During the summer season, a lowering in hydraulic head is observed
followed by an increase in vertical gradient. As a result, the vertical
flow velocity is expected to be higher in summer. During the winter, the
reverse phenomenon is observed. As the hydraulic head rises, the
vertical gradient lowers and flow velocity reduces. It is seen from the
vertical hydraulic gradients at WP 6.2 that the hydraulic gradient
reduces considerable in winter as compared to that in summer.
The average reduction in regional vertical hydraulic gradient in winter
as compared to summer is 32 % from 3.55 to 0.55 mTAW depth and 4 %
from 0.55 to -5 mTAW. However, Vandenbohede & Houtte (2012) reports
that the reduction of infiltration capacity in winter ranges from 33 -
50 %. Thus, the variation in vertical hydraulic gradient alone does not
contribute to the overall fluctuation of infiltration rates. Hence, the
assumption that hydraulic conductivity is constant over time does not
stand valid and it is essential to take into account the variability of
hydraulic conductivity as well.