CSUB: Skeletal Storage, Compaction, and Subsidence Package Pane

The Skeletal Storage, Compaction, and Subsidence package simulates subsidence and compaction due to interbeds.

Interbeds tab

The Interbeds tab is where the user defines the number of systems of interbeds and whether they are delay interbeds or no-delay interbeds. With no-delay interbeds, water is released from the interbeds immediately. With delay interbeds, the interbed is simulated as a series of vertically stacked sub-cells within each cell and release of water from the interbed is delayed because of the resistance to flow into or out of the interbed through the multiple sub-cells. The CSUB package does not require that any interbeds be defined. However, if none are defined, transient CSUB data must be defined. The transient CSUB data can be defined in the CSUB: Skeletal Storage, Compaction, and Susidence pane of the Object Properties dialog box.

Options tab

The Options tab is where input options in the CSUB package are specified. The following information comes from the documentation for the CSUB package input format in mf6io.pdf which is distributed with MODFLOW 6.

•gammaw—unit weight of water. For freshwater, GAMMAW is 9806.65 Newtons/cubic meters or 62.48 lb/cubic foot in SI and English units, respectively. By default, GAMMAW is 9806.65 Newtons/cubic meters.

•beta—compressibility of water. Typical values of BETA are 4.6512e-10 1/Pa or 2.2270e-8 lb/square foot in SI and English units, respectively. By default, BETA is 4.6512e-10 1/Pa.

•HEAD_BASED—keyword to indicate the head-based formulation will be used to simulate coarse-grained aquifer materials and no-delay and delay interbeds. Specifying HEAD BASED also specifies the INITIAL_PRECONSOLIDATION_HEAD option.

•INITIAL_PRECONSOLIDATION_HEAD—keyword to indicate that preconsolidation heads will be specified for no-delay and delay interbeds in the PACKAGEDATA block. If the SPECIFIED_INITIAL_INTERBED_STATE option is specified in the OPTIONS block, user-specified preconsolidation heads in the PACKAGEDATA block are absolute values. Otherwise, user-specified preconsolidation heads in the PACKAGEDATA block are relative to steady-state or initial heads.

•ndelaycells—number of nodes used to discretize delay interbeds. If not specified, then a default value of 19 is assigned.

•COMPRESSION_INDICES—keyword to indicate that the recompression (CR) and compression (CC) indices are specified instead of the elastic specific storage (SSE) and inelastic specific storage (SSV) coefficients. If not specified, then elastic specific storage (SSE) and inelastic specific storage (SSV) coefficients must be specified.

•UPDATE_MATERIAL_PROPERTIES—keyword to indicate that the thickness and void ratio of coarse-grained and interbed sediments (delay and no-delay) will vary during the simulation. If not specified, the thickness and void ratio of coarse-grained and interbed sediments will not vary during the simulation.

•CELL_FRACTION—keyword to indicate that the thickness of interbeds will be specified in terms of the fraction of cell thickness. If not specified, interbed thicknness must be specified.

•SPECIFIED_INITIAL_PRECONSOLIDATION_STRESS—keyword to indicate that absolute preconsolidation stresses (heads) will be specified for interbeds defined in the PACKAGEDATA block. If SPECIFIED_INITIAL_PRECONSOLITATION_STRESS is not specified then preconsolidation stress (head) values specified in the PACKAGEDATA block are relative to simulated values if the first stress period is steady-state or initial stresses (heads) if the first stress period is transient.

•SPECIFIED_INITIAL_DELAY_HEAD—keyword to indicate that absolute initial delay bed head will be specified for interbeds defined in the PACKAGEDATA block. If SPECIFIED_INITIAL_DELAY_HEAD and is not specified then delay bed head values specified in the PACKAGEDATA block are relative to simulated values if the first stress period is steady-state or initial GWF heads if the first stress period is transient.

•EFFECTIVE_STRESS_LAG—keyword to indicate the effective stress from the previous time step will be used to calculate specific storage values. This option can 1) help with convergence in models with thin cells and water table elevations close to land surface; 2) is identical to the approach used in the SUBWT package for MODFLOW-2005; and 3) is only used if the effective-stress formulation is being used. By default, current effective stress values are used to calculate specific storage values.

Output types tab

The CSUB package can generate several types of output data sets.

•The final interbed strain file is a comma-separated list final strain values for every interbed. It contains the following data. Interbed_Number, Interbed_Type, Cellid, Initial_Thickness, Final_Thickness, Total_Compaction, Total_Strain, and Percent_Compaction.

•The coarse-grained material strain file is a comma-separated list final strain values. It contains the following data. Node, Cellid, Initial_Thickness, Final_Thickness, Total_Compaction, Total_Strain, Percent_Compaction.

•Compaction for every time step for which head is saved in binary format.

•Elastic compaction for every time step for which head is saved in binary format.

•Inelastic compaction for every time step for which head is saved in binary format.

•Interbed compaction for every time step for which head is saved in binary format.

•Elastic coarse-grained compaction for every time step for which head is saved in binary format.

•Z displacement for every time step for which head is saved in binary format.

ModelMuse can import data from the binary files in the Select Model Results to Import dialog box.