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.