Dynamic Contributions of Stratified Groundwater to Streams Controls Seasonal Variations of Streamwater Transit Times

Streamwater transit time distributions display a variable proportion of old waters ( ≥1 yr). We hypothesize that the corresponding long times result from groundwater contributions to stream and seasonal streamwater variations 1) different flowpaths (overland flow, seepage flow baseflow) 2) stratification residence times. develop parsimonious model capture contribution discharge its effect on transient Infiltration is partitioned according aquifer saturation between Boussinesq overland flow. Time-variable are obtained with new 2D particle tracking algorithm. Hydraulic conductivity, total drainable porosities calibrated by using CFC tracer data crystalline catchment located in Brittany (France). The models succeed reproducing CFCs concentrations dynamics. controlled hydraulic while age porosities. Old yr) source for approximately 75 % streamflow strong (between 40 95 %). Mean 13 years, varying 6 20 inversely proportional contribution. These driven versus partitioning. plays minor role but key dynamics stream.