3.3 Influence Range of Water Infiltration in Bioretention Facilities
A water content map of the loess site was drawn based on data gathered at different positions at different time points during the water infiltration process (Fig. 8).
[Insert Figure 8]
In Bioretention I, 4 h into the process of infiltration, the vertical diffusion velocity of water in the site was greater than that in the horizontal direction. The shape of the soil infiltration range was slender and pear-like. With an increase of infiltration time, the horizontal diffusion of the soil accelerated and the vertical diffusion decelerated until finally becoming stable. In Bioretention II, the infiltration range in the initial stage has a round, flat pear shape. The pear shape was gradually elongated as the infiltration progressed because the vertical diffusion significantly increased over the horizontal diffusion before becoming progressively stable.
In the initial stage of infiltration, water moving through Bioretention I significantly influenced the site’s water content. After about 4 h of infiltration, the influence range was smaller in Bioretention II than in Bioretention I. The wetting front was located at the position where the water content increased by 3%, so in Bioretention I, the wetting front diffused to 1.5 m away from the centerline of the facility in the horizontal direction at a depth more than 2.54 m. In Bioretention II, the diffusion range was 2 m in the vertical direction and 1.5 m in the radial direction. The water infiltration range increased over time and was more intense in Bioretention II than elsewhere in the site. When the infiltration time reached 24 h, the horizontal infiltration effect was 3 m within Bioretention II, which was 1.75 m greater than that in Bioretention I.