## 4 Results and Discussion
### Numerical Simulation of Precipitation Infiltration in the Field Test Site
#### 4.2.6 Simulation Results
The cumulative water flux of the cohesive soil layer at the depth of 1100 cm coincided with the cumulative water flux at the lower boundary (1500 cm), which means that the cumulative water flux of the cohesive soil layer at the depth of 1100 cm could be considered as the actual recharge from the cohesive soil layer to micro-confined groundwater. During the simulation period of the two hydrological years, the cumulative water flux of the cohesive soil layer at the depth of 1100 cm was 349 mm, so the recharge of the thick cohesive soil moisture to the micro-confined groundwater was349 mm, which was greater than the cumulative water flux of the cohesive soil layer at the depth of 200 cm. The difference between the recharge values of the soil layers at these two depths indicated that thick cohesive soil released water to recharge groundwater in the dry year in the field test site. From the cumulative water flux at different depths of the thick cohesive soil in the test site shown in Figure 10, it can be found that with an increase in depth, the cumulative water flux of the cohesive soil layer at different depths shows an increasing trend and a periodic approaching phenomenon in terms of years, indicating that the thick cohesive soil water in the test site migrates downward, generally, to recharge micro-confined groundwater. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reference** & **Location** & **Method** & **Recharge Coefficient** \\ \hline _Handbook of_ & Anhui & \(\backslash\) & 0.10–0.15 \\ _Hydrogeology_[46] & & & \\ \hline [PERSON] et al. [47] & North China Plain & Bromine tracer & 0.14 \\ \hline [PERSON] et al. [48] & Hengshui & Hydrus 1D & 0.19 \\ \hline [PERSON] [49] & [PERSON] & Bromine and \({}^{3}\)H tracer & 0.20 \\ \hline [PERSON] et al. [50] & Hengshui & Hydrus 1D & 0.13 \\ \hline This article & Jianghan Plain & Hydrus 1D & 0.1389 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of recharge coefficients. Figure 10: Water migration simulation results of critical depths of mass balance zones. The effective precipitation infiltration recharge decreased with less precipitation in dry years (2018 and 2019), and the same result was found with respect to the pressure head of the micro-confined aquifer in the field test site. The capillary saturation zone moved down, and the thickness of the vadose zone increased. Soil water of cohesive soil layers below 200 cm was released to charge deeper soil layers and the groundwater aquifer, which caused the total water storage of the thick cohesive soil profile to decrease. The effective precipitation infiltration recharge increased with more precipitation in wet years (2020), and the same result was found with respect to the pressure head of the micro-confined aquifer in the field test site. The capillary saturation zone moved up and the thickness of the vadose zone decreased in wet years. With the effects of \"soil water of upper layer moves down and groundwater level moves up\", the soil water content of the cohesive soil layers and total water storage of the thick cohesive soil profile increased in general. Taking the depth of 500 cm as the boundary, the cumulative water flux of the cohesive soil layer in the upper vadose zone was mainly affected by precipitation and evaporation, and the cumulative water flux of the deeper cohesive soil layer was mainly affected by micro-confined groundwater level changes (Figure 10). The annual exchange capacity of soil water and groundwater was controlled by the micro-confined groundwater pressure head to a great extent. The exchange capacity decreased as the micro-confined groundwater pressure head increased, leading to a decrease in the actual recharge rate of the groundwater.On the contrary, the actual recharge of the groundwater increased. The trend variation in the cumulative water flux of cohesive soil at different depths clearly revealed the water storage adjustment effect and water migration rules of the thick cohesive soil profile.