than measured cross-sections. DEM data has limitations in accurate hydraulic modeling.The description of the riverbed by DEM data is insufficient due to the ignorance of the terrain below the water surface as LiDAR scanned the terrain.The overflow capability provide by the DEM cross-sections is insufficient.The water level calculated by the DEM cross-sections is not consistent with the actual observed water level process,and the simulated submergence depth and submerged range deviate from the simulation results using the measured cross-sections.In the flood routing simulation,using the improved cross-section construction method proposed to correct the DEM data below the water surface can achieve similar to field measured river cross-section data,which is better than the method of directly extracting the river cross-section only from DEM data.By improving the river cross-section data in the digital elevation model data,the time and effort required for field survey.The methods of obtaining river cross-section data apply to plain river network areas,and the DEM data has a high resolution.In the future study of mountainous rivers or areas with only coarse DEM that can be obtained,the accuracy and applicability of different acquisition methods of river cross-section data to the calculation results of the hydrodynamic model still need to be further studied.
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