InSAR data produce specific storage estimates for an agricultural area in the San Luis Valley, Colorado
Abstract
The San Luis Valley (SLV) is an 8000 km2 region in southern Colorado that is home to a thriving agricultural economy. This valley is currently in a period of extreme drought, with county and state regulators struggling to develop appropriate management policies in order to sustain water levels in the confined aquifer system. The water level from 1970 - 2000 remains a key, but poorly known, component for characterization. Some relevant data, such as water levels measured in wells, were collected during this period and incorporated into a groundwater flow model. However, data with finer spatial and temporal resolution would be very valuable in understanding the behavior and therefore the management of the system. Spaceborne interferometric synthetic aperture radar (InSAR) data provide maps of the deformation of the Earth’s surface at a spatial resolution of 50 m; these data are acquired approximately once per month. The deformation measured by InSAR can be related to water levels in the confined aquifer system. However, changes in cm-scale crop structure in agricultural areas lead to signal decorrelation over long periods of time, resulting in low quality data. Here we apply the recently developed small baseline subset (SBAS) analysis to InSAR data collected by the European Space Agency’s ERS-1 and ERS-2 satellites over the western SLV for the years 1992-2001. The SBAS measurements show high levels of InSAR correlation, denoting high quality data, in areas between the center pivot irrigation circles, where the lack of water results in little surface vegetation. By using SBAS analysis, we are able to estimate the magnitude of the seasonal deformation and compare it with hydraulic head measurements in nearby wells. We directly compare, at three well locations, specific storage parameters estimated from InSAR data to those estimated using traditional pump test techniques. The InSAR and pump test estimated parameters are: 3.4 x10-5 ft-1 vs. 1.7 x 10-5 ft-1, 2.2 x 10-6 ft-1 vs. 2.2 x 10-6 ft-1, and 5.3 x 10-6 ft-1 vs. 4.7 x 10-6 ft-1, at wells denoted ALA 6, ALA 13, and CON 2, respectively. Thus the well and radar data estimates agree within a worst-case factor of two at locations where we analyzed both data sets. The ability to obtain such high quality specific storage estimates suggests that integrating InSAR data into the current groundwater flow model may allow us to describe the finer-scale heterogeneities of the entire SLV confined aquifer system. This new form of data analysis could significantly advance our approach to groundwater management in agricultural areas lacking modern infrastructure around the world.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.H11K..08R
- Keywords:
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- 1846 HYDROLOGY / Model calibration;
- 1855 HYDROLOGY / Remote sensing;
- 1884 HYDROLOGY / Water supply