Filtering of Periodic Infiltration in a Layered Vadose Zone: 2. Applications and a Freeware Screening Tool

Core Ideas Infiltration forcings are filtered (time lagged and damped) with increasing depth. Filtering generally increases with increasing infiltration and cycle period. We show where forcings can produce variable recharge in Central Valley (California). We have developed a screening tool to visualize and conceptualize the filtering properties of a layered vadose zone. Climate projections indicate that rainfall timing and magnitude may change and impact groundwater resources. This increases the importance of understanding how the vadose zone filters infiltration variability and ultimately affects recharge and groundwater resources. An approximate solution for the filtering of surface forcings through soil layers was developed previously, and the soil and conditions where its approximations are appropriate was evaluated. Here we present a screening tool based on the solution for estimating how periodic infiltration forcings filter in a layered vadose zone for different soil properties and surface flux conditions. The solutions identify time‐varying elements of surface forcings that persist to the depth of the water table, leading to transient recharge. We investigated the filtering properties of the vadose zone in Central Valley, California, and identified areas where surface forcings are essentially damped and recharge can be approximated as steady. We also determined the travel time for infiltration pulses to reach the depth of the water table.