The SOIL: Farm Process V4 Soil Options pane is used to activate the soil options in the Farm Process in MODFLOW-OWHM version 2 and specify options for it. It is in the Farm Process group on the MODFLOW Packages and Programs dialog box.
The pane has several options on it.
The effective precipitation option determines whether precipitation is measured in units of L/T or or as a fraction of the available preciptation in the Effective Precipitation Table.
The remaining options in this pane are similar to options on the other panes for the Farm Process in MODFLOW OWHM version 2. This is explained in FMP: Farm Process (for MODFLOW OWHM Version 2). Four options are available
Capillary fringe: CAPILLARY_FRINGE is the height of the capillary fringe for a particular soil. It can be specified as either as a list in the Farm Soil Properties dialog box or on a cell-by-cell (array) basis in the Capilary_Fringe data set.
Coefficient: COEFFICIENT is only required if you specify "ROOT_PRESSURE" in the LAND_USE Block. It is used to determine the water pressure on a crop root and the root pressures determine its groundwater uptake and soil stress
If not specified then the groundwater uptake and anoxia follows a linear model as described in Appendix 4 and 5 of the MODFLOW OWHM version 2 documentation.
COEFFICIENT is specified in the Farm Soil Properties dialog box either are a keyword or set of soil coefficients (A, B, C, D, and E)
Accepted soil COEFFICIENT keywords are: SILTYCLAY, SILT, SANDYLOAM, and SAND.
Surface K: SURFACE_VERTICAL_HYDRAULIC_CONDUCTIVITY is an optional keyword that allows specifying a maximum infiltration (soil leakage) rate (L/T). SURF_VK is specified by soil type (LIST) in the Farm Soil Properties dialog box or on a cell-by-cell (array) basis in the Surf_Vert_K data set. . SURF_VK limits how much deep percolation can pass through the soil zone. If deep percolation (DPERC) exceeds SURF_VK, then DPERC - SURF_VK becomes rejected infiltration and becomes runoff.
Effective Precipitation Table: EFFECTIVE_PRECIPITATION_TABLE is an optional keyword that allows tying soil type to potential consumption of precipitation. This limits how much precipitation can be consumed as evaporation and transpiration based on the quantity of rainfall and is analogous to specifying an effective precipitation, which represents the quantity of rainfall that is not runoff nor deep percolation. For each soil type, you specify a lookup table in the Farm Soil Properties dialog box
Each LookUp table specifies in the first column a precipitation rate (L/T) and the second column depends on the effective precipitation option.
BY_LENGTH indicates the second column represents a L/T upper limit of consumption. That is the effective precipitation for the given precipitation.
BY_FRACTION indicates the second column represents a fraction from 0 to 1 of the precipitation that is available for consumption. That is the the fraction times precipitation is the effective precipitation.
Precipitation that is not available for consumption becomes either runoff or deep percolation.
Precipitation that is available for consumption, but is not consumed as ET becomes either runoff or deep percolation.
See also Precipitation potential consumption.
