Research On The Effect Of Snow Melting Agent On Bioretention Based On HYDRUS-1D Model

With the acceleration of the construction of sponge cities,the number of sponge facilities in the northern region has gradually increased.Among them,bioretention is one of the most widely used technologies in sponge city construction facilities.However,the application of snow melting agents in winter in the north makes sponge city facilities threatened by salinization.Studying the effect of snow melting agents on salinization of bioretention is of great significance in the research,development,construction and management of bioretention.Based on the precipitation data of spring and winter and the application of snow melting agent in Dalian City,Liaoning Province,a water and salt transport model of the bioretention under different snow melting and rainfall conditions is constructed using the HYDRUS-1D software.We examine the effect of snow melting agents on the salinization of bioretention and put forward reasonable suggestions for reducing salt damage in this study.First of all,this research sets up physical models of small bioretention tanks with different lithological planting soil layers.By comparing the measured values of electrical conductivity at different depths and software simulation values,the feasibility of the mathematical model simulation is verified.The results show that the mathematical model has a high degree of fit with the physical model.The mathematical model simulation results in consideration of evaporation are more in line with the actual situation,and the simulated deviation of the planted soil layer was lower than that of the sand layer.The minimum and maximum deviations of the planted soil layer are 1% and 28%,respectively,and those of the sand layer are 1%and 39%,respectively.In order to reduce the salt damage caused by the snow melting agent and selectsuitable planting soil and snow melting agents,the daily variation of the electrical conductivity(EC_e)of the bioretention pool in Dalian in 2015 is simulated.It is found that the calcium-magnesium mixed salt snow-melting agent posed a relatively small threat to salinization in the bioretentionl.The surface EC_e value of the planted soil layer is proportional to the salt content and inversely proportional to the water content.The longer the dry period corresponds tothe greater soil evaporation and higher EC_e value,but the dry period has little direct effect on the EC_e value of the sand filler layer.Choosing sandy loam as the planting soil for bioretention tanks during small precipitation is in favor of discharging salt and reducing the retention of salt,When the spring precipitation is fixed,it is beneficialto discharge salt through rainwater scouring.In order to further study the effect of the precipitation,evaporation and the snow melting agent applicationin winter on the salinity of the bioretention and reveal the impact of desalination and salt drainage by spring rainfall,the accumulation of salt in the sand loam bioretention and scour simulation is carried out based on the precipitation data of Dalian in 2008-2017.The results show that after winter,the bioretention in different years are all in salinity,and plants need to be replanted in spring.The simulation of the leaching effect of spring precipitation found that spring precipitation has a significant effect on desalination.The cumulative precipitation is greater in May than in April,and the salt removal is more thorough.Plants replanting should reasonably consider the time and quantity distribution of precipitation.For the years when precipitation is concentrated earlier,the date of replanting can be relatively moved up,otherwise the time for replanting should be delayed or carried out appropriate irrigation before replanting.The software is used to simulate the desalting effects of different amounts of irrigation water,so as to seek reasonable and effective irrigation management measures to ensure the soil layer in an appropriate state when replanting plants.It is found that greater amount of irrigation water led to a better salt discharge effect.When the spring dry period is long,the maximum 8.91 cm irrigation water can be used to fully leach out the salt,and the subsequent detention ponds will not be re-salted with the dry period.When the spring dry period is short,multiple irrigations with small amounts of water can be used.By shifting the salt downward,the EC_e value of the upper soil layer is kept below 4 ds/m,and the natural precipitation in the subsequent spring with a larger precipitation is used to effectively remove salt to reduce irrigation water.