Field determination of the water balance of the Areuse River delta, Switzerland

The water balance during a period of one year (15 October 1990-15 October 1 991) was determined at an experimental site in the Areuse River delta (Swit zerland). The groundwater recharge rates were found to be 36 and 33% of tot al precipitation according to evapotranspiration estimates based on the Pri mault (1962) and the Penman-Monteith methods, respectively. Variations in t he water storage were obtained by weekly measurements with a neutron probe. Observed hydraulic gradients indicated a zero-flux plane between depths of 0.55 and 1.02 in that separated the infiltration zone from the zone of eva potranspiration in all seasons.