A method of estimating sequential average unsaturated zone travel times from precipitation and water table level time series data

A method to estimate sequential average unsaturated zone travel time with high temporal resolution has been developed. The method is built upon the conventional cross-correlogram analysis, while the estimation errors are significantly reduced by the proposed schemes. In addition, an analytical relationship between the estimated travel time and the corresponding parameter of a physically-based water table (WT) fluctuation model has been newly established. For validation, applications were performed using WT and precipitation data from two locations with contrasting properties. The method was found to derive distinct characteristics in the estimated travel time, which reflect the unsaturated hydraulics by estimating large means and variations in travel times for low permeability unsaturated zones; whereas, the values are typically small for highly permeable unsaturated zones. The overall results suggest that the proposed method can be potentially adopted to complement other methods in the assessment of groundwater vulnerability to surface contaminants and the hydraulic characterizations of unsaturated zones.