Use of SFR2 and LAK Package in the Modeling of Bracciano Deep Volcanic Lake (Italy)

Bracciano vocanic caldera lake (Italy) is in direct contact with the main aquifer, which is part of the Sabatini Hydrogeological Unit. The area surrounding Bracciano lake is stressed by several public and private pumping wells tapping the aquifer. Climate change has led to changes in temperature and precipitation conditions, which in turn have affected aquifer recharge and the lake water budget. Furthermore, over the last thirty years withdrawals from the aquifer have increased. A numerical groundwater flow model centered on the Bracciano lake and its hydrogeologic basin was constructed using the finite difference code MODFLOW2000. The model was first calibrated for steady state, then used for transient simulations (monthly time steps over six years). The model was applied to simulate possible future climate change and water-use scenarios to better understand the behavior of the volcanic lake under multiple stresses. The use of the Streamflow Routing (SFR2) and Lake (LAK3) MODFLOW packages allowed a sophisticated simulation of groundwater/surface-water interactions including activation and deactivation of stream outflow (lake outlet) as a function of lake level. Model output allowed comparison of lake sources including net groundwater and surface-water inflows, precipitation, lake evaporation and surface runoff. Storage parameters influence the transient aquifer behavior and were considered when analyzing models results. The Bracciano transient model results help understand the different contribution of lake water balance components in relation to lake level fluctuations as well as the vulnerability of lake conditions to changes in inflows/outflows driven by climate change and aquifer pumping.