In many places around the world, much attention is focused on managed aquifer recharge (MAR) because of reduced groundwater levels due to droughts. To assess the suitability of a site for MAR, detailed three-dimensional (3D) information about the subsurface materials and their hydraulic properties is needed. In areas where the groundwater level is at an intermediate depth (e.g., 20-40 m), such information is needed from the ground surface down to a minimum depth of ~50 m. To achieve this goal, we used a new geophysical imaging system: a towed time-domain electromagnetic system that is efficient for acquiring data at a significantly improved resolution and a scale needed for MAR. During a 2-d period, we acquired ~92 line-kilometers of data in one almond [Prunus dulcis (Mill.) D.A. Webb] grove, one pistachio (Pistacia vera L.) grove, one open field, and two active recharge basins in the Tulare Irrigation District in the Central Valley of California. At each site, a detailed 3D resistivity model with a resolution down to the 10- by 10-m scale is presented in terms of resistivity distribution plots, which are then used to assign a saturated-unsaturated boundary. In addition, we used a resistivity-lithology transform to interpret the resistivity models and create lithology maps at each site. We used this information to assess the suitability of each site for MAR.
- Programområde 2: Vandressourcer