Interbed storage changes and compaction in models of regional groundwater flow

Water released from permanent compaction of compressible fine‐grained interbeds within confined aquifers may be a significant source of pumped water. Permanent or inelastic compaction of the interbeds occurs when head declines from pumping cause the effective stress or grain‐to‐grain load to exceed...

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Bibliographic Details
Published in:Water resources research 1990-09, Vol.26 (9), p.1939-1950
Main Author: Leake, S. A.
Format: Article
Language:English
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Summary:Water released from permanent compaction of compressible fine‐grained interbeds within confined aquifers may be a significant source of pumped water. Permanent or inelastic compaction of the interbeds occurs when head declines from pumping cause the effective stress or grain‐to‐grain load to exceed the elastic limits of the interbeds. As a result, the grains in the interbeds rearrange and excess water is expelled. The amount of inelastic compaction generally is proportional to the increase in effective stress and the decrease in head. A common approach for the simulation of elastic and inelastic compaction in groundwater flow models is to assume that head changes in the aquifer result in instantaneous storage changes in the compressible interbeds. A term is added to the groundwater flow equation to account for the storage changes. Changes in specific storage may be computed explicitly from the results at the previous time step in the finite difference formulation of the groundwater flow equation. A better approach is to implicitly apportion storage changes between elastic and inelastic components within a time step. If storage changes cannot be considered to occur instantaneously with change in head in the aquifer, another approach is taken. Equations for horizontal flow in the aquifer are coupled with equations for vertical flow in the compressible interbeds to simulate flow in half a representative doubly draining interbed. Storage changes and compaction are calculated for the representative half thickness and are extrapolated to the entire thickness of all interbeds within each cell. This approach was applied to an existing model of groundwater flow in the Central Valley of California. The simulation demonstrates that solving coupled systems of equations is feasible for a regional flow model.
ISSN:0043-1397
1944-7973
DOI:10.1029/WR026i009p01939