Influence of surface runoff velocity on urban flood inundation
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Abstract:
To analyze the impact of surface runoff velocity on urban flood inundation,the dynamic coupled model is applied to generate the flood inundation map of a typical area in Dalian.The characteristics of flood inundation are compared and analyzed under several combinations between surface runoff velocities and return periods of design rainfall.A series of surface runoff velocity schemes are set up to simulate the dynamic process of flood inundation given different return periods of design rainfall,and also to quantitatively analyze the influence of surface runoff velocity on flood inundation,which provides support for urban flood analysis as well as flood disaster prevention and control. The one-dimensional pipe network model consists of 181 manholes,4 outlets,193 drainage pipelines and 181 sub-catchments.The largest and minimum area of sub-catchments is 2.29×10.4 m2 and 116 m2,respectively.The two-dimensional terrain model is divided into 4 032 rectangular grids with a grid size of 15 m×15 m.The surface runoff velocity is set to be 0.02 m/s,0.05 m/s,0.1 m/s and 0.3 m/s.40 simulation schemes are generated in combination with ten types of rainfall return periods.The pipeline pressure state is evaluated by the pipe filling,and the water accumulated over the study area is evaluated by manhole overflow.The risk of flood inundation is divided into three levels,namely,high-,medium-,and low-risk areas. The results show that the drainage load of the pipeline becomes smaller and the qualified rate of the pipeline becomes higher with the decrease of surface runoff velocity under the two-hourly design rainfall.And the qualified length and rate can be increased by 4.7 km and 48.05% with the decrease of surface runoff velocity.Moreover,surface runoff velocity has a significant influence on the volume of accumulated water.When the surface runoff velocity decreases,the peak value of accumulated water volume becomes smaller,and the delay of peak time is longer.The reduction effect of accumulated water is weakened with the increase of rainfall return period.With the decrease of surface runoff velocity,the peak value of total accumulated water can be reduced by 2 750 m3 at most,and the peak time can be delayed by 56 min at most.Meanwhile,under the 24-hourly design rainfall,the area of low-risk and high-risk areas decreases largely as the surface runoff velocity decreases.With the decrease of surface runoff velocity,the areas of low-risk and high-risk areas can be reduced by 1.64×10.4 m2 and 8.37×10.4 m2,respectively,while the area of a medium-risk area changes irregularly. The main conclusions are as follows: The surface runoff velocity has a significant impact on urban flood inundation.It affects the degree of urban flood inundation by changing the drainage load of the pipeline,the amount of ponding,and the area of the risk area.Overall,the decrease of surface runoff velocity,the harm of urban flood inundation is smaller.The relevant conclusions can provide decision-making references for relevant workers.
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