# Dynamic Monitoring of the Water Flowing Fractured Zone during the Mining Process under a River
## 4 Results and Discussion
### 2D Modeling Results  
Figure 13 shows the water flow velocity of the vertical cut line. The flow velocity was 0 m/s at \(t=0\) s. When the water inflow was loaded (simulating the connection between the WFFZ and the aquifer), the water began to flow down. The flow velocity increased quickly and then tended to be stable after \(t=2000\) s. The maximum flow velocity of the model reached \(1\times 10^{-2}\) m/s at \(t=4000\) s. As there was no water supply, the flow velocity gradually decreased after \(t=4000\) s and tended to be stable after \(t=6000\) s, with the maximum flow velocity of \(1.5\times 10^{-5}\) m/s. In the vertical direction, the water flow velocity increased from the top of the aquifer to the roadway. The flow velocity reached the maximum at the position of 30 m (under the entrance of the WFFZ). As can be seen from Figure 13, there is an inflection of a sudden increase in flow velocity at 1 m beneath the top of the aquifer. That is because the flow velocity at the top of the aquifer was not affected by the lateral seepage while the lower part was affected. At the position of 20 m on the vertical line, another inflection of sudden increase occurred due to the great change of permeability and porosity at the interface of the aquifer and WFFZ. After a rapid increase, the flow velocity tended to be stable in the WFFZ.  
Figure 12: Comparison of water levels of different survey stations. The horizontal axis represents the survey days, and the vertical axis represents the water levels. The data of day 0 is the experimental data. T11 represents the survey data of 1 st survey station of line 1. T13 represents the survey data of 30 th survey station of line 1. T31 represents the survey data of 1 st survey station of line 3. T33 represents the survey data of 30 th survey station of line 1.  
Figure 14 shows the water flow velocity of the horizontal cut line. The flow velocity in the aquifer also increased at first, then stabilized, decreased and finally stabilized. It can be seen that the lateral recharge phenomenon existed in the aquifer, which caused the increase of water flow velocity from left to right and reached the maximum at the position of 75 m. The maximum flow velocity in the aquifer was 3.9 \(\times\) 10 \({}^{-3}\) m/s at \(t\) = 4000 s, and occurred at 20 m to the right boundary of the aquifer, which was above the interface between the aquifer and the WFFZ. During the decline process of the water flow velocity in the aquifer, the gap between the velocity of the left and right side became smaller. The maximum flow velocity declined to 5.5 \(\times\) 10\({}^{-6}\) m/s at \(t\) = 6000 s, and the flow velocity at 50 m was 4.1 \(\times\) 10\({}^{-6}\) m/s. Since there was still an area of aquifer between them, it can be considered that the downward flow of water mainly came from the lateral recharge. Combining with Figure 15, the lateral recharge dominated the water flow at \(t\) = 6000 s and later.  
Figure 13: Water flow velocity curves of the vertical cut line at different times. The horizontal axis represents the distance from the top of the aquifer to the interface of the WFFZ and the roadway.  
Figure 14: Water flow velocity curves of the horizontal cut line at different times. The horizontal axis represents the distance from the left side of the aquifer to the right side.  
Figure 15: The velocity arrow of the model at \(t=6000\) s. The color bar represents the flow velocity of the corresponding arrow.