Research On The Regulation Effect For Rainwater Runoff By Bioretention Based On HYDRUS-1D

In recent years,in response to frequent urban waterlogging and deterioration of the water environment,my country had begun to implement and promote the construction of sponge city throughout the region.As one of the main single sponge measures,bioretention had received widespread attention in the industry.At present,most of the research on bioretention was concentrated in laboratory research,which was easily restricted by experimental conditions and was quite different from the actual rainfall distribution process.To this end,bioretention were used as the research object,and a bioretention model was established through HYDRUS-1D to study the rainwater runoff regulation efficiency of bioretention.The modified Morris screening method is used to determine the sensitivity of the model parameters.For the four output results of total runoff,total runoff reduction rate,peak flow,and peak flow reduction rate,the sensitivity of each parameter is not the same.Judge the comprehensive sensitivity of parameters through the coefficient of variation method,its main sensitive parameters include water intake(q)and aquifer height(H),as well as saturated water content(θ_s),saturated hydraulic conductivity(K_s)and pore size distribution parameter(n).The model parameters were calibrated and verified based on the measured bioretention data.During the periodic rate and verification period,the simulation results are compared with the measured results.the root mean square error RMSE is 0.038～0.134,the relative error RE is-2.28%～7.59%,the simulation efficiency coefficient NSE is 0.849～0.999,the determination coefficient R~2is 0.894～0.999,the simulation results are reliable.The verified model was used to study the hydrological regulation process of rainwater runoff in bioretention.When the rainfall return period is 0.5a to 5a,the total runoff and peak reduction rate are reduced from 53.53%and 36.22%to 25.05%and 2%,respectively,and the runoff and peak emergence delay time are reduced from 25 min and 2 min to 16 min and 0 min,respectively.When the rainfall duration changes from30 minutes to 180 minutes,the total runoff and peak reduction rate range from 37.94%to 70.24%and 2.72%to 57.37%,respectively.The range of runoff generation and peak-occurrence delay time ranges from 15 minutes to 65 minutes and 0 minutes to 5minutes.The total runoff and peak reduction rate of bioretention,runoff generation and peak emergence delay time decrease rapidly with the increase of the confluence ratio.When the confluence ratio is greater than 10:1,the downward trend tends to be flat,respectively 26.11%～100%,2.1%～100%,18 min～60 min,1 min～36 min.As the height of the aquifer increases,the total runoff and peak reduction rate,runoff and peak emergence delay time vary from 13.84%to 100%,3.26%to 100%,2.25 min to 60 min,0 min to 36 min,and All showed a rapid linear growth trend.When the initial water content increases from 15%to 30%,the total runoff and peak reduction rate are48.81%～54.11%and 22.40%～45.37%,respectively.When the initial water content is greater than 25%,the peak reduction rate appears an inflection point,and the overall downward trend is fast and then slow.The runoff and peak emergence delay times are24.1 min～25 min and 1 min～2.5 min,respectively,and the overall change trend is not obvious.According to the orthogonal test range analysis,the influence of different influencing factors on the simulation results of the bioretention is different,and the influencing factors are normalized,and the hydrological regulation and control degree of the bioretention is determined as a whole.The order is:Confluence ratio>Rainfall duration>Rainfall return period>Aquifer height>Initial water content.The bioretention facility is designed according to the planning target of capture ratio of annual rainfall runoff volume.Through the simulation of the facility runoff control process,it is found that the capture ratio of annual rainfall runoff volume meets the facility control goals of different hydrological years.Finally,the long-term operating efficiency of the bioretention is simulated through the multi-year meteorological data in the study area.The infiltration,overflow and evapotranspiration are 76.25%,8.48%,and 15.44%of the water inflow,respectively.The amount of infiltration plays a major role in the regulation of rainwater runoff in bioretention.The overflow rate is relatively small,and the evapotranspiration of the facility has little inter-annual change,and it occupies a certain position in the reduction of rainwater runoff by facilities.By simulating the results of years of operation of bioretention,capture ratio of annual rainfall runoff volume is 73.41%to 100%,and the average capture ratio of annual rainfall runoff volume reaches over 80%,and the control effect meets the requirements.