Abstract

Dispute settlement over groundwater issues is hampered by the fact that groundwater is not discussed in existing bilateral treaties between Mexico and the United States whereas aquifers frequently span the border zone. Accurate, international data on groundwater resources and dynamics are therefore needed to assist formulation of bi-national groundwater policy, particularly in the Colorado River delta region. We will present our preliminary InSAR (Interferometric Synthetic Aperture Radar) measurements of cm-scale vertical displacements of the surface above the Mexicali Valley aquifer/ Mesa d'Andrade, using these as a proxy for aquifer depletion and recharge events. It is anticipated that this InSAR monitoring will allow characterization of aquifer behavior across the border zone over the past decade, and prior to (or during) the planned lining of the All-American Canal and the federal reductions in Colorado River surface water allocations to urban and/or rural California consumers. Either action could seriously alter a major aquifer recharge zone and, consequently, groundwater volumes in Mexico (655 private and federal pumping sites) and southeastern California. We will present preliminary deformation maps for a roughly 650 km2 area of the Mexicali-Calexico region; a first step in characterizing regional and local `pre-lining' subsidence signals due to groundwater pumping, geothermal energy operations, tectonic creep and, possibly, changes in soil properties.