Geophysical investigation of unsaturated zone transport in the Chalk in Yorkshire

Electrical resistivity imaging of field-scale solute transport in the unsaturated zone of the Chalk in East Yorkshire is described. The study involved application of an electrically conductive tracer to the surface of an 18 m 2 plot at a rate of 49 mmd -1 for two days (representative of very heavy rainfall). The resistivity response of the upper 25 m over the following ten months is reported. These results are interpreted together with geological and hydrological data. The hydrogeological interpretation is that rapid bypass flow occurs along steeply inclined joints during high intensity rainfall in autumn and winter, but not usually during the summer. Joint saturation occurs locally, progressing upwards from horizons rich in thin marl layers.