Abstract:

Rainfall recharge is a principal source of shallow groundwater in the North China plain. Long-term over-exploitation of groundwater has resulted in the decline of water table in the past decades which made some low-permeability clay lenses moved from saturated zone to unsaturated zone and thicker vadose zone with complicated heterogeneity. It is an essential issue for infiltration process and rainfall recharge estimation effected by low-permeability clay lens in thicker vadose zone. The HYDRUS Software Package is used to establish models mainly considering the buried depth, width and thickness of low-permeability clay lens and simulate the effect of the three factors on infiltration path, recharge time and recharge quantity under single rainfall event. The simulated results show that low-permeability clay lens will restrict vertical infiltration and form faster flow around the lens relative to flow inside of the lens. It will decrease recharge peak and delay recharge time, rather than altering the starting time of recharge. The potential recharge quantity is determined by the relationship between the buried depth of lens and the limit depth of soil evaporation, and it will decrease when the buried depth of lens or the perched water caused by the lens is above the limit depth of soil evaporation.

Key words: vadose zone, low-permeability clay lens, rainfall recharge, HYDRUS, numerical