## 4 Results and Discussion
### Soil Water--Groundwater Recharge Mode Analysis
#### 4.1.2 Moisture Migration Rules of Thick Cohesive Soil
Heavy rain after a long drought period brought layers of thick cohesive soil into the water absorption period, and the soil moisture response showed a lag from surface to bottom in thick cohesive soil. The lag time increased from surface to bottom, indicating that the groundwater level rise on 6 January 2020 contributed little to the increase in soil water content above the depth of 6.0 m. The increase in soil water content above the depth of 6.0 m was mainly caused by the accumulation of rainfall infiltration. The monthly rainfall increased gradually in the field test site from January 2020 to July 2020. The monitoring layers of thick cohesive soil were all in the water absorption period, a continued increase in soil volume content (Figure 5). The total water potential gradient value (\(I_{\text{usa}}\)) of the profile was positive and close to 1 (Figure 5), which means that soil water continued moving downward throughout the whole profile. The climate of the field test site is a subtropical monsoon climate with abundant rain; soil water in the unsaturated zone can infiltrate gradually into the saturated zone and finally recharge the groundwater under multiple rainfalls' accumulation. The \"water absorption period\" and \"dehydration period\" cycle of the thick cohesive soil had a significant buffering effect on groundwater recharge. The infiltration recharge was stored in thick cohesive soil in the \"water absorption period\" and then released into the groundwater aquifer in the \"dehydration period\". This can help reduce the influence degree on groundwater of drought via the release of soil moisture to maintain the water recharge to the groundwater aquifer, which increases the recharge amount of groundwater in drought periods. On the other hand, it can also help in obtaining much more groundwater recharge from the weathered fissure water aquifer (Qb\(W_{2}\)) and storing it in thick cohesive soil in the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Water Absorption Period**} & \multicolumn{2}{c}{**Dehydration Period**} \\  & **and Dehydration Period** & **Lag Time** & **and Water Absorption** & **Lag Time** \\  & **Transition Time** & & & **Period Transition Time** & \\ \hline Rainfall end time & 29 June 2019 09:00 & \(\backslash\) & 5 January 2020 08:00 & \(\backslash\) \\ \hline  & 0.2 & 30 June 2019 00:00 & 15 h & 5 January 2020 10:00 & 2 h \\  & 0.5 & 1 July 2019 06:00 & 1 d 21 h * & 6 January 2020 03:00 & 19 h \\  & 0.9 & 10 July 2019 01:00 & 10 d 16 h & 6 January 2020 03:00 & 19 h \\  & 1.4 & 27 July 2019 05:00 & 27 d 20 h & 6 January 2020 19:00 & 1 d 11 h \\ Soil & 2.0 & 5 August 2019 05:00 & 36 d 20 h & 7 January 2020 06:00 & 1 d 22 h \\  & 2.5 & 22 August 2019 13:00 & 54 d 4 h & 9 January 2020 11:00 & 4 d 3 h \\  & 3.0 & 31 August 2019 10:00 & 63 d 1 h & 8 January 2020 23:00 & 3 d 15 h \\ depth (m) & 3.5 & 3 September 2019 04:00 & 65 d 19 h & 9 January 2020 03:00 & 3 d 19 h \\  & 4.0 & 5 October 2019 20:00 & 98 d 11 h & 18 January 2020 01:00 & 12 d 17 h \\  & 4.5 & 6 October 2019 11:00 & 99 d 2 h & 19 January 2020 00:00 & 13 d 16 h \\  & 5.0 & 25 July 2019 14:00 & 26 d 5 h & 16 February 2020 21:00 & 42 d 13 h \\  & 6.0 & 22 July 2019 09:00 & 23 d & 18 February 2020 06:00 & 43 d 22 h \\ \hline GWL response time & 1 July 2019 00:00 & 1 d 15 h & 6 January 2020 17:00 & 1 d 9 h \\ \hline \hline \end{tabular}
* 1 d 21 h means 1 day and 21 h.  
\end{table} 
Table 3: Information about transition time, response time, and lag time of soil water and groundwater. \"water absorption period\" due to the buffering effect. Many more available water resources can be provided by groundwater aquifers for water resource management in the Jianghan Plain area because of this \"water absorption period\" and \"dehydration period\" cycle. This finding will be helpful for low-permeability medium water recharge evaluation. Figure 4: Transition times of soil water at monitoring layers and groundwater response times to rain in the field test site.