4. Conclusion
The overall objective of this study was to identify the primary factor responsible for the seasonal variation of recharge rate from the infiltration ponds at the St-André MAR facility in Belgium. Infiltration rates across the pond bed have been studied for a period of 2 years and lower infiltration rates have been noticed in the winter months. Two major factors impacting the variability of infiltration rates are the alterations in vertical hydraulic gradient and hydraulic conductivity of pond bed.
Observed heads at the monitoring wells are mostly found to be higher in winters and lower in summers, creating a higher gradient in summers. A 32 % reduction in vertical hydraulic gradient observed in the top portion of the aquifer directly influenced the recharge rates. Regarding the variation of hydraulic conductivity, temperature has been identified as the dominant factor influencing this process. Results show that there is a strong correlation between temperature and infiltration rate on a daily scale. The temporal variation of temperature causes variation in kinematic viscosity. With increase in viscosity of recharge water, higher resistance is imparted by the pond bed to the flow of water.
In addition, the temperature of water influences the hydraulic conductivity of the soil. With the data obtained from the St-André MAR site, it is theoretically found that there is a 30 % increase in hydraulic conductivity in summer as compared to that in the winter. Lowering of temperature causes a reduction in hydraulic conductivity, thereby providing additional resistance to the flow of water through the pond bed. MODFLOW models have been used to simulate different conditions for summer and winter and it is found that with a lower leakance of the pond bed in the winter months, the recharge rate decreases by about 27 %.
Temperature of recharge water changes as it moves into the subsurface and it is highly influenced by the previously residing water. Temperature at different depths in the aquifer creates a definite response in the hydraulic conductivity of the media. Lack of temperature data at multiple depths hindered the study of the impact of groundwater temperature on the soil properties. This can be a scope of future study and would greatly enhance the understanding of the water flow and availability in the area.