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Clone wiki# pflotran / Depreciated / Documentation / QuickGuide / SubsurfaceFlow

## SUBSURFACE_FLOW Block

### Required Cards

MODE <string>: Specifies the flow mode to be employed. Follow the links below for a description of each flow mode's options.

#### Water Modes

RICHARDS: single-phase variably saturated flow

GENERAL: two-phase air-water-energy

TH: variably saturated flow and energy (and optional ice phase)

#### CO_{2} Modes

MPHASE: two-phase CO

_{2}-water-energyIMMISCIBLE: immiscible two-phase CO

_{2}-water-energyMISCIBLE: miscible H

_{2}O-glycolFLASH2: two-phase CO

_{2}-water-energy

### Optional Cards

OPTIONS: MODE-dependent block for defining options for each flow process model.

MAX_XXX_CHANGE: Attempts to govern the time step size based on the specified value of the variable.

MAX_PRESSURE_CHANGE <float> (default = 5.d5 [Pa])

MAX_TEMPERATURE_CHANGE <float> (default = 5.d0)

MAX_CONCENTRATION_CHANGE <float> (default = 1.d0)

MAX_SATURATION_CHANGE <float> (default = 0.5d0)

- PRESSURE_DAMPENING_FACTOR <float>
- Dampens the update vector by this value.
- MAX_CFL <float>
- Restricts flow process model timestep size based on Courantâ€“Friedrichsâ€“Lewy constraint (essentially limiting advection to MAX_CFL cells per timestep).
- NUMERICAL_DERIVATIVES
- Flag toggling the calculation of derivatives in Jacobian using perturbation (in the case where flow derivatives are calculated analytically by default).

### Examples

SIMULATION SIMULATION_TYPE SUBSURFACE PROCESS_MODELS SUBSURFACE_FLOW flow MODE GENERAL OPTIONS ISOTHERMAL TWO_PHASE_ENERGY_DOF TEMPERATURE GAS_COMPONENT_FORMULA_WEIGHT 2.01588d0 MAX_PRESSURE_CHANGE 1.0d6 PRESSURE_DAMPENING_FACTOR 0.6d0 MAX_CFL 1.d0 / / / END

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