IGCP 565 Project Workshops

IGCP 565 Workshop 5: Water Security for Africa: Bringing Together Research, Monitoring, and Managing October 29-30, 2012 Johannesburg, South Africa

Integrated Geodetic Observations in Support of Hydrological Studies

Richard Gross, Felix Landerer, Donald Argus
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA; e-mail: Richard.Gross@jpl.nasa.gov; fax: 818-393-4965

Groundwater in aquifers is naturally discharged by subsurface flow and is artificially discharged by withdrawal from wells. Groundwater is naturally recharged by infiltration of runoff from precipitation, stream flow, and subsurface flow and can be artificially recharged by, for example, infiltration of treated wastewater in spreading grounds or by injection in wells. Changes in the amount of water in aquifers cause local changes in gravity that can be measured by gravimeters located on the ground and in space. GRACE is a NASA satellite mission that has been measuring changes in Earth gravity since its twin spacecraft were launched in 2002. Gridded fields of the GRACE-measured gravity changes are available from the GRACE Tellus web site at http://grace.jpl.nasa.gov. These publicly available gravity fields can be used to study changes in surface and groundwater on spatial scales of a few hundred kilometers and on time scales of a month or so. Examples of using GRACE measurements to study water resources in California and Africa will be shown.

Recharge and discharge of groundwater in aquifers cause changes in the elevation of the ground surface. During recharge, pore fluid pressure increases causing the basin to inflate and the surface elevation to increase. During discharge, pore fluid pressure decreases causing the basin to deflate and the surface elevation to decrease. Such changes in surface elevation can be measured using complementary observations from GPS positioning and InSAR radar. GPS provides highly accurate estimates of the 3-dimensional positions of sites on the Earth's surface. InSAR provides spatially dense estimates of range change of Earth's surface in the direction of the satellite in the time between two satellite passes. An example of using GPS and InSAR measurements to study changes in surface elevation caused by pumping of groundwater in the Los Angeles Basin will be shown.