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.