Modeling the unsatured zone for assessing groundwater recharge

A methodology for assessing the zenithal groundwater recharge was tested over an area of the Lombardy Plain between the rivers Ticino and Oglio (northern Italy). This estimation system is based on the use of the Macro numerical code (Jarvis, 1994) in simulation scenarios characterised by lithological profiles differing for the type of soil, thickness, geology of the unsaturated zone, climate conditions and farming practices. This methodology was previously tested on sample profiles in a portion of the Milan Province by comparing the fluctuation measurements of the water table. It was carried out on the whole study area in the 1980-2005 period, taking into account representative soils and two different situations as regards climate and depth of the water table. The simulated daily recharge, which was higher in the mid- and high fluvioglacial plain, showed an increasing temporal trend in conformity with the pluviometric trend and a regime dephased by about one month with respect to precipitation. The effect of the presence of impermeable areas due to urban expansion is also assessed as a function of the area surveyed and the rate of development.