Hydraulic head levels and aquifer parameters inferred from a joint analysis of InSAR and well data in the San Luis Valley, Colorado

Abstract:

Groundwater extraction is the primary source of irrigation water in many agricultural regions throughout the world. A set of spatially dense hydraulic head measurements adequately sampling the aquifer is a critical metric needed for effective water management. Because the total compaction due to pumping is nearly proportional to the change in hydraulic head, land subsidence measurements derived from InSAR data can be used to obtain head measurements in confined aquifers when well data are unavailable or insufficiently dense.

Reeves at al. (2013) demonstrated that C-band ERS InSAR data acquired between 1992 and 2000 over the San Luis Valley of Colorado suffice to fill temporal gaps in the hydraulic head field dataset at 3 well locations. Here, we further analyze whether the InSAR deformation time series can be used to infer head levels over a larger region than Reeves et al. analyzed. We processed 17 L-band ALOS radar scenes over the San Luis Valley acquired between Jan., 2007 and Mar., 2011 and applied an adaptive interpolation filter between persistent scatterer pixels to reduce vegetation decorrelation artifacts. We estimated the InSAR deformation time series at each image point using a least-squares SBAS approach. We then jointly analyzed the InSAR and the well data to estimate the local skeletal storage coefficient and the time delay between the head change and deformation and converted the InSAR deformation time series to InSAR head levels. The resulting InSAR-head and well-head measurements in the San Luis valley show good agreement with all 18 well measurements in the region with confined aquifer pumping activities. Assuming that geologic parameters such as skeletal storage coefficients often vary slowly in space, we interpolate the obtained skeletal storage coefficients at each well spatially to relate InSAR subsidence measurements over the entire SLV to changes in head with improved spatial resolution over the well data. This demonstration shows that InSAR is a promising technique for measuring confined aquifer head levels and hence groundwater management.