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.