Documentation for the Skeletal Storage, Compaction, and Subsidence (CSUB) Package of MODFLOW 6

First posted March 3, 2022 For additional information, contact: Director, Integrated Modeling and Prediction DivisionWater Mission AreaU.S. Geological Survey12201 Sunrise Valley Dr., MS 411Reston, VA 20192-0002Contact Pubs Warehouse This report describes the skeletal storage, compaction subsidence (CSUB) package of MODFLOW 6. The CSUB simulates vertical compressible sediments land subsidence. groundwater storage changes elastic in coarse-grained aquifer sediments. also inelastic fne-grained, interbeds, or extensive confning units. can account for effective stress-dependent properties. explicitly contribution water compressibility to changes.Compaction is formulated using Terzaghi’s elastoplastic model assumes total a small fraction initial thickness Compaction controlled by head pore-pressure overburden stress associated with water-table changes, thus within coarse-and fne-grained If unit less than preconsolidation stress, (recoverable). sediment greater (irrecoverable) permanent occurs.The propagation interbeds represented numerically transient, one-dimensional (vertical) fow equation. equation accounts delayed release from uptake into interbeds. Vertical hydraulic conductivity, specifc interbed control timing changes. Interbeds that are thin, have relatively large specifc-storage values equilibrate quickly heads/pore pressures surrounding be as no-delay use simulated cell calculate do not need solved vertically discretized equation.In addition applicability confned systems, several features make it applicable shallow, unconfned systems. Geostatic treated function elevation, computed stress. porosity, void ratio, shallow deep sediments, units vary time based on calculated strain.