landlab

SoilInfiltrationGreenAmpt: Model infiltration of surface water according to the Green-Ampt equation

class SoilInfiltrationGreenAmpt(self, grid, hydraulic_conductivity=0.005, soil_bulk_density=1590.0, rock_density=2650.0, initial_soil_moisture_content=0.15, soil_type='sandy loam', volume_fraction_coarse_fragments=0.2, coarse_sed_flag=False, surface_water_minimum_depth=1e-08, soil_pore_size_distribution_index=None, soil_bubbling_pressure=None, wetting_front_capillary_pressure_head=None, **kwds)[source]

Bases: landlab.core.model_component.Component

Infiltrate surface water into a soil following the Green-Ampt method.

This code is based on an overland flow model by Francis Rengers and colleagues, after Julien et al., 1995. The infiltration scheme follows the Green and Ampt equation.

It was implemented in Landlab by DEJH, March ‘16. Please cite Rengers et al., 2016, Model Predictions of Water Runoff in Steep Catchments after Wildfire, WRR.

Examples

>>> from landlab import RasterModelGrid
>>> from landlab.components import SoilInfiltrationGreenAmpt
>>> mg = RasterModelGrid((4,3), spacing=10.)
>>> hydraulic_conductivity = mg.ones('node')*1.e-6
>>> hydraulic_conductivity.reshape((4,3))[0:2,:] *= 10000.
>>> h = mg.add_ones('node', 'surface_water__depth')
>>> h *= 0.01
>>> d = mg.add_ones('node', 'soil_water_infiltration__depth', dtype=float)
>>> d *= 0.2
>>> SI = SoilInfiltrationGreenAmpt(
...     mg,hydraulic_conductivity=hydraulic_conductivity)
>>> for i in range(10):  # 100s total
...     SI.run_one_step(10.)
>>> mg.at_node['surface_water__depth']
array([  1.00000000e-08,   1.00000000e-08,   1.00000000e-08,
         1.00000000e-08,   1.00000000e-08,   1.00000000e-08,
         9.88530416e-03,   9.88530416e-03,   9.88530416e-03,
         9.88530416e-03,   9.88530416e-03,   9.88530416e-03])
>>> mg.at_node['soil_water_infiltration__depth']
array([ 0.20999999,  0.20999999,  0.20999999,  0.20999999,  0.20999999,
        0.20999999,  0.2001147 ,  0.2001147 ,  0.2001147 ,  0.2001147 ,
        0.2001147 ,  0.2001147 ])

Kinematic wave approximation overland flow component.

Parameters:

grid : RasterModelGrid

A grid.

hydraulic_conductivity : float, array, or field name (m/s)

The soil effective hydraulic conductivity.

soil_bulk_density : float (kg/m**3)

The dry bulk density of the soil.

rock_density : float (kg/m**3)

The density of the soil constituent material (i.e., lacking porosity).

initial_soil_moisture_content : float (m**3/m**3, 0. to 1.)

The fraction of the initial pore space filled with water.

soil_type : {‘sand’, loamy sand’, ‘sandy loam’, ‘loam’, ‘silt loam’,

‘sandy clay loam’, ‘clay loam’, ‘silty clay loam’, ‘sandy clay’, ‘silty clay’, ‘clay’}, or None

A soil type to automatically set soil_pore_size_distribution_index and soil_bubbling_pressure, using mean values from Rawls et al., 1992.

volume_fraction_coarse_fragments : float (m**3/m**3, 0. to 1.)

The fraction of the soil made up of rocky fragments with very little porosity, with diameter > 2 mm.

coarse_sed_flag : boolean, optional

If this flag is set to true, the fraction of coarse material in the soil column with be used as a correction for phi, the porosity factor.

surface_water_minimum_depth : float (m), optional

A minimum water depth to stabilize the solutions for surface flood modelling. Leave as the default in most normal use cases.

soil_pore_size_distribution_index : float, optional

An index describing the distribution of pore sizes in the soil, and controlling effective hydraulic conductivity at varying water contents, following Brooks and Corey (1964). Can be set by soil_type. Typically denoted “lambda”.

soil_bubbling_pressure : float (m), optional

The bubbling capillary pressure of the soil, controlling effective hydraulic conductivity at varying water contents, following Brooks and Corey (1964). Can be set by soil_type. Typically denoted “h_b”.

wetting_front_capillary_pressure_head : float (m), optional

The effective head at the wetting front in the soil driven by capillary pressure in the soil pores. If not set, will be calculated by the component from the pore size distribution and bubbling pressure, following Brooks and Corey.

SOIL_PROPS = {'sandy clay loam': (0.319, 0.2808), 'clay loam': (0.242, 0.2589), 'loamy sand': (0.553, 0.0869), 'clay': (0.165, 0.373), 'sandy clay': (0.223, 0.2917), 'silty clay loam': (0.177, 0.3256), 'sandy loam': (0.378, 0.1466), 'silt loam': (0.234, 0.2076), 'silty clay': (0.15, 0.3419), 'sand': (0.694, 0.0726), 'loam': (0.252, 0.1115)}
static calc_moisture_deficit(soil_bulk_density=1590.0, rock_density=2650.0, volume_fraction_coarse_fragments=0.0, soil_moisture_content=0.0)[source]

Calculate the moisture deficit in a soil.

Parameters:

soil_bulk_density : float or array of float

Bulk density of the soil [kg / m3].

rock_density : float or array of float

Density of rock [kg / m3].

volume_fraction_coarse_fragments : float or array of float

Volume fraction of sediment made up of coarse grains [-].

soil_moisture_content : float or array of float

Fraction of soil filled with water [-].

Returns:

float or array of float

Moisture deficit.

static calc_pressure_head(lam, h_b)[source]

Calculate pressure head.

Pressure head is set using lambda and h_b, using an equation after Brooks-Corey (1964), following Rawls et al., 1992.

Parameters:

lam : float, optional

Pore-size distribution index. Exponent that describes the distribution of pore sizes in the soil, and controls effective hydraulic conductivity at varying water contents, following Brooks and Corey (1964) [-].

h_b : float (m), optional

Bubbling pressure. Capillary pressure of the soil, controlling effective hydraulic conductivity at varying water contents, following Brooks and Corey (1964) [m]

static calc_soil_pressure(soil_type=None, soil_pore_size_distribution_index=1.0, soil_bubbling_pressure=0.0)[source]

Calculate capillary pressure in a soil type.

Parameters:

soil_type : str, optional

The name of a soil type.

soil_pore_size_distribution_index : float

Pore-size distribution index [-].

soil_bubbling_pressure : float

Bubbling pressure [m].

capillary_pressure

Capillary pressure of soil.

hydraulic_conductivity

Hydraulic conductivity of soil.

min_water

Minimum surface water depth.

moisture_deficit

Moisture deficit of soil.

run_one_step(dt)[source]

Update fields with current hydrologic conditions.

Parameters:

dt : float (s)

The imposed timestep for the model.