201-2 Short Records, Longer Consequences: How Data Gaps Shape Subsidence Forecasts

Abstract:

Many subsidence models are calibrated using limited subsidence observations but somewhat longer groundwater-level histories—a common condition for GSAs across California. This presentation quantifies how shortened monitoring records affect subsidence model calibration and predictive uncertainty by systematically truncating long-term groundwater-level and subsidence datasets and recalibrating 1-D MODFOW CSUB models. Multiple scenarios are explored, including full subsidence and water-level records, short subsidence records paired with long water-level histories, and cases where both records are limited. Results demonstrate that long groundwater-level histories alone are insufficient to constrain key subsidence-related parameters such as elastic and inelastic skeletal storage, interbed vertical hydraulic conductivity, and preconsolidation head. In particular, incomplete subsidence records reduce the model’s ability to distinguish elastic from inelastic deformation and to characterize lag behavior, leading to biased estimates of critical head and increased uncertainty in future subsidence forecasts. The analysis highlights the importance of capturing multiple stress cycles and rebound periods and provides insight into how data limitations propagate uncertainty into long-term predictions used for SGMA planning.

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