That Sinking Feeling - Using InSAR Data to Analyze Land Subsidence and Earth Fissures

In many aquifers, water withdrawal leads to land subsidence and earth fissure development that can damage wells, canals, sewer lines, and other structures.  While the underlying equation used to estimate land subsidence at a single location is simple, predicting the magnitude, timing, and location of land subsidence is complex in practice and is often limited by the high cost of collecting regional site-specific data sets.  

In many cases, subsidence prediction is best performed by analyzing water level and subsidence time series data, then applying empirically observed relationships to other geologically similar basins or the expected future conditions within a basin.  Interferometric Synthetic Aperture Radar (InSAR) is a powerful but low-cost remote sensing method used to monitor subsidence across large areas.  This presentation documents a number of empirical relationships derived using Geographic Information Systems (GIS) techniques and publically-available InSAR and water level data provided by the Arizona Department of Water Resources (ADWR). Some of the relationships discussed include the distribution of earth fissures relative to differential subsidence magnitude, curvature, and trend, subsidence magnitude and basin morphology, the observed range of subsidence for a given unit water level decline (specific compaction), statewide observed subsidence rates, elastic rebound at recharge structures, and the predicted time to reach maximum subsidence following the stabilization of water level declines.