A field experiment was performed to monitor the variations of the hydraulic head in the vicinity of a ditch during a water infiltration experiment and using the self-potential method. The coupling between electric and hydraulic flows is electrokinetic in nature. The electrical signals are measured at the ground surface with a set of ten non-polarisable Petiau (Pb/PbCl2) electrodes over a section perpendicular to the ditch. The electrical potential is linearly related to the depth of the water table, which is here quite shallow (between ~1 to 2 m). A rough estimate of the electrokinetic coupling coefficient obtained in the field is ~-10 mV per meter of hydraulic head (~-1000 mV MPa-1 of pore fluid pressure). The order of magnitude of this estimate agrees with a laboratory experiment performed with a soil sample from the test site. The good correlation found between electrical potential and hydraulic head variations opens the door to direct tomography of hydraulic head fluctuations with many innovative applications in hydrogeology, especially because the potential depth to which this method could be applicable is high (several hundred meters).