Project File:Infiltration – Optional

Infiltration may be calculated using four different infiltration options. Green and Ampt (GA) (Green and Ampt, 1911), a multi-layered Green and Ampt Model, Green and Ampt with Redistribution (GAR) (Ogden and Saghafian, 1995), and Richards’ equation (RE) (Richards, 1931). Only one of these four methods should be selected.

Card	Argument	Description
GREEN_AMPT	none	Specifies Green and Ampt (GA) infiltration calculations.
INF_REDIST	none	Specifies Green and Ampt with Redistribution (GAR) infiltration calculations.
INF_LAYERED_SOIL	none	Specifies three layered Green and Ampt infiltration.
INF_RICHARDS	none	Specifies Richards’ Equation be used for infiltration.

3.6.1 Green and Ampt (GA)

When GREEN_AMPT is selected, values of hydraulic conductivity, wetting front suction head, porosity, and initial moisture are required. Parameter values may be input using the Mapping Table file or with the series of GRASS ASCII maps using the cards below.

Card	Argument	Description
CONDUCTIVITY "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of soil saturated hydraulic conductivity (cm hr-1). REQUIRED for GREEN_AMPT or INF_REDIST. Mutually exclusive with Mapping Table file assignment.
CAPILLARY "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of Green & Ampt wetting front capillary head parameter (cm). REQUIRED for GREEN_AMPT or INF_REDIST. Mutually exclusive with Mapping Table file assignment.
POROSITY "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of soil porosity. REQUIRED for GREEN_AMPT or INF_REDIST. Mutually exclusive with Mapping Table file assignment.
MOISTURE [value]	map name or none	Used to assign the initial soil moisture content. If followed by a filename, the file will be read in as a GRASS ASCII initial soil volumetric water content map. If no input is specified, then the initial soil volumetric water content s will be input using the Mapping Table file. REQUIRED for GREEN_AMP or INF_REDIST.

3.6.2 Green and Ampt with Redistribution (GAR)

When GAR is specified, the GA parameters plus two additional parameters must be provided: the pore-distribution index, and residual saturation. These may be input in the Mapping Table file or by providing two GRASS ASCII maps using the cards below.

Card	Argument	Description
PORE_INDEX "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of the Brooks & Corey (1964) pore-distribution index. REQUIRED for INF_REDIST. Mutually exclusive with Mapping Table file assignment.
RESIDUAL_SAT "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of the volumetric water content of the soil at residual saturation. REQUIRED for INF_REDIST. Mutually exclusive with Mapping Table file assignment.
FIELD_CAPACITY "filename.ext"	map name	Name of GRASS ASCII map containing spatially varied values of the volumetric water content of the soil when gravity drainage ceases. REQUIRED for INF_REDIST. Mutually exclusive with Mapping Table file assignment.

3.6.3 Multi-layered Green and Ampt

The multi-layered GA parameters are assigned with the table described in Section 11, and referenced to an index map. The required project cards are listed below.

Card	Argument	Description
SOIL_TYPE_MAP "filename.ext"	index map file name	Name of GRASS ASCII map containing index numbers related to soil type.
SOIL_LAYER_INPUT_FILE "filename.ext"	file name	Input ASCII file containing values GA parameter in three soil layers for each soil referenced to in the SOIL_TYPE_MAP.

3.6.4 Richards’ Equation

When INF_RICHARDS is selected additional cards are required. There are also a number of optional input and output cards, as described below. Richard' Equation parameters may be specified in the MAPPING_TABLE, as well as in separate ASCII files.

3.6.4.1 Required Inputs

Card	Argument	Description
INF_RICHARDS	none	Specify Richards’ equation for calculation of soil moisture, infiltration, and ET if doing LONG_TERM simulations.
RICHARDS_C_OPTION [value]	character string	Type of water-content/head curve and hydraulic conductivity/head curve. BROOKS - Brooks and Corey (1964), as extended by Hutson and Cass (1987), into the wet profile; or, HAVERCAMP – Havercamp (1977) as modified by Lappala (1985).

3.6.4.2 Parameter Assignment - Required

Select either SOIL_TYPE_MAP and SOIL_LAYER_INPUT_FILE or use the Mapping Table.

Card	Argument	Description
SOIL_LAYER_INPUT_FILE "filename.ext"	file name	Input ASCII file with soil layer input parameters. Not used with MAPPING_TABLE
SOIL_TYPE_MAP "filename.ext"	index map file name	Name of GRASS ASCII map of soil type integer values corresponding to SOIL_LAYER_INPUT_FILE. Not used with MAPPING_TABLE

3.6.4.3 Optional Inputs

Card	Argument	Default	Description
WATER_TABLE "filename.ext"	map name	no water table	Simulate effect of water table on soil moisture. Specify filename of GRASS ASCII map that contains starting elevations of water table (m).
AQUIFER_DELTA_Z ##.##	real	none	Size of unsaturated cell to use in all cells below the soil column specified in the SOIL_LAYER_INPUT_FILE or Mapping Table (m).
SEASONAL_RS	none	no seasonal canopy resistance (when card is absent)	Vary the vegetation canopy resistance during the year.
RICHARDS_UPPER_OPTION [value]	character string	NORMAL	Method used to calculate hydraulic conductivity at ground surface under ponded conditions: NORMAL – from cell-centered water content of first cell, GREEN_AMPT - saturated hydraulic conductivity (K_s) of cell 1 AVERAGE - average of K_s and NORMAL
GW_ASSIGN_THETA	none	do not assign initial theta assume equilibrium values	Assign soil moisture from the file specified in the SOIL_LAYER_INPUT_FILE card, if simulating the water table.
RICHARDS_ITER_MAX ##	integer	1	Maximum number of iterations on non-linear coefficients.
RICHARDS_WEIGHT ##.##	real	1.0	Weight on inter-cell hydraulic conductivities: 1.0 - forward 0.5 - centered 0.0 - backwards
RICHARDS_K_OPTION [value]	character string	ARITHMETIC	Averaging method for inter-cell hydraulic conductivities, GEOMETRIC or ARITHMETIC
RICHARDS_DTHETA_MAX ##.##	real	0.025	Maximum allowable water content change during a time-step.

3.6.4.4 Optional Output

Card	Argument	Description
IN_THETA_LOCATION "filename.ext"	file name	Input ASCII file that contains locations of cells to output time series moisture data.
OUT_THETA_LOCATION "filename.ext"	file name	Filename to output time series moisture data every HYD_FREQ time steps at cells specified in IN_THETA_LOCATION.

3.6.7 Special Infiltration Cards

Card	Argument	Description
READ_SM_HOTSTART "filename.ext"	file name	Input GRASS ASCII map file that contains starting surface soil moistures specified for every grid cell in the watershed. Works with all infiltration options.
WRITE_SM_HOTSTART "filename.ext"	file name	Filename to output GRASS ASCII map of soil moistures for every grid cell in the watershed at the end of the simulation. Works with all infiltration options.