Evaluating bioretention hydrology and nutrient removal for restoring wetland function at artificial rainfall

In recent years, the rate of impervious area increase has been rapidly growing with respect to urbanization making it necessary to construct an effective water circulation system. The impervious area in Korea was only 3% in the 1970s, and increased to approximately 8% in 2013. According to the literature, when the urban impervious surface increases to 75–100%, urban outflow increases from 10% to 55% compared to the natural state, and the infiltration decrease from 50% to 15%. In order to prevent the effects of increased impervious surface area, bioretention, a natural low impact development (LID) facility, has recently been developed and installed in many parts of the city. Artificial rainfall monitoring was conducted ten times for three years to evaluate bioretention performance. Monitoring results showed that the average flow reduction efficiency of the bioretention was greater than 85%, and nutrient removal efficiency was significantly high at 82.5% for TN and 95.6% for TP. As a result, the correlation between runoff reduction and nutrient removal was analyzed. Initially, the correlation coefficients of TN and TP were low, 0.0439 and 0.0216, respectively. However, after removing an outlier result from the 7th monitoring event, the correlation coefficients of TN and TP were 0.969 and 0.897, respectively. This is very high correlation index, so to restore wetland where are need to manage nutrients, bioretention can be a good alternative than other LID facilities.