Interferometric SAR for Hydrology Applications

The Chino Basin is a large, adjudicated groundwater basin located in Southern California. It contains about 6 million acre-ft of water in storage and is a primary supply for about 20 municipal agencies, several private entities, and about 400 agricultural and dairy operations. Total groundwater production is about 190,000 acre-ft/yr. The Chino Basin Judgment (1978) established an agency (Watermaster) to oversee the implementation of a physical solution to problems in the basin at that time. It also required the agency, at its discretion, to prepare an Optimum Basin Management Program (OBMP) to address ongoing quantity and quality issues in the basin. One of these issues is land subsidence and related ground fissuring that apparently occurred as a result of groundwater production and excessive drawdown of groundwater levels. Future plans must address the subsidence and fissuring phenomena while accommodating basin-wide storage and recovery programs.

InSAR has figured prominently in several aspects of Chino Basin aquifer system characterization and is playing an important role in the development of the groundwater management plan. Neva Ridge Technologies has let the InSAR effort in this program. The strategy here employs both historical and ongoing InSAR measurements. A dense historical series of SAR acquisitions, with subsequent InSAR processing, has provided an areally and temporally detailed record of historical inelastic aquifer system compaction as well as a component of elastic compression and expansion resulting from the strong seasonal pattern of drawdown and recovery of water levels. For part of this historical period, the available InSAR data are reinforced by periodic resurveys of a network of horizontal and vertical control benchmarks. These historical data provide an important comparison between the two measurement techniques and demonstrate good agreement.

A major contribution of InSAR to the work in this area is its use in characterizing basin hydrogeology. The close correspondence of InSAR surface measurements to the distribution and thickness of stressed aquitards, as inferred from well logs and water-level records, has provided important inputs to the structure of the groundwater flow model. A key development in basin characterization was the discovery of a groundwater barrier, believed to be a buried fault in the deep confined aquifer system, apparently aligned with the zone of historical ground fissuring. InSAR measurements confirmed a narrow band of focused differential subsidence coinciding with the fissured zone and extending well beyond the observed ground failures into an area where sparse water-level data had been insufficient to define the barrier effect. This discovery triggered a subsequent multi-site pumping experiment, corroborating the InSAR location of the barrier and providing a key to understanding some of the dynamics of the basin.

The work described here has been funded by Chino Basin Watermaster.

Figure 1

This InSAR ground motion result is derived from data acquired during the period 1993 - 1995. It shows ground subsidence in Chino, CA, due to overdraft of the underlying groundwater basin. In this common representation of ground displacement data, each color cycle represents a surface height change of about 3 cm. The inset shows a transect along the dashed line, with a peak subsidence of about 12 cm.

Figure 2

This image shows a slightly different representation of InSAR subsidence data in Chino together with a black line showing the position of leveling survey monuments (along Schaefer Avenue).

Figure 3

This figure shows a comparison of leveling and DifSAR measurements along the same transects during the time period 1995 - 2000. Note that the time periods for the two techniques are not identical.

For more information, contact David Cohen or see this overview.

CBWM Wildermuth