Impact of Environmental Factors and System Structure on Bioretention Evaporation Efficiency

Bioretention is an important low impact technology that has prominent stormwater detention and purification capacity. Current study focused on analyzing the impact of environmental factors and system structure on bioretention evaporation efficiency. In operational phase, the moisture content in bioretention packing changes constantly, directly affecting the stagnation efficiency of the bioretention. Therefore, it is very important to study the evaporation efficiency of the bioretention for objective evaluation of hydrologic effects. In this study, an artificial climate chamber was used to investigate the effect of environmental factors and bioretention structure on the evaporation efficiency of bioretention. The evaporation capacity of bioretention was analyzed under different temperature and relative humidity conditions in a laboratory-scale artificial climate chamber. The result showed that evaporation rate at the initial stage was close to the maximum evaporation capacity under an environmentally controlled rapid decrease. Results revealed that after 15 h, the evaporation rate decreased more than 60%, and the evaporation rate decreased rapidly at the higher temperature, whereas the evaporation rate in the third stage was low and stable. It was about 1 mm/d (0.82~1.1 mm/d) and formed a dry soil layer. The results revealed that cumulative evaporation of the bioretention with a submerged zone was notably higher than that without the submerged zone, and the cumulative evaporation after 50 h was 16.48% higher. In the second stage of evaporation, the decreasing amplitude of the evaporation capacity of bioretention with the submerged zone was also relatively slow. Moisture content in upper layers in bioretention packing was recharged from the bottom submerged zone by capillary action and water vapor diffusion. These research findings can be used to evaluate the hydrologic effect of bioretention and can also be used to guide its design.