3.2 Variation of Water Content in Different Sections
The water profiles in different sections of Bioretention I and II from the center of the structure outward changed with time, as shown in Fig. 7.
[Insert Figure 7]
As shown in Fig. 7(a), the initial water content of each water profile in the loess site was different. The maximum and minimum water content values were 18.8% and 13.4% respectively. The initial water content at 2.5 m was the largest. This may be due to the changes in soil density during the backfill compaction process of the horizontal hole containing the sensor, which created different water content levels.
At the section about 0.5 m from the centerline of the facility, the water curves were scattered at the beginning of the infiltration process and grew close to each other after 4 h. After this point, the water content of the site increased rapidly with further infiltration time until the water content of each position became stable. The maximum water content in the whole process was 39.8%.
The subgrade is located at 2 m and 3m to the left of the facility centerline, where the water content did not change significantly with different infiltration depths at different time points. That is, the water infiltration at the bottom of the facility had little effect on the water content of the subgrade within 24 h. Further, as shown in Fig. 7(b), the initial water content was similar in each water profile except for Section B. The maximum and minimum initial water content in Section B was 20.9% and 14.2%, respectively. This may be attributable to uneven backfill compaction of the exploration wells after the sensors were embedded.
The wetting front of the profile at 0.5 m to the left and right of the facility center line gradually decreased with time. When the infiltration time was 24 h, the maximum water content was about 40% at 1.5 m and 2 m. The curves at 2 m and 3.5 m to the left of the facility centerline were approximately coincident, that is, the water content at these sections tended to be stable throughout the infiltration time. The infiltration appears to have little effect on the water content at this section.
As shown in Figs. 7(a) and 7(b), the water infiltration in the retention type of bioretention mainly affects the bottom of the facility. For the water profile at the bottom of the facility, in the bottom of Bioretention I, the wetting front gradually tended toward stability rather than decreasing with time, while the wetting front under Bioretention II moved downward with time.