Seasonality in Intermittent Streamflow Losses Beneath a Semiarid Mediterranean Wadi

Streamflow losses beneath ephemeral and intermittent streams are potentially major contributors to groundwater recharge. Compared to ephemeral streams, intermittent streams often have more than one season of streamflow and often experience shorter zero-flow periods during the dry seasons and typically longer wet season of steady streamflow. Intermittent streams losses are lacking significant investigation on their variability over wet and dry season, and on the influence on potential groundwater recharge of flooding streamflow compared with more gradual wet seasonal baseflow. To address these issues, both streambed-sediment water content and temperature were continuously logged over a year for an intermittent stream (wadi) under semi-arid conditions in Central Morocco. Water content measurements uniquely distinguished between downward percolation and upward advance of the wetting front due to the rise of the water table, whereas temperature modeling was used to estimate vertical fluxes of percolated water. For the year of data, more than 90% of the estimated potential recharge occurred during winter and spring, when the alluvium typically has a higher water moisture, with most recharge generated during flooding conditions. Winter and spring baseflow generally generated low infiltration, though importantly contributes to wetting the sediment for rapid, deep percolation during flooding. Alternatively, summer flashfloods over dry sediment resulted in shallower infiltration despite higher peak streamflows. Thus, clear seasonality (seasonal variation) in relations between amounts of streamflow, streamflow loss, and depth of wetting into the streambed were distinguished over the study year. Finally, lateral recharge was detected, leading to additional seasonal water-table fluctuation beneath the wadi.